Differing tread depth...Problems? (1 Viewer)

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Joined
Jan 25, 2008
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Location
Opelika, AL
Will having 2 different tread depths reak havoc or have negative effects on drivetrain? for example: 2 new tires and 2 50% worn tires. From what I've been told it does on full time 4wd. It's kinda hard to believe that 1/3 of an inch or less would cause that much trouble on something that should be engineered to perform with inconsistencies since tread wear is a fact of life and uneven tread wear is too, for those of us that don't get their alignment checked like they should. :eek:
 
My understanding was that you need ALL 4 tires to be within the allowable tolerance of each other. I've seen the following guidelines (probably depending on manufacturer etc):
within 1/4" to 1/2" cirumference of each other, or measure another way they need to be within 2-4/32" tread depth of each other.

For example if one tire was 5/32" and the rest are 8/32" tread depth, then you have a problem that can damage your driveline. If your two front tires are 5/32" and your two rear are 8/32", as long as you're driving straight you're in good shape but when you turn the front and rear tires are travelling at different speeds and this is where I believe you are putting extra strain on your driveline.

One service I think some shops provide is to shave the tires - so if you buy 1 new tire which is 10/32" and the rest are 8/32", you can pay ~30 bucks to get the new tire shaved down to 10/32". I don't know how well accepted this is, but tirerack offers the service and suggest it as a way to deal with this problem. My local Lexus dealership didn't offer the service.

Here's a link from tirerack on the topic: Tire Tech Information - Matching Tires on Four-Wheel Drive and All-Wheel Drive Vehicles

Curious whether replacing 2 alone is really OK or not. Anyone have more info?
 
With L.C. size tires, about a half inch difference in tire diameter (about a quarter inch of tread wear) means a difference of about 10 tire revolutions per mile. How much difference is ok for the center or axle differentials, and over what period of time? When the CDL is on, it seems like a good idea to have the same diameter tires on the front and rear axles. With tire size differences, are ATRAC and VSC computers affected in loss of traction or skid situations?

Several sites provide calculations for even small differences in tire sizes.

Tire size calculator
 
My understanding was that you need ALL 4 tires to be within the allowable tolerance of each other. I've seen the following guidelines (probably depending on manufacturer etc):
within 1/4" to 1/2" cirumference of each other, or measure another way they need to be within 2-4/32" tread depth of each other.

For example if one tire was 5/32" and the rest are 8/32" tread depth, then you have a problem that can damage your driveline. If your two front tires are 5/32" and your two rear are 8/32", as long as you're driving straight you're in good shape but when you turn the front and rear tires are travelling at different speeds and this is where I believe you are putting extra strain on your driveline.

One service I think some shops provide is to shave the tires - so if you buy 1 new tire which is 10/32" and the rest are 8/32", you can pay ~30 bucks to get the new tire shaved down to 10/32". I don't know how well accepted this is, but tirerack offers the service and suggest it as a way to deal with this problem. My local Lexus dealership didn't offer the service.

Here's a link from tirerack on the topic: Tire Tech Information - Matching Tires on Four-Wheel Drive and All-Wheel Drive Vehicles

Curious whether replacing 2 alone is really OK or not. Anyone have more info?

With L.C. size tires, about a half inch difference in tire diameter (about a quarter inch of tread wear) means a difference of about 10 tire revolutions per mile. How much difference is ok for the center or axle differentials, and over what period of time? When the CDL is on, it seems like a good idea to have the same diameter tires on the front and rear axles. With tire size differences, are ATRAC and VSC computers affected in loss of traction or skid situations?

Several sites provide calculations for even small differences in tire sizes.

Tire size calculator

I just can't believe that the driveline would be so volatile as to be damaged. After I think about it more....what is a differential for? to differentiate between the two sides of the axle traveling at different speeds. So if I turned my steering wheel to the left and drove around in a circle for 20 miles my axle would explode because the passenger side tires turned a ton more revolutions than the driver side tires? Somehow I don't think so.

As far as having the center diff on...I don't believe you should be driving on the pavement with it on and it should be fine offroad since the friction on dirt vs. pavement is less...the tire can slip. That goes for lockers too. Maybe someone with greater knowledge on that last part can chime in.
 
Just to be clear - I didn't say anything about the center diff being locked. If the center diff is locked, all the tires could be exactly the same diameter and if you drive in circles you'll bind your driveline.

From what I had read everywhere (reputable sources included) they say different size tires will cause an issue for AWD cars - no qualifications on limited slip differentials only, etc. However your question "isn't that what differentials are for" makes sense. Unfortunately I can't find definitive explanations. I wasn't able to find anything in the FSM about the allowable differences in tire circumference/diameter/tread depth. In fact even more surprising (if it were really a problem) is that in the owners manual there are two pages that talk about replacing tires (for 05 lx470 p.393 and 394 http://drivers.lexus.com/lexusdrive...45U&href=xhtml/OM60B45U_OM0023.html&locale=en).

Here's what it says:
"Tire selection
When replacing a tire, use a tire of the same size and
construction, and the same or greater maximum
load as the originally installed tires. Also, all the
tires must be the same brand and have the same
tread patterns.
Using any other size or type of tire may seriously affect
handling, ride, speedometer/odometer calibration,
ground clearance, and clearance between the body and
tires or snow chains."

Nothing about damaging the vehicle's driveline etc. As far as when it describes if a tire is damaged or tread is worn down below tread bars etc *the* tire should be replaced. Doesn't say anything about replacing more than the single tire that needs to be replaced.

The only other 2 explanations I can think of are:
1) having two sides of the diff constantly at different speeds is not what it was intended for (really only intended for turning), so forcing the two sides of the diff to always work at different speeds could cause excessive wear and premature failure?
2) with limited slip differentials or mechanically locking differentials there would be definite damage if they're constantly working due to different size tires. However, my understanding is that LC100s (at least 2000 and up) don't have limited slip differentials.

So, maybe someone that understands more can clarify - by this reasoning, if front/center/rear diffs are all open, you can replace any one tire and ignore the difference in tread depth. The original poster should be able to just replace the one tire, no need to replace both on one axle even? Would like to see what others can explain on this topic.

While digging for more info, I found this old school explanation of how differentials work - amazing how when the technology is new, the decisions and steps to get there make more sense but when we're light years ahead of where axles were with horse and buggy, it's hard to find a good explanation of how the evolution occurred and why. This video gave me some of that insight. (first minute of the motorcycle troop is a waste).

YouTube - How Differential Gear works (BEST Tutorial)

- Art
 
I was responding to tha 2nd quote when i was speaking of tha center diff being lockd.
 
Was never able to find anything definitive on this. On one hand we have an open center diff so as long as each axle has same tread depth (within tolerance) mechanically it shouldn't hurt the driveline.

However, couldn't different wheel speeds could throw VSC/ABS off? Should that be a concern?
 
No, just turning a corner causes different wheel speeds.

(Sorry to the OP for the 'hijack' - we know your intent is not to run different size wheels long term, but it brought up a great topic)

Toyota/Lexus have us covered with the Steering Angle Sensor that works in conjuncion with ABS and VSC - not only does the vehicle account for wheel speed difference while turning but it uses it as an input. At a basic level, VSC uses the steering angle and speed sensors (and yaw rate sensors and other sensors) to detect and prevent understeer/oversteer and brake on the wheel that needs it.

And as far as ABS, see below from the FSM's description of the ABS with EBD Function:
"This function controls the brake fluid pressure acting on the wheel cylinders to help prevent the wheels locking and thus helps to maintain good directional stability and steerability on slippery surfaces and during panic braking.
Based on the signals received from the speed sensors, the EBD detects the difference in the speed between the front and rear wheels, and operates the brake actuators to control the fluid pressure in order to effect an appropriate front/rear wheel braking force distribution in accordance with the vehicle’s driving conditions. This functions like an electronic load-sensing proportioning valve."

I would expect 4mph difference b/w front and rear axles to throw off this feature as well.

Look - huge deal? I don't know. Does it make a difference to VSC and ABS - seems pretty clear to me that it does. I can't say how much of a difference or what the tolerances are for the system (in terms of tread/diameter difference what's the threshhold - 1/16, 1/8, 1/2, 1", and in terms of wheel speed is it .5, 1, 2 mph difference) but the VSC and ABS systems are sophisticated and rely on the data they are getting from various sensors to make decisions that can save our lives. Bad inputs = bad outputs.

A quick search on VSC and ABS and Different Tire Sizes will yield many other toyota (and other manufacturer) forums discussing the same topic.


FWIW (without supporting data/evidence I don't give it much weight) most posts seem to agree that all tires same size even if they're different from stock is ok for vsc and abs (although there are references from FSMs that a different wheel size than stock can cause problems with ABS), but different sizes on same vehicle (regardless of configuration - same on each axle or not) can cause issues with VSC and ABS.
 
I wouldn't worry about it at all to be honest with you. Make sure the more worn are on the same axel, and just keep doin your thing.
Go do some donuts in your LC, drive around without an alignment to wear down your new tires some, and then you'll be good :p
 

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