Can you replace only two tires on the SHO?

[Bullitt5094]

Somewhere along the way the toe-in got out on my 2016 SHO. Of course it was toe-out so all the wear was on the inside of the tire where I didn't see it until I started to rotate the tires. The rear tires are fine and have a lot of tread left. Do I need to replace all the tires because this is and AWD car or is a slight mismatch in tire circumference harmful to the transfer case on our cars? The internet is all over the place on this. I don't think our cases ever lock up completely but I'm still interested in input from those that understand the construction and operation of our transfer cases better. I certainly don't want to wear out any clutches.
Thanks!

 

[bpd1151]

Recommendations have been consistent across the years to replace all four at once.

When you say there's "lots of tread left" on the rears, have you measured the depth? Would be better knowing how many thousandth's you actually have.

From my own research (albeit years ago) when I was desiring a staggered set up (which I ended up actually doing) I recall the variance between the front and rear's had to be between 3%-4% in order for the AWD system to "play nicely".

So as long as the new set (presuming you'll go with just two new shoes up front) and whatever tread is remaining on the rears falls within that tolerance percentage, I'd say you'll be fine.

If it'll end up outside of that, then you're better served to do all four. Hope that helps. Happy New Year.

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[Texas Marauder]

Yes, you can replace just two tires. If needed, you can replace one tire. The difference in circumference between a new tire with 10/32 tread and a worn out tire with 2/32 is approx. 5/8 of an inch. Negligible difference. Also, you should always have the new tires mounted on the rear.

 

[Bullitt5094]

Interesting Michelin video. But it really doesn't address the AWD situation which is what concerns me. At the end it does list AWD but not until then. And 5/8" on every tire rotation adds up pretty quickly in my book. I'm really more interested in how the difference in axle rotation is dealt with in the transfer case in our cars. I'm pretty sure I'm going to go ahead and replace all of them. But I'm interested in the answer to that question. If you think about it, there is wind-up every time you go around a corner. Side-side is handled by the differential, but I'm sure the wheels in the back and front track differently enough to cause some front to rear wind-up on every corner too. Or I would believe so...

 

[Majestic]

The SHO is not AWD.

 

[bpd1151]

From what I recall....

FWD bias (70%)

Remaining 30% dumps to the rear.

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[Texas Marauder]

Interesting Michelin video. But it really doesn't address the AWD situation which is what concerns me. At the end it does list AWD but not until then. And 5/8" on every tire rotation adds up pretty quickly in my book. I'm really more interested in how the difference in axle rotation is dealt with in the transfer case in our cars. I'm pretty sure I'm going to go ahead and replace all of them. But I'm interested in the answer to that question. If you think about it, there is wind-up every time you go around a corner. Side-side is handled by the differential, but I'm sure the wheels in the back and front track differently enough to cause some front to rear wind-up on every corner too. Or I would believe so...

5/8 inch is the difference between new and worn out.

The RDU never locks up. It is an electronic clutch. There is always some slippage.

 

[Texas Marauder]

From what I recall....

FWD bias (70%)

Remaining 30% dumps to the rear.

Sent from my SM-S928U using Tapatalk

With FORScan you watch percentage of engagement of the RDU. It varies from 3.53% to 80+%. Normal stopped and steady state driving is 3.53%. Normal take off from a stop light is 25-35%. It's interesting to watch. I don't know how that translates to power transfer.

 

[Jordan_R]

Yes, you will be fine replacing only two tires.

 

[Zpak]

If it really bothers you, good tire shops can shave new tires to match the tread depth of your existing two.

I’ve done it once because I blew out a sidewall and had to replace only one.

 

[SHOrod]

Our PTUs have no clutches, no electronics, they simply mechanically split where the torque goes but as mentioned above, the rear wheels are engaged by the RDU which is where the electronic clutch resides.

-Rod

 

[1636mcs120]

Yes, you can replace just two tires. If needed, you can replace one tire. The difference in circumference between a new tire with 10/32 tread and a worn out tire with 2/32 is approx. 5/8 of an inch. Negligible difference. Also, you should always have the new tires mounted on the rear.

Funny, would’ve thought with a FWD vehicle, you’d want the new tires up front for better traction.

 

[PaulTAutoX]

Funny, would’ve thought with a FWD vehicle, you’d want the new tires up front for better traction.

Mfr's recc is always conservative, which translates to "never let the vehicle oversteer off of the road". So they usually say put the good ones on the back. This may go back to when they gave performance RWD cars open diffs so that the application of power coming out of a corner didn't cause it to go off, just spun up the inside tire. Most tires these days will have better dry traction at the limit with lower tread depth. This equates to lower tread block squirm/deformation.

Of course more tread depth = better rain traction, so it could go either way, though front traction in the rain will generally mean less water on the rears that are following in line. On my Subie the mfr says not to have more than (IIRC) 2/32" difference between any tires, I might be off by a 1/32 there. I've ended up having to replace 4 when I was well into the tire life and two got road damage. And I've actually taken a new tire and had it shaved down to average depth of remaining tires when they had 75% life left and I lost one due to road hazard. That way I didn't have to pay for an entire new set.

So to the OP I'd say look in the owner's manual for guidance. You can also get pulling to one side behavior under power/braking when the tire diameters are different. I've not seen this on the Gen II Taurus FWD but have seen it on the AWD Subaru (STI).