My experience is that lowering a C5 causes the front end to toe-in and the rear end to toe-out; the difference between the two is because of the fore and aft tierod positions on each end of the car. Realigning after the car has settled is IMO highly recommended. Note that the factory's nominal rear toe spec is -0.01 (negative is toe-out). Also, soft shocks with lowering will result in hitting the bumpstops without much provocation, which will upset the car if it does so in the corner. Stiffer shocks are IMO highly recommended, especially if you have base equipment and are otherwise stock suspension. I would also seriously consider replacing the hard factory bumpstops with an aftermarket progressive bumpstop, which will reduce shocking the tires. Koni and others sell them in a variety of stiffness and lengths, see any distributor.

The lower rear shock mount is rather long too; it can be modified to be about 1" shorter by any good fabricator. CAUTION: DO NOT WELD ON SHOCK BODY - HIGH GAS PRESSURE!!! By doing this you change the travel range position to provide 1" more shock compression travel before hitting the bumpstop. I do not recall the motion ratio for the C5, but the wheel will travel further for a given amount of shock travel. I have not yet checked to see if there is enough upper wheel well clearance to accomodate that much extra wheel travel. 1" of extra shock compression travel by modifying the lower rear shock mount is what's readily available, but you may need to use less due to other restrictions. Should have an answer on that situation soon.

Unfortunately you don't have this luxury on the front shock. Accomplishing the same requires more money than is worth investing in an OE shock and unlike the rear what you gain in compression travel you lose in overall stroke. Basically you would have to machine the top of the front shock shaft to be shorter.

Otherwise you can run a variety of custom-aftermarket shocks that can achieve all that and more; Penske, Moton, JRZ, Koni, etc.

Mark :cool:


[Modified by TeamZ06, 4:42 PM 12/8/2001]

 

Just installed my A&A kit today. I even welded the front brackets with
my mig welder. A little paint touchup and they look like factory. It will
give you peace of mind.

 

Gentlemen, the physics of springs is fairly simple. The reactive force of a spring is a function of its deflection and is a constant RATE. Since the weight of the car is constant the only thing that can change is the deflection, ie, ride height.
Why does the car feel loose?? you are lowering the center of gravity and hence the moment arm (torque..not same as engine... FT-LBS) caused by the product of car weight times the distance to the center of gravity.

 

the car is loose because the rear end toed out when it was dropped without realigning and/or the rear shocks are hitting the extremely stiff bumpstops creating an infinite rear spring rate; i.e. solid fixed axle like a go kart, though a go kart chassis is designed to twist and the C5 chassis is not.

no need to go **** with the analysis, the C5 chassis can be made to handle extremely well at the lower ride height, just need to address alignment and shocks.

Mark


[Modified by TeamZ06, 5:53 PM 12/8/2001]

 

Huh?

 

The position of the tire changes..its relative distance from the center of gravity ( this is a three dimensional situation) changes, ie, toe setting. For instance if the toe changes .1-inches..times a 3000lb car divided by 4 tires equals 75 ft-lbs.. maybe that will loosen you up.

I need to correct this. The .1 is not exact... it is a function of the amount of tire tread contacting the ground that deviates from O degrees(straight ahead vs toe angle... to whatever toe setting... ita an tire angle/friction thing.
Guys, even though the dimension is small the weight of the car and distance from CG is enough to move the numbers.


[Modified by jawski, 1:00 AM 12/9/2001]

 

actually you would get more of a change from negative camber addition; the contact patch of the tire is pushed outward, than from a toe change; generally moves about the centerpoint of the contact patch, for your reasoning, but in either case I still stand by my previous statement on the real reason, especially with the smaller swaybar and softer springs & shocks of the base suspension.

Mark

 

I agree that shocks and sway bars assist in this situation and that alignment is affected. I just wanted to point out the possible magnitude of traction torque loss that may be experienced. My explanation is purely theoretical from a simplified physics standpoint to the novices out there... suspension physics is a very complex science and diverse, that's why there are so many different types of suspension out there.
Thanks for your knowledge/understanding.

 

jawski, it seems to me that both you and SAXN8R are right. It would appear that lowering changes the geomerty of several things, and the ill handeling that was experienced due to lowering was caused by a combination of the things that both of you have suggested. :yesnod: I agree with both of you. The bottom line is: if you lower your Vette, be sure to adjust the allignment to the correct settings and take any other appropriate messures to avoid bump steer or the effects of the changed ride height or lower center of gravity.

I think we all have learned something from this discussion, at leasst I know that I have. Thanks for your insight and inputs. :cheers:

 

JAWSKI, Thanks for sharing. I understand how different types of suspensions work, but I'm kind of a "gotta see it to understand it" kind of person. To understand what is happening lowering a Corvette, I still need to get under it and see what cranking on those bolts actually does. For all I know, all it does is suck the body down closer to the suspension (and/or frame), which would have zero effect on the suspension geometry.

Based on the earlier posts in this thread, I don't think many people really understand what it is doing, and I still don't. I'll be under my car, probably next weekend understanding it. Any additional input on this would be appreciated. This has been a great thread in that lot's of forum guys are lowering. Probably very few are taking the car to the alignment shop afterwards. :cheers:

 

I specifically asked the alignment guy about bump steer, and he said it shouldn't be effected if you are in alignment. I agree that this thread has been fun and I have learned alot as a result of it. Jim, I looked under the car at the suspension many times, and I still don't get the whole bump steer thing. I only lowered 3/4 of an inch or so, so I don't think there could have been much geometry changing going on w/ my suspension. Any more than hitting a bump or putting my fat butt in the drivers seat....LOL :D

Corey

 

Thanks Corey. I'll be lowering mine, maybe next weekend.

 

:cheers: :cheers:
[QUOTE] For all I know, all it does is suck the body down closer to the suspension (and/or frame), which would have zero effect on the suspension geometry.

You've lowered the center of gravity. hence, suspension geometry and physics of motion.

The :cool: thing is that the car is so simple to remake adjustments time after time untill you're satisfied :lol: But most of us on this forum are never satisfied :cry