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Old 05-07-2018, 01:25 PM
 
6,128 posts, read 1,497,034 times
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I notice this every time Im stopped on a bridge, and Im not talking about large steel bridges, this is happening on smaller concrete over pass type bridges. I have my foot on the brake (stopped at a light) and it feels like the back end of my car is swaying/wobbling around.

This ONLY happens on bridges/ overpasses when Im at a dead stop.

Any theories?
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Old 05-07-2018, 02:35 PM
 
37,069 posts, read 38,262,371 times
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No theories involved, bridges are supposed to move. They need to expand and contract based on the temperature, they also need to flex to accommodate different weight loads. One thing that is common is a split steel plate crossing the road surface on either sides of a bridge or they may be in the middle on bridges with longer stretches.That split plate is not one piece and accommodates for the contraction/expansion/movement.

If the bridge isn't moving it's time to get off the bridge ASAP.
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Old 05-07-2018, 03:47 PM
 
1,119 posts, read 815,589 times
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You'll catch a lot more wind on a bridge. That could be part of it.
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Old 05-07-2018, 04:17 PM
 
Location: Texas
5,586 posts, read 11,831,318 times
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Lots of might be's but I'd tend to look at the tires for radial ply runout. That's where the belt of the tire has slipped and no longer runs on the bottom of the tire against the pavement. Reasonably easy to see. Have someone drive along side of you at the rear wheels and watch the tred of the tire while driving real slow. If it moves from side to side even a little, that's the problem and new tires are the fix. They will get worse before they get better. At speed, the centrifugal force has a tendency to balance out the wobble so you won't feel it speed, only slow or creeping kinda driving.You can jack the rear tires up and spin them by hand. You'll see the tred not running straight, if it's a slipped belt.
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Old 05-07-2018, 04:26 PM
 
8,142 posts, read 5,998,122 times
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thecoalman is right. Bridges flex and move.. That's what you're feeling. If you can catch the right bridge at the right time.. Where two 18 wheelers are going under it while you are on it.. You can really feel the air moving it at that point.

It's far more noticeable (to me at least) on newer bridges. I think newer construction does allow more 'slack' for lack of a better term.

It's not your car, it's the bridge. And he's also right that it's a real problem if the bridge ISN'T moving. Though, it's a big problem if it's moving too much as well. See "Tacoma Narrows Bridge".
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Old 05-08-2018, 05:22 AM
 
37,069 posts, read 38,262,371 times
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Quote:
Originally Posted by Labonte18 View Post
it's a big problem if it's moving too much as well. See "Tacoma Narrows Bridge".
In that case it turned into a big sail. The overall construction was too light, that by itself may have not posed a huge problem with the wind but the light construction meant a very thin deck/supports which produced a related but separate aerodynamic problem.
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Old 05-08-2018, 05:34 AM
 
Location: Metro Detroit Michigan
2,577 posts, read 680,930 times
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Quote:
Originally Posted by TrapperL View Post
Lots of might be's but I'd tend to look at the tires for radial ply runout. That's where the belt of the tire has slipped and no longer runs on the bottom of the tire against the pavement. Reasonably easy to see. Have someone drive along side of you at the rear wheels and watch the tred of the tire while driving real slow. If it moves from side to side even a little, that's the problem and new tires are the fix. They will get worse before they get better. At speed, the centrifugal force has a tendency to balance out the wobble so you won't feel it speed, only slow or creeping kinda driving.You can jack the rear tires up and spin them by hand. You'll see the tred not running straight, if it's a slipped belt.
Itís the bridge not the car forget about the tires if it were the tires you would feel it every time your driving the vehicle.
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Old 05-08-2018, 07:47 AM
Status: "More than chromosomes." (set 3 days ago)
 
Location: Anderson, IN
4,059 posts, read 1,141,670 times
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Quote:
Originally Posted by rstevens62 View Post
I notice this every time Im stopped on a bridge, and Im not talking about large steel bridges, this is happening on smaller concrete over pass type bridges. I have my foot on the brake (stopped at a light) and it feels like the back end of my car is swaying/wobbling around.

This ONLY happens on bridges/ overpasses when Im at a dead stop.

Any theories?
Well it's obviously scared. I'd worry about a bridge collapse too if I were a car.


(I have no idea, I'm just the resident goofball, I hope you get your car fixed though if there's something wrong with it.)
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Old 05-08-2018, 11:13 AM
 
Location: North Idaho
20,998 posts, read 25,737,156 times
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Aw, sweetie, that's sad. Your car is afraid of heights.
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Old 05-08-2018, 11:27 AM
 
Location: We_tside PNW (Columbia Gorge) / CO / SA TX / Thailand
20,773 posts, read 37,441,293 times
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Be careful about stopping on bridges!!! (especially if you are driving an 80,000# semi truck and on a 'small' bridge)

You can easily transfer your momentum to the lateral supports (stationary) and the bridge can fail. Then you will feel like you are moving!

A few yrs ago a semi (loaded) was blown from a bridge near my home in the Columbia River Gorge.
I don't apply my brakes, nor stop on bridges (just as my dad insisted when I was learning to drive / hauling loads of grain across small country bridges!). My grandfather was a wooden bridge maker and he would literally FLY over those country bridges. Everyone knew when he was coming down the road... HUGE cloud of dust, fast rumbling sound of his truck, and 'hop' over the bridges... He may have known more about those bridges than what you or I want to know. In theory... he was ALSO overstressing the 'static' nature (desire to sit there in a suspended state) of the bridges and stressing their structure (attachment points).

Slow and EZ would be preferred to fast and furious when it comes to bridge design, construction, and use.
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