S2K track suspension set up???

[jimrankin]

Even though each S2K is a bit different, and every driver has his own preferences I'm thinking that having a reference point from a "sorted out" track set up car can give me some comparison points to see where mine differs. Has to be better than just "dialing for grip" anyway.

I've always had a problem with the car being tail happy, almost frightful with the original tires. Helped a lot when I installed new Nito NT-01's but it was more of masking the problem with better overall grip than curing it. Now that the NT's have about heat cycled out it's getting past the "fun point" on track and i want to try to find the underlying problem before I just get new tires.

My S2K is on the "heavy" side at just under 1,400 Lbs and close to 50/50 with the front just a bit heavier.

A few details and such. Tires are NT-01's as noted, 17" 235/40 fronts, 17" 275/40 rears. Seem to have no problem with the front grip, only the rears. Initially the fronts seemed to show a little more wear than the rears but as rear grip has gone away the rears have now outworn the fronts. Wear is consistent across all four tires, no unusual on either edge or centers. I can never seem to get the rear tires to heat up past about 130-140 degrees and it's within a few degrees in/center/outside with a probe pyrometer right off track on a warm and sunny day.

I'm kind of thinking maybe it's spring rate related buthave no comparrisons to what I'm running. Fronts are 525#, rears are 340#. No anti-roll bars. shocks are QA1 coiul over with non-adjustable rebound and I don't know just where the factory set them.

Anyone with an S2K that has been through setting it up and is happy with what they have is beseached to please lend me some advice. Caster, camber, toe, spring rates, anything they can think of will be of help I'm sure.

Car was set up with the new tires three years ago but it was a "best guess" four wheel alignment. Thanks for any help. JR

[joshesh]

I'm guessing not enough camber in the rear for the nt01

[jimrankin]

Hi Josh,

Inside tire edge is fully heated so that usually rules out being under cambered. I'm hoping to see if someone has had any of these issues and found a correction. I'd say that my problem was all due to my driving ability but since I'm pretty familiar with the tracks, driving lines and my times from before something seems strange. If the front didn't still feel so planted and the turn in so sharp I'd say it was all due to tires having fallen off. Unfortunalely I can't swap front to rear because of offset and tire size so stuck there. Come on up to the next track day and we'll put my tires on yours and you can take a free skating lesson. LOL.

How were the slicks at the Autocross compared to the Nitos?

[jlumba81]

How about adding a little rear toe in? Maybe 1/8"?

[joshesh]

Jim,

 

I really liked the new slicks, nothing like having 11" wide tires coming from the NT01 "street tire" that it came with. My car has 225 front and 255 rear, so you may have a slightly harder time getting heat into them.

 

Here is a video from Saturday with the new tires:

 

The toe idea will help some.

[Mondo]

I'm sure Loren will chime in soon. He told me the rear needs to be pretty soft and squat down a bit. He recommended 250-275lb springs He likes it a little stiff and has 525lbs up front (probably best for track).

I had a similar problem with it being tail happy after getting it corner-weighted (mine came in at 1450lbs with 3/4 tank). Plus I had 350lbs springs on all four corners (probably same QA1 shocks too). I thought it might be that the rear was so low, it didn't seem to have much travel and felt like it bounced around. I raised the spring collar 3/4 on all shocks and now I have understeer. Probably should of took measurements of the chassis and raised it the same on all corners. Anyway, I think I like a little understeer at the limit.

Now I've put 450/250 and it's a lot more neutral (with worn out Falkens). I'm going to go with some NTs but I think I'm going to reduce the rear tire size from 275 to 255s (225s up front). I need to get it corner-weighted, with me in it, again..

Bottom line- go with softer rear springs

http://www.qa1.net/qa1_motorsports/drag-and-street/springs/1-875-in-i-d-coil-springs.html

Edited June 12, 2012 by Mondo

[WestTexasS2K]

Shocks that come with the car are entry level units. A set of good adjustable shocks make a big difference. I like Advanced Racing Suspension but there are others. I think your rear springs seem a bit stiff. If you are experiencing oversteer try droping your spring rate 25lbs. Experiment with tire pressures too.

 

For alignment on the front I like 1.2-1.5 degrees of Camber same for the rear. This can vary with type of tire you are running most radial construction tires run well in this range. Check and make sure you are not getting bump steer in the rear. If the rear bump steer bar is out of adjustment you can get some rear steering with the body roll. I prefer mine mounted in the upper bracket or just about that point. If you have it located on the bolt with locking collars that the car originally came with then you might be having toe change in the rear. There is no one set up that is best. It can change from track to track, driving styles, tires and the whole host of variables. There are numerous books on tuning the suspension and even a few quick refrence guides to help you sort these issues out. What works for me doesnt mean you will like it. I prefer the rear of my car a little loose and tend to drive a little more with throttle than just the steering wheel.

[jimrankin]

I'm going to check into getting softer rear springs first and then might want to upgrade the shocks after I see what spring change does. I have the bar mounted in the upper bracket and as soon as (or if) I find the print out I'll check what I have for camber but I think it's about where Loren noted he likes it.

Still would like to hear from any other S2K drivers if they had the same problem and found a fix.

[rnr]

I'm going to check into getting softer rear springs first and then might want to upgrade the shocks after I see what spring change does. I have the bar mounted in the upper bracket and as soon as (or if) I find the print out I'll check what I have for camber but I think it's about where Loren noted he likes it.

Still would like to hear from any other S2K drivers if they had the same problem and found a fix.

 

 

I have some (relatively) softer springs you can try out before buying anything new.

[jimrankin]

I've been dealing with a really huge drop off in the traction, mostly rear wheel, for the first four track days this year over the last one last year. I just did the fifth track day and what a difference 40 degrees+ makes. Both my Laguna Seca and Infineon days were all COLD, like padded ski jacket cold. I was getting rear wheel hop/lock up under braking, loose to the point of heart stopping half spins at what used to be 80% speeds for me and was beyond frustrated as tire pressure seemed to make no difference and everything else was unchanged.

Was at ThunderHill yesterday with the Golden Gate lotus Club and the temperatures were well above 100 degrees early and climbing. Whoopee for heat, all my problems seemed to have vanished! Started to realize that I hadn't done any early season track days in '11 due to my wife having been injured and me being a good hubby didn't just leave her to fend for herself. I thought that three years and probably over 100 heat cycle have about done in the NT01's but they sure got sticky again. I had never gotten my probe pyrometer above about 115 degrees at the first four events but was well up into the 160's yesterday and everything was working. I guess I'm running too much tire for cold days so it's now either wait for hot weather or go "skinny" on another set. .

[JohnK]

This is a great discussion. Sorting out my car, so far, has shown me that it wants a stiffer front to avoid oversteer. The target/ideal behavior I'm aiming for is understeer through most of the range with final oversteer. To limit camber change problems I'm running front and rear ARBars, and finding that it wants way more front than rear. Unequal parallel links on the rear (all s2ks that I know of have this) put the roll center on the ground which gives low weight xfer giving great traction. So there's gotta be some strange geometry going on as things work to generate the oversteer that everyone sees. The rear setup has very little camber change in ride (i.e. bump/droop) but camber can equal roll giving awful changes in camber (which is why I'm running ARBs). And ride steer at the rear can cause behavior that you dont want. With 50/50 weight distribution, oversteer shouldn't be a problem, but of course then there's the fact that it is.

[rnr]

So there's gotta be some strange geometry going on as things work to generate the oversteer that everyone sees.

 

 

With 50/50 weight distribution, oversteer shouldn't be a problem, but of course then there's the fact that it is.

 

Not all of us have oversteer issues. In fact I originally found it quite difficult to rotate with a lift and it was only this year that I finally got the car to repeatably and reliably lift-off oversteer at the track. Power oversteer on the other hand is always available and IMHO very controllable.

[jimrankin]

I think the basic suspension set up of the S2K provides for lift oversteer and it might be that the larger rear tires some of us run might overcompensate this a bit making it hard to rotate. When I was having the "cold tires" problem earlier this year I was getting snap oversteer with lift which really compounded the induced (with very minimum power)oversteer. I could over-rotate the car with minimal power or a lift and really had to feather the power to get the car back "in line".

My rear tires have much more wear than my fronts and now that they have "gone off" a bit and I was running them in enough heat to get them up to temp I found the car to be really balanced, much more so than when the tires were newer. I am running a staggered 235-275 and probably should have gone with less rear tire. I had a set of 205's F/R to start with and found the car so easy to oversteer that I probably over did the rears for that reason. "Too much of a good thing" syndrome.

Just as a point of reference, the front end stuck like glue with both the 205's and the 235's. I've never had to worry where the front tires were going. LOL.

[joshesh]

You can borrow my 255s for the rear on the next track day. I think my car has 225 fr 255 rear

[Mondo]

I'm thinking new tires and will probably go 255 for the rear this time.

[jimrankin]

Thanks for the offer and I may take you up on it. Also a great way to get you up to the track one of these days and see what your car does on the new slicks. Since RNR's car has been out with engine problems I've been the only "7" at my last three track days.

[twnpipe]

What tire pressures are you starting from ? With a modified CMC framed car on track days I started with 18/20 rr, 205/50/15 on 15x8 wheels, modifed CMC framed. At a local autocross I tried 18 and went to 16 which was wrong.

[jimrankin]

Starting "cold" at about 14.5 rear and about 15 front. That is at around 65-75 degrees. With the cold track days I wasn't even raising the pressure more than one degree after a session, probably because I wasn't generating enough traction to work the tire body enough to get any stretch in the core where the heat is generated. The readings were fairly consistent across the whole traction patch with centers so close to the edges that dropping the pressure to get more core flex would probably have just cooled the center and raising the pressure might have taken away any edge bite.

With your 205 width and a tall sidewall your going to need quite a bit more pressure to keep the tire contact patch and sidewalls shaped.

I didn't buy a pyrometer until last year. If I had had one three years ago I would have known after my very first track session with the new tires that I was just riding on the centers.

I started tracking these tires (NT01's) 3 years ago with full tread. Having seen just how long they have lasted I should probably have had them shaved to start with even though I also do a little street driving with them. I'm sure that on almost anything but a "7" they would have heat cycled out or corded a year or more ago.

When I first changed to these "big" tires I did two complete spins on the first day, both through snap oversteer at corner exit under too much throttle. I had started at 25 pounds cold and that was WAY too high. Dropped to about 18 hot by the end of the day by taking out a couple of pounds after each session and that seemed to be pretty good, no more power spins.

I think that if Josh does a track day with his 235-255 stagger he will probably find it more ballanced.

The fronts of these cars seem to be able to use anything from a 205 to a 235+ without any issues. Possibly more rear brake lock up issues with the larger front tires fitted but that can be dealt with and who doesn't like all the "stop" they can get. I had to change my rear brake master cylinder to a larger bore, set the mechanical bias to full front and crank the hydralic bias to the least possible rear pressure but it now feels like the fronts are at least approaching lock when the rears get there. Took me a while to reach that set up and I still find myself lifting or breaking too early because of past issues being tatooed into my mindset. Also, I have 12" rotors front and rear and for anyone building a "7" at this point take my advise, that is too much rear brake.

[twnpipe]

Is your pyrometer used just for surface temp? I was thinking of trying my HF cheapy but if it is core temperature that is needed it will not work.

For an autocross i tried 18/20 and then dropped to 16/18 and the car would not turn at all even with an increase of track temp. of 10 -20 degrees as it was midday. thanks

[jimrankin]

I use a probe on my pyrometer as the surface readings are too apt to be changed by either air cooling them rapidly or having the temperature evened out by the cooler padock surface as you drive back to where you have parked.

It's important to get the probe point all the way in at each reading point as the tire is "hotter" the deeper in you go. All the way in keeps the depth even.