Need help with tire size

[HWG09]

I recently picked up some Borbet 964 Cup wheels on the cheap. 17x9 rears and 17x7 fronts.

I have an '87 911 I'm looking to mount them on. I have an aftermarket widebody kit.

Currently have 16x10 BBS and 2" spacer in the rear and 16x8 w/ 1" spacer in the front.

Fronts run 225/55/16, rears are I believe 245/50/16.

Much more tire options with 17" but want to make sure I nail the fitment. I used to have 3" spacer in the rear but I sold them. I lose some width in the back so perhaps getting 3" spacer in back I can go with 245s. Not sure on the fronts.

Any suggestions?

Tires will be for mostly summer driving (I'm in Omaha so car does get on the road Dec-Feb) and the occasional track day. Currently have Toyo Proxes on there.

Thanks!

[Bill Verburg]

Originally Posted by HWG09

I recently picked up some Borbet 964 Cup wheels on the cheap. 17x9 rears and 17x7 fronts.

I have an '87 911 I'm looking to mount them on. I have an aftermarket widebody kit.

Currently have 16x10 BBS and 2" spacer in the rear and 16x8 w/ 1" spacer in the front.

Fronts run 225/55/16, rears are I believe 245/50/16.

Much more tire options with 17" but want to make sure I nail the fitment. I used to have 3" spacer in the rear but I sold them. I lose some width in the back so perhaps getting 3" spacer in back I can go with 245s. Not sure on the fronts.

Any suggestions?

Tires will be for mostly summer driving (I'm in Omaha so car does get on the road Dec-Feb) and the occasional track day. Currently have Toyo Proxes on there.

Thanks!

You have to provide the old & new width & ET

Also are you happy w/ the old fitment in terms of where the tire sits relative to the fender lips?

[HWG09]

Originally Posted by Bill Verburg

You have to provide the old & new width & ET

Also are you happy w/ the old fitment in terms of where the tire sits relative to the fender lips?

Yes, I'm happy with current fitment. I changed tires and dropped down in spacers on my rears and lost probably 1/2 inch but it's all good.

Offsets on new ones are 47 in the rear and 55 in the fronts I believe.

[Bill Verburg]

Originally Posted by HWG09

Yes, I'm happy with current fitment. I changed tires and dropped down in spacers on my rears and lost probably 1/2 inch but it's all good.

Offsets on new ones are 47 in the rear and 55 in the fronts I believe.

Still need the ET on the old set

the new are 964 fitment w/ high ET, that means larger than usual spacers will be needed

[HWG09]

Originally Posted by Bill Verburg

Still need the ET on the old set

the new are 964 fitment w/ high ET, that means larger than usual spacers will be needed

Thanks Bill I'll get everything measured out this weekend.

[HWG09]

Ok, so I measured these out and test fit them.

The rear BBS I had on where offset of 23 vs new ones which are 9 wide instead of 10 but offset of 47 so when I put them on it actually looked pretty decent. I could maybe use another inch (too bad I sold my 3" spacers, have 2 on there now).

Fronts look pretty good too. Currents were 28 offsets.

Question is how wide of a tire can I put on these? I currently have 245s on the rear 10s which I could probably go wider but hard to find wider on a 16. 17" wheel should give me more options.

Fronts have 225s on them.

Thoughts?

[Bill Verburg]

Originally Posted by HWG09

Ok, so I measured these out and test fit them.

The rear BBS I had on where offset of 23 vs new ones which are 9 wide instead of 10 but offset of 47 so when I put them on it actually looked pretty decent. I could maybe use another inch (too bad I sold my 3" spacers, have 2 on there now).

Fronts look pretty good too. Currents were 28 offsets.

Question is how wide of a tire can I put on these? I currently have 245s on the rear 10s which I could probably go wider but hard to find wider on a 16. 17" wheel should give me more options.

Fronts have 225s on them.

Thoughts?

Usually 225/45 is the widest that is recommended for a 7 some will stretch that to a 235/45

Ona 9 you could go to 265/40. The issue is retaining f/r balance and keeping tire od down.

The most common 7 & 9 fitment is 225/45 & 255/40

[HWG09]

Originally Posted by Bill Verburg

Usually 225/45 is the widest that is recommended for a 7 some will stretch that to a 235/45

Ona 9 you could go to 265/40. The issue is retaining f/r balance and keeping tire od down.

The most common 7 & 9 fitment is 225/45 & 255/40

Thanks Bill!

[HWG09]

Dredging up this old post. I found a deal on some Sumitomo rears 255/45/17 that I picked up. If I go with these and 225/45/17 is that gonna really throw everything off? I know I'm trying to match ride height closely. Maybe a 225/50/17?

[HaroldMHedge]

Original rear tire size Pirelli P Zero Rosso N4 overall diameter, per Tire Rack:

245/45ZR16 - 24.6"
225/50ZR16 - 24.9"

They list the Sumitomo HTR Z II 255/45ZR17 with an overall diameter as 26.4". For me that would be too far off from the factory diameter. The 245/40ZR17 would be a better choice with diameter 24.8".

[HWG09]

Originally Posted by HaroldMHedge

Original rear tire size Pirelli P Zero Rosso N4 overall diameter, per Tire Rack:

245/45ZR16 - 24.6"
225/50ZR16 - 24.9"

They list the Sumitomo HTR Z II 255/45ZR17 with an overall diameter as 26.4". For me that would be too far off from the factory diameter. The 245/40ZR17 would be a better choice with diameter 24.8".

Good info. Thanks!

[Bill Verburg]

Here are the Summis that pair well, you want them to be in agreement on the X axis and staggered on the y, the more motor the more stagger.

[HWG09]

Originally Posted by Bill Verburg

Here are the Summis that pair well, you want them to be in agreement on the X axis and staggered on the y, the more motor the more stagger.

Interesting. These are on a wide body '87 3.2 (non-turbo). I have some spacers on right now as well.

Pretty clear I need 225/45/17 for my fronts and looks like 244/45/17 don't pair up well with those. Honestly thought i was buying 255/40s until I picked them up.