I recently bought a 4’ x 8’ trailer I want to take on a trip up north this summer. The 4.80-12 tires say speed rating “K” which works out to 68mph max. Our highway speeds are 70mph on most of I-75, and anybody doing less than 75mph is probably going to be honked at and flipped the bird many times. Can I push the speed up a few over 68 safely on a 400 mile round trip, or should I look for higher speed tires?
I personally would keep it at 65 mph max. Those going 75-80 will understand that you have a trailer and shouldn’t expect you to be going so fast. As long as you keep the right lane, I don’t think you’ll be pissing off as many people as you think you will.
One of the factors in tire failure is heat, which is going to be important here because the frictional heat will be greater at 75 mph than at 65 mph. Considering that you plan on doing this during the summer, presumably on a hot day, I think you might be pushing your luck.
I was a Dunlop/Kelly/Dayton dealer.
All their literature said speed rating was almost entirely tied to tires ability to shed heat.
The tire store was in Texas (on I-35 in Denton Co) and I can assure you just like when it rains, we got tons of flat repairs, when it was that special Texas hot we got tons of blowouts.
Under inflated, over loaded, over speed all equal over temp…Boom.
Good luck with the trailer, be safe.
How new are the tires? Trailers are something which you tend not to use a lot so they still have lots of tread left on them after several years–even though the tires are going bad because of aging. Do you know how to read age codes?
I would agree on keeping the speed under 65 mph or buying different tires (in any event make sure you have a spare tire).
And be double-dog sure to keep the trailer load below the rated weight spec for the trailer, hitch and tow vehicle. Also be sure that the load is balanced left/right and fore/aft.
I second engineer_comp_geek’s response. If a tire blows, that extra weight shift could cause you to lose control if you do not have decent reflexes, not to mention the undue strain on your hitch/trailer attachment assembly which many times is bolted to skid covers next to fuel tank mounting pounds, very expensive to repair.
You could attempt to get away with it by keeping the tires 2 or 3 PSI underinflated if extremely hot and sunny out but I really wouldn’t push 75. Just do the speed limit and you’ll be fine.
You could get L(75mph) or M(81mph) rated tires.
They normally put the crappiest tires they can get away with on new trailers. Replacing them is always a good idea.
Underinflation will raise tire temperatures, not lower them, Anomalous1. If anything, overinflation is better than underinflation.
Also, tire temperature ends up being a product of load, speed and initial pressure. If the trailer is empty or otherwise not loading the tires near their max load rating, going 5-10 mph over the rated speed is likely to be fine.
But my point here is that underinflation makes the tire run hotter, not cooler.
Friction with the road, yes. But 2-3 PSI is good wiggle room for expansion to recommended PSI from heat without significant detriment and can stave off a violent blowout if the tires are tubed. If it were 5 or more PSI then I would be absolutely inclined to agree.
But the recommended PSI already takes heat-induced changes into account. That’s why you check pressure cold, not hot.
Of course it does, but not when exceeding the rated speed. If one is to do that, heat is going to build past specification anyhow and cause the air to expand more than the max pressure rating. Dropping 2-3 PSI may allow just enough room for this extra expansion to safely happen at the higher speed. The temperature and PSI will reach a safer equilibrium this way. The drop in PSI is negligible, but can be important when it counts, if that makes sense. Just trying to keep OP safe on his/her adventures.
Best answer.
Yes. Also, a hot day and hot pavement surfaces will increase the chances of tire failure, especially for old tires.
Get tires rated for how fast you’ll be driving and how heavily you’ll be loading the trailer.
Also, in some states the speed limit when towing is different than when not towing.
California highway speed limits are 65 or 70. But when towing, your max allowable speed is 55.
along with the other good advice … i’d like to interject my own … oof which has not yet been covered.
might be such a thing the trailer had been sitting for an extended period of time … after a while, all tires succumb to tire-rot and all sorts of other maladies … some evidence can hide behind the tire-wall. if i was in position to acquire a trailer … i’d seriously consider slapping on new puppies. and, even if you decide to go with higher grade … you’d still want to stay in the outer-most lane of the highway (because of your vehicle and because of courtesy).
'nuff said.
They don’t explode due to a pressure increase… they let go due to damage from either excess force , or excess heat which leads to melting, or the combination.
The underinflated tyre allows more wobble… Wobble creates more heat, and higher forces in the wall and tread.
I thought that too. Last month I tried a cross country trip with my 8200lb trailer with 65mph rated tires. They appeared in good shape, with the correct inflation. They were 4 years old, and never in the sun (except for trips). I stayed right at 65 mph. I’m getting estimates this week to fix all the fender well damage. 
After lying on the blazing hot shoulder of a Texas highway working the jack, I pulled into the next city and bought M-rated Goodyears.
I wouldn’t recommend traveling at the max. At least not in the heat.
No. Heat in a tire doesn’t come from “friction with the road.” It comes almost exclusively from hysteresis in the rubber.
You seem to think that the primary cause of failure in tires is overpressure, but as Isilder points out, heat itself is the real threat. If you lower your tire pressure 2-3 PSI to provide “wiggle room,” you’ll still reach the pressure marked on the sidewall, but your tire is now hotter at that pressure. Lowering pressure is absolutely the wrong thing to do. It does not increase the margin of safety; rather, it subtracts from it.
Many motorsports competitors fill their tires with nitrogen, but that has nothing to do with the nitrogen itself[sup]1[/sup]. They use nitrogen because it is truly dry. Air compressors tend to condense liquid water and periodically push it into whatever they’re feeding, whether it’s an air wrench or a tire. Even small amounts of liquid water are a big problem, because racing tires often exceed 212 degrees F.
Liquid water turns to steam and expands ~1400x in the process. THAT’s when you have a blowoff. This doesn’t matter for road tires, though, because they don’t get close to 212 deg F unless underinflated. (Hint, hint).
Heat is the enemy not because it raises pressure incrementally, but because it degrades the structural integrity of the tire. Underinflation removes “wiggle room” and adds heat. Adding heat is bad, full stop.
[sup]1[/sup] Tire shops love to upsell consumers by charging them for “nitrogen,” which ignores the fact that air is about 80% nitrogen. It’s true that nitrogen diffuses through rubber more slowly than oxygen, but this means tires are effective nitrogen concentrators. After you top up your air-filled tires a few times, they’re filled with something like 98% nitrogen anyway.
Thanks for all the replies!
The tires are new- I just bought the trailer this spring in order to carry 4 kayaks. So, kayaks being relatively light, I doubt the trailer will be anywhere near its max load. Still, with the talk of crappy stock trailer tires and disastrous blowouts, I think I will look into some better, higher-speed rated tires.
and since they’re likely to be bias-ply tires, for all of the reasons EdelweissPirate explains, you do not want to exceed any of their ratings. the crossed cord plies will try to “scissor” across each other as the sidewall flexes, further increasing the amount of internal stress and heat generated in the tire.
worth remembering that blow-outs were far, far more common in cars back when car tires were still bias-ply.
Hysteresis is pretty much a euphemism for “rolling friction”. Friction or lack of it being the cause is why I reference it plainly as ‘friction’. It does add heat. I don’t seem to think overinflation is a problem. It is a problem when it is couple with heat, slight underinflation will not cause harm and can only benefit. When it comes to all of these variables there is only a small margin of it working out, I choose practice instead of theory on this one. Anyhow, I digress. OP is getting higher speed rated tires anyhow so all is good for him/her either way. 