PTU Affected by tires???

[Seraphim.312]

So my SHO was giving me some trouble over the weekend where as I was accelerating there was a loud knocking sound coming from the car and it sounded like it was coming from the driver side front of the car. The knocking would get worse as I would turn the wheel.

I decided to take my car to a Ford dealership for inspection and the mechanic called me back saying that it was the PTU.

He said that I needed new tires because the current tires I had on the vehicle made the computer read a certain way and because of that it would affect the PTU.

I've never heard of tires affecting such a mechanical part of a car before. I recently just bought this car and all the tires match as a set and are brand new so I would believe that this guy is trying to scam me in buying the tires.

Does anyone know if what this mechanic is saying is factual? I can't find it anywhere on Google unfortunately.

 

[Ta2dResqr]

I cannot think of any reason a set of matched tires would affect the PTU. Provided they are all the same size and about equal wear, they should all spin at the same speed (except when turning, or slipping) and should not be an issue.

 

[802SHO]

For a long time I ran 245/40 in the front and 275/35 in the rear, slightly different rotational speed and never had any issues. One of those things that to me seems highly suspect, depending on where you go…the dealership will try to sell you a dream if you are unsuspecting.

 

[joe raptor]

Time to take it to another shop and have a different opinion !!!

 

[Shadow351]

Yep, Get a second opinion. Mismatched tires might cause the computer to over-actuate the clutches in the RDU, but the PTU is basically a 90 degree gearbox, it is completely mechanical.

 

[Seraphim.312]

For a long time I ran 245/40 in the front and 275/35 in the rear, slightly different rotational speed and never had any issues. One of those things that to me seems highly suspect, depending on where you go…the dealership will try to sell you a dream if you are unsuspecting.

Can you elaborate?

 

[Seraphim.312]

Time to take it to another shop and have a different opinion !!!

I think thats what im gonna do.

 

[Seraphim.312]

Yep, Get a second opinion. Mismatched tires might cause the computer to over-actuate the clutches in the RDU, but the PTU is basically a 90 degree gearbox, it is completely mechanical.

So in that case tires shouldn't affect it that much right?

 

[802SHO]

Can you elaborate?

Yeah what I mean is dealerships unfortunately take advantage of unsuspecting ppl. So if you have some general knowledge you’ll be able to realize they’re full of ****

 

[RoketRdr]

So in that case tires shouldn't affect it that much right?

Correct. Like what was previously posted the PTU is nothing more than a mechanical reduction gearbox off the transmission. No way mismatched tires can affect that. The RDU and trans would be a different story.

 

[SeanDev]

So in that case tires shouldn't affect it that much right?

Tires can greatly affect the PTU, always make sure you have same tread depth or within a 1/10 on front. Different sizes on the front causes the PTU to turn at different speeds on each side. Not good for the PTU. Reason why AWD is recommended to have tire rotation every 5,000 miles. Plus if your tires are not OEM size, it's a good idea to change the size in the cars computer, easily done with forscan. And if your hearing knocking, especially backing up or turning, look at your sway bar link. When the ball joint goes out the link will make a knocking sound. When the PTU is going out it will sound like rocks in a coffee can. I know all this because its all happened to me at least once. Ford owner for 32 years.

 

[Seraphim.312]

Tires can greatly affect the PTU, always make sure you have same tread depth or within a 1/10 on front. Different sizes on the front causes the PTU to turn at different speeds on each side. Not good for the PTU. Reason why AWD is recommended to have tire rotation every 5,000 miles. Plus if your tires are not OEM size, it's a good idea to change the size in the cars computer, easily done with forscan. And if your hearing knocking, especially backing up or turning, look at your sway bar link. When the ball joint goes out the link will make a knocking sound. When the PTU is going out it will sound like rocks in a coffee can. I know all this because its all happened to me at least once. Ford owner for 32 years.

I guess what I don't understand is tires wear out eventually anyway. Is this car not conditioned to function properly even when the tread starts to wear? I guess that just sounds a little weird to me for a car to do. It was definitely a knocking/clanking sound and the car would shake a lot between giving it a little gas and breaking.

 

[SeanDev]

So in that case tires shouldn't affect it that much right?

Tires can greatly affect the PTU, always make sure you have same tread depth or within a 1/10 on front. Different sizes on the front causes the PTU to turn at different speeds on each side. Not good for the PTU. Reason why AWD is recommended to have tire rotation every 5,000 miles. If you do not have OEM size tires, you can change tire size on the cars computer, forscan makes it easy to do. And if your hearing knocking, especially backing up or turning, look at your sway bar link. When the ball joint goes out on the link it will make a knocking sound. PTU going bad will sound like rocks in a coffee can.

I guess what I don't understand is tires wear out eventually anyway. Is this car not conditioned to function properly even when the tread starts to wear? I guess that just sounds a little weird to me for a car to do. It was definitely a knocking/clanking sound and the car would shake a lot between giving it a little gas and breaking.

It's all about the revolutions per minute when it comes to AWD tires. If the car is doing that while your breaking, definitely have someone look into the suspension or cv axle on that side. Passenger cv axle has a carrier bearing that holds it due to its length. Your symptoms are not good either way, and I personally wouldn't drive a vehicle that was doing that.