# 45 mph U-Haul trailer speed limit **URL:** \ **Category:** Factual Questions\ **Created:** [May 6, 2003, 7:36pm UTC](https://boards.straightdope.com/t/45-mph-u-haul-trailer-speed-limit/173481 "2003-05-06T19:36:57Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Howard\_Juneau](https://avatars.discourse-cdn.com/v4/letter/h/bb73d2/32.png) [@Howard\_Juneau](https://boards.straightdope.com/u/Howard_Juneau)\ **Post date:** [May 6, 2003, 7:36pm UTC](https://boards.straightdope.com/t/45-mph-u-haul-trailer-speed-limit/173481/1 "2003-05-06T19:36:57Z")
U-Haul rental trailers have a “Speed Limit 45 mph” sign painted on their fenders and tailgates. Most Interstate highways have “Minimum Speed 45 mph” signs. U-Haul won’t let me go over 45, the state won’t let me travel under 45. Explain this to me. Are U-Hauls not to be driven on the Interstate? (Seems odd – much of their business is interstate moves…) Can’t the U-Haul people engineer a trailer safe at highway speeds? Is this a scam to let U-Haul out of any liability for anything that happens to one of their trailers on the road? Who can give me the Straight Dope? ---
**Author:** ![Mike\_H](https://avatars.discourse-cdn.com/v4/letter/m/ecd19e/32.png) [@Mike\_H](https://boards.straightdope.com/u/Mike_H)\ **Post date:** [May 6, 2003, 8:09pm UTC](https://boards.straightdope.com/t/45-mph-u-haul-trailer-speed-limit/173481/2 "2003-05-06T20:09:03Z")
I don’t the answer to your questions, but I once saw someone driving down the interstate with one of those trailers, going 65-70 MPH, in total disregard of the warning on the trailer. The trailer was wildly fishtailing behind him. He would slow down, the fishtailing would stop, and he would speed up again . He kep doing this. So I assume there’s a good reason to follow the speed limit. ---
**Author:** ![Duck\_Duck\_Goose](https://avatars.discourse-cdn.com/v4/letter/d/50afbb/32.png) [@Duck\_Duck\_Goose](https://boards.straightdope.com/u/Duck_Duck_Goose)\ **Post date:** [May 6, 2003, 8:11pm UTC](https://boards.straightdope.com/t/45-mph-u-haul-trailer-speed-limit/173481/3 "2003-05-06T20:11:02Z")
My guess would be that that “45 mph” recommended speed is designed to accommodate the Lowest Common Denominator of drivers, the ones who have never towed a trailer in their life and who will panic at the slightest hint of fishtailing. The slower the trailer is going to begin with, the less chance there is that the Virgin Driver will flip it and rack it up in the interstate median strip. ---
**Author:** ![pipper](https://avatars.discourse-cdn.com/v4/letter/p/c2a13f/32.png) [@pipper](https://boards.straightdope.com/u/pipper)\ **Post date:** [May 6, 2003, 8:19pm UTC](https://boards.straightdope.com/t/45-mph-u-haul-trailer-speed-limit/173481/4 "2003-05-06T20:19:12Z")
From personal experience towing the enclosed trailed behind a Jeep Wrangler from Chicago to DC: 65 mph was not a problem. Above 75 there was a bit of a vibration and you could feel that it wanted to start fishtailing, so we tried to keep it below 70 mph. I asked the Uhaul guy about the 45 mph limit and all he said was “That’s what’s recommended, but you should be fine on the highway.” Sounds like a “don’t ask, don’t tell” while using the 45 mph limit to provide protection against lawsuits ---
**Author:** ![brad\_d](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@brad\_d](https://boards.straightdope.com/u/brad_d)\ **Post date:** [May 7, 2003, 12:09am UTC](https://boards.straightdope.com/t/45-mph-u-haul-trailer-speed-limit/173481/5 "2003-05-07T00:09:44Z")
I’ve driven an open 4’x6’ U-Haul trailer on the freeway at 65 mph with no problems, as well. I used a Mazda B2300 pickup. It was loaded on the only occasions I had it on the freeway; perhaps it would have been a bit more skittish at such speeds while empty. ---
**Author:** ![Early\_Out](https://avatars.discourse-cdn.com/v4/letter/e/6f9a4e/32.png) [@Early\_Out](https://boards.straightdope.com/u/Early_Out)\ **Post date:** [May 7, 2003, 1:54am UTC](https://boards.straightdope.com/t/45-mph-u-haul-trailer-speed-limit/173481/6 "2003-05-07T01:54:44Z")
This is just a WAG, based upon some half-remembered factoid, but I thought the speed limit was based on the fact that the trailers have very small diameter wheels, and at high speeds, they turn so fast that things like axle bearings are prone to crapping out from the heat build-up. A 12" diameter wheel, for example, will turn at roughly one-and-a-half times the rate of a 17" wheel traveling at the same speed. ---
**Author:** ![Howard\_Juneau](https://avatars.discourse-cdn.com/v4/letter/h/bb73d2/32.png) [@Howard\_Juneau](https://boards.straightdope.com/u/Howard_Juneau)\ **Post date:** [May 7, 2003, 2:10am UTC](https://boards.straightdope.com/t/45-mph-u-haul-trailer-speed-limit/173481/7 "2003-05-07T02:10:57Z")
Thanks for the input, everyone. **DDG** , the “Lowest Common Denominator” theory has the ring of truth about it. That triggered an “Institutional Inertia” theory in my mind: Lots of those trailers are probably 40+ years old, when 45mph wasn’t that far off of normal highway speed. Years go by; heaven forbid that we should repaint any of those old buggies; we always order up the same decal sets from our suppliers; etc… Still, I’d appreciate hearing from someone who has seen something in the rental contract boilerplate about the speed limit, or even from a law enforcement Doper who has maybe ticketed a U-Hauler Hauling \*\*\*, so to speak… ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [May 7, 2003, 2:30am UTC](https://boards.straightdope.com/t/45-mph-u-haul-trailer-speed-limit/173481/8 "2003-05-07T02:30:46Z")
Also remember that posted legal minimum speeds are for unencumbered vehicles – check with law enforcement personnel, but I’d venture to guess that in most jurisdictions they’ll tell you to subtract 10 mph if you’re towing something, driving an unusual sort of vehicle (e.g., school bus, self-propelled construction crane), or otherwise unable to safely travel with the flow of traffic and/or at the posted speeds. ---
**Author:** ![Slartibartfastt](https://avatars.discourse-cdn.com/v4/letter/s/5e9695/32.png) [@Slartibartfastt](https://boards.straightdope.com/u/Slartibartfastt)\ **Post date:** [May 7, 2003, 3:40am UTC](https://boards.straightdope.com/t/45-mph-u-haul-trailer-speed-limit/173481/9 "2003-05-07T03:40:38Z")
I always figured it was an anti-lawsuit device. If U-haul could prove that the renter was driving over 45mph when they got into an accident they could claim the accident was due to improper use(and therfore not their fault) and not due to any design flaw of the trailer.