A note on steering

[JohnK]

A note on steering.

 

In the process of exploring how my Se7en works, I've discovered things about the steering I fitted that just knock me out.

 

Building my “kit”, I wound up designing, engineering and fitting a completely new steering system to solve a problem. In doing this I had considerable help from the mfg of the rack and pinion I used: really extraordinary documentation, and advice along the way, which not only allowed me to solve the problem that caused me to tackle the work in the first place but wound up giving me benefits way beyond what I was shooting for.

 

That everything had come together even better than I had hoped for became clear out in some hilly country over some very familiar stretches of aging blacktop. At 70+ MPH I found I was placing the car on the road exactly where I wanted with very little steering effort and very small movements of the steering wheel. I wasn't feeling any of the kick-back I expected from the roughness of the road, but still the steering feedback was excellent – the system was filtering road irregularities without killing feedback, and it was getting through rough stretches without the car being tossed all over the place. Nirvana!

So the nett is that I have a really communicative steering system that offers really precise control, and allows me to toss the car around without needing the muscles of a weight-lifter.

 

Getting to this point was really hard and fairly expensive (so what else is new?) So how did all of this play out?

 

The starting point was Ride Steer. If you're going down a straight stretch of road and suddenly the car decides to point itself in a new direction when it runs over a bump, that's Ride Steer. Obviously this is a bad thing, particularly so if you're going around a corner when it happens. On my “kit” this problem was considerable and was due to the geometry of the steering, and the rack couldn't be repositioned to get rid of it. Having opened Pandora's box, I began the long journey of searching for a solution. Along the way I got a Woodward Precision Power Steering catalog from a dirt track guy at Zakiris Garage. The catalog had a really excellent section spelling out the geometry involved in placing a steering rack and the reasons why the different aspects of the geometry were important. It had equally superb sections explaining other steering issues. I had found a gold mine of steering information.

 

Phase I.

Woodward offered a rack that was a good fit for a Se7en and its construction was modular: when you ordered a rack you specified the dimensions of all of the parameters that define a rack (rack length, rack rod length, steering ratio, pinion placement, ...). Thus you could determine the optimal geometry for a rack for your car and then order a rack to fit. So armed, I fabricated a jig that allowed me to explore different rack dimensions, placement of the rack in different positions in the available space, different rack rod length and stroke, … and then assess the effect of each trial on Ride Steer and Ackermann and steering lock, and be able to capture the position for fabricating rack mounts. Yeah, it was a lot of work.

 

Phase II.

Woodward has a great section which talks about steering ratios - and I found that Pandora has another box. Being able to turn your front wheels really quickly is a very good thing, but this takes more force at the steering wheel. There are three ways of dealing with this. 1) Start an exercise program so you've got big enough muscles to handle the load and still be able to deliver good finesse at the steering wheel. 2) Decrease positive Caster, which will lighten the steering effort as the Caster value gets small. However, this comes at the cost of high speed directional stability (as self-centering of the front wheels). Taking this path also makes Caster adjustment really critical; adjusting for maybe +1.5° of Caster (I'm guessing at an appropriate value here), and getting it exactly the same on both sides of the car is at the minimum, time consuming. If you've done your own aligning you know that this involves a lot of work, and you wind up chasing your tail because other things change when you change Caster – and vice versa. 3) Power Steering. No need for an exercise program, Caster issues essentially go away, and, as I'm happily finding out, there are a lot of other benefits one gets along with these. Cost is higher for a power assisted rack and one has to select and fit an appropriate power steering pump. Woodward, in yet another excellent section, provides help with this latter issue by having done research on several different pumps, showing which delivers constant flow rate with changes in engine speed. This means that steering feel will not change with engine speed. Think about steering that becomes much more sensitive at high engine speeds and when in top gear. Clearly to be avoided.

So, reflecting on all of this, I decided to fit P/S – and keep trying to come up with a reasonable sounding explanation as to why the heck do you need P/S on a car that weighs 1650 lbs.

 

Phase III. Integration.

With everything assembled, the steering geometry gave zero Ride Steer and 6° of Ackermann at full (22°) lock. The steering ratio was approximately 11° of Steering Wheel turn to 1° Front Wheel turn. Caster remains +3.8° and +3.9°, left and right, zero front Toe, zero front Camber, 5” front ride height.

 

Very generally, a Power Steering system presents itself differently than a system that's unassisted. My steering is now quick enough that you can easily chirp the front tires with a flick of the wheel. The system damps the unwinding of the steering wheel when coming out of a sharp turn unlike an unassisted system, but on my car the steering ratio is quick enough that this is not much of an issue, and it disappears as an issue when driving at speed. At speed (see also below) there is a huge difference in feel and control. Once acclimated, fine control at high speed becomes almost magically easy, even lighter than on a, say, 250 cc GP bike where it seems all you have to do is 'think' to turn the bike.

 

When first driving the car I wasn't too happy. It felt really darty and I expected that it was going to take a long time before I got used to its quickness and sensitivity.

With more seat time I became more relaxed, recognized that much of what I felt as dartyness was due to my overcompensating, and the steering became progressively smoother as I became more and more comfortable. In this regard, one thing that became apparent was how easy it was to create unintended steering input due to being jostled by bumps in the road. I'm learning ways of positioning myself in order to steer precisely through stretches of rough road.

One pretty dramatic finding was the difference tires can make. Out on a straight stretch of some pretty bumpy blacktop I'd gotten to the point where 80 MPH seemed like the limit. The car was becoming just too difficult to keep on the road, likely due to my being jostled causing unintended steering input. But whatever, I just didn't feel comfortable going any faster under those conditions. Working on a different issue I changed front tires from the cool-looking (but apparently useless) Falken Azenis RTs that came with the “kit” to a pair of Yokohama S.drives. The transformation was stunning. That same stretch of road was now comfortable at 90+ MPH, and more importantly, overall the steering was vastly more precise and steering feel was hugely improved.

 

With respect to the superb feel that the system delivers:

The rack has a torsion bar connected between the steering column and the solenoid in the rack that controls the flow of fluid from the P/S pump. This spring is light enough and works through a small enough range before it connects solidly with the solenoid that one can mistake its being twisted for free-play in the steering system when the car isn't running.

Finally, when I was out in the country on familiar roads, having gotten comfortable with the steering, and having fitted good tires, I was able to get focused to the point where I was working completely within the range of the torsion bar on relatively straight stretches of road and realized how little muscle it took to make the car go where I wanted and how accurately I could position the car on the road. The mfg offers a selection torsion bars covering a range of different spring rates so you can tune the steering feel to fit your car's properties and driving conditions. Related directly to this is the importance of the power steering pump delivering a constant flow rate to ensure that this sensitivity does not vary with the how the car is being driven.

 

I'll bet that folks who develop purpose-built sports-racing cars accomplish this sort of thing all the time. But for a retired Biologist who's dreamed for years of having his own Se7en, pulling all of this together and having it work so well makes me feel just like the King of the Mountain :-)

[MHKflyer52]

John K,

Nice write up.

Post some photos of the system if you would.

As a side note my wife’s new car has electric over manual steering instead of hydraulic assisted steering and I am very impressed with how her car drives and handles with that setup. It is truly amazing as to what new technology is bringing to the table I do believe.

[Alaskossie]

I'm not planning on p/s for my Seven, but I have a Volvo 6X6 ex-military truck that at low speeds steers like an Olympic weight-lifting qualifying test.

 

A fellow in Europe has developed a p/s mod with a European Opel electric p/s unit grafted onto the Volvo steering column. Even thought I've never used electric p/s before, I'm sorely tempted.....

[rnr]

The starting point was Ride Steer. If you're going down a straight stretch of road and suddenly the car decides to point itself in a new direction when it runs over a bump, that's Ride Steer. Obviously this is a bad thing, particularly so if you're going around a corner when it happens. On my “kit” this problem was considerable and was due to the geometry of the steering, and the rack couldn't be repositioned to get rid of it.

 

Thanks for posting such a long and detailed explanation of your issues. Did you experience the ride steer issue in your Ultralite after you initially built it? I ask because I have one as well and I havent noticed any issues on either street or track

 

Being able to turn your front wheels really quickly is a very good thing, but this takes more force at the steering wheel. There are three ways of dealing with this. 1) Start an exercise program so you've got big enough muscles to handle the load and still be able to deliver good finesse at the steering wheel. 2) Decrease positive Caster, ....... 3) Power Steering. No need for an exercise program, Caster issues essentially go away, and, as I'm happily finding out, there are a lot of other benefits one gets along with these.

 

Two more options to reduce steering effort are:

1) larger steering wheel (even an single inch in dia makes a massive difference). This is also a cheap thing to try as you can often borrow wheels from different people at track days and see how you like them.

2) different tire width and/or compound for your front tires. More expensive than swapping wheels and harder to "tune" but equally effective.

[JohnK]

Thanks for posting such a long and detailed explanation of your issues. Did you experience the ride steer issue in your Ultralite after you initially built it? I ask because I have one as well and I havent noticed any issues on either street or track

 

I made the decision to do the steering when I was finishing up the car, about to put it on the road. After doing all the other alignment, including +4 degrees of caster, when I went to do the front Ride Steer, I found that whether I put the tie rod on the top or the bottom of the steering arm I got lots of ride steer - I didn't bother recording the magnitude of the numbers but they were large enough to cause me to stop and see what others said about the effect. What I read left no question that it was a problem and, given the existing setup, there was no good solution but to start over. While this took a lot of time and money, I have no doubt that what I left behind was simply wrong, and that what I managed to pull together is well worth the effort. I'm not religious about this, but I have to take seriously what people who have managed racing teams have written and engineers who developed racing cars have written.

One observation, from memory, is that the shocks delivered with my car had VERY stiff springs, perhaps stiff enough that the ride change was small enough that steering defects were masked. I was impressed riding in Kitcat's old crossflow Caterham that it had a very comfortable ride, yet it handled very well. Currently my car rides similarly.

 

 

 

Two more options to reduce steering effort are:

1) larger steering wheel (even an single inch in dia makes a massive difference). This is also a cheap thing to try as you can often borrow wheels from different people at track days and see how you like them.

2) different tire width and/or compound for your front tires. More expensive than swapping wheels and harder to "tune" but equally effective.

 

I agree on both issues. 1) But all the modern racing and high-end sports cars I see have small steering wheels implying that they don't need drivers with the strength of weight lifters to overcome steering issues, and that finesse is more important than physical strength when going fast in a sports car.

and 2) Currently working on figuring out how to balance the suspension in my car, one of the clues as to the oversteer in my car is pointed to by the fact that the builder shipped the car with brakes that delivered the same stopping power at both the front and the rear of the car. This can be taken as strong evidence that the builder had no understanding of longitudinal weight transfer, and this ignorance may well apply to the sizing of the tires that were fitted to the car.

[JohnK]

MHKflyer52 asked for some pictures, and, of course, I got carried away. Also, for the terminally technical.....

 

Note on Steering, II

 

After I understood the costs and benefits of Power Steering and decided to go that route, it was clear that fitting the pump was the first thing that should be tackled. It also happened to be the easiest and most straightforward task to accomplish (however both of those terms are relative to the rest of the work ;-) ).

The KRC Aluminum pump is both light and small and tucked nicely into the nook on the side of the engine where the A/C pump used to live.

https://www.dropbox.com/s/t2h79gfxt6879aw/ab02PSPumpInSitu.JPG?dl=0

The pump has a red-line, and doesn't output much at low RPMs, so I did the arithmetic and found the pulley size I needed so I wouldn't hurt the pump at 8K, and still had an easy time when parallel parking. Jones stocks such things and makes adapters to different pumps.

https://www.dropbox.com/s/hfz5mk9phizctz8/ab01PSPumpInSitu.JPG?dl=0

Happily I could even use the mounting bolt holes from the A/C and line it up relatively easily with the serpentine belt. Grainger carries a huge selection of lengths and the worst part was only figuring out how to measure the length over the pulleys.

Fabricating the mounting bits made me happy I'd bought such a good TIG machine.

https://www.dropbox.com/s/b0bjzbckyoj1fex/ab00PSPumAndFittings.jpg?dl=0

 

The plumbing took some fiddling but wasn't too bad.

Notes: It's not obvious that the KRC pump is a 3 HP motor! (http://www.krcpower.com/ as well as Woodward's catalog http://woodwardsteering.com/ ) The electric-hydraulic pumps sufficient to power assisted racks are much bigger, heavier and require a higher output alternator. I wonder why Mosler (https://en.wikipedia.org/wiki/Mosler_MT900) chose that path for the one they fitted to their MT900 when they're so much into lightness. The electric assisted P/S that for instance came with the Honda S2000, I will guess, can't have anywhere near the muscle.

 

After I digested the info provided by Woodward (https://www.dropbox.com/s/hlrj6pdnwgknau0/tech%20section%20guide.pdf?dl=0) I made a mock rack using 2x2 heavy wall tube and fitted a 3/4x3/4 rack rod inside it with bearings that allowed changing of the length of the rack and allowed the rack rod to be moved in and out. I also jerry rigged tie rods out of cheap rod ends and bar stock. Preliminary stumbling about gave me a reasonable idea of how long the rack should be which is dependent on how long the rack rod should be so I could measure the amount of plunge as the rack rod swung the wheel through its range. This part is all wonderful until you get done and try to put things like fenders on and find that they run into other parts of the car at full lock, and even worse, at full lock at full droop/bump. I guess I was careful (or paranoid) enough to avoid major disasters here. I wound up with 22° of lock on the outside wheel and 6° of Ackerman added to that on the inside wheel. The car's wound up with turn-in you can brag about. I wound up re-making tie rods and rack rod only a few times. Once you get all of this set up for measuring Ride Steer it goes quickly and you can home in on a position for the rack without too much time.

 

https://www.dropbox.com/s/0av03sz0ymgp7hn/ba00BumpSteerPlate.JPG?dl=0

Shows the Ride Steer gage I made, as described by C. Smith. All that mucking about with dial gages may be really accurate, but when you think about it is really is overkill. When you get close to zero, you can use a feeler gage or a graduated wedge to give you any accuracy you need. If you're not close to zero, why bother reading off of a dial exactly how much toe you've got? The rollers contacting the plate are from the sliding door section of Lowes and give highly repeatable behavior, and if you put radial lines on them, as you raise/lower the upright, you can easily see when one is no longer in contact with the plate and make whatever correction is needed. What's not shown is that the frame pivots on rod end brgs that are bolted to a 2” heavy iron channel. The plate and its wheel mounts require more than a little care. Woodward has a great description of Ride Steer which made the work easier to accomplish. I wanted to make Ackermann adjustable over a range but found there just wasn't that much space to play with. A CAD system could have made this process faster but inputting all the pieces would have taken many times as long as the trial and error method.

I spent a lot of time measuring the chassis and deciding what to use as the reference points, the chassis' symmetry was not awful, but certainly less than what one would call "true". Referencing

https://www.dropbox.com/s/lvy79jlmmm7n3iv/ba01JigFront.JPG?dl=0

that framework at the front is an alignment jig that plugs into to the inboard suspension pickups on the chassis. It's pretty rigid and I made the forward most horizontal bar movable fore/aft via screw mounting and the screw mounts clamp on the jig verticals so it can be leveled. So once you attach the jig, you adjust its reference points (like centerline and the front and sides of the reference rectangle) by hanging plumb bobs off the front bar to align to a reference rectangle laid out beneath the car, which in turn is centered on the chassis front and rear inboard suspension pickup clevises, averaging these dimensions to come up with a car centerline. After the car was completed, commercial equipment found that the Thrust angle was 0.13 degrees, so this approach is reasonably accurate. Matter of fact, all of the alignment was damn near spot on when measured with commercial equipment – so you can align the car yourself, but it takes quite a bit of work and time.

Then I worked with the mock up and jig to find the position in the chassis that gave no Ride Steer, as much Ackermann as I could get, and ensure that nothing ran too close to anything else at full lock and full Bump/Droop.

 

https://www.dropbox.com/s/0rpb5dmywoz3y04/ba02JigFrontRight00.JPG?dl=0

https://www.dropbox.com/s/705kpgb418zro3n/ba03JigFrontRight.JPG?dl=0

https://www.dropbox.com/s/tgmb9yu384s5ffo/ba04JigFromRight00.JPG?dl=0

https://www.dropbox.com/s/fr3hpolcmpy3cjt/ba05JigFrontLeft00.JPG?dl=0

show details of such work. Note shorter steering arm mock up, path of the tie rod through other suspension parts, clearance of anti roll bar link and attachment of plate to measure Ride Steer.

https://www.dropbox.com/s/y5goz78r13q3xxw/ba06JigFrontLeft.JPG?dl=0

https://www.dropbox.com/s/7gjop9lqtwhdn7k/ba07JigLeftInside.JPG?dl=0

show a Diamond 13" wheel fitted to the left side and show clearance issues with the ARBar blade and the tie rod.

At this point, I had the height of the rack in its space and its lengths. Using the specs provided by Woodward I knew how tall the rack would be and where its mounts would be located along the rack. Given this and the locations of the tubes on the chassis I could fabricate the mounts for the rack on the chassis. I used another 2x2 to capture the final position of the mock rack and then built two triangular boxes to match the actual rack's mounting bosses. Some of this is shown in

https://www.dropbox.com/s/jfys9a2h4udiz0m/ca01TackingMountsInPosition.JPG?dl=0

https://www.dropbox.com/s/y5oj1lgxzxbsmme/ca02TackingMountsInPosition.JPG?dl=0

https://www.dropbox.com/s/k0qa1gyj2h4phlq/ca03TackingMountsInPosition.JPG?dl=0

https://www.dropbox.com/s/trhyycf5zd3e2gi/ca04RackMountsPostTacking00.JPG?dl=0

I then cut the tacked-together boxes from the chassis and completed the welding of these boxes at the bench, as per

https://www.dropbox.com/s/trhyycf5zd3e2gi/ca04RackMountsPostTacking00.JPG?dl=0

When I got the rack I bolted these boxes to the rack and used the same capturing jig to position the rack

https://www.dropbox.com/s/yi73hdwj4jbk9l6/cc00RackPositioned.JPG?dl=0

xx https://dl.dropbox.com/u/49212285/ANoteOnSteering/cc00RackPositioned.JPG

and tacked the boxes to the chassis, and removed the rack and completed the welding.

https://www.dropbox.com/s/58erfql14e29yfs/cc01RackMountsPre-finalWelding.JPG?dl=0

shows the space where this was put and

 

https://www.dropbox.com/s/61vw3etzw409378/cc02RackMountsPreFinalWedlin01.jpg?dl=0

xx https://dl.dropbox.com/u/49212285/ANoteOnSteering/cc02RackMountsPreFinalWedlin01.jpg

shows the finally positioned rack mounts. This worked well. When I explored how everything finally worked I got absolutely zero Ride steer and nothing ran into anything else - so much for those who make claims about TIG welding creating distort

 

 

SEE PART 2 FOLLOWING

Edited January 30, 2017 by JohnK
add direction

[rnr]

I agree on both issues. 1) But all the modern racing and high-end sports cars I see have small steering wheels implying that they don't need drivers with the strength of weight lifters to overcome steering issues, and that finesse is more important than physical strength when going fast in a sports car.

 

Small steering wheels in race cars are often done due to space restrictions in an extremely confined cockpit (see NASCAR vs F1). And high end road cars often do it for marketing reasons (the MP4-12C claims to have the same wheel dia as Lewis Hamilton plus 1mm to account for the lack of gloves). I personally have gone to a very small wheel as well as that way I get more knee room which allows me to work the pedals more effectively. This is not to say that power steering is bad - just that racing cars optimize to a different set of conditions (outright speed) that the average street or even track car.

 

 

and 2) Currently working on figuring out how to balance the suspension in my car, one of the clues as to the oversteer in my car is pointed to by the fact that the builder shipped the car with brakes that delivered the same stopping power at both the front and the rear of the car. This can be taken as strong evidence that the builder had no understanding of longitudinal weight transfer, and this ignorance may well apply to the sizing of the tires that were fitted to the car.

 

+1 on the brake sizing. It took me a long time to sort out the brakes on my Ultralite (http://www.rahulnair.net/blog/2012/02/03/brake-bias-issues/) and I plan to actually go use narrower tires for my next set as well.

Edited September 24, 2012 by rnr

[coffee break]

John,

Great research and implementation. Is it legal to have that much fun?

Carl

[WestTexasS2K]

This power steering works fantastic and cost under a 1k. If you order it from John Meyers. He ran it on his car and Chuck Spera runs it on his and they love the feedback and responsiveness of the unit. It is pretty easy to retrofit and runs on a 12v circuit. http://www.unisteer.com/

 

It important for other Ultralite owners to realize the front suspension on Johns car is one of the later model units Brian built and it has much different spindles, control arms, inboard shocks and different steering arm locations. So even though John has done good home work to correct the issues he was having doesn't mean that you should all go cutting up your cars to move the steering rack. I would recommend checking your bumpsteer and most of it can be corrected with height adjustment of the tie rod loction on the spindle if you need to. Running 6 degrees of caster will keep the car tracking straight and true. This will provide a heavier steering feel and more effort at low speed to turn. This can easily be corrected with the electric unit listed above. I can easily turn lock to lock with 12" wide racing slicks standing still with one finger. I will be putting one on my new personal car.

[JohnK]

And here's the continuation of Steering II, Part 1.

 

I've jumped ahead a little here, because there was one thing left to do before I had all the specs necessary to order the rack. This was to configure the steering path, with the goal of having the pinion (where the steering column connects to the rack) as close as possible to the CL of the car. The longer the tube between the pinion and the end of the rack, the better supported will be the bushing at the end of the rack. This prolongs the life the bushing that the rack rod runs through and is the reason you have to have the rack serviced due to wear. Starting at the beginning, the question was where to put the steering wheel re its height. The chassis dictated that the Steering Wheel was going to be either high or nearly in my lap. I chose the latter and think I guessed correctly. Compare this

https://www.dropbox.com/s/pjwx1x2ew7hf4pp/da01DrivingPosition.JPG?dl=0

with (Crock's?) superlight R

https://www.dropbox.com/s/h6m5g3tk2lkpaqi/da02DrivingPos00cat-superlight-R.jpg?dl=0

 

What I'm finding as I learn to live with the steering is that I tend to move my hands down on the wheel so my bet paid off. Comparing the pictures, Caterham gives you a whole lot more length in the cockpit – I'm envious.

 

Steering path had consequences that kept me awake at night. If you look to the far left of

https://www.dropbox.com/s/xetm4ffmabtztob/ea01StCol01.JPG?dl=0

that tab clipped next to the secondary steering shaft represents where the U-joint that connects the steering column to the rack goes: it has to pass between the ARBar cantilever tube, serpentine belt idler pulley and P/S pump pulley. None of those parts can be moved – so if I ordered the pinion a bit too far toward the centerline, I'd have to redo the entire rack.

 

https://www.dropbox.com/s/yp3jztdeu6zzfbe/ea02StColumn03.JPG?dl=0

shows the complete steering assy in place (read Woodward's directions for fitting the different assy's he makes – 'course what my “kit” came with didn't take much coaxing for me to replace it.

https://www.dropbox.com/s/5nn2g8c6p51drk3/ea03StColumn04.JPG?dl=0

shows a support that needed to be fabricated and a closer look at the collapsible primary steering column (when fitted properly, it's designed to prevent the column from trapping the driver's legs in a crash).

https://www.dropbox.com/s/8y6a16t8y2eb32h/ea05StColumn.JPG?dl=0

 

Welding is coming along – it's hard to do when you're bent over the piece and standing up.

https://www.dropbox.com/s/bjvawl0hhpbubys/ea07bStColum.JPG?dl=0

Mock-up . . .

 

https://www.dropbox.com/s/w8nksmh3fyhin5k/ea07StColumn.JPG?dl=0

Reality. I've got 0.020” clearance at the PSP pulley and not a lot more on the idler and ARBar cantilever. Whew!

 

Plumbing the system wasn't nearly as bad as it looks, though it took some care fitting the PSP reservoir to conserve space. The blue hoses are right and left rack assist feeds, the black ones are high pressure feed (maybe 1200 psi) to the solenoid and solenoid exhaust. Feed to the pump comes from the bottom of the reservoir. Woodward sells what seems to be a special (at least to me) Gates Green Stripe hose and the fittings for this particular hose, all of which you can buy separately. I haven't seen this series of product available anywhere else and they're particularly valuable. The hose, for hydraulic hose, is relatively thin wall and can be bent to a very small radius. The fittings are screw together to the hose and reusable. So the series is light, can handle space constrained applications, and offers multiple fabrications if you're fitting a system together for the first time. I used a lower spec product for the solenoid exhaust due to the tightness of the fit and the fact that it was low pressure.

 

https://www.dropbox.com/s/7mjmpdl9ummvqk6/ec02PSPlumbing.JPG?dl=0

https://www.dropbox.com/s/flrgqh1odvk2r7l/ec03PSPlumbing.JPG?dl=0

 

The complete system is shown installed in

https://www.dropbox.com/s/tngmcr0jt6awx7h/ra00Rack.JPG?dl=0

https://www.dropbox.com/s/rdpeixqa9bqy29j/ra01RackTieRodAndStArm.JPG?dl=0

https://www.dropbox.com/s/d19qgmbjghsm7jr/ra03RackStColumn003.JPG?dl=0

and

https://www.dropbox.com/s/jx1jt6tvumdisto/ra04RackStColumn01.JPG?dl=0

 

Modification of the steering arm from a single shear to a clevis and shortening to give 11:1 steering is shown in

https://www.dropbox.com/s/oebslkfsfdv4gtr/ra02StArmClevis.JPG?dl=0

 

I forget what ratio rack I ordered, but I measured 22° lock on the outside wheel and 1 1/3 turns lock-to-lock at the steering wheel. With Caster at 3.8° and 3.9° I think that unassisted steering would be pretty hard to take advantage of.

 

I know I'm going to get PMs from folk recommending 12-step programs for people that get this carried away with their work... But I think if you went to, like, Dallara Automobili, you'd find them doing pretty much the same thing I'm doing here, 'cept it'd all be done in CAD/CAM which would have a bunch of accessory programs attached that would read out the consequences resulting from any particular placement decision. And the mechanicals they could handle would be much more integrated, detailed and informative.

There was also the fact that I learned that I could rely on NOTHING about the “kit” I received to be trustworthy and, if I valued life and limb, had to verify everything. So all of this was pretty much a necessity.

If you think the following is a bit more than over the top, then the other side of the picture lets you know why I have no respect for builders that throw a bunch of pieces together and expect you to believe that what they're selling is just like what the good Mr. Chapman created to become a legend. E.g. Caterham's been spending lots of money over the years doing very sophisticated analysis and development of their Se7ens and the performance of the car reflects that.

 

Anyway.... I put all of this together in the hopes that other people who enjoy build/developing a Se7en have some sort of reference for developing this part of the car and might be able to find a few bits that are helpful in their efforts. This is also payback for all the people who have taken the time to share their work and discuss their experiences over the years which has helped me along.

Edited December 26, 2016 by JohnK
changes mandated by Dropbox, clean up

[JohnK]

 

It important for other Ultralite owners to realize the front suspension on Johns car is one of the later model units Brian built and it has much different spindles, control arms, inboard shocks and different steering arm locations.

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The uprights/spindles on my car were and are stock Fiero. The car came with inboard shocks articulated by bellcrank but it was,. . . I'll just say it didn't work and leave it at that. The rack was the standard MGB aftermarket unit that Flaming River sells used in the Ultralite, repositioned in my car so that it cleared the inboard shocks, but wound up interfering with the suspension. Brian sent me pictures and descriptions of the rack in a stock chassis and I, after cutting out all the inboard suspension additions mounted the rack exactly as told and shown by the photos. So it is a "standard" system.

 

...]So even though John has done good home work to correct the issues he was having doesn't mean that you should all go cutting up your cars to move the steering rack. I would recommend checking your bumpsteer and most of it can be corrected with height adjustment of the tie rod loction on the spindle if you need to. Running 6 degrees of caster will keep the car tracking straight and true. This will provide a heavier steering feel and more effort at low speed to turn. This can easily be corrected with the electric unit listed above. I can easily turn lock to lock with 12" wide racing slicks standing still with one finger. I will be putting one on my new personal car.

 

My decision to start with a blank sheet of paper and to not use the supplied rack was taken only after spending a bunch of time wrestling with the geometry/relationships explained so well in the Woodward catalog and measuring what could be gotten from my car - and realizing that my car's setup had been developed to fit the available rack, rather than specifying a rack to provide the car with good steering.

 

Another of my intentions in putting together all of this material was to make very clear the amount of development effort necessary to size and place the rack for a steering system that had good geometry and gave good behavior. This was also prompted by people saying things like they wanted to buy "an anti-roll bar" or "a rack" for their car as if either were generic items that worked perfectly well in any setup. Such things have to be developed to suite each car, and that development takes time, skill and experience (or access to it).

 

The electric assist you reference might be perfectly fine: "whatever suites your needs" is the key. However, in my review of possible solutions, and as I noted in my post, the pump recommended for my rack is equivalent to a 3 HP electric motor. Commercial vehicles (a Honda Civic or S2000) have different requirements than something that aspires to being a race car so maybe an electric assist is just what is needed in these situations - but they don't have the requirements that a race car does, and neither do they behave as one.

For more visceral creds, the Mostler MT900 and Saleen S7 run the same rack (with its hydraulic assist). I can't be in too shabby company here, deciding on what system to fit to my car.

[Kitcat]

Hmmmm. Here I am, too lazy/busy to fix my Birkin's sticking E-brake and John is redesigning his steering system from ground up. And having witnessed John's obsessive attention to detail and doing things the "right way", I am sure his end product here is a work of art.

 

Old timers may recall that when Mazda did the Miata, purists cried so much about it having power steering, they finally offered manual (I had the manual version). Everyone (including me) agreed the power version was much better, better feel, easier to place the car where you wanted, etc. But car prejudices die hard.

[m wirth]

I'd just like to say that having the standard suspension and steering on my car and having had it set up by a very good alignment shop with corner weighing done with me and a full tank in the car, I''m totally happy with the way my car handles both street and track and have been complimented by several SCCA drivers that have lapped in it as to how easy it is to place on the track and the g's attained in the corners.

[JohnK]

Mike W

So how is your car concigured with respect to tire diam and section,, spring rates, and what was its weight distribution?

[WestTexasS2K]

John I have built 4 Ultralites over the years and tell you for a fact yours is different than all the S2k models I have seen. Yours appears to be a hybrid of the S2k body and Xr7 chassis components. That being said I'm glad you are getting it set up to your liking.

 

I've raced my Ultralites for over 9 years and have pretty good success with them. In all types of venues Auto X, Road Racing, drag racing, touring and One lap of America 3 times and thousands of road miles covered too. It took a few adjustments to get it dialed in. The biggest improvement I feel was upgrading the shocks to a set of Advanced Racing shocks. The ride is much smoother and has much improved over the QA1 units that come with the kits. The QA1 units can be revalved for better results but its much easier to turn a knob on the Advanced Racing units.

 

John curious what tire pressures you are running on your car? I have found tire pressures can really make huge difference in handeling characteristics. It can vary from brand to brand as well.

[m wirth]

Hi John, 225-45-17 front and 245-45-17 rear, stock size, my new wheels are 5# lighter each than the previous ones and the Nittos are about 1# each lighter than the older falkens. I put a new set of falkens on the same wheels for my street tires and use the nittos for track only. I have the stock QA's and never checked the spring rates. I'm not sure how accurate his older scales were but it would be relative to whatever was being compared to: lf 415# rf 385# lr 460# rr 440# these are with me 190# and a full tank of fuel 13gal in the car. Not perfect but good for a beginner, I'm going to give it another try later with better scales, it was level though.

[JohnK]

. . .

John curious what tire pressures you are running on your car? I have found tire pressures can really make huge difference in handling characteristics. It can vary from brand to brand as well.

 

Loren,

Changed from Falkens that came with the car (probably too old by now but definitely not a pattern that aids straight line stability) to Yokohama S.drives, and these made a huge difference in steering. Currently running 18# on both ends. Have not played with pressures. Am I correct in assuming pressures are for fine rather than coarse suspension tuning, unless they're varied by a large amount?

 

Thank you for the feedback. Next goal is to get it to understeer, which I have had no success achieving so far. Approaches have been to go down on front section tire width from 225 to 205 (which has helped considerably) and to stiffen the front anti-roll bar successively over several steps. Rear ARBar is just barely there (weakest position on a weak bar) Tried Chuck's suggestion of -1.5 deg camber and there was a bit of a change, but after some time spent pushing it in the twisties, the inside and middle of the rear tires were warm while the outside edge was cold - this leaves me wondering if it's good or not. Disconnected rear bar completely and found a very slight decrease in over steer, but when the rear stepped out, it did so much more sharply than with the bar connected.

 

Much head scratching. An even narrower front section (195) is a logical thing to test (he was last heard to say) but I'm wondering if there's a geometry issue involved. Spent no small amount of time getting rear ride steer to zero in bump and less than 2 degrees at full droop. Spring rates in front are 425# and 375# left and right (different motion ratios here side to side) and 170#s in rear (different mounts here than stock) - the fronts should be reasonably comparable to a 'std' car. VERY comfortable ride, little roll at turn-in. To select appropriate spring rates I calculated the wheel frequency since it takes corner weight and motion ratio into account along with spring rate. Do you use this metric? Corner weights, via Longacre scales, me in drivers seat, 3/4 tank fuel, are

LF: 424 / 342 RF: 379 / 279 LR: 423 / 349 RR: 437 / 366 wheel Load / un-sprung

48-52% Front - Rear

Wheel freq are

122 125 Front L & R

110 114 Rear L & R

 

Shocks are Koni 8212s. Haven't begun playing with the bump and rebound adjustments, but I gave Koni the spring rates and they set the internal valving from that. Calculated the right size and stiffness for the Bump Stop rubbers so that the shocks will not bottom at full bump. Shocks are designed to limit suspension travel at droop, and with my measurements, Koni fitted droop limiters to ensure the suspension never runs into the chassis at full droop. Woman across the street claims to have mystical powers and offered to channel Mr. Chapman or Mr. Smith to come help me out but I declined. ;-)

Thanks.

[WestTexasS2K]

Yes I used the wheel frequency to get it close and then will change rates up and down from there for fine tuning.

 

I found tire pressures make a huge difference on my car. I can run it at 21-22 psi and it will under steer 18 psi it turns right in. If you run them at 35 psi you can hardly keep the car on the road. It will want to skip over every bump in the road. I have found driving on the highway it is going to be very difficult to creat heat in any kind of tire on a 7. Even on the track pushing really hard with street tires they are still 20 degrees under desired temp at the end of the session. I have used from 205 and 225 and didn't notice much difference. I used the tire temp with a tire probe across the tire to see if camber is within reason.

[gjd6640]

I'm using Falken Azenis tires at the moment and have observed that in autocross-type conditions (including very spirited street use) running 18 to 20 lbs is a recipe for snap oversteer.

 

Setup: 18" wheels & the resulting low tire profile, zero degrees camber & ride height is set fairly high for clearance on the street.

 

When I run 30+ lbs I get good behavior from the rear. Grips well in a straight line, breaks away progressively (when I want it to), and just generally works really well. When running 18-20lbs at a club autocross-style 'driver skills' event one of the very experienced guys there advised me that what was happening was that the tire was 'rolling over' under load which greatly reduces the contact patch and causes the snap oversteer. Later I tested his theory by upping my pressures and have been very happy with the results.

 

What explains all of the 18-20lbs recommendations that I find here? If tire rollover is indeed the culprit are others dealing with that by running just enough camber to prevent rollover?

[Kitcat]

Most 7's including mine, run 1&1/2-2 degrees neg camber, some run more. I am a big believer in results trumping theory, so if higher pressures work, great!. Tire mfg makes a difference along w/sidewall stiffness. Hoosiers are said to "like air".