Commuting - newbie question about front suspension efficiency on paved road
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07-25-10, 06:19 PM
i have watched several videos of people riding front suspension bikes (1) very fast (15-18 mph easy) on flat trails (2) climb at a decent speed on big hills.
front suspension is tuned so there isn't much bobbing as they climb hills or sprint on flat ground. its very efficient and moves only when riders hit something. even when riders brake hard, there isn't much fork dive. this is nothing like how i hear in the forums. people say front suspension robs energy or that "it isn't fun to be bobbing up and down when climbing".
question: if hardtail with front suspension very efficient on a mountain, why can't it be just as efficient on the road? let's assume you change the tire to slicks like schwalbe big apples. to be clear, i'm comparing a hardtail mtb with only front suspension to another mtb or hybrid with a rigid fork. NOT comparing mtb to a road bike.
is it because the ht is efficient on road but a rigid is even more or is this another case of theoretical not translating to reality? i don't mind $65 / year maintenance and a little loss of efficiency for the freedom to take my only one bike (pre-ordered trek cobia 2011) wherever i please.
07-25-10, 06:54 PM
Your Trek Cobia has a lockout on the front suspension. Just lock out the front suspension when riding on pavement and it will be like you have a rigid fork.
07-25-10, 06:56 PM
The answer to your question is: Because front suspension doesn't provide any benefit during road riding (if you define efficiency as maximum speed derived from pedal input).
If you define efficiency as arriving at destination with least amount of fatigue, or any other formula that attempts to quantify comfort, then the equation may yield different conclusions.
Until recently, I had a bottom of the line suspension fork which did not have a lockout. When climbing out of the saddle on short, fairly steep hills on my commute, with weight shifted forward, the suspension would move with each pedal stroke. Rather than the effort going into moving the bike forward, a substantial amount of energy was lost in the fork movement.
When I removed the suspension fork, I was surprised to find it weighed about 2 pounds more than the rigid cromo replacement fork. Riding on the flats is about the same speed with the rigid and suspension, with small bumps probably handled a little better by the rigid and larger bumps/curb drops better with the suspension.
I think there are two general kinds of suspension forks. The cheap ones are just sprung, a lot of people call them pogo sticks. They do bob up and down a lot and the bobbing robs you of energy from friction in the fork and by shaking your body around. These are generally found in hybrids and department store bikes. Hard tail and full suspension mountain bikes by reputable manufacturers will generally have forks with springs of some kind and shock absorbtion too. The shock absorber controls the bobbing very well by dissipating energy! On a mountain bike you need suspension to cover the terrain at high speed and to get the best control you need shock absorbers too to control the rebound. The energy loss is secondary. On the road the better models of both types of fork will have a lock out and like someone else has said you can eliminate the energy loss by locking the suspension. You still have a heavier and less aerodynamic fork but if you need that fork for your other riding or for the roughest sections of your commute, well you take the good with the bad and might well end up with the solution that works best for you. We don't all want or need the same things, so don't be afraid to be different.
07-25-10, 11:18 PM
^^^Gotta agree with the posts about cheap "pogo stick" forks. I too experience the bobbing when out of the saddle, particularly when climbing. It's aggravating to think that my forward energy is being robbed by my fork. I just bought a new rigid-forked bike and the suspended one will be getting a new fork over the winter. If I ever want to go single-tracking I'll buy a nice MTB.
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