_snowbird_

Hi all - I just bought a set of 996 Turbo hollow-spokes for next year's DE's, and they came mounted with Toyo R888's.

The fronts seem fine at 235/40, but the rears are large at 315/30.

Any thoughts about using these tires on my C4S? They're also 4 or 5 yrs old, so coming up on the end of their service life I think...

Comments appreciated!

certz

I run the Falken Azenis RT615K 315/30 on the rear of my C2S on the 996 turbo wheels without issue - I do not remember my ride height off hand though. At 4-5 years, I would give yours a very close look and consider replacing, but that is me. I am sure guys will chyme in about running tires much older.

cgfen

that size worked for me on my kinesis wheels first (two pics).

last pic is 295s on 996 Turbo wheels

Have fun

WOW, that car is pretty, why did I sell it?????????????????

_snowbird_

Beautiful! Ok - sounds like it's worth a shot. Thanks!

P-daddy

Maybe ok on a 2S but I wouldn't do it on a 4S. Something to do with maintaining correct rolling diameter front/rear ratio so you don't kill the viscous coupler.

certz

The Falken 235/40's and 315/30's have the same diameter at 25.5". I would prefer them closer to 25" but finding sizes that match front to rear with that diameter are difficult. I have run Yoko AD08R's 225/40 and 295/30 that are 25" diameter, but I like a little more meat up front than the 225 offers.

_snowbird_

Stock 225f & 285r have different overall diameters. The rears are slightly smaller in diameter than fronts. Does that ratio need to be maintained?

il pirata

On the 993 AWD you want to have less than 3% difference between F/R diameter.

To the OP, here is a calculator, shows only .15 difference. Not sure how the sizes will that effect alignment, etc.

http://www.1010tires.com/Tools/Tire-...0R18/315-30R18

Knight

With such a large size rear, wouldn't this promote more understeer?

_snowbird_

That was also my concern. At my DE, I felt like I was fighting understeer with my 225f's. Having so much more tire out back could accentuate the problem?

On the other hand, maybe a grippier tire up front will be enough to combat my understeer. I was running Conti DW at my DE.

il pirata

Larger tire in the rear will increase understeer if everything else stays the same.

To quote Bill V.

"you can reduce understeer by,
increasing rear spring rate
increasing rear roll bar rate
increasing front wheel width
using more camber in front, less in back
softer front shock and or harder rear shock
remove weight from the front
higher front tire pressure, lower rear
bigger(more efficient) front spoiler, smaller rear
mre rear brake, less front"

I like Conti DW for the street but it seems most think they are not very good for DE/xcross.

Opo

R888's 315's on the rear and NO issues here ...

race911

Not one mention about how truly awful an R888 is? I know many use them, but I'd rather leave the car in the trailer than even run a single session with those.

NYC993

I would not run 4-5 year old track tires for sure, and R888s heat cycle out.

Larger wheel in the rear should take the preload off of the coupler so AWD should not be working at all...not like it does anything.

But 315 is a lot of tire in the rear but it also doesn't always mean more grip. The contact patch will have a different shape.

I run 225/275 NT01 combo on C4S and haven't really needed more grip in the rear. The car rotates well under light braking and stabilizes quickly if rear starts moving in high speed turns.

_snowbird_

Thanks for those insights. I'm a little hesitant to run these older tires. I didn't consider the heat cycling impact.

I was intending to get new, dedicated DE tires - and I thought I'd go with slightly larger with 235/295. But maybe I should do some more research.