Bicycle Mechanics - Granny chainwheel converter
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07-14-08, 04:56 PM
I have a 16 speed road bike that is way overgeared, 53-42 on front. 11-30 rear. I would like to use the 42 as the outside ring and add a 22 ring with making or buying a converter. It is a nice Shimano 105 crankset. It this doable? I am willing to tinker. I spin fast and use very low gears. I know the 42F and 11R is high enough as it usually too high for me even with a tail wind.
07-14-08, 06:34 PM
If the 105 is a triple crank, you can add as small as a 24T granny to the inner 74 mm bcd. If it's a double about all you can do is use a "tripilizer" middle ring that will allow you to add a granny ring.
Harris Cyclery sells Willow and TA triplizer rings. Here is the URL showing what sizes are available in 130 mm bcd (that's what your 105 has): http://www.sheldonbrown.com/harris/chainrings/130.html
Note there is no 42T Willow triplizer but they are available in 40T and 46T. There is a 42T TA triplizer ring but Harris says they are hard to get.
BTW, you will probably need a longer bottom bracket and possibly a different front derailleur too.
07-14-08, 07:09 PM
The way I see it, is that you currently have too many high gears.
I think that if you could go to a 22T ring, you'll have the opposite problem with having so many non usable low gears, that you'll end up using the 42T ring anyway, to avoid frequent "inconvenient" double shifts.
Also, with a 20T difference between rings, shifts would probably be a little "ugly".
Wouldn't something like 30-42 make more sense?
Use this link to determine what you actually can use-
When I get a gear that when pedaling at 90 rpm and I can't keep the bike from falling over, then I have a gear that is too low. I love low gears and just recently put a mountain bike tripple on my old road bike and the tripple is staying. Since I can spin better my speeds up hills has even improved.
Get the low gears you will love them if you are a weak rider like me.
07-15-08, 07:52 AM
When I get a gear that when pedaling at 90 rpm and I can't keep the bike from falling over, then I have a gear that is too low.
Not going to happen. Even in a 20 gear-inch low gear, 90 rpm is over 5 mph and most people can keep a bike stable at 3 mph or a bit less.
I do agree with Bill Kapaun that while having a very low gear is good, there can be to many of them for routine riding. I think the OP would do better to fit a MTB crank (say 22/32/42) which would provide the same low and high gears he wants but a lot more useful ones in between.
07-15-08, 09:21 AM
I guess my real question was, can I move my inner 42 tooth ring to the outer position of my Shimano double crank (currently outer 53, inner 42) and then drill holes and attach a 22 or 24 tooth ring to the spider with whatever spacers I would need. I have a friend who builds cars and has a full and precise workshop.
07-15-08, 09:30 AM
I guess my real question was, can I move my inner 42 tooth ring to the outer position of my Shimano double crank (currently outer 53, inner 42)
Yes except the shifting won't be very good as all of the shaped teeth, etc. are set up for the 42 to be the middle ring.
...and then drill holes and attach a 22 or 24 tooth ring to the spider with whatever spacers I would need. I have a friend who builds cars and has a full and precise workshop.
Probably not. A double crank doesn't have the cast in bosses needed to take a 74 mm bcd chainring and the crank arms aren't thick enough to accept the threading properly without those bosses.
A new crank is a much better and safer alternative.
I agree that you can have too many low gears. Some of the radical cassettes with a 34 to 11 tooth setup can help with that problem.
For me I end up with too many high gears because I really don't want to go faster than 25 mph so I end up coasting down most hills.
My lost cost conversion for gears was to buy an old mountain bike and transfer the parts to my road bike.
make that low cost not lost cost. sorry.
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