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The last part of my commute to work has some significant bumps in the road which are really quite jarring, since I'm on a road bike that, of course, has no shocks (but has a carbon fork).

Most of the bumps are caused by cracks in the asphalt that have separated or curb corners that don't totally flatten to the road level at the crosswalk... or tree roots that have started to push up from beneath the pavement.

Should the bike take most of the concussion from hitting bumps? If I lift myself off the seat only barely and just for a moment, I don't have to feel the brunt of the force, and my bike has more freedom to take the hit instead of me. (These aren't so large that I am at much risk of totally flying off the bike if I stand up slightly for those moments. I'm still holding on, but maybe more lightly.)

Will the bike last longer if I kind of use my legs as springs, or should I stay firmly planted and take the jolt from the bump? What's the tradeoff, if any, between my health/safety and the longevity of the bike?

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5 Answers

up vote 25 down vote accepted

This is not an either-or proposition. Your bike is hitting the bumps and supporting your full weight (minus the very small proportion of weight that might be falling at that exact moment) regardless of how you stand when you hit the bumps.

The difference is whether you're going to let the additional damping effects of the down tube, seat tube, bottom bracket, cranks, and pedals absorb some of the shock before hitting your body, and whether you take that shock on your feet (which are protected by hard soles and socks and are connected to your springy ankles) or just take it right on the sit bones (which are hard and part of your skeleton). Obviously one of those is going to feel a lot worse than the other.

It's helpful to imagine an analogous system: a very light car carrying a heavy load. Our choice is whether the load is supported on a suspension system or not. If we rigidly attach the load to the frame of the car, the load isn't "taking the hit" when the car hits a bump -- rather, the shock is worsened because there's nothing to absorb some of the energy of the shock. If we suspend the load, the total weight the car is carrying remains the same (it has to), but we let the suspension system absorb some of the energy.

You and your bike are both better off if you get off the seat a bit and let your legs (and the frame, to some extent) act as a suspension system.

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+1 for the car analogy... puts it into context beautifully. –  Zeus A. Jun 6 '13 at 18:40
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You have it backwards.

When you stand up, your legs (bent at the knee) provide suspension, separating the unsprung mass (the bicycle) from the weight of your body. This is easier on the bike, not harder. Though the bike complies with the bumps, it does not have to deal with your mass in doing so.

(Well, strictly speaking, standing is harder on your pedals, cranks and bottom bracket, but overall it is easier on the frame.)

When you're seated, there is still some suspension from your butt and whatever springiness is in the seat, but it's not as effective. The jolts you're feeling are being transmitted through the wheels and frame.

Your bike can't "take it instead of you" because if you're taking it, you're taking it through the bike, not directly from the road.

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And keep in mind that your body weights roughly 10 times more than your bike. –  Daniel R Hicks Jun 7 '13 at 11:10
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If I see a significant bump coming (on my touring bike -- no suspension), or just a stretch of fairly rough pavement, I'll generally raise my bum a few inches off the seat and flex my arms, so that my legs and arms are the "springs".

This in not only more pleasant than taking the hard bumps, it also helps the bike maintain contact with the road, reducing the chance of the wheels sliding out from under you. And, of course, it's easier on the wheels. Plus, I suspect the physics of it all makes it better from an energy expenditure standpoint -- less of your forward momentum is lost to the bump.

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+1 for clearly explaining that the arms and legs are functioning as suspension. –  amcnabb Jun 6 '13 at 20:31
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Rather than acrobatic movements with your bike, could you not find a cycle lane to your destination to avoid this? I had the same problem as you but got over it once I used cycle lane for part of my journey. They are usually better in this kind of circumstances. I would recommend you do that for once.

I know that it would be mental, but could you possible post a picture of the actual road surface? We could give you an improved answer based on that.

If you really need to be on the road, the best way is to balance out the concussion between yourself and the bike. YOUR SAFETY IS FIRST, you can buy another bike not your limbs or arms. A solution would be to determine if you can streer your way around the contiguous cracks and potholes. This will help you to improve your attention to the road surface too. BE CAREFUL OF THE CARS BEHIND YOU. If this is not possible, the other way (which has worked for me so far) is to find course through that specific road which would result into less number of bumps and concussions to yourself and your bike.

What you mentioned (i.e. lifting yourself off the seat for a short while to avoid experiencing the concussion) works sometimes, but may be not in favour of road bikes. MTB users often perform a basic bicycle lift where they lift the front wheels first, raise themselves from the saddle a little bit, dash back, and perform a jump around obstacles. This is however, not recommended for road bikes....... I would have thought.

There may be youtube videos where people have done this type of safe cycling around cracks and holes. I also recommend you find them.

Again, post some pictures if possible please.

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Do you have any evidence that standing on the pedals is harmful to the bike? I had never heard this assertion before? –  Alex Jones Jun 6 '13 at 17:44
    
BMX and MTB users, how do they do it then? As I said, Road bikes are not probably very suitable for that kind of moves. –  hagubear Jun 6 '13 at 18:01
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Thanks. And to clarify: A paved trail joins my path about halfway up my commute. It's less maintained than the road and has more signs of decay than the concrete of the actual road. Many of the cracks go all the way across the trail, and the curbs often don't go down to the same level as the road, causing about a 1- or 2-inch wall. In other words, without going off the trail into the grass, there's no way to avoid some of these bumps, unless I ride on the (mostly shoulderless) busy road. –  Matt Jun 6 '13 at 19:06
    
@Matt Thanks for the details. I guess you are quite limited by options then. I also think DanielRHicks have given you a solution, something similar to what I told you already about MTB and BMX bikers! I still think road bikes may not be for this kind of stunt, especially when you do it everyday. –  hagubear Jun 6 '13 at 19:25
    
Don't get me wrong... my ride is still awesome, but there's just some bumps near the end. After 2 years with a MTB I was so ready for drop bars and having a lot of fun riding to and from work. :) –  Matt Jun 6 '13 at 19:41
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You should be light on your bike.

It's not really an either or thing. If you're light on the bike (letting it jump under you), it takes the hit but then is able to move how it wants after that. If you've got your full weight on the bike, then it still takes the jolt, but can't move - you're holding it down. Roughly, the bike gets squeezed between you and the pavement. There's force up on a wheel or two, and force down on the seat, and possibly the bars and pedals.

Having your weight on it is something like putting an object on a table and giving it a sharp whack with a hammer; letting the bike move under you is like hanging that same object from a string and whacking it. If it can move freely, it won't take as much damage.

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To elaborate, you should shift your weight back as your front wheel travels over the bump, and shift your weight forward as your back wheel travels over the bump. –  Kibbee Jun 6 '13 at 19:08
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@Kibbee I was thinking more of just letting the bike buck under you, for bumps small enough that you take them at a speed at which you don't really have time to shift back and forth much, but yup, that too! –  Jefromi Jun 6 '13 at 19:10
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