85 mph for 2 Bike IH Trailers w/Maxxis ST205/R15 (D) tires
95 mph for WB IH Trailers w/Maxxis ST225/R15 (D) tires
*While the speeds above are physically possible as long as each trailer’s actual loaded weight does not exceed the trailer’s GVWR—IH is in no way recommended that you tow this fast. Doing so could be dangerous–to your wallet and your health. What we are telling you is that there is one heck of a safety factor built in to these tires.
Older IH’s can be retrofitted!
Many trailering veterans believe durable high speed ST tires for trailers is an oxymoron. After a dozen years of building trailers and buying various brands of ST trailer tires, we were beginning to believe that too.
At one point, we thought that Goodyear Marathon ST tires might be the answer to the durability issue but the more we looked the more complaints we found. Then we found the Maxxis 8008’s. Not only were they not built in China, they are warranted five years from the date of manufacture. Nevertheless there’s so much marketing hype out there that we weren’t easily convinced. So we hit the internet for a year and read a lot of customer reviews and forum reports for a year or two. While we did find a few complaints about receiving tires with date codes that were a year or two old, the rest were overwhelmingly positive.
But seeing is believing. So we bought a couple of trial batches of Maxxis ST tires and mounted them on our standard Hi-Spec wheels. Standing and watching Maxxix M8008 tires being balanced was a revelation! A surprising number didn’t need any lead weights at all. The rest used on average less than 50% as much weight as the best of any ST tires we’ve previously used. That implies a level of manufacturing process control unprecedented in our experience with ST tires. So in early 2015 we put the durability issue to bed by making Maxxis tires standard on all new Ironhorse Trailers.
But what about high speed? You may have heard that even a blind pig finds an acorn sometimes. That’s the way we felt when looking through a sales brochure for a new type of car hauler. They claimed their standard ST tires (from a rival tire manufacturer) were built to an 85 mph speed standard. That light bulb moment caused us to take another look at the specs on the Maxxis M8008 ST tires that we adopted last year. Much to our surprise and delight we discovered than it was built to a Q (99 mph) speed rating. That opened our eyes as well as some interesting opportunities for our customers.
But understanding all the “qualifiers” that went with that discovery was not easy. What we found was that the International Tire and Rim Association dictates maximum inflation pressures and load limits for ST (Special Trailer Tires) assuming ST tires built for a maximum speed of 65 mph. But the Association does NOT prohibit manufacturers from over building ST tires to a higher speed standard. In fact they stipulated the way over built ST tire’s inflation pressures and load limits should be adjusted for higher speeds.
The Association’s rule makes it clear that there is a tradeoff between tire inflation and tire load. For every ten miles faster than 65 you want to run, up to your tires designed and built-in speed standard, your tire’s load limit must be cut by 10% OR your tire pressure must be increased 10psi provided the increased psi does not exceed the maximum inflation pressure stamped on the tire.
The table that follows assumes Maxxis M8008 ST tires built to a Q (99 mph) speed rating. The first two columns are straightforward but the third one is a little trickier. It reflects the maximum Ironhorse Trailer GVW, assuming the PSI on that row, that the tire in question is supposed to be able to support when towed at the speed in that row.
If you have a fully-loaded one bike Ironhorse Trailer, Maxxis ST205/R14 (C) tires inflated to 50 psi are strong enough for towing speeds well beyond most drivers’ comfort level.
If you have a fully loaded two bike Ironhorse Trailer, Maxxis ST205/R14 (C ) tires inflated to 50 psi, you need to restrict your towing speeds to 65 mph, or lighten your load!
If, on the other hand, you have a fully loaded two bike Ironhorse Trailer, Maxxis ST205/R15 (D) tires inflated to 65psi, your tires are strong enough to support an 85 mph towing speed.
Finally, if you have a fully loaded Ironhorse WB Trailer, Maxxis ST225/R15 (D) tires inflated to 65psi, your tires are strong enough to support a 95 mph towing speed.
Keep in mind that the pairs of 14” wheels we use have a 3800 lbs load limit and the pairs of 15” ones have a 4300 lbs load limit. Likewise the GVW’s for the One Bike, Two Bike and Widebody trailers are 2000, 3500, and 3500 lbs respectively.
So to determine how much safety factor you have at various speeds:
- Identify which Maxxis tires you have or want to put on your trailer.
- Identify the load limit for the size wheel those tires require.
- Identify the smallest of the load limits for the wheels and the tires