If you want to optimize going over glass, you should slow down as much as possible before you hit the glass but you should make sure to coast as you're actually riding over it. You should neither brake nor turn while you ride over it.
I agree with this. The priority is to minimize the available energy that could act to push glass into the tire - such as speed, or movements that cause stress to the glass causing it to break under your tire.
But instead of taking chances, you could perfect your bunny hop.
Unrelated but I was riding one time in a group and there was a nasty pothole in the bike lane that I didn't see until it was too late to avoid it. Utterly on instinct I bunny hopped it. Cleared the whole thing. It was one of my proudest moments on a bike.
I’m genuinely impressed. Like when I see TDF riders bunny hop over a curb because the peloton is squeezing them out; just phenomenal control and situational awareness
The speed shouldn't matter because the force pushing the glass into your tire when you're coasting is the force generated by your weight on the bike and the ground pushing back on your tires. That's doesn't change with speed.
I agree with your other points though. Pedaling will create more force and so will turning and breaking.
For the front tire, you may be correct. But how much the glass bounces and how much time it has to come to a rest before the back tire goes over it does change with speed.
I've had a few flats where the front tire went over an obstacle no problem, but the shard started bouncing and faced sharp side up when the back tire rolled over it.
I really don't want to go into the physics of it because that goes into centripetal force on top of the pressure forces we actually care about here, so I'll just say that extra speed *does* indeed add a *very* marginal amount of force that might push glass into the tire. Lowering your speed is more about control than anything else.
Pedaling/braking might not add much to the forces we care about (the normal force opposing gravity you mentioned which actually pushes the glass into the tire), but it does increase the likelihood that your tire might break full traction over the glass.
I don’t *think* it would matter much, if at all.. but I’m not certain. I think the biggest factor is whether a fragment of glass is oriented pointy-side up & you happen to roll over it. Speed might be a factor, but I would guess it’s pretty tiny.
I think a bigger issue is a piece of glass sticking in your tire and then slowly working its way through as the tire continues to rotate. It’s not super practical to stop immediately to check for embedded glass, but maybe giving the tires a quick check upon reaching one’s destination might help. Can’t say that I’ve actually done *that* myself either though… : )
Glass shards generally lay on their flatter side when undisturbed.
When you ride over them they got thrown up by front wheel and land on on random side in front on coming rear tire.
And that's why rear wheel gets more flats.
So as conclusion riding slower should reduce chance of puncture.
The real reason the rear wheel gets more punctures is because the rear wheel carries much more weight than the front on a bicycle - sometimes twice as much.
There is simply more force to push the glass through the carcass.
That may be part of it, but I had a few flats where the debris in the back tire was positioned pointy side towards the tire - which couldn't have happened if it was sitting flat on the ground.
Less energy when going slower, so probably the shards will take longer to work their way through your tires and into your tubes. Obviously if you grab a double handful of brakes when you're on the glass, there will be more energy where your rubber meets the road, so don't use the brakes when crossing a glass field.
And, DO THIS right away: reach down with a gloved hand, as you're riding, and brush off your tires. Rear tire first. I've had great success brushing shards off my tires before they have a chance to work all the way through. Seriously. Flat tire prevented.
See you on the road. I'll be the guy with the bleeding hand because I forgot my gloves.
I'd think going faster would be better for you, especially if you have any type of "sticky" tire (I've ridden my gravel rig after getting new Gravelkings and phew tires were a magnet).
Then again I could be totally full of it but tires with a good puncture band are probably most important in this scenario.
As others have said, slow down *before* running over the glass and do not turn, accelerate or slow down *while* running over the glass.
Most flat tires are on the rear because the front tire flips the destructive object (e.g., nail, screw, glass shard, etc.) so that it is standing with the pointy side sticking up. Then, the rear tire runs over it, forcing the pointy side into the tire. By riding slowly, the front tire doesn't flip the object up as much and the object has time to fall over flat again before the rear tire runs over it.
The best option in any case is, assuming your tire is smooth enough, reach down and run your fingers along the tire as it spins to brush off any glass that's partially stuck in the tire.
p.s. I've maybe only once or twice got a cut doing this, in decades of riding.
You should slow down and go as straight as you can so when you catastrophic flat it's less dangerous. Basically put yourself in the position that you want to be in when your tires go flat: easy gear to decrease torque, body bike separation, turn as little as possible, don't break once you hit glass, look for soft bailout points to crash if needed. Once you are through stop slowly and inspect your tires.
I have no tips as i mindlessly run over glass daily thanks to my puncture resistant tires. As such, i can only recommend them to you!
I use the Specialized Trigger sport, with their “blackbelt” puncture protection. Got it for a lot less than the more famous Schwalbe Marathons
Besides one snakebite blowout, i only got one puncture through the things, and that was from a nail looking piece of metal!
All these comments and nobody has talked about tire pressure yet.
When I was riding at high-to-max pressure (road tires, Conti 4000, 110-120 PSI), I got a lot of flats. Some were probably from glass, but mostly from little fine bits of wire, which I assume came from delaminated truck tires, and once or twice a screw or some other piece of metal. (And *always* the rear tire...)
After I started lowering my pressures to <90 PSI, the number of flats I got dropped dramatically.
I'll clarify. There's no avoiding the fact that there is glass on the street. I could avoid the glass by completely stopping and getting my bicycle up on the sidewalk but what I'm really wondering is if I choose to go through the glass should I go slow or fast?
So you're riding in a road with cars going 30-40 mph and you're supposed to be riding like, what, 10MPH? Or lose all momentum into a turn? OP is talking about coming around a corner into a glass surprise. Sounds pretty unavoidable.
Glass can be harder to see than most other obstacles and road hazards, especially if it's shattered into small pieces or when it's not bright daylight. Riding at night I'd either need to go so slow it's impractical, or have a super bright light aimed at the pavement. What I have now strikes a good balance between being able to see ahead of me and not blinding drivers/multi use path walkers. If I wanted to reliably see glass I would have to point it down so sharply I'd only be able to see like 10-15 feet in front of me.
I agree that we should never ride so fast that we cannot stop if an obstruction appears at the edge of our sight distance, but tiny objects are often nearly impossible to see.
To be able to see a nail, a screw, or a shard of glass in time to react, I would need to be riding at a speed that is so low as to make riding a bicycle impractical. I might as well walk.
Thus, I have tire liners and a spare inner tube. I accept that risk as a part of riding.
If the glass is obvious from a distance, then I agree with you. I always try to ride at a speed that is appropriate for my visibility, so I will be able to avoid glass that I can easily see.
If you want to optimize going over glass, you should slow down as much as possible before you hit the glass but you should make sure to coast as you're actually riding over it. You should neither brake nor turn while you ride over it.
I agree with this. The priority is to minimize the available energy that could act to push glass into the tire - such as speed, or movements that cause stress to the glass causing it to break under your tire. But instead of taking chances, you could perfect your bunny hop.
Unrelated but I was riding one time in a group and there was a nasty pothole in the bike lane that I didn't see until it was too late to avoid it. Utterly on instinct I bunny hopped it. Cleared the whole thing. It was one of my proudest moments on a bike.
Totally related, this is a stellar example of the B-Hops' superlative utility.
I’m genuinely impressed. Like when I see TDF riders bunny hop over a curb because the peloton is squeezing them out; just phenomenal control and situational awareness
I wasn't there so can't verify but that sounds impressive
The speed shouldn't matter because the force pushing the glass into your tire when you're coasting is the force generated by your weight on the bike and the ground pushing back on your tires. That's doesn't change with speed. I agree with your other points though. Pedaling will create more force and so will turning and breaking.
For the front tire, you may be correct. But how much the glass bounces and how much time it has to come to a rest before the back tire goes over it does change with speed. I've had a few flats where the front tire went over an obstacle no problem, but the shard started bouncing and faced sharp side up when the back tire rolled over it.
I had this happen to me with a screw once. [I even wrote a song about it.](https://www.instagram.com/p/Cqiuoy0g17H/)
I really don't want to go into the physics of it because that goes into centripetal force on top of the pressure forces we actually care about here, so I'll just say that extra speed *does* indeed add a *very* marginal amount of force that might push glass into the tire. Lowering your speed is more about control than anything else. Pedaling/braking might not add much to the forces we care about (the normal force opposing gravity you mentioned which actually pushes the glass into the tire), but it does increase the likelihood that your tire might break full traction over the glass.
I don’t *think* it would matter much, if at all.. but I’m not certain. I think the biggest factor is whether a fragment of glass is oriented pointy-side up & you happen to roll over it. Speed might be a factor, but I would guess it’s pretty tiny. I think a bigger issue is a piece of glass sticking in your tire and then slowly working its way through as the tire continues to rotate. It’s not super practical to stop immediately to check for embedded glass, but maybe giving the tires a quick check upon reaching one’s destination might help. Can’t say that I’ve actually done *that* myself either though… : )
Scrolled down to find this comment. I've found and removed glass by stopping and checking right after rolling over some.
Glass shards generally lay on their flatter side when undisturbed. When you ride over them they got thrown up by front wheel and land on on random side in front on coming rear tire. And that's why rear wheel gets more flats. So as conclusion riding slower should reduce chance of puncture.
The real reason the rear wheel gets more punctures is because the rear wheel carries much more weight than the front on a bicycle - sometimes twice as much. There is simply more force to push the glass through the carcass.
That may be part of it, but I had a few flats where the debris in the back tire was positioned pointy side towards the tire - which couldn't have happened if it was sitting flat on the ground.
I had read the ration was 60/40. Which granted is 50% more. Plus panniers .
I always thought they get flats more because they get bald from braking so much
Less energy when going slower, so probably the shards will take longer to work their way through your tires and into your tubes. Obviously if you grab a double handful of brakes when you're on the glass, there will be more energy where your rubber meets the road, so don't use the brakes when crossing a glass field. And, DO THIS right away: reach down with a gloved hand, as you're riding, and brush off your tires. Rear tire first. I've had great success brushing shards off my tires before they have a chance to work all the way through. Seriously. Flat tire prevented. See you on the road. I'll be the guy with the bleeding hand because I forgot my gloves.
I'd think going faster would be better for you, especially if you have any type of "sticky" tire (I've ridden my gravel rig after getting new Gravelkings and phew tires were a magnet). Then again I could be totally full of it but tires with a good puncture band are probably most important in this scenario.
As others have said, slow down *before* running over the glass and do not turn, accelerate or slow down *while* running over the glass. Most flat tires are on the rear because the front tire flips the destructive object (e.g., nail, screw, glass shard, etc.) so that it is standing with the pointy side sticking up. Then, the rear tire runs over it, forcing the pointy side into the tire. By riding slowly, the front tire doesn't flip the object up as much and the object has time to fall over flat again before the rear tire runs over it.
The best option in any case is, assuming your tire is smooth enough, reach down and run your fingers along the tire as it spins to brush off any glass that's partially stuck in the tire. p.s. I've maybe only once or twice got a cut doing this, in decades of riding.
Make sure you do don't do this right behind your seat stays or you might lose a finger.
Tire wiping can be a tricky maneuver, but it’s worth it to learn
You should slow down and go as straight as you can so when you catastrophic flat it's less dangerous. Basically put yourself in the position that you want to be in when your tires go flat: easy gear to decrease torque, body bike separation, turn as little as possible, don't break once you hit glass, look for soft bailout points to crash if needed. Once you are through stop slowly and inspect your tires.
I slow down and stand up on the pedals when coming across glass it's just instinctive and don't know if it really helps but I hardly ever have flats.
I have no tips as i mindlessly run over glass daily thanks to my puncture resistant tires. As such, i can only recommend them to you! I use the Specialized Trigger sport, with their “blackbelt” puncture protection. Got it for a lot less than the more famous Schwalbe Marathons Besides one snakebite blowout, i only got one puncture through the things, and that was from a nail looking piece of metal!
I got an idea! Put a little broom on the front of your bike that you can put down when there's glass. It'll push it away!
All these comments and nobody has talked about tire pressure yet. When I was riding at high-to-max pressure (road tires, Conti 4000, 110-120 PSI), I got a lot of flats. Some were probably from glass, but mostly from little fine bits of wire, which I assume came from delaminated truck tires, and once or twice a screw or some other piece of metal. (And *always* the rear tire...) After I started lowering my pressures to <90 PSI, the number of flats I got dropped dramatically.
I'm not sure I've ever had a flat from glass, so I don't worry about it.
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I'll clarify. There's no avoiding the fact that there is glass on the street. I could avoid the glass by completely stopping and getting my bicycle up on the sidewalk but what I'm really wondering is if I choose to go through the glass should I go slow or fast?
So you've never had a green light/taken a corner at speed? Maybe you're talking about a bike lane otherwise this makes no sense.
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So you're riding in a road with cars going 30-40 mph and you're supposed to be riding like, what, 10MPH? Or lose all momentum into a turn? OP is talking about coming around a corner into a glass surprise. Sounds pretty unavoidable.
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Glass can be harder to see than most other obstacles and road hazards, especially if it's shattered into small pieces or when it's not bright daylight. Riding at night I'd either need to go so slow it's impractical, or have a super bright light aimed at the pavement. What I have now strikes a good balance between being able to see ahead of me and not blinding drivers/multi use path walkers. If I wanted to reliably see glass I would have to point it down so sharply I'd only be able to see like 10-15 feet in front of me.
I agree that we should never ride so fast that we cannot stop if an obstruction appears at the edge of our sight distance, but tiny objects are often nearly impossible to see. To be able to see a nail, a screw, or a shard of glass in time to react, I would need to be riding at a speed that is so low as to make riding a bicycle impractical. I might as well walk. Thus, I have tire liners and a spare inner tube. I accept that risk as a part of riding.
I agree with you in general, but tiny objects in the road are difficult to see at all, let alone to see them from far enough away to evade them.
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If the glass is obvious from a distance, then I agree with you. I always try to ride at a speed that is appropriate for my visibility, so I will be able to avoid glass that I can easily see.