bike geometry for idiots

[lewis1641]

anyone fancy explaining the basics of bike geometry in layman's terms?

i understand shorter stays climb better, but when it comes to head angles, stem lengths, fork rake and the like i'm at a bit of a loss.

are there any key rules? is there a relationship between the front axle and handlebar for example?

i'm not planning anything clever (certainly not before 5/5/10) but just curious really.

 

[cyfa2809]

yes im with you, i have no clue! especially what a slack head angle means? closer to 90 degress or less? :?: :roll:

i know a shorter stem is less responsive but more control :? and a longer stem is more responsive but less control? wrong way round? :?:

just ride lol i give up!

 

[BerthaPog]

This any help?

http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry

 

[ferrit]

heres a handy tool, for anyone contemplating different forks with longer/shorter A2C than the original.

http://bikegeo.muha.cc/

 

[Neil G]

Slack head angle = slower steering and often seen on AM/FR & DH bikes, better for going downhill quickly.

Typical angles for most XC rides are 73 seat and 71 head

 

[orange71]

If you take slack to an extreme you get a chopper (motorbike-type chopper that is, not the old Raleigh).

So imagine the steering on that, then how it will get more responsive as you wind the head angle steeper. This is what happens also if you put forks in that are too long for a frame, it slackens the head angle and so make the steering very unresponsive and flip-flop.

Sorry, probably not a good explanation :roll:

 

[legrandefromage]

shorter rear stays for roadies means a stiffer frame for acceleration, longer for flex and comfort. So they say.

 

[perry]

i understand shorter stays climb better

But that completely contradicts this

http://www.youtube.com/watch?v=ZjKVITPo7To

http://www.youtube.com/watch?v=07KPlT4Ommc

http://www.youtube.com/watch?v=-c_7fRq_ ... re=related

I used to watch it on the telly loads .

 

[Andy R]

i understand shorter stays climb better

But that completely contradicts this

http://www.youtube.com/watch?v=ZjKVITPo7To

http://www.youtube.com/watch?v=07KPlT4Ommc

http://www.youtube.com/watch?v=-c_7fRq_ ... re=related

I used to watch it on the telly loads .

Well, shorter stays = more weight transfered to the rear wheel = better traction, but that also equals easier looping out and less straight-line stability too.
Like with most things, it's all a trade-off......but those roadies have no problems with traction so they must be talking bollocks...

That's as much sense as I can make after a bottle of bubbly and half a bottle of nice Pinot Noir (between two of us I must add, lest you think that I'm a complete piss-artist......)

And we haven't even touched on rake and trail yet

 

[Neil]

The short seat stays thing is about the distance from the BB / pedals area, and the rear hub being as short as possible - therefore less energy lost in flex or frame movement.

Clearly how much the bottom bracket area flexes and moves, has an impact, but also, the longer the rear triangle (by merit of the chainstays, and as a consequence (in traditional frames) the seatstays, the more give it will have when power is being applied at the pedals.