Lblackman

Okay folks ... I am sure there is an answer out here somewhere. I have been trying to get some straight information on tire sizes for DE use and am mostly stumped.

Car is an 07 997S. I plan to buy a set of 18 inch Carrera III wheels, 18 x 8 and 18 X 11, from Wheel Enhancements for DE use. What I cannot get is a straight answer on tire size and clearance for the rears.

Question .... with a narrow body car, will a 315/30ZR18 Michelin Pilot Sport Cup, or similar size tire, fit? Do I want a tire this wide, on these wheels, for DE use?

The Wheel Enhancement folks are challenging that tire size, saying I should be closer to the 265/40ZR18 OEM size.

I would really appreciate some information from folks who have gone down this path and have real experience.

Many thanks.

Lorne

Crazy Canuck

295 to 315 is 20mm (2 cm) . Not much really.

I had 18" Toyos on my S. I think they were 315 in the rear.

roberga

you need to be careful with this. If you go wide in the back and do not have it balanced with the front you will end up with understeer and gain nothing. The cups might be tough to fit at 315 as well. With only and 8 inch front you will be limited with the front.

mdrums

245/40/18 front and 305/35/18 rear is what you need. I use these sizes driving to and from the track on Toyo RA1's. my wheels are CCW's C14's...the C10 are now out too ccwheels.com and are 18x9 front and 18x12 rear.

RonCT

If you have wheels built for your car by companies like Fikse, Forgeline, etc. they will suggest 8.5" front wheels and 11" rear wheels with proper offsets - CCW likes 9/12. The 11" rear OEM wheel you mention above will have the wrong offset - those are from widebody cars. The best tire I know of for our cars is 245/305 as Mike mentioned above - correct width and rear tire diameter - and it's a great all-around tire choice as well (good in rain, cold, and dry). The RA1 in 305 is also the only correctly sized tire that has 26" diameter, which matches OEM - use a smaller diameter and you will throw off your speedometer, odometer, and risk having some impact on PSM / ABS.

Lblackman

Thanks - very helpful. Sounds like 245/305 is the way to go. Now about those wheels ... will have to inquire further. I thought the OEM Carrera III in the 10" width was from the 987 and the 11" was from the 997. I did not realize there was a narrow body / wide body offset difference.

So much to learn! Life was simpler with the Boxster S!

Lorne

mdrums

10" wide wheels are not wide enough for a 305. You need 11.5-12" wide.

RonCT

True and Not quite - Correct, 10" is too narrow. But you don't need 11.5-12" - Check the tire specifications for yourself and see what the professional racers, wheel builders (Fikse, Forgeline, BBS, etc.) say... The only person I've heard say 12" is CCW, but a year ago when I was shopping for wheels, John was saying 11" (per the several emails he sent me and the quote). He's changed his mind, but I don't believe anyone else has. I'd say 99% of the people I know running 305 RA1s are doing so on 11" rears.

http://marktg.toyotires.com/file/18968.pdf

245 rim range is 7.5-9 with 8" highlighted.
305 rim range is 10-12 with 11" highlighted.

Per everything I've learned -
245/40-18 RA1 should be on an 8.5" rim for optimal performance.
305/35-18 RA1 should be on an 11" rim for optimal performance.

I so wanted the OEM 18" wheels to work, but they just don't unless you are willing to run 225 / 265, because the OEM 18s with correct offsets are 18x8 and 18x10. Unfortunately, the 11" rear is the widebody offset, which you cannot correct.

Lblackman

Looks like I am going to have to re-think the whole puzzle, starting with the wheels. Too bad ... the OEM ones were very inexpensive. I suppose it is false economy to go with a set of 19 inch lobster forks -- very light (by OEM standards) and very cheap - $1400 for a full set from Wheel Enhancements.

LCB

RonCT

The thing about any 19" size is you won't be able to get a "real" R-compound tire. Yes, Michelin and Pirelli make a hybrid that they even call an "R-comp" but if you read the materials, you'll find the rubber compound and the tread design of even the Pilot Sport Cup is not the same as a "real" PSC. The real thing in all sizes up to and including 18 is a real R-comp. But for the Porsche 19" GT3 OEM tire, they knew they needed something that would be more like a summer tire that would channel rain better, deal with cold temperatures, etc. So, the "hybrid" PSC was born and is available in 19".