I started gathering this info as part of a bigger project, but I think it has some value on it's own, so here it is.
The following spreadsheed (because I love spreadsheets... no not really, just an easy way to do some math with common software) lists several coil forks, the "firm" or 'firmest' springs for those forks (in lb/in), the force at full compression, and some other stuff, discussed below.
Now if you scroll over, you'll see the stanchion diameter, wall thickness (which was mostly a guess, see the next paragraph), which gives me ID, which in turn gives me cross sectional area. And finally, the pressure on that area from the above max spring force.
For the wall thickness, I measured the ID of a RockShox Totem and assumed the thickness was the same for all other forks. Obviously not the most accurate, but not a ridiculous guess either. No RockShox forks appear in this list because they don't list the spring rates for their forks, at least not anywhere I could find. Also worth noting that the Marzocchi fork listed uses an air assist rather than different springs, for rate tuning, which is why it's rate is so much lower than the others.
The idea here was to figure out, for an air spring, the maximum pressure ever encountered by the fork. This tells us, or at least suggests, the pressures the seals will have to resist, and possibly some other stuff related to design of suspension.
Saturday, November 24, 2012
Thursday, November 15, 2012
Favorite Tools: T-handle Ratchet Set
Every mechanic has a favorite tool. This feature I'm going to talk about some of mine.
Bikes use a number of specific tools, yet for probably 85% of routine stuff all you need is an Allen or Hex wrench set, though torx is making inroads. Big, comfortable hex keys are a 'really nice to have' tool for shop work. T- or P-handles are even better, but this guy...
Is a comfortable handle, ratcheting hex-bit driver. It's not only reversible but has a center position, which locks both directions. I got it from Sears, it's their cheaper, stupidly named evolv line, but apparently comes with a full craftsman warranty - something Park can't claim about any of their tools.
In that handy holder thing there is 3-10mm and 1/8 - 3/8" hex bits, T20-T45 torx, a 1/4" square ratchet driver and 6, 8, 10mm and 1/4, 5/16, 3/8 and 7/16" sockets. True, the SAE stuff doesn't get much use, it does have the metric and torx sizes most commonly found on a bike. It doesn't have the tiny 2 and 2.5mm sizes, but I don't think I'd want a tool like this for those tiny bolts in brake lever reach adjusters and lock-on grips.
The ratchet is just the thing for brake rotor bolts (or most any other) with loctite pre-applied, that causes enough friction, you can't just finger tighten them. Bits lock into place and are easy to release. My only real complaint is how hard it can be to get some of the bits out of the holder, but that also means they don't fall out accidentially.
Not bad for $20.
Bikes use a number of specific tools, yet for probably 85% of routine stuff all you need is an Allen or Hex wrench set, though torx is making inroads. Big, comfortable hex keys are a 'really nice to have' tool for shop work. T- or P-handles are even better, but this guy...
In that handy holder thing there is 3-10mm and 1/8 - 3/8" hex bits, T20-T45 torx, a 1/4" square ratchet driver and 6, 8, 10mm and 1/4, 5/16, 3/8 and 7/16" sockets. True, the SAE stuff doesn't get much use, it does have the metric and torx sizes most commonly found on a bike. It doesn't have the tiny 2 and 2.5mm sizes, but I don't think I'd want a tool like this for those tiny bolts in brake lever reach adjusters and lock-on grips.
The ratchet is just the thing for brake rotor bolts (or most any other) with loctite pre-applied, that causes enough friction, you can't just finger tighten them. Bits lock into place and are easy to release. My only real complaint is how hard it can be to get some of the bits out of the holder, but that also means they don't fall out accidentially.
Not bad for $20.
Monday, November 12, 2012
Front Derailleurs
Intro/Justification
What font derailleur works with what frame and gearing combination has become a reasonable question to ask, where fairly recently, it was pretty self-explanatory; you could tell from looking at the frame what type you needed, at most what you needed was calipers, or even a keen eye (to differentiate between a 1 1/4" and a 1 3/8" OD tube, for example).
Where 5-6 years ago there were 2 versions of a typical front derailleur, in the current BTI catalog, there are 37 variants on the Sram X0 front derailleur. Thirty seven... Since only one of those 37 is the proper one for your bike, I thought it would be worth a second to look into identifying compatibility.
Differences
Front derailleurs are categorized for the most part by 3 factors: mount type, cable pull (both of which are determined by the frame), and the cranks/chainrings they will shift (which is a factor of the crank/chainring, oddly enough).
Number of speeds in the rear is also an issue. 8, 9, 10 and 11 speed systems all use different chains - the more speeds, the narrower the chain. The cage plates - the 2 parallel plates that sit on either side of the chain - are closer together on 10 than 9-speed setups, for example. It is possible to run a mis-matched derailleur, but the more mismatched it is, the harder it will be to get it to perform well (11s derailleur with an 8s chain will rub in many of the gear combos, for example).
Examples
Road
These are much, much simpler than mountain derailleurs, so we'll start here. The only top-pull 'road' front derailleur I know of is the Shimano CX, which is for cyclocross, and not really road. All other road front derailleurs I'm aware of are bottom pull - the cable goes around a guide, usually under the bottom bracket shell, pulling the derailleur from below.
Clamp Mounts
These vary by diameter, which has to either match the diameter of the clamping area of the seat tube, or be larger with a shim. Some derailleurs have a flexible, variable diameter clamp.
"Braze-On"
These have a curved tab with a single, slotted hole, the derailleur bolts to. The reason for this can be cosmetic, for fragile, thin-walled tubes that shouldn't be clamped, or because the frame doesn't have a conventional tube to clamp to.
All the derailleurs pictured are for double chainring setups. Triple ring derailleurs also exist, in all these mount varieties, which are capable of more travel, and have guide plates to suit the greater difference in ring sizes. Derailleur specifications will also list a maximum chainring. Note in the last picture, how the curvature on the derailleur cage closely matches that of the chainring. Too large a ring would require the derailleur to be so high on the mount or seat tube, it would not be able to shift properly.
The other variable is the Shimano Di2 and Campagnolo EPS electronic variants. These have an electrical connection instead of a cable, mounts are similar to the conventional cable models.
Mountain - Clamp
Now things get a bit more complicated...
This is a high-clamp (in Sram terminology), or down-swing in Shimano, sometimes called "traditional", with a top-pull cable. Most mountain derailleurs these days have arrangements to pull from either direction, but on this frame I had to cut that feature off the derailleur because the rear triangle would hit it when the suspension compressed.
The feature to look for with regard to cable direction on the frame is the housing stop on the seat tube above the derailleur: marked in the picture
This is a high clamp, using the bottom-pull option. Note the cable anchor point, and how the cable wraps around the guide feature. If I were to use this derailleur on a frame that needed a top pull, the cable would skip the reversing feature and simply approach from above.
Note that on both these frames there are suspension components below the derailleur, and a low-clamp (see below) would not work.
This is a low-clamp, or "top-swing" in Shimano. The clamp is below the top of the chainring. It has a cable pull direction-reversing feature similar to the high-clamp derailleur above.
And here is another low-clamp, this one with a top-pull cable. This derailleur has the reversing feature, but it's not being used. Both of these examples are rigid bikes (hardtails), and can use either type of derailleur - though on this example, a water bottle cage mount bolt interfered with a high-clamp. Some suspension frames have components in the area where a high-clamp derailleur would mount, and require a low-clamp.
If your bike uses a 83 or 100mm bottom bracket shell, some front derailleurs will not work, because they don't swing far enough. Frames like this are not common, 83mm shells are primarily found on downhill bikes that don't have front derailleurs, 100mm shells are common on snow or fat bikes, the maker should have a suggestion for derailleur compatibility. Again, unless you went out of your way to get a bike like this, you probably have a 68 or 73mm bottom bracket, and "normal" derailleurs will work.
Confused yet? Don't worry, if your bike uses a clamp-on derailleur, it's pretty simple: is the clamp area above or below the top of the biggest chainring? If it's above, you need a high-clamp, below requires a low clamp. Dual-pull and 34.9mm clamp with shims for smaller sizes mean you really only need to address the high or low clamp question.
Things are about to get a lot more confusing...
Mountain - Direct
"E-Type"
Apologies, I don't own any bikes that use this type of derailleur, nor do I know anyone that does, and to really see what it looks like mounted, you'd need to remove the crank, and I couldn't find any images.
These are Shimano derailleurs, they have "-E" suffix to the part number (i.e., FD-M780-E), Sram does not offer anything that mounts this way.
This is the original direct mount mountain derailleur. The plate with the large hole is pinched between the bottom bracket and the frame, and a single bolt keeps it from rotating.
This design offers no position adjustment at all, it's designed for a specific chainring configuration and that's all it does.
These are dual-pull.
High Direct Mount
Shimano models have a "-D" suffix, Sram calls this "H0" mount. These are dual-pull, and have a cable stop for the top-pull option, which is used in this example.
Here, I removed the derailleur, so we can look at the mount. It has a single threaded hole, and an alignment notch. The derailleur has a matching ridge. No angular adjustment is possible on these - the frame maker had to align the mount with the bottom bracket shell face. Note on this example how no clamp could have worked: there is no tube where a low clamp would be, and no place to clamp around a high mount.
Low Direct Mount
Again, I don't have easy access to any bikes that use these mounts. Similar to how the High Direct mount was essentially a high-clamp or down swing derailleur, with the clamp removed, these are low clamp models, only without the clamp.
Shimano models have an "-E" or "-E2" suffix. Wait, wasn't it E-types that had the "-E"? Yes; you remove the mounting plate, and use the same bolt-holes to mount to the frame. The "-E2" models have no base plate, but the mounts are slotted, so you can adjust for different chainring sizes.
Sram models are for "S3" mount. Sram models are not dual-pull, you need to select a model that has the correct cable pull for your frame. Sram models also do not offer any vertical adjustment, instead they offer different models for different size chainrings. These two facts are a big part of why there are so many models (2 mounts times 2 cable options and up to 5 chainring options for Sram, vs one for Shimano).
The mount uses 2 bolts, 22.1mm apart (red lines in the picture), with the forward mount farther out from the centerline of the bike than the rear. This is because the forward bolt is what held the derailleur to the mounting plate, while the rear secured alignment to the frame.
Sram "S2" mounts have the same 22.1mm spacing, but with both holes flush. Only a few bikes used this type, and Sram appears to have dropped it from the lineup, at least in aftermarket.
Sram "S1" mounts are also 2 bolts, this time 42.7mm apart, and flush. As far as I can tell, only Specialized bikes use this type. These also are chainring specific and not dual pull.
If your frame uses a direct mount, they should give you more info as to which direct mount to get.
Conclusion
This is getting ridiculous. That's the only way to summarize the state of front derailleurs. Why is this so complicated? One word: suspension. Road derailleurs are all basically the same design with different attachment mechanisms. Mountain derailleurs are all over the place because some frames just won't work with some derailleurs. Thank goodness the component manufacturers have tried to accommodate, otherwise suspension designs would be limited by whatever Shimano felt like making.
The good news is, I think most of this will shake out and disappear, the bad news in that is some people are going to be left with frames that they can't find derailleurs for. I wouldn't even be shocked to hear that clamps go away, though I think that would depend on what the big frame manufacturers do. I don't see any need that wouldn't be met with either a H0/D or S3/E2 mount. From their perspective direct mounts make a lot of sense - they are quicker to install, and don't require as much skill to get shifting well. Trek bikes (for example) live in fear of a loudmouth on the internet saying "Treks don't shift well" because a mechanic at a shop didn't set up the derailleur correctly. They'd like to make that impossible.
But let's think about a bigger question: the future of multiple chainrings. It seems pretty clear that we're asking the chain-derailleur system to do things it was never meant to: accommodating suspension movement and dealing with the shock we're subjecting it to. Downhill bikes these days don't generally have any front derailleur options - you have to run a single chainring. True, it's not really necessary, but if it were easy to provide an option, I think at least some frame makers would. Hammerschmidt was Sram's attempt to get rid of the front derailleur while retaining multiple speeds in front. It was a good idea and a decent first attempt, but hasn't been widely adopted; I think if they improved the weight and drag it might be. The other idea is XX1 - offering the whole range of gearing you'd want in back, with a single ring.
As I see it, there are competing engineering problems, and whichever is easier to solve will win: on one hand is the difficulty of fitting a derailleur to new suspension designs and making it work well, not just at shifting, but at keeping the chain where it belongs. On the other is the difficulty of designing a new system that provides the overall gearing range we need but that doesn't require a front derailleur. Which will be the easier problem to solve? I guess we will see.
What font derailleur works with what frame and gearing combination has become a reasonable question to ask, where fairly recently, it was pretty self-explanatory; you could tell from looking at the frame what type you needed, at most what you needed was calipers, or even a keen eye (to differentiate between a 1 1/4" and a 1 3/8" OD tube, for example).
Where 5-6 years ago there were 2 versions of a typical front derailleur, in the current BTI catalog, there are 37 variants on the Sram X0 front derailleur. Thirty seven... Since only one of those 37 is the proper one for your bike, I thought it would be worth a second to look into identifying compatibility.
Differences
Front derailleurs are categorized for the most part by 3 factors: mount type, cable pull (both of which are determined by the frame), and the cranks/chainrings they will shift (which is a factor of the crank/chainring, oddly enough).
Number of speeds in the rear is also an issue. 8, 9, 10 and 11 speed systems all use different chains - the more speeds, the narrower the chain. The cage plates - the 2 parallel plates that sit on either side of the chain - are closer together on 10 than 9-speed setups, for example. It is possible to run a mis-matched derailleur, but the more mismatched it is, the harder it will be to get it to perform well (11s derailleur with an 8s chain will rub in many of the gear combos, for example).
Examples
 |
| Front derailleur cable is the one that pierces the chainstay bridge on this one. |
These are much, much simpler than mountain derailleurs, so we'll start here. The only top-pull 'road' front derailleur I know of is the Shimano CX, which is for cyclocross, and not really road. All other road front derailleurs I'm aware of are bottom pull - the cable goes around a guide, usually under the bottom bracket shell, pulling the derailleur from below.
 |
| Mountain bike, but has a typical road bottom bracket cable guide. Only front derailleur cable present. |
Clamp Mounts
These vary by diameter, which has to either match the diameter of the clamping area of the seat tube, or be larger with a shim. Some derailleurs have a flexible, variable diameter clamp.
"Braze-On"
These have a curved tab with a single, slotted hole, the derailleur bolts to. The reason for this can be cosmetic, for fragile, thin-walled tubes that shouldn't be clamped, or because the frame doesn't have a conventional tube to clamp to.
 | ||||||||||||
| Braze-on derailleur on a titanium frame. The curve of the mount allows rotational adjustment, the slot allows up/down adjustment. |
 |
| Here is a braze-on derailleur on a carbon frame, with no round tube to clamp. Note that the mount is actually a separate part, bolted onto the frame. This piece was included with the frame. |
The other variable is the Shimano Di2 and Campagnolo EPS electronic variants. These have an electrical connection instead of a cable, mounts are similar to the conventional cable models.
Mountain - Clamp
Now things get a bit more complicated...
This is a high-clamp (in Sram terminology), or down-swing in Shimano, sometimes called "traditional", with a top-pull cable. Most mountain derailleurs these days have arrangements to pull from either direction, but on this frame I had to cut that feature off the derailleur because the rear triangle would hit it when the suspension compressed.
The feature to look for with regard to cable direction on the frame is the housing stop on the seat tube above the derailleur: marked in the picture
This is a high clamp, using the bottom-pull option. Note the cable anchor point, and how the cable wraps around the guide feature. If I were to use this derailleur on a frame that needed a top pull, the cable would skip the reversing feature and simply approach from above.
Note that on both these frames there are suspension components below the derailleur, and a low-clamp (see below) would not work.
This is a low-clamp, or "top-swing" in Shimano. The clamp is below the top of the chainring. It has a cable pull direction-reversing feature similar to the high-clamp derailleur above.
And here is another low-clamp, this one with a top-pull cable. This derailleur has the reversing feature, but it's not being used. Both of these examples are rigid bikes (hardtails), and can use either type of derailleur - though on this example, a water bottle cage mount bolt interfered with a high-clamp. Some suspension frames have components in the area where a high-clamp derailleur would mount, and require a low-clamp.
If your bike uses a 83 or 100mm bottom bracket shell, some front derailleurs will not work, because they don't swing far enough. Frames like this are not common, 83mm shells are primarily found on downhill bikes that don't have front derailleurs, 100mm shells are common on snow or fat bikes, the maker should have a suggestion for derailleur compatibility. Again, unless you went out of your way to get a bike like this, you probably have a 68 or 73mm bottom bracket, and "normal" derailleurs will work.
Confused yet? Don't worry, if your bike uses a clamp-on derailleur, it's pretty simple: is the clamp area above or below the top of the biggest chainring? If it's above, you need a high-clamp, below requires a low clamp. Dual-pull and 34.9mm clamp with shims for smaller sizes mean you really only need to address the high or low clamp question.
Things are about to get a lot more confusing...
Mountain - Direct
 |
| Source |
Apologies, I don't own any bikes that use this type of derailleur, nor do I know anyone that does, and to really see what it looks like mounted, you'd need to remove the crank, and I couldn't find any images.
These are Shimano derailleurs, they have "-E" suffix to the part number (i.e., FD-M780-E), Sram does not offer anything that mounts this way.
This is the original direct mount mountain derailleur. The plate with the large hole is pinched between the bottom bracket and the frame, and a single bolt keeps it from rotating.
This design offers no position adjustment at all, it's designed for a specific chainring configuration and that's all it does.
These are dual-pull.
High Direct Mount
Shimano models have a "-D" suffix, Sram calls this "H0" mount. These are dual-pull, and have a cable stop for the top-pull option, which is used in this example.
Here, I removed the derailleur, so we can look at the mount. It has a single threaded hole, and an alignment notch. The derailleur has a matching ridge. No angular adjustment is possible on these - the frame maker had to align the mount with the bottom bracket shell face. Note on this example how no clamp could have worked: there is no tube where a low clamp would be, and no place to clamp around a high mount.
Low Direct Mount
Again, I don't have easy access to any bikes that use these mounts. Similar to how the High Direct mount was essentially a high-clamp or down swing derailleur, with the clamp removed, these are low clamp models, only without the clamp.
Shimano models have an "-E" or "-E2" suffix. Wait, wasn't it E-types that had the "-E"? Yes; you remove the mounting plate, and use the same bolt-holes to mount to the frame. The "-E2" models have no base plate, but the mounts are slotted, so you can adjust for different chainring sizes.
Sram models are for "S3" mount. Sram models are not dual-pull, you need to select a model that has the correct cable pull for your frame. Sram models also do not offer any vertical adjustment, instead they offer different models for different size chainrings. These two facts are a big part of why there are so many models (2 mounts times 2 cable options and up to 5 chainring options for Sram, vs one for Shimano).
 |
| Source |
The mount uses 2 bolts, 22.1mm apart (red lines in the picture), with the forward mount farther out from the centerline of the bike than the rear. This is because the forward bolt is what held the derailleur to the mounting plate, while the rear secured alignment to the frame.
Sram "S2" mounts have the same 22.1mm spacing, but with both holes flush. Only a few bikes used this type, and Sram appears to have dropped it from the lineup, at least in aftermarket.
Sram "S1" mounts are also 2 bolts, this time 42.7mm apart, and flush. As far as I can tell, only Specialized bikes use this type. These also are chainring specific and not dual pull.
If your frame uses a direct mount, they should give you more info as to which direct mount to get.
Conclusion
This is getting ridiculous. That's the only way to summarize the state of front derailleurs. Why is this so complicated? One word: suspension. Road derailleurs are all basically the same design with different attachment mechanisms. Mountain derailleurs are all over the place because some frames just won't work with some derailleurs. Thank goodness the component manufacturers have tried to accommodate, otherwise suspension designs would be limited by whatever Shimano felt like making.
The good news is, I think most of this will shake out and disappear, the bad news in that is some people are going to be left with frames that they can't find derailleurs for. I wouldn't even be shocked to hear that clamps go away, though I think that would depend on what the big frame manufacturers do. I don't see any need that wouldn't be met with either a H0/D or S3/E2 mount. From their perspective direct mounts make a lot of sense - they are quicker to install, and don't require as much skill to get shifting well. Trek bikes (for example) live in fear of a loudmouth on the internet saying "Treks don't shift well" because a mechanic at a shop didn't set up the derailleur correctly. They'd like to make that impossible.
But let's think about a bigger question: the future of multiple chainrings. It seems pretty clear that we're asking the chain-derailleur system to do things it was never meant to: accommodating suspension movement and dealing with the shock we're subjecting it to. Downhill bikes these days don't generally have any front derailleur options - you have to run a single chainring. True, it's not really necessary, but if it were easy to provide an option, I think at least some frame makers would. Hammerschmidt was Sram's attempt to get rid of the front derailleur while retaining multiple speeds in front. It was a good idea and a decent first attempt, but hasn't been widely adopted; I think if they improved the weight and drag it might be. The other idea is XX1 - offering the whole range of gearing you'd want in back, with a single ring.
As I see it, there are competing engineering problems, and whichever is easier to solve will win: on one hand is the difficulty of fitting a derailleur to new suspension designs and making it work well, not just at shifting, but at keeping the chain where it belongs. On the other is the difficulty of designing a new system that provides the overall gearing range we need but that doesn't require a front derailleur. Which will be the easier problem to solve? I guess we will see.
Friday, November 9, 2012
Cassettes; gearing part 1
First post with actual technical content!
Please bear with me as I figure out how I'm going to format these. Figuring out what constitutes "enough, but not too much" information can be difficult - especially something like this that is related to so many other topics.
Below are the individual tooth counts for 10-speed cassettes. The first column in each box is individual cog sizes, second: the inverse of the cog number in the second column (obviously expressed as a percentage - this represents the minimum difference between the cog and another larger cog), and the difference between the cog and the next smaller, also expressed as a percentage.
Sram and Shimano cassettes are interchangeable - they use the same cog-cog spacing (meaning a Shimano shifter-derailleur combo will shift a Sram cassette, provided they are all 10-speed, and vice-verse), Campagnolo have a different spline, and thus require a specific hub (and to my knowledge, there are no disc, 135mm or thru-axle, Campagnolo-freehub hubs on the market) and slightly different cassette spacing. There are ways of re-spacing Shimano cassettes to Campy spacing, as well as Shimano-splined, Campy spaced cassettes out there, but I'm not going into that yet (mostly because I feel those options are fairly pointless now, as good quality setups are available with either spline and spacing).
I think it's worth pointing out that on some "sizes" i.e., 11-36 (smallest and largest cog) between Shimano and Sram, there are a number of different intermediate cogs. Generally, the goal of the cassette designer in selecting cog sizes is to have an even percentage jump on every cog (the last column), but since cogs have to have an integer number of teeth, this isn't possible (the gap can only be a multiple of the second column).
Another interesting note is how the line between what is "road" and "mountain gearing has sort of disappeared. With 9-speed the smallest mountain cassette had a 32t large cog, where the largest road had 26 or 27 depending on the brand with nothing in between available. Now Shimano offers 36, 34, 32, 30, 28, 27, 26...
I believe all Sram and Campy cassettes available are included in the list. Shimano offers a number of "Junior" gearing options (the UCI has maximum gearing rules for junior racers; so standard gearing isn't allowed in Junior races): 13-25, 14-25, 15-25, 16-27 that they don't publish individual cog lists for (while I'm pretty sure I could guess correctly, I'm trying to avoid writing anything I don't know to be correct).
Sram recently rolled out an 11-Speed mountain setup - interestingly enough they are the only company that doesn't yet have an 11-speed road offering, and the only one that has 11 mountain. Currently they only offer one cassette option, 10-42, the system is single chainring-specific, this article explains why. The 10-tooth cog required a special freehub, as the standard shimano-splined freehub is larger diameter than a 10-tooth cog would be.
The above linked article also talks briefly about the limit of how small cogs can get: the polygon effect. A chain wrapped around a cog is not actually round, it forms a polygon - the chain pins being the corners, the links being the sides. Obviously the bigger the cog, the more sides it has, the closer it approximates a circle.
Above is a list of the same information as the first chart, but for 11-speeds. Shimano just introduced Dura-Ace 11-speed, and I wasn't able to find individual tooth-counts for their cassettes - the overall size are listed. Sram XX1 uses it's own freehub design, Shimano requires an 11-speed specific hub, Campy 9, 10, and 11-speed freehubs and cassettes are all compatible. All these systems require dedicated chains, derailleurs and shifters.
The XX1 drivetrain uses specific chainrings (See the heading "No chain guide required?")
In order to keep the chain in phase with the alternating rings, only rings and cogs with even numbers of teeth are allowed, furthering the size-increment issue.
Please bear with me as I figure out how I'm going to format these. Figuring out what constitutes "enough, but not too much" information can be difficult - especially something like this that is related to so many other topics.
Below are the individual tooth counts for 10-speed cassettes. The first column in each box is individual cog sizes, second: the inverse of the cog number in the second column (obviously expressed as a percentage - this represents the minimum difference between the cog and another larger cog), and the difference between the cog and the next smaller, also expressed as a percentage.
Sram and Shimano cassettes are interchangeable - they use the same cog-cog spacing (meaning a Shimano shifter-derailleur combo will shift a Sram cassette, provided they are all 10-speed, and vice-verse), Campagnolo have a different spline, and thus require a specific hub (and to my knowledge, there are no disc, 135mm or thru-axle, Campagnolo-freehub hubs on the market) and slightly different cassette spacing. There are ways of re-spacing Shimano cassettes to Campy spacing, as well as Shimano-splined, Campy spaced cassettes out there, but I'm not going into that yet (mostly because I feel those options are fairly pointless now, as good quality setups are available with either spline and spacing).
I think it's worth pointing out that on some "sizes" i.e., 11-36 (smallest and largest cog) between Shimano and Sram, there are a number of different intermediate cogs. Generally, the goal of the cassette designer in selecting cog sizes is to have an even percentage jump on every cog (the last column), but since cogs have to have an integer number of teeth, this isn't possible (the gap can only be a multiple of the second column).
Another interesting note is how the line between what is "road" and "mountain gearing has sort of disappeared. With 9-speed the smallest mountain cassette had a 32t large cog, where the largest road had 26 or 27 depending on the brand with nothing in between available. Now Shimano offers 36, 34, 32, 30, 28, 27, 26...
I believe all Sram and Campy cassettes available are included in the list. Shimano offers a number of "Junior" gearing options (the UCI has maximum gearing rules for junior racers; so standard gearing isn't allowed in Junior races): 13-25, 14-25, 15-25, 16-27 that they don't publish individual cog lists for (while I'm pretty sure I could guess correctly, I'm trying to avoid writing anything I don't know to be correct).
Sram recently rolled out an 11-Speed mountain setup - interestingly enough they are the only company that doesn't yet have an 11-speed road offering, and the only one that has 11 mountain. Currently they only offer one cassette option, 10-42, the system is single chainring-specific, this article explains why. The 10-tooth cog required a special freehub, as the standard shimano-splined freehub is larger diameter than a 10-tooth cog would be.
The above linked article also talks briefly about the limit of how small cogs can get: the polygon effect. A chain wrapped around a cog is not actually round, it forms a polygon - the chain pins being the corners, the links being the sides. Obviously the bigger the cog, the more sides it has, the closer it approximates a circle.
Above is a list of the same information as the first chart, but for 11-speeds. Shimano just introduced Dura-Ace 11-speed, and I wasn't able to find individual tooth-counts for their cassettes - the overall size are listed. Sram XX1 uses it's own freehub design, Shimano requires an 11-speed specific hub, Campy 9, 10, and 11-speed freehubs and cassettes are all compatible. All these systems require dedicated chains, derailleurs and shifters.
The XX1 drivetrain uses specific chainrings (See the heading "No chain guide required?")
...alternating tooth thicknesses that are synchronized with the gaps in the
chain – slightly narrower to fit in between inner chain plates and
wider to take advantage of the extra space between outer chain plates.
In order to keep the chain in phase with the alternating rings, only rings and cogs with even numbers of teeth are allowed, furthering the size-increment issue.
Saturday, November 3, 2012
Welcome!
I'm going to try to keep this intro short since it isn't really saying much. This is a blog about bicycles; the focus will be on the technical aspects. I'll be writing about maintenance and repair, tuning, products and technology, and general technical discussion about bike in general. The focus will be more about mountain bikes than road, mostly because I find them more interesting, but also because there is just more to talk about.
I'm an engineer. I've been riding and working on mountain bikes since 1988. I ride road and mountain, have raced both, but my racing these days is pretty limited to triathlon. I'm what you might call a Clydesdale i.e., tall (6'4") and heavy (currently around 230). While I'm not particularly hard on parts, I can't really help but see things through the big/tall lens.
I'm an engineer. I've been riding and working on mountain bikes since 1988. I ride road and mountain, have raced both, but my racing these days is pretty limited to triathlon. I'm what you might call a Clydesdale i.e., tall (6'4") and heavy (currently around 230). While I'm not particularly hard on parts, I can't really help but see things through the big/tall lens.
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