Duke

I have to look up the data, but I'm pretty sure 50Nm + stock bars won't equal 708 lb/in effective!
By effective I thought you meant wheel rate?

333pg333

Sorry Duke, I think I meant to say 'equivalent', not 'effective'. Here is the text from Karl when I was first asking him about this matter.

"The info on Paragons site is stuff they got from me a few years ago. In any case, the 47% is a number that I have calculated by taking measurements. I am now pulling out one of Porsche's own Motorsport sheets that shows all the rates of their Turbo and "Cup" cars back when they ran competitively.
Porsche lists the 25.5 mm bar as 31 N/mm which is 177 lbs/in. They also then give the variable rate coilover helper spring rates at 34-65 N/mm which is
194 lb/in - 371 lb/in. They then give the total Rate at the wheel(T-bar plus
coilover) as 45.4 - 58.5. Back out the rate at the wheel due to torsion bar which they list as 31 and you have 14.4 - 27.5 at the wheel due to the coil over. So take your pick, 14.4 / 34 is approx 42% or 27.5/65 is 42%.

Bob is right about them being inboard but his numbers are off. Actually they are correct I think in that the motion ratio is about 65%. But when calculating wheel rates from spring rates it is the motion ratio squared that is uses. So 0.65 ^2 is , guess what,... 42.25% which is the number that Porsche's own sheet claims as I outlined above. So your torsion bar is 177 at the wheel, and your helper spring rate is a 285 which is 119.7 lb/in at the wheel. So working backwards 177 plus 119.7 is 296.7 pounds per inch at the wheel. Divide this by .42 and that is you equivalent coilover, or 706 lb/in coilover (initially I had 661 lb/in which is attributable to my measurement error - I had 47% and Porsche lists it at 42%).

So it may be a bit stiffer in the rear than I might run but with the ability to tune sway bars etc... you should be Fine. Your setup is actually much stiffer in the front than the Porsche cup setup which ran progressive front springs (200 - 371 lb/in) with the rear setup I described above which is not that far from what you have( yours is 296 at the wheel and theirs was 259 -
334 lbs/in at the wheel).

Hope this make sense, but believe me, what is above is 100% correct. I can fax you the Porsche motorsport sheet if you think it will help."

Duke

Thanks for posting that info. I've seen it before but couldn't find it when I needed it
I wonder what he thinks the correct calculation is for the front.
IMHO your spring setup looks good. Could probably be a lot stiffer but who knows if that really would decrease lap times.

333pg333

Well I have never had it all quite working just how I want it. Currently it is choppy around some corners (on a particular track), it was better on my 'home' track against that Nissan. Still not how I wanted it, but better. I think there is something fundamental that I'm missing. What we need to do is more tests with some hard data, but unless you have a job like Anders, this is not easy
I would like to try some significantly harder springs just to put this matter to bed. Not knowing leaves me in doubt.
btw, what rates do you run? In fact it would be interesting to take a poll to see just what rates everyone is running. Also in a lighter car you would not need as heavy springs, yet you hear of these dedicated track cars with 1000lb coils so that makes me curious even more.....

Chris White

To answer yesterdays questions! –
No torsion bars (actually 10mm bars – stock ones turned down to meet the rules – less than 10lb/in rate)

It does sound odd, a lot of guys start out with the ‘balanced’ set up thinking that it is important to get the functional spring rate the same for front and rear (Why? I don’t know…people just assume it matters!)

The rear ‘seems’ to behave right in the 550 – 800 range

The fronts were originally set to balance the rears but the ‘experimental’ folks kept adding more front spring. The turn in got better and the ‘feel’ got better. No change in understeer. For smother and faster tracks some guys have ended up over 1000 in the front (these are the really fast guys with a lot of car control skills). BTW – this is for ‘stock class’ cars – so 3000lb +/-

450/850 sounds weird to me!

Van

I'm currently running 450 in the front and 750 in the rear. That gives me a wheel rate of 372 front and 279 rear. I'm pretty happy with it, but I'm going to increase the front springs to 550 (because I have them laying around and I want to experiment - and also because I'm going to run CPR's splitter). That'll give me a front wheel rate of 455.

Oh, with my current setup - 450 F and 750 R - I have my rear Tarret sway bar full soft to battle oversteer. Increasing the front rate should also help that.

So, Chris, there might be something in your anecdotal evidence there!

Have any of you guys played around with Bosch LapSim? http://www.bosch-motorsport.com/cont...809A16EA4A4C14

Chris White

Hmm..only 8370 euros for the full version...

Van

Can't you "expense" it?

The lite version is free.

Chris White

Yeah, so is the first hit of crack...

Duke

Interesting indeed. It's funny how different the setup's can be, and still be fast and feel good.
Spring rates are so easily compared, a bit too easy. As we all know there's a lot of parameters that make the total setup and feeling but damper curves etc. are usually too hard to a) come by b) understand

Perhaps the best setup I've had personally was a Leda setup. 550/650 springs and stock swaybars. After some adjustment of the shocks I found that setup very balanced and very easy to drive at the limit. Too bad Leda shocks need a service almost yearly.
I'm currently using a Bilstein Turbo Cup setup as a compromise between street&track. I'm using the softer front shocks and 450/650 springs. Very good quality on the Bilstein's but I'm having some turn in oversteer and mid-corner understeer

333pg333

I'd just like to say "Chicken Tetrazini" at this point....there, got that out of the way.

Might have to try some stiffer springs just to satisfy my curiosity but it seems a lot of people are running stiffer in the rears and by some margin. Guess we have to cover off other parts of the equation too. Such as tyres and staggers. Be good to get some info going like the 3L thread just to have as a reference point?

gt37vgt

well MY option is based not on solid experience but on the word of other experts ..
Genrally tracks are a bit better /smoother in the US so the ideal set up for a 951 heres is having the rear a bit harder then the front ..
also the other reason for having the rear harder is the rear camber and toe chance as the car moves the as the rear is a bit out dated and the front not so out dated it stands to reason that we try to stop the rear moving so much ..

anders44

I think I have 70-80N fronts and 110-120N rears (no torsion bars) on my KW competition 2 way. and it's STIFF AS #"¤#¤%# looking at like 1cm bodyroll when pushing hard at track, and shocks are adjusted much softer now so working better.

think shocks comes in to play a lot, not just springrates.

333pg333

I'd be interested in what it says printed on your springs nevertheless Anders? I reckon you have quite a bit higher than 70-80Nm on the fronts.

333pg333

Also I reckon we learn to drive around our setups if that makes sense. In other words we automatically react and make our cars do whatever it is we need them to do to get around as best as possible. Without hard data we may never know just how poorly our cars are setup?