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Discussion Starter · #1 ·
For my own edification, I'd like to understand what sort of compromises are involved in gear spacing and what methods of evaluation are used to determine suitability.

Can someone please elucidate?

Thanks
 

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Banned forever.....or not
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Compromises ?????

Once you get over 17 teeth, a one tooth skip isn't noticed. Cassettes that skip more than one tooth are designed for old ladies.
 

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old school drop out
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Three things to care about:

1) What's the smallest cog? This tells you when you will spin out. Most cassettes have either an 11, 12, or 13 small cog. The smaller the cog the faster you can go without spinning out. This matters most if you like to pedal on long downhills, are super strong, or are using a compact crank-set with a smallish "big" ring.

2) What's the biggest cog? The bigger the rear cog, the easier steep hills are. Care about this if you live in a hilly area and are not a super strong climber. If you never use your biggest cog, you have the wrong cassette. If a climb near you hurts too much too climb, you need a bigger rear cog.

3) How big are the jumps? An 11 to 30 cog sounds perfect - you can climb any hill as well as pedal down any hill. However, you suddenly find on flat rides, that one gear is "too high" but the next one is "too low." You've just discovered that the "jumps" between the gear is too high (i.e. you have a 15 and 18 cog, but really need a 16 or 17 in there too). Having smaller jumps between gears makes finding the "right" gear easier.

Pick a cassette that satisfies your need for these three things and you should be okay.
 

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I thought he meant actual cog spacing... which is a whole different can of worms, from the frame spacing to the chainline to the wheel dish to the hub width, nm non-linear cable pull and proprietary non-uniform Campy spacers!
 

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I use the following evaluation method to determine gear suitability...

1. If it hurts, I change down.

2. If I spin too fast, I change up.

If you can't find a gear to suit on a modern 10sp cassette then take up golf.

Grumps
 

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laffeaux said:
Three things to care about:

1) What's the smallest cog? This tells you when you will spin out. Most cassettes have either an 11, 12, or 13 small cog. The smaller the cog the faster you can go without spinning out. This matters most if you like to pedal on long downhills, are super strong, or are using a compact crank-set with a smallish "big" ring.

2) What's the biggest cog? The bigger the rear cog, the easier steep hills are. Care about this if you live in a hilly area and are not a super strong climber. If you never use your biggest cog, you have the wrong cassette. If a climb near you hurts too much too climb, you need a bigger rear cog.

3) How big are the jumps? An 11 to 30 cog sounds perfect - you can climb any hill as well as pedal down any hill. However, you suddenly find on flat rides, that one gear is "too high" but the next one is "too low." You've just discovered that the "jumps" between the gear is too high (i.e. you have a 15 and 18 cog, but really need a 16 or 17 in there too). Having smaller jumps between gears makes finding the "right" gear easier.

Pick a cassette that satisfies your need for these three things and you should be okay.
Good to know, right now I feel I'm in between the "right" gear for flats...you've just enlightened me :)
 

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MR_GRUMPY said:
Compromises ?????

Once you get over 17 teeth, a one tooth skip isn't noticed. Cassettes that skip more than one tooth are designed for old ladies.
19 on the big ring.

That's pretty much where you're starting to go fast (with wind resistance increasing with the square of velocity, it's a big deal to go a bit quicker when not going up-hill where it's linear) and get overlap with the small ring where you have smaller jumps.

There's a comfortable spot between 17 and 19 provided by an 18; but I've never wanted something between 19 and 21.
 

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captain-ahab said:
Good to know, right now I feel I'm in between the "right" gear for flats...you've just enlightened me :)
That's where triples and/or larger starting cogs come in.

50-34 x 11-12-13-14-15-17-19-21-23-25

and

53-39-30 x 12-13-14-15-16-17-18-19-21-23

have essentially the same range.

Or you could just accept that a 50 x 13 is good enough for most purposes (30 MPH with a good spin with a good tuck down hill taking you faster than than higher gears and pedaling) and go for

50-34 x 13-14-15-16-17-18-19-21-23-26
 

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Discussion Starter · #10 ·
I'd like to thank you all...

My recent acquisition of a wheelset with a 8/9 cassette hub replaces first a 14-28/6 and then a 13-28/7 freewheel set. The seller was kind enough to include an 11-30 SRAM 850 that got me started on the right foot. In all three cases I I felt that closer spaced ratios would be nicer. To that end I purchased a Tiagra 13-25/9 and a Miche 18t. I've been playing with ratios and riding to determine what sort of bailout I would need for the "hills" here in Central Michigan. So far a 13-21/9 using mixed cogs (dropped 23 and 25, added 18 and 20) is a bit much and not fun with D/T shifters. I've put together a 13-30/9 that I'll try out today.

My question was prompted by what my friend calls a tendency to over-analyze. I have a gear spreadsheet that I've assembled with graphs and such, and I've noticed that most of the commercial cassettes exhibit a linear ratio progression. I guess I assumed that this was a design goal and wondered what other methods of choosing ratios there were.

Thanks for the comments.
 

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3v1lD4v3 said:
My question was prompted by what my friend calls a tendency to over-analyze. I have a gear spreadsheet that I've assembled with graphs and such, and I've noticed that most of the commercial cassettes exhibit a linear ratio progression. I guess I assumed that this was a design goal and wondered what other methods of choosing ratios there were.
In that case you should get a power meter (iBike and Polar have entry level models) and start plotting your power vs. gear vs. grade and climb length.
 

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Info.

3v1lD4v3 said:
Most of the commercial cassettes exhibit a linear ratio progression. I guess I assumed that this was a design goal and wondered what other methods of choosing ratios there were.
That linearity is there because most trained cyclists like the changes between the gears they use most often to have about the same percentage difference. But to get that, the number of teeth on the cogs need to be in logarithmic steps. You'll see that when you plot the cog sizes of many cassettes.
 
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