Bicycle Mechanics - Need help with gearing
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09-08-09, 06:41 PM
I just bought a Raleigh Sojourn and I have been trying to use it as my commuter but the gearing seems wrong for what I need it for. I carry two wald folding baskets full of groceries and a full trunk bag home a couple times a week. I am having trouble getting up the hills home.
It came with a 50/39/30 and an 11-34 cassette. My mountain bike which has a 42/32/22 and an 11-34 cassette was much easier to get home, but I don't like loading it up with up to 50 or 60 pounds of stuff from the store. It looks like I could rebuild the crankset, I just don't know where to get the parts or what I should change it to. I would hate to lose all the upper end speed it has over my mountain bike, but if there isn't a way around it I could live with that.
Thanks in advance for any advice anyone could give me.
09-08-09, 07:01 PM
I'm assuming your triple granny ring is a 74BCD. In that case, you can simply purchase a Sugino (or like) granny ring. They go as small as 24T.
Try licktons . . . http://www.lickbike.com/productpage.aspx?PART_NUM_SUB=%270095-24%27
09-08-09, 07:15 PM
I am not sure if it is that or not, here is what is on it Shimano FC-R453 Octalink 30/39/50t. Will those smaller chainrings work with that? And do I have to change the front derailler too? or would mine be ok. It's a Shimano Tiagra. And thanks for the link.
You should be able to replace the 30t chainring with a 26 or 28, 74 BCD. Shifting performance may suffer a bit, hard to tell without trying it.
The smaller front chain ring (22 vs 30 teeth) , marginally smaller outer tire circumference (approx 26" vs approx 27") , and possible slightly longer crank arms (175 mm vs 170 mm) on the mountain bike, all together give it about a 30% lower bottom gear, so it's not a surprise you can tell the difference. The store should be able to tell you if you can add a smaller front chain ring. Lots of people consider it if they plan loaded touring.
With a 24 tooth granny, you will still not equal the mountain bike but you will be closer.
Mountain bike lowest gear (in gear inches): 22/34*26 = 16.8 gi (lower is better for uphill hauling)
Sojourn with 24 tooth granny: 24/34*27 = 19 gi (that's still pretty good!)
Soujourn with 26 tooth granny:26/34*27 = 20.6 gi
Sojourn as is: 30/34*27 = 23.8 gi
The probably longer crank arms account for an additional 3% advantage for the mountain bike (equivalent to about 0.5 gi).
09-08-09, 08:35 PM
Thanks a lot for the explanation. I think I will order the 24,26 and 28 and see if the 24 causes any major shifting problems. If not than I will see if I can return the other 2 if not I'm sure I can save them if I want to change them again or put on another bike. Thanks again.
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