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Suspension Geometry

 
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pcarfanatic  



Joined: 18 Nov 2005
Posts: 6
Location: South Africa

PostPosted: Thu Aug 10, 2006 11:29 pm    Post subject: Suspension Geometry Reply with quote

Hi, I have a race prepared 924 and it is lowered. Consequently, the lower control arms do not sit parrallel to the ground (they face upwards towards the shock). Is there any way to rectify this? Regards
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morghen  



Joined: 21 Jan 2005
Posts: 8177
Location: Romania

PostPosted: Fri Aug 11, 2006 4:04 am    Post subject: Reply with quote

at first i wanted to ask why in the world you want that rectifyed...but today i hit my front spoiler lip 4 times ! and my control arms are sitting paralel to the ground !

i feel like a godamn ricer...

new springs maby ?
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fiat22turbo  



Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR

PostPosted: Fri Aug 11, 2006 4:06 am    Post subject: Reply with quote

Replace the ball joint with a spherical bearing insert and use a longer bolt to space the end of the control arm down?

Or you can look at raising the mounting poinrts of the inboard side of the control arm.

Either way it will be a lot of work, but the upside is that you won't have as many ball joints fail due to running out of travel.

If you're concerned about the ball joint failing, then perhaps you could have a control modified or built that angles the ball joint closer to parallel to the ground at your current ride height.
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flosho  



Joined: 01 Jul 2004
Posts: 3153
Location: Eau Claire, Wisconsin

PostPosted: Fri Aug 11, 2006 5:32 am    Post subject: Reply with quote

This is the big discussion over on Rennlist. The guys that run coilover suspension in the front have to worry about lowering the front TOO much and putting extra stress on the ball joint. I think there is a "rennlist ball joint kit" that helps correct this problem.

Otherwise check out lindsey racing, because I believe they sell differnet control arms and everything that are reinforced and what not. Check them out..

www.lindseyracing.com
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924RACR  



Joined: 29 Jul 2001
Posts: 8320
Location: Royal Oak, MI, USA

PostPosted: Fri Aug 11, 2006 10:17 pm    Post subject: Reply with quote

Mine aren't level either... but if you run enough spring, the car doesn't roll enough for it to matter!!! LOL

Really, what front spring rate are you running?

For fixes - there's two parts you need to be aware of. You'll want to relocate the a-arm mounting points (I'm not allowed to do this, per the rules). You also need to be mindful of steering geometry to reduce bump steer induced by the lowering.

Do like the factory did on the D Prod cars.

To correc the a-arm geometry (and gain a bit of track as well), raise the a-arm mounting points as suggested. Drill a hole in the cross-member higher up and further out from the original point, as needed to get the arm level. This may require reinforcement of the new mounting point on the cross-member; I don't recall how thick it is there. You also have to relocate the rear mounting point (the caster block). This is done by removing it from the bottom of the frame rail and relocating it to the outer side of that frame rail. Naturally this will require welding in some reinforcement and captive nuts. Since both mounting points go outward, you end up w/ a wider track while you're at it.

To fix the bump steer, what you want to do is drill out the taper in the steering arms on the uprights/knuckles, replace the outer tie rod ends with a rod end, and use a long bolt with spacers (washers or better-engineered spacer) to relocate the attachment point further down, returning the steering arm to level at rest.

Yes, you could use rod ends in place of the balljoints, but this would require some reengineering of the attachment point to the knuckle, not trivial, and our stock balljoints are pretty good IMO. If anything, I'd take that energy and put it into reinforcing the a-arm. Though I'm not allowed to do that, so I run stock a-arms and trailing arms... not a bad idea, when you're prone to hitting walls and such as I am - the bendable steel acts as a sort of fuse against body damage, and suspension arms are a lot cheaper and easier to replace than straightening the shell...
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pcarfanatic  



Joined: 18 Nov 2005
Posts: 6
Location: South Africa

PostPosted: Mon Aug 14, 2006 9:17 pm    Post subject: Reply with quote

Hi all, Thank you for the replies - they have been very helpful!!! I am currently running front coilovers hence the problem. I do not know what my front spring rate is - they are springs and shock setup from a 944 turbocup (bilstein).

Another question - I have a fair amount of understeer in slow corners. I do not really want to stiffen the back as a solution but rather find ways to increase front grip. i am currently running 2.5 degrees neg camber in front. I'm thinking of changing to solid bushes, increasing track marginally and getting the front end lower. comments/ideas? thanks in advance
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924RACR  



Joined: 29 Jul 2001
Posts: 8320
Location: Royal Oak, MI, USA

PostPosted: Mon Aug 14, 2006 10:06 pm    Post subject: Reply with quote

Well, to really pick apart your setup and make suggestions - I'm going to need all the details of your setup. Spring rates front and rear, torsion bar size, sway bar sizes front/rear, shocks, bushings, alignment, everything.
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John Brown  



Joined: 07 Nov 2002
Posts: 903
Location: Leesburg VA

PostPosted: Mon Aug 14, 2006 11:15 pm    Post subject: Reply with quote

pcarfanatic wrote:
Hi all, Thank you for the replies - they have been very helpful!!! I am currently running front coilovers hence the problem. I do not know what my front spring rate is - they are springs and shock setup from a 944 turbocup (bilstein).

Another question - I have a fair amount of understeer in slow corners. I do not really want to stiffen the back as a solution but rather find ways to increase front grip. i am currently running 2.5 degrees neg camber in front. I'm thinking of changing to solid bushes, increasing track marginally and getting the front end lower. comments/ideas? thanks in advance


This is pretty severe setups we're talking about here. It would be useful to know what kind of racing you are doing? When you say slow speed corners, how slow? Are we talking autocross or Road Atlanta?

If it's stock 44 Turbocup, then they are probably not so stiff as one might think. But if that was done with nothing in back that certainly would driver toward understeer and the solution is to up the rates in back. Period.
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80 931 - #931 44Cup
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