Confused about gearing

[sgw]

I require new chainrings for my M - 60 crank. I have found the following information about original rigs fitted on the web:-

Super Glide chain rings, light alloy anodized finish, 26/36/46 or 28/38/48 with Biopace or round rings.

Mine has 48/38/28 fitted but knacked. When I look online at current chainsets on offer I notice that most are under 48 on the big ring and the few that have a 48 big ring, have mid and smaller ones of less than 38 and 28.

I would have thought that the M - 60 was a mainstream crank in its day so what has happened? Have theories on suitable gearing changed over the years? Should I look for original sizes or would more modern and smaller rings fit?

My riding is steady rather than competitive and often carrying quite some weight. An off road tourer really. Advancing age means that when fully loaded I do have to resort to pushing uphill quite often but I still need bigger gears for the road sections.

Any advice on what I should consider would be appreciated but be gentle with me, gear tables give me headache.

 

[drystonepaul]

In about 1992 Suntour released 'Micro-Drive' which was a concept based around making all the chainrings smaller by reducing the bolt circle diameter (BCD) on the crankset. This was to reduce weight and offer lower gears for off-road riding. The smallest sprocket was also reduced from 12 teeth to 11 to maintain the higher gears.
Shimano also tagged along with their version called 'Compact Drive'.
The BCD was reduced from 110mm for the middle and outer chainrings, with a 74mm inner ring BCD, to a 94/58mm BCD on compact drive.

It quickly became the standard as it allowed smaller chainrings. Larger 48, 38, 28 combinations were still available, but generally 42,32,22 more or less became by far the most common set up for a triple ring set up.

Anyway these chainring sizes have also continued with more modern 4 arm chainsets.

If you want to keep your crankset, and there's no reason you shouldn't, for off road touring I'd change your set up slightly to give some lower gears.

The smallest inner chainring you can fit will be a 24t. The smallest middle chainring that you can still find would be a 34t.
I'd recommend going for a 46, 34, 24, or a 46, 36, 24 front set up. And a 12-28, 11-28 or 11-30 cassette on the back.
That will give a good range of gears within the capacity of your front and rear long arm mech.

I've toured in the Alps with a 44, 32, 22 compact drive chainset matched to an 11-28 eight speed cassette on some big climbs and full panniers without too many problems.

For 110 BCD rings look at TA chainrings (Spécialités TA). They are good.

 

[paininthe]

In about 1992 Suntour ...

Excellent post!

 

[sgw]

Thanks very much for taking the time DSP.

That is exactly the sort of advice I was looking for. I will further digest it and may be back for more.

 

[sgw]

I have hit my first complication. Sorry!

I did intended to use an XT Deore rear mech. Problem being that it is short cage. I realise this will seriously restrict the largest rear cog. Can this limitation be compensated for by reconsidering the front rings?

or

I also have an SRAM 9 rear long cage. Would you suggest that I would be better of to use that to extend the range at the rear and follow the advice as above on sizes?

 

[velomaniac]

The chainring sizes you seek are still the norm in touring bikes, you'd need to look at touring bike specialists. If using cassettes with up to 33-34 teeth on largest sprocket a long cage would be best but 30 teeth or less should be fine with a medium cage mech.

 

[drcarlos]

12-28 is the max on a short cage XT mech.
What you need to run to achieve the same sort fo gearing on your setup is;
24, 36, 46 on the front with the 110 BCD, and a 12-28 rear cassette. This is what I run on my Claudbutler or the same vintage with the same rear mech.

Carl.

 

[sgw]

Great stuff guys, thanks.

I don't want to use the SRAM as it needs jockys, have you seen the price! :shock:

 

[mountainloz]

also, be careful mixing shimano shifters and sram mechs,
some sram mechs have a different actuation ratio,if mixed the indexing wouldnt work
i hope this has helped

 

[Anthony]

I did intended to use an XT Deore rear mech. Problem being that it is short cage. I realise this will seriously restrict the largest rear cog. Can this limitation be compensated for by reconsidering the front rings?

The only problem that a short-cage mech could cause with a 11-30 cassette is that if you make the chain long enough to reach round the biggest ring and the biggest sprocket, then it will be too long for the mech to take up the slack when you are in the smallest ring and the smallest sprocket. With the result that the chain would hang down, rather than being tight. But are you ever going to be in the smallest ring and the smallest sprocket? If not, the problem is just theoretical and would never arise in practice.

Many people with short-cage rms compromise and make the chain slightly too short to cover the big/big combination, because they will never be in that one either. That way, your chain will be reasonably taut and you won't in practice encounter any problems at all, provided you stay in the right chainring at all times.