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Dunlop MX3S.

Dear MXA,
I ride a 2015 Honda CRF450. I currently run 120/19 rear tires. I’m thinking of switching back to 110/19 tires because I think I can feel a difference between them. What size rear tire does MXA prefer?

First, you need to know that the width numbers on rear tires are not accurate, nor comparable‚ which defeats the purpose of sizing them. According to Dunlop, the tire width number is derived by measuring from shoulder block to shoulder block, but this is an inexact science and depends on how the tire manufacturers choose to make this measurement. Thus, most 120 rear tires are not true 120s. There are 120 rear tires that are narrow and ones that are wide. And one tire company’s 120 may be smaller than a competitor’s 110. As a rule of thumb, as long as you stay within the same brand and model of tire, a 120 will wider than a 110. As a rule of thumb a 120 is slightly less than a 1/4-inch wider than a 110. But, if you switch from a Dunlop 110 to a Michelin, Maxxis, Pirelli, Bridgestone, STI, Full Bore, Gibson or Kenda 120‚ all bets are off.

As for your question—almost every tire manufacturers recommends a 120 for 450cc four-strokes, but every MXA test rider prefers to run a 110 rear tire. Why? A 120 rear tire makes a poor handling bike feel even poorer. Most MXA test riders think that the 120s are harder to roll over in turns and make the bike stand up more in ruts. They also have a tendency to push the front tire in flat corners—especially when the engine chugs into a turn at low rpm. On the bikes that come stock with 120 rears, we almost always return to a 110 rear. However, for straight line acceleration, a 120 will put more rubber on the ground, but you give to get.