Tire Matching

[m85476585]

First of all, I have a 2007 V8, so it's fulltime 4WD.

I bought a set of winter tires (Blizzak WS965) on 5th gen wheels from a co-worker for $200. A good price for the wheels alone, but I'd like to use the tires too. My current tires (Michelin LTX MS2) have about 4/32 left on the rears and 6/32 on the front, so not ideal for driving in the snow this winter.

The tires he sold me have some uneven wear. One of them is at 9/23, two are at 11/32, and one is at 15/32 (does his truck drive with one wheel in the air?). If I buy one replacement from Tire Rack I could have them shave it down to 15/32 (they are 18/32 new) to match the best one, then put the 15/32 pair on one axle and the 11/32 pair on the other axle. Is that too much mismatch for the center diff?

Alternatively I could attempt to shave down the 15/32 tire to 9/32 myself. At that point I could get maybe a season or two of winter use out of them at most. Or I could buy one from Tire Rack shaved to 9/32, but that seems like a waste to spend $200 on a tire then shave off most of the usable life. I don't think there are many tire shops that will shave a tire.

Edit: The tread blocks are connected by rubber higher than the deepest grooves, so the 9/32 tire only has a little over 4/32 left between the tread blocks. Or in other words, when the tires are worn to 5/32 in the groove, instead of individual tread blocks there will just be three solid strips of tread with four grooves between them instead of individual tread blocks.

I found a matching used tire that has about 15/32 left. And based on this thread it sounds like 4/32 mismatch might be OK. http://www.toyota-4runner.org/4th-gen-t4rs/166697-safe-replace-just-2-tires-4wd-v8-2.html

 

[ElZilcho]

It'll be fine. The 4/32nds guideline is for viscous coupling/clutch style diffs (which are always transmitting torque no matter how small the slip angle) and is a relatively conservative guideline. Ours is a Torsen type center diff and only starts to engage if a slip angle greater than 3-5% is sensed. The worst example you described was under 1%. If there is a problem with tire mismatch you'll notice that the ABS and ATRAC activate more frequently and unnecessarily and they will warn you long before you're at risk of mechanical damage. Toyota (and every other manufacturer I know of) recommends replacing fronts and rears as matched pairs regardless of drivetrain (AWD, 4WD, FWD, RWD) mostly because mismatched tires wreak havoc with ABS computers.

They also recommend putting new tires on the rear and rotating older tires up front. This is to bias the vehicle towards understeer... but it completely fails to account for the fact that understeer sucks! Oversteer is the fun one!:eyebrows:

 

[m85476585]

It'll be fine. The 4/32nds guideline is for viscous coupling/clutch style diffs (which are always transmitting torque no matter how small the slip angle) and is a relatively conservative guideline. Ours is a Torsen type center diff and only starts to engage if a slip angle greater than 3-5% is sensed. The worst example you described was under 1%. If there is a problem with tire mismatch you'll notice that the ABS and ATRAC activate more frequently and unnecessarily and they will warn you long before you're at risk of mechanical damage. Toyota (and every other manufacturer I know of) recommends replacing fronts and rears as matched pairs regardless of drivetrain (AWD, 4WD, FWD, RWD) mostly because mismatched tires wreak havoc with ABS computers.

I did some research about Torsen differentials, and it sounds like some difference is not a problem. It's the same as going around a gentle curve, and a Torsen diff works like a regular diff as long as the shaft speeds are not too mismatched.

They also recommend putting new tires on the rear and rotating older tires up front. This is to bias the vehicle towards understeer... but it completely fails to account for the fact that understeer sucks! Oversteer is the fun one!:eyebrows:

The recommendation also doesn't account for the fact that the front tires seem to wear faster. I plan to put the ones with more tread on the front to hopefully even them out.

I drove up to the mountains this weekend and I almost got into an accident at least once, with a couple other close calls. The conditions on I-70 were the worst I've ever seen, and combined with the fact that my all season tires are fairly worn, it was terrifying.

In case anyone is interested...

The forecast was calling for a lot of snow Saturday morning, so we left early. The road was dry until Georgetown and the conditions were normal winter conditions from there to the Eisenhower tunnel. There was surprisingly little traffic. After the tunnel it's something like 12 miles of 6% grade down to Silverthorne.

Coming out of the tunnel, the Icy Road sign was on, but it's often on, sometimes even when the road is clear. It turns out there was a patch of ice a little ways out of the tunnel, and I think everyone slid a little. A semi truck was folloiwng a few feet behind a car. I think he had no traction, and luckily narrowly avoided plowing into the car. I went pretty slow after that, maybe 30mph.

A little ways down, A Subaru Crosstrek spun out and ended up perpendicular to traffic, blocking the center "lane". (There are three lanes and a shoulder here, but the road was completely snowpacked, so the lanes are determined by consensus.) I was a decent distance back when I first saw the car slide out, but when I tried to brake nothing happened, the road was just ice. ABS was going for a couple seconds, but I barely slowed down. I was pretty sure I was going to hit the Subaru, but I was able to move left just enough to avoid it. I think I cut off some people moving faster in the left lane, but thankfully they were able to avoid me. A few other cars were on the shoulder here, at various angles as if they had slid off.

I went 15-20mph the rest of the way down. After the Subaru there were very few cars the rest of the way down, so most people must not have made it past. A couple snow plows passed me at one point, but it was only a little better behind them. And they turned around at the snowplow turnaround halfway down. At the last curve from the bottom of the hill, there was another patch of ice. I saw a semi truck with its trailer sliding sideways 1/2 mile ahead of me. Luckily I was able to get around that too.

When I stopped in Silverthorne to take a break I was shaking. I considered putting on chains, but I saw two snowplows head up the onramp, so I figured it would be fine without them. It's only a few miles to the Breckenridge exit. But when I got back on the highway, the plows hadn't even plowed anything!

At the top of the hill coming out of Silverthorne there was another patch of ice. A pickup was sliding around, and I was having a hard time staying in a straight line when I got close. Luckily he was able to get to the right, along with a couple other cars. I was able to get by slowly, and a few other cars were able to get by quickly on the left.

I stopped in Frisco and put on chains. They were surprisingly easy to put on, it took maybe 5 minutes. And of course by Murphy's law the highway from Frisco to Breckenridge was perfectly plowed (as well as it can be during a snowstorm), so I was in the right lane doing 30 while everyone else was passing. But I didn't know if it would be good the whole way, and I knew the road to the trailhead would be snowpacked, so I left the chains on.

We made it to the trailhead and had a great time at the hut we skied to. We got 1-2 feet of snow while we were there!

I rinsed off the chains when I got home today, and they have a little wear, but they are still in great shape. I estimate they might last a couple hundred miles at most on pavement. Obviously they are meant for snow but there are not always safe places to stop and put on/take off chains.

I-70 was closed for a while later Saturday morning, and there was apparently a 20 car pile-up and a 15-car pile-up later in the day. Moral of the story is, 99% of the time good all season tires are fine in Colorado. I've never had a problem with them before. But if snow tires avoid one accident they pay for themselves.

 

[Terminator03]

After that experience I’d never even bother trying to cheap out, and just buy a brand new set of 4 in whatever type makes sense for your region. It sounds like it would be most sensible to use your old rims to mount Blizzaks for the winter, then put some nice A/S tires on the TE rims. Obviously not the cheap option, but being that tires are your only connection to the road, I don’t take chances with them, especially in the winter.