Has anyone used a 15" spare after 16" conversion?

LarryJM wrote:

AH64ID wrote:
1/2" on standard axle spacing is about 1.5% difference, while it's noticeable its not the end of the world.

Chances are if upgrading from 15" to 16" the 15's were OEM and will support the axle rating. The 16" combo should support more than the 15" combo and everything will be fine.

There are some more torsion axle TT's but they are still not very common.

I guess we can all guess at what the real effects are, but IMO I think the issues are greater than they might appear at first glance. Just as those that don't think there are problems can't cite specific facts to support their view I really can't either except by extension in the caution about towing a torsion trailer level, replacing both tires on the same side when only one has failed, and the very slight difference in diameter on duals of only 1/4" as cited HERE, not to mention the caution from almost all reputable sources to not mix tire sizes on tandem axle trailers. Finally, as I stated originally using a car as a similar situation is not appropriate.

I think the risks are simply not worth the couple of hundred $$$ in short term savings when you could be risking Thousands of $$ in damage from a catastrophic tire failure.

I seldom see mentioned or people actually saying they replace both tires when only one has failed on a tandem axle trailer, but I for one have followed that practice and will continue to do so.

Larry

Speaking from actual experience of using tires with up to 2 1/2" different diameter tires as a spare on several different size equipment trailers over many years and over 800k+ miles of continues service in my business, I found my trailers had no short term or long term damage from using them temporarily the ground (several hundred miles) as a spare.
The biggest issue I found was braking issues between the two different diameter tires because of the different wheel speeds.

I have towed two trailers, one had very small tires, And I upgraded to the next size up and kept one of the old ones as a spare Used it a couple times.

The other trailer I believe I got a full set of larger rims when I upgraded.. That was the 13 Foot Scamp I towed to the dealer the day I came home with this A I'm sitting in. And blew a tire on the way :)

AH64ID wrote:
1/2" on standard axle spacing is about 1.5% difference, while it's noticeable its not the end of the world.

Chances are if upgrading from 15" to 16" the 15's were OEM and will support the axle rating. The 16" combo should support more than the 15" combo and everything will be fine.

There are some more torsion axle TT's but they are still not very common.

I guess we can all guess at what the real effects are, but IMO I think the issues are greater than they might appear at first glance. Just as those that don't think there are problems can't cite specific facts to support their view I really can't either except by extension in the caution about towing a torsion trailer level, replacing both tires on the same side when only one has failed, and the very slight difference in diameter on duals of only 1/4" as cited HERE, not to mention the caution from almost all reputable sources to not mix tire sizes on tandem axle trailers. Finally, as I stated originally using a car as a similar situation is not appropriate.

I think the risks are simply not worth the couple of hundred $$$ in short term savings when you could be risking Thousands of $$ in damage from a catastrophic tire failure.

I seldom see mentioned or people actually saying they replace both tires when only one has failed on a tandem axle trailer, but I for one have followed that practice and will continue to do so.

Larry

1/2" on standard axle spacing is about 1.5% difference, while it's noticeable its not the end of the world.

Chances are if upgrading from 15" to 16" the 15's were OEM and will support the axle rating. The 16" combo should support more than the 15" combo and everything will be fine.

There are some more torsion axle TT's but they are still not very common.

For the last two posters, don't forget there are more and more of the torsion type axles used on tandems and there the manufacturer even warns about towing in a nose up or down (i.e. "NON LEVEL ATTITUDE") causing undesirable load distribution between the axles and I feel the same would go for the tires on such a suspension system with different sized diameter tires and a 1/2" delta over only a couple of feet is one heck of difference IMO. I admit with the older style equalizer/spring type the difference might be less, but no one knows really just how much and with TT tires normally already almost at their full load capacity in many cases right from the factory I still say that "will probably" an overloading on the larger diameter tire.

Biggest issue is there is no way to tell just how much damage you might have done until that tire fails and causes a significant amount of damage for lack of $100 to $150 in the cost of a know good new tire.

Larry

LarryJM wrote:

copeland343 wrote:
No problem I have a 14" spare with 15" wheels on my flat bed trailer. The 14s came off another trailer. I look at it like using a doughnut tire on a car. Its a spare to get you out of trouble not to stay on permanently. Don't worry enjoy your trips.

Really poor analogy, most TTs are tandem with two tires very close to one another so for load bearing like diameters are important whereas on non AWD, LS normal cars the tires are at the corners much further apart and can rotate at slightly difference speeds w/o issues or load concerns.

While you could probably put a tire one size smaller on one side of a tandem TT you will probably overload the other tire to the point of damaging it beyond the point of it being reliable and necessitating replacement of that tire in addition to the other smaller tire sooner than later.

Larry

If the trailer did't have a equalizer bar suspension then your theory would come to play.
However were talking maybe 1/2" difference in diameter which the equalizer bar helps with distributing the load between the two tires. Notice I didn't say distributes evenly.

Using a 15" as a spare with 16" on the trailer works just fine. In fact it works better than on the trailer than it would on a car/truck.

Mount a 15" tire on the front of a car and a 16" on the other side and we have severe tracking issues/braking issues.
Put a 1/2" different diameter tire on the rear of a car with a rear diff leads to severe diff wear issues leading to premature failure.
............................................................

Most of my trailers have the smaller OEM tire/wheel as a spare.
My current RV came with a ST225/75-15 D.
It now has LT235/85-16 E tires.
The OEM 15" Carlisle is still hanging under the front of the trailer.

No issues, unless your planning to finish a 3K mile road trip with the spare. A smaller tire can cause uneven wear on the tire at the other end of the axle.. Not an issue if you get the 16" tire fixed/replaced.

I'm doing the same thing this year, and keeping both of my spares 15".

LarryJM wrote:


While you could probably put a tire one size smaller on one side of a tandem TT you will probably overload the other tire to the point of damaging it beyond the point of it being reliable and necessitating replacement of that tire in addition to the other smaller tire sooner than later.

Larry

Your going to have to get some scale slips to prove that one....

The suspension of a tandem axle will keep the load much closer than you think.

copeland343 wrote:
No problem I have a 14" spare with 15" wheels on my flat bed trailer. The 14s came off another trailer. I look at it like using a doughnut tire on a car. Its a spare to get you out of trouble not to stay on permanently. Don't worry enjoy your trips.

Really poor analogy, most TTs are tandem with two tires very close to one another so for load bearing like diameters are important whereas on non AWD, LS normal cars the tires are at the corners much further apart and can rotate at slightly difference speeds w/o issues or load concerns.

While you could probably put a tire one size smaller on one side of a tandem TT you will probably overload the other tire to the point of damaging it beyond the point of it being reliable and necessitating replacement of that tire in addition to the other smaller tire sooner than later.

Larry

Op back, thanks for the replies...I'm running the 16's on a fifth wheel by the way.

Ron W.

No problem I have a 14" spare with 15" wheels on my flat bed trailer. The 14s came off another trailer. I look at it like using a doughnut tire on a car. Its a spare to get you out of trouble not to stay on permanently. Don't worry enjoy your trips.