Any geometry geeks wanna help me out?

guava · Joined: 11 Aug 2008 Posts: 143 Location: kingston, ny

Im looking at building up a new bike. The frame I'm looking at is a hardtail with a super slack 68 degree headtube angle, designed around a 120 fork. I want to race it. I like a little slackness, but I'm worried thst 68 and a 120 are overkill. Can anyone tell me how big a difference putting a 100 fork on would make, in real numbers Its a 27.5 bike,if that matters.

Richard · Joined: 13 Apr 2007 Posts: 49

Without more information about the geometry, exact calculations cannot be performed. Need fork offset for each fork so that the effect on trail can be calculated. All things being equal, you will be steepening the head tube angle by lowering the front end by about an inch. As the fork compresses this effect is increased (of course, the effect occurs under braking regardless of the fork length, too). The steeper head tube angle will result in "quicker" steering as compared to the slacker head tube angle (less effort to turn the front wheel). At some point, it would be too twitchy for a mountain bike. Maybe that can be compensated for with narrower bars to reduce the steering effect of small inputs.
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harry · Joined: 20 Sep 2006 Posts: 94 Location: mill river ma

Simplifying things 1" of travel is about 1degree. so if you take away 20mm you can add 1 degree of head angle. this is not exact. but gives you a rough idea

smctigue · Joined: 26 Mar 2013 Posts: 98 Location: Union Vale

Guava, is the 68 degree HA with sag?

Tim845 · Joined: 02 Sep 2006 Posts: 3684 Location: Poughkeepsie

120 for racing would make you a huge minority, irregardless... Adjustable travel if the wallet allows.
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