scooterdog

Hi - my wife hit the curb a bit too hard last night in our '04 GX470, and a front Michelin LTX M/S tire (about 17 months old) blew out.

The full-size spare is installed, and a replacement won't arrive until next week.

Was told by a tire technician that I shouldn't drive it for a 250mi road trip we're planning this weekend, but I'm wondering whether this is just a standard mfr recommendation for a 4WD owner to get a set of tires whenever replacing only one.

I'm not planning to do this long-term, just a 250mi trip (out and back) and would welcome any comments. Thanks!

470reasons

From The Tire Rack:

Four-wheel drive and all-wheel drive vehicles are equipped with additional differentials and/or viscous couplings that are designed to allow momentary differences in wheel speeds when the vehicle turns a corner or temporarily spins a tire. However, if the differentials or viscous couplings are forced to operate 100% of the time because of mismatched tires, they will experience excessive heat and unwarranted wear until they fail.

This necessitates that four-wheel drive and all-wheel drive vehicles use tires that are very closely matched. This is because different diameter tires roll a different number of times each mile as a result of the variations in their circumferences. Tire diameter variations can be caused by accidentally using different sized tires, tires with different tread designs, tires made by different manufacturers, different inflation pressures or even tires worn to different tread depths.

Is the GX exempt from this info? Don't know.
If you have another vehicle I'd take that. If not, try to rent. But time for that is running out.
Good luck.

ALAN553

Don't quite get it...the spare is an OEM tire, not a temporary...drive it for 50,000 miles or until you replace the michelin. unless it has been used already, and it is bald.

470reasons

"Don't quite get it...the spare is an OEM tire, not a temporary...drive it for 50,000 miles or until you replace the michelin. unless it has been used already, and it is bald."

If the 4 tires on the car are worn, the circumference of the spare tire will be greater than the other three tires. Full time 4-wheel drive vehicles unusually need all tire circumferences to be close or damage will occur.

If someone can show that the GX does not need to follow the circumference rules, please post. I really don't know the official Lexus position on this issue.

danmm7

The real question is..... how old is the spare tire?
What is the date of manufacturing stamped on the sidewall?

Tires are usually unsafe to drive for long after they reach 6-7 years of age, due to rubber becoming a lot less flexible and less durable over the years. Old tires can explode under heat.

My spare tire looks brand new, never been used, but the date stamped on the sidewall is from the early 2004. This is almost a 10 yr old tire!!! I can also see visible crack on the sidewall, just from aging. I would not feel safe driving on this tire for very long.

ALAN553

Wait, you mean, the measurable circumference difference between and old tire and a new tire might be Enough to confuse all the electronic skid control, ABS, and may not even put enough of the tire on the road in a 5000 lb truck....I don't think so...the only down side to using the spare is its general condition, ie bald or cracked.

scooterdog

Excellent point danmm7 - It is the original tire (never used before) so it is 9 years old. The other tires have only 8K miles on them, so the circumference 'mismatch' isn't that much. (The warranty credit was 82%, don't remember the inches of tread.)

This cold weekend (dry but temps in the 30's here in the East Coast) mean less risk of a tire exploding but still makes sense to use the alternative. Not much space though!

470reasons

"Wait, you mean, the measurable circumference difference between and old tire and a new tire might be Enough to confuse all the electronic skid control, ABS, and may not even put enough of the tire on the road in a 5000 lb truck....I don't think so."

I don't think ANY reputable tire shop would put a 'new' (unworn) tire onto an all-wheel drive vehicle that had three worn tires on it.

lesz

It isn't a matter of whether there will be "enough of the tire on the road". The worn tire will have a smaller circumference, and, thus, it will need to make more revolutions per mile traveled than will the other tires. That said, according to my calculations, even if one tire had 2/32 or 3/32 less tread, the difference in circumference would only be somewhere in the range of .5%. It is hard for me to imagine that a difference in circumference of .5% would mess up the ability of the differentials and safety systems to operate properly. Between tire rotations, it can be the case that there will be 1/32 or 2/32 difference between the remaining tread on some tires compared to others, and I'm confident that there would be an even greater difference in circumference if you were running one of the four tires with a few pounds more or less pressure than the others. Of course, I could be wrong, and I'd want to consult with someone with greater knowledge before running the new tire with three tires that have some wear.

ALAN553

As long as all the tires are within safe wear spec, mixing one new tire with three old, or vica versa will not make any difference to the operation of the trucks differentials. The circumference and revolutions per mile vary in the same size between different models. So if you had to mix a tire because of availability there is no way it would affect the AWD system. I am sure it happenes every day. I have another 4 WD and had to replace two tires...the other two were fine...e truck can't tell the difference.

RCsGX

For what it's worth, several car manufactures say to keep the tires within 2/32" of each other on full-time 4wd and AWD vehicles.