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Frame geometry question

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Frame geometry question

Old 08-11-20, 01:25 AM
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derrickhulsey
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Frame geometry question

In terms of handling in the front end, if 2 bikes have the same trail but different fork offset and head angle, will the handling be the same?
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Old 08-11-20, 10:18 AM
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xroadcharlie
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Originally Posted by derrickhulsey View Post
In terms of handling in the front end, if 2 bikes have the same trail but different fork offset and head angle, will the handling be the same?
Funny you brought that up. I wonder about that too. To my way of thinking, A higher head tube angle will tend to make the front wheel right itself more readily from off center for more stability. But will make it more difficult to control in some circumstances.

A very low head tube angle with a lot of fork offset, even if the trail is the same could conceivably be turned completely around and ridden if there where enough clearance without an overwhelming urgency to flip back around. Very unstable.

The correct fork offset and head tube angle will provide the right ballance between stability and control for the type of bike, as well as enough front wheel clearance to the frame.

Last edited by xroadcharlie; 08-11-20 at 03:22 PM.
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Old 08-11-20, 10:45 AM
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fietsbob
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Test ride both and find out.

'Pneumatic trail' is a factor ; size of tire contact patch, then PSI is a variable ..

Many Opinions to follow..




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Old 08-12-20, 05:29 AM
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dsaul
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No. The handling and feel will not be the same. Trail is not the only thing that affects the handling of the front end of a bicycle. Wheel flop increases with a lower head tube angle, even if the trail remains the same due to increased fork offset. In basic terms, wheel flop is the tendency for the wheel to fall toward the direction of the turn.
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Old 08-12-20, 06:02 AM
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cycology
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Maybe wheel flop is also why my low trail touring bike is less stable at low speeds than higher trail Litespeed. But the low trail bike is easier no hands at speed, there are a lot of factors, maybe wheel weight and wheelbase.
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Old 08-13-20, 02:20 AM
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ShannonM
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As others have said, no, the two bikes will not handle the same, although they may well steer quite similarly. Trail differences seem to me to have the most influence on the steering feel of the bike. Steering effort and "weight", self-centering, low-speed wheel flop... stuff like that.

Your weight distribution is going to be different, and this has a huge, (maybe even primary,) influence on the overall handling of the bike / rider unit. Front and rear centers, bottom bracket drop, stem length, handlebar size and shape... all of it matters, to varying degrees. The degrees of variation also vary, from rider to rider and from bike to bike. There are some rules of thumb, that are mostly true for most riders on most bikes most of the time, but that's about the limit of what can be predicted from a geometry sheet.

This is all just opinion, based on my having owned and ridden a lot of different bikes over the years... I've never built a frame. So take it with as much salt as you prefer. It is a fascinating subject, and fascinatingly subjective.

--Shannon
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