Tire width?
 

Tried doing a search and didn't come up with any direct answers. What's the largest width tire size you can fit on the rear of a 986. I have seen some people say 295s. Is that true? Is there room for 305s?

Stock fenders you can shoehorn a 275 in there with exactly the right wheel.
Roll the fenders and you might get 285.
Break out the fenders and create a widebody, 305 no problem.

Question #2- How much tire can you actually use? Top drivers suggest 245/275 is maxed for a stock 986 motor. Drop in a 3.6L and you can also run more rubber. There is always a point of diminishing returns unless your goal is "freak of nature at a car show" vs measurable performance gains.

I run 235 fronts and 275 rears on stock carrera light rims, no problems.

245 35 18 front, 275 35 18 rear works for me.

Tire widths are not very uniform. That is some manufacturer's "275" may be closer to being a "285" or visa-versa. The bast way before you purchase is to compare data from TireRack.com, or from the tire manufacturer's site.

That said, on my 986S, I am running 285 rears with Hoosier A6's, which generally run quite wide. These are a 11.5" section width when mounted on a 10" wide wheel. I have not rolled my fenders at all and this works, but if I was lowered a bit more there would probably be some contact.

So, running a 285 is possible, but it depends on wheel offset, ride height, and suspension stiffness (max wheel movement).

Take careful measurements.

Too much tire makes a car feel numb and heavier. I think this is one of those places where 'more is less'. I bought the stickest tire I was willing to pay for, in the stock size. Also, overall diameter affects ABS, PSM and overall gearing-if you change the FR/RR stagger you may trigger these devices. Bigger tires slow you down except when at steady state max cornering speeds-because they're heavier. Even on the street ( and that is what I'm talking about), I think tire/wheel weight matters more than trying to get every last 'G', especially on a Boxster which is engineered for agility and steady-state cornering.
Next year I'll be going ultra-light with 18 and 20LB wheels and 225/265(or 255) tires. My car will be more responsive and will react to bumps- from minute to large) better. It will also feel like it's overall weight has been reduced and it will accelerate and brake better. What's not to love? Sometimes bigger looks better though- to each his own.

I also have the 18" Carrera rims that came on the car (2004 S.) Over here in Europe I can't get the tires I want in OEM 265/35-18 but I can get them in 275/35-18. Sounds like this should be fine? Any comments?

Difference in diameter is just 0.3" (7.62mm) larger, with 822 revs/mile OEM and 814 revs/mile for the 275's.

Don't forget that changing the tire stagger (the difference between the width of the front tires vs the rear tires) will affect handling.

The 17" stock tire widths (205F/255R = 50mm difference) were selected to ensure that the car would understeer at the limit. Adding more stagger (205F/285R) will typically result in even more understeer (I would expect a 205F/285R car to handle like pig, i.e., terminal understeer).

Most Boxster owners reduce stock stagger to 30mm by running 225F/255R. This reduces understeer and moves the car towards more balanced handling. Many track cars run 235F/255R (20mm stagger) to further reduce understeer. And yes, some track cars run a so-called "square" setup of 255F/255R (zero stagger) to dial out most if not all of the tire width induced understeer (this setup also typically requires some other changes (alignment and sway bar settings) to keep the car from too much oversteer).

So remember, when going wider in the rear to also consider going correspondingly wider in the front to maintain whatever stagger (and handling characteristics) you prefer. This will keep the car's overall handling characteristics relatively constant.

Thanks for the info, I didn't know that about the stagger, so I have learned something useful there.

OEM on the 18" Carrera wheels are 225/40 and 265/35. So 40mm of stagger. Following your advice then, if I go with 275's in the rear I should also upsize the fronts to 235's. Or downsize to 255s in the rear, though I don't know if my desired tires are available in that size over here or in the correct aspect ratio.

235/275's work nicely on my Carrera lights

My thoughts about street driving exactly. My car is much more nimble & fun to drive on stock 17" tires. If CarreraII wheels were made in 17" that's what I would have on my car. :)

Yes, this can result in a lot of searching for specific tire sizes that may or may not exist. At the end of the day, most of us just do the best we can in balancing all of these tradeoffs. :)

On 8" front, 10" rear rims, run the stock sizes. You don't want or need big fat meats on there. I had 235/40 and 275/35, and I went to the stock 225/40 and 265/35 sizes. The car is now more nimble with lighter steering. Also the 235s were rubbing a hole in the front wheel liner when I turned sharply.

Good to know. though as I pointed out we don't have the selection of sizes in Europe like you guys do stateside, so I'm struggling to find what I want. I'd just go stock if that was an option.

Ok, so the tires I really want are the Michelin Pilot Super Sports. Not available in 265/35-18 in Europe, not in 255/35 either but are available in 275/35. Stock 225/40 is available, but not 235/40.

So I have limited choices that are as follows:

1) Increase stagger to 50mm by using a 275/35 rear without changing from front 225/40. How negative will that be with regard to understeer, etc?

2) Choose a different tire: Michelin PS2, PS3, or Bridgestone S02A are my available choices in stock sizes. The S02A and PS2 are N rated.

Please don't suggest other tires then these, I've already narrowed down the list to these based on my preferences and what is actually available. You US guys are lucky with TireRack. Of course I could get 'em shipped for a meeeelion dollars. :eek:

What to do?

Well, I approach this problem a little differently. I figure out what sizes I want to run and then shop for tires in those sizes. I do leave a little room for adjustment +/- 10mm in width. If they match the diameter goal, fit the rims, and have the desired grip characteristics, brand name is less important to me. YMMV

If you really want the Michelins, try a set in 225/275 and let us know how you like them. Lots of drivers run that size and are happy with them.

Still struggling with this one and understanding if an extra 10mm of stagger will have a particularly big effect on handling. 225 front and 275 rear. 255/35 isn't available either so I can't downsize. Any more opinions?

I added 10mm of width on the front of my 987, which did minimally reduce understeer. So yes, going to a 275 will increase the factory push, but if you're not pushing the limit often, you probably won't notice.

P.S. It did NOT make feel it any less "nimble" or "responsive", change the steering feel, or noticeably reduce acceleration.

If you gotta have the Super Sports, the 10mm extra stagger probably won't make a difference unless you're pushing hard. If you never get to the limit, you're likely to never notice any difference. If you do push to the limit, the car will definitely push/plow because those 275's in the rear are going to keep the back end glued to the road.

Otherwise, go with the PS2's in the stock size.

I tend to not agree with everyone
I run 285/30/18 on 10" and car is lowered 1" all around
rear offset of 48 but will fit 45
fenders not rolled