Hypothetical Autocross Question - Effect of Stiffer (Not Lower) Springs?

Hypothetical discussion: lets say you have a 3000 lb rwd sports car that's been pretty well-prepared for Stock Class auto-x. The car has fairly neutral handing and the shocks have been upgraded to high-quality adjustable rebound units which are generally run at maximum damping to help improve response. Springs are OEM as required by Stock Class rules.

Now, what would be the effect of swapping to stiffer springs (spring rate can be anything you want, presumably much higher)? For argument's sake, lets assume that the static ride height is unchanged and nothing else about the suspension geometry is altered. How would this change the way the car handles?

In my mind, this will result in a car with less body roll and quicker weight transfer (faster response to steering input, and faster weight transitions to the nose or tail during braking or acceleration). Since the car is not lowered though, it shouldn't result in significantly higher ultimate grip in a corner though, right? I guess to really answer that appropriately you would need some information about the camber curves, since with the stiffer springs the outside suspension will not compress as much during hard cornering, but assuming in either case, you were able to dial in the static camber to optimize your steady-state cornering, there shouldn't be much difference between ultimate grip with either spring setup, right?

In any case, if you were to make this change and, say, double your spring rates, what magnitude of improvement would you expect in times from a car that was already sorted and a driver who is national-level? (Assume a nominally 60 second long course). I realize no one can give a definitive answer here, but in ball-park numbers are we talking tenths or hundreds of a second?

I can't begin to guess a percentage change in times, but I suspect that the reduction in total body roll will result in a significant gain in cornering traction. I don't think most stock cars can run enough static negative camber to begin to compensate for the amount of roll they generate, and if they do, by that time they'd be forfeiting substantial acceleration/braking traction by running on the inner edges of the tires.

I suspect somebody more knowledgeable may also be able to give a rough idea of the time gained by being able to get the car settled at max cornering quickly, and transition quickly back to acceleration. If the time spent changing direction is reduced, that's more time back on the gas, so you'd see gains both in midcorner speed and straightline speed from braking later and accelerating sooner.

Okay, I'll go out on a limb and suggest that it'll be more like tenths than hundredths, and possibly more.

Awesome. Yeah, this is just the kind of discussion I was looking for. Keep 'em coming.

I think Ransom pretty much covered it. Unless this car has very good camber curves (that is, anything that doesn't use SLA suspension all-around is immediately ruled out) it should give a major improvement.

Also this really belongs in the GRM section.

GameboyRMH wrote: Also this really belongs in the GRM section.

Yeah, my mistake. I was looking at the build threads and posted it here by accident. If any GRM folks see this and can move it, that would be great.

Another thing to consider is the extra driver confidence that the better springs can provide. I've seen many times at our local autocross where someone will make a big leap in times after a particular mod. Not necessarily that the mod was that big of an improvement, but gave a better feel and the driver felt more comfortable pushing the car further. Kind of a psychological effect of having a more stable car.

I suppose that said springs will boot you from the stock classing?

Aside from theoretical advantages, one has to also considered legality. Note: Spoolpigeon has already mentioned it.

If the organizing club uses an SCCA-based ruleset, replacing stock springs is a breach of the rules. Check this link; page 77, section 13.8 for clarification: http://scca.cdn.racersites.com/prod/assets/2013%20SCCA%20Solo%20Rule%20Book%20Draft%20.pdf

While the substitution of springs is not specifically mentioned, remember the underlying tenet of the rules; "if they don't say you CAN do it, you CAN'T".

What is wrong for using a "4dr/wagon" spring instead of the original 2dr sedan spring? This is what I see being mentioned about without coming out and saying it.

Talk about worrying about all the wrong things....

Yeah, as far as legality goes, it would bump me out of stock class if I replaced the springs, even if they cam on another sub-model (the car has to be setup completely as a single trim level; can't mix and match parts from wagon/coupe/sedan, etc).

That's why I'm asking this as a hypothetical question.

You know the Yunickian workaround for this is to install hard-as-hell shocks...they won't last long but the suspension won't move so much.

Topic moved to the general forum since this is not a project car build thread.

The idea of a much stiffer but basically the same length spring is the basis of Shine suspension kits for VW Mk IV's due to the nasty camber curve when lowered combined with limited room for adding negative camber via adjustable top plates.

Another consideration - the difference in spring rates front to rear will effect front to rear weight transfer. If you get more work out of a previously underworked pair of tires you could signigicaltly up the overall grip and change the handling balance.

I wonder how this would work for a multi purpouse track, autocross, rallycross etc car. No as a cheat, but because you don't want to lower the car for rallycross, but want improved handling for the sealed surface stuff.

In reply to Adrian_Thompson:

I had similar thoughts behind getting GC coilovers for my E30, specifying an adjustment range that had "OE" in the middle. Lower for auto-x. Lift for rally-x. Since my car has H&R Sports (1.5" drop) on it now, I know for damn sure I'd never want the car any lower. It's annoyingly too low now.

Ian F wrote: In reply to Adrian_Thompson: I had similar thoughts behind getting GC coilovers for my E30, specifying an adjustment range that had "OE" in the middle. Lower for auto-x. Lift for rally-x. Since my car has H&R Sports (1.5" drop) on it now, I know for damn sure I'd never want the car any lower. It's annoyingly too low now.

The thing is I have a classic Saab 900, no easy way to do coil overs. Some people have built adjustable stuff using modified circle track weight jacks, but it's not easy. A one size fits all is needed.

To quote something I just read:

"Any suspension will work if you don't let it."

In effect, you are building a go-kart. You are now asking the tires to do all the work and making the job a bit harder by "Jolting" the tires every time you transfer weight. If the tires can hang on, you should be OK. Leaving the car at the same height is going to make it harder for the tires to survive the jolt.

An example of where this won't work is in the rain. The quick transfer of energy exceeds the available grip and you go sliding all over the place. Races have been known to disconnect sway bars to counter the low friction situations.

NOHOME wrote: To quote something I just read: "Any suspension will work if you don't let it." In effect, you are building a go-kart. You are now asking the tires to do all the work and making the job a bit harder by "Jolting" the tires every time you transfer weight. If the tires can hang on, you should be OK. Leaving the car at the same height is going to make it harder for the tires to survive the jolt. An example of where this won't work is in the rain. The quick transfer of energy exceeds the available grip and you go sliding all over the place. Races have been known to disconnect sway bars to counter the low friction situations.

That quote is normally credited to ACBC (Colin Chapman)

But I’m not sure I agree, I wouldn’t be talking about making it so nothing moves. I’d be looking at stiffening the car up to help with transitions and keep the suspension in a more favorable part of the camber curve and prevent extreme weird wheel tire angles. I’m also interested in getting rid of the front sta bar to help FWD corner exit traction without an LSD.