i've been reading motorcycle magazines for over 25 years at this point.

and i thought i knew wtf i was doing/looking at, but apparently not.

could someone PLEASE explain to me what trail is, with regard to suspension?

i have several theories, but everytime i read another article or magazine, it seems to cancel sections out of it.

thank you in advance.








ceiling cat watched me give myself a dirty sanchez.

Shoot a line down straight through the middle of your fork tubes until it hits the ground.

Drop a vertical line from your axle to the ground.

Measure between. That's your trail.

As you might imagine, if you steepen the fork angle, you will decrease your trail.

Fixed.

Right you are, Ken!


Well, nobody said there weren't any dumb answers, right?


Not to mention that technically, trail is the distance from the intersection of the angle of the steering head to the ground measured to the center of the contact patch of the front tire. But a vertical from the axle is the most appropriate way to define it.

A picture is worth a thousand words. Pic here about 1/2 way down:

Trail

Right you are, Joe! I should say that it's not a straight line through the steering stem, but rather the steering head tube since this is static. There are bearing cups available for some bikes with a rake built into them to achieve different trail so using the stem wouldn't be accurate in that particular case.

Actually, the steering stem axis is the correct reference for trail. With offset bearing cups, which vary rake angle, the trail will follow. It is not appropriate, in that case, to use the steering head centerline. The same applies to offset triple trees, although they complicate the calculation as the fork angle resulting increases trail while the rake angle of the steering stem remains the same. Both are useful tools for the race engineer to change handling characteristics although the primary use of the latter is in the chopper world where handling is an oxymoron.

You're right about the offset bearings......the front still pivots at the angle of the stem no matter how it's oriented in the steering head. However, trail will be affected by rake angle and not "follow". The more rake you put into a system, the more trail will result.

I've never dealt with offset bearings but have experience in offset trees to obtain a desired amount of trail (offset trees typically reduce trail) on a longbike (chopper). Handling in the sense of cornering like a sportbike isn't possible, of course, but getting a front that's 30" over stock to turn without flopping is definately possible by getting the trail right through the use of offset trees.

Offset bearings?


Cripes, wasn't there anything better to do that day? Jeepers, guys will go to any lengths to compound an issue, won't they? Who came up with that clever idea?


"lessee....if we move the center of the bearing, and use offset triples, and use a leading axle, maybe we could get something harder to manouver than an ocean liner...

If I remember right, Bimota started it, shortly followed by Ducati and, I think, Aprilla. The Superbike and F1 folk use them as well to fine tune handling. We are not talking choppers here, 1/2 a degree or so can be dramatic.

Speaking of choppers though, it is one advantage of using a springer style front end. Trail can be moved around just by changing the rockers.