26'' front fork on a 20'' wheel
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Yeah, I wouldn't have mounted all the way to the top. I figured 2 inches higher than my current setup.
Just curious--how did you determine how much change would give how much better higher speed stability?
What speed do you lose stability at now, and how does the stability fail?
What speed do you need it to be stable up to?
Keep in mind that slackening the fork angle (more "chopper-like") means more wheel-flop at lower speeds, which may affect lower speed handling adversely.
It also makes the suspension itself less effective, as it isn't as vertical, so it will do more bending of the fork vs pushing it along it's length.
I understand. I get front wheel wobble past 50mph. Currently I'm running a taller rear wheel which is effecting the angle. I figure I can get maybe 5 degrees more rake to solve the problem. Plus I hate the current front suspension.
It might not solve your wobble issues. That can be related to tires or tire pressure, bearings, or worn front or rear suspension components. Are your headset bearings in good shape?
It can also be caused by frame flex.
I've run it with two different tire setups and the bike is brand new. I've tightened the forks as much as safely possible as well. The one question is the rear suspension. It will wobble earlier with added weight on the rear. I'm getting new forks regardless as there's too much flex in the stock tubes. Just a matter of 20'' or 26''.
I lean toward the headset, only because when I had a headset issue (binding/too tight), my bike was super dangerous to ride. I had a similar thing on one of my motorcycles after a crash. The forks were of kilter in the triple clamps, with a similar binding in the headset. I was able to ride home and straighten things out. The amount of movement required to ride a bike without tipping over is tiny, but if something impedes those tiny movements and it gets scary fast.
Do both forks have the same travel?
My frame has a slack head angle and was designed to work with a broad range of fork lengths, depending on application. For cross county, 115mm, for freeride, 160mm, the former being more nimble at slow speeds and the latter being more stable at higher speeds.
Most 20" forks average between 80mm to 100mm travel and 26" forks between 100mm to120mm. You could have longer travel versions of either. So going from 20" to 26" will provide a 76mm increase in height (and corresponding change in head tube angle) due to wheel circumference, plus or minus the difference in travel of the two forks. A 20" fork with 80mm and a 26" with 120mm, is different than a 20" with 100mm and 26" with 100mm. My frame geometry handles a 45mm difference in fork height fine. Not sure about 76mm (or more) though.
I haven't chosen which forks I'm going with yet. Thanks for the information. My current head tube angle is 75 degrees. That seems way steep to me. I'm shooting for 68-72.
75 is like a BMX frame; not really built for speed. You can just do the math, or even just put something under the front tire and measure the angle to see what increase is required. The iPhone level apps are good enough to measure it with. Maybe a 24" fork with work.
Wow, that's a awful stock angle.
I'd consider cutting it halfway:
24" fork or 26" fork that isn't super tall..
reduce the rear wheel size and lose a little rear shock length..
As a bonus, this will give you a longer wheelbase in the rear and front. You could use it at these high speeds.
I'd consider cutting it halfway:
24" fork or 26" fork that isn't super tall..
reduce the rear wheel size and lose a little rear shock length..
As a bonus, this will give you a longer wheelbase in the rear and front. You could use it at these high speeds.
I'm part of the problem here. I changed the stock rear shocks from 330mm to 360mm...
