N00B question on suspension tuning. Be kind.

Car - 86 951. Current setup is 400lb nose springs, 30mm rear torsions, koni yellows, camber plates, stock sways. Usage is DEs. Curbs out at about 3000lbs with me in it. Staggered, stock rims. (Agree some adjustable sways would be nice and am working on a set of 968 MO30 front and rear sways).

Car has a little more push in the nose than I would like. Generally thru the entire turn vs just on initial turn-in. I would classify it as mild to light moderate understeer.

Was wondering how much impact a 25 lb or a 50 lb reduction in nose spring rate would have on the turn-in? Have seen discussions on similar setups with the 30mm bar with others running slightly lighter springs.

Never have swapped out springs so it's not clear to me how much impact a change like this might have. Can anyone enlighten me?

Thanks!

Jeff

 

I don't know that I would mess around with springs too much until you get those sway bars. Those will definitely help. Making the front softer might not help that much... just make it roll over more. I run 450's up front on 30mm effective rear sways with 968 M030 on the NA race car. Still working the setup a bit but sways definitely made a difference.

 

Yeah. Figured that. What shocks you running? Konis or do you have something more elaborate that adjusts both ways. Trying to get a bit smarter about all this.

BTW, you gonna be up this way for the IRDC event? Didn't I see you mention that? Might be fun to meet up.

 

how much stagger in tires? running equal psi's front and back? a 3or4psi change in the rear tire pressure might be enough to balance it. are u scrubbing tires?

i'd say try psi change then up the rear sways. it's less effort to do than redoing the springs and ride height and another alignment.

 

Yes...I have 400 lb springs in the front...30 mm T bars in the back. It does push a little...I'm going to soften the front struts and front sways for the next track event in 10 days..will report back...if the snow clears...

 

put on some stud tires and go out even if the snow doesn't clear

 

Can you get your wheels/tyres to be of a more square setup front to rear? Do you only have one set of wheels that you use for street and DE? If so, it won't hurt to buy another set and put on some race oriented rubber if you don't have that already. Our cars typically exhibit exactly what you describe. Most cars are designed this way in fact. There are many different ways of tuning this out. Some are way cheaper than others. Depends on your budget and also what you want from this car.

 

What alignment settings are you running? A little more negative camber in front would solve the push. Borrow a probe pyrometer and check tire temps across the tread face (inner, middle, outer). This will tell you alignment and tire pressure adjustments to make.

Can you even buy springs in 25 in lb increments???

 

If you have push on corner exit then more front spring rate will make it worse. You want to make the rear stiffer. More rear sway bar could help.
The other thing is that you can play with turn in balance by technique more than corner exit. Corner exit is all about applying power and move forward. Corner entry you can adjust by trail braking and the way you turn in.

This weekend at the track I move my front sway bay by 3mm and it was a noticeable change in on track performance. At this track it was worth about 0.5 second on a 1:12 lap even when adjusting technique.

 

IMHO 400 lb springs are really soft. The last thing that you want to do is go softer in the front and have more brake dive. Find another way to dial out the understeer. You didn't mention how much front camber you run. I took my son's 951 (with 450 lb front springs) and bumped the front camber from -2.1 to -3.0. Voila, no more push, at all.

 

Thanks everyone. Hearing the words not go softer. More than OK to look at other solutions.

Answering some questions:

- tire is 225/50 in the front, 245/45 in the rear. RA1's, shaved. Yes, like to square them out but still need to get my hands on a second set of rims. Push is worse if I run streets (same size) or in the wet. Don't think I'm overdriving the front (too much brake & turn or too early accel)

- Running about 40 PSI hot in all for corners.

- Kystar - can you clarify about "scrubbing" tires. New term, not sure what that means.

- No, haven't done a tire temp test. That would be a good idea but need to locate some help, pyrometer to do this. Hoping to do it this summer.

- Camber was initially set at 2.5 front, 1.3 rear. Was getting a bit more front edge where than I liked so I rolled in some more (uh...more...but not sure how much) front camber. Did help the wear but less so the turn-in. Hoping the bar upgrade will help things out.

- Jerome, thought I could buy hypercoils in 25 lb increments. Remember trying to decide if I needed to do 375 or 400s for the initial setup. Maybe I'm wrong...

- TedA - love to hear the results of your changes. Good luck with the snow.

 

I ran (400 lbs F, 30 effective rate TB in R, and 968 m030 sways, with Koni sports F and R) before going coilover. You can get the puush out with alignment. FWIW, Koni says that 400 lbs is the max you can get on Sport yellows without revalving.

 

If you are talking about changing the ACTUAL front spring rate by 25 ft/lbs, the EFFECTIVE spring rate change will only be about 12 ft/lbs. That will have very little effect on a 3000# car. Personally, I wouldn't drop the front rate, but would look elsewhere (some ideas mentioned above) for a solution.

FWIW, I added 1/16" toe out on the front and the turn-in was completely transformed.

 

Rule of thumb:

1lb. of air in the tires is approximately the same as 10-20lbs. of spring.

Try before you buy.

Usual qualifiers and cautions apply.

 

Jeff,
One thing you are seeing is that there are 50 different ways to acheive what you want. However everything comes with a compromise.

Case in point. This weekend I ran fast times, However I had too much oversteer on turn in in 1 key spot on the track. So I did my 3mm stiffer sway bar adjustment. Worked like a charm in that turn. However what did not count on was how much it hurt me in 2-3 other places. That cased my lap times to get slower overall. So I just went back and had to 'drive around" the issue in that one corner. The proper solution may be different still, however no time to find it yet.


So front push could be made better, by lowering the spring rates, but that will probably may the car worse less stable at turn and in at straight line braking. More rear rate is probably better. You could also adjust the shocks to deal with the understeer or change camber. Stiffer rear t-bars might help too as well as wider tires.

I can't tell you which once is right for you.