tubescreamerules

Hello all,

i've recently lowered my 07 gt3 following fc-racer's post (great write up and pics!). i've lowered the front by 8mm, makes it read 100mm at factory measuring point, and it was pretty straight forward. what really frustrated me was the rear, the factory setting is 108mm front and 133mm rear, should I lower the rear by 8mm as did to the front, or should i lower it by the same ratio (ie 100/108 = x/133, x=~123)?

thanks in advance guys!

Larry Cable

I know *nothing* about this, but I would be tempted to maintain the factory rake ratio f&r...

Carrera GT

Ride height specs are absolute numbers, not offsets. Adjust to spec front and rear, independently. This creates the option to raise and lower front and rear the same amount as you suggest, but not to use the arbitrary settings of you individual car and then compensate, apply a ratio or adjust -- that way lies misery. The conventional approach is:
1. ride height
2. corner balance
3. set rear caster -> camber -> toe
4. set front caster -> camber -> toe.

Simply dial in the absolute settings and then deal with the change in each of the subordinate geometry changes. If the changes to ride height are incremental, the car will remain square and issues of front caster and corner balance and so on, all tend to stay within tolerances (of steering geometry, bump steer and more esoteric adjustments.)

jrgordonsenior

Tire diameters can also play a determining role in computing ride heights. If you've change the diameters from OEM those specs are then no longer comparable. ie: cup car rear height is 115mm with the 680 series rear tire. If you run a 650 rear, you've just dropped 15mm off that height (30mm/2). Just a little something else to mess with....

utkinpol

i think it is quite typical to have at least 1/2" diff between front and rear.
so if your front is set to 100mm you can set rear to 112-115. going by books - lower to maintain same ratio as it was.

TRAKCAR

That's what I do, I am about 10mm lower all around and it seems to work well.

jrgordonsenior

Factory rake as reported by OP is 25mm. Cup is 30mm (85f, 115 r). We tried something different since lower is usually better and went down to 95f, 105r, on my C2 race car. I use 280/650 rear tires so height would be 120mm on 280/680's. The car handles better than my cup with half the spring rates and JRZ 2-way shocks so something's working....

tubescreamerules

thanks guys for the info.

i think i will just stick with the 25mm factory rake ratio.

a year ago i corner balanced the car but i think the shop messed up with the rear's ride height, last week when i took in the car to the dealer, they measured the rear was sitting at 118mm, which was way too low. i asked them to rise the rear to 125mm and adjust the front to 100mm. on the way back home, i can tell the steering was a bit more sharp than before and the rear end tend to 'swing' a bit more on a bumpy road. haven't take the car to track yet, i will put some new Cup tyres and re-dial the ride height, take the car to the track to see if there's significant difference.

tcsracing1

take it to a pro