Suspension considerations and all these RS/RSR clones...JackO you may be of help

Dueller · 03:52 AM

You Pelicans have created some of the most beautiful RS/RSR/Widebody conversion creations on the planet. I apologize for the ignorance of this query, but are suspension mods necessary to end up with a great handling car? I don't mean heavier TB's or sways or shocks, but mods/reinforcements to A arms/trailing arms, suspension pick up points, etc?

JackO...I vaguely recall mention in the Excellence article (BTW, most Excellent!) on your car about some mods you made to correct suspension geometry....Was this merely to improve performance or to bring it in line with how the factory cars were designed?

Forgive my ignorance (I'm amazed at how much I'm learning from you guys), but were wide body cars built with essentially the same components as narrow bodies? Just seems to me it isn't a matter of big flares and wider tires/rims crammed in there....with expanding the track so radically, aren't the original narrow body suspension components stressed beyond design capabilities? Try not to flame me...I've tried to search this but apparently can't come up with correct terms.

javadog · 04-02-2006, 06:49 AM

Dueller,

You'll find that most of the suspension changes on the converted cars are limited to torsion bars, shocks and sway bars. Beefing up the basic components is generally not done. There are benefits to relocating the rear pick-up points but they are done for cars intended mainly for the track and there isn't even a consensus among those guys-some prefer the original geometry. Likewise, the front struts may be modifed, on cars that are going to be lowered beyond what is sensible for street use, to keep the strut operating in it's normal range of travel. There are other modifications done, primarily to facilate adjustments and alignment, or to be able to achive alignment settings not possible with the stock parts.

Wide body cars were built with turbo brakes as well so the suspension is more like the turbo cars. There are some exceptions, particularly in the later years (in the 90's) but largely they are similar. I wouldn't worry about stress on the components, unless you run wheels with a large offset that force you to run really wide spacers. Narrow spacers are no problem, if properly done.

JR

Tyson Schmidt · 04-02-2006, 11:54 AM

The mods I did to Jack's car were very different than what came on the Factory RSR's and Turbo cars. Those were heavily based on normal 911 components.

The major differences between the 911 and the Factory RSR and Turbo suspensions are:

Rear pick-up points for the rear trailing arms moved rearward, and a shorter arm used to alter camber curve.

Mounting points for the front and rear of the front control arms altered to achive anti-dive geometry. This is done by lowering the front mounting points, and raising the rears. The rears are actually the cross memeber that supports the steering rack.

The spindles were raised on the RSR front struts to raise the front roll-center height.

Spacers were used front and rear to widen the track.

On Jack's car, I changed the front control arm length. (longer)

Raised the spindles beyond what was possible on the RSR, due to utilizing 17" wheels versus the RSR's 15's.

Changed the steering axis inclination with custom geometry front struts for better scrub-radius in conjunction with deeper offset front wheels. (The altered geometry allowed deeper offset while retaining the wider track.)

These changes result in improved steering balance, particulary under hard braking. (from the reduced scrub-radius)

Higher front roll-center height, for more built-in resistance to body roll- also keeps camber curve in the proper range when car is set very low. (raised spindles)

Less roll-center height change as the suspension moves through it's travel, for more consistent/predictable handling. (longer control arms)

Reduced scrub-radius also benefits tire clearance during turns, since the wheel pivots closer it's center-line instead of swinging forward and rearward in the wheel-well. (Notice how oblong the front flares are on an original RSR, which were necessary for tire clearance with it's very positive scrub radius, combined with it's 9" wide wheels)

That's the front. I'll have to go into the rear later, since my typing fingers are cramping up. The front of jack's car has my own unique geometry ideas, and the rear is all stuff that can be bought Smart Racing, so the front warranted me going into more detail. There's more to it than I can put in print, but this should give you a rough idea of what I was trying to accomplish.

Dueller · 04-02-2006, 02:23 PM

Tyson...

Thank you greatly for that explanation in a manner that a non-engineer can understand. You obviously put a lot of thought and engineering into designing JO's suspension.

From a purely intuitive perspective, I really am trying to understand the effect of mods to all these clones. Having built a few "amateur" race cars, I at least realize you can't just slap wild offset wide wheels under some fiber glass flares and end up with a suspension that performs competently. What prompted my curiosity was a post asking about the "RSR Look" without giving much thought that the end result would actually stop and turn. Or do they do "OK" with just the wider setup?

Thanks again. I look forward to you analysis of rear set up on these clones.

jim

Jack Olsen · 04-02-2006, 03:03 PM

The factory Turbos do "OK" with wider front wheels and spacers to widen the track. It's not the most elegant thing Porsche engineers ever did. Turning effort is increased because the tires are wider and the scrub radius is worse. Under braking, the steering wheel will fight with you a little more with spacers pushing the wheels out so far apart.

On the rear, Porsche made changes that often aren't made with non-factory widebody conversions (as Tyson pointed out: the different trailing arms and revised mounting points). For street driving, this isn't going to make a huge difference for most drivers. But if it's a car you're going to race, and it fits in the budget, then you want to maximize more of the potential benefits from the wider track. In my case, we didn't use Turbo trailing arms (replacement costs are crazy), but we did re-position the rear mounting points (at the cost of rear seat room) and add coil-overs and some of the ERP/Smart Racing goodies.

Tyson's goal with the front end of my car was to eliminate some of the compromises Porsche engineers made when the 911 stance was widened for the Turbo models. My car's scrub radius is better than a stock early 911 on 6-inch wheels, which is quite an accomplishment when you consider that I run 275's in front on 9.5-inch wheels. With a lot of street driving and no power steering, it's something I appreciate every time I drive the car.

Dueller · 04-02-2006, 03:19 PM

TY for the input, Jack...fascinating stuff

pmajka · 04-02-2006, 03:55 PM

Oy, Javadog, what would you consider a really wide spacer?

javadog · 04-03-2006, 03:46 AM

I think the widest the factory used was 28mm. I have seen people use spacers much wider than this. You have to keep in mind a couple of things. The wider the spacer that you use, the higher the load will be on the wheel studs. Also, the factory cars got some of their rear track increase from the shape of the turbo trailing arms.

There is a type of spacer that I am not fond of. It is the type that bolts to the hub with the original wheel studs and has a second set of studs offset from the first ones to actually bolt the wheel to. I would not use one of these. If I had to increase the rear track on a regular 911 to fill turbo flares, I'd probably use the factory spacers and wheel studs and get the rest of the track increase from wheel offset.

JR