NJ-GT

Let's say 3,300 lbs car with driver.

If the car runs on 265/325 tires, it needs to run 25mm higher due to fender clearance. If the car runs on 245/305 tires, it can run 25mm lower.

At the two ride heights (75mm front 95mm rear, or 100mm front 120mm rear), I set the car to run the same toe and camber.

Tires are the same brand and compound.

So, the question is which setup is more convenient for track use?

Veloce Raptor

I dunno, depends on the mix of tracks IMO. Super-tight technical tracks and a wider contact patch will always be good. More open tracks and sometimes the extra aero drag from wider tires & higher ride height is a bigger disadvantage that advantage..

Bill Verburg

Wheel width is important too, you'll get better performance from a given tire when it's mounted on the widest possible wheel than when it's mounted on the narrowest

I don't know what tires or wheels you run but lets just say Michelin Pilot Sport Cups on 9 & 11 x19

the 9 & 11 are the narrowest wheels that 265 & 325 are recommended for

but 9 & 11 are in the middle to top of the range for 245 & 305.

Just me, but I'd go lower w/ wide wheel for the tire size ie 245/305

Larry Herman

I think that part of the answer lies in your spring rates. Not familiar with Ferraris, but if they are like most else, the roll centers drop a lot as you lower the car, and so it leans more with the same spring rates, further reducing contact patch on what will be a narrower tire.

So where is it now and how does it handle? Are you runnning stock or stiffer springs?

IcemanG17

more tire isn't always better.......if you have too much tire, then you can't get it up to its ideal temp & your overall grip will suffer...... However with the power of a Ferrari and 3300lbs it doesn't sound like you would be over tired....

Is it a pure race car? Is it street legal? Do you drive it on the street? These are all things to consider

Van

I think that's easy - the lower ride height. Most car builders would kill to be able to lower the center of gravity of a vehicle by 25mm!

38D

Tire width, spring rates, are all important, but the most important thing IMO is the the suspension geometry. You can run a car too low, and which point it becomes undrivable. 75mm seems like it would be too low for any modern porsche (the 986/996 varieties don't like to be below ~90mm). Also 20mm of rake seems like an awful lot to me.

ProCoach

ALWAYS 25mm lower.

DOUGLAP1

This guy is right on the mark. It all depends on what happens with your camber curves, and there is no way to know that unless you either experiment, or take a lot of measurements of the suspension, and run a WinGeo model, or make some paper dolls as Carroll Smith advocates in Tune to Win.

In my experience, lowering a McStrurt car like a Porsche goofs up the camber curves very quickly. For an unequal length A arm geometry, you never know, unless you model it all.

Good luck...

ProCoach

WinGeo3 FTW!

Nick Wong

That Mitchell program's been around since the dawn of Windoze. Definitely the way to go!

NJ-GT

Suspension uses double a-arms (wishbones) at each corner. Delrin bushings and monoballs all around, with no rubber on any of the links.

Weight with driver is 3,300 lbs (maximum weight), and as light as 3,080 lbs when running with CCB brakes, race exhaust and low on fuel.

Wheels are 10x18 and 12x18. Spring rates are up high (close to 2000#), stiffer than what the Challenge cars use, in the same range of the F430 GT2 ALMS car, shocks are matched to the springs (revalved over a year ago). Car has very little body roll, almost none, at Sebring the suspension uses 33mm of travel from at rest position, despite of the bumpy and grippy track.

Street car barely driven on the streets, just to/from racetrack, few autocrosses once in a while, local tracks: PBIR, Sebring, Daytona, Homestead Double Infield and Homestead Grand-Am, running DE and time trials.

I just noticed that the narrower tires (255/35R18 and 315/30R18 Hoosier) drop the car even more than the 25mm lowered through the suspension (lowering the spring perches). Currently the car runs mostly Hoosier 295/30R19 and 345/30R19. In reality the 345/30R19 is a 335 tire with a 26.8" diameter, and the 295 tire is a 26.1" tall tire with a 285 width. On the 255 (which really is a 275 tire) diameter goes down to 24.8" and the rear 315 goes down to 25.6".

The actual ride height difference is 40mm running narrower tires (275/315x18 named 255/315 by Hoosier) compared to the wider tires (285/335x19 named 295/345 by Hoosier).

My guess is that at 60mm front/80mm rear compared to 100mm front/120mm rear, the airflow underneath is significantly reduced, less lift, less drag, ending on more downforce.

Factory rake is 22mm with a range of 12mm to 32mm. I have played with rake, camber and toe for a few years, and 20mm is where I like the car. The F430 GT2, F430 GT3, Challenge use similar rake.

Thanks for the feedback.

IcemanG17

Since it still is a partial street car....that limits things A LOT.....

Since you are running DE and TT and not racing....I would run the 18's....they are MUCH cheaper...

Lots of great ideas already mentioned....but I would take your actual tire temps...that will tell you everything you need to know....

My example....my new 928 racer came with 295/35-17 front and 315/35-17 rear tires with 130mm front and 190mm rear (I know too high).....I adjusted it all the way down to 95mm front and 140mm rear and now run 275/645-18 Pirelli slicks all around (I get them used for cheap)....its 2.5 seconds per lap faster running lower and narrower tires....I ran the front as low as 85mm...but that was a bit crazy...its very settled at 95mm

C.J. Ichiban

I'm all for lowering the car-

too much tire (you're not doing super long race stints of 3Hrs) and the car won't even need that whole contact patch anyway...295 fronts?? yeesh.

with GT3 cup cars (same ballpark power/weight to the scud) and even grand am cars in our CT series (nowhere near the power), too much tire is extra mass (impedes acceleration), and extra drag (impedes acceleration)-

so I'd think if you've got the rake correct, the lower the nose, the better underbody airflow you're gonna get and the better acceleration you'd get- just from a wind tunnel standpoint and not even considering the dynamic advantage of a lower CG for changing directions...

smlporsche

Drop the car