Tires: How many to change at once?

[SHO307]

The question stems from some information I got at the dealer today. The OEM tires will be coming up for replacement soon, and I had thought that I would replace them in a progressive manner---that is to say, I'd do two first, and then the other two later.

The service writer and I were discussing this as I was picking the car up from an oil change today. He says that you can't change the tires that way, or I'll burn up the AWD PTU.

What's the real story? It sounds plausible, but I can't help wondering if the service writer's just trying to bring in some extra money for the dealership.

 

[Irish Pride]

When leaving the Minn. convention in 2012 Kirk Doucette hit a pothole in his 2010 SHO and put a small hole in the side of one of the tires. A group of us hung out for a couple hours while he got it sorted. Took several phone calls to find a tire dealer that had the tires he needed. When he got there he found out that they would not sell him just one tire or two. They would only sell him a set of 4 at a time and they told him the same exact thing that you were told. The mixture of old/new would do harm to the AWD. I think they gave him trade in credit towards his 3 good used tires and applied it to the new set. I don't know if its true or not but that's what he had to do to get back on the road.

 

[thebigjimsho]

I think that in theory, this may be true. However, most tires carry the same characteristics from 100% tread down to about 20%. Most. If you had 2 that were bald and 2 brand new and the bald ones had no traction, you'd mess up the algorithms somewhere. If the two you weren't replacing had plenty of tread left and are of good quality, you'll be fine.

Nevertheless, if you keep the tires properly rotated, they'll last longer. It means you pony up for 4 all at once, but the cost in the long run is less...

 

[SHOdded]

If you decide to replace 2 at a time, and someone actually does this for you, I'd go with the same tire to maximize the efficiency of the AWD (including braking) system. Even if tires are rated similarly, you really don't know what will happen at the limits, which is really the important thing. Even if you drive conservatively, you cannot predict when you will need the max capabilites of the car.

The advantages of doing all 4 at the same time are a) you get to choose the tire YOU want, and b) the AWD system works at peak efficiency.

 

[rubydist]

on any all wheel drive vehicle, it is very important that all of the tires have the same rolling radius, as close as the tolerances of the tires allow. This keeps all the wheels rotating at the same rpm and reduces the 'slippage' of the f/r transfer case asm. This is why it is important to rotate the tires regularly so the tread depth stays as consistent as possible from tire to tire, and why the rule is to always replace all the tires as a set.

If there is a significant difference in the rolling radius (even 1-2%) then the transfer case must always be adjusting for that and can overheat and fail/wear out prematurely. This is obviously more of an issue if you drive for extended periods of time at highway speeds compared to drive at city speeds for short periods of time.

I always suck it up and replace all 4 at once on all wheel drive and 4 wheel drive vehicles.

 

[integrity6987]

Here's my experience with AWD. Before this SHO I had a 04 Vue Red-line with 3.5L Honda engine and AWD.

Drove that car 120K - thru 3 sets of tires. Almost all of these miles are very straight and level highway. I keep my cars well maintained and always rotate tires with each oil change every 5K.

In each case, including now with the new SHO, the tires begin "cupping" - this does not noticeably impact performance (traction in rain/snow - even in cornering) that I can tell. This is however annoying because it does increase the road noise.

For these cars I have always replaced all 4 at one time. I can't change how /where I drive and believe the wheels are properly aligned and balanced at all times. So I accept this as common for AWD.

Anybody else have this experience?

 

[rubydist]

usually, the tires cup from too little toe-in. in my opinion, the manufacturers provide a range of acceptable toe-in that allows them to be toed out more than they should, and if they are toward the 'high' end of that range, then they will cup.

I have also found that certain tires will cup no matter what you do, and on the exact same vehicle other tires will not cup, even at the same toe setting. This is one reason I do not like/buy General tires, because the vast majority of the tires with which I have had that problem have been Generals.

 

[integrity6987]

Going to put a new set on Candy this fall. Will ask for low end of toe-in spec when aligned. Thanks for the input.

 

[Racer X]

All 4 must be replaced at the same time, and this is especially true for cars with Haldex sourced running gear like the SHO is.

On the Volvo V70R and S60R (both running the same Haldex AWD system), having mismatched tires would cause the car to eat the angle gear like a bag of Lay's. Can't say the same holds true for the SHO, but why be the one who has to find out the hard way?

 

[SHO307]

So...looks like the verdict is do all four at once.

Okay. I felt a need to call in some BS detectors on this one, just to be sure. We ran some prices this afternoon at the Ford place, and compared between Ford, Tire Rack, Discount Tire, and Walmart. Walmart and Discount Tire didn't even have the right size either in-stock OR at the warehouse, so that put them out. The difference between TR and Ford was really negligible---less than $9 for four Pirelli Cinturato P7s, less than $6 for four Continental DWS's, either brand in the stock size. The Continentals were the least pricey, in a comparison between the OEM Michelins, the Pirellis, and the Continentals.

Michelin's always been pretty good quality, but you're gonna pay for that name. Pirelli, surprisingly enough, was less than Michelin this time. I'm leaning toward the Conti's, unless somebody here can give me a good reason not to.

 

[Crash712us]

The conti DWS is a excellent choice. But with all AWD drive cars replacing a four tires is standard practice. However discount tire or tire rack you can order a tire shaved down to match the wear of your other tires. This helps off set the cost of hitting *** hole and having to buy 4 new tires.

 

[esfoad]

My experience:
I bought the Conti DWS's for my Vette. Great tire. Smooth, quiet and seem to handle great though I dont't drive the car at 10/10ths.
When it came time for tires for the SHO, I found the P7's. The lifespan of the P7's made me want to try them, especially after reading great reviews about a quiet ride. So I bought them and they are also great. Again, I don't drive the car hard.
Bottom line, both are excellent. Others may chime in with preference based on driving characteristics but in my opinion you cannot go wrong with either.

 

[Turbosixx]

Ok, I'm in need of front tires on my PP SHO. My rear tires still have plenty of tread left. There's no way I can just replace the front tires with the same tire?

My front tires are already down to the wear bars, rears are no where near. With that said I know my front tires are already slightly smaller in diameter than my rears. Not one issue with my awd system.

I have an appointment to have the two fronts replaced tomorrow.

 

[SHOrod]

Ok, I'm in need of front tires on my PP SHO. My rear tires still have plenty of tread left. There's no way I can just replace the front tires with the same tire?

My front tires are already down to the wear bars, rears are no where near. With that said I know my front tires are already slightly smaller in diameter than my rears. Not one issue with my awd system.

I have an appointment to have the two fronts replaced tomorrow.

I think the consensus would be, "Not recommended, but possible." From this point forward though, you should really consider rotating the tires to even the wear. If rotated properly you will not run in to a situation where only 2 of the 4 tires are wearing at such a drastically different rate.

-Rod

 

[Turbosixx]

Thanks!

 

[Turbosixx]

Two front tires changed and all is good.