Adrian

Eric also talks about the brakes. The NA rear brake discs (rotors) do not fit the Turbos and vice versa. Even 964 TL owners need to know this.
I also agree that as you up the power you need more rubber to be able to transmit the power to the ground.
My GT-2 runs 315s on the rear and I can spin them up at speed in second.
With the RUF RCT Evo I was also able to spin them up at 140 kph in second (much lighter than the GT-2).
There is no point having power if you cannot get it to the ground.
Ciao,
Adrian
964C4
GT-2

JBH

Yes - my objective is to fit a larger tire in the rear. I am not certain you can accomplish this just by reducing the offset - I thought I remember reading there was a problem with the sway bar being in the way.

I am upgrading suspension (Moton Clubsports) and transmission (closer ratios) at the same time so I think the wider tires make sense.

Jeff: I looked at what Eric is doing, but he has not driven the car on the track - I was hoping someone had track tested this modification.

jeff91C2T

Yes, it would be nice to have some first hand experience. The closest I can think of is a pre 91 Turbo that can run 315's on the back. But these are torsion bar cars and it's not a direct comparison.

For my car, I'm running 450 inlb springs up front and 600 in the rear. Shocks are H&R sports. Sway bars are from an RS. The car is loose which makes it reasonably fast in autoX but on the track it's too much. I would rather have more rubber in the back. But from a cost stand point, as Eric mentions, it's expensive to get those few extra mm of tire. If I were to come across the parts at a reasonable price, I would do it.

Kumho is coming out with 295's (17") in their V710's next year. I'm going to try and run these instead of the 275's. This for me is the most "cost effective" solution.

What spring rates are you running with the Moton's?

How did you go about the gear ratio change? Are you using C2 gears? I'm considering doing this over the winter and have been looking into swapping out to the c2 2-5 gears. I'm very interested in your thoughts on this....thanks

JBH

Rennsport Systems is doing the work - the project is just getting started. I'll give all the information as it progresses.

djimenez993tt

JBH,

Any updates on this project?

Thank you,
David

JBH

Jeff Gamroth (Rothsport, Portland, OR) recommended the modification. When I posted this thread, my car was in his shop undergoing suspension, brake and transmission upgrades. I suggest calling him if you want the details. He is very good and all the West Coast racers know him. If he says it can be done, I believe it.

Since starting this post, it seems I have read of one or two successful conversions. IIRC, the replacement of the trailing arms is straightforward, but it changes the length of the drive axles so those need to be custom made.

New tires, new wheels, trailing arms, custom axles, CV joints, sway bars, bushings, etc. and it all adds up to a pretty expensive conversion.

If I don't sell my car, I'll start putting money into rebuilding the engine. this conversion will have to wait.

underpsi

i have 235 fronts and 295 rears on my stock speedlines using yoko 048 with no problem and still have room left; i think 265 fronts with 9" rims and 315 rears with 10.5" is possible.

cobalt

Really,

I am running the same size using PS2's and I have less than .300" in space between the tire and trailing arm, It is also pretty tight on the outside, I think if I went wider it would rub for sure. Is your car lowered?

JBH

The tire brand has some influence, but I don't think any brand of a 315 tire will fit. I can tell you that on the track, a 10" wheel with 61 offset will rub the inside oil line under the passenger-side rear quarter panel. That is just 0.5 cm off the OEM offset, so there is not a lot of opportunity to push the wheel/tire deeper into the wheel well. If you car is lowered, you might have another 0.5 cm toward the outside, but that's it.

I used 245 in front for awhile, but that was rubbing under moderate cornering loads and really wasn't doing anything positive for the handling. The wheel I used was stock offset, so it may be possible to squeeze a larger tire using a different wheel.

BTW: from a handling perspective the motivation for going to larger rear tires was to offset some of the oversteer. Others may have experience to the contrary, but I don't see an advantage of increasing the width in front without also increasing the back.

underpsi

yes, the yokos fits slightly narrower as they don't have the protection bar on the side wall; you can look up the spec/sizes on tirerack.com

my car is lowered and with 2.2 neg camber on the rear with 295 048s, i have tried putting a 14mm spacer and it seems to be ok as long as if you have stiffer suspension; therefore this leads me to believe that the 315 yokos will fit as it is really 17mm wider.

however with the fronts i have tried with a 14mm spacer as well as it seems to be within the fender and i think there is half inch to go on the inside.

38D

I ran 245/295 Hoosier and 235/295 MPSCs. The 245s would rub at full lock, but the 235s were fine. There is no way a 315 would fit unless it was absurdly narrow.

underpsi

the tire section width on the MPSC 295 is 12.1" and the yoko 048 315 section width is 12.3"; this is as per tirerack website specs.

what were the offsets of your fronts when you ran the 245s? maybe there is room to go on the inside? did you run the hoosiers 245/40/18 or 245/35/18??

nathanUK '81 930 G50

Miles965 has changed the rear arms on his euro car. A 3.6T, formerly Jeans car.

paul_23

On the subject of rear trailing arms, the bushing in mine are shot but the garage here (Dubai) says I will need to replace the whole trailing arm on each side. How easy is it to replace the bushings and what equipment/part is needed. Any advice is appreciated to avoid very costly parts!

Cheers
Paul

Miles965uk

having 315s on the rear is awesome! It used to slide out a bit on tight cornering but now it sticks like glue.
Cost of conversion isnt that bad- I got a set of used arms and the driveshafts with it- you use the same NA ones.
You need NA handbrake cables as well.
The geometry will need setting up too.
As said before the brakes are different- same size but thinner so you could use RS rears or put some spacer inside the turbo caliper.