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Bridge Expansion Joint vs Wheel

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Bridge Expansion Joint vs Wheel

Old 05-08-10, 07:29 PM
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2runco
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Bridge Expansion Joint vs Wheel

So, one of my regular ride routes crosses a bridge over an arm of a lake, about 1/4 mile long. The bridge has 3 of those metal expansion joints. These are like meshing "W" shaped metal fingers, with gaps between the fingers. The method that I had been using to cross these joints involved slowing, lifting the front wheel over the joint, then pulling the rear wheel over the joint. This worked OK until the last ride. Managed to drop the rear wheel into the expansion joint. Resulted in a pinch flat, scrapes on both sides of my new Ultegra rim, and a small ding in the rim . The scrapes I was able to mostly remove with light sanding, and I don't think the ding is serious enough to be a problem. Guess I was lucky to not be dumped, or thrown into the traffic lane.
Mentioned this to the owner of the LBS, and he said he hears of it happening all the time. His recommendation for the safe way to cross these joints is to maintain speed, look farther down the road, and cross the joint in a straight line as if the joint were not there. He crosses them several times per week with no problems. Will try this next time out, but have to admit this will involve some puckering on my part. The thought of dropping a front wheel in a joint at speed is a little unnerving.
Anyone else had bad experiences with expansion joints?
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Old 05-08-10, 07:57 PM
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I learned to bunny hop back when I had my mountain bike, so now if I see something queer in the road, I just jump it. Helps when you have lots of spokes, deep v rims, and lots of pressure. Good luck
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Old 05-08-10, 08:01 PM
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ravenmore
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I haven't seen what you're dealing with, but my commute took me over a bridge with expansion joints daily. I just hit it at speed and usually everything was fine. I did break a spoke once though. To be fair it was a 20 spoke count wheel and was built with alloy nipples (broke at the nipple).
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Old 05-08-10, 08:15 PM
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you can always keep speed but lift the front wheel a little bit. these joints must have some sizeable gaps parallel to your line of travel? got a picture? is there on on the internet that resembles your situation? do these bridges have sidewalks with a better treatment of the joint? meaning: more bike friendly?
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Old 05-08-10, 08:32 PM
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I got a pinch flat on an expansion joint once. I'm pretty sure my tire was under-inflated at the time, though, because I had another flat (staple) earlier in the day and don't think I inflated my tire to a high enough pressure with my frame pump. It was also a crummy tube. But anyway, I've found that some expansion joints are worse than others, i.e., have much larger gaps, and the one that gave me the flat has the largest gaps I've seen in an expansion joint. For that one, I now slow down quite a bit before I ride over the joint.
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Old 05-08-10, 09:03 PM
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2runco
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The joint gaps aren't exactly parallel to the line of travel, but angled slightly, like the legs of a "W". The gaps between the teeth of the joints vary a lot in width. Some are very narrow, and some are wider than my tire. No pics, but I may take one on the next ride. The joints all span the width of the bridge, so no way to avoid them.
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Old 05-08-10, 09:05 PM
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alpha_bravo
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Originally Posted by rumrunn6 View Post
you can always keep speed but lift the front wheel a little bit. these joints must have some sizeable gaps parallel to your line of travel? got a picture? is there on on the internet that resembles your situation? do these bridges have sidewalks with a better treatment of the joint? meaning: more bike friendly?
I believe it's one like this:
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Old 05-09-10, 04:25 PM
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I'd just ride like I was launching off of a tooth (the bottom "tooth" in the picture if going from right to left.

If you pinch flat on one of these while trying to bunny hop you probably drove the rim into the edge of the further joint. If you have good pressure and unweight the bike you should be fine without doing anything.

Air pressure solves a lot of flat tire problems. If you were complaining about glass/nails/etc I'd think differently, but impact? That's about air pressure.

cdr
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Old 05-09-10, 04:48 PM
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Mountain biking rule of thumb: if the front wheel makes it over the rest will follow. Just hop the front wheel over the joint.
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Old 05-09-10, 05:42 PM
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+1 on bunny hopping. I go over some pretty nasty (way nastier than that) bridge joints over by BU on a daily basis. I learned the hard way that stronger wheels are worth it. The weight gain is totally unnoticeable.
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Old 05-11-10, 06:53 PM
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Finally got back to the bridge to snap a couple of pics. The joint is similar to the one in the pic provided by alpha, but not the same.


As you can see, some of the joints are wide enough to let a wheel slip in. And the angle of the teeth is pretty steep, nearly parallel to the line of traffic flow.
I used the technique recommended by the LBS guy today to cross 5 of the joints, with no problems. Hit the joint directly perpendicular, with some speed, and don't worry about them. So far, so good. I'm sure a bunny hop would work, but I'm not too skilled at the hop and would likely mess it up and land in a slot. My rear tire pressure was probably around 100. Could be higher, and I am running between 105 and 110 with the new Conti tires. But if a wheel drops in to the depth shown in the above photo, I'm not sure higher pressure would be enough.
Thanks for all the input.
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Old 05-11-10, 07:11 PM
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Those expansion joints in the images above look pretty smooth compared to the joints for the bike/walk path attached alongside the Ben Franklin bridge.
BTW, I was riding in Reston VA. The overpass bridges on the W & OD Trail have a rubber covering over the expansion joints. Never saw that before - very nice.
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Old 05-12-10, 01:29 AM
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crap those are horrible!

can you cross them diagonally? meaning run down that yellow line and when you approach the joint jog right to cross it diagonally so you wind up at the right edge, then reverse for the next joint ...
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