We have wanted to incorporate the MPSC 345/30-18's on the rear of our 2001 996tt for sometime. The obsticle has been having to to use 315/30-18's up front to come up with PSM compatible OD's. This would require major reworking of the front and a much more minor reworking of the rears. We're willing to do the additional rear work but 315's up front would not be very street friendly even if we did the work.

Currently, we are considering using 235/40-19 MPSC's in the front and 345/30-18 MPSC's in the rear. The OD's of this combination is within 3%.

We would be interested in any good comments.

We would be interested in your thoughts carnut.

 

To you have extended side fenders?.... cause my 315/30-19 is already sticking out the sides... its actually boarder like getto... what will it look like with a 345?
I tried a 335 but It looked so bad that I never left my garage.
Just my thoughts.

 

MARKSKI,

Yes, the fenders and interior fender would need a little work. I have run 335/30-18's on 12.5" Fiske's with proper offset wheels and minor interior fender work.

Take a peek.




We would need one inch on each fender for the 345's to fit correctly. My original question relates to how this combination would handle, not the work required to make them fit. Remember, we are talking 18's rear and 19's front.

 

It sounds like a good idea, especially since you've changed the gearing. Are 235/40-19's available? The taller tires may cause more clearance problems on the front with the wheels turned. 235/40-19's are nearly 2" taller then stock. I considered running 335/35-17 on the rear with 245/40-18 on front but the custom wheels seemed too expensive.

 

Yes, 235/35-19's are available in MPSC's. Actually, there is less clearance problems than the 265 or 275/35-18's that we have currently been using. Yes, there was mods made to wheel offset, flairing, internal fenders and oil coolers. The 235/35-19s have a 25.5" OD. THe 225/40-18's have a 25.1" OD. Only half inch difference.

 

I think you mean 235/35-19.

 

Yes, thanks ............ I just made the correction. The MPSC 225/40-18's are 25.1" OD and the 235/35-19's OD is 25.5". Only 3/10's of an inch difference.

With the MPSC 235/35-19 being 25.5" and the MPSC 345/30-18 being 26.2", there is only a 7/10's deviation which is under 3% and very workable.

 

I don't give a ****, call my contribution toward this matter worthless, function over form or not, 19's in the front and 18's in the rear is going to look straight up wack.

 

18" on the front and 19" on the back i can live with but definately not the other way around

 

Chad - I know you've invested tons in your suspension, but with 235 fronts and 345 rears won't it be dificult to keep it neutral? Also, would a stiffer front sidewall (19s) and softer read (18s) add to an increased propensity to understeer?

Mike

 

Mike,

Good question. We have run 275/35-18's with 335/30-18's. We have also run 265/35-18's with 315.30-18's. Both have a stiffer fronts but the car's handling is very good with either set up.

I guess if we were going for a matched set then the 235/40-18's on 9.5" rims and 315/30-18's om the 12.5's would be ideal.

I was hopefull that someone had tried this combination. I guess not. I really don't want to hear another "Johnney come Lately" post this isn't anything that the European tuners haven't already experimented with.

 

CJV
A 235/315 combo on your car will not be the ideal setup, other than looking at it from an O/D point of view. The gap is large in terms of front/rear contact patch differential and you might have a hard time setting your car to neutral handling with suspension components.
I drive on the street and track 265Fr -315Rr MPSC and the balance is perfect, enhancements to the car's behaviour are quickly done through tire pressures, shocks and sway bars, and throttle steering when needed is a piece of cake due to the excellent bias.

A 265 is already a heavy tire upfront for a street car, I think anything wider will not be fun to drive. Your car has a very different setup therefore only you will be able to tell after thorough testing.
BTW, a lot of European tuners have BTDT maybe they can help? j/k

 

You have a sickness Chad. lol

 

What tire size do you optimally want to run on the front, it sounds like you want to go 235 merely to keep the computers happy.

Forgive my ignorance here of the car's electronics (maybe someone here who knows the workings can weigh in) but why not just run the tire size you want and then fool the car by transfroming the signal from the speed sensors)

I don't know how hard it would be to implement that, and I also don't know what kind of stress (if any) it would put on the AWD system.

Just an idea.

-Adam

 

Adam,

I want the car to handle on the track as good as possible. The car handles best when the tire OD front/rear is a close to zero as possible.

We have been playing with the PSM system for three years and the only success we have had was to defeat the TB shutdown. As for the stress, the drivetrain has been completely rebuilt using stronger parts.