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Sometimes on a bike I see a short spring, most often covered in rubber, connecting the fork with the frame:

What is the purpose of it? The only thing that comes to mind is stabilising the fork so it does not wobble to the sides so much. Is that its purpose? Why do some bikes have it?

  • I just noticed this bike has hydraulic rim brakes. Nice! Notice the pale-green bike in the background does not have such a spring, that I can see. I still think you should disconnect it and try a safe quiet ride to see if it impacts on handling at all. Please do report back - I'm quite intrigued. – Criggie May 15 '16 at 7:13
  • @Criggie: Yeah, I also have hydraulic rim braces on my touring bike, a beautiful thing. And unfortunately I cannot report back, it's not my bike, I've never had a bike with such spring in my hands. – Emmit May 15 '16 at 8:29
17

The purpose of such a steering damper is to stop the front wheel from turning when using a (two-leg) kickstand or while pushing the bike. Not much use otherwise.

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    Good idea, but if it doesn't disconnect then its active all the time, not just while on a stand or pushing. – Criggie May 14 '16 at 21:22
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    This is the correct answer. @Criggie : Yes, that is true, but that is not really an issue. Just a little force is needed to keep the front wheel straight, so it is just a weak spring. Handlebars give you enough leverage to compensate. – jilles de wit May 14 '16 at 21:36
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    Also, even primarily, it's for stabilizing the front wheel when you're carrying load (ie; kids in a carrier, front basket, groceries, etc) - try to load up a bike in a rack and it will flop over, etc. The damper is there to hold the bike straight while you stick your paniers on and fasten your cargo - the impact to steering response when riding is minimal. – J... May 15 '16 at 1:39
4

It's steering damper. It prevents your handlebar from self - turning. Increase comfort. Steering damper

  • Despite the common misnomer, it's not a actually damper, it's a spring. The losses in that spring aren't enough to dampen much of anything. It'll centre the steering, it won't dampen wobbles. Hopey, for example, make actual dampers – Móż May 18 '16 at 5:18
1

I'm going to guess that the bike's fork is lacking in follow (ie it has straight forks, or forks without enough bend) so that without the spring, the bike will not self-center. It will likely feel that it wanders over the road and the rider has to actively keep it centered. You probably can't ride hands-free without the spring.

The spring provides some pull back towards the center position. If its your bike, try disconnecting the spring and going for a short ride. Does it feel different in steering and front-wheel braking?

Personally I've never seen a bike with such a spring. If they're not uncommon in your area then there may be a regional influence on them. Is it mostly step-through frames that have this? Is it budget/BSO bikes?

EDIT: Thanks Moz - Trail is the word I meant. Here's my idea. Your bike looks like a sit-up bike rather than a racer, so its an older shape/design. As per this image, older bikes had little trail, so to get them going straight you had to hold the bars all the time, which is tiring. Riding this hands-free would be a challenge.

enter image description here

So by comparison here's a more modern bike geometry, that will self center a lot easier. Riding hands free on this would be easy.

enter image description here

Further information at http://davesbikeblog.squarespace.com/blog/2007/5/4/trail-fork-rake-and-a-little-bit-of-history.html

I think the spring reproduces some of the trail that would otherwise be absent.

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    It's in Amsterdam and I've seen it on all kinds of bikes. I have not seen it anywhere else but I guess it's because I see more bikes here every day than in other places combined in all of my life. – Emmit May 14 '16 at 21:30
  • @Emmit Then there's a fair chance bikes there have springs because that's what customers want. I'd guess its more the upright town bikes that have them, could also act as one leg of the path for power from a dyno hub. Grease and bearings in the headset may not be a good ground wire. – Criggie May 14 '16 at 21:33
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    @Criggie I think the term you're after is trail? – Móż May 15 '16 at 6:38
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    A good guess, but nope : dutchbikebits.com/hebie-steering-damper – J... May 15 '16 at 11:49

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