Tires/rims/offset

[rgallant]

Hi all,

 

I have read everything on this site and far too many others to get a decent understanding of this issue.

 

I know what I want, but I believe it is not likely going to happen.

 

Note I don't need advice on tires, I like these what I am looking for is fitting advice.

 

Basics

 

97 Pathfinder

OME MD springs all round

Current tire worn 265/70/16's about 29 inch high and about 8.5 wide

 

Want

 

Cooper Discovery ST MAX

 

Problem

 

They only come in a 265/75/16 this works out to a 8.5 inch wide by 32 ish inch tire.

 

Given my setup will getting a rim with sufficient offset put undo stress on the front end. My concern is half shafts and bearings primarily. Assuming it will not I am correct in my understanding that I need a negative offset. That is negative offset pushes the centre point of the tire further out from the axle.

 

Which ever offset I need can someone point me to a way to calculate it ? I would like to have the minimum required to fit the tires. A basic measurement with a tape measure suggests about 1 to 1.5 inches. I can deal with rubbing issues.

 

I do have a backup plan if this is unreasonable,and very flame proof suit.

Edited April 3, 2012 by rgallant

[devonianwalk]

A 32" tire on our rig will require at least a 3.75" back spacing. You are correct in your understanding of the back spacing. However, I will warn you that you may need larger (or longer, if you will?) fender flares to keep your ride clean. Personally, I don't mind the "permanent" dirty look but, you might not want to deal with the constant dirty rocker panels. I'm not sure about the pre-facelift R50 flares but, my 99.5 flares don't do squat for my 8" wide wheels and the 31" Duratracs.

 

Hope this helps you a little?

[XPLORx4]

I'm currently running 265/75R16 BFG MT KM2's on 16x8 wheels with 4.875" BS. I have previously run 32x11.50R15 tires on 15x8 wheels with both 4" and 3.75" BS. The only real difference between the wheels with less backspacing is that the tires extended further out from the body, which also had the effect of preventing the tires from rubbing the strut. My Pathy has over 175000 miles on it, and I've yet to observe any real effect on wheel bearings due to the increased offset.

 

Here' a chart that correlates wheel offset and backspacing:

Edited April 3, 2012 by XPLORx4

[rgallant]

Thanks guys I am so close on my rims 4.5 backspace, Toyota alloys basically free. The mud thing does not bother me at all, I get that already it will just be worse. Nice to know you have that high a milage with no issues Xplorx4.

 

I suspect this will be a case of have on fitted and see where I am.

[devonianwalk]

Keep us posted on the out come. The Cooper Discovery ST's may have better clearance of the shoulder blocks as opposed to the GY's. I'm going with 32's when my treads wear down.

[rgallant]

I will most certainly keep this updated. The backspace/offset issue is the most confusing part of rims as they work together and it is not as simple as cool rims that fit my truck. The only thing worse is picking out a VHF antenna.

 

If I am right my problem may be that my rims are slightly positive,in which case a wheel spacer would solve the issue as the size would be minimal .5 to .75 of an inch.

[dynomax]

Keep us posted on the out come. The Cooper Discovery ST's may have better clearance of the shoulder blocks as opposed to the GY's. I'm going with 32's when my treads wear down.

When I was tire shopping, I compared side by side a goodyear Duratrac (which I bought), and the BFG AT KO. THE BFG had a wider footprint if you will in the same size tire when compared to the Duratrac.

 

We used to run those Cooper ST's at work here, and they have a wider, sprawling tread like the BFG AT KO did.

 

I guess What i'm trying to say is it looks like the Goodyear would fit a little better when the backspace was getting tight where the BFG may not, as the Goodyear appears to narrow in a bit with its tread footprint, where the bfg kind of sprawls out the side a little more.

 

Did anyone else notice this in their tire experience?

[rgallant]

Doing research on tire widths was a pain, you have the right idea, it is basically rim and tire. So the same rim and different tire brands of the same size (ie 265/75/16 in my case) can vary by about 3/4 to inch in width. Every combination is different, buying on line when things are tight would be a nightmare. My local guy does has to order these in for me, but I won't have him order until I have my issues sorted.

[rgallant]

Just a small info update

 

Stock Rims are a 15 x 7 with a +20mm Offset

 

Stock 16 x 7's are generally the same

 

recommended offset range is +20 to +8

 

A 16 x 7 rim with +7 Offset will fit a Pathfinder with 265/75/16 KM2's and a 2" Pedders Lift (Aus)

 

The difference +20 to +7 is about a 1/2 an inch (13mm)

 

That matches up with my eyeball measurement, I am taking a tire off tomorrow to get a more exact measurement but it looks like rim change or spacer is in order.

[rgallant]

Just an small update, my local tire guy is going to get a tire in and pop it on my rim and we will see where we are. In the mean time I am picking up a single rim with less backspace from a local wrecker so I can test that as well. With luck this will be done this weekend 28 April and I can give him a bunch of money and have nice new tires.