Dear MOby,

So is it the rake or the trail that determines how fast or slow a bike steers? Lot of things I read and hear seem to use the two interchangeably at random? Which is it?

Heavy Handed


Dear Heavy,

Well, the two numbers are so closely related it almost doesn’t matter. Rake, or caster, refers to the angle from vertical at which the steering head is positioned, generally anywhere from 20 to 45 degrees – really sporty bikes being closer to 20 and custom choppers being more like 45. But the main purpose of that rake angle is to achieve the trail that the designer is after, because it’s trail, really, that determines how quickly, and with how much effort, the motorcycle will bend into a turn. A steep rake angle will almost always be accompanied by a trail figure on the short side.

Fork offset, ie., the distance from the fork centerline to the steering head, is another thing designers can play with to move trail back and forth. (Thanks for the cool gif, TagTeam.com, where there’s also a really interesting story about why things are never as simple as they seem.)

Fork offset, ie., the distance from the fork centerline to the steering head, is another thing designers can play with to move trail back and forth. (Thanks for the cool gif, TagTeam.com, where there’s also a really interesting story about why things are never as simple as they seem.)

Motorcycle guru and all-around genius Tony Foale conducted some experiments back in the day, circa 1982-83, which have now found their way onto his website. Basically he modified a BMW R75/5 so he could try various rake angles, and found that changing rake from the standard 27 degrees, to 15, then to 0 degrees, really didn’t hurt the BMW’s handling at all; in fact it improved it, as long as trail remained around the standard 3.5 inches or so.

What decreasing rake did affect, and not in a good way, was braking, which suddenly became juddery – but Foale postulated that was more to do with the BMW’s flexy fork tubes than with the modified geometry. You can read the whole thing at the site linked above, under “Experiments with Steering Geometry.” Basically, his experiments prove it’s trail that really determines a bike’s steering characteristics.

If you really want to get technical, visit dataMC, run by Andrew Trevitt and Kaz Yoshima, to get into even more detail, i.e., normal vs. mechanical trail and all sorts of other moto mysteries.

If you really want to get technical, visit dataMC, run by Andrew Trevitt and Kaz Yoshima, to get into even more detail, i.e., normal vs. mechanical trail and all sorts of other moto mysteries.

As long as there’s some trail, things should remain stable, and the bigger the trail number, the more stable the motorcycle tends to be, for reasons probably similar to why it’s easier to torque around a 16-pound bowling ball than a 16-pound ladder.

042417-ask-mo-rake-trail-chopper

Steer clear, ahem, of modifying your custom chopper with raked triple trees unless you do your calculating first, since it’s entirely possible to get into negative trail territory if you don’t know what you’re doing. And that doesn’t typically end well.


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  • Old MOron

    Raked is how Buzz wears his hat.
    Trail is the trail of tears he leaves with the women folk.

  • Jon Jones

    Great bite-sized explanation and illustrations.

  • Buzz

    Think of Zero trail as what a shopping cart wheel does when you see it flailing back and forth when you push it too fast.

  • mybluestar

    Excellent explanation, great illustrations, thank you

  • Vrooom

    What I don’t get is how can a motorcycle have zero rake but still the same amount of trail? I get that lengthening the forks could make up for reducing the trail to some degree, but it would seem like if everything else is equal, reducing the rake would reduce the trail? Damn, I thought I understood rake and trail before this article. 🙂

    • RyYYZ

      Triple clamp offset. Think of a shopping cart caster – the rake is essentially zero (the pivot between the wheel and the cart frame is essentially vertical), but the wheel is offset, giving you trail. In a typical motorcycle application, with zero rake that would require a triple clamp where the fork tubes are considerably behind the steering stem, or angled towards the rear of the bike. This would look bizarre and really limit lock to lock steering angle, though.

      • Vrooom

        I didn’t think of offsetting the triple clamp so the tubes were behind the steering stem. Thanks.

        • not-a-fanboi-honest

          There are also bikes where the wheel axle is moved forward from the forks. Presumably that has the same affect.

      • john burns

        if you click that link and go to the Tony Foale article there are pics of how he did it.

  • John A. Stockman

    Great illustrations/examples. I love Tony Foale’s book. My copy of the first edition “Motorcycle Handling and Chassis Design” is well used and read…and I do not loan it out anymore Ed! I’m enthralled by the science and physics at work, the why and how of what makes single-track vehicles operate the way they do. Tony Foale has done so much to explain and illustrate all of that. Thank you!

  • Wanderlei Santos

    I sometimes wonder if all those custom bike builders on tv are actually building safe bikes.