max backspace?

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well....we need to know what car you have, year & model. what rim size, 14, 15, 16, 17 18....and the width of the rim you choose to run..whether it be 5 or 6 , 7, 8 so on & so forth...might help us out a little bit...lol
 
I was more concerned with bearing load and wheel stress with too much backspace.
 
It is impossible to give you serious reply without more info so I will give you a common number I see pop up on here.

4 1/4"
 
It can vary on material of wheel, 1 piece cast, 2 piece or 3 piece wheels.

I have a 3 piece wheel that is 8" with 6.25" of BS and can go more. The manufacturer of the wheel you are looking for can tell you for sure.
 
The question wasn't about any particular vehicle or wheel just wondering if a wheel could be unsafe with too much back-set and if the bearings would be put under any extra stress.
thanks for all the responses
 
rjsjea said:
It can vary on material of wheel, 1 piece cast, 2 piece or 3 piece wheels.

I have a 3 piece wheel that is 8" with 6.25" of BS and can go more. The manufacturer of the wheel you are looking for can tell you for sure.
Click to expand...

Back spacing is a simple measurement from the mounting surface of the wheel to the edge of wheel. Wheel material, size or construction has no baring.

However, size of wheel will impact whether a wheel with a given back spacing will fit a given car.

The OP question regarding how much you can off set the center of force before it impacts bearing life I don't really know. I don't think you could enough on an A body before you would be hitting hitting body or suspension parts. Remember typically as the back spacing increase/decreases the rim width changes and the center of force stays the same. An exception I can think of is the old style chrome reverse or a FWD rim on one of our cars.

5" would be the max before the rim would be hard against the springs on the rear. I have 4.5" on the back of my car and with the tire bulge I have 1/2" of clearance to the spring. Up front the wheels are 4.25", I have never checked the clearance with the wheels at full lock to see how close they are to touching the inner fender.

It's only the off roaders that I have heard of wearing out bearings due to off set.
 
I see new rims/wheels,18,20 inch allday at work(Ford Plant)These rims look to have atleast a 7-8 inch b.space.The face of the rim is almost flush with the tires.So I believe it depends on the brand of rim?Have a look at some new cars like Vipers,Vettes,same thing with the b.spacing.Good luck.
 
But those wheels won't work on an a-body without interfering with the body or suspension. It really has nothing to do with the brand, it's the application. Those wheels with 8" of backspacing still put the center of force pretty close to the bearings for the cars they were designed to go on.
 
dgc333 said:
But those wheels won't work on an a-body without interfering with the body or suspension. It really has nothing to do with the brand, it's the application. Those wheels with 8" of backspacing still put the center of force pretty close to the bearings for the cars they were designed to go on.
Click to expand...

Are you sure they wont work? Cars pic'd below have mostly stock style suspensions and modern car wheels

Oh and thanks for clearing up what backspacing means for me, ("Back spacing is a simple measurement from the mounting surface of the wheel to the edge of wheel. Wheel material, size or construction has no baring.")[/I]

I would agree with you in that in a STOCK application on an Abody the amount of bS has no effect on wheel bearing life

275 fronts.jpg


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DSCN2809.jpg
 
Adapters and spacers are available to use late model wheels on early model cars.
http://www.wheeladapter.com/wheel_adapters.php

The physics involved between the bearings and the wheel are not that complicated.
Our cars use a pair of bearings on the front so the load really won't make much dif one way or the other...unless you are a SoCal mexican driving around in something that slightly resembles a skateboard...LOL

The rear has an outer bearing and the inner is part of the dif...absolutely no effect here.

The wheels themselves, which is what the OP is asking I think, come down to materials and workmanship. The more the wheel is off set from center, the stronger the joint between the round and the mount flange will have to be. Does that make sense to ya?

Basically, if you are buying your wheels from a reputable manufacturer (and you should be), you won't have a problem in wheel strength.
 
I'm not an engineer, but knowing what I know about loading from work, I think that less backspacing is actually harder on bearings and axles than more.

The load of the car is going to be centered on the tire, and with more backspacing that load is actually going to move closer to the bearing, or perhaps even beyond it towards the differential. I would think that would actually be the best as then the load of the car is being supported by the axle with a bearing on either side of the load and splitting the load between them (not evenly but still sharing the load).

The opposite case is the real problem in my opinion. Less backspacing moves the load away from the bearing and towards the outside of the car, making the axle carry the load by cantilevering the axle past the bearing. The farther the load is away from the bearing, the greater the load becomes due to leverage, and now the outside bearing is pretty much carrying the load all by itself.

I would guess that the same applies on the front, for the most part.
 
rjsjea said:
Are you sure they wont work? Cars pic'd below have mostly stock style suspensions and modern car wheels

Oh and thanks for clearing up what backspacing means for me, ("Back spacing is a simple measurement from the mounting surface of the wheel to the edge of wheel. Wheel material, size or construction has no baring.")[/I]

I would agree with you in that in a STOCK application on an Abody the amount of bS has no effect on wheel bearing life
Click to expand...

In the back if they fit without rubbing the springs and the springs are in the stock location then they won't have more than 5" of back spacing, 8" of backspacing won't fit, not sure what you could get away with up front. It's real easy to check; lay a straight edge across the surface the wheel mounts to on the brake drum/rotor and measure the distance to the spring at approximately the radius of the wheel, that is the maximum backspacing before the rim hits. You need to be less than that to accomodate the side wall deflection and bulge in the tire (you don't need as much with the real low profile tires).

A lot of modern wheels push the spokes of the wheel to the outside but the actual mounting surface is much further back which is where you measure back spacing from. This is done to accomodate the big calipers they use on modern cars.
 
DionR said:
I'm not an engineer, but knowing what I know about loading from work, I think that less backspacing is actually harder on bearings and axles than more.

The load of the car is going to be centered on the tire, and with more backspacing that load is actually going to move closer to the bearing, or perhaps even beyond it towards the differential. I would think that would actually be the best as then the load of the car is being supported by the axle with a bearing on either side of the load and splitting the load between them (not evenly but still sharing the load).

The opposite case is the real problem in my opinion. Less backspacing moves the load away from the bearing and towards the outside of the car, making the axle carry the load by cantilevering the axle past the bearing. The farther the load is away from the bearing, the greater the load becomes due to leverage, and now the outside bearing is pretty much carrying the load all by itself.

I would guess that the same applies on the front, for the most part.
Click to expand...

You have got the concept. As I stated before I don't think you could go either way enough to make a real difference without hitting parts of the car.
 
dgc333 said:
In the back if they fit without rubbing the springs and the springs are in the stock location then they won't have more than 5" of back spacing, 8" of backspacing won't fit, not sure what you could get away with up front. It's real easy to check; lay a straight edge across the surface the wheel mounts to on the brake drum/rotor and measure the distance to the spring at approximately the radius of the wheel, that is the maximum backspacing before the rim hits. You need to be less than that to accomodate the side wall deflection and bulge in the tire (you don't need as much with the real low profile tires).

A lot of modern wheels push the spokes of the wheel to the outside but the actual mounting surface is much further back which is where you measure back spacing from. This is done to accomodate the big calipers they use on modern cars.
Click to expand...

It was sarcasm dude..............I know how to measure for wheels and tires.
 
rjsjea said:
Are you sure they wont work? Cars pic'd below have mostly stock style suspensions and modern car wheels

Oh and thanks for clearing up what backspacing means for me, ("Back spacing is a simple measurement from the mounting surface of the wheel to the edge of wheel. Wheel material, size or construction has no baring.")[/I]

I would agree with you in that in a STOCK application on an Abody the amount of bS has no effect on wheel bearing life
Click to expand...

Not meaning to hijack the thread but what size rims, backspace and suspension mods have been done to the duster
 
I think you`ll find that if you have standard opening rear wheelwells and put the largest rim you can in it, (8 inch) a backspacing of 4.00-4.50 inches should be about what will fit before you have to roll wheel lips and/or move leaf springs. Each car is different, even the same year, make, and model are often slightly different.
 
Not an answer to the question but a similar note. The advantage of using more backspace when designing the whole system is that given the same track width you can use a longer axle if it attaches as far out as possible. The longer the axle the stronger it is, it basically can actually twist some. Same goes for gears mounted on a shaft. They will always try and fold the surface of the gear back over the shaft making the shaft as long as possible still fitting withing the allowed space.

In this example of putting different backspacing on an existing axle does nothing for the strength. But were you to use say a B-body axle and modern mustang wheels you would in theory pick up more strength in the axles, while maintaining the same footprint on the tries.
 
With everything else being the same making an axle longer does not increase it's strength. Yes there will be more twist along it's length than a shorter axle but they will both reach their yeild point with the same torque being applied. The one advantage a longer axle might have is if it was subjected to very high shock loading for a very short duration the twisting may act as a shock absorber preventing the metal from reaching it's yield point.
 
You are right. I just remember something from a class on naval reduction gears were folded back over the shaft and attached as far out as possible to more then double the length of the shaft for strength. After looking at shaft yield formulas I see nothing about length only diameter so now I don't know why they do that in reduction gears.
I also tried then to see why they went to positive offset wheels and it seems like it may be to allow larger scrub radius to make steering easier and it moves the hub assemblies out further making more room in the engine bay for a transverse FWD setup. Why modern RWD cars and suvs are also using more and more positive is still a mystery to me but then again I wish every car made used the same bolt pattern, LOL! Even my GMC SUV (Envoy) with a 6 lug pattern is different then a same year GMC SUV 6-lug pattern (Tahoe), and they both are different than a current GMC (Arcadia) 6-lug pattern. What idiot came up with that? Now I can't add affordable common aftermarket wheels.
 
It's annoying and can't be cost effective.

I think ya nailed it with your theory of why the new cars have the max offset wheels.

They are more compact and pushed out to the corners. Performance is improved along with the packaging of components. The Germans have been doin it forever...everyone else copied...
 
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