duane Posted February 5, 2006 Report Share Posted February 5, 2006 Hi All,I have searched the forum trying to figure out how a longer or shorter stem is going to affect my bike, while there are plenty of stem related posts, I haven't found any that refer to whether the stem over hangs the front wheel or not, which is surely the most relevant factor to how flickable the back of the bike will be ?My Scott Aspen MTB has a negative overhang of 145mm, that is the center of the handle bars is 145mm behind the center of the front axle which probably explains why its so hard to get the back wheel up. As the bike is a cross country FS bike this is ideal, you want the back wheel to stay stuck down for power when climbing and safety when decending.However thats not what I am using the bike for. Now to get the stem where I think it should be, more or less directly over the center of the front axle I would need a stem of 245mm, which is plain wrong.Is my thinking all wrong, what sort of over/under hangs do you have on a purpose designed trials bike ?Duane. Quote Link to comment Share on other sites More sharing options...
Endohopper Posted February 5, 2006 Report Share Posted February 5, 2006 (edited) Well explained , but you forgot two variables : fork rake and handlebar sweep . These will only account for minor differences , but can radically affect the " feel " of the bike . I don't think there's any right or wrong here , it's largely down to personal prefference and the other componentry you will be running . Edited February 5, 2006 by Endohopper Quote Link to comment Share on other sites More sharing options...
ScotchDave Posted February 6, 2006 Report Share Posted February 6, 2006 Well, 145 mm stem is damn big in any direction, but with a bit of work you can probably turn it round. If you take a photo of your handlebar are and bike I can probably tell you how to sort it. Quote Link to comment Share on other sites More sharing options...
Tomm Posted February 6, 2006 Report Share Posted February 6, 2006 Well explained , but you forgot two variables : fork rake and handlebar sweep .Head angle is probably more important that either of them.But seriously, I've never heard anyone use "stem overhang" - and certainly not in trials. Basically any decent trials frame will have geometry that is just about right for trials. We tend to talk in terms of stem lengths and head angles of the bike, which will essentially add up to the same thing. I wouldn't worry about your stem overhang anyway. Quote Link to comment Share on other sites More sharing options...
duane Posted February 6, 2006 Author Report Share Posted February 6, 2006 (edited) Hi All, The bike I have is a normal FS MTB, while I realise that any decent trials bike has a trials specific head angle, I am interested to know how different this is, if at all from my mountain bike. Looking at the handlebars and stem as a lever acting around the front wheel axle, it would seem to me that a stem that positions the bars forward of the front axle would make the bike very tippy, whereas with the bars way behind the front axle its going to be extremely hard to lift the back wheel in an endo. This is regardless of the head angle which primarily effects steering response. I realise there are a million other factors like BB height, wheelbase etc, but ultimatley when you put the front brake on and rock forward, the further foward your bars are in relation to the front axle the more you will be pushing over, rather than through the front axle and the easier the back will lift.Its possible that I am completely wrong, so if anyone has a plumb line and a tape measure handy, go drop the plumb line from the center of your bars and measure the distance in front of or behind the center of the front wheel axle, then let me know how easy moves requiring a back wheel lift are, we might learn something, Regards Duane. Edited February 6, 2006 by duane Quote Link to comment Share on other sites More sharing options...
Bucky Posted February 6, 2006 Report Share Posted February 6, 2006 The bike I have is a normal FS MTB, while I realise that any decent trials bike has a trials specific head angle, I am interested to know how different this is, if at all from my mountain bike. jump on any zoo echo onza koxx and then youll realise exactly how much differnce there is.http://www.koxx.fr/popup.php?lg=fr_FR&sec=...DB4198af2bbafd9http://www.btt.com.ar/foto/o/10/84/1084202693_chameleon_geo.jpg Quote Link to comment Share on other sites More sharing options...
SQuiT-man Posted February 6, 2006 Report Share Posted February 6, 2006 To be honest stem overhang doesnt really matter too much for front wheel moves- as your technique/body positioning will adjust to whatever stem length you have.For backwheel moves, there are two things to consider-a) a shorter stem COULD to a degree make it easier to go to backwheel, because (i) you have less cockpit space, hence more freedom of movement, and (ii) perhaps more importantly, your bodyweight is further backwards, not learnt over the front of the bike.However, a longer stem could make the force needed to support your own weight while on the backwheel less, due to the increased leverage ratio you obtain between (rear axle-bar distance):(chainstay length)There are a million different factors to include, but these two are major ones, which are part of the reason you may find most trials riders have VERY short chainstays, to get the best of both worlds from both of the above Quote Link to comment Share on other sites More sharing options...
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