Measuring trail
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Measuring trail
Does anyone have a good method for measuring trail on an existing bike?
Getting the point on the ground perpendicular to the hub axle is easy (plumb line) but extending the steering axis is a bit tougher. I usually eyeball a straightedge down the centre of the headtube for this one. There has got to be a more accurate way. Hmmmm, maybe if I made a little jig that would hold the straightedge at 1/2 the diameter of the headtube...............
Getting the point on the ground perpendicular to the hub axle is easy (plumb line) but extending the steering axis is a bit tougher. I usually eyeball a straightedge down the centre of the headtube for this one. There has got to be a more accurate way. Hmmmm, maybe if I made a little jig that would hold the straightedge at 1/2 the diameter of the headtube...............
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click on the "Download XCL file" link inside this hyperlink to Anvil Bikeworks calculators to get an excel spreadsheet that does the trig for you.
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Originally Posted by fore
Trail = (R * cos(H * pi / 180) - K) / sin(H * pi / 180)
1) I have the ability to do something with that formula stuff.
2) I know the head angle.
I have an angle finder and a 3' level (to find a level piece of floor) but the graduations on the angle finder are so fine as to make its reading inaccurate at best. I would think that even a mildly incorrect head angle reading injected into your formula would produce a very inaccurate answer.
I do think and actual "on the floor" measurement would be the way to go. Thanks for your formula (or whatever that is!) anyway.
#6
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I did a rough estimate this way: I took a digital photo of my bike ...I leaned it against a wall with the front wheel straight, and I stood some distance from the bike and lined the camera up on what I thought was the front wheel axle line. Then opened the photo in MS-Paint, and drew lines on it down the head tube, to the ground, and vertical from the axle to the ground. I measured the trail distance between the two ground points using Paint's pixels as units, and the diameter of the rim in the photo and calculated their ratio. Then I multiplied that by 27" since it's 27" wheel. It ended up being about 1.5 " or about 4 cm, but it may have been out by about 1 cm
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Originally Posted by Bing
click on the "Download XCL file" link inside this hyperlink to Anvil Bikeworks calculators to get an excel spreadsheet that does the trig for you.
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Except for those square pies, they're definitely square.
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Originally Posted by Thylacine
Except for those square pies, they're definitely square.
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Originally Posted by Mike T.
Does anyone have a good method for measuring trail on an existing bike?
Getting the point on the ground perpendicular to the hub axle is easy (plumb line) but extending the steering axis is a bit tougher. I usually eyeball a straightedge down the centre of the headtube for this one. There has got to be a more accurate way. Hmmmm, maybe if I made a little jig that would hold the straightedge at 1/2 the diameter of the headtube...............
Getting the point on the ground perpendicular to the hub axle is easy (plumb line) but extending the steering axis is a bit tougher. I usually eyeball a straightedge down the centre of the headtube for this one. There has got to be a more accurate way. Hmmmm, maybe if I made a little jig that would hold the straightedge at 1/2 the diameter of the headtube...............
hold a ruler up to your front wheel and measure from the ground to the center of the front axle - then multiply by two for the tire diameter
head angle:
get a $0.49 plastic protractor - they have a hole at the origin - put a string in the hole and tie a weight to it - makes a dandy angle meter
fork offset:
tricky - use a ruler and eyeball it
calculation:
convert everything to millimeters and use our trail calculator - you'll need to have Flash installed:
click here to load the trail calculator
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Thanks Kogs that's a dandy trail calculator! It's within 3mm of what I crudely measured on the ground.