kevsgt

how do I know if I should replace my spare tire?

over the past 8 years, I have used it a few times and lost track of the mileage. The owners manual (2006 Mustang) doesn't seem to specify a mileage, altho the rule of thumb seems to be 50 miles.

is tread depth the limiting factor? given that i am probably at or above 50 miles, i will probably replace it to be safe, but just asking because it looks to be about a $100-200 hit to the wallet.

Also, how do I know if my OEM spare is ok to use on the rear, with the stock 17" tires? Or should I definitely move a front tire to the back?

Lem-06

spare tires should be on non powered wheels, if the rear goes, move a front to its place and put spare in the front.

ive always heard 50 miles at 50 mph, but always see people going much longer/faster on them, but i get away as soon as possible.

at least with our cars its hidden in the trunk instead of exposed to elements, but even 8 years and a few trips I'd probably want to replace it

Siber Express

The 50 Miles and 50 MPH is put on it because it has the possibility of getting hot and blowing out, not that the tire is worn after 50 miles. If the tire still has tread on it, is not showing dry rot and holding air I never worried about it. But like Lem-o6 with an 8 year old spare that has been used I would at least check it out.

kevsgt

So are you suggesting that the 50 mile limit is per usage, to limit heat buildup (which over flex/stress the rubber components)? So if the tire returns to normal temp, it is good for another 50?

Theoretically, if the tire is driven in good conditions (never hits potholes, properly inflated, etc), I figured the only thing that wears/weakens from usage is the tread. I had not thought about the affect of heat (which is unavoidable even in good conditions) so that is a good point.

Because bumps and such are unavoidable in the real world, I guess that is another factor that weakens the rubber with usage. Since it is not easy to quantify that damage (like measuring treads), perhaps that is what leads to the distance limitation. Tire manufacturers could assume a certain number of potholes and heat over a 50 mile drive, and test to that.

kevsgt

Will I be able to get a new spare tire put on the doughnut wheel, or should I just get a whole new spare with wheel assembly? I see 1 fully assembly on eBay, but not sure if it is legit.

Siber Express

Not sure, but I have seen the Spare and jack set up on Ebay for $250, and truthfully I still do not have one in my car, just the mobility kit with the air pump and tire sealant. I do have another set of tires and wheels in the garage, but that would only help if I were at the house.

kevsgt

has anyone ever had a spare tire blow? has anyone ever replaced the tire on their S197 donut? tirerack doesn't seem to sell that mini size.

cruisin5268d

I really think you are overthinking this spare tire thing. There are millions upon millions of the "donut" spare tires on the road in trunks.

kevsgt

How is that over-thinking?? Like you said, those donuts are in the trunks, how does that pertain to my topic? My donut was in use sporadically over a period of 10 years. I pointed out that I probably overused it more than the average person in that time. Sure, some people perhaps ride their spare for hundreds of miles, usually on clunkers or because they can't afford new tires. If any of those people are on this forum, I'm simply asking if their donut ever failed?

Norm Peterson

At 8 years old I'd be almost as concerned about that tire's age as I would be about the effects of its actual use. There is going to be some degradation in use, and really, these tires are undersized for the car's weight - they're inflated to something like 60 psi as a crutch to bring their load rating up, but the fatigue/heat generation/impact issues remain somewhat higher than for your car's "real" road tires. Hence the usage restrictions, which are intentionally somewhat conservative. This helps cover for anybody who ends up having to drive more than 50 miles or who might not observe the 50 mph too closely (maintaining 50 on a fairly busy 70 - 75 mph Interstate is likely even riskier).


It's much preferable to avoid using different diameter rear tires on the drive axle - and especially if your car's differential is a limited slip type. All of the differential gears will always be turning more than they should, and the LSD's clutch plates will be continually slipping against each other (and wearing out).


Norm