I recently bought some 31x10.50x15 tires for my 98' Ford Ranger 4x4. My stock wheels are stamped on the back (15x7), but a tire salesman and I measured them with one of those plastic wheel gauges and they came out to be (15x7.5)

I am going to go with wider (15x8 )black rock crawlers.

My question is, do I use the same backspacing as my factory wheels.

I've got plenty of wheel well space on my truck and I also have rack & pinion steering, so there is really nothing for the tire to come in contact with. Also the tire doesn't measure a full (31 inches). According to the PepBoys website, the tire only measures (30.20) inches tall.

I would suggest the same back spacing or maybe 1 inch more at most. BTW, when you measure rim width, you measure it between the flanges where the tire bead rests, not at the outer edges.

Thank's for the answering my question, I guess that I will go with the original backspacing. My brother in-law also said the same thing as you did and to stay with the original backspacing.

I can't wait to get the money together for the new wheels. I'm ready for a whole new look for my truck.

Black wheels, blackwall tires, on a blue truck.

I definately need an alignment right after I get them installed as its out of spec.

i just bought some wheels like your from summit racing the balck ones are series 84 i believe and i really like the looks of them. they were very reasonably priced also.  

In regards with using the factory backspacing when buying new wheels, how important is offset and how would I know the proper offset to get for my wheels? Is this a BIG deal?

I'm going to order them from Summit Racing and unless someone knows on this forum about proper offset, I would fiqure the tech line at Summit would know.

I want to make sure that I get the info. right before I order them. I'd hate to have to send them back if there not the right ones and if I mount the tires on them, then I have bought them.

The problem with backspacing is that it chaged the way that the wheel loads the axle. THe further out it is the more leverage it places on axle and in effect reduces its capacity too. On the front axle it changes the contact load center relative to suspension piviots and can effect handling and larger offsets increase strain on ball joints or axle pivots from increase leverage and can shorten there life. Also when you use offset wheel with a IFS from axle you should increase camber sets over stock specs to attempt to restore load center relation to axle pivots and improve overall handling. Sorry if I got a bit too technical but you asked for a explaination.

In the Summit catolog, it says nothing about offset. It just says to measure the backspacing from your original wheels and thats it.

Do I need to worry about it, or do I need a zero or a negative offset wheel.

I know what your saying about positive offset, I definately don't want a wheel that sticks way out of the fender well. Like you said, it just puts more strain on the axles and bearings and looks pretty stupid too!!

I tryed to find the specs. on my factory wheels on the web, but I couldn't (offset specs.- if any)

I'm going to take one of the wheels off Saturday to measure the backspacing and to see exactly if they are 15x7" or 15x7.5" wide wheels.

Wise idea to measure offest on factory wheels and then you have a starting point.Also, rim width it distance between bead  seating surfaces, no distance bewteen edge of rim.

I know how a rim is measured. The plastic gauge is used on the outside and compensates for this and gives you the inside measurement.

Many moons ago, I used to install tires and this gauge was used to determine wheel wideness before balancing a tire.

I went into Summit's tech pages last night and found my factory backspacing to be at 4.00". I'm still going to take a wheel off just to see if this # is correct. Better to be safe than sorry.

I meant nothin bad by saying how to measure it because a lot of people do not know the correct way. If you want to get really scientific about it factor back spacing into a new rim width and adjust new back spacing so that the relative center  of tire on ground is the same relative to stock tires and rims. (space permitting of course)

In your second sentence, I was thinking of the same thing. I definately can't go with more backspacing as I would never get the wheel on.

I just got done putting my toolbox back on my truck and put another serpentine belt on. I had a much longer than anticipated phone conversation with a friend of mine, so my time was cut short due to it getting darker earlier, so I didn't have the time to take a wheel off and measure the backspacing.

The backspacing options for the wheels that I want from Summit are 3.75", 4.00", and 4.75". Just by looking at them, I would guess that they were 4.00" or more.

If the current backspacing options won't work on my truck, I can have custom wheels made for about $20.00 more each from Summit.

How are you Snoman? I'm probalbly not your favorite person to talk to, but I thought I would drop you a line. My old screenname was 4x4 Ranger, but I couldn't sign on using this old screenname. Three weeks ago my 98' Ford Ranger was rear ended at about 50 mph. while I was on my way to work. I was also pushed into the car in front of me. I saw it coming, but had no place to go to get out of the way. Of course my truck is a total loss. I really miss my truck.  

That sucks man! From a fellow Ranger owner I feel your pain! Be sure to let us know what truck you get next!  

Actually, I'm thinking of buying another Ranger. If I do, it will be a 93' to 97'. The only thing that I really did not care too much for on my 98' was the torsion bar suspension. Makes for a rough ride with reduced ground clearance. I found one now that I have my eye on. It's a 93' with a 4.0, 5-speed, and a lift already on it.

Since your Four Wheeler Web Editor, why can't I log in with my old screenname and password? I notice that others on this website are still using their old screennames. I first became a member in February of 2006.  

Thats cool! I too ditched the torsion bars in favor of coil-overs.

I am not 100% sure why some of the users got lost in the move. Best I can figure it had something to do with the way they were signed up, either not providing a correct email, or just being unfortunate and lost by the system. The developers didn't tell me exactly why.

But.. if your old account was lost you should still be able to re-register with the same name, as it is not in the system anymore.