Specific Question On Gearing

Pross

I know there are hundreds of threads about gearing but I have a specific query that I was hoping some of you technical experts can help with.

I ma just getting my old 7 speed steel framed bike back on the road after 13 years. The bike was originally kitted out with Ultegra 600 but I replaced the front mech years back with a Campag mech (Chorus I think). My old gearing was a 52 / 42 chainset and a variety of cassettes with a maximum 21 sprocket. Obviously a minimum gear of 42 x 21 now appears very high for cycling in South Wales, especially with me being unfit and overweight so I bought a 38t front ring and a 13-23 cassette. Unfortunately I damaged the spider on the chainset changing the rings and have finally got a second hand Campag chainring but this has 135 BCD and so the 38t doesn't fit and it appears you can only get a 39t for it. With a bit of research I have come up with the following options to get lower gears:-

1. Just buy a 12 - 28 cassette (cassettes from about £10 plus lockring tool). Cheapest and simplest option but big gear jumps on a 7 speed casette.Could also go for a 39t chainring and 13-26 cassette.

2. Buy a cheap compact chainset (about £40) but not sure that the Campag front mech can handle a 16t jump so may need to buy a 36t ring as well.

3. Get a 9 or 10 speed cassette and ditch one sprocket (smallest?) with say a 27t max sprocket. This would give me something like a 13-27 8 or 9 speed without changing the existing 7 speed hub (and works according to Sheldon Brown). Would also require a new 9 or 10 speed chain but the downtube shifters are set to friction so should be fine. This would be the most costly option but would give lower gears without big jumps due to gaining 1 or 2 sprockets. However, would the narrower chain work OK with a 7 / 8 speed front chainring?

Does anyone have any advice? The alternative would be to MTFU and just fit a 39t with the 23 sprocket which would give the same as the second lowest gear on my best bike. For the majority of my riding I can get by with a 39x23 on my best bike but I occassionally need the 25 and the old bike is heavier so harder to lug uphill hence looking for something a bit lower. I'm particularly keen to know if anyone has done my option 3 and, if so, will the wider front chainrings cause a problem?

stigofthedump

If you go for the split down a 9 speed cassette option you will need to have the sprocket spacers from your original. Also you need to make sure that the cassette is lined up properly so that the hyperglide will work. If your old setup is not hyperglide then you will need to modify your freehub body to accept the sprokets, hyperglide has one narrow spline to line up the shifting ramps.

Good luck with the project.

Pross

Cheers, current set up is hyperglide. With regards to the spacers I thought it needed the narrower spacing of the 9 or 10 speed in order to work which is how the cassette with more sprockets can fit the hub?

John.T

If you are using friction shifters then any cassette that you can fit on will work. Not sure if losing the smallest would work but it may well do and would be the best option. I would feel inclined to try a 10sp one on. If you can take one off another bike to test with it would save buying one straight away. You are in 'suck it and see' territory but I don't see why you should not get something to work cassette wise.

markos1963

If you are on friction shifters why not fit a triple? Some cheap Campag ones on Ebay etc Less hassle than messing around with cassettes

Pross

Cheers John, I can try the 9 speed off my best bike - didn't think of that. My only real concern with using a 9 or 10 and removing a sprocket is whether the narrower 9 or 10 speed chain will be OK with the chainrings which are 7 or 8 speed width (also, if I remove a sprocket from the middle it may be tricky getting the sprockets correctly aligned for smooth shifting).

Markos, I thought about a triple but I don't really need to go so low on the gears and it would mean a new BB and front mech (I don't think the existing Campag front mech can cope with the jump from big to small ring, the same reason stopped me going for a 50 / 34 compact).

John.T

9sp chain will be OK. Probably 10sp as well. The inside dimension is very similar, it is the overall width that differs most.

Pross

Will be finding out in the next few days, I've ordered the 10 speed cassette and 10 speed chain. I was forgetting that it is the external width of the chain that differs rather than the internal. Apparently the only possible issue is that the chain may drop when changing between the chainrings.