The Max PSI for Trailer Wheels Versus Tire Max PSI

Question:

My understanding is that ST tires are speed-rated at 65 MPH at their rated max pressure, but that by increasing the tire pressure 10 PSI above that, an M-rated 81 MPH tire like the one that is part of this wheel / tire combo - could safely be used at say 75 MPH. Could you confirm that I have the correct understanding and then answer the following questions: 1. Why does eTrailer.com not show the manufacturers max pressure rating for each WHEEL it sells? That is, its not just TIRES that have max pressure ratings wheels are also rated for maximum pressure. Would it not be a good idea to *list* this number in your specifications for each wheel? Or, if all the wheels you sell have max pressure ratings of at least, say, 100 PSI - then why not say that somewhere so that users are not left wondering about whether it is safe to inflate the tire 10 PSI above its nominal max - when used on the matched WHEEL with which the tire is being sold? 2. Why does eTrailer.com not list the wheel OFFSET in its specifications? I gather that trailer wheels are typically zero-offset but, since this is an important factor when replacing existing wheels i.e., to match the offset, why not simply list this in the specs? For this tire / wheel combination I had to read through the QandA section to finally locate this information, when IMHO, it should simply be thereinch in the specs... Thanks

asked by: Stephen D

Helpful Expert Reply:

The max psi rating is specific to each tire as it is tested, so you cannot simply increase tire pressure to get a higher speed rating or increase weight capacity. Your tires could overheat or wear quickly because they are not designed for that pressure rating. Overheating is the number one cause of tire failure including blow outs and it is almost always due to improper inflation or traveling over the speed rating of the tire. The Karrier ST175/80R13 Radial Trailer Tire with 13" Aluminum Wheel - 5 on 4-1/2 - Load Range D # AM32001HWTB for example should be filled to 65 psi prior to travel, and should not travel over 81 mph.

We don't pressure rate wheels/rims because they are able to handle the psi ratings of all the trailer tires that will fit them when using the correct valve stem. Most of our wheels do not come with a valve stem so that needs to be purchased separately. For instance # AM20903 is rated for up to 65 psi, # AM20904 is rated for up to 80 psi, # AM20907 for up to 100 psi, and # AM20906 is rated for anything over 100 psi.

Wheel offset is given for any wheels we carry that have a positive or negative offset like the Dexstar Conventional Steel Wheel with Offset - 15" x 6" Rim - 5 on 4-1/2 - Black # AM20504 which has a positive 0.5 inch offset. As you stated most trailer wheel have a zero offset because trailer tires are made with a stiff sidewall and designed to carry the weight directly on the center of the tread. It is rare that a trailer axle requires an offset wheel for that function.

I've attached an article to help further.