boon racoon Posted March 28, 2007 Report Share Posted March 28, 2007 elloright what's with this new fangled UCI style geometry? From what i can see toptube length has all gone out of the window and it's all done by measuring the front centre now?a question - does front centre in this case work horizontally and vertically whilst keeping the head angle the same?i.e if you had a front centre of X and you wanted to make it longer..could you jack the headtube upwards as well as horizontally (i.e making the TT longer) to increase the distance? or is it a happy medium of the two?i guess decent geo is back ends of about 380mm now and bb is +20ish?that make any sense?! haha Quote Link to comment Share on other sites More sharing options...
NVWOCI WVS Posted March 28, 2007 Report Share Posted March 28, 2007 that make any sense?! hahanope, not at all! Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted March 28, 2007 Report Share Posted March 28, 2007 i guess decent geo is back ends of about 380mm now and bb is +20ish?Sounds good to me Quote Link to comment Share on other sites More sharing options...
boon racoon Posted March 28, 2007 Author Report Share Posted March 28, 2007 This is what I mean...They have the same front centres, and the same head angle.Yet the position of the headtube is different.What i'm asking is, how do you know where's best to place the headtube?! Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted March 28, 2007 Report Share Posted March 28, 2007 Most frame geo is usually quoted when running a 400mm (or somewhere near that mark) fork.That would mean only one place for the headtube to be really, if you are assuming the head angle and reach (front centre on the pics) are known and fixed Quote Link to comment Share on other sites More sharing options...
AdamR28 Posted March 28, 2007 Report Share Posted March 28, 2007 how do you know where's best to place the headtube?!Well usually there's these two tubes called the down tube and the top tube - you put it on the end of those... Being a little more serious, the head tube just ends up where the rest of the geo tells it to. If your wheelbase is X, back end A, head angle B, fork length C and the BB rise Y, then the head tube will just end up in the right place to conform to all these other dimensions.That make sense?Of course you could make head tube placement one of the things you base the rest of the bike's geo around, but for all other frames at the moment it seems to be the other way around... Quote Link to comment Share on other sites More sharing options...
NVWOCI WVS Posted March 28, 2007 Report Share Posted March 28, 2007 What i'm asking is, how do you know where's best to place the headtube?! right, length of fork, length of wheel-base, bb rise and length of chainstay, do some math and you get the answer surely?!?!?!? Quote Link to comment Share on other sites More sharing options...
boon racoon Posted March 28, 2007 Author Report Share Posted March 28, 2007 (edited) having thought a little more, yeh it makes sense and forks are measured from the dropout (or horizontal on the diagram) to the bottom of the headtube? or do you have to take into account the crown, headset etc? Edited March 28, 2007 by the boon Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted March 28, 2007 Report Share Posted March 28, 2007 Centre of dropout to crown I believe Quote Link to comment Share on other sites More sharing options...
RobinJI Posted March 29, 2007 Report Share Posted March 29, 2007 Forks are the virtical distance from the axle to the crown.Dodgy paint drawing solve all!http://i138.photobucket.com/albums/q271/ringwams/Forks.jpg (grr can't put images in posts at college) Quote Link to comment Share on other sites More sharing options...
dave85 Posted March 29, 2007 Report Share Posted March 29, 2007 There you go.Altho I would call what you've termed as rake, "offset". Traditionally, the rake is what we now call the head angle. Another term, the trail, refers to the distance along the ground from a line drawn through the headtube centre, to a line drawn vertically from the front wheel axle. Quote Link to comment Share on other sites More sharing options...
manuel Posted March 29, 2007 Report Share Posted March 29, 2007 think of it this way - fix your headtube angle first as thats going to affect steering and taps n stuff like that. go for a standard headtube length of 10- 11 cm ?. then the only thing that affects reach will be bb height - which you want at 20 mm (too high..) and overall wheelbase.probably didnt help Quote Link to comment Share on other sites More sharing options...
Brian Bleech Posted March 29, 2007 Report Share Posted March 29, 2007 HA: 72BB: +20CS: 380WB: 1060 Quote Link to comment Share on other sites More sharing options...
RobinJI Posted March 29, 2007 Report Share Posted March 29, 2007 (edited) Altho I would call what you've termed as rake, "offset". Traditionally, the rake is what we now call the head angle. Another term, the trail, refers to the distance along the ground from a line drawn through the headtube centre, to a line drawn vertically from the front wheel axle.Yeah, I know its not traditionally rake, but that's what its called on tarty, which to be fair, is probably where most people find out there forks dimensions.Leedstrials, that geometry sounds perfect for a stock Edited March 29, 2007 by Dont you Just Hate it When... Quote Link to comment Share on other sites More sharing options...
Ash-Kennard Posted March 29, 2007 Report Share Posted March 29, 2007 HA: 72BB: +15CS: 385WB: 1095 Quote Link to comment Share on other sites More sharing options...
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