Spring rates

[SK400]

Winter is here!  Which means I’m now shifting gears to maintenance and slight upgrades on the car.   I finally plan to install the AP racing brakes (rear) I had ordered several yrs ago and considering changing my shocks / springs to nitron or core systems as I feel the car rolls a bit too much when leaning heavily into curves when using full slicks.   With that said, I’m reaching out because I’m trying to find out what spring rates I have on my car right now (and wonder if changing the damper system will indeed improve or not the handling or should I only upgrade the sway bars). Suspension is stock 2012 R400 superlight (wide track) for s3 chassis.   Any input or advice would be welcome.  Thanks all.  

[KnifeySpoony]

Can you take pictures of your current springs/dampers? Do you have the progressive rears? From the image above it looks like you have the softer springs up front which I believe are either 150 or 170 lbs/in. The "race" rates were 250F 215R, which is what I have on my car. This is what came with the "track" setup, as well as the uprated "race" dampers that they put on the R300/420R race cars until a couple years ago. However, now that those cars are on slicks, they run 300 front and rear. If you read the UK forums, people suggest running much softer rear rates like 140, but even with my 215 rears there is still quite a lot of roll and heave, but not enough to bother me (at least on ZZR). However, the balance on my car is excellent with these rates. On slicks, I think I'd want stiffer though. 300/300 seems a good place to start. Make sure you have adjustable rear bar to fine tune things.

[MV8]

If you drive on normal, bump, poor roads, I'd just try a slightly bigger front bar and leave the spring rates as-is, expecting it may shift the handling toward understeering. Keep the old parts just in case you want to go back. A bar would be more effective since the springs don't compress much in a couple degrees of roll, so the rate change would need to be much higher (living with the downsides) to match a small change in bar od. The bar is a better tool for roll either way. Front rates can fine tune over/understeer. Rear rates are enough to prevent bottoming.

If you can't find the spring rate info, the rate can be determined without removal using a dial caliper for the actual od (versus advertised 2.5") and the wire thickness (may need to lift to spread the spring to get the caliper tips in there far enough to measure), and how many coils have any gap at ride height (looking straight down a line between centers). I wrote a spring calculator if you want to share that info but there are calculators online too.

Exactly how much a rate change would affect the actual wheel rate would require more measurements and calculation. I don't know the details of the wide track mod. I assume the mod is lower control arms that move the coilover attachment outboard to maintain arm strength but reducing the effective ratio.

 

Apples to oranges I know, but the standard S1 and S2 have rates around 95# front, 60# rear but the effective ratio of the coilover mounting is probably very different (higher effective ratio). If the chassis moves up over bumps instead of the suspension compressing, you may be giving up some road holding plus high rate springs can come off the seats in droop with no weight on the tire for traction. No more than a 10% rate change if any is what I'm suggesting.

[IamScotticus]

After attending few courses on throttle steer from YouTubiversity Im considering stepping down my sway bar from the 5/8(red bushes) it is now to a 1/2.

Anyone want to swap out? I have the 90s uprated live axle suspension with balls on the bar.

[SK400]

Thanks all for the replies and apologies for the delayed answer back on the forum.  
 

KnifeySpoony - correct. After some research I do have the 170 lbs spring in front and progressive in the rear (probably 110 lbs).  I think this is the standard Road setup that came with the R400 car when I bought in 2012.  I’m quite amazed with the handling and until I started to drive with full slicks and with an R500 spec engine, I could argue that the setup was well sufficient for both road and track.  
 

I connected with Simon Rogers from meteor Motorsport in the UK.  He recommends a set of Core dampers and track spring setup with 250 lbs in front and 150 lbs in the rear.  He suggests that the ARB that I have from stock are sufficient (arguably the front one being a bit too stiff).   
 

i think I will pull the trigger and order a set.  They come with bright red springs that will match my car quite well. (As the NJMP gang knows, these little things and color coordination matter a lot to me… ). What’s more, I think I’ll save a few more pounds of weight compared to the stock shocks.  

 

Curious to know if anyone in the US has already bought and driven with the above mentioned Core spring damper setup.   Let me know.  
 

thanks all. 
 

 

[JohnCh]

I have a set, although I can only comment on appearance and weight as I'm still in the build stage.  For my SV, Simon recommended digressive valving in front with 275 lb springs and standard valving with 150 lb progressive springs in the rear.  They shipped with Hyperco springs though, which are blue.  I forgot to weigh the fronts before installation, but the rear pair are 5lb 4.8 oz lighter than the factory 420R Bilsteins.  

 

-John

[KnifeySpoony]

1 hour ago, SK400 said:

 

I connected with Simon Rogers from meteor Motorsport in the UK.  He recommends a set of Core dampers and track spring setup with 250 lbs in front and 150 lbs in the rear.  He suggests that the ARB that I have from stock are sufficient (arguably the front one being a bit too stiff).   
 

 

I don't see how that spring setup won't give you a big push in the car. With my 215 rear springs, I have my ARB on the 2nd hole from full stiff (4 positions total) and the car has a mild push at steady state, easily controllable with weight transfer and right foot.  You could get a bigger ARB in the rear to balanced things better, but on slicks, I'd really think you'd need more spring front and rear. I can try to find some pics of my car and show how much it rolls and compresses under G outs on track with my stiffer rates.

[SK400]

I asked that very question to Simon.  He assured me no understeer.   I too currently have my rear ARB set at the second hole from its stiffest. Now perfectly balanced.   I agree that I may have to get the next level of rear ARB diameter to balance things out.   

[KnifeySpoony]

You can always play around with springs on your new setup to end up where you want. Although you may need to get dampers revalved with big spring changes. And of course it depends on how and where you drive the car and your driving style. However, I still just don't get that rear spring rate on slicks on a track car. Especially if you are trying to go up in rate from where you are at now. Your current progressive rear springs may actually be stiffer in bump than a 150lb straight-rate spring, and you could end up on the bumpstops more with the new springs. Worse if you ever take a passenger. I know Meteor has a good reputation, but based on reading the UK forum, most of those guys do sprints and hillclimbs, which is very different to circuit racing in driving style and car setup. I don't know where all the racers hang out, but I'd love to know hey they feel about the current spec suspension rates.

 

Check out how the current top spec cars move around on track. Knockhill is bumpy so you can really seem them moving around and compressing over undulations. To me the cars hardly look like they are oversprung. 

 

 

  

Edited November 21, 2022 by KnifeySpoony

[SK400]

Based on your experience, are you then suggesting the Caterham “race” setup?  You seem pretty happy with it, are you ?

[Croc]

 

Lets reset some of this discussion as both SK400 (Seb) and KnifeySpoony are right but seemingly conflicting which gets confusing.

 

The video is from Academy Cars at Knockhill Circuit.  Academy Caterhams have 125hp Sigma and are considered an "R" setup (think 150R versus say a 150S).  It is a blend of road and track suspension.  So yes they are softly sprung and move around a lot but they run on a control tire (Avon CR322 from memory - much less grip than an Avon ZZS let alone a ZZR) and have single suspension option for all weather conditions, which in the UK can be all 4 seasons in a few hours.  So the suspension softness is by design.  

 

Meteor Motorsport is not just sprint and hillclimb.  Yes thats what you read about on Blatchat but Simon does a lot of work with circuit racers - Caterham and other forms of motorsport, such as British Touring Car Championship.  

 

A lot of this discussion above is relying on anecdotal from an expert being consulted plus seat of the pants from a good driver - good stuff.  But it needs context.

 

The right way to set up a car for track is to calculate what you need.  That gets you ballpark which you then tune through testing to get it to the fine point what feels right.  This is an awfully complex topic and there are individuals on this forum with a lot of knowledge in this area and some with not so much.  Starting at the lowest common denominator (apologies for the experts reading), have a read of these 3 links:

 

How To Pick The Right Spring Rate - Rated A For Fun (motortrend.com)

 

2017-Motorsports-Catalog.indd (qa1.net)

 

Spring Rate Calculator - Ridetech

 

There are some superb books available on this topic if you are interested or have trouble sleeping.  I have some titles lurking in my library at home or the garage - need to find where they are.

 

This does not touch on dampers which are a whole other world of complexity.  

 

Keeping this really simple to level the discussion, lets talk to some rules of thumb:

 

1) The less mechanical grip a tire has the softer the spring you want.  Why?  A more accentuated weight transfer of a vehicle will maximize the grip available via the contact patch.   So a slick-shod car can get away with a much firmer suspension as the forces acting on the car are higher thanks to higher mechanical grip and/or possibly the weight of the car itself.  

 

2) The springs are integral on how you set up the suspension - toe, camber and caster - as these will impact the contact patch.  So for example, I have an 1985 Holden Commodore World Touring Car Championship race car.  It weight 2700lb and runs 800lb front springs and 300lb rear.  Why are the front springs so hard on a relatively light car?  Because it is a production car not designed to race it will resolutely plow understeer under standard settings.  But if I dial in -2.5deg camber and max out the caster it will turn in like a champ and rotate through the corner off the front wheels.  This compares to my BMW E9 CSL race car which is the same overall weight but runs 350lb front springs.   Whats my point?  A spring rate is single part of the overall puzzle to make the car handle.  

 

 

It is not a given that a 250lb front spring Caterham will push on the front end.  I am sure Meteor has run the numbers to confirm plus has other customers where they have data to prove it works.  Seb is planning to run slicks so mechanical grip is high and he has (for the moment) 250hp to play with plus he is the fourth best driver on USA7s.  

 

However, the catch with that firm set up is the moment grip gets compromised (e.g. it rains and the track is wet or it is spring and it is a cold morning) then that set up is too hard.  You want to soften for the wet conditions as the accentuated weight transfer from a softer suspension maximizes the grip available through the contact patch.  What a race team would do is change the springs to something softer for the conditions.   Seb will not have that easy option and will have to slow down (or just spray off into the scenery again...).  This is why I believe a Caterham used for track days should just stick with a slightly softer suspension as a compromise.  There are no trophies and no prizes for the winners.  Nothing wrong with a softer set up on track - I run it on my silver CSR with slicks.  Yes she rolls but the sacrifice is only maybe a second a lap and I gain the ability to use the car through all 3 seasons without any faffing to change set up.   

 

CatKong (if it ever gets finished) will run 300lb front springs and 225lb rear.   Yes I did the calcs myself as I did not believe they could be that high when told initially.  

 

I reached out to a Caterham UK race team manager with a fleet of race and track Caterhams to ask what the consensus is with his various cars.  Will add to this thread once I hear back.  

[KnifeySpoony]

15 hours ago, SK400 said:

Based on your experience, are you then suggesting the Caterham “race” setup?  You seem pretty happy with it, are you ?

 

I actually have the "track" setup, which used the same race-rate springs at the "race" dampers but using the standard lower-spec Bilsteins. When I ordered my kit, I didn't know that much about these setups tbh. The track setup was a minimal (I think like $200) upcharge over the standard R dampers, while the race setup was something like $1500 iirc. Honestly, i'm kind of a suspension snob (run double clicker Penske on my prior exige, and my track bike), so I thought I would almost immediately pull out the bilsteins and put on some adjustable Penskes or similar. However, I've been pleasantly surprised with the standard track setup and after 2 track seasons have no plans to upgrade yet. I feel the damping is pretty good and the spring rates are right for a mostly track-driven car (I still drive it to/from the track) on either the ZZS or ZZR. The balance is great and the car handles Sonoma (with its 3rd world surface) very well with plenty of compliance. It does heave a bit over some undulations, which is much worse when 2 up (I occasionally will take a passenger). It definitely needs more rear spring and damping if it was to be driven 2 up regularly. The car pushes much worse with a passenger on board. With more mechanical grip than the ZZR, I would also want to go up on spring rates, maybe 300/250 or somewhere thereabouts.

 

 

 

5 hours ago, Croc said:

 

 

The video is from Academy Cars at Knockhill Circuit. 

 

My link was supposed to start right before the first race of the video which is actually the UK Championship cars, AKA 420R  formerly known as R300. They are on slicks with 300/300 springs.

 

 

5 hours ago, Croc said:

 

It is not a given that a 250lb front spring Caterham will push on the front end.  I am sure Meteor has run the numbers to confirm plus has other customers where they have data to prove it works.  Seb is planning to run slicks so mechanical grip is high and he has (for the moment) 250hp to play with plus he is the fourth best driver on USA7s.  

 

It's not about how stiff the front springs are. It's about the relative roll stiffness of the front vs the rear axle. Stiffening the front but not the rear is what generates the understeer.

 

 

5 hours ago, Croc said:

 

 

I reached out to a Caterham UK race team manager with a fleet of race and track Caterhams to ask what the consensus is with his various cars.  Will add to this thread once I hear back.  

 

I'd be very interested to hear his feedback as well.

[CarlB]

Despite all the manufacturers know about vehicle dynamics it has never been defined quantitatively. The manufactures and the Formula One teams all use a combination of

qualifiable and subjective analysis to tune a cars handling. There are two distinct areas

that haven’t been quantified: the driver and the vehicle dynamics of the car. If you look at

a vehicle like a rocket, the control system directs the rocket. The control system in a car

is the driver. Every driver is different, even among elite race car drivers. That is why

great race car engineers and great drivers sometimes do not work out. When you drive a

car what do you sense that conveys control? What inputs do you use when given feedback from the car? The car is as complicated a problem. There is very good math for figuring out the kinematics of suspension systems, and good rules of thumb to pick spring

frequencies and percentage of damping. This is the type of thing I assume Croc was

referring to. However, it isn’t complete. The manufacturers and high-level race teams

have models of the dynamics, but they still are not complete and require subjective

analysis. Tire models are a particularly difficult problem. Trying to quantify vehicle

dynamics has been going on for a long time. Mercedes Benz was working on it before

World War Two. There were big improvements in the 1960s because of work sponsored

by GM and conducted primarily by Bill Millikin. The six-wheel Tyrell was part of a

effort by Goodyear to quantify vehicle dynamics. A Ford engineer named Mikey White

put transmitters/antennas on a car and multiple receivers around a racetrack. It took

weeks to set up and they got tons of data they couldn’t properly analyze. This was done

in conjunction with the Ford Stewart F-1 project, but it was seen as very useful to Ford.

 

Having said all this, is it useful to us? Even figuring out the kinematics,

spring frequencies and damper percentages takes a lot of time measuring

the car and input it into a software program. There is a lot to be said about

paying for experience and buying components from someone with a good

reputation. He might not have what is best for you, but time and

experimentation might cost you more time and money.  

 

If you would like to read something I would suggest one of Croc’s country men. The Dynamics of the race car by Danny Nowlan. I will warn you it gets into math really quick. It is a newer book and has the current approaches. Bill Millikin is still the gold standard. 

[Croc]

On 11/21/2022 at 10:49 AM, KnifeySpoony said:

 

 

I'd be very interested to hear his feedback as well.

 

Thank you to @JohnCh for inadvertently reminding me that I had not posted this feedback this morning.  Its amazing what random notes in a briefcase clean out can do.  

 

 

The TFL UK race team 420Rs generally run 250lb springs allround, 10mm pre-load on fronts and 5mm pre-load on rear.  If the driver finds the rear a little too lively then the solution is drop back to 215lb springs at rear.  

 

If they are in a race series they use a standard Bilstein non-adjustable control damper - thats what they are limited to.    If not restricted by the race series then he moves to a single bump/rebound adjustable damper to allow finer tuning for the driver preferences and/or weather.  

 

Given a number of the guys driving have done Top 10 results in European series races then it obviously is working.  

[CarlB]

Thank you Croc! best information I have seen. Do you know what tire they are using? 

[Croc]

All are using the softest compound version of the Avon ZZR tire.  All are on 13 inch wheels.  Widths vary for preference between staggered front/rear set up or square set up.  Most are running 13x7.5 square set up using the Caterham wheels - Apollo or Orcus styles.