Help with stepping up to 17" wheels

[Mesozoic]

I've decided to step up to 17" wheels on my '71 fastback. I'm a little concerned about backspacing and hoping I can get some help from you folks. Here's the current situation:

Fronts: 15x7 Weld Draglites, 3.50" BS (WLD-90-57346)

Rears: 15x10 Weld Draglites, 5.50" BS (WLD-90-510350)

The rubber is a set of BFG Radial T/As in 235-60-15 up front and the rears are 295-50-15. The stance is great, car looks good, even handles good, but since I've upgraded the suspension quite a bit lately, I want larger brakes and better handling. I've decided on a set of 17" wheels based on size and backspacing as well: Centerline Nitro2s.

The rears are available in 17x9.5 with 5.50" BS. The fronts are available in 17x8 with BS between 3.50" and 5.50" in steps of 0.50" increments. What is going to be the best BS fitment and tire sizes for my '71 on 17s? I was thinking 285-40-17 for the rear and 235/245-40/45-17 up front.

 

[Totalled]

You'll need shallow backspacing on the front. I tired to put the stock wheels from my 09 grand marquis on as rollers, and they wouldn't even bolt on. The rim was up against the upper control arm. They have the same backspace as the 05-14 mustang.

 

[Mesozoic]

You'll need shallow backspacing on the front. I tired to put the stock wheels from my 09 grand marquis on as rollers, and they wouldn't even bolt on. The rim was up against the upper control arm. They have the same backspace as the 05-14 mustang.

What sort of backspacing would you consider shallow? Is 3.50" shallow? My 15x7 with 3.50" backspacing seem to be working pretty good right now. Not sure about 17s, though.

 

[Totalled]

I think the SN197 wheels are like 5.5" so, probably.

 

[Mesozoic]

Well, I'm thinking of running 17x8 wheels with 4.0" BS, but I've read that as you add more BS to the front wheels, the handling goes to shit. So basically, I want to run the minimum amount of BS necessary to accomodate 245-45-17s. Will 17x8 with 4.0" BS contact any stock suspension components? My car is lowered 1".

The rear wheel is a whole different deal. I'm now considering running 17x11 with 6.5" BS to fit a 315-35-17 out back. From calculations it looks like it will fit my car.

 

[Jeff73Mach1]

My fronts are 17x8's with 4.25 backspacing and clear up front without any issues.

One problem with 17's in back is a limited selection of larger tire sizes. If you will ever have 400+ RWHP you will want a more flexible rim size such as 15's or 18's

 

[Mesozoic]

My fronts are 17x8's with 4.25 backspacing and clear up front without any issues.

One problem with 17's in back is a limited selection of larger tire sizes. If you will ever have 400+ RWHP you will want a more flexible rim size such as 15's or 18's

I'm definitely going to be generating significantly more power than 400 RWHP. That's why I was thinking of running 335-35-17 on a set of 17x11s with 6.5" BS.

Thanks for the info on the 17x8s, I'll make sure I order greater than 4.0" BS then. Cheers! ::beer::

 

[Jeff73Mach1]

An interesting tire size, made only by 2 manufacturers that I see for street use. and very expensive.

Look at 18's for your rear and see what options it opens up

 

[Mesozoic]

An interesting tire size, made only by 2 manufacturers that I see for street use. and very expensive.

Look at 18's for your rear and see what options it opens up

I don't think I was going for cheap in this case. Considering how much money I've put into my car at this point, a $250 tire is a drop in the bucket. Interestingly enough, Sumitomo offers tires in this size for about $150 each.

I did some investigation and it appears that there are several options for 315-35-17 tires:

1. http://www.kumhousa.com/tire/category/car/675DCE77-813E-4027-B467-2BEA0466BD5C
   
2. https://www.nittotire.com/Tire/Street/nt555#size
   
3. https://www.nittotire.com/Tire/Street/nt05#size
   
4. http://www.bfgoodrichtires.com/tire-selector/size/315/35/17/tires
   
5. http://www.sumitomotire.com/assets/products/performance/HTRZSpecs.pdf
   
6. http://www.goodyear.com/en-US/tires/eagle-f1-gs-d3?ub=Y&updatecase=passivelyStored&action=save&webprodid=56&productcode=70926015400000
   

There's more, including Hoosiers and Toyos too, but I believe this is a kind of common sports car tire size. It looks like with a wheel with 6.5" BS they will fit with a good amount of clearance in and out.

 

[mustang7173]

Mesozoic,

If you decide that you need spacers, here is one to look at.

http://www.mustangwheelspacers.com/index.aspx

mustang7173

 

[cazsper]

On my '73 Mach-1, I'm running 17x8 (4.5"BS) and 245/45-17's for the front and 17x9 (5" BS) with 275/40-17's in the rear. Fitment is great. I have also been told I could use a 17x9.5 with a 5.5" BS.

 

[71_resurrection]

Luxstang has an excellent post from a few years ago about this, you should check it out.

 

[Mesozoic]

Luxstang has an excellent post from a few years ago about this, you should check it out.

Yes, I've read practically all the threads on this site about 17" and 18" wheel fitment. However, after doing some measuring this morning I realized that I can run a 6.5" backspace and still clear all of my suspension while keeping the rear tire inside the quarter wheel well. For that reason, I've ordered some 17x11 wheel with 6.5" backspace. For the fronts, I ordered some 17x8 with 4.5" BS. Planning to run 245-45-17 up front, 315-35-17 out back. I'll hopefully step up to some 13" rotors up front and 12" rotors out back eventually as well.

Does anyone have any pictures of their '71-73 with 315s on the rear?

 

[71_resurrection]

wow, 315's will look nice out back, definitely post pics when they are installed!

 

[Mesozoic]

I know there's a few people running 315s on this forum. I would love to see some photos.

I also had another thought: I believe 335-35-17 will also fit!

 

[TommyK]

I know there's a few people running 315s on this forum. I would love to see some photos.

I also had another thought: I believe 335-35-17 will also fit!

XolieX posted a couple. If you search his other posts there are threads where he gives some advise on backspacing and clearance issues.

http://www.7173mustangs.com/thread-quest-to-fit-15x12-s-a-little-bit-of-fat-work-of-course

Another member:

http://www.7173mustangs.com/thread-new-member-1971-mach1-restomod

 

[Mesozoic]

Oh my word... so I got my wheels installed to check fitment. 6.5" BS is perfect for my '71, but the 12.4" treadwidth that's supposed to come with a 315-35-17 is actually exactly the same width as my old BFG 295-50-15 on a 15x10. I think that a 335-35-17 would fit perfectly with no clearance issues at all and is probably what I should've gone for, although it would've cost a significantly larger sum. Basically, going from 295-50-15 on a 15x10 to a 315-35-17 on a 17x11 is a lateral move. You gain the benefits of having a 17" wheel for improved handling, but the treadwidth is the same, although the height is slightly shorter (25.7" from 26.7"). In any case, it looks great and now I have some much need Z rated rubber, so whatever. With the transmission I'm about to install, my top speed should be around 187 mph at 6000 RPM, so that Z rating matters.

The original, 295-50-15 on a Weld Racing 15x10 with 5.5" BS.



The new 315-35-17 on a Centerline Nitro 2 17x11 with 6.5" BS.



Not much space to take a great shot, but this gives a rough idea.



Here you can sort of see the 17" wheel on the left, the original 15" on the right.

 

[Mesozoic]

I've been driving it around for a little while and the ride is noticeably smoother and crisper handling than before. I believe the BFGs I had on the car previously were 20 years old! I'm not sure why the Sumitomos are so cheap, but they're excellent sticky tires. Very happy with them.

 

[rottenralph]

I have 17x8 up front with 225/45/17's in front and 17x9.5 in back with 245/45/17 . I would go 20 wider on both sizes if I did it again. think front have 45mm offset and rears are 112 offset. Not sure what the difference between offset and backspacing is