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Rear Toe- How Much Is Okay?


bento

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I installed offset bushings in the trailing arms over the weekend to correct for excessive camber. I maxed them I out and they did the job.

Since they give me a new variable to play with, I checked rear toe with my longacre plates and measured 1/4" toe in.

I found an old post with alignment specs and it looks like I should be shooting for zero toe but is a 1/4" enough to eat tires?

Since I maxed out the offset bushings to decrease camber, I'll have to give up some camber correction to decrease toe.

Just trying to get a feel for where I can strike a healthy balance.

Car is street driven and I'd prioritize tire wear over at the limit handling.

On a related note, any recommendations for a camber gauge? I've seen them from $40 to hundreds. I'd like to spend just enough to get a fairly accurate reading but it'll essentially be a one time use tool.

Thanks!

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That is way too much toe. 0 to 1/16 inch in better.

Those offset bushing are pretty limited in what they can correct. You need the weld on adjusters to really align it.

Thanks. I figured as much but found a post with a pretty wide range and it didn't seem right.

I know these bushings aren't ideal but I figured they're better than nothing.

I'll see if I can get in that zero to 1/16" range. Thanks for that.

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I disagree with Marshall just a bit- 1/4" total across both tires is within the limit for obscene tire wear.  1/8" would be better, but

unless you're doing autobahn- style driving OR have 30-profile tires, the tires can absorb that amount of misadjustment without

too much punishment.

 

Now, combined with negative camber, it's going to be worse, of course.

 

My compromise in your circumstance would be to try to get rear toe to 1/8" and see how the camber goes.

As far as handling is concerned, Marshall's dead- on- 1/16" toe in, and a couple of degrees of negative camber is about

what you want for street driving.  But 1/8" rear toe- in will actually HELP stability in crosswinds.  Nothing I've done seems

to help stability in road ruts...

 

Don't ever go to zero rear toe, though.  Under braking, that could go to rear toe out, and having done that, it's pretty spooky

even when you know it's coming. 

 

And yes, agreed, weld- ons are much better.  But only if you are trying to fix more than -2.5 degrees of negative camber. 

Because it NEEDS that

for a couple of handling and safety reasons...

And check those offset bushings- racers who have to use them hate 'em because, in racing, they tend to loosen...

 

My '02,

 

t

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Okay, I think I can take 1/16" out of each side using the bushings.

When I get everything dialed as close as I can, I'll have a shop throw it on the rack and see if they can dial it in any better.

As an ounce of prevention, I'll mark everything so it's easy to spot if anything slips and I'll make it a routine part of my pre-drive checklist for a while.

Worst case, I'll pull the offset bushings, replace with urethane, and try different springs to bring ride height up a bit.

I'm using uncut, off the shelf BAV Auto springs. While they're supposed to be a tad lower than some other options, I didn't expect them to be such a hassle...

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You guys are missing an important factor: what is the wheel/tire diameter in question? The above numbers are correct if you have the original 13" wheels, but will be slightly different if you have larger diameter wheels and tires.

 

The Longacre toe plates appear to use the wheel rim as the reference point, so it is important to factor in your wheel diameter. The actual toe-in angle of the wheel is inversely proportional with wheel diameter; in other words, 1/4" of toe on a 13" rim will result in a much greater actual toe-in angle than 1/4" of toe on a 16" wheel.

 

Here is a handy conversion chart:

 

http://www.smartracingproducts.com/smartcamber/toe_conversion_table-cw-v3.pdf

 

BMW's factory specs for the 2002 call for 1.5MM of toe per side in the rear, which equals 0.06" per side if rounded up, which is close to the 1/16" per side suggested above (0.0625"). So, with the 13" wheels, 1/16" toe-in per side is equal to about 0.27 degrees per side, which is how the electronic alignment equipment at a professional shop would measure it.

 

My 2002tii has 15" wheels, so to achieve the same 1/16" of toe per side, the prescribed toe angle would actually be less at about 0.24 degrees. This doesn't sound like a lot but it is. I would need to dial in more toe in distance per side (about 0.01" more) to achieve the factory-specified angle. 

 

Another factor to consider is that BMW factory alignment specs, both old and new, assume that the car is "normally loaded," which means a full tank of fuel and a full passenger/luggage load (the 2002 manual says 143 lbs on each front seat, 143 in the center of the rear seat, and 66 lbs in the trunk!). Most alignment shops miss this on newer BMWs and this is why many chew up the inner edges of the rear tires so badly.

 

That said, set the alignment with YOUR normal load. If you mostly drive by yourself on back roads with the car mostly empty, only put ballast in the front seat(s) and go with 1/2 to a full tank of fuel. Most track guys use only their weight in the driver's seat and their average on-track fuel level.

 

I hope I didn't over-complicate things, but there is a lot that goes into a proper alignment!

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I'm here to learn so don't be afraid to overcomplicate things. Just be prepared to speak slowly and use small words. :-)

Here's the info you didn't have for the above;

Longacre plates rest against broadest part of the tire sidewall, not the rim, and the tapes I'm comparing are ahead and behind the tire. Distance between the tape measures when in the plate slots is roughly 21" center to center. The tire sidewall probably isn't the most precise surface to use, so this is largely academic, but the theory is interesting. Anything smaller than 1/32" is probably pushing it.

If I'm following your logic, I should be adding around an extra 1/16", or 3/16" total toe, since the slots are further than the distance BMW assumed in their spec. Correct?

Interesting point about ballast. I mostly drive solo, so I'll have to approximate my weight in the driver's seat and see what happens. I guess a 1/2 tank of gas would be ideal too?

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You guys are missing an important factor: what is the wheel/tire diameter in question? The above numbers are correct if you have the original 13" wheels, but will be slightly different if you have larger diameter wheels and tires.

The Longacre toe plates appear to use the wheel rim as the reference point, so it is important to factor in your wheel diameter. The actual toe-in angle of the wheel is inversely proportional with wheel diameter; in other words, 1/4" of toe on a 13" rim will result in a much greater actual toe-in angle than 1/4" of toe on a 16" wheel.

Here is a handy conversion chart:

http://www.smartracingproducts.com/smartcamber/toe_conversion_table-cw-v3.pdf

BMW's factory specs for the 2002 call for 1.5MM of toe per side in the rear, which equals 0.06" per side if rounded up, which is close to the 1/16" per side suggested above (0.0625"). So, with the 13" wheels, 1/16" toe-in per side is equal to about 0.27 degrees per side, which is how the electronic alignment equipment at a professional shop would measure it.

My 2002tii has 15" wheels, so to achieve the same 1/16" of toe per side, the prescribed toe angle would actually be less at about 0.24 degrees. This doesn't sound like a lot but it is. I would need to dial in more toe in distance per side (about 0.01" more) to achieve the factory-specified angle.

Another factor to consider is that BMW factory alignment specs, both old and new, assume that the car is "normally loaded," which means a full tank of fuel and a full passenger/luggage load (the 2002 manual says 143 lbs on each front seat, 143 in the center of the rear seat, and 66 lbs in the trunk!). Most alignment shops miss this on newer BMWs and this is why many chew up the inner edges of the rear tires so badly.

That said, set the alignment with YOUR normal load. If you mostly drive by yourself on back roads with the car mostly empty, only put ballast in the front seat(s) and go with 1/2 to a full tank of fuel. Most track guys use only their weight in the driver's seat and their average on-track fuel level.

I hope I didn't over-complicate things, but there is a lot that goes into a proper alignment!

Toe plates do not use the wheel diameter. They use the set distance between the notches on the plates. Wheel diameter is irrelevant. The factor is the distance from axle centerline to the measurement point on the plates.

if you use angle instead of a distance measurement, then the wheel diameter is really irrelevant. The angle does not change with wheel size or distance from centerline....

but yes, set alignment at normal car load for how you drive, not for some artificially loaded condition.

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You guys are missing an important factor:

 

No, I just wasn't too worried about it.  Like Marshall,

I assumed toe plates, but even if you don't use 'em,

the OD of most 2002 wheel and tire sets is something like

22 inches.  So the change in DEGREES isn't going to

be enough to matter much.

 

If we were tuning for Bathurst with a 600 hp engine, yes, it'd be more involved.

Since it's a 100 bhp car not driven too aggressively, it's not so painful.

 

t

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Toe plates do not use the wheel diameter. They use the set distance between the notches on the plates. Wheel diameter is irrelevant. The factor is the distance from axle centerline to the measurement point on the plates.

if you use angle instead of a distance measurement, then the wheel diameter is really irrelevant. The angle does not change with wheel size or distance from centerline....

but yes, set alignment at normal car load for how you drive, not for some artificially loaded condition.

 

I completely understand that wheel diameter is irrelevant if using toe angle, this is what I was attempting to convey in my previous post. I incorrectly assumed that the Longacre toe plates used the wheel rim edges as a reference point as do the SmartStrings that I am used to using. I like knowing the actual toe angle so I can compare apples to apples, so I use the chart that I posted for calculation.

 

However, the distance between the two measuring points of the toe plates is a consideration. Unless there is some universal distance standard among toe plate manufacturers that I am unaware of, the actual toe angle will be different if the distance between these two points varies between toe plate designs, even if the toe distance measurement is the same front to rear. Probably not enough to matter on a street driven 2002 on large sidewall tires and stock bushings, however.

 

 

No, I just wasn't too worried about it.  Like Marshall,

I assumed toe plates, but even if you don't use 'em,

the OD of most 2002 wheel and tire sets is something like

22 inches.  So the change in DEGREES isn't going to

be enough to matter much.

 

If we were tuning for Bathurst with a 600 hp engine, yes, it'd be more involved.

Since it's a 100 bhp car not driven too aggressively, it's not so painful.

 

t

 

Duly noted. I am accustomed to using SmartStrings if setting toe by hand; they use the rims as the reference point for setting toe (so the wheel diameter is a critical consideration), or I use my shop's Hunter alignment rack. We align a lot of track driven 911s and Boxsters, etc that are very sensitive to toe settings, so I am used to being very precise about such things.

 

On a street-driven near-stock 2002 with large sidewall tires and large and possibly worn rubber suspension bushings, toe plates that use the tire sidewalls as a reference are more than adequate, and the settings suggested above should be good if they are achievable. Many old BMWs have a long "history," so you sometimes have to accept the rear alignment settings as is if they are close enough, or take corrective measures like offset bushings as Bento did.

 

Rear camber and toe adjusters are on the "some day" list for my tii, though the rear bushings are in decent shape and the rear alignment is acceptable for the time being.

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