It's the off-season and I've been pondering why my car works better with 33x10.5 tires versus the 14x32 tire.

The extra 1" of height seems to make the 4 link happier. The issue I have is since I'm a bottom bulb guy I can't hit the tree with the 33" rear tire. Trust me ive tried everything on that front.

Anyway I put 14x32s back on but what chassis adjustments could I try to make it happier? The car still works pretty good but it could be better.

My first thought is raise the body one bolt but I don't think that's the solution.

Anyway maybe a moparts chassis guru can help me understand how rear tire height effects the 4 link geometry. ☺

If it does not change the location of the rear housing in the chassis, I.E. move the housing up or down in relation to the chassis brackets, it doesn't change the geometry, which is the relationship between the chassis brackets and the housing brackets. If the reaction times go away with the tall tire, what makes you say the car works better?

In the past, I've turned a car that was not aggressive enough to begin with, into a real turd, simply by taking a 100" tire off and putting a 104" on it.

If you are shortening the shock length or moving shock mounts to lower ride height back to where it was before putting the tall tires on, then you are changing geometry.

The 33s are dropping the lower bars down in the
front so the IC has changed.. check both tires
to see your change

Your correct.. the IC shouldnt change just the
tire dia did

Given the same axle to chassis dimensions (no suspension adjustments) what you are changing (slightly) is the center of gravity (forward &up) and lowering the anti squat line.
The chassis should separate easier with the same shock settings.
To get the chassis to do the same thing with the shorter tire, you would need to change the static i/c slightly rearward and slightly up.
You must also consider the tire compound & sidewall. It may not be so much the tire HEIGHT that is giving you the changes you are noticing.

I think it has to do with the body pitch at the hit. With the 33's the body sits slightly higher in the rear which puts the nose down. At launch the front end comes up much more with the 33's rather than with the 32's. Better weight transfer or stored energy I'm guessing.

I know Jed of the 'Luke and Jed podcast' fame put larger front tires on his Nova and it caused a massive wheelstand compared with his smaller front tires.

What can I adjust to move the instant center slightly rearward and up?

Its a 4 link roadster with anti-roll and a-arm front end. The car has a mountain of front end travel which really helps on crappy tracks. I'm usually one of the fastest no box in the class but always looks for better.

See if you can tighten the front shocks... you
can try loosening the rears just a little

What is the actual measured circumference of both tire sizes at race pressures in the centers?
Are both sets stiff sidewalls or not?
How about actual weight of the tires and wheels ready to race?
Lots of variables out there on race parts

I've tried 14x32 stiff sidewalls and regular sidewalls. The 10.5x33's were more consistent.

The rear shocks are usually full loose or 1 click if the track is great. Front shocks are around 5 or 6 clicks depending on the track. It has the strange shocks and probably needs a softer rear shock.

What is the MEASURED roll out of the two tires. Could be a significant difference in rollout simply changing the effective gearing and SLR...There is a very small difference in IC, height and distance between the tires Id guess. Likely small enough that unless you have something like a slider 4 link deal you would not be able to make it the same with the two tires. The 10.5W stuff is a pretty big tire might just be an SLR deal..