H/T Vs. A/T Tiresby Richard Rowe
With the dozens of different acronyms and designations on the market today, tire shopping can be a confusing and almost arbitrary experience. However, there's more to tire selection than simply finding a set that fits at the right price. You need to take an honest look at how you drive, where you drive and what you expect from your vehicle.
Highway performance boils down to how much rubber your tire puts on the road. For acceleration, braking and cornering every bit of rubber in contact with the pavement equates to increased dynamic limits. However, the broad patches of rubber used on highway tires tend to float over the surface of sand, mud and grass without digging in for traction. This is the primary difference between H/T (highway tread) and A/T (all terrain) tires.
Off-road traction is all about putting as many mounds-per-square inch of pressure down as possible. A/T tires are designed like football cleats; their knobby tread breaks the surface upon which they ride, allowing you to put more power down. H/T tires are basically passenger car tires with very straight tread groove (sipes) to siphon water away while providing as much contact as possible between the vehicle and the road.
H/T and A/T are internally similar, but A/Ts tend to have thicker and stronger rubber to withstand the rigors of off-road abuse. H/T tires generally have thick metal reinforcing belts and stiff sidewalls, which helps them to keep their round shape when cruising down the road.
H/T tires are specifically geared toward highway driving, which means that fuel economy is a higher priority than outright traction. H/T tires use specialized tread grooves, rubber compounds and internal structures to reduce rolling resistance. Rolling resistance is a function of how well the tire grips the road. High rolling resistance makes for more traction but worse fuel economy; lower resistance does the opposite. Almost without exception, H/T tires will get better fuel economy than A/Ts.
The A/Ts knobby tires are specifically designed to increase point-contact pressure. While this is a good thing for off-roading, it puts a lot of stress on the tread when on asphalt. The A/T's high contact pressure will tend to make it wear out more quickly than a similar H/T when used on the highway. Although many consumers using A/T tires will opt for wider tires (which helps to offset the wear problem), A/T tires will almost always wear out quicker than H/T tires with similar dimensions.
Off-road oriented A/T tires tend to have large, square tread blocks. As they contact the road, these tread blocks emit a certain amount of vibration that manifests as a high-pitched hum or drone. H/T tires have chevron or back-angled tread blocks that help to reduce the acoustic effects of tire contact. Although tire noise may seem inconsequential, anyone who's driven a vehicle with really aggressive A/T tires can attest to the deafening roar they can cause at freeway speeds.
Richard Rowe has been writing professionally since 2007, specializing in automotive topics. He has worked as a tractor-trailer driver and mechanic, a rigger at a fire engine factory and as a race-car driver and builder. Rowe studied engineering, philosophy and American literature at Central Florida Community College.