what pound springs are you track people running up front
05-14-2012, 04:46 PM
#46
Sorry to tune in late...
The front motion ratio is 0.91 and the rear is 0.63.
These are calculated by taking very careful measurements - I raised up the wheel exactly 1" and measured exactly how much the shock compressed.
Now, these measurements are probably a little different for early offset cars and cars with steel rear control arms...
The front motion ratio is 0.91 and the rear is 0.63.
These are calculated by taking very careful measurements - I raised up the wheel exactly 1" and measured exactly how much the shock compressed.
Now, these measurements are probably a little different for early offset cars and cars with steel rear control arms...
Edit: does it matter where in the shock's travel you do that measurement?
Last edited by pontifex4; 05-14-2012 at 04:47 PM. Reason: Question
05-14-2012, 05:57 PM
#48
Rennlist Member
Yes, start at ride height. And, in fact, since the springs were removed, I started from ride height, then went 1/2 inch compressed, set my zip tie, then went 1/2 inch extended below ride height (for 1" total travel). Then I measured how much of the strut was exposed under the zip tie (for this picture it was 0.911").
05-15-2012, 02:34 AM
#51
Rennlist Member
Oh, just to add to this. There is a particular fast road/track 951 which was put into the hands of a suspension analyst who suggested to go with the 850lb front springs that he should increase the rears to 1200lbs and even 1400lb on certain tighter tracks. I believe it was largely based on matching front and rear spring rate frequency (which as most readers would note doesn’t get much of a mention in these pages). This was not on a race car but as I said, a fast road / track weapon. No aero to speak of and running on R spec rubber.
It will be interesting to see how this progresses.
It will be interesting to see how this progresses.
05-15-2012, 08:23 AM
#52
Three Wheelin'
Ideally, you would probably want to run the Bilstein Cups with HIGH spring rates and WITHOUT torsion bars. The H&R RSS kit that comes with 500 front, 800 rear spring says to take out the torsion bars and that running 800lbs rear is perfectly fine with the proper rubber mounts. I'm pretty sure the H&R RSS uses the Bilstein Cup shocks and struts as a starting place.
The misinformation for this topic on here is stunning.
Cheers,
Mike
05-15-2012, 09:13 AM
#53
Rennlist Member
Clearly there is a very large range of springs that is being run by us in these cars. Seems almost unbelievable that we're all getting them to perform and go around corners (well some of us 
) with such a large variety of springs. Obviously there is a lot more that goes into a suspension setup than the springs themselves and there is scope for tuning with tyres, shocks, sways, aero...
Still, the whole thing is interesting even though it represents a black art to me. Nothing like trial and error backed up by data I guess.
) with such a large variety of springs. Obviously there is a lot more that goes into a suspension setup than the springs themselves and there is scope for tuning with tyres, shocks, sways, aero...Still, the whole thing is interesting even though it represents a black art to me. Nothing like trial and error backed up by data I guess.
05-15-2012, 10:02 AM
#54
Drifting
Sorry to tune in late...
The front motion ratio is 0.91 and the rear is 0.63.
These are calculated by taking very careful measurements - I raised up the wheel exactly 1" and measured exactly how much the shock compressed.
Now, these measurements are probably a little different for early offset cars and cars with steel rear control arms...
The front motion ratio is 0.91 and the rear is 0.63.
These are calculated by taking very careful measurements - I raised up the wheel exactly 1" and measured exactly how much the shock compressed.
Now, these measurements are probably a little different for early offset cars and cars with steel rear control arms...
Where did you learn to do it like this? Just curious as I do it a different way. In your set up there is no accounting for leverage. The lower control arm acts as a lever on the spring with the fulcrum being the mounting point at the crossmember. This, depending on the design of the suspension, can have a dramatic effect on spring rate.
05-15-2012, 10:03 AM
#55
Rennlist Member
Clearly there is a very large range of springs that is being run by us in these cars. Seems almost unbelievable that we're all getting them to perform and go around corners (well some of us ) with such a large variety of springs. Obviously there is a lot more that goes into a suspension setup than the springs themselves and there is scope for tuning with tyres, shocks, sways, aero...
Still, the whole thing is interesting even though it represents a black art to me. Nothing like trial and error backed up by data I guess.
) with such a large variety of springs. Obviously there is a lot more that goes into a suspension setup than the springs themselves and there is scope for tuning with tyres, shocks, sways, aero...Still, the whole thing is interesting even though it represents a black art to me. Nothing like trial and error backed up by data I guess.
Actually crunching the numbers is relatively straightforward when you look at either one axle or the other. However tying the front and rear together all of a sudden becomes a multi-variable matrix calculus problem (I think it's a 4x4? Can't remember at the moment)...meaning it's something my puny Excel model can't handle. Fortunately I have access to Matlab!
And you're totally right -- how cool would it be for us to enter in a few choice geometry measurements, plus the alignment, spring/shock, and wheel/tire data for the car, and be presented with force numbers and see the changes in geometry over B + C. My current version is about 50% done with the front suspension; it's a bit rudimentary, in that it uses stepwise simulation to represent dynamic loading, given that all measurements/specs are based off of static figures. Should be close enough to get good approximations for things though, especially as a prototype model.
05-15-2012, 10:23 AM
#56
Rennlist Member
Where did you learn to do it like this? Just curious as I do it a different way. In your set up there is no accounting for leverage. The lower control arm acts as a lever on the spring with the fulcrum being the mounting point at the crossmember. This, depending on the design of the suspension, can have a dramatic effect on spring rate.
Once you have the motion ratio, you use the formula for wheel rate which is: spring rate * (motion ratio)^2
The motion ratio is squared because it has two effects on wheel rate - both the force and the distance traveled.
05-15-2012, 10:44 AM
#57
Drifting
I didn't say you were wrong I said I did it differently.
I have another question. In your post above you stated you started at ride height and lowered the jack 1/2" and then raised it 1" or 1/2" above ride height. Why did you not measure 1" of compression and 1" of droop?
Springs are rated in lb/in of compression which you use in your calculation but you are only working the MR to .5". The other .5" being droop.
I think your MR number is invalid as written.
Thanks. Good convo.
I have another question. In your post above you stated you started at ride height and lowered the jack 1/2" and then raised it 1" or 1/2" above ride height. Why did you not measure 1" of compression and 1" of droop?
Springs are rated in lb/in of compression which you use in your calculation but you are only working the MR to .5". The other .5" being droop.
I think your MR number is invalid as written.
Thanks. Good convo.
05-15-2012, 11:05 AM
#59
Rennlist Member
I used 1 inch of total travel to make the math easier. If I'd used 2 inches, I'd have had to divide my strut measurement by two - and, with stiff track springs, I think 2" of suspension travel isn't very realistic.
Someone made the point earlier about suspension frequencies - and that's all very important and valid. It's been a while since I've ready my racing books, but I seem to recall that non-aero race cars are usually in the 2-4 Hz range. An F1 car is 10 Hz and Grandpa's Cadillac is about 0.5 Hz.
I see in my 944 setup spreadsheet that I'm using: 187.8 * (sqrt (wheel rate / sprung weight)) to calculate frequency at each corner in Cycles per Minute - then divide by 60 to get Hz (cycles per second).
05-15-2012, 11:08 AM
#60
Nordschleife Master
650 springs on all four corners with T-bars deleted (Leda coilovers with appropriate valving). 275/40-17's on all four corners. M030 bars front and back. Camber is -3.5 front, -2.25 rear. I've been playing more with corner balancing and adding weight so that I can add power and stay in class. Left/right balance is now 50/50, front/rear is 50.3/49.7 and cross weight is within 0.1.
I think the car handles exceptionally well. Will have a pro coach in July, so will get his impression on the setup.
I think the car handles exceptionally well. Will have a pro coach in July, so will get his impression on the setup.