Bike setup

[Jon]

Just wondering about two things-1.Why do chain guides always have a roller on the leaving side of the chain ring ie the bottom.Surely you would want one on top if anywhere.I know most do have this but why do all have a roller at the bottom? 2.The other thing is why are dh stems so short?Is it to enable the rider to get as far back as possible? And how does this affect the steering if you are coming from a long xc type stem? Any info would be appreciated.
cheers jon

 

[t]

Most people drop their outside foot when cornering, this means that half the time you do a 1/4 turn backwards with the cranks, often over rough terrain and alway leaning over so it's quite plausible for the chain to de-rail. Also as your rear end goes over bumps, the deraileur bounces around and especialy on a dually as the suspension activates little ripples get sent along the chain.

Short stems are primaraly to shift weight back on the wheelbase, it speeds up the steering, but the slack head angles slow it down so these counter act each other. the combined effect is that the bikes are steered more by hip movments and less by shoulder movments than an XC bike

 

[S.]

The main reason chainguides have a roller at the bottom is because when you hit a bump or land on the ground or whatever, the chain's inertia/momentum pushes it downwards. At the top this just wraps it further around the chainring, but at the bottom it "unwinds" and is much more prone to coming off.

 

[Jon]

Fair enough ,thanks guys .I will be sussing out the bikes tomorrow at ourimbah,see you there.
cheers jon