hadn't seen this before; trail calculator

[eddief]

http://kogswell.com/trail.php

[FierteTi52]

Nice link, thanks for sharing it.
Jeff

[Smiley]

I wonder if one should measure the front wheel with tire as an actual measurement to make this dead on . Thanks Eddie and when did Kogswell add this to their site , Matt is smart about putting this there.

[eddief]

I found the link in one of thre messages on the Kogswell Yahoo Group message board. MG has been discussing trail as it relates to the new all purpose bike he is on the verge of selling. Says he'll have a variety of forks with different trail available for that bike.

[dbrk]

I can't speak for Mattew Grimm/Mr Kogswell, he being one heck of a fine fellow, smart and wonderful to work with, but I think I know why this version of a trail-maker doesn't need the actual wheel diameter. To wit, when you add in the size of a 650B tire to the rim's diameter it is the very, very near equivalent of a 700c rim and tire (which is usually not at wide). You'd not need to calculate for 559mm rims (mtn bike) because, well, who cares what the trail is! Or to put it more congenially, mtn bike geometries belong to a different realm, there's not the same notions of speed, pavement, distance, etc., mtn bikes being a different sort of riding. So, it seems to me that this little device is an easy way to calculate for both 700c and 650B (and likely for 590mm rims too). I'd agree that it could be more precise but the math's not that tough because, well, I can do it! (And no one has ever mistaken the Sanskrit Professor for the Math Professor who comes into my classroom as I am leaving...).

dbrk

[FierteTi52]

I had to adjust the tire diameter to 675 to get the trail result to match my Serotta build sheet using a 72* head angle and a 5cm fork rake.
Jeff

[Dave]

R/tanH - (rake/sinH) where R is the tire radius and H is the head tube angle.

Obviously the tire radius must be correct to get the correct answer. To get the tire radius, take the value that you put into your cycling computer (tire circumference), divide by 2 then divide by 3.14 (Pi).