245/275

[BYprodriver]

Originally Posted by The Radium King

thanks lots. so, my understanding is that a smaller overall wheel/tire diameter will increase torque but reduce top end. on the rear you went from an OEM 265/35 to 275/35 which in an increase in diameter (25.3 to 25.6 or +.3"). however you noticed an increase in acceleration so one can assume that the increase in diameter was more than offset by the reduction in rotational mass (lighter wheels and tires)?

odd on the hoosiers. must be cheater tires (if you have the right rim width) - do you think you were rolling onto your sidewall?

Don't forget spacers weight. I don't believe there is any way to increase acceleration by installing taller tires on a Boxster unless you are testing 0-60 & don't mind sacrificing a clutch. I've never seen a 275/30/18 tire.

[The Radium King]

Originally Posted by BYprodriver

Don't forget spacers weight. I don't believe there is any way to increase acceleration by installing taller tires on a Boxster unless you are testing 0-60 & don't mind sacrificing a clutch. I've never seen a 275/30/18 tire.

holy trump, you're right. no 275/30, and a 275/35 is bigger diameter than a 265. what to do? 285/30 fit ok? that's a lot of rear tire. perhaps stuck with a 265 in the back.

[The Radium King]

so, after some sober review of what is actually available in tire sizing, and with the intent to not increase the rear tire diameter, I am here:

OEM:

225/40 (25.1) 265/35 (25.3)


Current (upsized fronts):

235/40 (25.4) 265/35 (25.3)


options:

245/40 (25.7) 265/35 (25.3) Even wider fronts - too much front tire?

245/40 (25.7) 275/35 (25.6) Wider fronts and backs, but can't get a 275 in a smaller sidewall so would see higher gearing.

255/35 (25.0) 285/30 (24.7) Super wide, smaller diameter - but will they fit?!?!?!?

so, anyone with experience running a 245/265 combo? anyone with experience fitting a 255/285 combo? i'm on coilovers, so hopefully no perch interference issues.

[BYprodriver]

Originally Posted by The Radium King

holy trump, you're right. no 275/30, and a 275/35 is bigger diameter than a 265. what to do? 285/30 fit ok? that's a lot of rear tire. perhaps stuck with a 265 in the back.

285/30/18 fit ok with proper wheel offset & give very noticeable acceleration improvement with stock 3.2L. However additional weight & treadwidth make the car less nimble which is why I just sold 2 pair of 10" Carrera II wheels. I say run the best 265 tire for your application.

[lkchris]

In the real world, here's what you'll accomplish fitting larger than oem tires:

You'll make the tire company happy because they've sold you a more expensive tire.

You'll have increased your car's unsprung weight, affecting handling and fuel mileage.

You'll have increased your car's rolling resistance, affecting fuel mileage.

You'll have decreased your car's traction capabilities on wet or snowy roads.

[The Radium King]

Originally Posted by lkchris

In the real world, here's what you'll accomplish fitting larger than oem tires:

You'll make the tire company happy because they've sold you a more expensive tire.

You'll have increased your car's unsprung weight, affecting handling and fuel mileage.

You'll have increased your car's rolling resistance, affecting fuel mileage.

You'll have decreased your car's traction capabilities on wet or snowy roads.

this is for track tires on a car that runs 20 min sprints, so don't care about fuel mileage. don't care about wet or snow - will use my streets as rain tires should it be raining at the track. currently have OZ Allegerittas so wheel weight is quite a bit lower than oem. yes, more tire does add more weight, however other factors can offset this - i want more front tire to improve turn-in so need to maintain balance in the rear, hence the question regarding performance of a 245/265 setup. would like rears a bit smaller diameter to improve torque/gearing and reduce sidewall (and, as a result, reduce tire weight). as bpd noted, spacers will increase weight, so overall fitment of wider setups becomes a consideration as well (ie, on front looking at a 7mm spacer w the move to 245).

bpd - 285's feel less nimble - is that because the rear gets glued to the ground? potentially not a bad thing if the fronts do the same?

[BYprodriver]

bpd - 285's feel less nimble - is that because the rear gets glued to the ground? potentially not a bad thing if the fronts do the same?[/QUOTE]

Yes very true depending on the track. My Box is my DD & I have given up tracking since I'm only competitive in a stockish class. I like the 235/265 combo for muti-purpose use.

Wider rear tires inhibit the ease of rotation.

[LAP1DOUG]

I normally run 255 Front / 285 Rear, and that size combination works well on track and on an autocross course. This is about the widest fitment that I can make work, and it works very well if sway bars are adjusted accordingly.

There are a few 285 /30 - 18 tire sizes available, but not many at all. A higher up at Bridgestone told me that they will finally be importing their RE-71R in this size within the next few months.

The NT-01 in 245 Front / 275 Rear also works well on my car with the same sway bar settings as my 255 Front / 285 Rear set-up. Obviously if you maintain the same front to rear stagger (in this case 30 mm), you can generally maintain the same balance set-up. As others have mentioned, you have to give up some acceleration with the NT-01 due to the OD of the tire, but that isn't too bad.

The larger OD occasionally helps by allowing you to carry a gear a bit longer. For example at the dip going into Turn 5 at Road Atlanta, I am just touching redline when running NT-01's with a tire diameter of about 25.6" , but I'm starting to bounce off the rev limiter with a 285 / 30 - 18 tire at 25" diameter.

The tire diameter is probably more important in autocross than road racing, as some slow corners can really catch you off the cam.

Have fun.

[The Radium King]

thanks folks, much appreciated. interesting info on the larger diameter - there's one straight into chicane on our local track where i'm faced with either short shifting or bouncing off the rev limiter (depending on how fast i come out of the corner before the straight); having more gear might be better here.

lots of choices; again i appreciate the discussion and info.

ps, if i were to try and squeeze 255/285s in there, what offsets would work? i currently am 1.5" lower w -1.5 front -1 rear camber. front wheels are 8.5" wide ET 53 and from what i can tell a 7 mm spacer should get me 245s, and somewhere in 10 to 15 mm will fit a 255. in the rear no idea; wheels are 10" wide ET 40.

and, not really related, if people are fitting 285 mm wide tires with no issue, and a 11" wheel is 280 mm wide, how come everyone on the internet says you can't fit 11" wheels? is it a coilover vs stock suspension thing? would certainly open up the range of wheels available if we could fit more 996 wheels.

[BYprodriver]

Originally Posted by lkchris

In the real world, here's what you'll accomplish fitting larger than oem tires:

You'll make the tire company happy because they've sold you a more expensive tire.

You'll have increased your car's unsprung weight, affecting handling and fuel mileage.

You'll have increased your car's rolling resistance, affecting fuel mileage.

You'll have decreased your car's traction capabilities on wet or snowy roads.

Wider yes, taller no.