Bike Build - Regearing Questions
#1
Miles to Go
Thread Starter
Bike Build - Regearing Questions
A little background: I purchased a Y2K Jamis Aurora a few months ago with the stock 30/42/52T and 11-25. Before taking my first short tour on it, I replaced the 11-25 with a SRAM PG 850 11-28 (stayed 28 due to short cage Sora derailleur. It did OK, but as you can imagine I wished for lower gearing.
So now I am ready for the re-gear with the following:
Shimano Deore RD-M592 SGS Shadow Long Cage Bike Rear Derailleur
SRAM PC 870 chain
SRAM s600 Crankset 22/32/42
SRAM PG 850 11-32 cassette
I took the 11-28 and 11-32 apart and have assembled the following: 12 14 18 21 24 26 28 32. The unique cogs I have leftover are: 11 and 16. This yields me a low of 18.6 gear inches... plenty low. I actually wanted to put the 14T as the smallest cog, but found out it doesn't have the extension on it to use it as the smallest cog.
My question here is will the bigger spacing in the higher gears (smaller cogs) be problematic? I am concerned about the 14-18 jump especially. If it is, I could go 12-16-18 as I never shift to the smallest cog anyway.
Second question is in regard to the crankset. I have it mounted, but it does not seem to go down on the cranks as far as the Sora crankset that came off. Unless my research is faulty, they both are square taper JIS. The BB is 68X113 currently. Any issue simply going to a 68X107 or even 103? The BB on the bike is a low quality Shimano BB-LP27 and is 15 years old, so I want to replace it anyway.
Anything else that could be an issue that is apparent?
So now I am ready for the re-gear with the following:
Shimano Deore RD-M592 SGS Shadow Long Cage Bike Rear Derailleur
SRAM PC 870 chain
SRAM s600 Crankset 22/32/42
SRAM PG 850 11-32 cassette
I took the 11-28 and 11-32 apart and have assembled the following: 12 14 18 21 24 26 28 32. The unique cogs I have leftover are: 11 and 16. This yields me a low of 18.6 gear inches... plenty low. I actually wanted to put the 14T as the smallest cog, but found out it doesn't have the extension on it to use it as the smallest cog.
My question here is will the bigger spacing in the higher gears (smaller cogs) be problematic? I am concerned about the 14-18 jump especially. If it is, I could go 12-16-18 as I never shift to the smallest cog anyway.
Second question is in regard to the crankset. I have it mounted, but it does not seem to go down on the cranks as far as the Sora crankset that came off. Unless my research is faulty, they both are square taper JIS. The BB is 68X113 currently. Any issue simply going to a 68X107 or even 103? The BB on the bike is a low quality Shimano BB-LP27 and is 15 years old, so I want to replace it anyway.
Anything else that could be an issue that is apparent?
#2
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The problem you ran into is that a mountain bike crank is designed to use a 50 mm chainline, and a road crank set uses a 45-46 mm chainline.
To find the correct BB length: mount your mtn cranks on your present BB, measure the chainline to the center chainwheel, subtract 45 mm from that number, multiply the results by 2, and subtract that number from your present BB length. Or you can just assume that the present chainline is 45 mm and subtract 10mm from the length of the present BB spindle.
Chainline is measured from the center of the seat tube to the center of the teeth on the middle chainring. An easy way to do it is measure the diameter of the seat tube, divide by 2, and add the distance from the edge of the seat tube to the chainring.
It probably took me longer to post this than it does to take the measurements.
I've found that a 103 mm BB works well when making the conversion on bikes with a 68 mm bottom bracket shell. However, if you go through the measurement drill, you'll know for sure if it will work.
Also, some of the newer road front derailleurs do not work well with only a 10 tooth difference in the large and middle chainrings. The rear cage of the front deralleur is too wide, and you can't get the FD low enough without interfering with the middle chainring when shifting. A 44/32/22 will work with most road derailleurs.
To find the correct BB length: mount your mtn cranks on your present BB, measure the chainline to the center chainwheel, subtract 45 mm from that number, multiply the results by 2, and subtract that number from your present BB length. Or you can just assume that the present chainline is 45 mm and subtract 10mm from the length of the present BB spindle.
Chainline is measured from the center of the seat tube to the center of the teeth on the middle chainring. An easy way to do it is measure the diameter of the seat tube, divide by 2, and add the distance from the edge of the seat tube to the chainring.
It probably took me longer to post this than it does to take the measurements.
I've found that a 103 mm BB works well when making the conversion on bikes with a 68 mm bottom bracket shell. However, if you go through the measurement drill, you'll know for sure if it will work.
Also, some of the newer road front derailleurs do not work well with only a 10 tooth difference in the large and middle chainrings. The rear cage of the front deralleur is too wide, and you can't get the FD low enough without interfering with the middle chainring when shifting. A 44/32/22 will work with most road derailleurs.
Last edited by Doug64; 02-07-15 at 12:01 PM.
#3
Miles to Go
Thread Starter
Thanks for the reply Doug. Yes it measures out at about 50MM currently. I ordered a 103mm BB. Hope it fits w/o clearance issues.
As for the front derailleur, I had 30/42/52 (10 gap already middle to large). Shifted the 22/32/42 OK with 113mm, until I changed to steeper cassette, and have yet to adjust it again, and will wait until new 103 BB is in place.
I am concerned about the gearing as they must provide small gaps in the smaller cogs for a reason, but will see how well it works.
As for the front derailleur, I had 30/42/52 (10 gap already middle to large). Shifted the 22/32/42 OK with 113mm, until I changed to steeper cassette, and have yet to adjust it again, and will wait until new 103 BB is in place.
I am concerned about the gearing as they must provide small gaps in the smaller cogs for a reason, but will see how well it works.
#4
Senior Member
From my experience, I would strongly recommend keeping the 16 cog. One of my bikes has an 8speed 11 to 28 and is 11-12-14-16-18-21-24-28 and missing the 16 would be an issue, in fact I wish I had a 13 and 15....
This bike also has a mtn crank, 42/32/22
This bike also has a mtn crank, 42/32/22
#5
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I really like the Sram 11/32 eight speed. It has 11,12,14,16,18,21,26,32
On a loaded tour in moderately flat to hilly terrain I probably spend:
- 85 percent of the time on the 14, 16, 18 & 21.
- 3 percent of the time in the 11 or 12 (downhill or tailwind only gears, rarely used but nice to have)
- 12 percent of the time in the 26 or 32.
Thus I am predominantly using only four (half) of my cogs, but with your setup I would only have three cogs in the range where I spend most time.
I am using a 52/42/24 crankset, if I had the crank you are going to, I would use the smaller 11 & 12 cogs more often, the 26 and 32 less.
The cogs are ramped to shift best when matched from the factory, your mix and match might not be as smooth.
On a loaded tour in moderately flat to hilly terrain I probably spend:
- 85 percent of the time on the 14, 16, 18 & 21.
- 3 percent of the time in the 11 or 12 (downhill or tailwind only gears, rarely used but nice to have)
- 12 percent of the time in the 26 or 32.
Thus I am predominantly using only four (half) of my cogs, but with your setup I would only have three cogs in the range where I spend most time.
I am using a 52/42/24 crankset, if I had the crank you are going to, I would use the smaller 11 & 12 cogs more often, the 26 and 32 less.
The cogs are ramped to shift best when matched from the factory, your mix and match might not be as smooth.
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I tried a mtn crank like yours for a short time when searching for lower gears starting with more of a road triple like you have. Ididn’t like the 32,42 combination as I found the split in the center of my common gearing and wanting to ride the 42 down to the point of cross chaining too often and then having to make the calculated shift off the center ring.Like Tourist in MSN I went back to the road crank liking the 42 in the middle only I run a 45/42/24 the 11-32 might not get you as low on the granny as you would want though but if you could come up with something in an 8 speed ending with 36 it would. Mine is a 9 speed 12-36 and I love all the gears.
You wont know if you love or hate the mtn crank tillyou start riding it. The low gears you will love I know I did but it was on the flats I wasn’t too happy.
You wont know if you love or hate the mtn crank tillyou start riding it. The low gears you will love I know I did but it was on the flats I wasn’t too happy.
Last edited by bud16415; 02-07-15 at 08:10 AM.
#7
Senior Member
as I ride my 42/32/22 11-28 8 speed bike a lot with maybe one pannier, sometimes two with up to about 25lbs on it, I would have to say that at times I too find the 32 chainring a bit too small, and when I ride my other bike with the 50/39/26 on it, I sometimes find the 39 too tall a bit with a load of lets say 40lbs. My preference--and specifically for a majority of the time where we are in the mid ring, a 34 for heavy loaded and more hilly would be perfect, allowing me to not have to shift from the 34 that often. With less load, a 36 would be great too--it all depends on how much weight you carry and how strong you are--I consider myself not a strong rider, very average.
This whole gearing thing has been on my mind lately when thinking of what crank would I put on a new touring bike. I certainly know that in very up and down and steep terrain, a mtn crank will work great, and considering even on the flats we tend to be speeds of 15-25kph max, for me a middle chain ring that covers that range and a cassette that doesnt have big jumps in the most common gears would be ideal, simply because of the high percentage of time we are at those speeds.
This whole gearing thing has been on my mind lately when thinking of what crank would I put on a new touring bike. I certainly know that in very up and down and steep terrain, a mtn crank will work great, and considering even on the flats we tend to be speeds of 15-25kph max, for me a middle chain ring that covers that range and a cassette that doesnt have big jumps in the most common gears would be ideal, simply because of the high percentage of time we are at those speeds.
#8
Senior Member
I really like the Sram 11/32 eight speed. It has 11,12,14,16,18,21,26,32
On a loaded tour in moderately flat to hilly terrain I probably spend:
- 85 percent of the time on the 14, 16, 18 & 21.
- 3 percent of the time in the 11 or 12 (downhill or tailwind only gears, rarely used but nice to have)
- 12 percent of the time in the 26 or 32.
Thus I am predominantly using only four (half) of my cogs, but with your setup I would only have three cogs in the range where I spend most time.
On a loaded tour in moderately flat to hilly terrain I probably spend:
- 85 percent of the time on the 14, 16, 18 & 21.
- 3 percent of the time in the 11 or 12 (downhill or tailwind only gears, rarely used but nice to have)
- 12 percent of the time in the 26 or 32.
Thus I am predominantly using only four (half) of my cogs, but with your setup I would only have three cogs in the range where I spend most time.
I personally dont like using the 11 that much as it feels "rough", not a problem here and there but I would never run in it for more than just a bit. The 12 already feels smoother (larger diameter for the chain to go around) but as you say, the 14, 16, 18 and 21 are where we really spend the vast majority of the time.
As I've said often, I just wish that commonly bought 9 speed cassettes were 12-32 and not 11-32, just to trade off the 11 for a 13 or whatever. The now common 12-30 ten speed is 12-13-14-15-17-19-21-24-27-30 which is a nice spread, but a 22 granny and 30t cassette might not be low enough a low for some situations (not to mention using 10 speed which may or may not be the best situation for various reasons)
as always, lots of things to ponder, I personally find it fun to ponder about gearing and can bore most people to death talking about it.
#9
Miles to Go
Thread Starter
I tried a mtn crank like yours for a short time when searching for lower gears starting with more of a road triple like you have. Ididn’t like the 32,42 combination as I found the split in the center of my common gearing and wanting to ride the 42 down to the point of cross chaining too often and then having to make the calculated shift off the center ring.Like Tourist in MSN I went back to the road crank liking the 42 in the middle only I run a 45/42/24 the 11-32 might not get you as low on the granny as you would want though but if you could come up with something in an 8 speed ending with 36 it would. Mine is a 9 speed 12-36 and I love all the gears.
You wont know if you love or hate the mtn crank tillyou start riding it. The low gears you will love I know I did but it was on the flats I wasn’t too happy.
You wont know if you love or hate the mtn crank tillyou start riding it. The low gears you will love I know I did but it was on the flats I wasn’t too happy.
#10
Banned
My question here is will the bigger spacing in the higher gears (smaller cogs) be problematic?
Like when I'm using my 3 speed ... A gear feels slightly too Low? slow down. till it feels right.. next higher feels too high, push the pace a bit till it feels right.
or drop back to the lower one..
Touring, at a modest speed I rarely use the High 80-95+" gears.. Its a Tour to see stuff, why rush through it? [Done Years of tours.. 6 speed freewheel triple crank]
Winter is time for overthinking, about summer cycling, it seems.. cabin fever ..
#11
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Thanks for the reply Doug. Yes it measures out at about 50MM currently. I ordered a 103mm BB. Hope it fits w/o clearance issues.
As for the front derailleur, I had 30/42/52 (10 gap already middle to large). Shifted the 22/32/42 OK with 113mm, until I changed to steeper cassette, and have yet to adjust it again, and will wait until new 103 BB is in place.
I am concerned about the gearing as they must provide small gaps in the smaller cogs for a reason, but will see how well it works.
As for the front derailleur, I had 30/42/52 (10 gap already middle to large). Shifted the 22/32/42 OK with 113mm, until I changed to steeper cassette, and have yet to adjust it again, and will wait until new 103 BB is in place.
I am concerned about the gearing as they must provide small gaps in the smaller cogs for a reason, but will see how well it works.
I'd also suggest running an 11-34 cassette combination through the calculator for comparison. I like the ability to drop down into that low range when conditions dictate.
#12
Miles to Go
Thread Starter
You might want to run your setup through a gear calculator. I like this one:Mike Sherman's Bicycle Gear Calculator
I'd also suggest running an 11-34 cassette combination through the calculator for comparison. I like the ability to drop down into that low range when conditions dictate.
I'd also suggest running an 11-34 cassette combination through the calculator for comparison. I like the ability to drop down into that low range when conditions dictate.
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I tried a mtn crank like yours for a short time when searching for lower gears starting with more of a road triple like you have. Ididn’t like the 32,42 combination as I found the split in the center of my common gearing and wanting to ride the 42 down to the point of cross chaining too often and then having to make the calculated shift off the center ring.
You wont know if you love or hate the mtn crank tillyou start riding it. The low gears you will love I know I did but it was on the flats I wasn’t too happy.
You wont know if you love or hate the mtn crank tillyou start riding it. The low gears you will love I know I did but it was on the flats I wasn’t too happy.
8 vs 9 speed is all about chain world wide availability aka the mall-wart factor.
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Here is another gear calculator:
HTML5 Gear Calculator
They all have slightly different interfaces and capabilities, pick ones you like.
Niagara and other places have Miche cogs; in 8/9 speed 1st position you can get any from 11T to 15T for your customization project.
Miche Shimano 14t First Position Cog, 8/9-Speed
I combined a Shimano 13-26: 13 14 15 17 19 21 23 26 with a Shimano 11-32 11 13 15 18 21 24 28 32 and a Miche 14T first position cog to get an 8 speed: 14 15 17 19 21 23 26 32 which suits me nicely.
Regarding cogs - Shimano HG are designed for the number of teeth difference between it and the smaller cog next to it. For example, they only have two different 15T cogs, one designed to be next to a 14T and the other designed to be next to a 13T. Even if you mess this up, they still shift nicer than cogs without ramps. Note Miche offers Shimano compatible cogs that are not ramped.
@timdow - you must spin a LOT faster than I; 42 makes a great deal of sense to me as the middle ring on the road - our tandem has a 44T middle and stock SRAM 9 speed 11-34 (next time we'll try a 12-36). We have a 26T granny, and a 54T big ring (way too big for a single bike, but just right for us on the tandem downhill or with a tail wind). The middle ring and big rings can access all of the rear cogs, the granny only the largest 5. I have the cranks positioned like a double, with the center of the cassette aligned half way between the middle and big rings.
Think about the gears you want to access and when, the position the crank to suit you, not some arbitrary standard. This is were gear calculators are invaluable.
HTML5 Gear Calculator
They all have slightly different interfaces and capabilities, pick ones you like.
Niagara and other places have Miche cogs; in 8/9 speed 1st position you can get any from 11T to 15T for your customization project.
Miche Shimano 14t First Position Cog, 8/9-Speed
I combined a Shimano 13-26: 13 14 15 17 19 21 23 26 with a Shimano 11-32 11 13 15 18 21 24 28 32 and a Miche 14T first position cog to get an 8 speed: 14 15 17 19 21 23 26 32 which suits me nicely.
Regarding cogs - Shimano HG are designed for the number of teeth difference between it and the smaller cog next to it. For example, they only have two different 15T cogs, one designed to be next to a 14T and the other designed to be next to a 13T. Even if you mess this up, they still shift nicer than cogs without ramps. Note Miche offers Shimano compatible cogs that are not ramped.
@timdow - you must spin a LOT faster than I; 42 makes a great deal of sense to me as the middle ring on the road - our tandem has a 44T middle and stock SRAM 9 speed 11-34 (next time we'll try a 12-36). We have a 26T granny, and a 54T big ring (way too big for a single bike, but just right for us on the tandem downhill or with a tail wind). The middle ring and big rings can access all of the rear cogs, the granny only the largest 5. I have the cranks positioned like a double, with the center of the cassette aligned half way between the middle and big rings.
Think about the gears you want to access and when, the position the crank to suit you, not some arbitrary standard. This is were gear calculators are invaluable.
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Thanks for the replies. Lots to ponder here. I briefly looked at a 26/36/46, and figured the mountain gearing would be better, but not so sure now. it is going to be interesting trying to get "just right" gearing. Point well taken about gears used most often. I really was looking for not such a big jump between 26 and 32, but I can set the 11-32 back to the way it came if the gearing I set up does not work out.
Here they are in order.
https://www.bikeforums.net/touring/760385-granny-isn-t-everything.html
https://www.bikeforums.net/bicycle-mechanics/850129-touring-big-ring-half-step.html
https://www.bikeforums.net/touring/852913-45-42-24-x-12-14-16-18-21-24-28-32-36-o.html
#16
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time and experience will teach you what is right for you. don't over think it.
#17
Miles to Go
Thread Starter
I am going from a 113mm to a 103mm BB, so the downtube to middle ring measurement should go from 50mm back to 45mm. Looks to me like the gaps between the rings is about the same in the road and MTB crankset. So won't I get the same chainline with the MTB cranks as the road cranks using the narrower BB? Or are the gaps between the rings actually more on the MTB crank?
#18
Miles to Go
Thread Starter
Here is another gear calculator:
HTML5 Gear Calculator
They all have slightly different interfaces and capabilities, pick ones you like.
Niagara and other places have Miche cogs; in 8/9 speed 1st position you can get any from 11T to 15T for your customization project.
Miche Shimano 14t First Position Cog, 8/9-Speed
I combined a Shimano 13-26: 13 14 15 17 19 21 23 26 with a Shimano 11-32 11 13 15 18 21 24 28 32 and a Miche 14T first position cog to get an 8 speed: 14 15 17 19 21 23 26 32 which suits me nicely.
Regarding cogs - Shimano HG are designed for the number of teeth difference between it and the smaller cog next to it. For example, they only have two different 15T cogs, one designed to be next to a 14T and the other designed to be next to a 13T. Even if you mess this up, they still shift nicer than cogs without ramps. Note Miche offers Shimano compatible cogs that are not ramped.
@timdow - you must spin a LOT faster than I; 42 makes a great deal of sense to me as the middle ring on the road - our tandem has a 44T middle and stock SRAM 9 speed 11-34 (next time we'll try a 12-36). We have a 26T granny, and a 54T big ring (way too big for a single bike, but just right for us on the tandem downhill or with a tail wind). The middle ring and big rings can access all of the rear cogs, the granny only the largest 5. I have the cranks positioned like a double, with the center of the cassette aligned half way between the middle and big rings.
Think about the gears you want to access and when, the position the crank to suit you, not some arbitrary standard. This is were gear calculators are invaluable.
HTML5 Gear Calculator
They all have slightly different interfaces and capabilities, pick ones you like.
Niagara and other places have Miche cogs; in 8/9 speed 1st position you can get any from 11T to 15T for your customization project.
Miche Shimano 14t First Position Cog, 8/9-Speed
I combined a Shimano 13-26: 13 14 15 17 19 21 23 26 with a Shimano 11-32 11 13 15 18 21 24 28 32 and a Miche 14T first position cog to get an 8 speed: 14 15 17 19 21 23 26 32 which suits me nicely.
Regarding cogs - Shimano HG are designed for the number of teeth difference between it and the smaller cog next to it. For example, they only have two different 15T cogs, one designed to be next to a 14T and the other designed to be next to a 13T. Even if you mess this up, they still shift nicer than cogs without ramps. Note Miche offers Shimano compatible cogs that are not ramped.
@timdow - you must spin a LOT faster than I; 42 makes a great deal of sense to me as the middle ring on the road - our tandem has a 44T middle and stock SRAM 9 speed 11-34 (next time we'll try a 12-36). We have a 26T granny, and a 54T big ring (way too big for a single bike, but just right for us on the tandem downhill or with a tail wind). The middle ring and big rings can access all of the rear cogs, the granny only the largest 5. I have the cranks positioned like a double, with the center of the cassette aligned half way between the middle and big rings.
Think about the gears you want to access and when, the position the crank to suit you, not some arbitrary standard. This is were gear calculators are invaluable.
As for how fast I spin... I won't know if this works until I try it for a while. it is very hilly here where I live, and while it is important to me to be able to tackle the hills, per your comments and comments from others here, I may not be happy on the flats.
I really enjoy making changes to the bike, so regearing is not really an issue. And that is good, because I will probably be making some kind of change soon.
#19
Miles to Go
Thread Starter
Like when I'm using my 3 speed ... A gear feels slightly too Low? slow down. till it feels right.. next higher feels too high, push the pace a bit till it feels right.
or drop back to the lower one..
Touring, at a modest speed I rarely use the High 80-95+" gears.. Its a Tour to see stuff, why rush through it? [Done Years of tours.. 6 speed freewheel triple crank]
Winter is time for overthinking, about summer cycling, it seems.. cabin fever ..
or drop back to the lower one..
Touring, at a modest speed I rarely use the High 80-95+" gears.. Its a Tour to see stuff, why rush through it? [Done Years of tours.. 6 speed freewheel triple crank]
Winter is time for overthinking, about summer cycling, it seems.. cabin fever ..
#20
Miles to Go
Thread Starter
Thanks for the reply. I will pay particular attention to this the first time out (probably tomorrow). I might end up going from 12 14 18 21 24 26 28 32 to 14 16 18 21 24 26 28 32 (or similar) by purchasing a 14T 1st position cog as was suggested in this thread. Time will tell.
#21
Miles to Go
Thread Starter
Sage advice, thanks. I enjoy doing the changes, and really want to know what works and doesn't by experience.
#22
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For those who like 8 spd cassettes IRD makes 12-28 and 12-32 cassettes. They aren't as smooth out of the box as Shimano but after a few hundred miles work fine.
7, 8 and 9-speed Comp MTB/Road Cassette ? Interloc Racing Design / IRD
7, 8 and 9-speed Comp MTB/Road Cassette ? Interloc Racing Design / IRD
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#24
Miles to Go
Thread Starter
Here is another gear calculator:
HTML5 Gear Calculator
They all have slightly different interfaces and capabilities, pick ones you like.
Niagara and other places have Miche cogs; in 8/9 speed 1st position you can get any from 11T to 15T for your customization project.
Miche Shimano 14t First Position Cog, 8/9-Speed
I combined a Shimano 13-26: 13 14 15 17 19 21 23 26 with a Shimano 11-32 11 13 15 18 21 24 28 32 and a Miche 14T first position cog to get an 8 speed: 14 15 17 19 21 23 26 32 which suits me nicely.
Regarding cogs - Shimano HG are designed for the number of teeth difference between it and the smaller cog next to it. For example, they only have two different 15T cogs, one designed to be next to a 14T and the other designed to be next to a 13T. Even if you mess this up, they still shift nicer than cogs without ramps. Note Miche offers Shimano compatible cogs that are not ramped.
@timdow - you must spin a LOT faster than I; 42 makes a great deal of sense to me as the middle ring on the road - our tandem has a 44T middle and stock SRAM 9 speed 11-34 (next time we'll try a 12-36). We have a 26T granny, and a 54T big ring (way too big for a single bike, but just right for us on the tandem downhill or with a tail wind). The middle ring and big rings can access all of the rear cogs, the granny only the largest 5. I have the cranks positioned like a double, with the center of the cassette aligned half way between the middle and big rings.
Think about the gears you want to access and when, the position the crank to suit you, not some arbitrary standard. This is were gear calculators are invaluable.
HTML5 Gear Calculator
They all have slightly different interfaces and capabilities, pick ones you like.
Niagara and other places have Miche cogs; in 8/9 speed 1st position you can get any from 11T to 15T for your customization project.
Miche Shimano 14t First Position Cog, 8/9-Speed
I combined a Shimano 13-26: 13 14 15 17 19 21 23 26 with a Shimano 11-32 11 13 15 18 21 24 28 32 and a Miche 14T first position cog to get an 8 speed: 14 15 17 19 21 23 26 32 which suits me nicely.
Regarding cogs - Shimano HG are designed for the number of teeth difference between it and the smaller cog next to it. For example, they only have two different 15T cogs, one designed to be next to a 14T and the other designed to be next to a 13T. Even if you mess this up, they still shift nicer than cogs without ramps. Note Miche offers Shimano compatible cogs that are not ramped.
@timdow - you must spin a LOT faster than I; 42 makes a great deal of sense to me as the middle ring on the road - our tandem has a 44T middle and stock SRAM 9 speed 11-34 (next time we'll try a 12-36). We have a 26T granny, and a 54T big ring (way too big for a single bike, but just right for us on the tandem downhill or with a tail wind). The middle ring and big rings can access all of the rear cogs, the granny only the largest 5. I have the cranks positioned like a double, with the center of the cassette aligned half way between the middle and big rings.
Think about the gears you want to access and when, the position the crank to suit you, not some arbitrary standard. This is were gear calculators are invaluable.
#25
Miles to Go
Thread Starter
The problem you ran into is that a mountain bike crank is designed to use a 50 mm chainline, and a road crank set uses a 45-46 mm chainline.
To find the correct BB length: mount your mtn cranks on your present BB, measure the chainline to the center chainwheel, subtract 45 mm from that number, multiply the results by 2, and subtract that number from your present BB length. Or you can just assume that the present chainline is 45 mm and subtract 10mm from the length of the present BB spindle.
Chainline is measured from the center of the seat tube to the center of the teeth on the middle chainring. An easy way to do it is measure the diameter of the seat tube, divide by 2, and add the distance from the edge of the seat tube to the chainring.
It probably took me longer to post this than it does to take the measurements.
I've found that a 103 mm BB works well when making the conversion on bikes with a 68 mm bottom bracket shell. However, if you go through the measurement drill, you'll know for sure if it will work.
Also, some of the newer road front derailleurs do not work well with only a 10 tooth difference in the large and middle chainrings. The rear cage of the front deralleur is too wide, and you can't get the FD low enough without interfering with the middle chainring when shifting. A 44/32/22 will work with most road derailleurs.
To find the correct BB length: mount your mtn cranks on your present BB, measure the chainline to the center chainwheel, subtract 45 mm from that number, multiply the results by 2, and subtract that number from your present BB length. Or you can just assume that the present chainline is 45 mm and subtract 10mm from the length of the present BB spindle.
Chainline is measured from the center of the seat tube to the center of the teeth on the middle chainring. An easy way to do it is measure the diameter of the seat tube, divide by 2, and add the distance from the edge of the seat tube to the chainring.
It probably took me longer to post this than it does to take the measurements.
I've found that a 103 mm BB works well when making the conversion on bikes with a 68 mm bottom bracket shell. However, if you go through the measurement drill, you'll know for sure if it will work.
Also, some of the newer road front derailleurs do not work well with only a 10 tooth difference in the large and middle chainrings. The rear cage of the front deralleur is too wide, and you can't get the FD low enough without interfering with the middle chainring when shifting. A 44/32/22 will work with most road derailleurs.
Also the Sora Derailleur works fine with the smaller rings and 10 tooth difference (22/32/42).