Handling - Increasing front end grip

[SK400]

Friends,

Hope you are all doing well. I had a fun Columbus day last Monday as i had the chance to spend it at LimeRock for an HPDE event with SCDA. I even had the luxury of having my family and kids join for part of the day to cheer me up! Felt like good old racing days..

 

Thanks to all of your driving coaching over the last few seasons, i'm getting more and more confident with the car and i'm slowly learning what this incredible machine can really do. Although i'm pretty happy with the handling, i still think she is understeering a bit too much for my taste the way she is setup and seeking for advice on how to increase front end grip (and not at the expense of back end grip!). I'm currently running:

- 13' ZZR tires, typically 18 psi rear, 17 psi front (although i tried to play with it a bit with little results)

- 0 deg toe in toe out (super neutral)

- 2.8 deg negative camber

- 10 mm rake angle

 

A few questions:

- would increase the rake to 15 mm help a bit?

- would giving the car a 1/8" toe out help or will it only increase corner entry responsiveness?

- would like to avoid touching the rear sway bar setting for now

 

please let me know what you think. With good setting, better front end grip, more clement temperatures and of course better driving, I think i can break the 1 min barrier on this track and get into the low 59 second range (missed it by 0.22 seconds..!!!)

thanks all in advance for your help

[Kitcat]

Wider front tires? Or, same size but stickier front compound? Why not play with the rear sway bar-that is the classic way of dialing out push? Assuming the bar is adjustable, just stiffen it one setting. If it's not, you can likely find an adjustable rear bar. And, maybe this a beware-of-what-you-wish-for deal: a little push is much safer than over-steer?

[Warren Nethercote]

I am inexperienced in this but 2.8 degrees negative camber seems a lot. Are you perhaps overdoing it? My estimates of roll angle for my Locost 7 in a 1g turn (using Staniforth's methods) are of the order of 1.1 degrees, so that much static camber plus camber gain in roll could be over-doing it. But it's purely a theoretical thought: my car still sits very static on its build table.

[Croc]

First things first - when dialing in a suspension, change one thing at a time, test and then evaluate the result. Dont change all at once as you have no idea what made a difference.

 

I would not change the camber. The Avon ZZRs require at least 2.5deg to work best on non-IRS Caterhams on track. I agree with Warren that it does sound too much but it works in practice on track. Hopeless on road that way though and only works with ZZRs or slicks.

 

Wider tires just scrub more so thats not the solution.

 

I have always disconnected the rear anti roll bar - I think sevens handle better with some rear end softness as it enhances the weight transfer effects. You state you don't want to change the rear end but often problems at one end of the car are solved by reworking the other end. Easy one to try out in session 1 at the track - even if only to rule it out.

 

You could drop the fronts to 15psi. Some have gone as low as 14psi in the UK but that feels too low. Easy one to try at the track in session 2.

 

Never tested rake personally but I would be curious if the 5mm gain to 15mm does anything. I know Westfields are very sensitive to rake but never tested a Caterham this way.

 

I am traveling and cannot look it up in my car files at home but what is the Caterham standard spec toe? Toe out generally improves your turn in but rapid turn in does not always translate into higher front in grip as it can still push.

Edited October 13, 2016 by Croc

[SK400]

Thanks guys.

It looks like changing rear sway bar setting could be the easiest way to help the front end turn in a bit more It feels like I should stiffen the bar a bit instead of releasing it completely to have the rear follow a bit more. I have to say that when I understeer, it's normally at the entry of of curve and I'm normally able to correct it decently well with throttle until very high speeds when the front end scrubs and slightly drifts regardless of what I do (which I think is normal for the Cats )

[yellowss7]

Seb, Are you using enough Front tire? These don't understeer at all.:seeya:

[Nick OTeen]

It looks like changing rear sway bar setting could be the easiest way to help the front end turn in a bit more It feels like I should stiffen the bar a bit instead of releasing it completely to have the rear follow a bit more.

Correct. There are a variety of measures that can be taken to combat understeer. Stiffening the rear anti-roll bar is one of them. Others include:

 

Soften the front anti-roll bar.

 

Raise the front tire pressure.

 

Reduce the rear tire pressure.

 

Install wider front tires.

 

Install narrower rear tire.

 

Increase front toe-out.

 

Reduce rear toe-in.

 

Decrease front ride height.

 

Increase rear hide height.

 

Soften the front shocks.

 

Stiffen the rear shocks.

 

Increase negative camber on the front wheels.

[Dan3030]

Surprised no Storker guys chimed in and suggested aero...

 

Also, Nick, you clearly know a ton more than I, but did you mean reduce front pressure and raise rear?

[Davemk1]

My sense is that unless your caster is very low that you have more camber than is optimum. I would want to autoX the car or set up a slalom and run it and take tire temps across the width of the tire tread. My money says that you will find that the insides are a good bit warmer than the outside and that you aren't effectively using the entire width of the tire.

 

 

dave

[Nick OTeen]

...did you mean reduce front pressure and raise rear?

No. When trying to reduce the tendency for a car to understeer you want to raise the front tire pressure and/or lower the rear tire pressure. However, as Davemk1 points out above, you want to be sure you aren't already running too much camber in the front. Checking tire temps is key.

[SK400]

Ha! I too would have thought the opposite e.g. Lowering the tire pressure in front, within reason, would help the front end bite a bit more. I definitively can try that. I ran 18 in the back and 17 in the front. Does not hurt to try 18 and 20 respectively. Btw - thanks Nick for the exhaustive list of tips. Very helpful.

 

As for wider tires, I should look into it. Perhaps I ll try myself with full slicks next season just to feel the difference (if any!)

[Nick OTeen]

It does seem a bit counterintuitive but it also depends a great deal on where you are with existing pressures. It may well be that, for a given condition (track, temp, tires) you are already running pressures too high on the fronts.

 

Dig around online and you'll find lots of good articles that address the question of understeer/oversteer and car setup.

[MichaelD]

First set your corner weights ( with your weight in the driver seat, a big bucket of stones will do) and get the car balanced the way you want it. I like mine as close to 50 x 50 x 50 x 50 as possible. Add a little toe out and take it for a track ride. Adjust as needed one item at a time and drive a few laps and adjust again.

 

Adjustment advice for Caterham Academy follows:

 

Ride Height

Description

Measured from the chassis rail to the floor just in front of the wishbone attachment point. This needs to be a minimum of 140mm for the Academy, although it is generally set at 145mm minimum as there is little benefit to running on the limit and this doesn’t allow for any suspension sag or tyre wear. It should be checked regularly. Track miles will wear out tyres and cause suspension to settle and sag a little.

Adjustment

To raise the ride height, the upper platform at the bottom of the spring/damper unit should be screwed further up (compressing the spring more). To lower the ride height, the top platform should be loosened (decompressing the spring). Once set, the lower platform should be tightened up to lock them in place.

Benefit

Lowered centre of gravity of the car. This aids in all cornering, braking and accelerating.

Drawback

Little drawback other than grounding out or sailing too close to the wind with the regulations.

Camber

Description

Camber is the angle off vertical that the tyre leans sideways. It can be positive, where the tyre leans outwards, or negative, where the tyre leans inwards. You will only ever want negative camber. The regulations allow for 3 degrees negative camber at the front.

Adjustment

Normally, this is set at 2-2.5 degrees for Academy cars. Front camber is adjusted by releasing the top wishbone from the upright. The ball joint assembly is on a thread and ‘tightening’ the ball joint onto the wishbone will increase negative camber and ‘loosening’ the ball joint will decrease the negative camber. Rear camber is possible to achieve with metal shim inserts. The De-Dion has in built camber and for the Academy, it is rare to add any different setting as this reduces traction under acceleration.

Benefit

Adding negative camber allows tyre to sit flat on the road when leaning over under cornering load, therefore increasing tyre contact patch and so, grip under cornering.

Drawback

In a straight line there is a reduced contact patch on the tarmac and therefore less grip available to accelerating and braking.

Caster

Description

Caster is the angle around which the front tyres pivot when being turned. (The front wheel of a bike has lots of caster).

Adjustment

Front caster is adjusted using the lower wishbone, by using washers to push the attachment points forward or backward. Factory set is even with two washers either side of the attachment points. It can be moved forward or backward where all 4 washers are one side of the attachment points.

Rear caster is not relevant as the tyres do not turn.

Benefit

When the wheel turns, the caster adds additional camber. It is a way of getting more camber at the front of the car without breaking regulations. Most race engineers will want to set large amounts of caster.

Drawback

The trade off is heavy steering, making it harder to finesse the car and the car is less sensitive at turn-in. Driving style will determine whether these drawbacks are costing more time the the additional camber offers in grip.

Toe

Description

Toe is the angle that the wheels point away from parallel to each other. Where the front of the tyre is closer to the car than the back of the car, that is toe in. Where the front of the tyre is further away from the car than the back, that is toe out. Toe out is set for Caterham’s as this makes the car eager to turn.

Adjustment

Caterham’s are generally set with a toe out maximum in the region of 1.5 degrees per side at the front. You adjust the toe of the front tyres by turning the steering pushrods at either side of the car. This adjustment can also be used to centre a steering wheel that is slightly off centre.

In order to measure the toe, you need to set up axle stands around the car with pieces of wood or similar across the front. Tie string around the wood so that it goes from front to back parallel to the side of the car. (The exact dimensions of the ‘box’ you create around the car doesn’t matter.) You then position the string box so that the centre of each wheel is exactly the same distance from the string. You can then measure the distance from the front and rear of each tyre out to the string and the difference between the measurements is your toe.

Benefit

The car is eager to turn into corners. It wants to be going around bends and so makes turn in more responsive and positive.

Drawback

The car is more unstable in a straight line and will tend to move about. The tyres pointing away from straight ahead also causes drag in a straight line on the tyre as it slips sideways slightly.

Rake

Description

This is the amount that the rear of the car is set higher than the front of the car. Rake pushes more (raised rake) or less (lowered rake) weight onto the front of the car and therefore adds/reduces front grip. Lower rake lessens oversteer and increases understeer. Increased rake increase oversteer and reduces understeer.

Adjustment

Normally, this is set between 10-15mm higher than the front ride height. It is adjusted by raising / lowering the top platform of the rear dampers. Loosen off the lower platform, turn the top platform to adjust and then tighten the lower platform again once complete.

Benefit / Drawback

It’s more a case of driver preference and track requirements rather than benefits/drawbacks. It is a good way of adjusting the amount of oversteer in the car.

Flat Floor Setup

This doesn’t refer to the car sitting flat relative to the floor, it relates to the setup being carried out on a perfectly flat floor. For this reason, carrying out the adjustments for a flat floor is generally beyond the scope of an amateur builder.

As the car sits on scales on the flat floor, the weight that the car is putting down at each corner can be measured. The weights can be adjusted by raising or lowering the damper platforms.

In Caterham’s it is important to have the weight balance even across the front of the car to ensure maximum stability in braking.

Repeat Process

As each suspension component works in conjunction with all others, changing one will affect the others. Generally speaking, the setup and flat floor process is then carried out again until such time a geometry and weights are as good as they can be.

Front Anti-Roll Bar

Another element of the suspension that Academy cars have an option over is the front anti-roll bar. This bar dictates how much the car is able to lean over in corners. Academy cars are only fitted with a front bar and there are only 2 options. An orange bar, that the car is supplied with, and a red bar, that you can buy.

Theoretically, a softer anti-roll bar should be quicker however, a harder anti-roll bar gives a far better feel to the car and therefore many opt to use the stiffer bar. However, in the wet, the orange bar would be preferable as you generally want to increase grip as much as possible in the wet.

 

http://www.academyracer.co.uk/setup-morning-notes-for-the-absent/

Edited October 15, 2016 by MichaelD

[SK400]

Sweet! love the list. Thanks a ton for digging this up Michael.

If the weather holds and time allows, i may give it one more try this season on a track. Perhaps in November and try a bit of these settings.

thanks all for the advice

[BruceBe]

Sweet! love the list. Thanks a ton for digging this up Michael.

If the weather holds and time allows, i may give it one more try this season on a track. Perhaps in November and try a bit of these settings.

thanks all for the advice

 

As Mike said earlier, change, test, and measure *one* variable at a time.

 

Start by making sure all of your suspension pivot points are in good service - no sloppy bushings, loose swaybar links, or excessive wheel bearing lash. At turn-in, we don't want the mass of the car achieving momentum due to "slop" in the mechanical systems. Make sure you don't have a dead shock. The great news - you don't need a track day to check all of that.

 

At the track, I would start with the rear bar. Make a large change, potentially overshooting "neutral", and then back it off. More rear bar *adds* roll-couple distribution to the rear, meaning, more of the lateral load transfer is being accommodated by the rear of the car. As a result, you'll be asking the front to do less work - in most scenarios, this will cure understeer.

 

However, in some cases, the outside front laden wheel is falling over on itself during turn-in, due to a combination of tire pressure, spring rate, and suspension geometry. Tire temps will help you determine if suspension geometry is in the ball-park. Ideally, you'll jump into the pits right after a hard corner - not after even a medium length straight.

 

Cheers,

-Bruce

[SK400]

Bruce

agree. The good news is that my car is relatively new (2013) with little mileage on it so she is "solid" and in perfect condition all around. One thing that I don't do is take tire temperature after lapping sessions. I normally look at tire wear patttern to tell me whether parts of the tire are overheating or not building enough heat (at least that's what I use to do during my Karting championship years). Perhaps i should start experimenting with real tire temp monitoring. As for the sway bar, theee is an easy setting option I can try. Thanks for the input.

Seb

[Kitcat]

Seb: you can also take tire temps by heading to a deserted lot and doing donuts and then checking with a pyrometer. Bruce's concern is that after the straight stretch and maybe the cool down lap and tippy-toeing into the paddock and parking the temps will even out and won't tell you much

[BruceBe]

Seb: you can also take tire temps by heading to a deserted lot and doing donuts and then checking with a pyrometer. Bruce's concern is that after the straight stretch and maybe the cool down lap and tippy-toeing into the paddock and parking the temps will even out and won't tell you much

 

Or - with negative camber, you will always see a relatively higher inside tire temperature after a straight.

 

Cheers,

-Bruce

[MichaelD]

Accurate tire temps should be taken as soon as you are off the track. Maybe have someone meet you at track out and take the temps before they cool down at all.

[Andy69]

The first step is to model the suspension. I have a spreadsheet I use that I got from USRT.com. There are online calculators you can buy for a period of time that are quite reasonable. I usually use more than one and compare the results just to make sure I;m on the right track.

 

If you don't know the dynamics of the car, you're basically just guessing, and you're going to throw a lot of money at the car experimenting. And conventional wisdom is often wrong.

 

I recently did this to my Honda, and will do it to the Caterham after I become more familiar with it. It's somewhat time consuming and garbage in garbage out but the results are rewarding. You can play around with it - what if I removed the rear ARB, what if I bumped the rear springs up, what if I did this or that. I ended up getting new stiffer dampers and adjusting the rear spring rate based on the model. After adjusting the front ride height, and then the rear to be slightly lower, I corner balanced it. The result was a car that was so neutral it would do a 4 wheel drift mid corner. I could adjust slight over or understeer by bumping tire pressures a half pound up or down.

 

But, suspension setups are like opinions, which are like you know what. Another fellow has the same car I have and it's set up completely different, but I can't argue since he won nationals with that setup.