Utility Trailer Spare tire Sizes question

[steve18080]

I have a tandem axle utility (car/equipment) trailer with ST205/75D15 tires (7k- 3500lb axles). I'm looking to have a spare tire, just in case, but since the trailer doesn't see a whole lot of mileage, I don't want to spend a lot. can't see dropping $100 on a spare that will probably sit around and dry-rot before I need it.



I have an old steel spare tire rim from an old 1981 ford pickup that had P215/75R15 tire. Also, My fiance's car just had new tires put on it, and I saved one of the old tires, which is 205/65R15. From what I looked up, all the tires can mount on 5.5-7.5" rim width range


So here's my question, can I safely mount the 205/65 tire on the 215/75 Rim and use it as a spare tire to run with the other 205/75 on the trailer?(only for a spare/emergency use) ?

Also, I tried the rim, and the 5 bolt pattern lines up, and fits on my trailer fine, however, the hub/axle hole on the wheel is a little larger (and slightly odd shaped) than the axle on the trailer....will this work? I assume the lugs will center the tire, or does the hub need a tight fit to hold the weight?

I do realize the 205/65 car tire isn't an "ST" trailer tire, and it also has a 1400lb load rating vs the 1750lb capacity for the trailer, since its rarely loaded to the max, and rare that I would need it, and it won't cost me anything....is it worth it to clean up the rim, mount it, and carry it along with me?

thanks for any help or suggestions, as I don't know a whole lot about tires and mis-matching sizes...being its just a trailer, I can't see it being to major of an issue, as long as it fits holds air and spins (hahaha)

thanks
- Steve

[JIMNLIN]

As I was thinking about it more, (if I'm correct?) ...the equlizer bar/triangle should distribute even weight to each tire on that side, regardless of the small difference in tire height, and being the hubs are independent (unlike a drive axle) the size difference shouldn't affect the larger tire on the other end of the axle

Good point as far as carrying the load. Many folks don't realize but when one tire goes flat its still carrying its share of weight through the equalizer bar. Thats why the flat tire shreds itself quick running down the road. And can start a beautiful spark show as it wears into a steel wheel at night.

A point on braking. Tires on a axle need to be fairly close to the same diameter for equal braking performance. Generally the brakes with the smaller diameter tire has a bit better braking performance as they are turning more rpms and may slide quicker under hard braking especially on wet pavement.
Also due to braking rotational forces the rear axle tends to lift the front axle through the equalizer bar which can lead to flat spotting the smaller diameter front tire on hard braking events.
I've used tires on my road trailers as much as 3/4" difference in diameter with no ill effects in wet pavement braking. I use the taller tires on the lead axle for that reason.

[steve18080]

Thanks for the responses! I cleaned up and am working on painting the ford wheel I have, and since its not going to cost anything, other than maybe a few bucks for mounting, I think I'm going to do it.

Since I'll have a regular supply of tires from her car, I can replace it every few years when she changes tires, where as if I buy a new one, it will just lay around and dry rot till I need it, so makes economical sense if it will work

I wouldn't run it permanently, but being a tandem, and sharing the weight with the other axle, I think I'll be alright just to get it off the road or get it home should I need it. Looking at the little "donut" wheels they have for spares on cars, I think I'll be alright with the size difference.

As I was thinking about it more, (if I'm correct?) ...the equlizer bar/triangle should distribute even weight to each tire on that side, regardless of the small difference in tire height, and being the hubs are independent (unlike a drive axle) the size difference shouldn't affect the larger tire on the other end of the axle

[JIMNLIN]

The passenger tire will do fine as a spare for the utility/car hauler that may never roll on the road. P tires are what we used on trailers with 3500 lb axles before the ST hit the streets anyway.

Your trailer wheels are lug centered. The center hole is for clearance and doesn't carry any load.

[MFL]

Steve, the tire you would be using would be a lower profile, with a softer sidewall. It would be shorter, and more side flex.

It would be better than nothing, in an emergency, but not a very good match. I don't think the center hole would matter for a short distance, as long as the bolt pattern was perfect.

Depending on the load, and distance before replacing the original, would be the issue. IMO it would work, but for $100, I'd do it right, just knowing that I wouldn't have an issue.

Jerry