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It would be nice if there was in my area an extended network of bike paths on regular roads.

Unfortunately the network is in its early phases, and given the speed it's introduced at, it may be another 100 years until it's done.

But I'm not here to preach to the choir.

Since bike lanes are a rarity, I generally use trails, even though they're not well-maintained. Every few minutes, I'll encounter root damage. It's usually visible enough because they're highlighted with an orange marker.

tree root damaging bike trail

With a mountain bike I don't worry about hitting these obstacles, even when they straddle the path perpendicularly. The tires will take it.

With a road tire on a road bike I'm less sure. What would you / do you do?

  1. If it seems like just a 1cm / 0.5 " protrusion and the tire is properly inflated, just fly over it. The rim will not become an oval after that. Nor will the aluminum rim have a nasty (and irreparable) dent.
  2. Reduce your speed, and go around the tree root. The unpredictable grass would in this case be more rim friendly.
  3. Avoid bike trails that have root damage altogether. Stick to city streets. At least pot holes are easier to go around.

Update

I see that lifting oneself off the saddle is the start, but beyond that it's unclear.

There could be two things going on, and I'd like to confirm which of the two you mean. I could simply unweigh the seat two to three instants before I hit the root. The advantage then is that my weight would not be 68% rear and 32% front, or some other ratio; the point is that it's never 50-50, hence an increased chance to damage the rear rim. It would be 50-50, balancing the wheels. I suspect though that you'd do something more sophisticated. I could unweigh only one instant before hitting the root. Getting it right will take practice. Then I would also be pulling the bike frame ever so slightly up. I would not be flying. But I would yank up mildly on the handlebar. With clipless I'd also yank with my legs simultaneously. Still not with objective of flying, but to reduce the weight of impact on both wheels. Could you clarify?

Update 2

I was able to appreciate the solution intuitively, but not rationally. If you've also been scratching your head wondering "but why would that help?", head on over to the Physics SE for the answer.

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    Additionally, if you have time, stop and photograph it, and report to your local authority using either their "snap/send/solve" app or email address for reporting issues. – Criggie Apr 5 at 11:06
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    The main thing you want to beware of is bumps running diagonally, especially if they are nearly parallel with the path. These can knock your tire out from under you. Bumps that are at right angles to the direction of travel may be jarring, but they seldom cause loss of control. – Daniel R Hicks Apr 5 at 17:53
  • @DanielRHicks: Exactly. Especially when they haven't be noticed first, possibly due to overcast weather without any shadow. If you see those bumps, it's easy to adjust just a bit. – Eric Duminil Apr 5 at 18:58
  • Over time these bumps will certainly not improve and will be the beginning of larger break-ups of the surface. Document the damage over a period of time and keep the metadata of the picture files. – Carel Apr 5 at 18:59
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    The point of lifting your butt off the saddle is to use your legs as springs. You do not have to physically lift the bike for this to be effective. – Daniel R Hicks Apr 5 at 19:22
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Simply unweighting the saddle is enough to roll over most tree roots even on skinny tyres. On my 28mm tyres I don't even need to bother doing that very often. You may want to lift the front wheel in severe cases, or on the very lightest (low spoke count) front wheels.

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    I agree with this, and given the bumps pictured, I would not anticipate much of a problem riding over these with some common-sense weight-shifting. Anecdotally, I commuted for years on a path with similar root bumps every hundred meters or so, and had no wheel issues with aluminum rims and 25mm tires. I weigh 220 lbs/100 kg, too. – Poquontchn Apr 5 at 10:25
  • I've always seen cyclists rise a little off the seat before jumping off sidewalks and before hitting small obstacles, whether with or without shock absorbers, and whether they're riding 2cm or 2in tires. Perhaps I've done that myself on occasion, but I've always done it with my body in mind, to protect my spine from the shock, and to avoid that the shock wave goes all the way to my brain, which would be a minuscule/trivial concussion, but a concussion nevertheless. I never thought that doing this protects the bike itself! The idea then is to use bent elbows and knees as shock absorbers. – Sam Apr 6 at 0:54
  • I don't understand the physics, but good enough. The consensus is that doing so does protect the rims. – Sam Apr 6 at 0:55
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    Physics, summarised to a comment without loads of maths: Imagine for a moment that your body keeps a level track when the bike hits the bump. This means that (unlike the bike) it's not accelerated upwards and by F=ma no force acts on your body. The only thing that can push up on your body is the bike, and the only thing that can push up on the bike is the ground, so there's less force acting on the bike (significantly less as you weigh much more than the bike). In reality your body does move up a bit, but much less than if you were sitting rigidly on the bike - less (peak) force. – Chris H Apr 6 at 6:16
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The bike can handle those bumps just fine. As noted in other answers, just use the usual techniques for dealing with uneven terrain: get your weight off the saddle, keep your arms and legs loose, and let the bike move with the bumps as you keep your body's center of gravity in one place.

That said, unless you're riding your bike completely stripped down of accessories, you'll probably also want to slow down. It's also useful when dealing with root damage like that to try to not cross them perpendicular, but instead find and ride the line that crosses the bump where it is most closely-aligned with the path (if you're riding the same path over and over, you'll learn the best lines to take). With respect to the latter technique, if the root damage is accommodating in that way and it's done properly, you'll barely notice the unevenness at all.

Not only will this be much more comfortable, not all of the accessories on your bike are built to take the kind of jostling that the bike itself can easily handle. More than once I've lost the cover and batteries from lights going over bumps like that — first time it happened, I didn't even realize until I got home, and I had to go back and search along the trail for my parts :( — and even if it stays on, a pannier will bang around and increase the wear on the rack or on itself having to handle that kind of movement. If you are carrying delicate items in the bag, in a basket, etc. that would also be a reason to make sure the bike itself isn't hitting bumps too hard.

As far as your specifically-mentioned options go:

  1. I agree that you're unlikely to suffer any damage to the wheel or bike itself from bumps like that. But there are other reasons to take it easy over bumps. You don't want to lose control of the bike, and as I mention above, you may have things attached to the bike that aren't as resistance to that kind of shock as the bike itself would be.
  2. Only ride on the grass if you are absolutely sure it's ride-able. Running off into soft or uneven grass at speed could be far worse for maintaining control of the bike than the bumps ever would be.
  3. You'll have to judge for yourself the trade-off between the badly-maintained trail and sharing the road with motorists. My commute has always been a mix of roads, sidewalks, and shared-use trails. I personally prefer the latter and will use them if at all possible, even if there's some damage like that. But if the damage is extensive and would account for a significant portion of the ride (e.g. a quarter of the distance or more), you may prefer to just avoid it and go with the other options. Though, in my experience, where the shared-use trail is not in good condition, often the sidewalks and roadways have also been neglected. But that's not always the case.


Addendum:

Per your recent edit:

The advantage then is that my weight would not be 68% rear and 32% front, or some other ratio; the point is that it's never 50-50

No, that's not the point. The point is to maintain your body position, while allowing the bike to move ("float", to use a vernacular term). This is the same purpose as a suspension on a bike; indeed, on a fully-suspended bike, you might just ride straight over the bumps and not worry about them at all.

I could unweigh only one instant before hitting the root. Getting it right will take practice. Then I would also be pulling the bike frame ever so slightly up. …

No need for all that. And for better or worse, a road bike just doesn't have a geometry that is very conducive to that sort of handling.

Lifting from the saddle can be viewed as just a "mode" of cycling. Lift yourself as you approach, keep your weight supported as you traverse the uneven terrain, and then when you are finally past the problem, go ahead and sit back down. The goal here is not to anticipate the bumps and try to specifically maneuver the bike in concert with them, but rather to simply allow the bike to react to them without moving your body around as well.

Because the bike's weight is so much less than your own, your own inertia will give you all the feedback you need in order to absorb the bike's movement with your legs and arms. You will move up and down slightly with the bumps, just as a vehicle with a spring-suspension will move a bit. But your own movement will be a small fraction of the movement forced on the bike by the bumps, and with that sort of tree root damage on pavement, that leaves your own body moving in a nearly-perfectly-straight line.

Still not with objective of flying, but to reduce the weight of impact on both wheels

Yes. Because you allow the bike to move with the bumps, the force the bump imposes on the wheels, and thus on the whole bike, is absorbed by the movement of the bike. If your full weight were on the bike and the movement not absorbed by your legs and arms, then a much larger force would be applied to the tires and wheels. Mostly likely they are strong enough to tolerate that force without failure, but a) it's obviously better to apply less force to machines if you can, and b) regardless of how strong the machine is, your comfort will be significantly greater.


Further reading:
How to properly ride over ripples on gravel roads (washboards)?
How can I reduce back pain on a shared bike with poor shock absorbers

…and for more advanced technique/scenarios:
Is it safe to go over roots at high speed on a cross-country bicyle?

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Assuming that your wheels are in good shape, they are designed to take bumps like that. Without knowing what type of wheels you use, it does help to have wheels with at least 32 spokes. I keep my elbows lose and my grip firm, and when I see those bumps coming I get ready to lift my butt a bit.

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Essentially the problem is because all of your weight as a static mass is trying to be moved upwards by the lift caused by the bump. As you can imagine, you and the path are essentially crushing the bike with all the force of your bodyweight times the acceleration.

The only way to fight this is to unweight your bike. your legs are not bad shock absorbers, however I’ve found via riding a cyclocross bike on corrugated roads, the only way to fix this problem is to add a suspension seat post.

the key to suspension seat posts is that they need to pivot backwards towards the rear wheel. it cannot be a seatpost that springs into itself.

There are options from $80 - $500 dependant on your budget.

I use the $80 option, my partner has the $500 option, and in my opinion, the only difference is the weight of the device. Mine works every bit as well.

Bottom end - Suntour suspension seatpost (I use this) Mid range - Cane Creek thudbuster Top end - Sirrus Kinekt

Warning though, once you’ve used one of these, you’ll never go back to a normal seatpost. it’s like riding on a cloud.

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  • Nice, but.. that's half a kilogram to 3/4 of a kilogram! Understood of course that it has to be this heavy. The bending moment on the seat tube during the moment of "impact" is so high that the tube itself must be designed to withstand it. Very cool concept, but a hefty one. – Sam Apr 6 at 18:48
  • Your intuition when you say "you and the path are essentially crushing the bike" is exactly right, by the way: physics.stackexchange.com/a/542017/259693 – Sam Apr 7 at 18:43
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2 things -

1st - PUMP UP YOUR TYRES! I believe keeping the pressure up helps stop punctures and buckling.

2nd - Get out of the seat. Stand on the pedals when you are going to hit something less than smooth, i mean why the hell wouldn't you, unless, like a incompetent boxer, you like getting pounded in the ring.

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  • lol re "incompetent boxer". Well, fat tires and shock absorbers do that to you. They make you complacent. – Sam Apr 8 at 15:17
  • you're missing out on all that free leg day mate :) – user2983931 Apr 9 at 8:38

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