I've done a bunch of searching on this forum (and others), but I'd like to get your opinions.

I'm going to buy some NT01s to put on my old factory 17x8 wheels, but I can't decide which size will be best. They will be used for autox and track days only, so I want to make sure they will be optimally sized.

The 245/45/17 specs optimally for the 8" wheel while the 255/40/17 calls for 8.5". I also wonder about the overall diameter of the 255 not being optimal. Which would all of you choose? Will I be happy with the 245/45/17, or is that not enough tire?

And yes, in the world where I had an endless supply of money I'd buy ultralight 18" wheels with fat tires, but I need to make do with what I have on a budget.

Thanks all!

 

One thing you need to consider is overall diameter. Your stock tires should be 27" OD but check this.

The benefits of smaller diameter tires are improved acceleration and lower centre of gravity.

The disadvantages are lower top speed in each gear, and this might put you on the rev limiter in 4th depending on where you run, less ground clearance, less clearance to get a jack underneath and stiffer ride due to less sidewall.

Some people might be concerned that the smaller tires looks "funny" in the wheel wheels

For track use I would only suggest sticking to the recommended wheel widths. For Auto-x the standard seems to be to run tires on narrower rims than the factory spec. Remember that on an Auto-x the runs are measured in seconds and on track days you can be running for up to 30 minutes at a time.

I love my NT01s - 275/40/18 (26.65" dia) on 18 x 9.5 x 35 mm offset Enkei PF01 rims. I'm considering replacing them with the 275/35/18s (25.55 dia) next time but have a concern about the rev limiter in 4th on the back straight at Mosport and getting the jack under the car. I'm also really concerned that the smaller tires might look funny in the wheel wells

 

Finances excepted, the only reason that autocrossers run their tires on narrow (sometimes unusually narrow relative to the tire size) wheels is because the Stock category rules won't let them run wider wheels than stock. Wheels that are wider than "measuring width" will generally make the car slightly more responsive on turn-in, because you aren't waiting for as much as much tire distortion to happen or coping with the greater amount. "Slightly" means a lot in autocross, because it's happening almost continuously for those 50 seconds or so.


egon - if you choose to run in either Street Touring or Street Prepared (or end up there by virtue of other mods), you've got a lot more freedom in choosing wheel widths that are more appropriate for the tire size you have in mind. I think ST has a 9" limit, but ESP goes a good bit wider.

It's worth remembering that the earlier S197 Mustang's 235/55-17, 235/50-18, and 255/45-18 tires all came stock on wheels at the upper end of the tire mfr recommended rim widths for those sizes (8", 8.5", and 9.5" respectively). I do not believe that Ford did that by mistake or even for appearance purposes. In spite of the stick axle rear suspension, the Mustangs have consistently been at the top of handling comparisons against the current Camaros and Challengers.

If you're serious about doing well in whatever competition class or track day activity, or even that you want the response in your daily usage - it's perfectly OK for your car look a little . . . ummm . . . different. It doesn't bother me in the slightest that the tires on most of my cars have a slightly "stretched" appearance, or that the Azenis for autocrossing my 626 stand about an inch shorter than the OE size that already left more tire to fender opening gap than most appearance-concerned folks care for. Knowing why you did something to improve your car and/or just make it work better for you should always count for more than satisfying the people who only get to look at your car from the outside.


Gratuitous picture of what tire distortion looks like with 255/45-18's on 9.5" wide wheels. Sorry for the picture quality, but it's all I've got (and I was looking elsewhere at that moment anyway). What you want to be looking at are the left side tires for lateral distortion (particularly the rear tire shape below and behind the axle) and the right front for an indication of lateral g's. On narrower rims, the distortion would be greater . . .



Same car/wheels/tires/driver/etc., at rest






Norm

 

Norn

In the "at speed" picture it does not look like there is much weight on the right front

 

Thanks for the responses!

No, I am not worried about appearance at all, so the smaller od won't bother me. I just wanted to make sure I was getting as much tire as possible with the limitation of my wheel size (can't afford new ones).

So, sounds like the 255/40 will be too wide and not offer any benefits over the 245/45. Will this be enough of a traction improvement over street tires to be worth the cost? I've only raced on street tires...

 

For me the 275 wide NT01s provided a noticeable difference over my 285 wide KDW2s in cornering grip, braking and the ability to get the power down sooner.

Now I just wish I could afford to run Hoosier R6s.

 

i would do the 255/40 17. more tire to the ground, less sidewall. perfect fit for a 8 inch wide wheel, no. but it will do fine..

lots of autox people stick 275s on a 8 inch wheel..

if you decide to go the other way, or have a place with a really good price on either size let me know.. i run 245/45 17 on my rx8 that is pretty much just a track car. would love to toss some nt1s on it..

btw, you can find some really light 17in wheels. search for oz superleggeras.. lots of race teams used to use them in the koni challenge series. they weigh 15.4 lbs.

beers

 

On a mostly street car, tread compound and carcass construction trumps width every time. When they were new and not heat-cycled out, the 205/50 Azenis were shockingly grippier than the 205/55 summer performance rubber on my 626.


Swoope - again, what autocrossers will use is primarily a consequence of the rules, and in this tire:wheel width case is not to be interpreted as a technically preferable solution generally. Let's just say that when a tire contingency payout is on the line every little bit helps even if it is in the larger sense a poorer solution that gives it to you (and does so under narrowly defined circumstances).


Norm

 

norm,

i know what autox people do..

but as the op does not really mention where he is aimed at.. he is not running for a series championship in autox and is not running tt at track events...

so i am going with stuff the 255s on the 8 inch wheels.. and on track pay attention to tire pressures hot..

if he has idea of the grip level of the n01

have fun..

beers

 

I don't think I'd be fully comfortable running on narrower than the min-recommended wheel width for an extended period of hard use such as a track session, and as far as I know DOT tires don't feature cantilever construction. 50 seconds at autocross is a different story.

Next round's on me.


Norm