Tire size question for RSR flares

[Sdgg91]

I have an 82 911 SC with RSR flares fitted too it.

I have been playing around with different wheel sizes and have a set of 16in wheels I am thinking of putting on and ideally running a thicker sidewall but my thought is they may be too thin of wheels. (7 and 9).


I have 16 by 7 & 9 which I would run 205/55 16 and 245 / 45 16.

Right now I have 17 in wheels on the car and they are 275 / 40 17 and 225 / 45 17. (Pic below)

Do you think the 16s are too skinny for RS flares?

[Bill Verburg]

Originally Posted by Sdgg91

I have an 82 911 SC with RSR flares fitted too it.

I have been playing around with different wheel sizes and have a set of 16in wheels I am thinking of putting on and ideally running a thicker sidewall but my thought is they may be too thin of wheels. (7 and 9).


I have 16 by 7 & 9 which I would run 205/55 16 and 245 / 45 16.

Right now I have 17 in wheels on the car and they are 275 / 40 17 and 225 / 45 17. (Pic below)

Do you think the 16s are too skinny for RS flares?

It's not the wheel diameter that's important, the tire width and OD are

first choose the rear tire width and OD
now you have a 275/40 x17, tire OD is ~25.6+/-.1 width is ~277+/- mm on a 9

that's a bit tall for a std geared mostly stock 3.0 to 3.2, you'd be much happier w/ a 275/35 x17 on a 9 -10.5 OD is ~24.6 and width ~275 on a 9,5

to balance the 275 rear you want a 235 -245 w/ a close to stock suspension setup
245/40 is ~24.8" OD and ~245mm wide on a 8.5
The only street tires in these sizes are Pirelli P Zero Rosso

in 16 245/45 is the widest rear w/o getting ridiculously tall use a 9 and balance the front w/ an 8 w/ 225/50 tire

in 15 P7 Corsa Classic come in 305/35 ~23.3" OD or 285/40 ~23.7" OD 235/45 ~23.3" OD is a better match for the 285 use 8.5 and 10

or go w/ Michelin TB15 18/60 & 23/62 on 8 & 10

[Sdgg91]

Hey Bill,

Thanks for the reply. I should add the car has a 3.8 in it so it makes quite a bit more power but I am curious since if I am understanding you right a shorter overall diameter would make it feel quicker through the gears?

On what you recommended 275/35/17 that will decrease OD to 24.6 vs 25.7. Will a smaller sidewall compromise ride quality? I wouldn’t want it to be more harsh


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[stubble88]

I’ve got 17x12.5 with 315/35/17 rear
17x9 245/40/17 front. And I still have room. Turbo glass flares.
It’s ridiculous and I’m anticipating some tracking issues I’ll
Have to work out.
No motor yet so…

[rswannabe]

My ‘74 has turbo width flares and I run 16x8 and 16x9’s with a bit more sidewall than is typical. Fronts are 225/55/16 and rears are 245/50/16. I think they fill out the arches nicely.





With modern sticky rubber, you don’t need huge width to put power down. I used to have a 370 HP 3.8 in my ‘69 and had no trouble putting the power dow with 225 trofeo R’s in the rear on both the street and at the track (though the trofeo’s got greasy on the track). So don’t feel you have to go wider. I like my street car to have less stick and be a bit more playful.

[Bill Verburg]

Originally Posted by Sdgg91

Hey Bill,

Thanks for the reply. I should add the car has a 3.8 in it so it makes quite a bit more power but I am curious since if I am understanding you right a shorter overall diameter would make it feel quicker through the gears?

On what you recommended 275/35/17 that will decrease OD to 24.6 vs 25.7. Will a smaller sidewall compromise ride quality? I wouldn’t want it to be more harsh


Sent from my iPhone using Tapatalk

a shorter overall diameter would make it feel quicker through the gears?

yes

Will a smaller sidewall compromise ride quality? I wouldn’t want it to be more harsh

yes, but there are other factors contributing to ride quality
for instance say a given tire is spec'd for 9 to 11" wide wheel, a 9 will give a comfier ride than an 11 while the best performance will be from the 11

I really hesitate to get into the ride quality issue as every one has different expectations and environment

When I was designing what I wanted from my C3 also w/ a 3.8 at that tie, i spec'd 235/40 and 275/35 x17 tires on 8 and 9.5 wheels, I never had an issue w/ ride quality

currently on run 225/45 and 255/40(~25" OD) on the same wheels but w/ a 3.6, the acceleration is similar to the 3.8 w/ 275/35 and way better than either w/ 275/40

I agree w/ others that it's very east to over tire a streetcar

w/ the right ETs 225/50 x16 and 245/45 x16(~24.6" OD) on 8 & 9 can fill the RSR wheel wells, but it's also nice to have a little more grip, w/ judicious tire selection a 225/45 and 255/40 can be found that at 24.8" OD is almost as short as a 245/45 x16

I and 245/40 x17 & 275/35 can be as low as 24.5" OD, Nanking CR-S

admittedly the bigger the tire the heavier but the weight difference of a few pounds makes little difference.

you just need to find the best compromise that works for you and your budget, don't forget that new wheel sets are expensive.

[PeteKz]

Gotta agree with Brooke and Bill V. I will add, don't make multiple changes at once. Try to do one change at a time. Of course, if you change the wheel diameter, you have to change the tires too.

Tires make much more of a difference in handling than different wheel diameters or widths. 16 by 7 and 9 is a very "tried and true" setup for a street SC/Carrera. You already have the 17's, so unless you have money burning a hole in your pocket and you really want a different look, stay with what you have. The 16" wheels and tires will be softer on the street than 17" wheels and tires. You expressed that you don't want a harsher ride on the street, so if you swap to 16" wheels, you should be able to sell the 17's easily.

The 3.2 engine in my 1973 is around 240-250 HP (crank), and I use 16x7 wheels with Michelin street tires. I've been tempted to install rear fender flares for the look, but I've come to appreciate the esthetics of a narrow body longhood car. I can't say that I've found myself wishing for "more tire" on the street. If I want more grip on the track, I'll buy racing tires for my 16x7 wheels.

I've driven cars with big wheels and fat tires and I can't say that I found them fun on the street. On the other hand, my 1973 with 16x7's is balanced and "delightful."

[Billiam 911 2.8]

Another consideration is tire availability. I am currently running 205/55 x 16 in front and 245/45 x 16 on my hot rod 911. I wanted to run 225/50 x 16 in front but cannot seem to do so with factory offsets. Do I go to 17s? Will the newest Fuchs work any better in a 17 x 7 or do I need to go custom offset wheels like Fikse? First world problems.

[Bill Verburg]

Originally Posted by Billiam 911 2.8

Another consideration is tire availability. I am currently running 205/55 x 16 in front and 245/45 x 16 on my hot rod 911. I wanted to run 225/50 x 16 in front but cannot seem to do so with factory offsets. Do I go to 17s? Will the newest Fuchs work any better in a 17 x 7 or do I need to go custom offset wheels like Fikse? First world problems.

You don't mention what chassis you have, The OP has an RSR flared car with very different wheel requirements than an SC/Carrera or n/b.

To use 911 15 or 16"wheels on a 911 chassis w/ RSR or 930 fenders or 930 chassis you need to to use large spacers or acquire wheels w/ more negative o/s

yes many use 7x16 ET23.3 wheels w/ 21mm spacers and 205/55 tires but this is a less than optimum match for 245/45 rears

w/ custom wheels say 8ET27+2/-1 you can easily fit 22550 or 225/45 x16 on the front of a 911 or w/ 21mm spacers on a 911 w/ RSR flares

here's a list of wheel/tires specs that fit a 911 SC/Carrera, each f/r pairing is balanced for the weight and torque characteristics if various 911 chassis setups
o.e Fuchs options are all in green and custom wheels in yellow, where only race tires are available in the spec'd sizes red



similar for 911 chassis w/ 930 or RSR flares, some of these require spacers


and just for completeness n/b 911

[Sdgg91]

Originally Posted by Bill Verburg

yes




yes, but there are other factors contributing to ride quality
for instance say a given tire is spec'd for 9 to 11" wide wheel, a 9 will give a comfier ride than an 11 while the best performance will be from the 11

I really hesitate to get into the ride quality issue as every one has different expectations and environment

When I was designing what I wanted from my C3 also w/ a 3.8 at that tie, i spec'd 235/40 and 275/35 x17 tires on 8 and 9.5 wheels, I never had an issue w/ ride quality

currently on run 225/45 and 255/40(~25" OD) on the same wheels but w/ a 3.6, the acceleration is similar to the 3.8 w/ 275/35 and way better than either w/ 275/40

I agree w/ others that it's very east to over tire a streetcar

w/ the right ETs 225/50 x16 and 245/45 x16(~24.6" OD) on 8 & 9 can fill the RSR wheel wells, but it's also nice to have a little more grip, w/ judicious tire selection a 225/45 and 255/40 can be found that at 24.8" OD is almost as short as a 245/45 x16

I and 245/40 x17 & 275/35 can be as low as 24.5" OD, Nanking CR-S

admittedly the bigger the tire the heavier but the weight difference of a few pounds makes little difference.

you just need to find the best compromise that works for you and your budget, don't forget that new wheel sets are expensive.

Unfortunately I can’t find 275/35/17 in stock anywhere to run this setup and the only option for the front is the Nankank CRS.

[Sdgg91]

Originally Posted by Sdgg91

Unfortunately I can’t find 275/35/17 in stock anywhere to run this setup and the only option for the front is the Nankank CRS.

Bill, thanks for your help.

Looks like there are a lot of options with:
255/40/17
225/45/17

Both are 25 in diameter however I lose about .8 in width in the rear vs the 275/40/17 so I am wondering if these tires will fit the wheels.

[Bill Verburg]

Originally Posted by Sdgg91

Bill, thanks for your help.

Looks like there are a lot of options with:
255/40/17
225/45/17

Both are 25 in diameter however I lose about .8 in width in the rear vs the 275/40/17 so I am wondering if these tires will fit the wheels.

225/45x 17 25" OD wants 7 to8.5
245/40 x17 ~24.7"OD wants a 8.0 to 9.5
255/40 x17 ~25" OD wants 8.5 to 10

the tire ods all have a little +/- depending on make and model

[gled49]

I skipped to 18’s on my outlaw to get tires I wanted. 70S with 9’s & 11’s x18. These are factory NOS RSR steel flares that measure 14” at the rear flare. I run 245 front and 295 rear with the tallest profile I could get in that size. The rears are within 1/2” of the spring plate bolts on the inside. Maxed positive camber for the street. When we raced the car with glass fenders, I ran 275 front and 315 rears on the same rims, those sizes wouldn’t fit with steel fenders.