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Trail, rake, rake, flop etc.

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Trail, rake, rake, flop etc.

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Old 03-12-18, 11:05 AM
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calstar 
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Trail, rake, rake, flop etc.

Below are a couple of calculations from Trail Calculator showing different frame geometries but with the same trail, are theses bikes going to handle/steer pretty much the same? This questions assumes all other aspects of frame geometry are the same, except of course for tt length which has to be different to accommodate ht angle change. Wheel flop differs by 3mm but from my understanding of wheel flop it mostly occurs at low(er) speeds and being only 3mm different seems negligible. I'd appreciate any input on this subject.

thanks, Brian

oops, title should have ht angle in place of one of the rakes
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Old 03-12-18, 01:33 PM
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No they won't handle exactly the same. Many of the forces acting on the steering are dependent on the head angle as to how they effect the steering. So a side force acting through a 73* HA and a 70* HA will have differing resulting steering effect.


But this begs the follow up question as to why a rider would want one geometry or another one. When I design a frame what tire sizes, fender clearances, load/weight balance the bike will see are very much a part of the geometry choice.


Since so many of my frames are on the short end of the bell curve I've found more need to kick out the front center (given the short TT) then many who build larger frames do. A slacker HA and more rake gets this done. Andy
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Old 03-12-18, 01:38 PM
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I don't think they will handle very differently from a pure steering point of view (angle and flop), but they will have to have either very different wheelbases or stem lengths to have such different head angles, and that will affect definitely affect how they handle.
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Old 03-13-18, 10:14 AM
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Originally Posted by Andrew R Stewart View Post
A slacker HA and more rake gets this done. Andy
So by doing this you get less trail which compensates for the slack HA, so it steers more like a steeper HA, correct?

thanks, Brian
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Old 03-13-18, 04:12 PM
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Originally Posted by calstar View Post
So by doing this you get less trail which compensates for the slack HA, so it steers more like a steeper HA, correct?

thanks, Brian

Actually I like the feel of about 60-63mm of trail and most all my bikes are very close to or within this range. But what I meant is that the slacking of the head angle can be looked at as increasing front center, "hinging" the steering axis at the TT so to speak. But also increasing rake will increase front center. So by doing a bit of both I can keep the trail in the range I like, increase the front center and not end up with chopper like steering.


The two "Sunday light" bikes I'm in the middle of making reflect this. My 5'3" wife is getting a 71*, 53mm rake and 60mm trail while I'm getting a 72*. 44mm rake and 63mm trail. Her top tube is 3cm shorter them mine, at 52cm. Andy
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Old 03-13-18, 06:11 PM
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Thanks for the explanation Andy. Brian
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