[Spike]

What are your favorite street legal track tires in widths wider than 245?
Why do you like 'em?

I really like my RA-1's. I have 9 inch rims incoming, and not sure 245 width will be the optimum width. I'm having a hard time finding any
16 inch tires wider than 245...like say 265's...

[APKhaos]

Toyo makes the RA-1 in 255/50 x 16. Section width is 10.3, which is 1/2" wider than the 245. Optimal rim width is 8.5" - 10.0", which is right on the money. Best news is that they are shown on Bob Woodman Tire's price list at the same price as the 245/45 - $165 for full tread [unshaved]. Radial Tire may be able to give you this price or better.

The diameter is 25.8", which is quite a bit larger than the 245/45 at 24.4". This may have an impact on gearing.

The Kumho Victoracer V700 is another candidate. Available in 265/45 x 16, and slightly less of a diameter problem at 25.3". Tire Rack price is $153. I've never run the Victoracer, but people who use them speak highly of them. May not have the extended life performance of the RA-1, but they are still a great tire.

See, there are probably still more options but this is a good start.

[Jase007]

This may have an impact on gearing.

Ahemmm .... "may" Mr. Kelly?

Jase

[APKhaos]

There I go, understating again! OK, it most definitely will effect gearing.

Manging effective diameter is the most frustrating part of tire selection. Everyone understands the width aspects of tire selection, but the diameter aspect is even more important.

We know that tires of a given size - say 245/45 x 16 from different manufacturers will be different absolute dimesions, right? A Proxes RA-1 adn Kuhmo Victoracer [and any onther tire] in this size will each have different dimensions.

Differences in section width can mean one brand fits your car fine, another brand rubs badly. It happens. In part, this is because the sectional width differences between brands, but it can also be caused by differences in sectional shape, which is harder to predict from the published specs. The classic case is one tire that fits on you fat rear Fuchs without a problem, and another brand - same size - that rubs itself to destruction on the spring plate bolts. This happens too!

Differences in rolling diameter are more subtle. While diameter can cause fit problems, it is the rolling diameter that can kill gearing.
First step is to figure out what the stock tire diameter is for you car. Look that up in the tire specs for the stock tire fitted to the car.

For example, lets say the stock tire on the stock wheel has a diameter of 24.5", which happens to be about right for the rear tire on a mid 80s 911.

If you look at the specs of the tire, you can quickly calculate the circumference of the tire to figure out the number of tire revolutions per mile. Tire vendors often show this figure in their spec charts - less math for us! For our stock 24.5" diameter tire, thats 853 revs per mile.

Now, lets say we want to go to a wider 16" wheel with a 265 tire, and we are looking at the two candidates I mentioned above:

Stock: 24.5" diameter, 865 revs per mile
The Victoracer: 25.3" diameter, 820 revs per mile
The Proxes RA-1: 26" diameter, 815 revs per mile

As you can see, each of these tires is result in significantly less revolutions per mile. That means that you have a higher final drive ratio than the stock setup. Its like fitting a taller ring and pinion.

In some cases this might be good, but in most cases it is not. Its best to keep as close as possible to the stock diameter to retain stock final gearing with your new wheels and tires.

This is especially important when you are increasing the diameter of your wheels as well as their width. So many ricers make the mistake of fitting larger diameter wheels with low profile tires [that have a larger overall diameter] and then wonder why their car is slower. They increased their gearing without ever knowing they had done it!

This is something to keep in mind when changing wheels and/or tires, or even when simply changing from one brand to another - say from streets to DOT R compound tires. Check the dimensions to be sure you aren't hurting your gearing in the process.

[cmartin]

I might be the 1 guy the taller tire might benifit, thanks for posting this.

[Spike]

Tony, the stocktire size (rear) was 225/50/16, which equates to roughly 24.85 inch diameter and 837 revs per mile. So, I guess this is where we start to make trade offs between traction/gearing/ and transmission regearing...?

Kumho does make 245's with a diameter of 24.3, Toyo's 245's are 24.6...so I could go with a 245mm width rather than a 255 or 265. This would let me get a bit wider than I am today with 225's on the rear.

I'd end up with 225's front and 245's rear.

For a track like summit point, with lots of turns and relatively few opportunities for top gear, is it generally wiser to go for wider tires and more traction or narrower tires with lower profile - assuming a choice has to be made?

I can't afford close ratio gears this summer

[APKhaos]

225F/245R is a nice setup in either tire. That what I ran on my 85 Carrera, and it worked very well. Nice balance, and all the tire you need for any of the tracks you run. Also keeps the unsprung weight down to reasonable levels. Increased unsprung weight is another downside of going to too much tire. I think you will be happy with that setup.

Chris, I was thinking exactly that when writing the post. I could help you quite a bit to go for a taller rear tire. It might be a good idea to talk to Steve Timmons about the 7/31 R&P with the 3.6 though. I seem to recall that the 7/31 might not be quite as strong as the higher ratio 915 R&Ps. No big deal, just something you should know about. I might be completely wrong on this.

[Jase007]

I might be the 1 guy the taller tire might benifit, thanks for posting this.

Chris:

We talked about this in another thread which was converted into a R&P swap thread. We were trying to get to the use of different circumference wheel / tire packages to increase / decrease final drive ratio which might prove cheaper than a R&P swap.

W/your 7:31 (that's 7 to 31, not 7.3.1 as I've seen it around the board) you could benefit from increasing the overall diameter of your rear tires (assuming you are keeping same wheels). If you run 15X6 fuchs like me, then extra sets of wheels are cheap and you can mount the extra / different sizes on a second set.

In my case, I regularly swap between 195/60/15 and 205/50/15. In my 356 it is worth about 3-400 rpm at the top end (using the 195/60/15). Makes a difference in motor longevity also as you may not be winding it out in every gear.

As long as you don't increase the sidewall height significantly, i.e. from a 45 to a 60, then I think the extra revs will outweigh (perhaps) the narrower tread width. You won't know until you try it. To really get into it you have to factor in torque curves, rpm power bandwidths, rpm drop between gears, aero resistance in top gears, etc... But, with a 3.6L and lots of torque, I don't see how this would hurt you. Borrow some wheels / tire and try it one DE.

I've done some experimenting and the difference in the two sizes that I run and the tread width is 1/4 to 3/8" of an inch at most. [between a yoko 008-R and a toyo RA1]. As Tony mentioned, you might end up with very similar tread widths although on is a 245 and another is a 255. Spend some time on tirerack.com.

FWIW

Emery:

For a track like summit point, with lots of turns and relatively few opportunities for top gear, is it generally wiser to go for wider tires and more traction or narrower tires with lower profile - assuming a choice has to be made?

I think this answer depends. Are you running out of revs in key corners (before track-out of most turns)? Is your 24.85 diam in the meat of your power curve in most gears? What would happen if you ran 2-300 rpm higher / lower in each gear? Picture where you shift and what the additional or fewer rpms would mean there. Also, if you have extra rpms in one corner it might translate to greater speeds carried to the next b/c you won't have to upshift and then quickly d-shift (thinking T2 - T3 stretch). Even "power shifting" takes time

More grip is always better until a point. Wider = more rolling resistance and on a high speed track like Daytona, a wider tire width (and accompanying bodywork) will decrease top end speeds. At SP I would go for grip over top end. Also, unless you have the extra hp to move the extra rubber ... it may work against you.

Volumes are written on this stuff. See the thread on books on track driving and car setup in another thread on the board.

Good luck.

Jase

[Trak Ratt]

Good stuff all
Personal note; have used RA1s and others with 245s - 9x16 and 225s - 7x16 on a stock bodied SC for several years and like the results. 205s and 225 would probably work just as well but I like the look. I don't think you can get away with the larger size wheels and tyres without suspension mods. Street maybe, track no. I also doubt very seriously if a stock HP SC or Carrera would see any advantage with wider/bigger tyres. It would be interesting to hear from those than run 17s and 18s on like cars. Heavier wheels but lighter tyres? Anybody do a comparison?

[BobNovas]

I'm running 17" wheels - 7.5" front and 9" rear. RA-1's - 235's front & 255's rear. I had to go to 17" wheels to fit over the big reds. Before that I ran 16" wheels - 8's and 9's with RA-1's 225/245. Also Kuhmo's, but they didn't seem to last as long. I just replaced the RA-1's I ran all last season. They still had some rubber, but they were making a lot of noise. Kuhmo's didn't last a season.