Tire sizes for 7 and 8 X 15's?

[thrown_hammer]

I am getting ready to mount tires on my rims. What size tires can I run?
She's a '73 911T W/ SC flares on the back. Local tire shop suggested 205/50 and 225/50.

[skinnerd]

205/50 are too small for 15x8's (although you'd have great acceleration)
for sure 225/50 will fit
I always used 245/50 without an issue (try finding them though?)
unfortunately that are not many tires made for the wider 15" rims anymore
this is why many people are changing to 16" and 17" rims, as the choices in tires go up greatly
good luck

[Elombard]

I have the same car and I run 225/50 R 15 all the way around. I think it looks kick a$$.

[gumba]

I use 205/60/15's on the front, 215/60/15's on rear of my '73 targa w RS flares. I use this for the street. The 60 series are going to give a better ride, and in my opinion look better. The 50 series 15's look too small. For the track I use 225/50/16's on 8" in the front and 245/45/16's on 9" in the rear.

[Todd Simpson]

I've read of people using the 205/50 in the front but IMO it's too small. 205/55 will keep the height around 23.9" in the front, very close to the 225/50 size for the rear. (These are the same width and aspect ratio for the stock 16" fuchs on the SC's and Carrera, BTW, but with 15's you're already 1" smaller in wheel height.)

I think stock for the front on the S was 185/70 on a 15x6 rim, that makes it 25.2" tall, 205/50's will give you 23" tall.

Lots of other considerations here. A 205/50 should have less sidewall flex than a 205/55, so there may be a handling advantage but cosmetically the 205/50's won't fill out the wheel wells as much.

[nick-moss]

205/50 and 225/50 were the original sizes when the low profile tyres were first introduced for the 1976 MY. I had them on 7 and 8 x 15's on a '74 Carrera with 240bhp, they were perfect.

[thrown_hammer]

Doug,
The 205's would be for the 7X15" rims on the front.
EW,
Do you run the 225's on 7" and 8" rims?

I would have 7X15's on the front and 8X15's on the back.

[cstreit]

I ran 225/50/15 and 245/50/15 on mine with SC flares.

[Glasgow 911SC]

thrown hammer,
Have a look at the dickster's recent thread.

[skinnerd]

Shawn:
I believe the optimum sizes for the street are the ones that CStreit mentions above. Little if any mods are needed to get these to fit beyond possible rolling of the fender lips. These tend more towards the high performance end of the sizes you could buy. Both my RS replica and 75 US Carrera had these size tires on the 15x7/8 Fuchs alloys (I'm currently moving away from the 15" wheels, and going with either 16" or 17" to get a better selection of tires). I would tend to agree that the 205's are too short thus lowering the front of the car excessively (but you might like that look?). You certainly can run 225's all around on your 7 & 8's. Given the availabe tires for 15" rims, that may be the best way to go, especially if this is a "street only" application. Elombard's car looks good with his 225's on all four corners.

For autocrossing and track events, I would definitely go with the 245's on the back... and would try to go for 16" rims to get the lower profiles available with the 245/45/16 tires. Believe it or not, I currently autocross with 17x8.5" in the front (and a 245 tire) and 17x10" in the rear (and a 275 tire) with the Carrera flares. It's tight, but it works, and it's definitely the "hot" set-up for autocrossing in this area.

I think some of what you do will be dictated by what sizes of tires are available for the 15" rims. You may be OK with the 225's, but I think the 245's are tough to find. Good luck in your search.

[dickster]

after careful research, i agree with 205/50's and 225/50's

[don911]

EW,
Do you run your 225 set up at the track. I'm thinking of doing 225's all aound with A032's just because Yoko doesn't make a 245x15. I know others that have run this set up but am interested in how your car handles with 225s all around.

[Bill Verburg]

When I ran 15" wheels on my Carrera I was very happy with 205/50 & 225/50

They will get the car very low.

[Eric Coffey]

Skinnerd-

Aren't 17's a bit too tall (physical height & gearing) for a dedicated AX car? For instance, going from 16's to 15's is supposedly better than switching from a 8:31 to a 7:31 Ring & Pinion. I've heard the R&P swap nets you about 300-400 RPM, while the smaller tires nets you 500-600 RPM (depending on tires). Also with smaller wheels (of the same type/brand) you should loose a lot of un-sprung weight, and have a lower CG.

[thrown_hammer]

My car is already very low. It was set-up for track at Autobahn Inc. Maybe I should try 225/50 and 245/50?

[dickster]

as i understand it, the 205/50 and 225/50's will give you no clearance problems. if you go wider you may have probs...........

seems that some do and some don't

take your pick

[skinnerd]

Originally posted by Eric Coffey
Skinnerd-

Aren't 17's a bit too tall (physical height & gearing) for a dedicated AX car? For instance, going from 16's to 15's is supposedly better than switching from a 8:31 to a 7:31 Ring & Pinion. I've heard the R&P swap nets you about 300-400 RPM, while the smaller tires nets you 500-600 RPM (depending on tires). Also with smaller wheels (of the same type/brand) you should loose a lot of un-sprung weight, and have a lower CG.

Eric:
Great questions. Believe it or not, the extra width and very low profile nature of the tires on the 17's more than make up for the increased physical height and gearing. I have the 17's on a light car (~2300 lbs) with sufficient HP (~245hp from a 3.2 Motronic) and a 7:31 R&P .... the bottom line is that the taller wheels don't really hurt me that much on acceleration. In the corners and braking, they are a huge advantage. They have so much absolute grip that I can carry way more speed through the corners with the 17's. In addition, since I'm using Fikse wheels with Hoosiers (both very light), the unsprung weight isn't that bad either. Also, the car sits a little higher but is still quite low.

I know it doesn't seem logical that the 17's would be better on an autocross course than 15 or 16's, but the results don't lie. At the NW region PCA autocrosses, the very fastest cars have the 17's. One other thing I like about the 17's and the gearing they present is that most autocross courses are completely in 2nd gear only. This is a huge advantage as I don't need to worry about shifting that much plus I'm always in the meat of the power band, no matter where I am on the course (this helps to makeup for the less than ideal gearing as well).

Bottom line is for "all-out" autocrossing, I'll take the 17's any day over the small diameter wheels.

[Glasgow 911SC]

Aren't 17's a bit too tall (physical height & gearing) for a dedicated AX car? For instance, going from 16's to 15's is supposedly better than switching from a 8:31 to a 7:31 Ring & Pinion

The roll diameter of the 17" isnt necessarily bigger than that of the 15's.
L@@K

[RallyJon]

From a looks standpoint, I'm not sure about big wheels on an early car. I have the same decision to make in a month or two, since the "Euro T/A"s I have now have less traction than the 4/$99 special at Pep Boys. I considered getting a set of 16s, but I really like the look of the 15s, so I'm going to try and find good rubber for them.

The highest performance option is 205/50 front and 225/50 rear. Many stiff and sticky tires are available in these sizes, such as the BFG KD, Yoko A032R, Toyo RA-1 and the new Michelin Sport Cup. If you go down a step to the S-03, Toyo T1S, or Dunlop 9000, you can get 205/55s for the front, which will look better and match the 225/50 rears in diameter. Unfortunately my favorite street tire--the Yoko AVS Sport--doesn't come in 15".

One thing to consider is that tire sizes vary widely between manufacturers. For example:

My 245/50 Euro T/As - 10.2" wide = really 259mm
245/50 SP8000s - 9.6" wide = really 244mm
225/50 BFG KDs - 9.2" wide = really 234mm
225/50 S-03s - 9.3" wide = really 236mm
225/50 Yoko ES100 - 9.0" wide = really 229mm

So, depending on the brand you choose, a nominally 225 width tire can be only a few mm narrower than the "monster" 245s. Plus, you'll get 2-3% lower gearing, which I know I can sure use.

Here is how it looks now. The rears are like big bouncy balloons!

[dd74]

You read my mind: I was wondering what 50 series tires would look like on a yellow 911, which is what I have, though mine is a narrow body.

I just want to clarify: do you have 55 series tires on the front and 50 series in the rear.

Also: is your car "lowered?"

I'm thinking of 50 series all around on 15x7 Fuchs (that's 205-50-15s). But since my car has been lowered - and at that "lower" than Euro height, I'm wondering about "bounciness" and "scraping," particularly since my body man suggests I get a chin spoiler.

Can you bring any light to my queries?

Thanks.