Tire selection for 15 inch rims

[deemsriddle]

I have an early gray market conversion 1979 SC Targa that needs tires. It is powered by a 1987 3.2 engine running through the original 915 transmission with the short Euro ratios. It was lightly optioned in the first place and remains so. It does not have, nor ever had air conditioning. It's not even burdened down with electric windows. The front and rear bumpers were replaced with lightweight fiberglass units. Now comes the problem of replacing the tires on the 7 and 8 by 15 inch Fuchs alloys. Currently I have been running 225/50 15 Toyo R888R all the way around with 2017 and 2018 dates. This car is one of the best running,handling and riding early 911s on the planet. I have had scores. The R888R tires provide plenty of grip, are moderately quiet and ride smoothly. The car is even steady in the rain. Fortunately I live in North Georgia and do not have to winterize any of my cars for the season. Thusly, do I keep with the Toyos, which work for me. I would like to run tires that are not limited to 40 degree temperature but do not find many choices in performance tires. I would also like to run a staggered fitment, but again I don't find what I am looking for. Lastly, if I keep with the Toyos, do I run the 235/50- 15s on the back? I do not run a "slammed" car so rubbing is not an issue. It's not my thing.

You guys on Pelican's "brain trust" are the greatest. Thanks so much.

Deems

[mnez]

My buddy with a similar car runs Toyo 205/50 and 225/45. 225/50 also works. Toyo RA1 another good option.

[Bill Verburg]

Originally Posted by deemsriddle

I have an early gray market conversion 1979 SC Targa that needs tires. It is powered by a 1987 3.2 engine running through the original 915 transmission with the short Euro ratios. It was lightly optioned in the first place and remains so. It does not have, nor ever had air conditioning. It's not even burdened down with electric windows. The front and rear bumpers were replaced with lightweight fiberglass units. Now comes the problem of replacing the tires on the 7 and 8 by 15 inch Fuchs alloys. Currently I have been running 225/50 15 Toyo R888R all the way around with 2017 and 2018 dates. This car is one of the best running,handling and riding early 911s on the planet. I have had scores. The R888R tires provide plenty of grip, are moderately quiet and ride smoothly. The car is even steady in the rain. Fortunately I live in North Georgia and do not have to winterize any of my cars for the season. Thusly, do I keep with the Toyos, which work for me. I would like to run tires that are not limited to 40 degree temperature but do not find many choices in performance tires. I would also like to run a staggered fitment, but again I don't find what I am looking for. Lastly, if I keep with the Toyos, do I run the 235/50- 15s on the back? I do not run a "slammed" car so rubbing is not an issue. It's not my thing.

You guys on Pelican's "brain trust" are the greatest. Thanks so much.

Deems

for 7 * 8 x15 the std size is 205/55 and 225/50, you could go 225/50 and 245/45

but a tantalizing option for hi perf street use is 215/50 and 235/45 Pirelli P700Z

[darrin]

Bill: Those p700z tires and their sizes sure look interesting for my next set! thx for sharing

I've really enjoyed my first summer street driving on 205/50-15 / 225/50-15 Yokohama A052 tires on my 15x7 and 15x8 fuchs, surprised by how well they're wearing and impressed with their grip/predictability. Huge contrast with the 205/55-16 Michelin x-ice winter tires I'm now running square on my 16x7f and 16x8 fuchs (though the sloppy rear end these deliver is a lot of fun too )

[kimlangley7]

When I refreshed my Euro-spec 911SC - I opted for 17" Fuch - and sold my cookie cutters.. I figured I'm only going around once - suck-it-up and get some 17"Fuch.. tire selection = way more-better

no regrets > fills out the wheel well beautiful!!

just sayin

kgl

[Bill Verburg]

Originally Posted by kimlangley7

When I refreshed my Euro-spec 911SC - I opted for 17" Fuch - and sold my cookie cutters.. I figured I'm only going around once - suck-it-up and get some 17"Fuch.. tire selection = way more-better

no regrets > fills out the wheel well beautiful!!

just sayin

kgl

that's a common enough comment and just not true except for some extreme fitments

looking at just the mainstream 205/225 fitments I have in my admittedly not fully comprehensive tire dB

15s have 21 different ways to go

17s have 8

16s have 15

What you do get is more flexibility of sizing w/o going too tall for instance if you want a 275 rear there are 2 17s and 3 15s9including 285 which isn't available in 17)

if you want 255then 17s or 18 is the only way to go

i mention 275 because i designed my car around 235/40 and 275/35 x17 but ended up using 225/45//255/40 xx17 because of the spotty availability of the 275s


Here are all the appropriate 15, 16, 17 and 18 911 SC/Carrera fitments

You can that there is a broader range of sizes if not individual tire choices in 17

[richardrobert]

Hey Bill

Thanks for the chart! I always thought the stock 15" 7s and 8s were 195/65 and 215/60 ???

Also, one of the sets on your chart 205/50 and 225/50 for the rears it is the only set on the whole chart that has the same aspect ratio... can you explain?... I have a set of RSR style fuchs 7/8s that I would like to get tires for.... not necessarily to drive, I have 16s for that.

[Bill Verburg]

Originally Posted by richardrobert

Hey Bill

Thanks for the chart! I always thought the stock 15" 7s and 8s were 195/65 and 215/60 ???

depends on the year
in '74 the first year 7/8x15 were offered retail 185/70 and 215/60 were offered
then in '76 for one year only 205/50 and 225/50 became available and were offered for the C3 and 2.7RS, That was what my C3 came w/. It was actually 2 options
1 the 7 & 8 x15 Fuchs
2) the /50 series tires and recalibrated speedometer

after that the 15s were 185/70 and 215/60 again till the 185/70s disappeared and that's when the 195/65 and 215/60 were offered.

Originally Posted by richardrobert

Also, one of the sets on your chart 205/50 and 225/50 for the rears it is the only set on the whole chart that has the same aspect ratio... can you explain?... I have a set of RSR style fuchs 7/8s that I would like to get tires for.... not necessarily to drive, I have 16s for that.

See above, these days the more usual way to go is 205/55 and 225/50 but 205//50 and 225/50 is still a viable way to go. For set up its convenient to have roughly equal f/r tire heights but not strictly necessary.

[darrin]

Originally Posted by richardrobert

Hey Bill

Thanks for the chart! I always thought the stock 15" 7s and 8s were 195/65 and 215/60 ???

Also, one of the sets on your chart 205/50 and 225/50 for the rears it is the only set on the whole chart that has the same aspect ratio... can you explain?... I have a set of RSR style fuchs 7/8s that I would like to get tires for.... not necessarily to drive, I have 16s for that.

richardrobert -- I run 205/50-15 / 225/50-15 Yokohama a052 tires on my Fuchs 15/s=7&8 wheels during the warmer months (run 205/55-16 winter tires on 16" Fuchs during the colder months) -- the smaller diameter of the tires on the 15" wheels coupled with their lighter weight (and, I'm sure, super sticky tread compound) make my '86 targa a VERY fun to drive. Highly recommended combo

[LJ851]

In addition to the Yokohamas mentioned above, Bridgestone Potenza RE71RS is also available in 225/50-15. Both great choices for a high performance tire.

[Bill Verburg]

The biggest thing wrt the tires accel/decel performance is the tire OD

here's a comparison of the difference between comparable 15 and 16s, the 16s lose ~38lb-ft of torque just to spin them up compared to the 15s, the a6s are heavier but the vast majority of the difference is due to tire OD



I agree RE71s are a great tire choice i have a set and they compare well w/ DoT Rs

[richardrobert]

Bill, what source for these? I can’t find the a052 or the RE71s anywhere

[darrin]

Originally Posted by richardrobert

Bill, what source for these? I can’t find the a052 or the RE71s anywhere

tirerack.com has both the ao52 and re71rs in stock in 205/50-15 and 225/50-15 sizes (at least for the 80209 area code I tried)

[Showdown]

Just keep in mind that a 50 series tire is fairly low profile and doesn’t have a large sidewall. This may be advantageous for autocross or track but for street use you may find it a bit harsh in addition to requiring 4000 RPMs at Highway cruising speed because of the smaller diameter tire.

Another thing to consider is how hard you’re actually driving this car. Modern tires are exponentially more advanced than what Porsche had access to when these cars were built and much of that may be lost unless you are a very accomplished driver on a track or autocross circuit.

And finally, a big chunky tire makes these cars feel very lively and fun to drive at moderate speeds; something that will disappear with a very high performance low profile tire

[David 23]

I have a highly modified '79 911 with 7&8s x15". I run Toyo R888r in 225 and 235 sizes without any rubbing or issues. I drive hard in the canyons, on the Targa California, and everywhere I can. The tires offer amazing grip, not loud, have managed common sense driving in the rain without drama. The sacrifice in wear, IMO, is far offset by the incredible grip and performance I am able to enjoy over every mile. To me, it's about the number of smiles, not the number of miles.

[Bill Verburg]

Originally Posted by darrin

tirerack.com has both the ao52 and re71rs in stock in 205/50-15 and 225/50-15 sizes (at least for the 80209 area code i tried)

+1

[Bill Verburg]

Originally Posted by Showdown

Just keep in mind that a 50 series tire is fairly low profile and doesn’t have a large sidewall. This may be advantageous for autocross or track but for street use you may find it a bit harsh in addition to requiring 4000 RPMs at Highway cruising speed because of the smaller diameter tire.

Another thing to consider is how hard you’re actually driving this car. Modern tires are exponentially more advanced than what Porsche had access to when these cars were built and much of that may be lost unless you are a very accomplished driver on a track or autocross circuit.

And finally, a big chunky tire makes these cars feel very lively and fun to drive at moderate speeds; something that will disappear with a very high performance low profile tire

yes the 15s have shorter sidewalls and will ride more harshly than 16s or 17s for the same width and profile but the return in the performance area is worth it, This are sports cars aren't they?

as to cruise RPM it depends on the trans but for a '76 915/44 w/ 225/50 x15 rear tires 4k rpm is 87mph /60 for early SC is the same. ;72-73 915/02 will be 82