lim@mit-eddie.UUCP (Pean Lim) (11/15/84)
I happen to have one of those pseudo touring bikes that has 74 degree head seat tubes, but is billed as a touring bike. Here's my question: does switching to a fork with more rake improve the ride appreciably? I have a 23" frame with a 39.3" wheelbase. The offset of the fork is 1.8". I'm wondering how much greater fork offsets are available and what difference it can make. [Side note: I just installed fenders and it turns out that I had to take drastic steps to make sure that the toe-clips will clear the front fender. I'm glad I found out that they wouldn't clear while riding at a relatively slow speed ... ] Pean
wagner@uw-june (Dave Wagner) (11/20/84)
> I happen to have one of those pseudo touring bikes that has 74 degree > head seat tubes, but is billed as a touring bike. Here's my question: > does switching to a fork with more rake improve the ride appreciably? > I have a 23" frame with a 39.3" wheelbase. The offset of the fork is > 1.8". I'm wondering how much greater fork offsets are available and > what difference it can make. Front forks geometry is pretty subtle stuff. By increasing fork rake, you will probably increase hand comfort; but you will actually destabilize your bike by cutting down on the amount of fork trail! Trail is the property that allows you to wheel your bike in a straight line without holding onto the handlebars. It should be much more difficult to control a bike if you reduce its trail substantially. Trail is calculated in the following way: project a line through the head tube down to the ground. Also drop a perpendicular to the ground from the hub axle. The distance between these two points on the ground is the trail. The more trail, the more stable the bike. Note that by increasing the fork rake, you move the hub axle forward relative to everything else, thus decreasing trail. Bicycling magazine used to have good discussions of frame geometry occasionally; I think they've moved all that stuff to their Bike-Tech newsletter (a real rip-off!). Note also that by having too much trail (or is it too much fork rake, I forget which) you can suffer from "wheel flop" - i.e. once turned, the wheel resists being straightened. This is because turning on the bike actually drops you closer to the ground; in order to straighten out you are fighting gravity. With the wrong fork geometry, you drop much farther on turns than you ought to and have to fight to get the bike back up! In summary, seek out an expert before you buy a fork. "Expert" means FRAMEBUILDER, not bike mechanic, because most bike mechanics don't know the slightest thing about frame geometry (but they believe they do, which is what makes them dangerous). Dave Wagner wagner@washington ...decvax!uw-beaver!uw-june!wagner