Hi guys,

I have another question regarding ride height as I am trying to get my car set up properly for the track after installing a new suspension. I'll be testing all weekend but would like to have some sound advice before I have to wrench too much at the track.
Ok.....ride height. Porsche recomends a 10mm rake from front to rear (rear should sit 10mm higher than the front) and at the moment I have set up my car that way. I am under the impression that Ernie from Mantis sets up his Cayman race car level (4.0" front and rear measured at the jacking points). I would think that Ernie has it right since we drive a mid engine car that has a near perfect 50/50 balance. Am I wrong? What are other track junkies doing?

Pre-load on helper springs:
The suspension I have (JIC cross) uses helper springs much like most other coil over systems that use linear rate springs that are quite short so as to keep tension on the spring at all times and not have the main spring get loose in the perch. How much pre load should there be on these springs (when sagging)? I have been messing with ride height and now the springs in the front (helper) are more pressed together...should I be adjusting the ride height at the bottom of the shock (shock body) and keep a certain pre load on the helpers? This would mean unbolting the shock from the knuckle and having to re-align the car (again)...
Suggestions?

Thanks
Chris

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'06 Cayman S -JIC Cross, Quaife, CCW C14 wheels,RA1's, Milltek cat back, GT3 seats Schroth harnesses, TC design bar, Pagid yellows, GT3 cup brake ducts,de-snorked, vanilla air freshener

I would take an initial height setting from someone like Ernie who has put in the work then corner balance to refine. Rake will have a more profound affect on braking than handling. Taking some rake out will allow the rears to do more of the work. Baseline ride heights need to take into account a lot of factors like: will it be driven on the street, are you a curb attacker, do the coilovers offer enough adjustment range at the given height to properly corner balance, are you still in an optimal alignment range, etc?

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FOR SALE: 2008 Cayman S, Black, Floormats

I see no physical mechanism for why a modest change in rake would have a discernable effect on front/rear brake balaance. Can anyone explain what I am missing here?

In modern braking systems much of the distribution is controlled via electronics or hydraulics but it is a matter of weight transfer. If you lower the rear less weight is transferred to the front when braking and the rear brakes are tasked with controlling more of the weight.

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FOR SALE: 2008 Cayman S, Black, Floormats

Why? I see no physical reason for that to be true... Why would the rake angle of the body make any difference at all? It seems like the weight transfer would be determined by the height of the cg above the axles. It wouldn't make any difference at all if the body was vertical if the cg height was the same. I'm still puzzled... Lowering the rear would lower the cg, and reduce weight transfer to the front, but lowering the front would accomplish the same thing.

Lowering the two unequal amounts is what determines rake.
The axles don't support the weight or transfer it to the tires, the control arms of the suspension do. Where the pickup points attached to the chassis will determine a lot of the affect the rake will have on weight transfer. Not being an engineer, I'm sure there is someone out there who can do a better job of explaining it than me. As a real world point I've built many a racecar and modded street cars. The extent of which rake affects brake use/wear has varied from car to car for me. My Elise was not nearly as sensitive as my M3 or my Cobra R for example.

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FOR SALE: 2008 Cayman S, Black, Floormats

I think the largest change would be in the roll couple front to rear. With a higher rear, the rear roll center is higher, likey causing the car to roll more at the front in cornering. This results in a larger weight transfer to the outside front tire and less to the ousdide rear. By balancing the car ride height you get more even roll front and rear.

-Trent

How can the car roll more at the front than at the rear? The chassis is essentially rigid in comparison to the suspension. Body roll is body roll - it is the same at the front and the rear.

This is about the same as our discussion on sway bars.
Sway bar question

No - it's not the same. I understand how different front/rear swaybar stiffnesses affect tire loads now.

This discussion is about rake.

Someone was saying recently that if you lower a Cayman that you throw some pivot point or weight centralization point (I forget the exact term) way out of whack and that you need to change the track of the car as well to compensate for it or else you are actually hurting your handling performance. I don't recall which member was saying that but I think he had a solution.

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K-Man S
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I understand the whole brake balance discussion and to an extent I agree. By lowering the rear more there is less transfer of weight to the front and thus more weight and traction can be kept on the rear tires, effectively being able to brake more with the rear....maybe.
I have the ride height set at (by memory) 4.25" front and 4.4" rear...

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'06 Cayman S -JIC Cross, Quaife, CCW C14 wheels,RA1's, Milltek cat back, GT3 seats Schroth harnesses, TC design bar, Pagid yellows, GT3 cup brake ducts,de-snorked, vanilla air freshener