Different size spare on LE

[flatspin]

I just got my new SCS Stealth 6 wheels and damn they are sexy. Trying to find a deal on tires (seems all the fall promos are over with) but recently read something about running a different size spare might not work on the LE's.

I WAS planning on keeping my standard 20 inch spare but going to a 275/70/17 LT tire. That would give me a couple more revolutions per mile (646) than the 20 inch tires (639). Since it's full time 4wd, will this cause me issues or be ok for a short period?

Wheel porn:

 

[1engineer]

What is the outside diameter difference.

 

[flatspin]

What is the outside diameter difference.

You mean the circumference? Here are the average numbers from tiresize.com

275/70R17
Diameter : 32.2"
Width : 10.8"
Wheel : 17"
Sidewall : 7.6"
Circum. : 101.0"
Revs/Mile : 627

245/60R20
Diameter : 31.6"
Width : 9.6"
Wheel : 20"
Sidewall : 5.8"
Circum. : 99.1"
Revs/Mile : 639

 

[bofa]

If you can hold off until march, Discount Tire Direct should have their $100 off $400 ebay deal again. :thumb3:

 

[1engineer]

You mean the circumference? Here are the average numbers from tiresize.com

275/70R17
Diameter : 32.2"
Width : 10.8"
Wheel : 17"
Sidewall : 7.6"
Circum. : 101.0"
Revs/Mile : 627

245/60R20
Diameter : 31.6"
Width : 9.6"
Wheel : 20"
Sidewall : 5.8"
Circum. : 99.1"
Revs/Mile : 639

No, diameter. 6/10ths divided by 2 equals 3/10ths or about 10/32nds. That's the difference between a new tire and a worn tire of the same size. I wouldn't worry about it, especially for a spare.

 

[Jhalko]

If you are off-road and get a flat do you really want a 20" rim and P metric tire as your way to get home?

 

[adaml]

No, diameter. 6/10ths divided by 2 equals 3/10ths or about 10/32nds. That's the difference between a new tire and a worn tire of the same size. I wouldn't worry about it, especially for a spare.

I don't know that I would follow this advice.

I don't know what Toyota says but I know my Quattro car explicitly stated that all tires had to be within 3/32 of each other.

Here's some info from TireRack basically saying the same thing.

Winter Tech Information - Matching Tires on Four-Wheel Drive & All-Wheel Drive Vehicles

Some vehicle manufacturers recommend that all tires maintain the same rolling radius and circumference, while others suggest that all tire circumferences remain within 1/4- to 1/2-inch of each other. Other vehicle manufacturers recommend that all four tires remain within 2/32-, 3/32- or 4/32-inch of each other, or within 30% of each other in relative remaining tread depth.

 

[Engineer]

I don't know that I would follow this advice.

I don't know what Toyota says but I know my Quattro car explicitly stated that all tires had to be within 3/32 of each other.

Here's some info from TireRack basically saying the same thing.

Winter Tech Information - Matching Tires on Four-Wheel Drive & All-Wheel Drive Vehicles]

Is that speaking for a spare or for a replacement tire? I bet that's regarding replacement and not to just slap on a new tire without checking the difference between it and the other three (you can either shave the new tire down or choose to by 4 new ones) but the issue is you have that difference for the life of the tire 20-60+k miles.

To the OP, you are fine with that spare size

 

[Toffees]

I don't know that I would follow this advice.

I don't know what Toyota says but I know my Quattro car explicitly stated that all tires had to be within 3/32 of each other.

Here's some info from TireRack basically saying the same thing.

Winter Tech Information - Matching Tires on Four-Wheel Drive & All-Wheel Drive Vehicles

Seconding 1Eng's question. Spare usage =! daily driver usage, and that looks like DD advice.

Of course, if your spare isn't the same size you can't rotate 5 wheels, but I guess that's obvious.

 

[1engineer]

I don't know that I would follow this advice.

I don't know what Toyota says but I know my Quattro car explicitly stated that all tires had to be within 3/32 of each other.

Here's some info from TireRack basically saying the same thing.

Winter Tech Information - Matching Tires on Four-Wheel Drive & All-Wheel Drive Vehicles

I stand by my statement.
Your Audi and our 4Runners are light years different with regards to the driveline. Even with exact matching diameters, just driving in a big circle can give you a difference of several tire RPM from the left side to the right side. If one tire is at 28 psi (still within TPMS spec) and the other tire is at 35 psi the loaded radius is over 1/2" (16/32") different! We don't have super low profile tires and the tread depth of our tires versus the Audi tires is again way different so our tire wear and the Audi tire wear is totally different. I wouldn't think twice putting a worn out spare of the same size on my 4Runner. Again, it's not an Audi.

 

[adaml]

I stand by my statement.
Your Audi and our 4Runners are light years different with regards to the driveline. Even with exact matching diameters, just driving in a big circle can give you a difference of several tire RPM from the left side to the right side. If one tire is at 28 psi (still within TPMS spec) and the other tire is at 35 psi the loaded radius is over 1/2" (16/32") different! We don't have super low profile tires and the tread depth of our tires versus the Audi tires is again way different so our tire wear and the Audi tire wear is totally different. I wouldn't think twice putting a worn out spare of the same size on my 4Runner. Again, it's not an Audi.

All cars are designed to have tires spin at different speeds while cornering. Theyre not designed to have tires spinning at different speeds in straight lines for miles at a time. But hey, it's your driveline

I know this discussion is about a "spare" but in the real world, you may have to put a spare on and then drive many miles on it before you're able to find the shop or the time to get it replaced.

 

[Toffees]

I know this discussion is about a "spare" but in the real world, you may have to put a spare on and then drive many miles on it before you're able to find the shop or the time to get it replaced.

OP is in Austin, but if he plans on taking his rig overland or significantly off the grid, that's good advice.

But if he's only going to Hidden Falls, for instance, can't see how using a spare hurts him.

 

[1engineer]

All cars are designed to have tires spin at different speeds while cornering. Theyre not designed to have tires spinning at different speeds in straight lines for miles at a time. But hey, it's your driveline

I know this discussion is about a "spare" but in the real world, you may have to put a spare on and then drive many miles on it before you're able to find the shop or the time to get it replaced.

Lol your vehicle has no idea if it is going through a gentle turn or in a straight line unless stability control comes into play. If your tires are REALLY different diameters then your wheel speed sensors won't know what to do and will light up your dash. Worn versus new diameters of the same size should be fine.

I would never offer advice on something I don't fully understand. My understanding of physics and mechanical engineering does not come from a quote on the internet. So to maybe help you to understand, please read this article 4WD or AWD? Know the Difference ? Gear Patrol and make sure you watch the video on open differentials that is included in the article. 4WD 101 level.

 

[adaml]

Lol your vehicle has no idea if it is going through a gentle turn or in a straight line unless stability control comes into play. If your tires are REALLY different diameters then your wheel speed sensors won't know what to do and will light up your dash. Worn versus new diameters of the same size should be fine.

I would never offer advice on something I don't fully understand. My understanding of physics and mechanical engineering does not come from a quote on the internet. So to maybe help you to understand, please read this article 4WD or AWD? Know the Difference ? Gear Patrol and make sure you watch the video on open differentials that is included in the article. 4WD 101 level.

The car may not "know" if you're turning or not but it doesn't need to. The point is if you turn in a circle, your tires rotate at different speeds for a few seconds (and at slow-er speeds) but if you're going straight, you'll have wheels rotating at different speeds for minutes or hours (and at high-er speeds).

I know the difference between 4WD and AWD and I also know none of this would matter if you have an open diff. However, the 4WD Limited's have a Torsen center diff which, guess what, that's the exact same setup as in your standard quattro equipped VAG car.

In fact, why don't you take the time to read through THIS THREADl on our very own forum where BlackWorksInc (an actual Toyota tech) says that they should all be pretty close to one another.

Again, I know differentials are made to handle differences but they're made to handle differences for short periods of time. You turn, you go straight, you turn the other way ... It's an ebb and flow thing. When you have a mismatch in tire sizing, you'll have differences in rotation almost non-stop.

Like I said, at the end of the day it's your driveline and not mine but I know what I would do (or rather wouldn't do).

 

[adaml]

OP is in Austin, but if he plans on taking his rig overland or significantly off the grid, that's good advice.

But if he's only going to Hidden Falls, for instance, can't see how using a spare hurts him.

Honestly, I'd disagree. I think the threat to an LSD with different sized tires is sustained high-speed highway driving (which is what I imagine a lot of TX to be)

 

[1engineer]

The car may not "know" if you're turning or not but it doesn't need to. The point is if you turn in a circle, your tires rotate at different speeds for a few seconds (and at slow-er speeds) but if you're going straight, you'll have wheels rotating at different speeds for minutes or hours (and at high-er speeds).

I know the difference between 4WD and AWD and I also know none of this would matter if you have an open diff. However, the 4WD Limited's have a Torsen center diff which, guess what, that's the exact same setup as in your standard quattro equipped VAG car.

In fact, why don't you take the time to read through THIS THREADl on our very own forum where BlackWorksInc (an actual Toyota tech) says that they should all be pretty close to one another.

Again, I know differentials are made to handle differences but they're made to handle differences for short periods of time. You turn, you go straight, you turn the other way ... It's an ebb and flow thing. When you have a mismatch in tire sizing, you'll have differences in rotation almost non-stop.

Like I said, at the end of the day it's your driveline and not mine but I know what I would do (or rather wouldn't do).

Next time you are on the interstate and come to a long sweeping curve remember that haha. Because of you and this thread I paid attention on a 45 mile drive today. I was turning slightly left for around two miles. I did a quick calculation and determined that my outside tire traveled over 30 revolutions more in that distance or 15 rpm. Every vehicle out there can do this but I digress. I have read Paul's stuff and respect him as a tech and a person. He has also read my stuff.

There is nothing wrong with being cautious and I applaud you for your argument. With that said I still have no problem using a worn spare with new tires of the same size.

 

[adaml]

Next time you are on the interstate and come to a long sweeping curve remember that haha. Because of you and this thread I paid attention on a 45 mile drive today. I was turning slightly left for around two miles. I did a quick calculation and determined that my outside tire traveled over 30 revolutions more in that distance or 15 rpm. Every vehicle out there can do this but I digress. I have read Paul's stuff and respect him as a tech and a person. He has also read my stuff.

There is nothing wrong with being cautious and I applaud you for your argument. With that said I still have no problem using a worn spare with new tires of the same size.

Fair enough but we're not talking about "worn" tires and a "new" spare. We're talking about 17" tires with a diameter of 32.2" compared to a spare with a diameter of 31.6". The difference is almost 20/32" so 10/32" rolling

All I'm saying is that the difference is pretty massive and I'd bet it's cheaper to get another tire+wheel than it is to replaced a burnt up torsen. Will anything bad happen if you had more than half an inch difference between the wheels for a mile? Maybe not but the longer you drive, the more stress you're putting on the diff over and above it's designed window of operation and why do that if you don't need to?

Like I said a few times now, it's not my drive line. However, if you can pony up tens of thousands of dollars for a Limited 4Runner and then throw down some more on other aftermarket parts, what's the real marginal cost to get that one extra wheel and tire? (presuming it fits in the spare well!)

 

[Antman]

The car may not "know" if you're turning or not but it doesn't need to. The point is if you turn in a circle, your tires rotate at different speeds for a few seconds (and at slow-er speeds) but if you're going straight, you'll have wheels rotating at different speeds for minutes or hours (and at high-er speeds).

I know the difference between 4WD and AWD and I also know none of this would matter if you have an open diff. However, the 4WD Limited's have a Torsen center diff which, guess what, that's the exact same setup as in your standard quattro equipped VAG car.

In fact, why don't you take the time to read through THIS THREADl on our very own forum where BlackWorksInc (an actual Toyota tech) says that they should all be pretty close to one another.

Again, I know differentials are made to handle differences but they're made to handle differences for short periods of time. You turn, you go straight, you turn the other way ... It's an ebb and flow thing. When you have a mismatch in tire sizing, you'll have differences in rotation almost non-stop.

Like I said, at the end of the day it's your driveline and not mine but I know what I would do (or rather wouldn't do).

As is often the case on this forum, while technically correct, this is way over-thinking things.

It isn't going to hurt a damn thing. Period.

 

[adaml]

As is often the case on this forum, while technically correct, this is way over-thinking things.

It isn't going to hurt a damn thing. Period.

I won't dispute that there is an "abundance of caution" in the post and I'll even admit that the driveline would likely be fine if it was only for a short period. However, I don't think anyone can legitimately argue that driving with one wheel almost half an inch smaller than the other three wheels on a car does anything but put extra (i.e. unneeded) stress on the system.

 

[Engineer]

As is often the case on this forum, while technically correct, this is way over-thinking things.

It isn't going to hurt a damn thing. Period.

Where is [MENTION=49845]marshall[/MENTION], he tends to be direct