# Trailer tire highway speed question **URL:** \ **Category:** Factual Questions\ **Created:** [June 16, 2018, 6:19pm UTC](https://boards.straightdope.com/t/trailer-tire-highway-speed-question/816212 "2018-06-16T18:19:27Z")\ **Posts on this page:** 10\ **Page:** 2
**Author:** ![Weisshund](https://avatars.discourse-cdn.com/v4/letter/w/ba8739/32.png) [@Weisshund](https://boards.straightdope.com/u/Weisshund)\ **Post date:** [June 18, 2018, 2:56am UTC](https://boards.straightdope.com/t/trailer-tire-highway-speed-question/816212/21 "2018-06-18T02:56:12Z")
FWIW i pretty much tow everything between 55 and 60, regardless of what the trailer tires are rated for. Towing has it’s own fun, and trailers have a bit of mind of their own, sometimes more so with the littler ones with their hopping and skittering. Lot of beating those little 12 inch tires will be taking. Also the smaller the tire, the faster it spins, meaning the faster the bearings are spinning as compared to a bigger 16 or 18 inch tire with bigger bearings Id rather go slower and have less troubles, they can honk and flip me off all they want ---
**Author:** ![EdelweissPirate](https://avatars.discourse-cdn.com/v4/letter/e/8491ac/32.png) [@EdelweissPirate](https://boards.straightdope.com/u/EdelweissPirate)\ **Post date:** [June 18, 2018, 3:28am UTC](https://boards.straightdope.com/t/trailer-tire-highway-speed-question/816212/22 "2018-06-18T03:28:09Z")
> [@anomalous1](#): > > Hysteresis is pretty much a euphemism for “rolling friction”. Nope. Hysteresis is not synonymous with friction; they’re different phenomena. And “hysteresis” is certainly not a euphemism for friction. > [@anomalous1](#): > > I don’t seem to think overinflation is a problem. It _is_ a problem Oh dear. No. [This study](https://rosap.ntl.bts.gov/view/dot/11664/dot_11664_DS1.pdf?) shows that worn passenger car tire burst pressures are typically around 200 PSI. It was published in 1977, but that actually makes it more relevant: they tested a mix of bias-ply and radial tires, which reflects the current state of the trailer tire market: it’s a mix of bias-ply and radial tires. So: how hot must a tire get if its pressure is to rise from 32 PSI to 200 PSI? Gay-Lussac’s law says that P[sub]1[/sub]/T[sub]1[/sub] = P[sub]2[/sub]/T[sub]2[/sub], where T is (absolute) temperature and P is pressure. if a tire is inflated to 32 PSI at 75 degrees F (297 degrees K) then it must reach 1856 degrees K before the expanding air reaches 200 PSI. That’s 2400 degrees Fahrenheit. [Tires typically catch fire](https://en.wikipedia.org/wiki/Tire_fire) at about 750 degrees F. Even if the tire temperature reaches 212 degrees F, its pressure only rises to 40.2 PSI. The tire fails from heat damage long before it reaches its blowoff pressure. > [@anomalous1](#): > > slight underinflation will not cause harm and can only benefit. Nope. The increased heat from underinflation causes harm. There is no situation where decreasing pressure lowers temperatures or increases the safety margin. This is dangerous advice. > [@anomalous1](#): > > 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. I’m baffled. You’re choosing to ignore many well-informed posters, including a former tire dealer and a mechanical engineer with work experience in tire analysis (me). The “practice” you’re choosing is dangerous to other drivers. Underinflating trailer tires by 5 PSI isn’t the most dangerous thing you can do, but it’s dangerous–a _lot_ more dangerous than overinflating by 5 PSI. ---
**Author:** ![anomalous1](https://avatars.discourse-cdn.com/v4/letter/a/e56c9b/32.png) [@anomalous1](https://boards.straightdope.com/u/anomalous1)\ **Post date:** [June 18, 2018, 5:13am UTC](https://boards.straightdope.com/t/trailer-tire-highway-speed-question/816212/23 "2018-06-18T05:13:17Z")
I am not choosing to ignore anything. Underinflation does have benefits. I may not be a tire dealer or have done analysis on tires, but I am speaking from pure experience from participating in drag strips and street racing, things I am well versed in. The overinflated tire will blow out faster than a slightly underinflated one and sometimes its more than heat that causes the issue or its a combination. I used to overinflate, many blow outs (and dented wheels/trashed wheels), now I underinflate knowing the tires will expand in practice, no blow outs and especially lower risk from road variances/potholes/detritus etc… If we remove heat from the dynamic here we still have longer stopping distance, instability and traction control issues (compounded by varying road surfaces or lackthereof), all of which increase with overinflation vs underinflation. Traction control is a very important aspect of all of it, especially if exceeding rated tire speed on a trailer. A small value of underinflation can only serve as a safety margin when it comes to traction control, hot or not. OP can take his/her pick on the advice which is largely pointless anyway at this point. ---
**Author:** ![Ionizer](https://avatars.discourse-cdn.com/v4/letter/i/5daacb/32.png) [@Ionizer](https://boards.straightdope.com/u/Ionizer)\ **Post date:** [June 18, 2018, 10:33am UTC](https://boards.straightdope.com/t/trailer-tire-highway-speed-question/816212/24 "2018-06-18T10:33:58Z")
> [@anomalous1](#): > > I may not be a tire dealer or have done analysis on tires, but I am speaking from pure experience from participating in drag strips and street racing, things I am well versed in. …snip You realize that racing is totally different than trailering, right? Usually 10-15 secs use, right, in street racing? (and much shame on you if it was on public streets) Versus possibly hours w/ trailering… ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [June 20, 2018, 4:29am UTC](https://boards.straightdope.com/t/trailer-tire-highway-speed-question/816212/25 "2018-06-20T04:29:20Z")
Second-hand advice, based on a friend’s experience: he bought a small trailer from Harbor Freight to tow tires and equipment to the race track, and the first trip out one of the wheels failed because the bearings weren’t adequately greased. Small trailer wheels spin much faster than your car’s wheels, so be sure to pay attention to maintaining their bearings. And don’t assume that just because the trailer’s new that there’s enough grease in them. ---
**Author:** ![zlexiss](https://avatars.discourse-cdn.com/v4/letter/z/ecae2f/32.png) [@zlexiss](https://boards.straightdope.com/u/zlexiss)\ **Post date:** [June 23, 2018, 11:12pm UTC](https://boards.straightdope.com/t/trailer-tire-highway-speed-question/816212/26 "2018-06-23T23:12:25Z")
Agree with the above posts that hysteresis is the problem and underinflation makes it worse. Friction is involved but not between surfaces - it’s internal to the tire. As the tire rolls, the sidewalls cyclically flex as they reach the bottom and become loaded. This flexing creates heat internal to the sidewall, which in excess causes structural failure and subsequent blowouts. Underinflated and/or overloaded tires make this worse - more flexing = more heat generated with each revolution. The same tire can carry greater load with more pressure (up to it’s inflation limit) to help reduce heat buildup. See: > **[application\_of\_load\_inflation\_tables\_20170203.pdf](https://www.toyotires.com/media/2125/application_of_load_inflation_tables_20170203.pdf)** > > 2.81 MB > **[What Is Maximum Load For A Tire?](https://www.tirerack.com/upgrade-garage/what-is-maximum-load-for-a-tire)** > > Maximum Load > A tire's maximum load is the most weight the tire is designed to carry. Since a tire's load carrying capacity is related to the tire's size and construction and how much inflation pressure is actually used, maximum loads are rated with... In Tire Rack’s words: “Additionally, while a tire’s maximum load is the most weight the tire is designed to carry, its load carrying capacity at lower inflation pressures is proportional to how much inflation pressure is used.” I don’t know if there’s a reason ever to underinflate tires except for offroading or racing purposes where you either need addtional contact patch on the drive wheels for straight-line traction, or for road racing in a temporary situation where you know temperatures will rise so much the tire will end up at steady state above the desired psi for peak handling. Underinflation in corners is a bad thing as the tires will bend over until you’re scrubbing the sidewalls and the car will be squirmy, less traction, and at times unpredictable in handling balance. (my tires would typically go up ~10-12psi on the road course, so I know where I want them to start at and need to be careful for a couple laps until they heat up and repressurize) zlexiss ---
**Author:** ![senoy](https://avatars.discourse-cdn.com/v4/letter/s/dbc845/32.png) [@senoy](https://boards.straightdope.com/u/senoy)\ **Post date:** [June 23, 2018, 11:33pm UTC](https://boards.straightdope.com/t/trailer-tire-highway-speed-question/816212/27 "2018-06-23T23:33:17Z")
You want to stay under the max speed for two reasons. The first is that speed ratings are determined by running the tire against a roller at speed in 77 degree rooms. Needless to say, that’s not real life. A pothole or a sunny day can cause failure even below max speed. The second is even more important. Let’s pretend you’re driving down the road at 70, the car behind you has a dash camera and your tire fails, flipping your trailer and it goes through the windshield of and kills the driver behind you. What would happen is that you sir are guilty of negligence and manslaughter. You were operating a piece of machinery in an unsafe manner leading to death and that is a sucky way to end up in prison. If on the other hand, you are driving at 60 and the same thing happens, it’s simply a horrific accident or perhaps the negligence of the tire manufacturer and you are off the hook. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [June 24, 2018, 2:20am UTC](https://boards.straightdope.com/t/trailer-tire-highway-speed-question/816212/28 "2018-06-24T02:20:42Z")
I have over 300k miles hauling largish trailers behind passenger vehicles. My advice would be to use tires with speed and load ratings that exceed anything they will see in actual service. The extra cost will be worth it if you avoid even a single problem typical of marginal tires (of which there are many). The extra peace of mind is a bonus. I’ll note that I always inflate to the maximum rated pressure. ---
**Author:** ![Weisshund](https://avatars.discourse-cdn.com/v4/letter/w/ba8739/32.png) [@Weisshund](https://boards.straightdope.com/u/Weisshund)\ **Post date:** [June 25, 2018, 1:49am UTC](https://boards.straightdope.com/t/trailer-tire-highway-speed-question/816212/29 "2018-06-25T01:49:21Z")
> [@anomalous1](#): > > I am not choosing to ignore anything. Underinflation does have benefits. I may not be a tire dealer or have done analysis on tires, but I am speaking from pure experience from participating in drag strips and street racing, things I am well versed in. The overinflated tire will blow out faster than a slightly underinflated one and sometimes its more than heat that causes the issue or its a combination. I used to overinflate, many blow outs (and dented wheels/trashed wheels), now I underinflate knowing the tires will expand in practice, no blow outs and especially lower risk from road variances/potholes/detritus etc… If we remove heat from the dynamic here we still have longer stopping distance, instability and traction control issues (compounded by varying road surfaces or lackthereof), all of which increase with overinflation vs underinflation. > > Traction control is a very important aspect of all of it, especially if exceeding rated tire speed on a trailer. A small value of underinflation can only serve as a safety margin when it comes to traction control, hot or not. > > OP can take his/her pick on the advice which is largely pointless anyway at this point. Drag racing is done on special tires, made from special rubber compounds that are designed to get sticky when hot (street tires do the opposite) Drag tires have special sidewall construction that is supposed to wrinkle up at high torque and low speed, and then the tire grows in height a large amount when up to speed. And the tires are made to last a very short time before destroyed. That same flexing of a car or trailer sidewall will cause the tire to fail, as it does that flexing a lot more than a few seconds, and the sidewall is totally different construction as is the entire tire. The tire will get super hot, and before it gets hot, it will have already been busy with destroying the sidewall from the low pressure. This is poor advice to recommend There is a reason that Trailer and LT tires designed to carry loads generally have a higher pressure than the same size standard tire. ---
**Author:** ![MikeF](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@MikeF](https://boards.straightdope.com/u/MikeF)\ **Post date:** [June 25, 2018, 4:06pm UTC](https://boards.straightdope.com/t/trailer-tire-highway-speed-question/816212/30 "2018-06-25T16:06:10Z")
It been my experience that underinflated trailer tires also increase the likelihood of trailer sway. I always inflate tow vehicle and trailer tires to the maximum pressure. [Previous page](https://boards.straightdope.com/t/trailer-tire-highway-speed-question/816212.md?page=1)