Danny Humphreys

Don't really need a how to, more of a how much. For a street/track car what is the maximum/optimal amount of lowering without adversely affecting suspension design/function?

SteveG

zero. You will degrade performance of suspension. Doesn't make sense that they would set it at something other than optimal.

Ducman82

not at all. your oil pan will be the first to go.

jeff spahn

Set to factory ride height and don't do anything else. Of course you set it when your suspension is fully settled.

FBIII

I would be hesitant to significantly drop a car with stock springs. A car with an aftermarket/stiffer springset and shocks would be a diffferent. I used my OB as a daily driver for years and never holed a sump or ripped off an alternator. I had my front fenders lowered almost to the top of the tires. I would also consider the general condition of your roads.

Danny Humphreys

The car will have aftermarket coilovers and springs. Factory settings on any car are always a compromise between ride comfort, safety and performance and are rarely optimized for maximum performance. Lowering a vehicle also lowers the center of gravity which improves body roll. I'm fairly certain that the racers on here have their vehicles lowered to a certain degree. Thats what I'm looking for information on.

jeff spahn

You can affect the bump steer on the car by lowering it. It changes street drive-ability a whole lot when you lower it to what the racers have as a setup on their cars. You can get some funky tramlining by changing ride height and thereby affecting the alignment.

GlenL

155mm all around

FredR

If you fit springs such as the Eibach units that are about 25% stiffer than stock you can lower the body to the bottom end of the factory range plus about 5mm lower still without any adverse effects that I Have been able to detect- just ensure you drop both front and rear proportionately and avoid the popular tendency to "**** in the air" and if anything, drop the rear end a llittle more than the front relative to stock. I have a feeling this is equivalent to what Glen says in post 8.

As a precaution I fitted the front bump plates that Carl makes at 928 Motorsports- they have earned their keep a number of times looking at the scrape marks on the underside.

Regards

Fred

tv

This thread reminds me of this car

http://lh4.ggpht.com/_D0RLA-LyvJA/S-...28oldboy_1.jpg

Carl Fausett

Lowering an inch is common, and our bump-steer study showed that changes to the bump-steer and alignment were negligible at that height. At an inch, the suspension is still within its normal arc range.

Race tracks are fairly smooth - and you can count on them to not have potholes. Ride height is higher on street cars because of potholes and curbs (that race tracks do not have). Rumble strips are different - not the same as curbs.

Beyond an inch - yes, you should install a bump-steer kit to straighten your tie rod ends again, and check the alignment of the car.

And in all lowering cases, a set of Protection Plates is wise to prevent panning on driveway approaches. The first things to hit the pavement on a 928 are the air conditioner and the alternator. In lesser cases it just costs you an alternator. In the worst cases I've seen it snap the cast air conditioner mounts off the block, spelling end-of-life for the motor.

For more information on these suggestions, you may follow these links:

Protection plates: http://www.928motorsports.com/parts/chinplate.php

Bump-steer kits: http://www.928motorsports.com/parts/bump_steer_kit.php

redpathtribe

150mm in front, slightly more in the rear is within factory specs for a car that's not right off the showroom floor, so that would be all of our 928's.

150mm in the front looks much better and still allows decent clearance for road obstacles. Be sure you are taking these measurements from the correct place on the front and rear suspension. This is fairly easy to do if you know the right spot to measure from.

I used to have the front of my GT set at 110mm in front. It looked and handled great, but caused issues just coming in and out of the best driveway curb cuts. After I moved it back up to 150mm, it does ride better.

Danny Humphreys

OK, maybe I'm missing something. 150 mm converts to just under 6 inches. Are you referring to the installed spring height? Would someone mind providing me with a wheelwell measurement front and rear of stock ride height and indicate what size tires you are running so i can do appropraite measurements? As I mentioned, I will be running aftermarket shocks and springs as well as excessively lightening the car and i already have the suspension off.

GlenL

These heights are to the official measurement points on the suspension. Fenders aren't good references.

Lizard928

Front lower control arm,
Rear attachment point there is an aluminium part which is bolted on to hold the rear point of the control arm to the cross member and frame rail. In the center of this there is a flat spot. This is the height measurement location for the front.

On the rear cross member, where the rear attachment point of the lower control arm attaches, there is a little flat spot just below the adjustment bolt. This flat spot is the measurement location for the rear.