Tire & Wheel size identification help ??

[Kansas Corey]

I have read through a lot of the previous (archive) threads about wheel size and backspacing. Currently I have 2 complete sets of wheels and tires in the garage but need some help to make sure I am looking at things correctly.

The first set of tires are Dunlop RV Radial Rover 31x11.5x15 on what I call chrome wagon wheels.

The second set of tires are BFG Radial All Terrain T/A 33x12.5x15 on what I was told were modular wheels.

I tried measuring backspacing and have looked at http://www.rsracing.com/tech-wheel.html#patterns but I'm still having problems

When I look at the back of the wheel, there are 3 different height areas to measure from. The very inside of the center opening is slightly raised (1), then drops down to the flat ring where the bolts go through(2), and then it raises slightly again before angling towards the front of the wheel(3). I know, clear as mud, thats why I attached the picture with numbers. If I measure from the highest ridge (3) then the wheel has a backspacing of 3 5/8" which sounds about right from what I understand - but is that the correct place to measure from?

Okay now for more confusion - I was also trying to figure out what the wheel width was. This time the measurement should be a little more straight forward. It looks like the chrome wagon wheels with 31" tires are 10" wide and the modular wheels with 33" tires are 8" wide.

So assuming I am correct in my measurements (big assumption I know) would the different wheel widths and tire sizes make such a big difference when the tires are mounted to the bronco? I have attached a couple of pictures again showing the difference in how far out the tires stick. I only changed the left rear tire - it is the modular wheel with 33" tire. Everything else are still the chrome wagon wheels with 31" tires just like the day I drove it home.

 

[Kansas Corey]

Just for $hit$ and giggles, thought I would post the other pics I took of the tires and wheels. Can you guess which is the 31" and which is the 33". Pretty obvious in the first picture, but I was surprised by the second picture. There is a little more of a difference in the second picture in real life. Thanks for the help - Corey

 

[Jeepster]

When I look at the back of the wheel, there are 3 different height areas to measure from. The very inside of the center opening is slightly raised (1), then drops down to the flat ring where the bolts go through(2), and then it raises slightly again before angling towards the front of the wheel(3). I know, clear as mud, thats why I attached the picture with numbers. If I measure from the highest ridge (3) then the wheel has a backspacing of 3 5/8" which sounds about right from what I understand - but is that the correct place to measure from? .

measure from #2 That would be the part that snugs up to the mounting flange...

Okay now for more confusion - I was also trying to figure out what the wheel width was. This time the measurement should be a little more straight forward. It looks like the chrome wagon wheels with 31" tires are 10" wide and the modular wheels with 33" tires are 8" wide.

So assuming I am correct in my measurements (big assumption I know) would the different wheel widths and tire sizes make such a big difference when the tires are mounted to the bronco? I have attached a couple of pictures again showing the difference in how far out the tires stick. I only changed the left rear tire - it is the modular wheel with 33" tire. Everything else are still the chrome wagon wheels with 31" tires just like the day I drove it home.

You never told us what the difference offsets were between the two rims. Yes it does look as if one might be a 10" and the other a 8". Sometimes the width of the rim is stamped on the backsidemof the rim.

 

[SaddleUp]

As Jeepster said measure from #2. Backspacing is determined by the spacing from the mounting flange itself (I.E. Where the wheel meets the flange) which is why it will be #2. For wheel width you measure the distance between the inside of the wheel beads or outside of the tire beads (Same thing). It is not unusual for either rim to be used with either tire. My preference for both is to run an 8" rim because it holds the bead better offroad. The sacrifice is that the rim doesn't stick out as far. (If it's further out then it will help keep it stable)

 

[Kansas Corey]

Unfortunately I will not be able to re-measure until this evening, but if memory serves correctly, from (#2) the backspacing on both sets of wheels is almost right at 4". From what I have read, that sounds like a pretty big number. I have not modified the Bronco from when I bought it, so I am using my detective skills here - 2" James Duff lift with both front and rear flares cut.

Does it stand to reason that 31x11.5x15 tires on 15x10 rims would NOT rub with a 2" suspension lift and zero body lift?

The really disappointing thing about this is that the new 33" tires give the Bronco a narrower stance and don't really look any bigger than the 31" tires. After I measure the backspacing tonight, I will take a picture from the side showing the difference between the two tires - :'( very disappointed :'( . I was really hoping to fill out the wheels openings more.

 

[SaddleUp]

Unfortunately I will not be able to re-measure until this evening, but if memory serves correctly, from (#2) the backspacing on both sets of wheels is almost right at 4". From what I have read, that sounds like a pretty big number. I have not modified the Bronco from when I bought it, so I am using my detective skills here - 2" James Duff lift with both front and rear flares cut.

Does it stand to reason that 31x11.5x15 tires on 15x10 rims would NOT rub with a 2" suspension lift and zero body lift?

Looking at your picture #2 will be less than #3 I think if your measuring from the backside rather than more. (If your measuring from the front then your measuring from the wrong side) 31" tires should fit without any problems with 2" suspension lift if the rear is cut.

 

[Kansas Corey]

sorry SaddleUp - I should be more clear. I am measuring from the back side. The smallest number when measuring (3 5/8") is from number (3). The next is (1) and the largest number when measuring (close to 4") is from number (2). It is probably hard to tell in the picture, but ridge (1) and ridge (3) are both raised up higher than the flat space (2).

 

[Kansas Corey]

I always love not knowing what the he$$ I am talking about - it makes these threads drag on forever - have I mentioned "Thank You" to everyone lately for always straightening me out?

Okay - measured wheels again:

31" tires on chrome wagon wheels:
1) 3 5/8
2) 3 3/4
3) 3 1/2

33" tires on modular wheels:
1) 3 3/4
2) 3 7/8
3) 3 5/8

So from what you guys have told me, the correct measurement is the middle number listed above for both sets of wheels?

There is acutally a method to the madness - trying to understand what I have so that I can make an informed decision going forward when I upgrade wheels and tires.

Just to verify then, if I compare two wheels (an 8" wide and a 10" wide) with the same backspacing........ the 10" wide wheel would in theory stick out 2" further than the 8" wheel? That would explain why my old tires (31" mentioned above) were out past the flares and the new tires (33" mentioned above) are now tucked in under the flares.

Still disappointed in how well they fill the wheel wells though :'(

 

[SaddleUp]

I always love not knowing what the he$$ I am talking about - it makes these threads drag on forever - have I mentioned "Thank You" to everyone lately for always straightening me out?

Okay - measured wheels again:

31" tires on chrome wagon wheels:
1) 3 5/8
2) 3 3/4
3) 3 1/2

33" tires on modular wheels:
1) 3 3/4
2) 3 7/8
3) 3 5/8

So from what you guys have told me, the correct measurement is the middle number listed above for both sets of wheels?

There is acutally a method to the madness - trying to understand what I have so that I can make an informed decision going forward when I upgrade wheels and tires.

Just to verify then, if I compare two wheels (an 8" wide and a 10" wide) with the same backspacing........ the 10" wide wheel would in theory stick out 2" further than the 8" wheel? That would explain why my old tires (31" mentioned above) were out past the flares and the new tires (33" mentioned above) are now tucked in under the flares.

Still disappointed in how well they fill the wheel wells though :'(

The wheel itself will stick out 2" further but the tire tread will not. The tire tread will be about 1" further out. The inside bead of the tire stays in the same position and the outside one is 2 inches further out, the tread itself moves enough to position itself half way between that. The sidewall will be around 1 1/2" (approx.) further out which is because the sidewall profile will change with the change in wheel width. I.E. The sidewall will not bulge as much. Don't expect a huge difference in the way a 33 will fill the wheel well as opposed to a 31. Even if both are the true size (which actually is seldom) then the tire will only be 1" larger in relation to the wheel wells. I.E. 1" closer to them. If there was 5" of room around them before then there would still be 4" with the 33's. To see a big difference you would need to make a bigger jump between tires but then you can also run into bigger issues elsewhere as well. (Gearing, etc.)

 

[Kansas Corey]

SaddleUp - thanks for the response. Scary, but I actually understood all of that.

Really helps to kind of talk through some of this stuff before moving on to making decisions.

I like the was the 31" tires on the chrome wagon wheels (15"x10" with 3 3/4" backspacing) look, but I want the tire to fill up the wheel wells a bit more. I hear you about the gearing though and other problems though. Currently have rebuilt 302, 3 spd on the floor, 2" suspension lift, and 3.50 gearing both front and rear - this is with the 31" tires. I am happy with the Bronco currently and a majority of the time this will be a street vehicle - 2nd car to play around with. My concerns are gearing and clearance, but I want it to look a little better. Guess I need to weigh my options.

 

[Jeepster]

SaddleUp - thanks for the response. Scary, but I actually understood all of that.

Really helps to kind of talk through some of this stuff before moving on to making decisions.

I like the was the 31" tires on the chrome wagon wheels (15"x10" with 3 3/4" backspacing) look, but I want the tire to fill up the wheel wells a bit more. I hear you about the gearing though and other problems though. Currently have rebuilt 302, 3 spd on the floor, 2" suspension lift, and 3.50 gearing both front and rear - this is with the 31" tires. I am happy with the Bronco currently and a majority of the time this will be a street vehicle - 2nd car to play around with. My concerns are gearing and clearance, but I want it to look a little better. Guess I need to weigh my options.

Your getting sucked into the domino effect. (Change one thing,5 others will need change) Get rid of the suspention lift (do you really need it?)and your delemma is solved. Try going around the block with the 33's on there and tell us the difference in git up and go from a stop. (I would like to hear your assesment) Your gearing might suffer a little. Stock height Broncos w/31's can look cool, too.

 

[Kansas Corey]

Okay - mentioned previously that I would take these pics and post:

The fronts are the 31x11.5x15 tires on 15x10 wheels with 3 3/4 backspacing.

The rears are the 33x12.5x15 tires on 15x8 wheels with 3 7/8 backspacing.

I can not believe that there is really no difference in looks. Has me really confused. If I was going from 31" to 33" but going to a wider wheel I could understand losing some of the height because the tire is being stretched onto a wider wheel, but this doesn't make a whole lot of sense.

The only thing I can think of is that there are differences in tires based on manufacturer (i.e. two 33x12.5x15 tires by different manufacturers can actually be different heigths).

As for the second picture, you get an idea of how much further in the 33" tires on 15x8 wheels with 3 7/8 backspacing sit on the Bronco. Not my tastes at all.

Quick question - are my flares cut higher than the norm to make the wheel opening look larger. I was really hoping to fill up the wheel well a little more with the 33" tires. Not sure, but I assume that 35" would be way way too big considering this thing has no body lift and only 2" suspension lift.

By the way - I will put the front 33" tires on this weekend to see how much rubbing I get.

Corey

 

[Jeepster]

yes, samesize tires from different manufacturers can be different. Put a flat board across the top of the tires and measure from the bottom of the board to the ground. compare but note the difference in vehicle height will only be 1/2 the dimention. (center of wheel-out). Face it man. The rig is cut and there really is gonna take a sizeable hunk of rubber to fill that void.

 

[Kansas Corey]

Thanks Jeepster - Don't get me wrong - I really like the cut fenders with flares front and back look. I wouldn't have it any other way. All three of my Broncos have been cut, but I didn't have the money/means/time to do much work on the first two. This is the first time I have started to play with wheel and tire combinations.

I plan on keeping this one around for a while and was really hoping that 33" would fill the gap enough to make me happy. So much cheaper than 35" which means new tires, wheels, gears, etc.

 

[SaddleUp]

In the side shot I can see a visible difference in tire heights. It also looks like the back sits a tad higher than the front so it will take more tire to make it fill the gap. Personally I think it looks about right. A truck/off road rig is supposed to have a gap between the wheel wells and the tires to account for the extra flex it needs. Fill the void much more than it is now and you could run into problems with the tires hitting.