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Re: Different treadwear on rear wheels destroys differential ???
BMW BMW General Discussions (alt.autos.bmw)
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Re: Different treadwear on rear wheels destroys differential ??? -
06-30-2003
, 10:55 AM
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I had to replace one of my front tires (stock Michelin MXV4+ 205/55/16) couple of months ago. At that time, tire salesman tried to make me buy two tires instead of one, saying that it is a bad idea to have different sizes of tires on same axle, especially on rear axle in my BMW. He claimed that different treadwear on rear axle tires makes wheels rotate in different speeds (of course), which will ruin differential (hmmm..). Well, I thought this is bullshit, and even if it wasn't it doesn't apply to me because I'm having new tire on front wheel. In addition, the rest of the tires had a pretty good tread wear left (6mm), so I just bought one tire to replace broken one. Now it is time to do a tire rotation, and I'm hesitating because of this salesman's words. Tell me if he is true with his claim that putting new tire (8mm of tread left) back with one of the original ones (5.5mm of tread left) will break my differential in long run? I just calculated that 2.5mm difference in wheel radius makes 15.7mm in circumference, which means that old one makes one additional round every 126 rounds = 251 meters. |
been apocryphal stories that the DSC is bothered by "radically" differently
worn tires.
You should be careful to not have different tire brands or types on
a car, but the situation you describe should not cause any problems.
For that matter, I've had to replace single tires on AWD vehicles
in very similar situations and never had problems - and that's three
diffs, not just one.
Floyd Rogers
#2
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"Juha" <jmnyman_a (AT) kuumamaili (DOT) com> wrote I had to replace one of my front tires (stock Michelin MXV4+ 205/55/16) couple of months ago. At that time, tire salesman tried to make me buy two tires instead of one, saying that it is a bad idea to have different sizes of tires on same axle, especially on rear axle in my BMW. He claimed that different treadwear on rear axle tires makes wheels rotate in different speeds (of course), which will ruin differential (hmmm..). Well, I thought this is bullshit, and even if it wasn't it doesn't apply to me because I'm having new tire on front wheel. In addition, the rest of the tires had a pretty good tread wear left (6mm), so I just bought one tire to replace broken one. Now it is time to do a tire rotation, and I'm hesitating because of this salesman's words. Tell me if he is true with his claim that putting new tire (8mm of tread left) back with one of the original ones (5.5mm of tread left) will break my differential in long run? I just calculated that 2.5mm difference in wheel radius makes 15.7mm in circumference, which means that old one makes one additional round every 126 rounds = 251 meters. He's a good bullshitter. The differential won't notice it. There have been apocryphal stories that the DSC is bothered by "radically" differently worn tires. You should be careful to not have different tire brands or types on a car, but the situation you describe should not cause any problems. For that matter, I've had to replace single tires on AWD vehicles in very similar situations and never had problems - and that's three diffs, not just one. Floyd Rogers |
#3
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Hi, I had to replace one of my front tires (stock Michelin MXV4+ 205/55/16) couple of months ago. At that time, tire salesman tried to make me buy two tires instead of one, saying that it is a bad idea to have different sizes of tires on same axle, especially on rear axle in my BMW. He claimed that different treadwear on rear axle tires makes wheels rotate in different speeds (of course), which will ruin differential (hmmm..). Well, I thought this is bullshit, and even if it wasn't it doesn't apply to me because I'm having new tire on front wheel. In addition, the rest of the tires had a pretty good tread wear left (6mm), so I just bought one tire to replace broken one. Now it is time to do a tire rotation, and I'm hesitating because of this salesman's words. Tell me if he is true with his claim that putting new tire (8mm of tread left) back with one of the original ones (5.5mm of tread left) will break my differential in long run? I just calculated that 2.5mm difference in wheel radius makes 15.7mm in circumference, which means that old one makes one additional round every 126 rounds = 251 meters. Is he right? - Juha - If you have a limited slip diff, it *will* notice it. The clutch pack |
pack prematurely.
#4
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Juha wrote: Hi, I had to replace one of my front tires (stock Michelin MXV4+ 205/55/16) couple of months ago. At that time, tire salesman tried to make me buy two tires instead of one, saying that it is a bad idea to have different sizes of tires on same axle, especially on rear axle in my BMW. He claimed that different treadwear on rear axle tires makes wheels rotate in different speeds (of course), which will ruin differential (hmmm..). Well, I thought this is bullshit, and even if it wasn't it doesn't apply to me because I'm having new tire on front wheel. In addition, the rest of the tires had a pretty good tread wear left (6mm), so I just bought one tire to replace broken one. Now it is time to do a tire rotation, and I'm hesitating because of this salesman's words. Tell me if he is true with his claim that putting new tire (8mm of tread left) back with one of the original ones (5.5mm of tread left) will break my differential in long run? I just calculated that 2.5mm difference in wheel radius makes 15.7mm in circumference, which means that old one makes one additional round every 126 rounds = 251 meters. Is he right? - Juha - If you have a limited slip diff, it *will* notice it. The clutch pack will be constantly slipping - slightly. This may wear out the clutch pack prematurely. |
#5
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For that matter, I've had to replace single tires on AWD vehicles in very similar situations and never had problems - and that's three diffs, not just one. |
think you just got very lucky with your 4WD.
Richard
#6
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"fbloogyudsr" <fbloogyudsr (AT) nwlink (DOT) com> wrote in message For that matter, I've had to replace single tires on AWD vehicles in very similar situations and never had problems - and that's three diffs, not just one. How big was the difference? If it was as big as 8mm vs 5.5...well then I think you just got very lucky with your 4WD. |
AWD diffs are open. All the diffs on my AWD vans are open. Even
if one tire were completely worn, it wouldn't be a problem.
IMO, even with a lsd it wouldn't be a problem - because they're slipping
virtually all the time unless you're on a perfectly straight road. How
often
does that happen?
Floyd
#7
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One way of doing it might be (though I am not sure) if you just jack up one corner, if you can rotate that wheel its no LSD, and if you cant its LSD...then again this is probably wrong:-) |
other wheel turns the opposite way it's a normal diff, if it turns the same
way it's limited slip.
As somebody already pointed out, the wheels are almost always turning at
different speeds anyway so a bit of tyre wear isn't going to cause a
problem. I would be more concerned about the handling because the worn
tyre will tend to break away earlier in the wet and the car's back end will
slide out more easily turning one way than the other.
#8
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AWD diffs are open. All the diffs on my AWD vans are open. Even if one tire were completely worn, it wouldn't be a problem. IMO, even with a lsd it wouldn't be a problem - because they're slipping virtually all the time unless you're on a perfectly straight road. How often does that happen? |
different sizes will mess that thing up :-(
Richard
#9
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IMO, even with a lsd it wouldn't be a problem - because they're slipping virtually all the time unless you're on a perfectly straight road. How often does that happen? I'm trying to think what my olds all wheel drive has...because I know different sizes will mess that thing up :-( |
sizes could cause it to think slippage was happening and lock...
In any case, virtually all recent BMWs have open diffs - M3 & M5
excepted. My '91 E34 has a 25% lsd, which probably wouldn't
even notice a different-sized tire L/R. A tire has to slip quite a lot
for the clutches to start working...
Floyd
#10
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Hi, I had to replace one of my front tires (stock Michelin MXV4+ 205/55/16) couple of months ago. At that time, tire salesman tried to make me buy two tires instead of one, saying that it is a bad idea to have different sizes of tires on same axle, especially on rear axle in my BMW. He claimed that different treadwear on rear axle tires makes wheels rotate in different speeds (of course), which will ruin differential (hmmm..). Well, I thought this is bullshit, and even if it wasn't it doesn't apply to me because I'm having new tire on front wheel. In addition, the rest of the tires had a pretty good tread wear left (6mm), so I just bought one tire to replace broken one. Now it is time to do a tire rotation, and I'm hesitating because of this salesman's words. Tell me if he is true with his claim that putting new tire (8mm of tread left) back with one of the original ones (5.5mm of tread left) will break my differential in long run? I just calculated that 2.5mm difference in wheel radius makes 15.7mm in circumference, which means that old one makes one additional round every 126 rounds = 251 meters. Is he right? |
straight line? Think of what all those nasty corners are doing to
your poor car
.He's full of it. Absolutely full of it.
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