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I just bought a used mountain bike, and it seems to be slow. Pedaling seems like very hard work, and at a normal casual pedaling rate, I can only reach 4-5mph. If I pedal like I'm being chased by a lion I can get up to 10-11mph for a few seconds.

For reference, I can run a 6-minute mile, so I can run faster than that.

I'm thinking it's probably the bike, because the chain looks dirty and the wheels make scraping sounds as it moves. (I don't know if it's scraping against the brakes or something needs oil, etc.)

How can I fix this?

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    Before doing any hard work, I'd first check if the tires are inflated properly (at least 40PSI for mountain bike tires) and if the brakes are not rubbing too much :) If that doesn't fix it, try cleaning the chain/cogs before disassembling stuff. – Antoine Mar 27 '15 at 11:49
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    What happens if you put the bike on a stand or turn it upside-down? Does the crank turn easily? If you turn just the rear wheel, does that turn easily? How about the front? – jimchristie Mar 27 '15 at 12:29
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    @Antoine I'd have thought that the brakes rubbing at all would count as "too much"! – David Richerby Mar 27 '15 at 16:32
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    Well I've ridden bikes with wheels out of true and brakes slightly rubbing , never killed me. – Antoine Mar 27 '15 at 18:25
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    @CaptainCodeman - There you go then. Adjust the brakes so they're not rubbing. And it sounds like you need a new chain as well. – Mike Baranczak Mar 28 '15 at 3:12
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At a minimum lube the chain and see what is scraping.

For the brakes just hold the bike up with one hand and spin the tire. Visually inspect if the rim is rubbing on the brake. Some times you can just adjust the brake and some times the wheel(s) need to be trued.
Some times you have the tire rubbing on the brake.

At this point need to decide if it is worth fixing.
Can the wheels even be trued?
A decent set of wheels is $200.

A good complete overhaul at a bike shop is over $100 and more like $200
If you need new parts can easily get over $400
Get an idea of how much it will cost before you start spending money

If you don't want to spend money then
- take off the tires and chain
- put the wheels (without tires) back on
- leave the brake released
- do the wheels spin freely
- does the crank (pedals) spin freely
- does the headset turn freely

At this point if things look okay and you don't want to spend money then repack all (unsealed) bearings. If you don't own any tools then probably not worth it.

If you need some new parts you will find out. Add em up and see if it is worth it.

A cheap bike in need of a lot of maintenance is typically not a good value. You are typically better off spending more money on a bike that does not need much maintenance.

  • Thanks, I didn't know an overhaul would be so expensive. I only spent £50 on the bike so wouldn't want to spend a lot of money. I'll see if I can get it running better with some cleaning, oiling, and inflating tires, otherwise I'll just buy another. – CaptainCodeman Mar 27 '15 at 14:58
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Since it's a new-to-you secondhand bike, for safety's sake as well as to deal with the sluggishness I recommend you take it to a bike shop for a complete overhaul. I'll bet you'll be astounded at the difference when they're done.

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I think that with a well-running bike you ought to be able to do three things:

  • The wheels ought to spin -- life each wheel in turn off the ground and set it spinning with your hand: it ought to spin and spin and spin almost without ever slowing down, almost frictionless

  • The tires shouldn't absorb energy -- that means you don't want knobbly tires because that takes energy, to deform the nobbles as you roll on them ... racing tires are slick, and touring tires have some tread/grooves (but not nobbles) ... also you want a kind of tire that expects to be inflated to more than 60 psi (and properly inflate them)

  • The drive train -- the chain should be lubricated etc and it shouldn't make a hardly any noise ... no scraping or creaking or rubbing, mostly just ticking from the 'freewheel' hub.

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First thing you can try is to disassemble and grease the bearings with the proper stuff.

To do that you have to do the following:

1) Disassemble them as unscrewing the cones' contra nut and the cones themselves.
2) Wipe the old grease with something ( I am doing it with toilet paper )
3) Wipe every individual ball of the hub.
4) After everything is clean, put some grease on the hub's ball beds.
5) Keep doing that till you do the entire circle.
6) Pick up and place every one of the balls back on, so they can sick into the grease
7) Put the cap back on.
8) Screw the cones !! BY HAND !!
9) Screw the contra-nut back on to hold it in place

After the procedure make sure that your rim is not playing around as you are trying to tilt it relative to the fork. If it does - Unscrew the contra-nut and repeat points 8-9 till you get it right :) Repeat this thin on the both sides of the hub !

Good luck !

  • Is this the one where you can do it wrong and end up with a wobbly misaligned wheel? – CaptainCodeman Mar 27 '15 at 13:29
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    This is not the first thing to do. – paparazzo Mar 27 '15 at 13:43
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    I agree with @Blam. The first thing to do is to check tyres and rubbing, as stated in a couple of comments - these are the easy things to check. What you're suggesting here is pretty advanced maintenance and is probably the "if all else fails" option. – PeteH Mar 27 '15 at 14:21
  • @Blam is right - this is not the first thing you should try, although it is something that should be done regularly. If your bearings are so messed up that you can't get the bike above 5 MPH, then they're beyond fixing. But I don't think that's the problem. – Mike Baranczak Mar 28 '15 at 3:06
  • @CaptainCodeman - possibly, but you'd have to try really hard. A "wobbly misaligned wheel" is caused by uneven spoke tension pulling the rim out of shape. Look up "wheel truing". – Mike Baranczak Mar 28 '15 at 3:09

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