Bicycle Mechanics - Need help with 6-speed drivetrain

I just picked up a 1986 Cannondale ST800 Touring bike. This bike is a time machine...

I bought the bike because its a 27" touring frame (68.5cm c-c, and 73cm to the top of the seat collar. I've been looking for a larger frame for a long time, and I'm very happy to have finally found one.

It has nearly a complete (and almost NOS) Suntour 6-Speed Accushift drivetrain. 6-speed Accushift barcons, Superbe front derailleur, Superbe Pro rear derailleur, Phil Wood hubs, 6-speed freewheel, etc.

The Suntour stuff just cracked me up. I'm no Luddite by any means, and I'm not out to prove a point by not having Shimano or Campy. In fact I really want a non-traditional group bike, and my heart is set on putting together a Mavic SSC project. The Suntour stuff I'm completely ambivalent about. If it works fine. The funny thing is how much Suntour stuff I actually have (come to think about it). For whatever reason I've picked up (and not on purpose) a lot of Suntour bits over the years. I think other than this nearly complete Suntour Superbe touring bike I've got some GPX hubs, Blaze shifters and derailleurs, an XC Pro front derailleur and crank, and I think one XC Expert thumbie (don't remember which)...

Some of the stuff like the Superbe Pro pedals which look like they are brand new I'm not going to use. I'll probably list those on eBay so someone who is trying to complete a vintage restoration can complete their product. Longterm, I have no plans to keep anything from the Suntour Superbe drivetrain, but I really just want to ride the bike right now.

The problem is that I've removed the Suntour BB and Sugino crank. In its place went in a Phil Wood BB and a set of custom Zinn 205mm cranks. Its a big bike and I've always wanted proportional length crank arms. I have a 980mm cycling inseam. The 205s are actually a bit conservative (using the .210 factor instead of the .216).

Well, now I don't know what chainrings to use on the bike. The Zinn triple crank uses 130/74 BCD five bolt rings.

Aren't chainrings speed specific? Considering everything is 9/10 speed these days where am I going to source high end rings?

I was thinking about using TA rings, as they are available in a wider selection of tooth counts. I'm not sure about the capacity of the Superbe front derailleur. I do have plenty of other derailleurs on hand if I need to swap out the front derailleur. If need be I could use a Suntour XC Pro front that I have or a Shimano XT front derailleur.

I'm not sure what range is allowed by a Superbe front derailleur, between the big/middle/small rings. Does anyone know the tooth difference allowed? Would the XC Pro front derailleur give me a wider range than the Superbe? How 'bout the Shimano XT front? A Mavic 870?

What is a good range of rings for a touring bike? I really want a low climbing bailout gear (I live in Colorado) for the mountains.

Can I use any current TA ring (they are available from Peter White and Harris Cyclery) or are front chain rings speed dependent?

I know 6 speed is outdated, however, the huge size of the bike and the 48 spoke Phil Wood hubs made me pull the trigger. The rear spacing is 126mm and its a freewheel, so I can't upgrade to 8 speed (which I think is the best touring choice).

What rings would work (any? all?), and what tooth counts? I know I want a 38 middle ring since that's the smallest the 130 BCD will handle. Does that dictate what the big and little ring will be due to max tooth difference on the front derailleur?

Chainrings aren't really speed specific. It's the crank spacing that might be a problem. 9/10 chainrings are the same (shimano anyways). You can go up to at least 7 speeds with 126mm.

Chainrings aren't really speed specific. It's the crank spacing that might be a problem. 9/10 chainrings are the same (shimano anyways). You can go up to at least 7 speeds with 126mm.

What about the crank spacing might be a problem?

By that do you mean figuring out which spacers to use with the chain rings? I checked the Sugino AT crank that came with the bike. It has a 74mm little ring. So I could take the 74mm little ring off the Sugino crank.

However, would I want to do this? I was reading about chainrings on Peter White's web site and learned that there is a difference between the way teeth are set on Shimano versus Sugino chainrings. I don't know what the Zinn crank is meant to use (Sugino or Shimano standard).

I'd like to keep that Sugino AT crank and rings 'whole' instead of pilfering it for its little ring. I think someone would appreciate having the nearly NOS older crank for their project. I just want something that works...

What about the crank spacing might be a problem?

By that do you mean figuring out which spacers to use with the chain rings? I checked the Sugino AT crank that came with the bike. It has a 74mm little ring. So I could take the 74mm little ring off the Sugino crank.

However, would I want to do this? I was reading about chainrings on Peter White's web site and learned that there is a difference between the way teeth are set on Shimano versus Sugino chainrings. I don't know what the Zinn crank is meant to use (Sugino or Shimano standard).

You're not understanding. 130bcd crank will fit all 130bcd chainrings, has nothing to do with how the chainring teeth are set. According to sheldon you should be fine on that crank for 7/8/9 *unless* it was originally designed for 10 speed - which puts the chainrings close together. You could mess with spacers as well but that will probably be an exercise in frustration. Also - not sure what you mean by high end rings. Shimano rings are perfectly fine.

I haven't messed with incompatibly issues like this before maybe someone who's a crank *speed* expert can chime in.

One other question, is the "cassette" really a cassette or a freewheel? I don't think Phil Wood ever made a Sun tour compatible freehub so it it has Sun Tour cogs, it's probably a freewheel.

One other question, is the "cassette" really a cassette or a freewheel? I don't think Phil Wood ever made a Sun tour compatible freehub so it it has Sun Tour cogs, it's probably a freewheel.

He said it was a freewheel 126/

He said it was a freewheel 126/
Yabbut. At the top of the OP, he said; "......Superbe front derailleur, Superbe Pro rear derailleur, Phil Wood hubs, 6-speed cassette, etc...." and I didn't read the rest of the fine print. I expected the 126 mm spacing from both the frame's age and the 6-speed whatever.

I'm not sure what range is allowed by a Superbe front derailleur, between the big/middle/small rings. Does anyone know the tooth difference allowed? Would the XC Pro front derailleur give me a wider range than the Superbe? How 'bout the Shimano XT front? A Mavic 870?

What is a good range of rings for a touring bike? I really want a low climbing bailout gear (I live in Colorado) for the mountains.


What rings would work (any? all?), and what tooth counts? I know I want a 38 middle ring since that's the smallest the 130 BCD will handle. Does that dictate what the big and little ring will be due to max tooth difference on the front derailleur?


I've not tried this with a Superbe FD specifically, but I've not had a problem using other doubles with rings from 24t to 48t. FD capacity is notoriously under-rated. But, since this is for crossover gears, you're better of with the XC Pro FD(or any vintage mtb FD for that matter).

Since you're using a 38t middle...... a 48, 50 or 52 all would work fine...... but 24-26 tooth difference may be about the limit of a FD. You didn't state anything about what size your FW is, or how strong you are.... so I can't say if you're better of with a 24,26, 28 or 30t small ring. A 26 or 28 would likely suit you fine though. A 24 or 26/38/48 is a pretty classic combo. ... that would give very low gear with a 13-28 FW for instance.

Chainring brands ? It sounds like a can of worms. TA rings are nice and all, but a bit overpriced . http://www.wiggle.co.uk/c/cycle/7/Chainrings/ sells them for quite a bit less. I'm not familiar with cranks being brand specific either ...... it sounds like either bunk or if it's true .... a PITA. Vuelta and Salsa make good rings for less also. http://www.cambriabike.com/shopdisplayproducts.asp?id=472&cat=Road+Chainrings Sugino makes good basic rings too.

I found this about the bike .... http://equusbicycle.com/bike/cannondale/catalog1986/pdf/1986cannondalecat%20-%200020.pdf

I'm not sure what range is allowed by a Superbe front derailleur, between the big/middle/small rings. Does anyone know the tooth difference allowed? Would the XC Pro front derailleur give me a wider range than the Superbe? How 'bout the Shimano XT front? A Mavic 870?
Sutherland's (4th Edition) gives 18 teeth as the maximum allowed by a Superbe front derailleur. The XC can handle a 22 tooth difference, as does the Shimano XT-M700. The Shimano XT-M700-GS is claimed to handle up to a 27 tooth difference. The Mavic 870 is supposed to handle up to a 26 tooth difference, according to Sutherland's 6th Edition.

One other question, is the "cassette" really a cassette or a freewheel? I don't think Phil Wood ever made a Sun tour compatible freehub so it it has Sun Tour cogs, it's probably a freewheel.

I made a mistake when typing. Its definitely a freewheel, not a cassette. I've edited the first post to fix that.

I've not tried this with a Superbe FD specifically, but I've not had a problem using other doubles with rings from 24t to 48t. FD capacity is notoriously under-rated. But, since this is for crossover gears, you're better of with the XC Pro FD(or any vintage mtb FD for that matter).

Since you're using a 38t middle...... a 48, 50 or 52 all would work fine...... but 24-26 tooth difference may be about the limit of a FD. You didn't state anything about what size your FW is, or how strong you are.... so I can't say if you're better of with a 24,26, 28 or 30t small ring. A 26 or 28 would likely suit you fine though. A 24 or 26/38/48 is a pretty classic combo. ... that would give very low gear with a 13-28 FW for instance.

Chainring brands ? It sounds like a can of worms. TA rings are nice and all, but a bit overpriced . http://www.wiggle.co.uk/c/cycle/7/Chainrings/ sells them for quite a bit less. I'm not familiar with cranks being brand specific either ...... it sounds like either bunk or if it's true .... a PITA. Vuelta and Salsa make good rings for less also. http://www.cambriabike.com/shopdisplayproducts.asp?id=472&cat=Road+Chainrings Sugino makes good basic rings too.

I found this about the bike .... http://equusbicycle.com/bike/cannondale/catalog1986/pdf/1986cannondalecat%20-%200020.pdf

Yep its a beauty. I had a .pdf of the whole catalog. Here is what it looks like (that's a handy link one page at a time):

http://equusbicycle.com/bike/cannondale/catalog1986/pdf/1986cannondalecat%20-%200021.pdf

The wheelset is not stock, its been upgraded to Phil Wood hubs with 48drill. The rear derailleur doesn't say Suntour Supberbe GT, but rather Superbe Pro. It does not have a Nitto Technomic stem but rather a Sakae one that says "Cro-Mo The Tube", however the Cinelli cork tape and the Cinelli tape hold the bar tape on looks like it was put on yesterday. The coolest thing is that the front and rear rack, and the three waterbottles were painted by Cannondale to match the metal flake. That .pdf doesn't do the paint justice.

I want to use a 38 middle because that's the smallest ring I can get with a 130bcd crank. I'd like to have the smallest little ring possible for climbing the mountains here in Colorado at altitude. What is the largest difference from the 38 tooth middle ring to the little ring that the Suntour Suberbe front derailleur can handle? How 'bout the Suntour XC Pro? The Shimano XT derailleur? The Mavic 870?

Knowing that max tooth difference isn't that the same from middle to little as it is from middle to big ring? Won't that tell us the max tooth size Big Ring I can have up from the 38 tooth middle? I'd rather have a lower range than higher...

Sutherland's (4th Edition) gives 18 teeth as the maximum allowed by a Superbe front derailleur. The XC can handle a 22 tooth difference, as does the Shimano XT-M700. The Shimano XT-M700-GS is claimed to handle up to a 27 tooth difference. The Mavic 870 is supposed to handle up to a 26 tooth difference, according to Sutherland's 6th Edition.

Thanks, is that total tooth difference (Big to little) for max tooth difference from Big to Middle, and Middle to little? Are the max values for both total tooth difference and max value for Big to Middle, and Middle to little given?

The Sugino Touring AT crank was set up as 48-44-26. Is that a strange setup having the Big and Middle ring so close? I would think there would be more than the usual overlap with only a four tooth difference there.

The Sugino Touring AT crank was set up as 48-44-26. Is that a strange setup having the Big and Middle ring so close? I would think there would be more than the usual overlap with only a four tooth difference there.
That used to be fairly common crank gearing and it was called "half-step plus granny" The closely spaced chainrings split the difference when 5 and 6-speed freewheels were all that were available and wide range freewheels had, of necessity, big gaps between adjacent cog tooth counts.

New cassettes with 8,9, 10 and even 11 cogs have pretty much eliminated the need for half-step gearing.

Yep its a beauty. I had a .pdf of the whole catalog. Here is what it looks like (that's a handy link one page at a time):

http://equusbicycle.com/bike/cannondale/catalog1986/pdf/1986cannondalecat%20-%200021.pdf


I want to use a 38 middle because that's the smallest ring I can get with a 130bcd crank. I'd like to have the smallest little ring possible for climbing the mountains here in Colorado at altitude. What is the largest difference from the 38 tooth middle ring to the little ring that the Suntour Suberbe front derailleur can handle? How 'bout the Suntour XC Pro? The Shimano XT derailleur? The Mavic 870?

Knowing that max tooth difference isn't that the same from middle to little as it is from middle to big ring? Won't that tell us the max tooth size Big Ring I can have up from the 38 tooth middle? I'd rather have a lower range than higher...


I can't give you a specific number from small to middle ring as I'm not using my Superbe FD at this time for my 26/44/48 rings. I'm using a 105 double FD. Let me make this clear ..... FD tooth ratings mean nothing. Most pre 10 speed double FD's can handle a 22-26 tooth difference. Since you say you have various FD's to try.... and they are the easiest thing to swap out .... I suggest trying any and all you have as it will take some trial and error to find what works for you.

Since you want the smallest ring possible, that would be a 24t. A 26t would be fine also. With a 24/38 .... a 48 big ring would be a good choice. Your bike came with a 26/44/48 .... I use this setup today with a 13-32 FW. As stated.... it's called half step plus granny..... but depending on your FW ..... you don't have to shift in a half-step pattern if you don't want to. A 13-28 6sp FW for instance offers a good shift pattern with no large jumps so you can shift with your RD most of the time, and use the FD to fine tune your gears as needed. There is zero overlap of gears. I find it more sensible than a typical crossover set up because there are no funky crossover shifts and you can use the entire FW in the middle ring.

If you choose a traditional crossover triple like a 24/38/48 .... a mtb FD may work better. You may as well try both though. If you use a 24/44/48 setup ...... I suspect the Superbe FD will work... if not try another double FD with a slightly longer cage as the Superbe is slightly shorter than some. I've used a vintage XT FD on my mtb bike and never really liked it... the funky shaped cage required too much trimming. I prefer the older type that has a straighter cage, like these vintage Deore's. http://www.velobase.com/ViewSingleComponent.aspx?ID=02b9040f-3241-4c11-94a2-94d0774e24df&Enum=113 These were unique as they came in both crossover and half-step versions. I've used the crossover versions on mtb's. I like them because they are all silver and have a straight-ish cage.

Use this gear calculator and check out any combos here ... http://home.earthlink.net/~mike.sherman/shift.html You'll see that a 24-26/44/48 hs+g or a 24-26/38/48 and a 13-28 6sp work out pretty good.

BTW ... What are the cogs on the FW you're using?


All in all ..... vintage drivetrain parts are more versatile than todays. All these limits on teeth you read about mean much less for vintage than todays indexed machine-like shifting. It's their beauty ... or curse ..... depending on the rider :lol:

So am I to understand that since the bike came with a 26-44-48 that I don't have to worry about the max number of teeth between the little/middle and the middle/big? That essentially the only thing that matters to a front derailleur is the total variance, that is the difference between the little and the big ring?

So my middle ring is not a function of my little or big ring at all, but a choice based on preferred ratios, shifting style, and aversion to crossover or duplicate gears.

I was playing around with that gear calculator and the one that Sheldon Brown came up with on the Harris site.

I'm a little frustrated trying to figure out what 'my' ratios would be like. I just assumed that a nice 28-38-48 gain ratio distribution would remain so with a larger crank. Plugging in the largest crank size the different gear calculators allowed definitely showed that a larger crank throws a wrench into the works.

Neither allowed the selection of a 205mm crank, to look at the ratios with my freewheel and different ring possibilities, which is after all the whole point.

Anyone know of a gear calculator that displays gain ratios that allows the selection of longer crank lengths?

I don't know what to want to get now. I'll need to find a gear calculator that allows the selection of longer cranks, or figure it all out in Excel myself.

How low of a gear is TOO low for a 'country' bike, a road bike, and for loaded touring?

Loaded touring you generally need a max of 1:1.

Loaded touring you generally need a max of 1:1.

Is that in Sheldon Brown's Gain ratio?

Okay, in creating a little Excel spreadsheet to calculate accurate gain ratios for different chainring combos using my 13-15-18-21-26-32 freewheel I've already learned something.

In order to approximate the Radius ratio of an average person on a 700c (622bsd) on 170mm cranks, which is 2.00, while using my slightly less than proportionate length 205mm cranks, I would need a custom bike built up around a 755bsd wheel. Let's just call it 750bsd and keep things simple.

Here are some common wheel sizes:

630bsd - 27" road wheels
622bsd - 700c road wheels and 29" mountain bike wheels
584bsd - 650b
559bsd - 26" Mountain Bikes
507bsd - 24" Kids Mountain Bikes

So the jump from 'my' needed 750bsd wheel from the common 700c (622bsd) is about the same as the jump from a 24" kids mountain bike all the way up to a 700c road wheel.

Man you people are all tiny!

I know Velocity just rolled up some really big rims for some high wheelers, what are the odds they would start making some bigger wheels for people that aren't five foot nothin'? It does seem kind of silly that every bike from a 52cm up through a 66cm is on a 700c wheel. That's a huge range.

Okay, I was playing around with some different chainring combos, and something weird kept appearing.

For whatever reason, with a triple 28-28-48 crank, and my radius ration, a gain ratio shift pattern emerges where you go from:

1.48 - small ring big (sixth) cog
1.82 - small ring fifth cog
2.01 - middle ring big cog
2.26 - small ring fourth cog
2.47 - middle ring fifth cog
2.54 - big ring big cog
2.63 - small ring third cog
3.06 - middle ring fourth cog
3.12 - big ring fifth cog
3.16 - small ring second cog
3.57 - middle ring third cog
3.87 - big ring fourth cog
3.64 - small ring little cog
4.29 - middle ring second cog
4.51 - big ring third cog
4.94 - middle ring little cog
5.41 - big ring second cog
6.25 - big ring little cog

It wan not nearly so clean with smaller crank sizes.

Which is all well and good on paper, but who the heck shifts like that? I can't imagine shifting up to a bigger ring and bigger cog and then having to drop down two rings and shift three cogs lower, only to start over. Who could keep that straight in your head? Does anyone look at gear ratios in a 'wholistic' fashion, or do you merely look at each ring's ratios seperately?

So am I to understand that since the bike came with a 26-44-48 that I don't have to worry about the max number of teeth between the little/middle and the middle/big? That essentially the only thing that matters to a front derailleur is the total variance, that is the difference between the little and the big ring?

Yes.


So my middle ring is not a function of my little or big ring at all, but a choice based on preferred ratios, shifting style, and aversion to crossover or duplicate gears.

Yes.



I'm a little frustrated trying to figure out what 'my' ratios would be like. I just assumed that a nice 28-38-48 gain ratio distribution would remain so with a larger crank. Plugging in the largest crank size the different gear calculators allowed definitely showed that a larger crank throws a wrench into the works.

Neither allowed the selection of a 205mm crank, to look at the ratios with my freewheel and different ring possibilities, which is after all the whole point.

Anyone know of a gear calculator that displays gain ratios that allows the selection of longer crank lengths?

I don't know what to want to get now. I'll need to find a gear calculator that allows the selection of longer cranks, or figure it all out in Excel myself.

How low of a gear is TOO low for a 'country' bike, a road bike, and for loaded touring?


Okay ..... what you may be experiencing is mathematical gear chart overload! Don't worry about your crank length not being a part of the equation . The ratios stay relative no matter the length of the arms.

That said .... if you have a 13-32 6 speed FW and want to use 28-38-48 rings ...... and you want a steady progression of gears .... it isn't happening with that combo. Look at the wisdom of the bikes original gearing ... a 26/44/48. Do a chart of that. You have a easy, steady progression of gears with no funky cross jumps to get the next gear. I'm using gear inches here.... I'm showing it with a 26t ring here . Can you get too low for touring? That depends on the rider.

26-44-48
_______________________________
_______26 - 44- 48
13_____ X 90.6 98.8

15_____ 46.4 78.5 85.6

18_____ 38.7 65.4 71.4

21_____ 33.1 56.1 61.2

26_____ 26.1 45.3 49.4

32_____ 21.1 36.8 X



vs. 28-38-48
________________________________
_____28 _ 38 _ 48
13___ X 78.2 98.8

15___ 50.0 67.8 85.6

18___ 41.6 56.5 71.4

21___ 35.7 48.4 61.2

26___ 28.8 39.1 49.4

32___ 23.4 31.8 X

The rear spacing is 126mm and its a freewheel, so I can't upgrade to 8 speed (which I think is the best touring choice).

Just spread the stays by hand and put a 130mm spaced rear hub in there. It will fit, more than likely, easily and without any other issues. Then you have your choice of 8, 9, or 10 speed gear.

Don't agonize too much over gear progressions. If you really want an evenly space series of steps and a rational shift pattern within the limitations of a 6-speed freewheel/cassette you have to use half-step chainnrings. Otherwise, there are too many duplicates and/or big jumps. BTW, "Gain Ratio" is a Sheldon Brown invention that never caught on so working in gear-inches is easier for most of us.

As to what is a too-low low gear, what terrain are you riding? A road rider who never leaves Florida can get by with a much taller low gear than someone who rides in West Virginia or Kentucky. For a loaded tourist who contemplates riding in all areas, there almost isn't a "too low". Typically they will want to have something below 25 gear-inches and usually down about 20 gear inches is desirable. Also, what's a "country bike"?

The OP lives in CO and has wheels with 48 spoke Phil Wood hubs, so I doubt he'll be ditching them anytime soon. Being they are PW hubs though .... he could get a 135mm axle for it, spread his frame .... and he'd be able to use a 13-32 7sp FW. He would not need to redish the wheel... but I'm not positive the end caps for the PW axles are the same for a 126 and 135mm hub.... something PW would know.

The OP lives in CO and has wheels with 48 spoke Phil Wood hubs, so I doubt he'll be ditching them anytime soon. Being they are PW hubs though .... he could get a 135mm axle for it, spread his frame .... and he'd be able to use a 13-32 7sp FW. He would not need to redish the wheel... but I'm not positive the end caps for the PW axles are the same for a 126 and 135mm hub.... something PW would know.
Well, eastern CO is table flat and the western part is mountanous but the climbs are usually gradual even if very long.

He could use a 7-speed freewheel with his existing 126 mm spacing and no other changes. There is no need for a 130 or 135 mm axle change. His frame is Aluminum so, while a 130 mm hub could be forced in, a 135 would be too much of a struggle and the frame should not be cold set.

Yeah .... I forgot his frame is AL. I wouldn't force a 130mm hub into it though.

The OP lives in CO and has wheels with 48 spoke Phil Wood hubs, so I doubt he'll be ditching them anytime soon.

I wasn't thinking about the attachment to the hubs when I replied. My suggestion would require a whole new rear wheel.

Okay ..... what you may be experiencing is mathematical gear chart overload! Don't worry about your crank length not being a part of the equation . The ratios stay relative no matter the length of the arms.

Actually that isn't true. Sure the gear ratios are the same (without considering the crank) but those ratios have to have a context, and that is pedaling them via the crank. Which is why Sheldon Brown's Gain Ratio way of looking at things is so useful. It puts the gear ratios into the proper context. Without including the crank length a cyclist can't really intelligently think about the cogs/rings they want. This is ESPECIALLY true for cyclists outside the norm, running different crank lengths than the Shimanoculture standard of 175mm.

I spent some time last night learning about gain ratios (which necessarily include crank length) and I was SHOCKED to see how my 205mm crank changes everything compared to a 175mm crank. :eek:

I emailed Mike Sherman, and he emailed me back, he said he'll add longer cranks to his online calculator.

I just developed an Excel spreadsheet, and did it on my own (Sheldon Brown had left all you need to calculate everything yourself).

Just spread the stays by hand and put a 130mm spaced rear hub in there. It will fit, more than likely, easily and without any other issues. Then you have your choice of 8, 9, or 10 speed gear.

You realize we're talking about an aluminum Cannondale frame here don't you?

Yeah .... I forgot his frame is AL. I wouldn't force a 130mm hub into it though.

My Cannondale is 126mm, but the forgotten thing is that many Cannondales came with a rear spacing of 128mm. To work with 126mm and 130mm.

I know they came this way for sure in '89, I don't know about '88 or '90.

You can source an epic Cannondale 3.0 frame for nothing as many people don't know about this...

38-52. 14 tooth jump is tough but doable. 38-50 is better but a 50/13 isn't 4:1 although descents on an loaded touring bike of this vintage were sketchy enough without pounding down on the cranks.
38-50 it is.

Actually that isn't true. Sure the gear ratios are the same (without considering the crank) but those ratios have to have a context, and that is pedaling them via the crank. Which is why Sheldon Brown's Gain Ratio way of looking at things is so useful. It puts the gear ratios into the proper context. Without including the crank length a cyclist can't really intelligently think about the cogs/rings they want. This is ESPECIALLY true for cyclists outside the norm, running different crank lengths than the Shimanoculture standard of 175mm.

I spent some time last night learning about gain ratios (which necessarily include crank length) and I was SHOCKED to see how my 205mm crank changes everything compared to a 175mm crank. :eek:

I emailed Mike Sherman, and he emailed me back, he said he'll add longer cranks to his online calculator.




According to the gain ratio theory then, to compare a 205mm crank to a 175mm crank ..... you'd need something like 46/58 rings? I'm using Sheldon's formula of the radius (340mm) divided by arm length........... multiply that times the (chainring divided by the cog). http://sheldonbrown.com/gain.html Using a 700x28 tire in this example.

To get comparable gears to a 28/38/48 w/175mm cranks would be appx. a 34/46/58 w/205mm cranks by my math using the formula. There's theories ..... and then there's the practical application of actually riding the bike. I'd try to talk to Zinn or High Sierra Cycles.... they guys who make it for Zinn .... as they would have some experience in the practical applications of gears with longer cranks.... meaning what others have used in the real world..... not on paper.

I could see going a few teeth larger on the high end ..... but nothing major. I use 185mm cranks and didn't change a thing compared to 175's. Sure, it's not as big of a jump in crank length ..... but I doubt you'll find a 34/46/58 useful for touring . I may be wrong ..... but I'm just sayin' ...........

Actually that isn't true. Sure the gear ratios are the same (without considering the crank) but those ratios have to have a context, and that is pedaling them via the crank. Which is why Sheldon Brown's Gain Ratio way of looking at things is so useful. It puts the gear ratios into the proper context. Without including the crank length a cyclist can't really intelligently think about the cogs/rings they want. This is ESPECIALLY true for cyclists outside the norm, running different crank lengths than the Shimanoculture standard of 175mm.

I spent some time last night learning about gain ratios (which necessarily include crank length) and I was SHOCKED to see how my 205mm crank changes everything compared to a 175mm crank. :eek:

I emailed Mike Sherman, and he emailed me back, he said he'll add longer cranks to his online calculator.

I just developed an Excel spreadsheet, and did it on my own (Sheldon Brown had left all you need to calculate everything yourself).


I think Sheldon Brown's 'Gain Ratio' system has a flaw...

While the force required at the pedals at any instant is the same when two systems have the same gain ratio, this only tells half the story. The definition of 'power' is ((force) X (distance))/(time). Two systems with equal gain ratios but different length cranks are only equal at any instant, not for an entire revolution of the cranks - the longer cranks much be pushed with the same force as the shorter ones, but for a greater distance and thus require higher power to operate.

Mtnbke - you are a big guy and likely have tonnes of power, but if you could spin a 58 X 13 gear at a relaxed 80 RPM you would be riding at 27MPH... close to Eddy Merckx's hour record in 1972.

Since the human body can only produce a limited amount of power (maybe 1/2 HP for a very short time), there is a limit to how fast we can ride, regardless of crank length.

According to the gain ratio theory then, to compare a 205mm crank to a 175mm crank ..... you'd need something like 46/58 rings? I'm using Sheldon's formula of the radius (340mm) divided by arm length........... multiply that times the (chainring divided by the cog). http://sheldonbrown.com/gain.html Using a 700x28 tire in this example.

To get comparable gears to a 28/38/48 w/175mm cranks would be appx. a 34/46/58 w/205mm cranks by my math using the formula. There's theories ..... and then there's the practical application of actually riding the bike. I'd try to talk to Zinn or High Sierra Cycles.... they guys who make it for Zinn .... as they would have some experience in the practical applications of gears with longer cranks.... meaning what others have used in the real world..... not on paper.

I could see going a few teeth larger on the high end ..... but nothing major. I use 185mm cranks and didn't change a thing compared to 175's. Sure, it's not as big of a jump in crank length ..... but I doubt you'll find a 34/46/58 useful for touring . I may be wrong ..... but I'm just sayin' ...........

I don't think you're wrong at all. I truly believe that a 28/38/48 makes for a very useful set of ratiosl, without any real overlap on 175mm cranks.

I ran the gain ratio numbers myself, like I said, and I too was shocked, just shocked at how the longer cranks made everything all zonky. :eek:

I went to Veloswap in Denver last Saturday and picked up a set of TA Alize 53/39 chainrings that were red anodized. The problem is that the 39 ring is an inner ring designed for a double, its not a TA intermediate ring, so it is missing the ramps and pins on the inner side. I also picked up a TA Alize 46 chainring in silver. I really wanted a low gear for really heavy loads and going over the continental divide, and elevations over 10,000ft where I'll be really struggling. I also picked up a 24t Middleburn chainring, though I'd never heard of them before, its anodized blue.

In the interests of working with the 26t capacity of the Mavic 870 front derailleur I mounted the silver 46t, then the red 39t, and the blue 24t on the crank. Kind of a half again half step plus granny like you guys were talking about.

The problem is that the crank looks freakin' ridiculous, its literally red, white and blue. Everyone is going to remember that 'fat Captain America' that rode by...

So what do my Gain Ratios look like with the 205mm Zinn crank 46/39/24 rings and a 13-15-18-21-26-32 freewheel?

Little ring:

3.12
2.71
2.26
1.93
1.56
1.27

Middle ring:

5.07
4.40
3.66
3.14
2.54
2.06

Big Ring:

5.99
5.19
4.32
3.71
2.99
2.43

To put that in perspective on 175mm cranks I'd need a 20t little ring to equal the same bailout gear. However, it should work with my Mavic triple front derailleur as I've only got a 22t range now from little to big ring.

I don't want to give up the 24t little ring, but I think I'll spin out that 46/13 on flats relatively easily.

My 5.99 gain ratio for my biggest gear is almost the same as someone on 172.5mm cranks spinning a 53/18.

I'll try and fight some super villains and spend some time on the bike, and then I can swap all the chainrings out for something else, once I get a sense of what those numbers 'ride' like.

I think Sheldon Brown's 'Gain Ratio' system has a flaw...

While the force required at the pedals at any instant is the same when two systems have the same gain ratio, this only tells half the story. The definition of 'power' is ((force) X (distance))/(time). Two systems with equal gain ratios but different length cranks are only equal at any instant, not for an entire revolution of the cranks - the longer cranks much be pushed with the same force as the shorter ones, but for a greater distance and thus require higher power to operate.

Mtnbke - you are a big guy and likely have tonnes of power, but if you could spin a 58 X 13 gear at a relaxed 80 RPM you would be riding at 27MPH... close to Eddy Merckx's hour record in 1972.

Since the human body can only produce a limited amount of power (maybe 1/2 HP for a very short time), there is a limit to how fast we can ride, regardless of crank length.=

I think I'd destroy my knees pushing a 58x13. I like cycling because its low impact. Years of competitive basketball (and the accompanying procedures) have left me with some beat up knees, patelar tendinitis, and torn mensicus to boot. I can't even imagine what turning over a 58x13 would feel like. I can say that I bet its easier than a 53x12 on clown cranks though...

I've always had a lower cadence for whatever reason I've always been able to push a bigger gear intermittently while my buddies spin away. I don't know whether that is good or bad. I'll tell you what though, after a 30 something mile ride sometimes I feel like I 'pedaled' ten of it and the hills just absolutely killed me. I can't wait to try the longer cranks on climbs.

=

I think I'd destroy my knees pushing a 58x13. I like cycling because its low impact. Years of competitive basketball (and the accompanying procedures) have left me with some beat up knees, patelar tendinitis, and torn mensicus to boot. I can't even imagine what turning over a 58x13 would feel like. I can say that I bet its easier than a 53x12 on clown cranks though...

I've always had a lower cadence for whatever reason I've always been able to push a bigger gear intermittently while my buddies spin away. I don't know whether that is good or bad. I'll tell you what though, after a 30 something mile ride sometimes I feel like I 'pedaled' ten of it and the hills just absolutely killed me. I can't wait to try the longer cranks on climbs.

I know where you are coming from, brother!

Keep in mind that the added movement in your knees might aggravate some of the problems you have been having... training yourself to spin a little faster might help alleviate this. And as a very tall person you are uniquely able to spin your new 205mm cranks...

Using a 58 tooth big ring will make spinning with any length cranks almost impossible... you will be relegated to grinding away at low rpms unless you are a world class track racer.

FWIW, the calculators say I should be riding on 195s, but I am too poor to swap out my 175s I got when I built my bike 13 years ago. I actually have 170s (!!!) on my rad bike, but I have had that bike since I was a teenager and my body has grown to fit it. However, I was ridingthe rollers in my basement last winter and I tried to spin both my 170mm equipped road bike and my 175mm equipped touring bike as fast as possible (I estimate around 180 - 200 rpm) and I had an easier time on the touring bike.

I know where you are coming from, brother!

Keep in mind that the added movement in your knees might aggravate some of the problems you have been having... training yourself to spin a little faster might help alleviate this. And as a very tall person you are uniquely able to spin your new 205mm cranks...

Using a 58 tooth big ring will make spinning with any length cranks almost impossible... you will be relegated to grinding away at low rpms unless you are a world class track racer.

FWIW, the calculators say I should be riding on 195s, but I am too poor to swap out my 175s I got when I built my bike 13 years ago. I actually have 170s (!!!) on my rad bike, but I have had that bike since I was a teenager and my body has grown to fit it. However, I was ridingthe rollers in my basement last winter and I tried to spin both my 170mm equipped road bike and my 175mm equipped touring bike as fast as possible (I estimate around 180 - 200 rpm) and I had an easier time on the touring bike.

I have bikes that have 175mm cranks, and I have bikes that have 180mm and 185mm cranks. I've got to say the 175s are just completely unrideable. They just feel like silly little clown bike cranks. A lot of people think that 5mm on the cranks don't matter much, but racing bike cranks come in 2.5mm increments and 5mm is jumping two crank lengths.

Bikes with the little cranks are just miserable for me to ride after I'd ridden on the longer ones. Even when the only bikes I was riding were the 175mm bikes, and I wasn't getting on the other bikes for over a year every ride would be punctuated with the miserable feeling of the tiny clown cranks.

I don't know that I'll like the 205mm cranks. That's a heck of a jump. A lot of people think that Zinn's numbers for proportional crank length are too aggressive. Which is why I passed on the 210mm cranks.