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i'm racing BSP this year on hankook rs3's (i know, not ideal, but that's where i am). just wondering what would be a good spring rate combo for these tires. i have front and rear sway bars and nearly all bushings replaced with urethane.
i have a selection of 2- 6k (i think) springs, 4- 8k springs, and 2- 10k springs.

on a side note, i have 2 kw brand springs that have "60-200 gbdc" written on the side. is there an indication of rate in that writing? i are confused....

 

in BSP you're going to want the stiffest rate you can out of your choices, so do 8k front 10k rear. Even then you'd probably want to go firmer.

KW 60-200 are 6kg/mm with a 200mm length.

- Andrew

 

thanks!

 

Andrew,
So why is it in general most of the evos cary lower spring rates upfront vs. higher in the rear?
Thanks and sorry if this question has been covered already!

 

Because most cars have similar suspension types front/rear generally leading to similar motion ratios. Though, even with the same basic type that doesn't really mean M.R. will be the same (2g DSM's are 0.74ft/0.91rr). The evo is of course mac strut front multi-link rear and the M.R. are very different.

Why do they put a heavier spring up front? These mass market suspension companies are just trying to be first to the market, SELL SELL SELL! They dont actually have a physical car nor would it be realistic they could have every car to actually measure and determine proper rates based on corner weights and geometry. So they just stick to an assumption that the car is gonna probably have x- weight distribution and our ****ty shocks can only handle y- springs rates without blowing up. So they just get in a range and call it good.

Average buyer things they have hardcore engineers designing this stuff and takes it as gospel cause now his car "Feels" faster cause the rates are stiffer and its usually way over-damped. Of course, its probably slower or maybe marginally faster due to less camber loss but definitely not balanced at the limit because who knows how its effecting weight transfer.

Then after all is said and done and people have really figured out what rates actually work the big mass market companies have moved on to new chassis and have no reason to A) spend money to re-do a suspension for a car that's years old and they already have a product for, and B) Admit they had it wrong in the first place.

The only two companies I would consider for my car personally are Ohlin and AST. They are both quality companies worth looking at for comparison, what do they run?

PS. This is a lot of my opinion/guess but I doubt Im very far off here.

 

^ thanks for ur input man! luckily we have a great group of knowledgably guys on here where mistakes can be avoided with their help.
cheers!

 

I think Dallas J basically nailed it. I've posted on it a couple of times and I think it's a combination of companies not really caring and not having the knowledge. For the most part I do not think it's a "stability" thing where they're intentionally trying to make the car understeer to cater to the average driver. I do not buy that for a variety of reasons.

- Andrew

 

I'd definitely agree. They dont know what theyre doing enough to make a balanced car so encouraging a specific amount of unbalance is pretty out of the question.

On another note, I would also like that their is no such thing as one spring rate fits all. It is clearly evident to anyone who has gone from bumpy to smooth courses in dry and wet weather with slick and rain tires that a still setup for dry with slick does not work well for wet and rain tires.

On top of that, you have to also look at the spring rate of your tire. Ive read in the past a standard street tire is in the 800lb/in range, a dot slick is around 2000lb/in, and I would guess the latest and greatest ultra hi-performance street tires are somewhere in the middle, maybe 1400ish. Ive personally stuck to an upper limit in wheel rate of 1/4 tire rate for what Ill be primarily racing on. Its very noticeable when you go from a dry/slick set up and try to run on street tires in the rain and you now have wheel rates that are ~50% of the tire rate. The car squirms around and is very un-compliant and overly sensitive to any kind of abrupt change.

With that said, spring rates should really be custom tailored. Its just one part of the equation, but IMO its #2 in priority behind tires.

 

Totally agree that there is no one spring rate perfect for every car/driver.

Interesting perspective on tire spring rate. Generally I look at the need for the spring rate to be able to control the body roll that the grip of the tire can provide. Needs to be stiffer with a slick or r-comp, as I think you're noticing with your set-up with springs on super sticky tires. Street tires on the other hand do not require ultra-stiff set-ups to control the body roll from the lower total grip they offer. You end up with good quick response and a nice "feel" but overheated/overloaded tires. EDIT: which is why "too stiff" can actually be kinda nice for auto-x on street tires.

- Andrew

 

Yeah, tires are definitely #1 priority. Choice of tire determines setup both in terms of the suspension (shocks, alignment, etc.) and brakes.

Having said that, I was pleasantly surprised at how well the Swift Spec-R spring held up with a set of 265 R1's on the car. I'm sure I could've used more spring, but overall the car remained nicely planted, about as neutral as my street tires, just a touch more sensitive to bumps in corners.

l8r)

 

I haven't been in here for a while and I was kind of surprised to see someone bring tire stiffness into the discussion. Tire rates and deflection is something that is often overlooked but plays a significant part in setting the car up.

This is a few screen shots of my 295/17 hoosiers in a suspension calculator



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Uploaded with ImageShack.us

 

Great thread!

I've noticed that most people generalize the tripod'ing as a rear "inside corner" problem. I understand the basic physics of inertia & traction related to the tripod'ing, HOWEVER...

After 17 pages of reading, I can't help but notice that 99% of the tripod photos are the right rear. I have to wonder, how many of those photos are with the battery relocated to the right side trunk to offset the drivers weight bias on the left?

 

Wouldnt that make it hard to get to the washer fluid cap in the right side of trunk? I have pictures of both sides lifting from 2010, but it was the photographer for our region that seemed to get more photos of passenger side, which could be common.