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-   -   More Gears (http://www.bikeforums.net/folding-bikes/400835-more-gears.html)

leroy 03-25-08 11:26 AM

More Gears
 
How much of a problem is it to add a second, smaller sprocket to the crank and a front derailer to gain 14 gears instead of 7? I've noticed a thread discussing this issue. My new Dahon D7 is really a good bike, but I'd would like more gears if possible without messing up the folding procedure.

LittlePixel 03-25-08 11:57 AM

You need to find a front derailleur that will fit the frame and a way of routing the cable to your bars - both doable jobs with the right parts and tool.

Alternatives to this could also be the fitting of a Schlumpf Speed or Mountain drive in the bottom-bracket housing which essentially allows you to double the amount of gears on your bike without having to have a derailleur, the system working a bit like a hub gear, but in the front.

Another would be to swap out the current rear cassette for a SRAM dual-drive hub which has a rear-derailleur setup married to a 3-speed hub allowing for the normal gears on the cassette x the three speeds inside the hub meaning you don't really need a front derailleur.

Bacciagalupe 03-25-08 03:22 PM

If you haven't done so already, it will be much easier to change the cassette. That will give you almost the same range as adding another chainring.

cmcanulty 03-26-08 08:11 AM

I did my downtube for $10, the cost of a 39tooth chainring. Just took off the chain protector ring and screwed on the 2nd ring. No front derailleur, just shift it manually. Give a nice low gear with 39 front and 32 rear. If you don't need the higher gears you could just change chainring.

leroy 03-26-08 06:52 PM

Thanks for Chainring Info
 
I'm not sure if I know what the "chainring" is---Is it a large front sprocket?----Please, what is it and how is it done?.......Thanks----Ev

Sammyboy 03-27-08 07:53 AM

The chainring is indeed the front sprocket. On double and triple cranksets, these are held in place by 4 or 5 bolts. On some single chainring bikes (like Downtubes) it's possible to add a second chainring, and cmcanulty has done that, but not added a derailleur, just shifts it by hand. Alternately, you can simply buy a double (or even triple) crankset fairly cheaply on ebay. Consider whether you want to go up, or down from the gearing you have at the moment. What might be trickier is finding a front derailleur that will fit - folders use very different sizes of tubing to regular bikes. Looking at the D7, it's hard to see where you could easily fit a derailleur.

As suggested, there is another option - the SRAM Dual Drive. This mounts your cassette onto a 3 speed hub gear, which more or less does the job of a front derailleur. 2nd on this is a 1:1 gear, so you get the same gearing you had before, 1st is lower, for climbing, and 3rd higher, for going faster. This is not a super cheap solution however, since you have to not only buy the hub and shifters, but have a whole wheel built.

leroy 03-27-08 12:10 PM

Thanks Sam----
 
Since I'd like to have greater low-gear capability, a front chainring, operated by hand would do fine----how is the shifting done by hand? By stopping and moving the chain to the other chainring by hand?-----Ev

Sammyboy 03-27-08 12:43 PM

Yep - you literally lift the chain off, and put it on the second chainring. It might be easier, however, to add a wider range cassette, and be able to shift it with the shifter. What cogs are on the current cassette?

Paul Braithwait 03-27-08 03:17 PM

When I bought my 8 gear Swift, I wasn't sure whether I would have enough gears after switching from my 20 speed road bikes. In practise I have found 8 gears to be fine. I did fit a new cassette of sprockets to lower the ratios (I live in a very hilly area) but I don't think I have ever used the full range on a ride. Don't get hung up on the number of gears - if the hill beats you, just walk it and enjoy the freewheel down the other side!

James H Haury 03-27-08 06:17 PM

clamp on derailleur
 
We had a post telling of dahon riders in Taiwan? These rider were using a special clamp on front derailluer which is available for purchase through the internet shipping may take a while though.

tcs 03-28-08 04:37 PM

Well, it's unlikely you'll get "fourteen" gears by adding another chainwheel. Typically this yields one or two more useful ratios.

Both the Shimano and Sturmey-Archer eight speed and SRAM iMotion9 internal gear hubs will give you a broader range in more steps than your current gearing.

You'd keep a single shifter and doing it this way would tidy up the bike for folding as well.

HTH,
tcs


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