15" vs 16" Fuchs for track use
 

From a pure handling perspective (i.e. forgetting for a second about tire availability and gear ratios), what wheel sizes do you consider more appropriate for track driving on R compound tires?

Car is an SC at 2200 lb (no driver, no fuel) with 230 bhp.

Cant say from experience but I saw Buckley Racing cars running on 15" hoosiers 275's on rear and they were killing everybody in their class at Topeka.

a lot of folks prefer the lighter unsprung weight and greater mechanical advantage afforded by smaller 15" wheel/tire combos -- One setup to look at is 15x7 and 15x8 fuchs with 205/50-15 fronts and 225/50-15 rears -- Bill V has recommended non-fuchs wheel options with different offsets that will support wider front/rear tires too.

I asked a similar question in a thread...

http://forums.pelicanparts.com/porsche-911-technical-forum/621811-911sc-wheel-fitment.html

To quote Bill:

My takeaway is that 15" is a better choice for track, but 16" present more tire options and are less performant.

There's not going to be any one size recommendation because of all the different restraints
Generally in a tire for performance you want as low a profile as possible, 70 < 60 < 50 < 40 etc, as wide as will fit the fender space 185 < 205 < 225 < 245 etc, as short as possible, and as well supported as possible(this means using the widest wheel for which the tire is spec'd and which also fits the allotted space and lastly but not least in importance sticky tread compound

for example
if you must have Fuchs 7 & 8 x15 street options like 205/50 & 225/50 or 205/50 & 225/45 or even 225/45 & 245/40 all can be used, but even here the latter gives up a bit of performance potential due to the wheels width you'd really like 8 & 9.5 but that requires custom ETs not available w/ Fuchs

lots of track guys use Hoosier R7 245/40 & 275/35 as w/ the above you can use these w/ 8 & 9 again no Fuchs in these sizes w/ he correct ET, but 8 & 9.5 would be better and 8.5 & 10 even better some use 225/50 & 275/35 but this moves grip to the back creating more under steer which will then need to be dialed out in other ways

A large part of the preference for these ultra low profile tires is from gearing edge followed by inertial edge and profile & width edge

lastle 15s have a wider selection than 16 for tires, w/ 7 & 9 x16(the most common Fuchs wider fitment) 205/55 & 245/45 is common, here the grip is again moved to the back creating under steer fir street use not a big deal but for track you's really want 225/50 & 245/45 or 225/45 & 245/45 w/ 7 & 8 you could get back the gearing and inertial cost edge by using 205/50 & 225/45 w/o losing a lot of grip or balance again for street use this is a good compromise for track maybe not so good but it would depend on the compound at that point. Even Hoosier doesn't have wider /lower tires like they do in 15

Thank you all for your insights.

Ok, it seems that tire availability in each size and gearing are important factors to take into account together with the under/over-steer balance induced by the tire widths.

Considering that I need to buy a new set of wheels and those can be in any size, would you rather go for 15" or 16" for a use 80% track 20% canyon?

Many of the racers outside of the PCA letter classes (so not limited to stock gearing, stock spindle height, etc) run 17x8/9 with 245/275 tires. There are way more performance tire options for 17 than 15/16.

This thread has a lot of info on wheel size.
http://forums.pelicanparts.com/porsche-911-technical-forum/1050536-what-tire-16x9-fuchs-225-245-45-50-a.html

Really it comes down to what tire you are willing to drive on the street and track. I like Toyo RA-1s. But you have to see what sizes are available, will work for your wheels and fit your car.

The trade off is something like a Hooser R7 may be too soft for the street, but then which street tire will work well on the track.

It's not just the tire width

take a 7x15 Fuch you could use a 195/50, 195/55, 205/50, 225/50 or 245/45 tire on on it Toyo R1 R comes in all those sizes but not all lines cover all the bases.
in general the 45 series will perform better than a 50 but the 195/50 is better supported by the 7 than the 225/45 is so which to use? You then have to think about the relative f/r grip and tread compound to make a decision.

so again you have to think about f/r wheels and f/r tires and how the grip level is going to be split between them. The more powerful the motor the more rear grip you will want, a 200hp SC will be fine w/ a 225/45//245/40 split on 8 & 9 but a 300 hp version of the same car will want more like 225/45//255/40 or even 225/40//265/35

You also don't want to overtire the car

For a typical SC/or Carrera and limiting to Fuchs 7 & 8 x15 I'd probably go w/ RA! 205/50 & 225/45 or 225/45 & 245/40 R& or Maxxis RC-1 or Hankook RS-4 final decision depending on budget, some of these tires will only last a few days others much longer but an argument can also be made for 205/50 & 225/50 A052s as well, especially when the budget enters in.

if going to 17 the custom ET are widely available, 8 & 9.5 x17 is the way to go and tire height and inertial costs become much more of a factor, 275/40x17 is a tall tire for a small air cooled car you be buch better off 225/45 & 255/40 or 225/45 & 245/40 as the better supported small tire doesn't give up a lot to the under supported and tall wider 275 tire but again the bigger the motor the less of an issue this is.

I came from 16's to 15's.



First and foremost I would say get the wheel that fits your tire and not the other way around.

Since you said (i.e. forgetting for a second about tire availability and gear ratios) I would say go 15's unless you have brakes/spindle modifications that require 16's.

I agree with Bill, you shouldn't overtire your car. From my personal experience, warmed (205/225) R888R's are overkill for my 3.2L.

At the end of the day, I would try a baseline then up one size up and another size down and see what works best for you. I once met a guy who preferred slightly narrower tires over his car's "forum recommended" specs because he felt as if it was less "mushy" which gave him more confidence - he was FAST.

That being said, I plan to keep my 15's wrapped in 205/225 R888R's.

I hope this helps..

That's exactly what I'm running at the moment. But I have those R888Rs mounted on cookie cutters (6x15/7x15) which I think is not ideal because they are too narrow and sit inboard of the fenders by a couple of inches.

With my moderate levels of power, I'm hesitant between my current tire combo:

205/50ZR15 (diameter 587 mm)
225/50ZR15 (diameter 607 mm)

and one with similar tire diameters but in 16"

205/45ZR16 (diameter 590 mm)
225/45ZR16 (diameter 608 mm)

Nice, I wonder how they feel on 6/7's. I have them on 8/9's and they're perfect for me.



http://forums.pelicanparts.com/uploa...1580176056.jpg

Looks like those 9x15 fit the fenders very well! Would you mind posting a picture of an R888R sidewall on a 9x15? I bet they don't balloon as much as in mine!

The only 9x15 Fuchs I have ever seen or heard of are ET3, they do not work on the back of an SC/Carrera

For an SC/Carrera rear 9 you need ET15 or a tad less, depends on the tire ride height alignment and how aggressive the fitment is.

225/on a 9 is stretched
here is a 225/40 x18 on a 9
http://forums.pelicanparts.com/uploa...1580187175.jpg

a 225/45 x16 A052 has an 8.9" section width on a 7.5" wheel, 16" Fuchs lips extend an additional 3/8" past the 9 on each side, similar to what you see above, the 225/45 x16 is only spec'd for a 8.5" wheel a 225/40 for an 8" wheel.

A lot of this depends on your driving style and the size of the track you're running on. Some folks like their car to be "loose" and to have body roll shift (because of weight) into a corner and they like to feel the looseness of the tires so to speak. Me, not so much.. The more planted the better. When i went from 205/225s to 225/245s my lap times went up instantly. Even more so when i went up to 245/275s. - this was on early cars and SCs.. (my current car has 275/325s - but thats another story...) .

That's a very good point. Maybe for a low-powered car like mine, it will be enough to use 8x15 with R-compound 225s at the rear.

After all, 9x15 ET 15 only stick 9 mm further outboard than 8x15 ET 11. If I'm worried about aesthetics, I guess I could always slide a thin spacer to reduce the gap to the fender.

Here's a comp of 2 efficient R options one in 15 and one in 16, both on 7 & 8 Fuchs, the 15s have a ~20.1lb -ft edge and both will have roughly the same grip and balance.

http://forums.pelicanparts.com/uploa...1580237537.gif

Thanks Bill, it's interesting to see the torque loss due to inertial effects.

Regarding gearing, I'm not overly concerned because I will eventually re-gear the car. Also, as we discussed a while ago in another thread, a lower diameter tire will produce more thrust at a given car speed and gear BUT it will force the driver to upshift earlier which means that, at certain speeds, the car with low diameter tires will be using a higher gear and have less thrust compared to the car with large diameter tires.

For the track; Slicks in warm weather on 18" wheels, Hoosiers R-comps when cold, nice big contact patch compared to 15's