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Old 09-05-11, 02:09 PM   #1
spunkyj
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Need new cassette for lower gearing: Capacity of Shimano 600 Tricolor RD?

I'm looking to put a new 7 speed cassette on my Shimano 600 Tricolor equipped steel road bike. The goal is to achieve some lower gearing for hills (the bike came used with a 12-21 cassette, and 40/52 chain rings). The offerings around town seem to be variations of the Shimano HG50 7 speed cassette with either 12-28, 13-28, 13-30, 13-34 etc. options.

I've heard different opinions from different local bike shop mechanics about which cassettes are compatible with my bike. One suggested the 13-30, and didn't seem to think there would be any issues with rear derailleur capacity. Another mechanic suggested that I wouldn't want to go with any rear cog larger than 28, and if I still needed lower gearing I should consider swapping out my smaller chain ring.

So my question is, what is the actual capacity of my rear Shimano 600 tricolor derailleur?

Further than that, are there mechanical reasons to prefer a 28 tooth cog with a smaller chain ring for lower gearing over a 30 tooth or 34 tooth largest cogs?

Cheers!

Last edited by spunkyj; 09-05-11 at 03:35 PM. Reason: updated title, fixed typo
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Old 09-05-11, 03:14 PM   #2
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I think it's rated for a max cog of 28T, but I'm running that RD with a 30T in the back, and I even tested a 32T which seemed to work, but the derailer wasn't too happy about it. It does depend on the derailer hanger a bit. I definitely wouldn't try a 34T. Keep in mind with the new cassette you'll need a longer chain. This is a good time to just ditch the old chain for a new one cut to the correct length.

If your crankset has a 130 BCD (most older road cranks do) the smallest ring you can put on is a 38, which won't be much of a drop from the 39, 40, or 42 that's probably on there now. If you're crank is 110 BCD you can go down to a 34 ring. The cassette is the easy swap, especially if you can't go down much on the chainring.
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Old 09-05-11, 03:17 PM   #3
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spunkyj: No opinions on which cassette you should choose, but if you put on a larger one you will need a longer chain as well. Conversely, if you fit a smaller chainring you will need to adjust the chain length to suit. I use the big-big method espoused by Sheldon Brown - http://sheldonbrown.com/derailer-adjustment.html#chain
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Old 09-05-11, 03:40 PM   #4
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Have you worked out the ratios to determine what you really need? 42:28 is a fair amount lower than 42:21, while 42:30 is only very slightly lower than 42:28. If the 28 isn't comfortably low enough, the 30 may still fall short.
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Old 09-05-11, 03:41 PM   #5
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Thanks for the tip. My chain is quite worn and I'm planning on replacing it along with the cassette. I'll have my LBS do the work.
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Old 09-05-11, 03:45 PM   #6
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Have you worked out the ratios to determine what you really need? 42:28 is a fair amount lower than 42:21, while 42:30 is only very slightly lower than 42:28. If the 28 isn't comfortably low enough, the 30 may still fall short.
I'm not really sure how to work out which combos I really need, other than trial and error. I know 40:21 is too high because I can't spin my way up even modest hills (6-7 degrees).
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Old 09-05-11, 05:54 PM   #7
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spunkyj, Of the cassettes you listed, I'd choose the 13-28 over the 12-28. Either will very likely work, but you'll have one extra intermediate gear that'll probably see more usage than the 13 or the 28T gears.

Brad

PS There will be a major difference between the 40-21T bottom gear and the 40-28T bottom gear combo

Last edited by bradtx; 09-05-11 at 05:57 PM. Reason: ps
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Old 09-13-11, 10:12 PM   #8
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I have a similar situation. I have a 1983 Trek 760 racing bike i bought used recently. I can ride it all over town but not up steep hills. It has these stock components: Suntour Superbe (short cage) rear derailleur, a 13-21t Suntour New Winner freewheel and a Suntour Superbe crankset (42x53). Wheels are 700c.

I have been advised that i can change the rear freewheel to a Shimano modern
mega seven freewheel and if i do that, i would need a modern mountain bike derailler such as a Deore long rear.

What I dont know is (1) would have to change the rear wheel? (I think answer is no but i dont know.) (2) would i be happy with the Shimano mega freewheel (because there is a big jump in cogs from the biggest cog) (3) woudl I be happy with the shifting (because right now the bike is SMOOTH shifting with the high end vintage parts, and I would be moving to a modern medium quality mountain bike derailler instead.

I am so confused about this i am thinking of leaving the bike as is and using it only for riding where theres no steep hills, and getting a modern bike with a modern triple setup. Any thoughts please advise.
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Old 09-13-11, 10:52 PM   #9
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(1) would have to change the rear wheel?

(2) would i be happy with the Shimano mega freewheel (because there is a big jump in cogs from the biggest cog)

(3) woudl I be happy with the shifting (because right now the bike is SMOOTH shifting with the high end vintage parts, and I would be moving to a modern medium quality mountain bike derailler instead.
1. No, the rear wheel could stay. You might have to re-dish it a bit to fit in the 7th cog though.

2. That's really personal preference. The Megarange freewheels have a massive 34T largest cog. That might be overkill for what you need, or it may be just right. How much are you struggling on the hills? Personally I like the Megarange setup as the 34T acts as a bailout gear, while the other 6 cogs have relatively close spacing.

3. Tough to say. New Shimano stuff *should* shift just fine, but it might not be what you're used to. If you put on a less aggressive freewheel (say a 14-28 six speed) you may not have to change your rear derailer OR re-dish your wheel. The 28T may give you all the gear you need.
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Old 09-13-11, 10:58 PM   #10
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HI I am doing group rides on some very steep hills (the group has sought out the local really steep hills. There are about 4-5 hills that collectively go from about sea level to about 800 ft elevation in the course of about 4-5 miles. ) If it is any indication of the hills, i can hit 33 mph downhill on the way back.

I have 2 hybrid bikes i have done these hills on. One is a Trek Multitrack 720. The other is a Univega Via Carisma. These both have triples and large cogs in the back. The gearing seems about the same on both bikes. I need to use the easiest gears to go up the hills. Everyone else is on a modern road bike and I am on these 1995-ish steel hybrid bikes.

On the Trek 760 I have never attempted these hills. I did try one steep hill and quickly realized i cannot do steep hills on the bike with the stock gearing.
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Old 09-13-11, 11:17 PM   #11
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In that case I'd say go for the Megarange freewheel. It will only require a new chain and rear derailer (and the possible wheel re-dishing.)

If that's still not enough you'll have to put on a triple up front. That will require a new crankset and front derailer. The good thing about all this is that you can use whatever derailers you want, because you have friction shifters. With modern bikes these swaps can be much more expensive, to get them to index correctly.
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Old 09-18-11, 02:51 AM   #12
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I met a recombent bike rider today who had the 7 speed megarange cassette on his bike with a double crank up front (not sure what crank set sizes.) I asked if he liked the megagrange and whether the big change in gears from lowest gear bothered him. He said it works for him and the jump isnt so bad, he can ride up any hill. On the other hand i met a biker today who had a 12-21 with a double in front (dont know the crankset sizes in front) and he said he can bike up any hill with that setup (he thought the smaller size up front was a 42 or 39.
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Old 09-18-11, 05:39 PM   #13
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On the other hand i met a biker today who had a 12-21 with a double in front (dont know the crankset sizes in front) and he said he can bike up any hill with that setup (he thought the smaller size up front was a 42 or 39.
It really depends on your fitness level and your willingness to power up hills in a higher gear rather than spinning up them slower in a lower gear. Here in Platteville (where I go to school) it's pretty hilly. I left my 12-23 cassette on with a 42/52 road double just for fun. I also brought back my single speed for even more fun! However, if I were touring or going on really long rides I'd want much lower gears.
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