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My girlfriend and I are looking at a new bike for her. The one we're looking at has a 70 degree head tube angle while her current bike has a 70.5 degree head tube angle. Unfortunately, none of the local shops has one in stock for her to try out. So my question is:

How much does the head tube angle affect the fit and feel of a bicycle? I'm sure that it has at least some effect over the fit of the bicycle, but how much? And I'm guessing it has an even bigger effect on the steering, but again, how much?

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A superset question: bicycles.stackexchange.com/questions/12374/… –  cmannett85 Oct 21 '12 at 19:54
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2 Answers

up vote 8 down vote accepted

there's a good write-up about this here: http://www.calfeedesign.com/tech-papers/geometry-of-bike-handling/

In general the steeper the angle the more agile the steering. If you like steeper you might say "quicker, more response", if you didn't like steeper you might say "twitchier".

A 1/2 degree difference is probably not going to make that much difference by itself. The other factors, which headset, installation of headset, stem length, handlebar type and setup, etc., will mask the differences here. As the Calfee page mentions, people will adjust very quickly.

Happy Riding!

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Also, handlebar reach (as adjusted by stem height and length) have a very significant effect on bike handling, for any configuration of angle/rake/trail, since it affects the torso-weight distribution over the handlebar (via each hands), thus making the self-centering effect on steering more or less pronounced. –  heltonbiker Oct 19 '12 at 14:14
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It should be noted that "steeper" means closer to 90 degrees -- vertical. And generally head tube angle is adjusted in concert with fork "rake" -- the degree to which the fork curves forward. There is a complex relationship between the two that determines stability vs responsiveness. –  Daniel R Hicks Oct 19 '12 at 15:28
    
With a recumbent, it's even possible to have a vertical or past vertical headtube, which won't be twitchy with an appropriate fork: fastfwd.nl/assets/images/nieuws2.jpg Obviously if you tried that on a conventional frame, the front wheel would hit the downtube. –  armb Jun 12 '13 at 11:14
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As you already suppose, the angle does make a difference.

To your first question: If you take the distance between the wheel axles as a constant measure, the handle bar will get further away from the saddle the higher the head tube angle gets, therefore the geometry gets "longer". This can for a certain amount be compensated by a shorter stem.

The bigger effect is - you guessed it - on the steering behaviour. A flat head tube causes the steering to get more stable, so its tendency to go straight is higher. This means that if you compare a bike with a flat head tube to one with a steep one, the flat one will feel like driving on rails, meaning you feel like you have to "force" it into curves as it tends to go on straight.

The most interesting question is if the difference of half a degree really would make a difference but I think it won't. I can remember that when I bought my last bike some time ago that the different bikes that made it to the final decision had some spread over some 1 or 2 degrees in head tube angle, but they were all from the same price and purpose class. So I would say that such a small difference will be more due to technical decisions of the manufacturer than due to better or different handling.

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