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Originally Posted by hingarfi
Anyone have experience or opinion on the consequences of putting 15 in wheels on a USED 2720 TM? I realize this would not increase the GVWR but the tires would be much less stressed. I have read the stories of tire failures but have not seen any axle failures. I plan on some really long distance hauls over the next couple of years. There is a site offering a packaged wheel and tire as follows:
Tire: ST225-75-R15BD Load Range D Load Capacity: 2540 lbs. at 65 psi. Bolt Pattern: 5 on 4-1/2. This tire is about 1.6 in larger in diameter and 0.3 in wider than the ST215/75R14. I also plan to add the 2.5 inch lift.
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Your logic matches mine...no reports of axle failures; many reports of tire failures. And that not loading a tire right up to its maximum weight should substantially reduce the likelihood of a blowout or other catastrophic tire failure. I don't anticipate really long trips in my future but because I do a lot of boondock camping, I usually depart on trips with the trailer heavily loaded (very close to the GAWR, the GVWR, and the tire ratings). In addition, 2005 will be 4th towing season on my trailer's tires so this is a subject that I've been doing quite a bit of thinking about as I expect to replace the tires before the beginning of the 2006 towing season.
I've already discussed this with the owner of a local tire shop...who also owns a TM
...he hasn't yet retrofitted his trailer's tires either. One thing he did mention during our initial discussion is that you may not want to run the larger tires at their maxiumum 65 psi pressure, but rather at one that provides a sufficient margin of load capacity. If running at max pressure, there's a good chance you'll get excessive wear in the center of the tire so he suggested getting some tire chalk and using that to determine if there was too much air in the tires.
The big issue is whether or not there's room for the tire inside the wheel well when the suspension is fully compressed (as in being fully loaded and hitting a big bump). There are two likely points where an oversize tire would rub...at the very top and the sides. With the lift (which I already have), I don't expect the top would be a problem since it adds 2 inches (at least) of additional separation whereas the larger tire would only consume about .8 inch (half of the 1.6 inch larger diameter). Could be real iffy without the lift though.
Separation of the tire at its widest from the wheelwell might be a different story though. One potentially quick way to find out is to simply call TM and ask if they use the same wheelwell for single axle 15 inch tire models (like the 3023) as they use for the single axle 14 inch models (2619/2720). A not so quick way would be to load the trailer, lift one side of the trailer enough to cause the other side to incur increased suspension squat, then do some measuring and estimating (it's not a good idea to jack up the axle itself).
From a manufacturing (and supply management) viewpoint, it would be logical for TM to use the same wheelwell on all models (sized for 15 inch tires). However I have a nagging doubt about this since TM has been quoted as saying that the few 2720s that have been ordered with 5K Axles/15 inch tires had to be pulled out of the regular production line. Why, they didn't say, but one possibility could be a larger wheelwell liner necessitated special cabinetry work. If you haven't already done so, before I do any retrofitting of 15 inch tires, I will certainly be discussing the issues with TM and doing some measuring.
It's seldomly a straightforward process to use non-OEM equipment...a thorough look at all the engineering issues is highly prudent.
FWIW, I
may go quite a bit beyond just retrofitting oversize tires...I'm currently mulling over also swapping the 3.5K axles on my 2720SL for 5K axles and, at the same time, fitting those axles with hydraulic disc brakes. The disc brakes will also require an electro-hydraulic actuator. Won't be for the 2005 towing season but just might happen for the 2006 season.
From everything I've read, the stopping power of trailers with hydraulic disc brakes is enormously better than with the traditional electromagnetic drum brakes (like a factor of 4 in the deceleration rate). The difference in stopping difference between discs and drums in a panic stop from 60 mph is on the order of 100 feet...about 7 car lengths.
In heavy traffic, that would likely be the difference between a destroyed rig with death/severe injuries and just a badly shaken set of nerves. Retrofitting with discs is, however, pretty pricey...I've been seeing prices on the order of $1200 to $1500 for a kit with discs/calipers, actuator (the really pricey part), and assorted lines.