Tire Diameter & Setup Advice

[DGRacing]

This question is _primarily_ for my honorable team engineer, Grant. ;D

So right now my setup is:

Front: 305/680/18 Ride Height: 27" ground to Fender Apex
Rear: 315/680/18 Ride Height: 27.5" ground to Fender Apex
Dampers: 4/12 compression. 4/10 rebound.
Springs: 750front. 350 rear. But going to 800 front, 275-300 rear.

I'm considering a tire size change to one of two possibilities:

1. 305/660/18 front with 315/680/18 rear. This is what DM runs in PWC. The natural rake between 660 front and 680 rear is like .7". Added to
my .5" coilover rake is 1.2" rake. Too much? What should the coil overs be set at? Probably need more than .5" rake to test with.

2. 305/660/18 front with 315/675/18 rear. Concerned about ground clearance for side pipes with this config at my current ride height.
But similar question as to how or if to adjust the ride height/rake.

Some other considerations. With an aggressive rake over 1" how to adjust rear wing? More/less angle (to level)? Parallel (to level)? Parallel to rake?
With various rakes how to adjust damper rebound/compression? With greater rake, it affects corner balance. thus, how to corner weigh the car with the higher rake, change in ride height? I will be getting scales soon so will be able to get real numbers then.

I realize this is trial and error process. Just looking for some initial thoughts to dial in something logical to start with.

Gracias!!!

 

[Grant 302]

@DG#56
^you can always use the 'mention' feature for work-related posts!

1. The 'added' rake from the 660/680 tires only makes less than .39" difference. (1/2 the diameter is roughly the difference in axle height = change in car heights/rake)

2. Did you take a ground clearance measurement for the pipes? Going to a softer spring, I'd suggest increasing the clearance a bit if you had any ground contact issues.

When you 'add' rake, you naturally increase the angle-of-attack AOA for the wing. To keep the same AOA you would need to reduce the angle (more level) by 0.22º for the .39" difference. I don't think a quarter of a degree is a lot or very practical to make an adjustment that small, but not sure if your wing's CFD data has a could of angles to compare.

 

[DGRacing]

Thank you chief! I'll get all the static chassis numbers soon.

 

[blacksheep-1]

Thank you chief! I'll get all the static chassis numbers soon.

I'd be interested in seeing those myself

 

[ArizonaBOSS]

I have my car set up basically for .5" to .75" rake after corner balance.