Bicycle Mechanics - can 2 casettes be combined into one?

(accidentally posted on the road bike forum first... mods can delete that post)

I have a SunTour cassette I just bought off of evilbay to put on my Trek 400, which is already equipped with a badly geared SunTour cassette...

What I have now is 14, 16, 19, 23, 27, and 30.. The 27 and 30 are totally useless.

The one i just bought has 13, 14, 15, 16, 17, 19, and 22... (one's a 6 speed, the other 7.. the spacing is the same between the cogs, as are the guts, from what I'm told.)

If I could make my own, I would do the 13, 14, 16, 17, 19, 22, and 23- or, maybe the 27 for in case I need to climb something...

here's how the gear ratios would end up, plus cadence at 17.5 mph...

13 14 15 16 17 19 22 (or 27)
52 4.00 3.71 3.47 3.25 3.06 2.74 2.36 (1.93)
56.0 60.3 64.6 68.9 73.2 81.8 94.7 (116.3)

40 3.08 2.86 2.67 2.50 2.35 2.11 1.82 (1.48)
72.8 78.4 84.0 89.6 95.2 106.4 123.1 (151.1)

now, on the bike the way it is now, the ratios and cadence look like this:

14 16 19 23 27 30
52 3.71 3.25 2.74 2.26 1.93 1.73
60.3 68.9 81.8 99.0 116.3 129.2

40 2.86 2.50 2.11 1.74 1.48 1.33
78.4 89.6 106.4 128.7 151.1 167.9


To me, this would make the bike more useable at the speeds I'm able to go right now, for much less than the $750+ for a new bike...

Can casettes be safely taken apart and remade, or is this an exercise in "what if's"...

the short answer is... yes.

the short answer is... yes.But care might be needed with paying attention to cog and spacer thickness. The 6 and 7 speed spacing may not be the same and suntour used different spacing on one end ot the cassette vs the other. The assumption is also made that he is really dealing with cassettes and not freewheels.

it's freewheels... (i'm a noob, still learning)

Someone said tht the 6 speed and the 7 speed freewheels are the same, except the 7 speed has a double cog for the two small one, and that's what I have.

i need to figure out how the freewheel comes apart so I can change gears around and make what I want...

it's freewheels...

i need to figure out how the freewheel comes apart so I can change gears around and make what I want...
Freewheeels don't allow cog changing to the extent that loose cog cassettes do.But since you got em, knock yourself out.

it's freewheels... (i'm a noob, still learning)

Someone said tht the 6 speed and the 7 speed freewheels are the same, except the 7 speed has a double cog for the two small one, and that's what I have.

i need to figure out how the freewheel comes apart so I can change gears around and make what I want...

To take the cogs off the freewheel, you need to spin off the top cog. Use two chain-whips. Put one in the middle of the freewheel, like on the 15 or 17t cog and face it to spin in the forward clockwise direction (tightens). Place another chain-whip facing backwards to spin the top cog off.

Be very, very careful with the order of the spacers when you take them off. The Suntour system uses fairly linear cable pulls from the shifter. This results in uneven lateral movements of the rear-derailleur and requries teh distance between each and every cog be different. The spacing varies from 3.1 to 3.6mm between the cogs so don't get the order of the spacers mixed up!

Also on the Ultra-7 freewheels, there's two types of small double cogs. There's a one-piece one with two gears, I think it's the 13/14th combo. Then there's another one with a 13t 2nd gear and a spin-on 12t 1st cog that spins onto that 2nd cog. Use the chain-whip to remove the outermost/smallest cog first. Then if that one comes off by itself only, you got the 2-piece one so use the chain-whip again to remove that 2nd cog. :)

Note also that the gears are stamped, so there's a bevel on one side of all the edges with a sharp 90-degree edge on the opposite side. Re-install your gears so that the beveled sides face the same direction as the original cogs.