245/275

[The Radium King]

hi. looking to go wider front and back on my car. 18" wheels. currently running:

235/40 (10mm wider in front) and 265/35 rear (OEM).

pretty content with the balance this gives the car. I want more front tire, so thinking I should widen the rear also. I realise there are pros/cons to this, and hope to report back on any changes I experience with this setup (ie, diameter impact on gearing and torque, impact on power given need to turn bigger rubber, any changes to front/rear balance, etc.).

I am thinking the following:

245/35 and 275/30

concerns are fit, diameter vs OEM, and diameter variation front/rear (so as not to mess w abs). here's my analysis of diameters:

225/40 (25.1) 265/35 (25.3) OEM
235/40 (25.4) 265/35 (25.3) current
235/35 (24.5) 265/35 (25.3) 3.3%
235/35 (24.5) 265/30 (24.3)
-
245/35 (24.8) 275/30 (24.5) proposed
245/35 (24.8) 275/35 (25.6) 3.2%
245/40 (25.7) 275/35 (25.6) confirm front fit

the proposed size reduces diameter front and rear, keeps front/rear diameters within tolerance, and should fit (front w spacers - ET53 and 7 mm spacer).

anyone have any experience with these widths that they could share? am I on track w sidewall heights? thanks.

[steved0x]

Originally Posted by The Radium King

245/40 (25.7) 275/35 (25.6) confirm front fit

I don't have any feedback on the other ones, but this size won't fit in the front if you have the OEM struts up front - the tire will hit the lower spring perch (or whatever it is called... ) I don't know about the back but I did fit a pair of 285/35/18 on the back, and although it looked successful I never drove on it because the fronts I had to go with it didn't fit (got them from a Cayman guy)

I have seen folks run this size successfully with PSS9 however since they don't have that big lower spring perch.

[j.fro]

I ran 245/40/18 NT01 tires on the front & 275/35/18 NT01 on the rear with 18x8 18x10 Carrera Lightweight reproductions for a few years. On the front I used 7mm spacers, 14 on the rear. This combo was lighter than my stock 18" turbo twists with inexpensive all season tires and acceleration was noticeably quicker. The nittos rubbed a bit at full lock in both directions, but that didn't bother me. The car NEVER had any understeer. Turn in was spot on. As the rears wore, or on cold days, I would get oversteer. I removed the rear sway bar and it cleaned this up very nicely.
Last year I switched to Hoosier A7 245/35/18 and 275/35/18. The rears are pretty much the same dimensions as the Nittos. The fronts are waaaay off. They are at least an inch wider, if not more. the tire is cantilevered on the rim and really should be on an 8.5 or 9". They react to both temp and tire pressure very differently, and I chased a horrible understeer problem all year. I couldn't get the rears to brake free no matter how hard I tried. It was a rough year.
I'm on coilovers, so I can't comment on how the diameter affects rub on the spring perch.

[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?

[j.fro]

Yeah, on the rears the bigger wheels/tires were about 5lbs lighter each. The fronts were about 3lbs lighter each.
When the Hoosier A7 tires came out, replacing the A6, there were a number of sizes that seemed way off from their predecessors. SCCA boards were lit up all over the place.

[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.

[Racer Boy]

Generally speaking, you want to avoid taller gearing (what taller tires will give you). Do you run at any tracks where you reach top speed? If you do reach the car's top speed, is it because you are on the rev-limiter? If not, then you'll gain more from the shorter gearing giving you quicker acceleration.

[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.

[heliguy]

I run 275/35/18 in the rear of mine on the stock Carrera Lights and they work just fine with spacers. No problems with the slightly taller profile. The height difference (92.75mm) vs (96.25mm) is only 3.5mm and is so negligible it wasn't a concern for me.

[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.

[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.

[anotherturbo]

As for fitment...I run 255/35/18 in the front and have the slightest rubbing at full lock, and 295/30/18 in the rear with no clearance issues. I do however have coilovers and rolled fenders.

[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.

[LAP1DOUG]

Originally Posted by The Radium King

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.

I have run 255's on the OZ 8.5" et 53 wheels with 7 mm spacers, BUT my car has coilovers and adjustable caster. Without the adjustable caster, you will probably have heavy scrubbing of the wheel liners at anything over about 1 turn of the wheel. Without any spacers looks like it would work without scrubbing according to my calculations, but you may have trouble with clearance to the OEM strut. I can't help you with any data on that, as I have never run the OEM suspension.

I have never done any trials or calculations with 11" wheels on the rear. The general internet wisdom is that it doesn't work, but I think I saw one post where some guy said it worked with just the right offset and lots of negative camber.

[The Radium King]

bah, humbug. toyo canada has no 255, 275 or 285 in stock. looks like I am forced to be prudent and get a 245F/265R setup or pay heinous exchange rates.