PIU - replace tires individually or in axle pairs/all 4?

[KayGee]

I know a lot of people like to post about how sensitive the PTU and AWD system is to tire sizing and many claim tires need to be replaced in axle pairs or even all 4 at the same time (5 if you include spare). Apparently that is not the case with the PIU and you can replace a single tire with a new one, even if the other 3 are completely worn - basically, no need to replace in pairs.

Major dissimilar tire sizes between the front and rear axles (for example, 17 inch low profile tires on the front axle and 22 inch high profile tires on the rear axle) could cause the AWD system to stop functioning and default to front-wheel drive or damage the AWD system. However, the AWD system is capable of tolerating any combination of new and worn tires of the same original tire size. For example, using 3 worn tread tires and 1 new tread tire all of the same original tire size, can be tolerated by the AWD system.

http://www.fordservicecontent.com/F...tleSelected=G1748348&topicHRef=G1748349&div=f

The statement about the low and high profile tires is awkward as I assume they are talking about rim sizes and the tire profiles would be the opposite of their statement (17" rim would have a higher profile tire than a 22" rim). Also, it shouldn't make a difference to the AWD system what diameter rims are used on the front or rear axle as long as the overall diameter/circumference of the tire/rim combo is the "same" for both.

 

[ScooterMcGee]

That's good and very useful information, thanks for posting this. There is a lot of whacky obsession over this topic.

I did have concerns about using the new spare tire, when the other three are always going to be further worn down, when on a long trip away from home. Would traveling the 300+ miles back home wreak havoc, would I make it before the PTU fails etc. etc. No worries any more!!

 

[kobresia]

It would probably still be a good idea to keep the spare in the rotation. However, of the Interceptors I've purchased which still had the spares, all but one were clearly unused, probably the spare they left the factory with, so it would seem a lot of fleets aren't in the habit of doing so. One more, and I'll have a full set of brand-new Goodyear Eagle RSA tires & rims...

 

[edougawa]

Thanks for bringing it up.
It sounds more like a sales strategy from the shop to sells more tires. I was told I need to replace all 4 tires when I went to replace a completely flat tire for my friend's Mercedes. Maybe Mercedes is more sensitive, or maybe I just got tricked.
Anyway, it's good to know my PIU doesn't need to replace all tires at once, as they are really expensive (somehow 200+USD each).

 

[eeeaddict]

I know a lot of people like to post about how sensitive the PTU and AWD system is to tire sizing and many claim tires need to be replaced in axle pairs or even all 4 at the same time (5 if you include spare). Apparently that is not the case with the PIU and you can replace a single tire with a new one, even if the other 3 are completely worn - basically, no need to replace in pairs.

Major dissimilar tire sizes between the front and rear axles (for example, 17 inch low profile tires on the front axle and 22 inch high profile tires on the rear axle) could cause the AWD system to stop functioning and default to front-wheel drive or damage the AWD system. However, the AWD system is capable of tolerating any combination of new and worn tires of the same original tire size. For example, using 3 worn tread tires and 1 new tread tire all of the same original tire size, can be tolerated by the AWD system.

http://www.fordservicecontent.com/F...tleSelected=G1748348&topicHRef=G1748349&div=f

The statement about the low and high profile tires is awkward as I assume they are talking about rim sizes and the tire profiles would be the opposite of their statement (17" rim would have a higher profile tire than a 22" rim). Also, it shouldn't make a difference to the AWD system what diameter rims are used on the front or rear axle as long as the overall diameter/circumference of the tire/rim combo is the "same" for both.

I'm a bit late but the statement is bullshit in my experience. PTU blew up really early from 1 tire being new. YMMV

 

[KayGee]

I'm a bit late but the statement is bullshit in my experience. PTU blew up really early from 1 tire being new. YMMV

The info posted is from Ford. If you think it's bullshit, maybe you should write them and let them know how you feel.