Kimmo

In a nutshell, closer ratios where you need em - up high. What with aerodynamic drag being the cyclist's enemy, and that bastard going up by your speed cubed (IIRC), it's a bit of a bummer that we're faced with an inescapable limitation of derailleur gears - that the gaps between ratios get bigger as you go up...

I've long thought the step between 15 & 14 was a bit much... let alone the jumps to make it to 11. So upon recently discovering Shimano had dabbled with 10mm pitch in the 80s (something I've daydreamed about before), I gave it another look, and tried to dig up what I could about it...



...Which is precious little, other than that they did have a track group out for a bit, using smaller diameters for lower weight, but it never caught on. I reckon the main reason it never gained traction was that Shimano failed to take proper advantage of 10-pitch; to my mind its actual benefit isn't allowing smaller chainrings and cogs - there's a good reason to maximise their size.

Which is to provide closer gearing on the road and more choices for the track. I'm thinking if they managed to make a 10mm track chain work in 1982, maybe they can make a 10mm road chain work in 2010... I wonder how the shorter links would affect shifting?

Anyway, I'd say the potential gains are worth more R&D than 10 pitch has received... see what you think of these numbers I crunched for the deal on ratios.

So, hopefully most of us are on the same page at this point re an ideal gear spacing (or debate it, by all means), and you'd say the green cassette below looks pretty good. Problem is, you can't have it cause we're stuck with discrete steps between cog diameters. But if we reduce the size of those steps, just look how much more corncob action we can get happening up high. BTW, that's a 12-cog cassette there just to cover the range from 28 to 11, so you can prolly find your preferred range in there somewhere.



Check out what happens when you subtract one ratio from another to see the steps between them. These cogs are pretty close in size; a 10mm 50t = 39.37t... it's a factor of 1.27.



If you think the ideal curve makes sense, that's what determined the non-integer ideal sprocket sizes in figure 1. The following then, is the difference from that, giving a flat graph of which side of ideal each step is. Maybe it's just me, but I reckon it's infinitely better to err below that line... especially as the ratios get taller.



I can't help thinking guys who cruise in a peloton doing 45-50km/h would be pretty interested in this... I would be too, for the much closer ratios in the middle of the cassette, where I spend most of my time. If the smaller diameters possible were made available, that could also cater to weight weenies and the small wheel crowd. I guess there'd be mixed reactions among the folks who paid big money on eBay for the old Dura-Ace kit...

Homebrew01

I must be mssing something. How do you get better ratios by having a smaller diameter chainring and cog ? Ratio is driven by the # of teeth, not diameter.

Voodoo76

A buddy of mine raced the Track group. Very cool, and at the time another advantage was it was tough to easily tell what gear he was running. I never saw any of the Road DA stuff, only heard rumors.

If nothing else it would be a cool marketing ploy, vs the current played out routine of adding another gear.

Kimmo

You're right - you're missing how I'm saying Shimano should give it another go, only this time use the normal diameters to give more teeth, and hence closer ratios.

It is all there in the graphs...

tspek

Technically, no...it's not the number of teeth that changes the effect of chainrings/cogs, it's the diameter. However, the number of teeth change that diameter.

Homebrew01

I must be mssing something. How do you get better ratios by having the same diameter chainring with more teeth ? Ratio is driven by the # of teeth, not diameter.

Kimmo

Did you read the OP? I spend a few words explaining that. Look at the graphs.

In short - shorter chain links, smaller steps between ratios for nominally equivalent size rings and cogs.

It really is quite simple.

Voodoo76

Lets say your "small" ring is now a 46, the jump from 46/18 to 46/19 is 5.5%. The jump from more conventional 39/15 to 39/16 is 6.7%. At least I think that's where this was headed.

Metaluna

But you don't really have the same diameter. The diameter will be a function of the number of teeth, which must be an integer. By making the teeth smaller, adding or subtracting a tooth changes the diameter by a smaller increment, thus you can get closer spacing between gears.. At least, I think that's the idea.

Kimmo

Bingo. I obviously failed to make that clear somehow...

If you still don't get it, just stare at this until you do.



If folks feel like having a play with my Excel spreadsheet, here it is.

Reynolds 

I think that's a good idea. As the OP said, maybe the shorter links could affect shifting, but with redesigned derailleurs it should work.
OT - And it will be another step to metric standards in bicycles.

carpediemracing 

Hm. Interesting. Although I was around for the System 10, and I even donated a track bike that had been built with it (the original owner kept the drivetrain parts), I never thought of applying it "full size".

i wonder what the weight penalty is at "full diameter" sizes. You'll have more pins/rollers (which I figure are heavier than just a side plate). Less negative space on teeth?

On the other hand you'd have better wear, quicker chain shifting (although maybe the closer teeth would be harder to shift onto - more ramp action needed), and, of course, fine tuned ratios.

Hm hm hm.

cdr

*Edit* I forgot to add that the higher number of teeth front/back is one reason why pros used huge rings in TTs - 55, 56 was normal. But they'd use a 55x15 in the TT itself, not the 55x12. The 55 helped because a one tooth jump (55x15 to 55x14) had a smaller overall effect on gear than, say, a 53x14 to a 53x13.

carpediemracing 

OP was talking keeping diameter same. Therefore teeth count goes up, front and back. Therefore ratios get closer.

I'm doing the bold cause I know you in real and you'll understand

cdr

Reynolds 

10mm chainrings and cassettes with same diameter as 1/2" will have more teeth, so 1 tooth difference is a smaller %.

Homebrew01

Let me retype my response. I get it, but those gear combinations could be done with current pitch (assuming manufacturers decide to make them). The benefit of 10mm is less weight (smaller diameter) for a given tooth count.

It appeared at first as though the claim was that 10mm would give you ratios not available with 1/2" pitch

Kimmo

I'd put up with a 150g or whatever weight penalty for it, especially if it delivered significantly longer life... This bloke reckons it feels smoother too; I guess it'd be smoother again at full diameter.

Kimmo

OMFG. If you want to do my ratios with 1/2", you're looking at a 68t big ring.

That is the claim, and you're dead wrong, like everyone's trying to tell you; the only way to have the all same ratios with a different pitch is to halve it, and then you've got twice as many potential ratios.

Just look at these numbers.

DiabloScott

Right. Otherwise V-belt drives wouldn't work because they don't have any teeth.

Smaller pitch means that an increase of one tooth gives a smaller increase in diameter than an increase in one tooth of regular pitch so you get smaller jumps between gears. You also get the ability to wrap around smaller diameters but there are other factors limiting that as well.

Kimmo

A 10mm chain of the same width might last longer; each link doesn't have to rotate as far... on nominally equivalent sprocket sizes.

urbanknight

It sounds to me that Homebrew is saying they could (if they wanted to) make those smaller step ratios in 1/2" pitch if they wanted to. For example, a 62/46 crankset with cogs ranging from 13 to 33 instead of 53/39 and 11 to 28. That would make for some rather large and heavy parts, though.

urbanknight

As for the OP's suggestion, the ability to fine tune the jumps is a nice idea. I'd wonder about the durability and cost of such a switch.

Voodoo76

Interesting that one of the few bike industry trends of late, compact chainrings, is the exact opposite of this proposal.

Kimmo

I reckon the compact cranksets blow for the very reasons I propose this.

Ygduf

Smaller teeth on same diameter = more teeth. More teeth (like a 60/30 setup or something) allows for smaller changes than can be made currently. It's like 1 degree Fahrenheit is smaller, more precise than 1 degree Celsius. They boil at the same temp (same diameter or range), but Fahrenheit has more "teeth" on it's ring..

Voodoo76

This is one reason why the track guys liked it. That and some voodoo belief that smaller rings accelerated faster.

I've never been a fan of compacts. It's the answer to a question nobody had. Guessing it saves $$$ for someone somewhere, hence it's existence.