6X16 and 7X16 as track wheels

[jkeithtalbot]

I am thinking about getting a set of 6X16 and 7X16 wheels(front/rear), and running 205/55 & 225/50ZR16 Toyo RA-1 tires for track events. I think that this would allow me to run comfortably on the freeway (at speed), but get a lower profile sidewall for better handling on the track.

Has anyone done anything like this for an early 911? Would I be better to just run 205/50ZR15, and not worry about high RPM on the freeway?


TIA
-Keith

[Gburner]

According to this tire calculator the 16" tire is 25" diameter and the 15" tire is closer to 23" diameter. That would be a big change for your gearing. If your engine and gearing is stock and you will be doing mostly short track events I would stay with the 15 inch rims. This would provide for a lower CG too.

If you drove to the event with the 15" combo what speed would you be going at 4k rpm? These cars were made for the autobahn and 4k rpm for an extended time is ok imho.

The taller tire might be ok at a high speed big track, where you absolutely ran out of gear in 5th. Most stock engines on big tracks rarely see 125mph tops, or less. The taller tire is going to be difficult to keep in the power band, if you short shift it may not pull well at all.

Here's 2 cents more.

But if you have to drive your car to the track and you don't want to buzz it on the way there a roof rack with four 15" wheels may be best. That way you can freeway cruise your 16" wheels if thats what you prefer. Besides the Toyo RA-1 tires are a good street tire at full thread but a better track tire when the tread is all gone. You are not going to want to drive long distances with RA-1 tires with no tread, when they are at their best.

My advice don't compromise get a roof rack and have both. With a roof rack you might consider some cantalever slicks, used at 80% remaining they are only $80. They are only 23" diameter and an absolute hoot on an AX or a short track.

Tortured track tires make lousy street tires. If/when you flat spot one you don't want to drive it daily and suffer the thump thump vibration.

Have fun at the track!

[jkeithtalbot]

According to this tire calculator the 16" tire is 25" diameter and the 15" tire is closer to 23" diameter. That would be a big change for your gearing. If your engine and gearing is stock and you will be doing mostly short track events I would stay with the 15 inch rims. This would provide for a lower CG too.

You calculation is off see below:

205/60-15 = 24.7” current wheel/tire
205/55-16 = 24.9”
225/50-16 = 24.9”

So overall tire diameter only goes up .2 inch, that’s a drop of 6 revolutions per mile, very minor change.

The idea of going up to a 16" rim is to keep the same tire diameter so that I don't have to change wheels at the track and I can cruse comfortably down the freeway at 85mph.

I could store a spare set wheels at the track (I have a garage there), but I want to be able to leave work at noon on Friday drive to the track do some laps and then go home (no fuss).


Thanks for the input
-Keith

[JackOlsen]

The idea of going up to a 16" rim is to keep the same tire diameter so that I don't have to change wheels at the track and I can cruse comfortably down the freeway at 85mph.

Here's where I'm not understanding, I guess. If you're not talking about changing your overall tire diameter (affecting rpm at cruising speed, gearing on the track, ride height, etc.), then what' s the concern? Do you think there's going to be a significant ride difference between a 25-inch tire on a 16-inch wheel and a 25-inch tire on a 15-inch wheel? Because of the sidewall?

[ttweed]

You calculation is off see below:

205/60-15 = 24.7” current wheel/tire
205/55-16 = 24.9”
225/50-16 = 24.9”

So overall tire diameter only goes up .2 inch-Keith

Your original post said:

Would I be better to just run 205/50ZR15

so Gburner responded correctly. You are listing a 205/60-15 in your comparison above. A 205/50-15 is indeed a much shorter tire than .2".

TT

[jkeithtalbot]

Your original post said: so Gburner responded correctly. You are listing a 205/60-15 in your comparison above. A 205/50-15 is indeed a much shorter tire than .2".

TT

Yes he is correct but I would be reducing gearing not increasing it with the 205/50-15s.... that is why I don't want to put the 205/50-15 on the car because it will reduce the gearing and run at high RPM on the freeway.

I guess I should have worded my questing like this:

I have 205/60-15 on the car, will I have any problems going to 16" Fuchs 6" in front, and 7" in rear with 205/55-16 and 225/50-16 respectively? (This will keep diameter ~the same)




Thanks again for the help
-Keith

[jkeithtalbot]

Here's where I'm not understanding, I guess. If you're not talking about changing your overall tire diameter, then what' s the concern?

I want a more aggressive tire that you can get with 205/60-15, so my options are smaller diameter w/15" wheel, or same diameter with a 16".

My concern(s) is(are) will I have any offset issues, am I going to increase the un-sprung weight to much, will I need bigger brakes to handle the increased rolling mass of the 16" wheels............


Thanks for the help.
-Keith


PS. I also want to show up at the track and run, I don't want to hassle with changing wheels at the track.

PSS. Jack I absolutely love the look of your car!

[Gburner]

Your original post said: so Gburner responded correctly. You are listing a 205/60-15 in your comparison above. A 205/50-15 is indeed a much shorter tire than .2".

TT

thanks TT, I thought my old eyes had failed me.

[Gburner]

My concern(s) is(are) will I have any offset issues, am I going to increase the un-sprung weight to much, will I need bigger brakes to handle the increased rolling mass of the 16" wheels............
Thanks for the help.
-Keith
PS. I also want to show up at the track and run, I don't want to hassle with changing wheels at the track.
PSS. Jack I absolutely love the look of your car!

You mentioned 16x7 and 16x6 wheels. What is the offset of your new wheels?
With that info someone here might be able to help you.

If you car is stock I would not expect any issues with unsrung weight or brakes. I mean the only change is the diameter of the rim will increase one inch, right? The tire diameter is near the same. This is not a big change.

I didnt know you were considering a 60 series 15. Given the choices I'd go with the 16 inch rims and the lower profile tires too.

For the reasons I stated above when you are ready for a cheap improvement consider the smaller diameter rims and tires.
I like Jack's black beauty very much too.
Your orange 911 looks very nice.
Enjoy your slide down the slippery slope.

[JackOlsen]

I'm still a little confused, but I think this can be sorted out.

I want a more aggressive tire that you can get with 205/60-15, so my options are smaller diameter w/15" wheel, or same diameter with a 16".

First off, the only tires that are going to change your effective gearing are your rear tires. They're the ones that move the car. So, if you have 15x7 wheels in the back now, your tire options are pretty much only 225/50x15 (23.9-inch diameter). With a 16-inch wheel, there are a few 225/45x16 tires (24.0-inch diameter), and a whole lot of 225/50x16's (24.9-inch diameter). So, if low gearing is your goal, it can be done with either size wheel -- but it might be easier (in terms of tire availability) with the 15's.

Now, that's assuming we're talking about moving from 7x15 to 7x16. Maybe you have sixes in the back now? In that case, if you're running 205/55x15 tires in back now, you've got 23.9-inch diameter tires as well.

Now, by 'more aggressive' you might also mean going from 205 to 225 width is your step toward 'more aggression.' You might also mean there are stickier tires available in 16-inch sizes than 15-inch. You might even think sidewall size will make handling more aggressive. I can't be sure. Can you be clearer?

In any case, if you go from a basically-24-inch tire on a 15 to a basically-24-inch tire on a 16, you're really not going to notice much of a difference at all. A 16-inch wheel weighs a little bit more than a 15-inch wheel, but the taller tire you'll need to put on the smaller wheel will make up for that difference. You're either going to have more tire and less wheel filling out your 24 inches, or more wheel and less tire. But with the exception of Hoosiers and non-steel-belt tires, 'more tire' in that overall diameter generally weighs more than 'more wheel' in the same space.

Some people claim they can distinguish handling differences between a taller sidewall tire and a lower one. I've driven both, and I can't feel a difference at all. The only thing that jumps out at me is overall diameter changes and overall weight changes. Of course, it's possible that I'm just not very sensitive.

My concern(s) is(are) will I have any offset issues, am I going to increase the un-sprung weight to much, will I need bigger brakes to handle the increased rolling mass of the 16" wheels............

You will not be changing the unsprun weight very much at all. If you maintain the same outside radius, you'll probably be a tiny bit lighter. And Fuchs offsets are the same in 15-inch and 16-inch sizes.

I think the only reason to go from one wheel size to the other is tire availability. With Fuchs, the overall weight and handling differences of same-radius-and-width wheel/tire combinations are going to be minimal.