Back spacing question (1 Viewer)

[John E Davies]

I have ordered a set of Mickey Thompson Classic II wheels in 16x8 with 3 5/8 inch back spacing. This is the recommended wheel for a '96 Series 80, using the MT website fitment guide. (Their other wheel has a 4 7/16 BS, which is very close to my stock Lexus wheels.)
http://www.mickeythompsontires.com/wheels.html

The new wheels will extend outward approx 1 1/8 inches further on each side, which is fine with me. I have 3 inches of lift and am running 285/75R16 MT/Rs. I don't have adjustable track bars so the axles are shifted a bit to the left. My question:

What is the best way to check for interference at the tire shop - can they mount the left front wheel/ tire and stuff it up into the wheel well witth a floor jack? What exactly do I look for? Do I need to work the steering?

I don't want to install the full set if they are going to hit when I am off-road.

Can anyone offer some advice?

Should I go with the other wheels with essentially stock BS?

BTW: These wheels don't have the same specs as the Classic Lock which has 4 inch BS and works fine, according to "Strap" in this post:
https://forum.ih8mud.com/showthread.php?t=28295

Thanks very much. John

 

[e9999]

seems like a small shop would help. Big chain may frown on fooling around with the wheel in the bay. Could always just buy one wheel and have a tire put on and then try at your leisure at home...

 

[Big_Moose]

John,

I have a set of 16x10 w/4" backspacing for my 35" Interco "Truxus" MT's, which DO rub when stuff on the front / against the rear of the wheel well, on the left side.

I have a 850J / 863 lift w/ARB front bumper & SC adding weight & a Hanna Bumper on the rear, but I haven't installed the panhard adjusters (sitting in the shop). Now the cruiser was placed on the alignment rack, and it is tracking straight - so the geometry is close to stock.

With your backspacing you are considering, I would assume they would rub, especially if you increase the tire size.

I'm planning on going back to stock backspacing - 4.5"

Joe

 

[hoser]

You can try on some 1" spacers with your stock wheels and wheel it. This would give you very similiar backspacing to the wheels you are considering. If your are happy with it, then get the new wheels.

 

[hoser]

The new wheels will extend outward approx 1 1/8 inches further on each side, which is fine with me.

Btw, 4-1/2" minus 3-5/8" equals 7/8" not 1-1/8".
Your wheels will stick out 7/8" further than stock.

 

[John E Davies]

Btw, 4-1/2" minus 3-5/8" equals 7/8" not 1-1/8".
Your wheels will stick out 7/8" further than stock.

My LX wheels have 4 3/4 back spacing. The new wheels have 3 5/8 inch BS. That makes 1 1/8 inch difference. The alternative Classic II wheel has BS of 4 7/16. I wasn't real clear on my first post....

I am working with Discount Tires in Spokane - they have always been happy enough to fart around checking stuff if they aren't crazy-busy mounting snow tires. I just need to time my visit for a slow day. I have bought tires and stuff from them for many years. and they see me as a loyal customer.

John

 

[John E Davies]

John,

I have a set of 16x10 w/4" backspacing for my 35" Interco "Truxus" MT's, which DO rub when stuff on the front / against the rear of the wheel well, on the left side.

With your backspacing you are considering, I would assume they would rub, especially if you increase the tire size.

Yeah, but I am running 285/75 tires on 8 inch rims. They aren't nearly as wide as your 35s on 10 inch rims. With equal backspacing and all other things equal, the outside of the tread is going to be further out on the 10 inch rim than on an 8 inch rim.

What confuses me is the the MT website specs these wheels for stock replacement. Maybe that is a goof?

John

 

[hoser]

My LX wheels have 4 3/4 back spacing. The new wheels have 3 5/8 inch BS. That makes 1 1/8 inch difference. The alternative Classic II wheel has BS of 4 7/16. I wasn't real clear on my first post....

Ah, there's the discrepancy. I'm pretty sure OEM wheels are 4.5" and also have Zero offset. But I could be wrong.

 

[hoser]

Just happened that I measured the BS on the (presumably original) alloys on my 97 today.
BS is 4.368" +/- 0.010"
There! That should settle it!
Eric

Or perhaps we are both wrong.

 

[Kalawang]

I assume you're buying the wheels and the tires. You should be allowed to mount and try the set, even if only in a stationary position, complete with turning the wheel from lock to lock just to verify the rubbing. The alternative is for them to give you a written guarantee that it won't rub on your car as is.

If they won't give you either, try another shop.


Kalawang

 

[IdahoDoug]

Not sure what you're trying to accomplish, but the real number to worry about when getting wider rims is the offset. Offset is the distance from the center of the rim to the mounting space, and the design of the front suspension, alignments and steering system were predicated upon this number.

Using backspacing, which is simply the distance from the mounting face to the inboard lip of the wheel, you can really screw up the way a vehicle drives as you'll often get conned into inadvertently changing the offset.

For example, the backspacing of an 8" wide wheel with zero offset is 4 inches. Now slap on a 10" wheel some shop has talked you into because it has "stock" backspacing of 4 inches. But what's happened to the key number - offset? Well, offset went from zero to an inch (whoops, never do math in public), which dramatically impacts steering, etc. The biggest thing you'll notice with offset changes are that the truck will want to follow cracks in the road, wander over bumps, and not steer well in hard braking.

So, unless you're making offset changes specifically for some large offroad tire clearance issue (in which case road manners are less critical), then stick to stock offset. Check out www.tirerack.com for a nice diagram about these differences.

DougM

 

[hoser]

Doug, have you forgotten about backspacing already?

https://forum.ih8mud.com/showthread.php?t=21223&highlight=backspacing

But, Doug is right, decreasing offset by 2" (-2") will make a significant on-road difference in handling/steering feel. But, like everything else, it's a compromise. It's just a matter of what's more important to you. Increasing the offset a little can be beneficial but extreme changes can lead to "wierd" handling.

 

[Rich]

If I were going to buy aftermarket aluminum wheels, especially for offroad use, I would most certainly get forged wheels. Much more durable than cast and more easily straightened with a hammer, if it ever comes to that.

I believe that the Mickey Thompson Classic II are cast wheels, as are the stock Toyota aluminum wheels.

I'd start by looking at Weld forged aluminum truck wheels.

 

[ginericLC]

I'm running 15x8 Eagle 589s with 3.25" backspacing and 35x12.50 BFG MTs. I don't rub.

 

[IdahoDoug]

Rich,

Just an FYI - the stock 80 alloys are forged. The little interlocking "JWL" on them means they conform to Japan's highest OEM standard for durability, which includes loading the vehicle being tested to its maximum GVW and driving it over a sharp square edged curb at around 50mph. There must be zero loss of air to pass this particular test regimen.

The letters stand for Japanese Wheel League - formed some 40 years ago due to a tragedy involving the top exec at an automaker when an alloy wheel failed.

DougM

 

[Dirk Diggler]

John,

Thanks for posting this question. I had the same question. I want 305's and it sounds like the backspacing should be approx. 4". Good post.