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Just yesterday, I was riding my mountain bike along a sidewalk and out of nowhere hit a stop sign pole mounted in the middle of the side walk. I guess that’s what happens when you get too preoccupied with the scenery around you while going at 20 mph (32 kph).

The crash created a really strong jerk that forcefully pushed me and my bike backwards. I was unharmed and still managed to stay on the bike seat; however, my bike acted rather strangely — it seemed that the force of the collision somehow adjusted my gears to the lowest setting, without me even touching the shifters on the handlebars. I assume that because right after the collision, I went to test ride the bike and noticed the pedals were turning really quickly, as if the gears were on the lowest configuration (I don’t know whether it was the front, back, or both gears). At that moment I knew something was wrong. But, after 5 additional seconds of anxious pedaling, the gears readjusted themselves back to their original setting I had them in before the crash. Again, this was without me touching the shifters. Fortunately, the bike seems to be in decent condition now, but what are your guys’ thoughts on the weird automated gear shifts? Is this normal? The bike looks Ok, but then again, I'm new to biking.

Thanks!

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  • "preoccupied with the scenery" at 20 mph? xD that's super fast. I would be worried about the buckled/bent wheel if I hit something head on at that speed.
    – Nhân Lê
    Jul 16, 2015 at 10:55
  • Consider not riding on the footpath.
    – Criggie ♦
    Sep 6, 2016 at 4:31

1 Answer 1

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The crash made the chain drop from the currently selected front chainring to a smaller one (i.e if you have 3 rings and you where on the middle, it jumped on the 1st - lefmost- smaller one).

The crash didn't change any gear on the shifter though, it just made the chain pop to a smaller ring. Maybe not fully, but partially.

Afterwards cranking a couple of pedal strokes made you feel that the pedals where "moving fast". After a while though, and since the front deraileur was still in the original position (maybe middle ring), the chain moved again back to the middle ring making the gearing ratio as previous.

Dropping the chain is common in MTBs without a chain guide. What happened to you is normal.

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    Seems very plausible. Given the speed prior to the crash, the OP would have likely been in the big ring. This is just my personal preference, but I would add a statement that its all speculation and the OP should have the bike checked out at a bike shop if other odd behaviours begin.
    – Rider_X
    Jul 15, 2015 at 14:23
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    Every answer on this site is speculation, since they are based solely on what the OP provides.
    – cherouvim
    Jul 17, 2015 at 7:36

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