mx_599

hi everyone!
i know some of you run lower cog numbers than "normal" so i have a question for you.

how large of a tooth gap can you get away with between succesive cogs and still have smooth engagement of ramps with chain, i.e. smooth shifting.

hope this is clear to everyone. put another way, i want to run around 5 cogs with a 11-34t range. can i?

thanks,

HillRider

If it's a 5-speed , I assume it's a freewheel with friction shifting and the cogs are neither ramped or shaped. The big gaps will cause quite a change in cadence but will be shiftable.

mx_599

huh...

no, i am modifying a standard sram 9 speed. it is ramped. grip shift x9 and derailleur

ridelugs

if its a 9 speed shifter you have to use 9spd spacing. if it was friction, you could get away with any gap, as long as it was narrower than the chain in use.

Retro Grouch 

14-17-21-27-34 used to be a common 5-speed freewheel. Of course, that was in the days of friction shifting. I kind of doubt you'll be able to get the shifting to work very well with the close 9-speed cog spacing but it's not something that I've ever wanted to do. It was common back then to overshift a bit and trim the shifter back when the chain went into gear. You can't do that with modern index shifting but honestly, compared to a modern 9-speed gear system, I personally wouldn't want to go back.

mx_599

i know, that had nothing to do with my question. nevertheless, i appreciate your time

Michel Gagnon

With indexed shifting, you need to keep the same lateral spacing between cogs. In other words, you need to keep a 9-speed cassette. Sheldon Brown explains towards the end of this page what is the spacing between each cog. So if you insist on having less cogs with the 9-speed shifters you have, you will probably have to use a few spacers (or useless worn out cogs) for the first two or three "gears". You could also mount your custom cassette on a narrower wheel which has a 7-speed freehub body. In other words, instead of having (for example):
11-13-15-17-20-23-26-30-34, you could have
xx- xx-xx- xx-14-17-21-25-34, where XX is either an old cog or a spacer.
Spacers are essential to make the new custom cassette as wide as the original one. This is necessary so the smallest cog and lockring end up in the proper position. And of course, you'll need to readjust the derailleur limit screws so the derailleur shifts between the newer bounds.

Things you can't do:
1. Just install 5 cogs and spacers, but no spacers "inside": the cassette won't be wide enough, therefore the lock ring won't lock anything.
2. Install wider spacers between cogs: indexed shifting won't work. You could do that – to a point – with friction shifting, but I don't know if your shifters even work in friction mode.

As for the other part of the question: can you shift through wider gaps? Yes. In theory, cogs on mountain cassettes (ex.: 11-34 cassettes) have ramps designed to jump through wider gaps. It may make a difference if you plan to shift while standing, for instance; however if you shift the old fashioned way, without putting too much pressure on the pedals (it's better for the drivetrain anyway), you probably won't have any problems. Just for example, I have a homemade cassette with: 12-14-15-16-17-19-21-25-34, and the 25 to 34 gap has never caused me any problems (except for the change of pace, obviously).

HillRider

There was absolutely nothing in your original posting to indicate this.

I believe Shimano made "Megarange" cassetts with this type of progression, i.e. a number of fairly closely spaced cogs and a very large jump to the largest bail-out cog and they shifted pretty well.

mx_599

well, it was not relevant if you read my original question. but like i said, i appreciate everyone's help. the most relevant piece of info i got out of this thread was that someone had a 25t to 34t difference that shifted fine. i already knew everything else.