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Old 07-11-2011, 05:23 PM
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Experiences going to 3.75" of backspacing?

I want to go 33x12.50R15s on my 2001 TJ with 3" suspension lift.

I figure I need 3.75" of backspacing on a 15x8 wheel.

Since 3.75" of backspacing will push my wheel out significantly further than stock, will my Jeep suffer ride quality, like getting squirrely?

I really like the handling with my 5.5" bs 15x8 running 33x9.50R15s. But they don't look nearly aggressive enough.

What are your experiences going from factory to 3.75" bs?

Thanks!

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Old 07-11-2011, 10:21 PM   #2
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I just went with less BS than that (3-5/16) and the only thing I've ran into is gauging how close I am to a curb when I parallel park.

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Old 07-31-2011, 07:05 AM   #3
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I've got 3.75" BS wheels, I didn't notice any ill effects in handling.
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Old 07-31-2011, 12:39 PM   #4
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I'd imagine the wider backspacing would give you better stability due to a wider stance. I have read this puts a lot more stress on the axles and knuckles though, especially with larger tires
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Old 07-31-2011, 12:57 PM   #5
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Originally Posted by MikalCarbine View Post
I have read this puts a lot more stress on the axles and knuckles though, especially with larger tires
I heard this too, but it makes no sense to me. I'd understand this if the BS was 0". The stock TJ Canyons have 5.5" of BS. That is 1.5" of offset on an 8" wheel. My MTs have 3 5/16 of BS which is only 11/16 of offset for an 8" wheel. Wouldn't the least amount of offset be the least harmful to wheel bearings?
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Old 07-31-2011, 01:11 PM   #6
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I'd need to crunch the numbers on offset vs BS but if you look at the scenario with just backspacing... (btw I'm no mechanical engineer) essentially you are increasing the horizontal moment arm on the bearings, therefore increasing the vertical torque applied onto them. I guess if you compared the same tires and rims with just different BS it would probably be negligible but usually you are adding a lot more meat plus new wheels, etc
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Old 07-31-2011, 02:41 PM   #7
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Originally Posted by BLK00TJ View Post
I heard this too, but it makes no sense to me. I'd understand this if the BS was 0". The stock TJ Canyons have 5.5" of BS. That is 1.5" of offset on an 8" wheel. My MTs have 3 5/16 of BS which is only 11/16 of offset for an 8" wheel. Wouldn't the least amount of offset be the least harmful to wheel bearings?
That would be true if you where talking about a 15x7 wheel. But a 15x8 like the factory canyon is actually 9" wide. So 0 offset would be 4.5". The Canyon rim is a 25mm (1 inch) positive offset.
The rim you are talking about is a 30mm negative offset. Doesn't matter how you look at it, you are pushing the wheel out over 2 inches farther. Adding stress to the parts. But I really doubt it would be enough do anything catastrophic.
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Old 07-31-2011, 08:55 PM   #8
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That would be true if you where talking about a 15x7 wheel. But a 15x8 like the factory canyon is actually 9" wide. So 0 offset would be 4.5". The Canyon rim is a 25mm (1 inch) positive offset.
The rim you are talking about is a 30mm negative offset. Doesn't matter how you look at it, you are pushing the wheel out over 2 inches farther. Adding stress to the parts. But I really doubt it would be enough do anything catastrophic.
Holy, moly. They are 9". I thought they looked wide when I had the tires taken off.

The way I'm looking at it, 0 offset should put less stress on the bearings, correct? So for an 9" wheel, 4.5 of BS would be the best. If we only drove on the outside of our tires, this would not be the case.

The problem is you can't put a 33x12.5 tire on a wheel with that BS. My Jeep needs longer axles.
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Old 08-01-2011, 02:29 PM
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Originally Posted by BLK00TJ View Post
I heard this too, but it makes no sense to me. I'd understand this if the BS was 0". The stock TJ Canyons have 5.5" of BS. That is 1.5" of offset on an 8" wheel. My MTs have 3 5/16 of BS which is only 11/16 of offset for an 8" wheel. Wouldn't the least amount of offset be the least harmful to wheel bearings?
Great question! Only if the mounting surface of the wheel were inline with the steering axis. In a Wrangler this is not the case. You have the steering axis (where the knuckle pivots on the axle housing), then the brakes then the wheel. The wheel's mounting surface is several inches from the steering axis. What is inline with the steering axis is the u-joint for the front axle, otherwise you couldn't turn the steering wheel.

I believe, ideally you would have the center of the wheel/tire inline with the steering axis. That way when the steering wheel is moved the tire pivots in the middle. This is called scrub radius.

I am confident of this, however if someone finds this inaccurate please correct me.
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Old 08-01-2011, 02:39 PM
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So the way I see it, there are 2 issues here.

1. The further you mount the tires out, the more stress there is on the bearings and other parts of the axle assembly. There's more leverage. This was mentioned above.

2. The further you mount the tires out, the more positive scrub radius, which effects handling. In what ways and to what degree, I am unfamiliar. I picture it as the further the tire is outward from the steering axis the more leverage is on the tire by the road. Which would cause the tire to follow the road more pulling you around.
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Old 08-01-2011, 04:30 PM
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And another thing.

Picture factory tires and wheels installed. Jack the front until the tires are off the ground. Lock the steering wheel. Now grab the tire and move it around feeling the amount of steering linkage slop. Imagine the tire sticking out a few inches further and picture how much more the tire would move.

As the tire is extended out from the steering axis the effect of the steering slop is amplified.

So, hypothetically, lets say you could move the factory tire/wheel around a 1/4" in any one direction. Let's say it's 1 degree. If the tire was moved out further, there would still be 1 degree of movement, but that 1/4" would increase.

So your steering slop might be OK with factory tires/wheels, but once you move the tire out, say by reducing backspace, it could become a problem.
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Old 08-01-2011, 04:35 PM   #12
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thanks, that explains it well. I never thought of it from a steering perspective, only a weight perspective in relation to wheel bearings.

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