I autocross with the local club in SM w/ a street tire index. I feel like Im getting too much roll and at first thought, my plan is to upgrade to some stiffer swifts.


Evo 8
~3020lbs w/o driver
FA510s, race valved w/ off the shelf 10k/12k springs
245/40/17 ZIIs
Tanabe front bar w/ cusco plates, hotchkis rear bar, both full stiff
RCK, offset PSRS, all front bushings replaced, LCA and trailing arm bushings replaced in rear.


My initial plan was to just get some swift 14ks now, put the 12s in the front until I jump to Rcomps, then get some 16s. But I talked myself into just doing swift 14/16k now.


Im ordering the springs through FA, the 14s are backordered, so I took the delay as an opportunity to ask them what they thought and they are suggesting a different valving profile and keep the 10/12s on it. Does this make sense? Is my problem more related to weight transfer and not steady state roll stiffness? Is the car just too low and its screwing up geometry? Are 14/16s going to be too much? Note that its not driven much on the street and as long as its drivable, Im good.


Here are a couple pics for reference.


any advice would be appreciated


Charlie

 

Just from looking at the pictures and considering you are running street tires instead of Hoosiers, you do have good amount of roll. You could use a bit more stiffness in the front even if you are staying with street tires. In general, good rule of thumb is to have up the 1.5" of travel with your tires. Anything more than that requires some settings that will have other issues (like more camber would be OK for turns, but it would be harder to put the power down). You also have to measure tire temps to see what kind of contact you are making with current setup and go from there.

 

Are those photos taken with your cusco bracket on full stiff? How does the car feel? Do you have any photos of the car static to see the ride height?

As you probably know I've been experimenting with stiffer setting on my FSB adjustable bracket thanks to your assistance with spacers and such. I will be going to the next stiffest setting on my car and see how it responds.

But back to the topic at hand. I see where you are coming from as I was questioning the same thing last year with my setup. I ended up jumping to 10k/ 11.7K this year which is essentially the same rates except Im lugging another 200lbs around with my pig of an evo which gives your rates an advantage in the stiffness department. In my case the car feels really good in terms of the balance. I really didnt feel much of a difference going up ~2k though; I thought it would be more noticible but it also wasnt a back to back comparison bc I threw on a set a stock struts in the winter before I made the switch.

What I question though is how detrimental to the cars handling is body roll? When I first jumped to my Ohlins coming from a Bilstein setup I really noticed the difference in the slaloms as the car felt way more stable and wasnt upset by the sudden changes in direction back and forth.

At what point does the car become oversprung? I know it varies given the surface you are racing on but a set of street tires can only provide so much grip. If the car is oversprung I could see it being skiddish or twitchy at the limit.

I wish I could give a solid answer here but unfortunately I'm more or less here to learn.

 

I think we all know by now my preference, but I would start with just upping the fronts to 12k springs and leaving the rear alone.

heel2toe: Over sprung really depends on the surface you race. Obviously a glass smooth track will tolerate stiffer than a rally course. Also, I have a suspicion tire rate is coming into play at the rates we run. Since a tire is in series with your spring between the ground and chassis, a street tire with a softer rate will tolerate more main spring that a race tire.

That idea is mostly theorized in my head, but it makes sense. My car is pretty light and courses I run on pretty bumpy so I don't want to be near that 3.0hz range. If I were making a track only time attack car with Aero, I would probably run in the 3.5hz range no problem.

 

Dallas- Am I understanding you correctly in that because the tire also acts as a spring, you can get away with more spring in conjunction with street tires relative to race tires?

I always assumed the exact opposite thinking that with more grip comes more body roll and thus more spring is needed...Im a complete newb when it comes to this stuff relative to all of you track junkies but I love learning and of course going fast so I'm all ears

 

thank you guys for the feedback



I will have to take some measurements, but I have a gut feeling its less than 1.5". Forgot to mention camber, Im running 3.0 in the front, ~2.5 out back.


Yes these pics are after I went to full stiff (Hole #3, there is 1 more, hole 3 is full stiff per directions) in the plates and rear bar.


I feel like its a tad pushy. It may be my driving though...


Im not sold on either side of the square rate argument. It seems like preference. I ultimately went with what FA suggested. The car feels more pushy as-is than I think it should, wouldn't 12s in the front make that worse? Since you are a proponent of bars+square setup, do you run a softer front bar than rear? Or square on everything?


do 12/14 and have the option to try 12/12 (swift/generic)?


Here is a pic of static ride height. Too low?

edit:added another pic

 

Isnt it also because the R comps have more lateral grip, so they don't need as much sprung force to grip? <also newb...>

 

Just the opposite actually. More front spring will reduce weight transfer increasing grip. Plus you'll roll flatter and dive less reducing inside rear lift, though there's no point in trying to eliminate it.

I dont necessarily run Square because thats what I think is right. I run less than 3hz up front and 0.2-0.3hz more in the rear. That happens to be 12k/12k for me with my car under 3000lbs.

Since I know my springs are fairly balanced in stiffness, I did the math and came close with the bars too running ~30% roll stiffness from bars up front and ~40% in the rear. If I had more rear spring I would run less rear bar to keep the balance somewhere near neutral.

Of course then you try something and take notes on how it feels. Then try something else and take notes again. If you can datalog, even better. I just get close based on what I think is right, then dial in based on my butt and the timer.

 

I will say that although the car is faster now, it "felt" more balanced with my Swift/Bilsteins/plates.

I need to do some research on how to do the math. And my responsible side is saying to spend as little as possible until then. You've got me really close to just buying 2 swift 12ks and trying it out. I suppose if I don't like it, its easy enough to get 2 14ks for the rear.

Is the majority of your wt reduction in the rear? Almost all of mine is, except acd pump and mini battery is back there. And I admit Im totally estimating weight based on my conservative spreadsheet full of info from the wt reduction thread, I need to take one of the locals up on corner balancing.

 

Definitely try it. You wont know until you do, and you'll learn something from it. Learn to do your own alignments and a suspension setup change stops being scary and starts becoming the norm.

Between two cars Ive tried 8k/10k, 10k/10k, 11k/11k, 10k/12k, 12k/12k, 12k/16k, 16k/16k, and I'm sure some other configurations in there I'm forgetting. For my SE and my buddies SSL, more front spring has always been a net gain in grip.

I have a decent amount pulled out up front with the AC, dash mat, small bat, light brakes, etc. Still, its a nose heavy pig. Working on some other things that should pull decent weight up front but nothing is going to really change our horrid weight distribution.

 

Ive got no ac, 5 spd swap, removed firewall padding, rear seat/belts, rear wiper delete, 7lb battery in trunk, acd pump in trunk, light exhaust, ti uicp/licp, ti strut bars, 11lb trunk, no emissions. Radio, 2 speakers, both air bags installed. Not sure if Im crazy enough to do the floorpan sound deadening, but its on the list. I changed my order to 12/14s and plan to try out some different combos.

Does anyone think it is too low, looking at the pics? Without looking right now, Id say the LCAs are a little past horizontal.

 

see my thread at the top of the forum!

 

Give this man some spring!!!

From a non technical point of view, when Terry set my 510's up, he knew that my EVO was mainly track only & he recommended 12K/14K

I chickened out thinking it was too much spring. Now after numerous track days at 10K/12K I wish I had taken his advice

 

From experience, the "softer street tire can get away with more spring" is complete nonsense from a practical perspective.

Softer Tire + Stiff Spring = BOUNCE!

The tire becomes the dominant spring. The problem here, the tire doesn't have a damper attached to it that does anything. The only damping you get is from the tire materials.

It would be very helpful if tire manufacturers at least provided a basic range of stiffness for their tires as realistically, you want to be almost an order of magnitude softer on your ride rate the the tire rate.

 

Ive been following. I just need to set aside some time to sit down and figure it out after Ive had a chance to weigh it.


Minus, funny I told him the same thing and he recommended 10/12... And I would think autocross can get away with and benefit from more spring than track, no?