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Swapping Cranksets

Old 06-05-17, 06:17 AM
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Widowmaker62
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Swapping Cranksets

I have a 48X36X26 110mm BCD and want to swap it to a 44X32X22 104mm BCD. The bike is a Jamis Aurora. Is this doable? Additionally, it has a 7/11-24 speed cassette and I want to swap it for a 9/11-32. Doable?

Thanks,
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Old 06-05-17, 06:56 AM
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Given the BCD's that you mention, it sounds like you want to switch from a road to an MTB crankset? If so you have a number of issues to be wary of, most of which revolve around the front derailleur. First, MTB triple cranks have a much wider "chainline" than road cranksets. Typically 50mm vs 45. This means the chainrings sit farther away from the centerline of the bike. If you're using a road-type front derailleur, it may not be able to swing out far enough to shift the chain up to the big ring. That means you will have to switch to an MTB front derailleur. If you are using friction downtube or bar end shifters, this is no problem. But no drop-bar shifters that I'm aware of, with the possible exception of Campagnolo, will index properly with an MTB FD. Gevenalles will work perfectly of course, but they are kind of a chimera -- bar end shifters bolted to brake levers, with pure friction shifting of the FD.

This means you will have to change your whole shifting concept, either moving to barends (I use Gevenalles), or switching the bike to flat or trekking-style bars and using MTB shifters. If that weren't enough, switching to MTB shifters means you may have to rethink your braking solution, since mechanical MTB brake levers typically aren't compatible with road caliper brakes, though there are ways to get them to work. I've been through this game a few times. It's amazing how much stuff has to change just to get the silly FD to move a few more millimeters outboard.

Second, depending on your rear derailleur, it may not be able to accommodate the 32t maximum cog or the added 8t of chain wrap that you will need to cover the shifting range. That means a new RD as well. Without more specifics it's hard to say.

It's not all bad news. Since you want to switch from 7 to 9 speeds, you will need to change to new shifters (unless you are using pure friction shifting for both front and rear), so you're going to be spending some money anyway. The incremental cost of going to an MTB crank may end up not being that much.

Last edited by Metaluna; 06-05-17 at 07:02 AM.
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Old 06-05-17, 06:56 AM
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sch
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Basically a complete drive train redo, from 7 to 9 spd? If the barend shifters are friction based then they should be usable.
You will need a new chain, ??new rear derailler, though unless the RD is a short cage, it should work ok on an 11-32 cassette.
FD should be usable as well. If the old cranks and new cranks differ in spindle type, you will need an appropriate bottom
bracket. 7 spd setup may be sq taper BB spindle, not splined so this should be checked. A 7 spd chain may work on a 9 spd
cassette (dunnoh) with the most likely problems occurring where adjacent cogs have single tooth steps. If no single tooth steps then
you might get away with the same chain, best to replace though for better match to crank/cassette and for chain length.

FWIW the stock cranks are FSA Alpha drive, an ATB crankset in 48/36/26 and the stock bike has barend shifters. I assumed the
bike was stock and ~12-15yrs old.

FD should be lowered on the seat tube about 3/4"

A bit weird you have a 7 spd cassette, as that raises the question of what type of rear hub you have so there may be a problem
there as well. See: https://www.sheldonbrown.com/k7-7.shtml

Last edited by sch; 06-05-17 at 07:12 AM.
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Old 06-05-17, 07:20 AM
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Nine won't fit on a seven speed freehub.
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Old 06-05-17, 08:30 AM
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As davidad said, a 9 speed cassette wont fit on a Shimano 7 speed freehub body. But you can replace the freehub body (not the whole hub) and then redish (I did just this on an older touring bike when I changed from 7 to 9 speeds).
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Old 06-05-17, 10:55 AM
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From looking at Bikepedia, your Jamis is probably an early/mid 90's because in 1996 the drivetrain was 8 speed. Back then the bike was considered a mountain bike with 26" wheels, so going to a 104 bcd should not be a problem.

You cannot go to a 9 speed cassette, as noted above. You can run a 7 speed 12-32 cassette if you want lower gearing.

The other consideration are the 7 speed shifters. Good ones are not easy to find these days, so if they are suspect, you need to find new ones or convert to 9 speed.

John
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Old 06-05-17, 12:49 PM
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Or,
you can switch to a mid rise mountain bike style handlebars with the correct brake levers for your brakes and use a set of 7 speed GripShift shifters. These will be compatible with Shimano derailleurs, assuming you're using Shimano.
There are still tons of 7 spped cassete available to you.
Inexpensive, try Universal Cycles for your parts, very affordable.
Your other option is to obtain an eight speed Shimano rear hub/wheel which will allow you to swap on a 9 speed cassete, but you'll still need shifters. Barend shifters are a nice alternative and last a very long time.
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Old 06-05-17, 06:09 PM
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Originally Posted by 70sSanO View Post
From looking at Bikepedia, your Jamis is probably an early/mid 90's because in 1996 the drivetrain was 8 speed. Back then the bike was considered a mountain bike with 26" wheels, so going to a 104 bcd should not be a problem.

You cannot go to a 9 speed cassette, as noted above. You can run a 7 speed 12-32 cassette if you want lower gearing.
+1 to this idea. Swapping to a cheap and easy-to-find 12-32 cassette will bring down the whole range of gearing nicely without touching the crankset or shifters.
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Old 06-05-17, 06:56 PM
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I built a few bikes with similar drivetrain changes and would love to offer helpful info.
(Actually started with bare frames but same basic idea.)
But my sense is that since you're starting with different parts and frame I could only offer bad info.
I'll say that used parts are good if you want older tech, and I'll say that after building up 7, 8 and 9 speed I think the 9 speed is easier to get good results with and worthwhile if you're changing it up.
If you go to MTB parts there are 9 speed shift/ brake levers that work with road sidepulls, but also some that don't, and I forget how to tell the difference. I used XT and XTR shifter levers. Research part numbers and compatibility, and you might find certain combinations are not documented.
A lot of stuff to match up and tune...
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Old 06-06-17, 01:43 AM
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You probably have a 74bcd for the inner chainring. You can swap out the 26t for a 24t. You'll have a 48/36/24.

John
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Old 06-06-17, 02:29 AM
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jeesh!
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