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-   -   23mm tires, potholes (http://www.bikeforums.net/commuting/927034-23mm-tires-potholes.html)

vanttila 12-24-13 09:46 PM

Quote:

Originally Posted by FBinNY (Post 16350181)
Skilled riders either hop over potholes, or do a maneuver quickly swinging the wheels around the hole, while their body barely moves off line.

...Many newer riders jam on their brakes trying to scrub off speed when facing an unavoidable pothole. This shifts weight onto the front wheel and drives it deeper into the hole so the tire hits the opposite lip as it would a curb. OTOH with enough speed the wheels don't drop as deep and only have to bounce back up a tiny bit at the opposite lip. The more speed, the farther across the wheel reaches and the less it drops, minimizing the impact.

The first part I agree with. If you ride with 23's, it's important to have a reflex of bunny hopping, swinging, and/or shifting weight in cases of potholes or other obstacles. Having clipless pedals/similars may help with this.

The second part, about impact, I'm a bit hesitant about. It probably wasn't your intention to say that (to paraphrase according to my understanding), 'going into a pothole at a faster speed will turn out better for you than going into it slower,' because this is often not the case since FΔt=mΔv. However, it is true, as you said, that braking is NOT a good response when you notice the pothole in front of you too late and will result in all sorts of damage to your tube, wheel, self-esteem, and even fork. As you explained, this increases the 'm' in the above equation, causing a larger force on the wheel.

So, don't brake into potholes. Instead, avoid them by any means possible. Until that becomes automatic, don't use skinny tires.

As a side-note, I've been riding with 23s for about 6 months now without any problems with the above advice. Our roads are so bad we got state grant money to fix a section of my daily commute.

FBinNY 12-24-13 10:06 PM

Quote:

Originally Posted by vanttila (Post 16357350)
.....

The second part, about impact, I'm a bit hesitant about. It probably wasn't your intention to say that (to paraphrase according to my understanding), 'going into a pothole at a faster speed will turn out better for you than going into it slower,'
.

I said what I meant and I meant what I said.....

Potholes are different that bumps or curbs. As you enter the pothole momentum carries the wheels horizontally while they fall. The faster you're going, the less time the front wheel has to drop. Since the drop is an acceleration process this also means it'll be have dropped less and be dropping more slowly when you reach the other side, so there's less vertical acceleration needed to start it back up to climb out.

Also, since it won't have dropped as far, the strike angle at the rim will generate a more vertical vector so there's less stress on the rim.

By analogy, watch a golfer out. At low speed the ball drops into the cup. At slightly more sped, the ball hits the cup's far lip and then drops in. Still more speed, and it hits the far lip and bounces up and back, but at very high speed, it bounces up slightly and keeps going.

Now obviously all this depends on the width of the pothole. Up to a foot or two speed is your friend, but as the width gets much more, there's no hope of skipping across and speed becomes your enemy.

There's another technique, but it depends on either blind luck, or an onboard computer. If your speed is such that the wheel drops to the bottom of a wide pothole at the middle, it'll rebound and already be on the rise at the far lip.

noglider 12-25-13 01:10 AM

Keep your tush off he saddle. Turn your knees into a suspension. Inflate your tires well. Don't carry too much weight on your or the bike.

vanttila 12-25-13 11:32 AM

Quote:

Originally Posted by FBinNY (Post 16357383)
I said what I meant and I meant what I said.....
.

I fully understand what you're saying and I certainly agree. Also, great analogy with the golf ball. You obviously put a great deal of thought into your posts.

Still, I think there're a couple things you may not have fully considered. The golf ball analogy demonstrates the behavior of the wheel and you explained the vertical forces, but not the horizontal ones. (We also haven't considered what happens to the back wheel, but that's probably not necessary.)

By analogy, imagine riding into and over a low curb, say an inch high, at a high speed versus running into a higher curb, say 2 inches high, at a lower speed. This simulates running over a pothole (short enough so that your wheel won't fall to the bottom, perhaps 1-2 ft long, as you said) at a higher vs. a lower speed (though I realize it doesn't take into account the vertical speed of your wheel when it hits the edge of the curb), since at a higher speed, the wheel has a shorter height to climb out of the pothole than at a lower speed, but the speeds are different.

It's also important to note that the difference in the vertical height the wheel has to climb out of the pothole (between the slow and the fast) depends on the square of difference in the bike's velocities and the square of the distance across the pothole.

So here's I'm getting at: You properly demonstrated that at a lower speed, the vertical component of the force on your front wheel is higher than at a higher speed (because the vertical Δa is smaller for a higher speed, which is directly proportional to the force), which means a higher speed is more beneficial into a pothole. However, the horizontal component was not taken into consideration, which is demonstrated by my analogy above. Is it better to run into a low curb at a high speed or a into a high curb at a low speed? I'm not sure but as you said, it seems to depend on the dimensions; that is, it all depends on how long and deep the pothole is as well as how much difference there's in the two speeds. Also note that the Δt in the impulse equation in my prev. post is higher at a lower speed, which makes the F lower at a lower speed. However, Δv on the other side of the equation is probably higher for the lower speed since the bump to climb over is higher, which would indicate a higher F at the lower speed.

In short, the vertical component (when ignoring the horizontal) would indicate that it's better to go into a pothole faster, but the horizontal component (when ignoring the vertical) seems to (though it's not entirely clear to me) indicate that it's better to go into the pothole slower.
So, whether faster or slower is better depends on the dimensions of the pothole, which realistically a rider won't have time to analyze in the short time between spotting a pothole and riding over it (since if the rider did have enough time, he/she would simply ride around the pothole).

In the end, then, it's almost irrelevant whether going faster or slower is better, since it's obvious that braking into a pothole is not advised due to the way it shifts your weight onto the front wheel, which means you can't do anything about the speed you're going until it's too late.
In other words, this isn't a debate worth having since the conclusion is the same either way and quite frankly, I think we both understand each other.
Cheers!

mklos1 12-26-13 03:47 PM

I think that 700x23 tire is a one of the worst tires one can imagine for commuting. 700x23 is meant to be a racing tire and that's all. I have pair of 700x23 Schwalbe Lugano on road bike and I think that they should remain there. I never meant to switch to such narrow tires on my commuting bike, moreover I switched from 1.75" to 2.0" balloon tires. It's slow, but it's "swallows" every pothole...

fietsbob 12-26-13 05:43 PM

Unlike Paris and the older parts of European cities, Not too many hand set cobbled streets in the USA.

some people like riding a racing style bike ,for commuting. Portland Oregon has quite a few , as jyl

a forum member will validate.

yea, the pot hole thing, avoid plowing through them, if at all possible.

trailmix 12-26-13 09:37 PM

My main commuter uses 23s, I don't see any downside other than the harsh ride. I use gatorskins which in my case have proved extremely (jinx) reliable.

Slaninar 12-26-13 10:16 PM

Quote:

Originally Posted by trailmix (Post 16360763)
My main commuter uses 23s, I don't see any downside other than the harsh ride. I use gatorskins which in my case have proved extremely (jinx) reliable.

And more prone to flats due to higher pressure.

And harder to pump up to propriate pressure using ordinary hand pump.

And less lasting.

vanttila 12-26-13 11:21 PM

Quote:

Originally Posted by Slaninar (Post 16360838)
And more prone to flats due to higher pressure.

And harder to pump up to propriate pressure using ordinary hand pump.

And less lasting.

The middle one makes sense, but care to explain the first and the last claim?

gregf83 12-26-13 11:57 PM

Quote:

Originally Posted by Slaninar (Post 16360838)
And more prone to flats due to higher pressure.

And harder to pump up to propriate pressure using ordinary hand pump.

And less lasting.

And less time spent commuting...

trailmix 12-27-13 06:51 AM

Well, I have only had 1 flat in the last 5000 miles and that was due to the fact that the gauge on my pump malfunctioned and I was running much less pressure than I should. I won't argue that wider tires are not generally better for rough roads but 23s are perfectly fine for commuting. There are many factors that will affect tire choice: rider weight, riding style, road surface etc. Are wider tires the better choice for most? Yes. Will narrow tires work for some? Yes.

e0richt 12-27-13 09:26 AM

Quote:

Originally Posted by Slaninar (Post 16355383)
I see people "commuting" on 23 mm tyres, just like I see people traveling on RR motorcycles...

um what is an RR motorcycle?

trailmix 12-27-13 09:33 AM

Race Replica aka sport bike.

Slaninar 12-27-13 12:01 PM

Quote:

Originally Posted by vanttila (Post 16360917)
The middle one makes sense, but care to explain the first and the last claim?

Narrower tyres need to be pumped up to higher pressure, which makes it easier for sharp stones and pieces of glass to puncture. Tyre inflated to a lower pressure gives in rather than being hard on the surface, so less prone to flats. That is my experience at least.

Thinner tyres will wear faster than fatter ones.

Slaninar 12-27-13 12:02 PM

Quote:

Originally Posted by gregf83 (Post 16360958)
And less time spent commuting...

Not neceserily. Thiner ones are qucker at high speeds (marginaly), and at stop-go, or climbing. But that is all really marginal.

gregf83 12-27-13 12:08 PM

Quote:

Originally Posted by Slaninar (Post 16361780)
Not neceserily. Thiner ones are qucker at high speeds (marginaly), and at stop-go, or climbing. But that is all really marginal.

Any tire that has significantly better flat resistance is going to be significantly slower. Perhaps not a problem if you only commute a short distance but for someone, like myself, who has a one way 33km commute, I prefer speed over flat resistance. I commute on the same roads I ride on recreationally and find 23 or 25s work well.

Slaninar 12-27-13 02:51 PM

Quote:

Originally Posted by gregf83 (Post 16361794)
Any tire that has significantly better flat resistance is going to be significantly slower. Perhaps not a problem if you only commute a short distance but for someone, like myself, who has a one way 33km commute, I prefer speed over flat resistance. I commute on the same roads I ride on recreationally and find 23 or 25s work well.

My experience is that on flats, aero is all there is. Don't notice much time difference between 23s and 42s. Really.

I use 23 road bike for nice weather, but hate changing flats when it's cold and raining, so most of the time I use the fatter tyres.


How do you cope with such a long commute? Do you work every day, or have some long hours-less days? How long does it take to work? I could consider over 15 kms to work only if it's flat and without bloody traffic lights.

gregf83 12-27-13 03:00 PM

Quote:

Originally Posted by Slaninar (Post 16362130)
My experience is that on flats, aero is all there is. Don't notice much time difference between 23s and 42s. Really.

I use 23 road bike for nice weather, but hate changing flats when it's cold and raining, so most of the time I use the fatter tyres.


How do you cope with such a long commute? Do you work every day, or have some long hours-less days? How long does it take to work? I could consider over 15 kms to work only if it's flat and without bloody traffic lights.

There is a big difference in rolling resistance between a 23 and 42mm tire. Those fat tires are probably costing an extra 20-40W. It takes me about 1:10 each was and I generally commute about 4 times/wk which works out well for me. I have very few lights and a typical ride would have less than 1min of stop time.

Because my commute is relatively long I don't want to spend any more energy than I have to getting to work so I ride a road bike which doesn't accept tires wider than 25mm. I'll normally spend 1/2 the time in the drops so aero is also important to me :)

acidfast7 12-27-13 05:10 PM

700 x 23 in England in a SS

This includes a fair bit of cobblestone.

No problems even in the winter.

This is on cheap Kendall tires.

link0 12-27-13 05:20 PM

I commute on 700x23 tires inflated to around 90 psi on the horribly potholed streets of LA. No real issues, except a somewhat harsh ride. I weigh 150lbs.

rms13 12-27-13 05:32 PM

I commute on 25s right now on less then perfect roads. I keep them inflated to max pressure and I do my best to avoid pot holes and other obstacles. I did hit a decent pothole the other day and did no damage to my tire or wheel. I've used 28, 32, 38 to commute and occasionally my road bike with 23 inflated to 130 psi and knock on wood I have not had one flat so far in about 9 months of commuting

cwar 12-27-13 06:35 PM

My fair weather bike has 23's. This is my fair weather commuter and weekend ride bike. My rain bike has 25's. This setup has worked well for me.

vanttila 12-27-13 10:41 PM

My fair weather bike has 23's as well. I'd prefer 25's since the roads are what they are, but the bike (a moderately recent purchase) came with 23's, so I'll use them up first. Potholes haven't been a problem, and no excessive flats to complain about. Rain/winter bike has 35's (or something), so this works well as my setup.

Rudz 12-27-13 11:00 PM

I commute on 23mm gatorskins and I memorize potholes on my route, if I ride some place new I pay attention, if I cant aviode then pothole, I rise up off the saddle and take it. Only pinch flat was from crappy tubes. I used to ride on 28mm kendss and I dont notice much of a difference.

Now riding critical mass in downtown LA, those are the worst streets ive ever seen. But I still didnt get a flat, just jarred the crap out of myself on my aluminum Giant Rapid.

Slaninar 12-28-13 01:00 AM

Quote:

Originally Posted by gregf83 (Post 16362147)
There is a big difference in rolling resistance between a 23 and 42mm tire. Those fat tires are probably costing an extra 20-40W.

Not realy. Not much measurable difference - if you compare similarly built tyres - not some super heavy super slow 42s against a racing 23. 42s ony have weight penalty which comes at stop and go and at going up hills.

Also, it really depends on road quality. Fatter tyres are more universal. When on a road bike I have to choose where I go for better and cleaner pavement. Riding 23s on cobblestones really slows you down due to all the vibrations. Same goes for many potholes, cracks etc. If roads were better where I ride, I'd probably stick with 23s.

BTW - for maximum efficiency - recumbent is the best - far better than a road bike.

Quote:

Originally Posted by gregf83 (Post 16362147)
It takes me about 1:10 each was and I generally commute about 4 times/wk which works out well for me. I have very few lights and a typical ride would have less than 1min of stop time.

Because my commute is relatively long I don't want to spend any more energy than I have to getting to work so I ride a road bike which doesn't accept tires wider than 25mm. I'll normally spend 1/2 the time in the drops so aero is also important to me :)

My road bike can take up to 32s I believe. 28s easily. I'm switching to 28s in the spring - for a piece of mind. Lots of debris that punctures 23s when they are inflated over 7 bar pressure. I guess 28s will hold my weight with around 6 bars at the rear wheel.



This road is a joy on 42s and a really jarring experience on 23s:
http://novinenovosadske.rs/wp-conten...ka-kaldrma.jpg


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