Hercules Rockefeller

My original assessment of what would be a good track suspension setup does not seem to be accepted by the road racing community, and I just wanted to know where I was going wrong. I thought the ideal track setup would have:

Stiff front springs, soft rear springs
Soft front sway bar, stiff rear sway bar

My thinking is, the stiff front springs prevent dive during braking, but the soft rear springs encourage the rear end to squat under power, giving more rear grip when you need it: at corner exit when putting down the power without incurring power oversteer.

The sway bars need to ensure the car with those spring rates will still have neutral/slight oversteer mid corner, which means you need to run a soft bar up front and a stiff bar out back to compensate for your individual wheel spring rates.

I know lots of guys run softer springs out back, but everyone seems to gravitate to heavier front bars and softer rears, which would seem to give the car massive understeer (a problem I frequently have).

Thoughts?

el es tu

from what ive seen here a lot of people go with stiffer (relatively speaking) front springs

the sway thing is a bit more up in the air and depends on your driving style and what you plan to do with the car

pfadt is in the understeer sway bar camp - you might want to pm them for some info

geerookie

WOW. Your looking to start a war....

Your reasoning is valid and in theory may work BUT....

Spring rates alone only cause confusion and misunderstanding. Spring rates are specific to a car weight and suspension geometry and if taken outside that context have little real value unless you are comparing to another car exactly the same.

Wheel rates result in a more fruitful conversation but still are somewhat specific for your exact car and situation.

These are the things that matter:
Corner weights in race setup
Motion ratios at all four corners
Wheel base
Camber gain at each corner
Ride height and CG height and location
Track width, front and rear
Tire and wheel sizes w/ offset
Unsprung weight per corner

I'm sure I'm missing something but that is a start off the top of my head. Give this thread a few hours and someone will pipe up with what I missed

You can compare wheel rates when cars have similar corner weights but all the other variables still have an overall impact on how the car will feel and whether it has understeer or oversteer in a particular situation.

geerookie

I think you may be talking about something else but I may be wrong.

Generally the discussion is about soft wheel rates and stiff sway bars
or high wheel rates and soft sway bars.

IMHO neither is wrong, they are just different

travisnd

Subscribed

FWIW most Corvette people run higher rear spring rates when using coilovers because the angle of the shock/spring results in a lower actual rate.

I.e. 600 F and 650 R springs still ends up with the rear end being spring softer due to the angles involved. I'm no expert, but this is what I've always read.

TriplBlk

This will be great info for my new GT2 coilovers/Pfadt HR's

el es tu

here is a condensed version of my experiences with messing with the c6 suspension.

note: im using oversteer and understeer in a relative nature - obviously you want a car thats balanced.
when i say oversteery springs im talking about the base springs, z06 springs, and t1 springs vs the z51 springs which would be more understeer oriented. The sway sets for the base and t1 are what might be considered more understeer oriented, while the z06 and zr1 fall toward the more oversteer side of the spectrum and the z51 falls around the center.

-------
running understeery springs took care of the rear end bouncing but kind of left the car understeering a bit more mid turn

running oversteery sways with oversteery (remember im talking in relative terms) spring set gave the car the easiest maneuverability and made it easier to keep the car closer to the limit, but the limit was lower.

running understeery springs and oversteery sways helped balance this out so i get the benefit of reducing the rear end bounce and decent turn in

I dont think you should run a stiffer front spring than rear, but I think you can change the ratio so the front is a bit stiffer in comparison to the rear
ie: I started with 420 front and 657 rear, and then went to 531 front/657 rear


as far as sway bars go, the front should be stiffer than the rear, but just as with the springs you can change the ratio a bit to make the car work the way you want more effectively
really you just want the car neutral

I think a bit a oversteer (mid turn especially) is a good thing, but some people are better with understeer

If you want, I can post a chart with spring rates and sway sizing along with f/r ratios to help you make comparisons

hope this helps!

Short-Throw

No ****!

Hercules, what type of shocks are you running?

People get stiff suspension mixed up with stiff chassis. You don't want a stiff suspension -- the suspension should be compliant and work with the car, not fight it. You do want a stiff chassis, a solid foundation will allow a properly set up suspension to work in harmony with the car's balance.

You'd be surprised at how low the spring rates are in some of the W/C and GTs cars running right now. You would lose all the adjustable settings of multiple bump and rebound the shocks offer theses days if the springs are too stiff.

Add in aero and now you're really increasing the permutations of desired settings. i.e. Running a large wing will push the rear of the car down possibly requiring more spring. Ideally you want springs and settings for each track you run. I run different bump/rebound settings for each track, but not springs as I'm simply not that talented to know.

Ultimately, it's what the driver prefers and most teams with multiple drivers in a race agree on a compromise.


Mike

RacePro Engineering

That thinking is correct, and it sort of works with 2-way adjustable damper settings. The problem with springs is that they work the same in compression as in rebound. So, one applies the brakes, the car wants to pitch forward, the stiff front springs resist (forming a sort of pivot on the front axle). BUT those soft rear springs allow the rear to rise, jacking the car up on its suspension.

Now the car is exiting the turn under power, and force is balanced to the rear, BUT those soft rear springs now allow excess roll, overloading the outside tire, and PRESTO: oversteer.

That is actually good logic, EXCEPT anti-roll bars can not compensate for any deficiencies in the springs. They are used to regulate how quickly cornering forces are transferred to the outside wheels/tires, and to target that transfer from front to rear.

I would also like to mention that racing suspensions generally need to be very stiff, so that settings remain -- well, set. If the car is not literally skittering over the track while braking, and toward the outside of the turn while cornering, you are not too stiff. And even if it is, the first thing to do is dial back on your damper settings, and see if that solves the skittering.

Hope this helps,
Ed

mountainbiker2

What is wrong with front end dive? I think it will help your braking. Just like the rear, you want squat when accelerating. Just the opposite for braking. When your turning, if you need more bite on the front, just tap the brakes and it will help transfer more weight on the front. Easier with softer front springs to get more reaction. I've tried the stiffer setup and I'm going to go back to a softer front. I'll find out this Sunday if it works.

Steve A.

Hercules Rockefeller

I think the problem with front end dive is that braking is a 4-wheel process, so limiting dive "spreads the grip" more evenly between the front and rear (although it's still mostly on the front, the more you can load on the rear the better). But when it comes to power, since the car is only driven at the rear wheels, softer rear springs could help improve grip at the rear at the expense of the front (which doesn't matter so much when exiting a corner). Might be different story with a 4-wheel drive car though.

Yes, hence the need for a relatively stiff rear bar; you still get rear weight transfer, but not much rear body roll.

This is the one I don't understand. Let's take the extreme theoretical example of a really softly sprung rear end, with a crazy thick solid rear sway bar. Such a car will drop like crazy in the back under acceleration, but the rear will have to 'stay flat' if the sway bar is so heavy that it doesn't allow one side of the car to move independently from the other, right?

fatbillybob

Rob...1:44 at ACS fastest TOD and nobody close and beating the T1 track record with a streetcar! Maybe your thread should be titled "I know what"s wrong with your spring and swaybar rates would you like me to tell you?"

RacePro Engineering

Right -- IF we do not consider the front of the car too, which of course, we must. In our theoretical racer, I agree about extreme squat under hard acceleration, especially if the front springs are equally as low a rate. However, it is the roll couple, or the front-to-rear roll axis, that limits how much force transfer that outside rear tire will see, and how quickly it will see it. For mechanical grip, that is much more important than whether or not the rear appears to stay flat from side-to-side.

Without getting deep into the geometry and formulae, it is safe to assume, with racing rubber, that "stiffer is faster". That applies to springs, dampers that are valved for those springs, and anti-roll bars. Can it be overdone? Probably not with anything that is commonly available. Now, whether or not the driver, at his stage of development, is capable of managing that degree of "immediate reaction" is sometimes an issue.

[Additional Note] Stiff suspensions stay better aligned with themselves. They also tend to control the attitide of the chassis more consistantly. And, if one adds under-car aero treatments, stiff becomes even more critical.

Our Formula Continental is a few pounds over 1000 with fuel and no driver. We use 750 PPI springs on the rear, and 450 PPI on the front. This 1000 pound car is supported by 2400 pounds of springing BEFORE anything compresses. And we are not the "stiffest" in the paddock. Just an example for oranges to apples comparison.

Ed

Hercules Rockefeller

OK, so let's include the front too, in our theoretical car, the front has crazy heavy rate springs and a soft (or non-existent) sway bar. The rear is softly sprung but has a crazy heavy rate sway bar. Such a car would have very little body roll under lateral load, since the front can't roll (due to the spings/shocks) and the rear can't roll (but here it's due to the sway bar). However, under heavy acceleration, the rear of the car squats like crazy and dumps maximum grip to the rear tires, allowing for early corner exit via a temporary understeer condition. Under hard braking, the car stays basically flat (thanks to the crazy front spring rate), minimizing braking distance by minimizing weight transfer to the front tires (and allowing more rearward brake bias). The only problems I see with this setup are that you would have to lengthen the rear shocks (or shorten the fronts) to get a sensible rake angle, and in the case where you have aero downforce, you might have a messed up rake angle at high speed (although you could also try to compensate for this with more static rake in the car).

Bottom line, and please correct me if I'm wrong: body roll can be controlled equally well with either heavy rate springs, or heavy rate sway bars. Therefore, even with soft rear springs (which allow for squat under power), you can still achieve rear roll resistance with a heavy sway bar. But since you never want brake dive, you might as well get your front roll resistance through the use of heavy rate springs up front.

Well, to be fair my street car was running on V710's. And my "street car" also has spherical suspension bushings, coilovers, heavy rate sway bars, and a rear wing But yeah, it moves pretty good on the track. That being said, i could always use a little more grip!

Hercules Rockefeller

This is exactly where I'm coming from. But my experience is that, at least with the Pfadt HR bars, the LG G2 coilovers with their stock 700/600 frnt/rear spings just gave too much understeer. I've since switched the springs to 600/650 and I like it much better, but I'm still getting a little understeer. Don't know how much more understeer I can eliminate by tightening up the rear bar, but if that doesn't do it, I might swap out the front HR bar for an LR bar (but keep the HR bar out back). If using the lower rate front bar eliminates my understeer and pushes me too far into over steer, i might correct it by going up to a 650 or even a 700 lb spring up front.

I'm starting to think the ultimate setup might look something like this: 700/600 front/rear, LR bar front, HR bar rear. Problem is, every time I screw with the spring rates, my alignment gets all screwed up... man I can't wait for my hubstands to arrive!!! What I really need is a full testing day at Buttonwillow, where I can change the springs/bars around, realign the car, test it for a few laps, bring it in, change and realign again, until everything is perfect. It would be a @#%# ton of work and it would take forever, but I'm sure I could squeeze a couple more seconds out of this car if I could get it to transition from mild oversteer in early-mid corner to understeer under power at corner exit. Along with a rear wing that steadily introduces more understeer as the car increases in speed (no oversteer at 100+ MPH for me, thanks!)

RacePro Engineering

Do Alonzo, Hamilton, Button, and Schumacher know about this?

mashinter

Yes they do, and it is a fundamental principle taught at the Bondurant School.

travisnd

To be clear that only applies when entering a turn. Doesn't exactly work for steady-state high speed turns.

RacePro Engineering

I didn't realize those guys were still going to school! Do you know when they will be there, 'cause I would like to sign up?

PushinTheLimit

Applying brakes to get more front end bite during a high speed turn...