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Just had new tires put on my 05 e250. I didn't notice until today, the shop installed the wrong tire size on the drivers side (235/70/16) and the right size on the passenger side (245/75/16). I drove about 150 miles between yesterday afternoon and today before I noticed.

Just brought back for correct size, but I am concerned if any damage could have been done to the rear differential? I'm not familiar with this sort of thing, so in hoping to get experienced opinions.

Thanks.
 

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No problem
The rear is designed to handle different tire speeds since when making turns one spins more than the other.
 

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Doh makes perfect sense. Wasn't thinking clearly in the rage I was feeling with the shop that did it.
 

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Obviously you do not have a limited slip differential (or the clutches need to be replaced).

As other said, no problem at all.

Tom
 

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There would have to be a lot more difference in speed between the 2 before the clutches would engage.

What you basically got is a warn tire and new tire difference in size. If you had a 18" on one side and a 16" of the other then perhaps that could have caused issues.
 

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There would have to be a lot more difference in speed between the 2 before the clutches would engage.

What you basically got is a warn tire and new tire difference in size. If you had a 18" on one side and a 16" of the other then perhaps that could have caused issues.
The clutches are always engaged. Change in radius (turning) or diameter cause the friction discs to slip on the thurst plates.

With the sizes listed in the OP the rolling diameter difference is 1.5". The clutched would slip.

Tom
 

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The clutches are always engaged. Change in radius (turning) or diameter cause the friction discs to slip on the thurst plates.

With the sizes listed in the OP the rolling diameter difference is 1.5". The clutched would slip.

Tom


Sorry I should have said LSD engaged. I still don't think it's 1.5"

My calculation shows less than 19mm difference which is nothing in LSD terms. Even a ABS sensor wouldn't pick up on that difference. I could be calculating this wrong though

The 235 is coming out as 164.5mm
The 245 is coming out as 183.75mm
 

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Discussion Starter #10
I had measured quickly from the floor to the wheel well with around a 1" difference, didn't actually measure the tire. I'm not sure if it is an lsd, the original owner mentioned something about it or could it have been posi? Not sure, but everything sounds and feels alright for now.
 

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Sorry I should have said LSD engaged. I still don't think it's 1.5"

My calculation shows less than 19mm difference which is nothing in LSD terms. Even a ABS sensor wouldn't pick up on that difference. I could be calculating this wrong though

The 235 is coming out as 164.5mm
The 245 is coming out as 183.75mm
Limited slip differential are normally engaged, they slip after a certain amount of torque is applied to the clutches.

My math puts them at 1.5" difference. Just to make sure I did not screw up, here are a couple of links for the sizes tires. Overall diameter in the specs. I just picked one brand and line I felt would work on the van.

http://www.tirerack.com/tires/tires...REVO2OWL&vehicleSearch=false&fromCompare1=yes

http://www.tirerack.com/tires/tires...REVO2OWL&vehicleSearch=false&fromCompare1=yes

All of this is out of the mold. I know rolling diameters change due to load, air pressure, road surface.

The 235 has a circumference of 7 feet 7 inches (rounded). To travel one mile the tire will need to rotate 696 times (rounded).

The 245 has a circumference of 8 feet (rounded). To travel one mile the tire will need to rotate 660 times.

There is a difference of 36 revolutions in one mile, or 273 feet.

In the 150 miles the van traveled, the 235 made 5400 more revolutions, and travel 40,950 additional feet (about 7.75 more miles).

The planet pinions (aka spider gears) will be in play to make up this difference. If there is a limited slip differential in the vehicle, the clutches will have to slip to allow the planet pinions to do what they are designed to do.

You are correct about the about the ABS, but not for the reason you set forth. The reason the ABS will not see the tire size difference is the rear ABS does not sense the individual rear wheels in this application. The ABS tone ring is sandwiched between the ring gear carrier and the ring gear, the sensor enters the housing from the front top on a slight downward angle.

Reading Nick's last post something called his attention to the problem, the sound was most probably the clutches or pinions working (again depends on limited slip or not)

Tom
 

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It's easy to calculate the tire wall size. If it's a 235-70-15 then that means the profile size is 70% of the tread width.

If it was a 235-80-15 then it's 80% of the tread width.

Well that's how it was explained to be years ago. But that could be wrong.

If that's still the case i don't see how a Diff can sense such a minute amount when ABS sensors couldn't even sense that even at 15x a second.
 

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It's easy to calculate the tire wall size. If it's a 235-70-15 then that means the profile size is 70% of the tread width.

If it was a 235-80-15 then it's 80% of the tread width.

Well that's how it was explained to be years ago. But that could be wrong.

If that's still the case i don't see how a Diff can sense such a minute amount when ABS sensors couldn't even sense that even at 15x a second.
Beyond easy.

Yes, the second number is the aspect ratio expressed in percentage of the tread with.

To show my math-taking the sizes in the original post;

235/70/16 70% of 235mm returns a sidewall height of 164.5mm

245/75/16 75% of 245mm returns a sidewall height of 183.75mm

16" wheel converted to metric is 406.4mm

164.5 + 406.4 + 165.4 = 735.4mm overall height

183.75 + 406.4 + 183.75 + 773.9mm overall height

735.4mm = 28-15/16"

773.9mm = 30-7/16"

30-7/16" - 28-15/16" = 1-1/2"

Like I said, I know how to do this and my math is correct.

Look at the difference in feet traveled per revolution, something balance that difference. That job falls to the planet pinions in the differential. The slightest change in one axle speed as opposed to the other will cause the planet gears to rotate at different speeds. Just shifting the steering wheel from side to side going down the street will cause a change in axle speeds. A limited slip differential planets will not react as quickly as an open differential.

As I stated above the there are not left/right attenuator (tone rings) on the rear of the van in the original post.

Tire size has nothing to do with the anti lock brakes. The change in rolling wheel speeds (not under a stop) (side to side) has nothing to do with the anti lock brakes. The change in tire size side to side will not affect the anti lock brakes.

If how (I think) you believe the anti lock brakes work, explain to me why the system is not screwed up when you make a turn. The front wheels do have separate tone rings. Anti lock brakes work by sensing the rate of change while stoping. If the sensors returns a signal that tells the processor the wheel has gone through a rapid deaccelertion rate that will lock the wheel the system will pulse the fluid to the wheel in question (in the case of the van in the original post, if it sees a possible rear wheel lock both brakes are pulsed). You could have a 12" tire/wheel assembly on one side and a 48" tire/wheel assemble on the other side and the anti locks, while the vehicle is rolling will have not affect on the ABS.

Tom
 

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No there's 19mm of difference in tread death. As I said it's the difference between a worn tire and a bald tire. Your adding both tread depths to get your total for complete tire size. It still leaves 19mm which as I said above and before that's like running a warn tire and a new tire.

Also when I say that's not even enough for a ABS sensor to calculate I'm talking about when one wheels spins faster than the other. So under acceleration and braking the ABS censors would notice one tire is slower or faster than the other because the difference in size they either cut power or activate the ABS. but either way it would still not be enough to cut either of them on.

So basically if his ABS lights didn't come on then it's highly unlikely his diff was even affected.
 

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No there's 19mm of difference in tread death. As I said it's the difference between a worn tire and a bald tire. Your adding both tread depths to get your total for complete tire size. It still leaves 19mm which as I said above and before that's like running a warn tire and a new tire.

Also when I say that's not even enough for a ABS sensor to calculate I'm talking about when one wheels spins faster than the other. So under acceleration and braking the ABS censors would notice one tire is slower or faster than the other because the difference in size they either cut power or activate the ABS. but either way it would still not be enough to cut either of them on.
Show me the math where it proves there is only a 3/4" difference.

There is 1.5" difference, not only does my math prove it so does the website links I posted. I'm not adding 2 tread depths, I'm adding 2 sidewall heights, the measurement is taken from bead edge to outer most point. I'm pretty sure the manufacture knows what size their tires are.

ABS does not sense well speed difference between the corners, it senses deceleration rate at each wheel. Again explain how the system would not be screwed up when your turning. The front wheels have separate tone rings and the inner and outer wheels are spinning at very different rates. The ABS could care less what the rolling wheel speeds are, it senses rate of change during deceleration.

Any change that cause one wheel to travel farther than the other cause the planet gears to react.

Lets take a 10 mile diameter circle at the inner wheel, a nice slow curve.
The inner circumference is 5280' x 10 x 3.141593 = 165,876' 1-1/8"

The rear track of a 2010 F 250 is 5' 7-3/16".

The outer circumference is (5280' + 5' 7-3/16") x 10 x 3.141593 = 166,051' 11-7/8".

In the above example the outer wheel travels an additional 175' 10-3/4". As small as that distance is considering the entire circle, the planet pinions had to rotate to keep the axles in harmony.

Tom
 

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Tom you do know your stuff on a lot of things but you don't seem to have the first clue here.

Let's clear some things up and see if I can make this simple for you.

He gave the tire sizes. It's extremely simple math. The measurements are on his tires. Calculating them measurements gives you the wall heights of the tires yes?

The wall height is 19mm different on the circumference of the tire. Call it more or less at 19mm. That 19mm is like running a warm tire compared to a new tire is it not.

We don't need to calculate the difference in rotation as its not gonna matter to the diff at them amounts.

You know how a LSD works right? The LSD acts like as a standard open differential when a car is moving straight or the rotational difference between left and right wheels are similar. As an example going around a corner. Once there is a rotational difference among wheels under power the cross axis which is set in the middle will press the pressure rings, then the pressure rings will transfer the movement to the clutch plates. When all the clutch plates are engaged, both wheels are locked and the torque is transferred equally to both wheels.

So to me the difference of a wheel that size is no different than the difference in speed between a inner and out wheel going around a corner.

There's a lot of info available on the net about how a LSD functions of you don't believe me.

Also ABS sensors are extremely sensitive. Depending on what brand you have. dodge systems ain't that good as I found out my self. But the ABS sensors are what control ABS, Traction control, RSC, etc etc. they can detect extremely small differences in wheels speeds and control the power to all 4 wheels in most vehicles. They can on most vehicles detect a wheel size difference of even a 1/4" on some vehicles and will give a warning light in most cases too. My brother sees it a lot because people are too cheap to replace all tires when they get a puncture of they stuff install complete different size tires.


Here's a good video breaking down how a LSD works. http://youtu.be/ujsxq9WBllU
 

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35rev a mile is nothing for a diff. Going around a roundabout will prob give you 10x that difference between in and outer wheels.

Of course all my info is worthless if you are going around corners under lots of power breaking traction on the inside tire then yes your clutch plates would have engaged(LSD activated to make Tom happy) but on straights there wouldn't have been enough difference in rotation to engage the LSD. What that rotation difference is depends on your diff but it's a work vehicle not a drift car or drag car so it's break away TQ is not that aggressive in that respect as
 

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Really would not be a lot diferrent the running a low tire. If it was a 4x4 and front to back that kind of difference then could be a problem. Short term not much of a problem, long temp could maybe be.
 

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Really would not be a lot diferrent the running a low tire. If it was a 4x4 and front to back that kind of difference then could be a problem. Short term not much of a problem, long temp could maybe be.

Space saver tires would also fall into this category as they are normally quit a but smaller than the stock wheels and tires on most sports models. Yeah you should do more than 50miles on them but that's due to safety and nothing to do with diffs.
 
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