Jump to content

What backspace should I use?


Recommended Posts

I’m looking to buy some weld wheel draglites for my 70. In gonna put 265/60r15 on them. The wheels will be 8” wide. What backspace should I get for the front and rear especially for the rear tires not hitting. The dimension of the tires are the same as 225/70r15 but are 1 1/2” wider.

Link to comment
Share on other sites

15x8 with 5” backspace should work nicely front and rear if you have stock height suspension. Note that if your front springs allow the front to sit low you could end up with some rubbing.

  • Like 2
Link to comment
Share on other sites

Here’s a Monte with 15x8 and 5” backspacing on all 4 corners. I can’t recall what his tire size was. It may be 255/60 on all 4 if I recall.

 

IMG_0879.jpeg

  • Like 3
Link to comment
Share on other sites

Tiresize.com says there are no tires available in 265/60-15.  Many of us are running 275/60-15s on the rear with 8" wide wheels and 5" backspace (+12mm offset) so maybe that is what you are thinking.  However, you will quickly get into tire rubbing on tight turns with stock suspension if you put anything larger than a 255/60-15 on the front, especially with a 5" backspace on an 8" wide rim.

If you want all four wheel/tire combos to be the same, 255/60-15s on 8 inch wheels with 5" backspace may be a practical limit.  If you want wider (and taller) rear tires, 275/60- 15s will work with your wheel choice.

  • Like 3
Link to comment
Share on other sites

On 7/12/2023 at 12:10 AM, MCfan said:

Tiresize.com says there are no tires available in 265/60-15.  Many of us are running 275/60-15s on the rear with 8" wide wheels and 5" backspace (+12mm offset) so maybe that is what you are thinking.  However, you will quickly get into tire rubbing on tight turns with stock suspension if you put anything larger than a 255/60-15 on the front, especially with a 5" backspace on an 8" wide rim.

If you want all four wheel/tire combos to be the same, 255/60-15s on 8 inch wheels with 5" backspace may be a practical limit.  If you want wider (and taller) rear tires, 275/60- 15s will work with your wheel choice.

Dennis,you are correct about the unavailability of 265/60-15. I was on tiresize myself and kept putting in diffent numbers in the comparisons to see what matches the height and tire exposure off the side of the rim to match 222/70-15 size.

Link to comment
Share on other sites

On 7/12/2023 at 12:10 AM, MCfan said:

Tiresize.com says there are no tires available in 265/60-15.  Many of us are running 275/60-15s on the rear with 8" wide wheels and 5" backspace (+12mm offset) so maybe that is what you are thinking.  However, you will quickly get into tire rubbing on tight turns with stock suspension if you put anything larger than a 255/60-15 on the front, especially with a 5" backspace on an 8" wide rim.

If you want all four wheel/tire combos to be the same, 255/60-15s on 8 inch wheels with 5" backspace may be a practical limit.  If you want wider (and taller) rear tires, 275/60- 15s will work with your wheel choice.

Dennis,you are correct about the unavailability of 265/60-15. I was on tiresize myself and kept putting in diffent numbers in the comparisons to see what matches the height and tire exposure off the side of the rim to match 222/70-15 size.

Link to comment
Share on other sites

I’m gonna go with 275/60-15 rear and 225/70-15 front. 2” wider in rear  but almost same height and sidewall exposure. Would 15x8 rear with 5.50 backspace and 15x7 with 4.50 backspace work with these above tire sizes?  I couldn’t find the 5”rear backspace and 4.25” front backspace on websites that sell the weld wheel draglites. I’ll call weldwheels tmrw to see if they make the 5” and 4.24” backspacing.

Edited by 70white402
Link to comment
Share on other sites

15x8 with 5.5 will work but a 15x8 with a 4.5 will be centered better. 

4.5 for the front on a 15x7 may be a bit much. I think the 15x7 I have on the front Big Red have a 4.0 backspacing with I believe 225/70 R15.

PXL_20211016_163051273.jpg

  • Like 2
Link to comment
Share on other sites

Jeff, I compared your proposed configuration to what I am running now and found the following:

Front: A 15x7 wheel with +12 mm offset (4.5" backspace) should work fine with the 225/70-15 tire. It will be just .2" closer to your fender well on top and have .55" more inboard and outboard clearance than the 255/60-15 I am running on the same wheel specifications.

Rear: A 15x8 wheel with +25mm offset (5.5" backspace) is questionable with the big 275/60-15 tire because it pushes the wheel tire assembly a full .5" further inboard than my current configuration using a 15x8 wheel with +12mm (5" backspace).  Of course, that also gives you .5" more outside sidewall clearance but your wheel/tire combo will not be optimally centered. If you try it and find that your tire is too close to your frame or inside fender well, you can add a 1/2" wheel spacer to move the assembly outboard to achieve exactly what a 5" backspace wheel would give you.  That assumes your current wheel studs are long enough or can be replaced with longer ones.  A 15x8 rim with 0 offset (4.5" backspace) will push the assembly a full half inch further outboard (than my current configuration) resulting in very little (approx 1/4") sidewall clearance with an untrimmed wheel well lip. That would not be an optimal centering of the wheel/tire assembly either.

If 15x7 +12mm offset and 15x8 +25mm offset are the only/best choices offered in the wheels you want, it might be worth taking a chance, but be prepared to use a wheel space on the rear if that combo give too little inboard clearance.  A 275/60 is a pretty wide tire so positioning it correctly is important.

BTW, most wheel manufacturers spec their wheels in mm of offset because that measurement is relative to the center of the rim regardless of width while the backspace measurement is relative to the inside rim lip which varies with each different rim width.  When you are talking about overall configurations that use different wheel widths it is best to focus on offset specs rather than backspace.  If your wheel supplier/manufacturer only communicates using the backspace spec, be sure you know which rim width you are talking about to avoid confusion.  Good luck.

  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...