advice on reducing from 21 speed to 7 speed

konahed

Kona Fan
My old Lava Dome has 21 gears and I'm thinking of simplifying it down to 7 gears. How do I go about getting the spacing right for the chainring, and can anyone suggest some good ratios for a 7 speeder?
 
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I'd have thought the easiest thing would be to swap your current outer ring to the middle ring position and away you go.
 
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ishaw":25w8ypc1 said:
I'd have thought the easiest thing would be to swap your current outer ring to the middle ring position and away you go.


+1, works fine :)
And gearing will depend on you and your terrain really

Mark
 
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What's the current gearing on your crank? I'd probably go for removing the granny, dropping a bash guard in place of the outer ring and go for a middle ring 2-4 teeth larger than your current one. If your riding a 32 or 34 I'd said get something like a 36 or 38. But as mentioned already it really depends on the sort of riding you do.
 
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Easy, go for it, nobody needs 21 gears really – it was just the thing back in the day though. Fit your ring of choice on to the middle ring position for optimum chain line and restrict your front mech from moving so you don't inadvertently flick the chain sideways. You'll need to retain the front mech as a chain retention device. If you like the set up, you could think about investing in more dedicated kit. I'm currently running a double chainset with one big ring (46t) fitted on the 'inboard' side of the crank. The cassette is a HG20 7speed (28t-11t). I've added a spacer and spare 34t cog to extend the range to a ditch climbing 8speed.
 
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groovyblueshed":1dz4dr50 said:
Easy, go for it, nobody needs 21 gears really – it was just the thing back in the day.

You never got 21/24/27/30 gears anyway as there is an overlap once there is more than one chainring.

The modern route is down to 12/11/10 gears, all different by having only one chainring. There is a compromise, either you go small on the front ring so you can climb steep stuff but then spin out downhill, or choose larger front and have inverse problem.

So yeah, as said, check your current gears and see which ones are important, you may need cassette with large big sprocket.
 
I have a 34 tooth narrow-wide chainring in the middle position on my santa cruz. It works well. It's a 1x10 set up. My rear derailleur is made to be used as either a 1 by or 2 by. I have dropped the chain but it isn't all that frequent.
 
^^^^ and rear mech with clutch stops chain coming off and/or bouncing around so no chipping of chain stay.
 

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