Dear ATV Connection:

Is it possible that my new 450cc four-stroke MX quad eats up tires much more quickly than my old two-stroke 250cc did? I race the same tracks in the same district and seem to be replacing a lot more front tires per season than I ever remember having to in the past. Is there any science to verify this phenomenon?

The good news is it is not simply your imagination, nor is it anything you are doing wrong. The scientific explanation for why this is happening has everything to do with physics and the very nature of the four-stroke engine’s principle in getting power to the ground versus that of the two-stroke.

Two-stroke ATVs often earn the moniker “rear handling” by nature and what this means is that the machine is literally steered by the rear tires rather than the front. Think about it for a moment, yes you turned your bars in the direction you wanted to go but with a two-stroke, punching the throttle to generate wheel spin was every bit as essential as cocking the front wheels in determining the direction in which the quad would be heading.

Chalk it up to the fact that power pulses happen twice as frequent in the cylinder of a two-stroke engine than a four-stroke, the throttle is relied on far more heavily in the process of making directional changes. This fact is compounded even further when you consider that two-strokes deliver their power in such an abrupt manner that the lightening (or sensation of wanting to wheelie) of the front end often results during the apex of a corner as well. Floating or skimming front tires are doing very little at that point, again leaving the rear of the quad the task of sliding the machine the rest of the way around.

On the four-stroke ATV the entire principle is reversed. Thanks to engine decompression (also called engine braking), four-strokes have a tendency to actually weigh the front wheels down when approaching a corner. Couple this to a slower, more metered power delivery and it becomes clear that the front end of the ATV is an integral part of the formula.

Even getting on the gas all the way through a corner on a four-stroke does little to un-weight the front end of the machine. What this means in plain English is that the knobbies on your front tires are digging in as they’re supposed to throughout the entire process. Because of this, the importance of having strong, meaty tread on the front tires of your four-stroke becomes clear as does the reason behind the pattern you’ve observed in having to replace your front tires more often than you’re used to.