Alternative to Truvativ Isoflow

[Dalesman1954]

I have jsut returned to cycle touring after a gap of 20 years. Having bought a new Raleigh Royal (greta value) I am finding the current Truvativ Isoflow 28-38-44 chainset too tough up hills when loaded. Can anyone advise on an alternative that I can fit to this chainset that will give me 22-32-44 (typical mtb set up I think)? Wuld prefer Shimano but don't know if BB would fit the Raleigh Royal.

Thanks

MT

 

[frank9755]

I have jsut returned to cycle touring after a gap of 20 years. Having bought a new Raleigh Royal (greta value) I am finding the current Truvativ Isoflow 28-38-44 chainset too tough up hills when loaded. Can anyone advise on an alternative that I can fit to this chainset that will give me 22-32-44 (typical mtb set up I think)? Wuld prefer Shimano but don't know if BB would fit the Raleigh Royal.

Thanks

MT

Firstly, unless you have changed something, you probably have 28-38-48 on there at the moment. If you had a 44T outer ring it probably wouldn't shift very well.


Don't change the chainset. A mountain bike chainset won't index properly with STIs in any case - and the 44T outer wouldn't shift well.


What you can do is just swap the inner ring. I'm not familiar with your specific chainset but you need to find out the bolt circle diameter (bcd) to determine what the smallest ring that your chainset will physically take. Many chainsets are 74bcd which will allow you to take a 24T. Spa Cycles sells steel 24T rings for about £8. I have one on my touring bike, for hauling camping gear up 1-in-5 hills.

Edit - just googled your chainset and it seems to be 64bcd - you should have no problems with a 24T (and probably could even go smaller, to a 22T).

Some people will tell you that with such low gearing you will not be able to keep the bike balanced. Ignore those people as they do not speak from experience!

 

[Dalesman1954]

Many thanks.

I was wondering about changing inner ring but unsure - that's really helpful. I'm near Spa Cycles so could pop in.

Once again, many thanks.

 

[GrumpyGregry]

the peeps at Spa are dead helpful. Keep the old chain ring handy, six months of riding and you will want to put it back on such will be the improvement in your legs and lungs

 

[andym]

I think I'd change the middle ring as well - 38 down to 22 or 24 seems like a big gap

 

[frank9755]

No - don't change the middle one!


The big gap to the small ring is fine but you need to have not more than 12T difference between middle and outer, or else the shifting will be poor. You could get away with a 36 but it will shift better if you keep the 38.

It's to do with the distance between the mech and middle ring. If the mech is too far above the middle ring it can't do the small to middle upshift properly.

 

[willem]

If you do indeed have a road front mech with sti, you need a 10t difference between outer and middle ring, and much lower than 38/48t middle and outer will indeed not shift very well. A 24t inner chainwheel should still shift quite well, and will be very cheap (get a steel one). You may also consider the rear. If you have a road rear mech you are limited to about 28t, but if you happen to have a mtb rear mech (unlike front mtb mechs rear mtb mechs work well with road sti shifters) you could fit an mtb cassette with 34t. 28 front 28 rear is indeed rather high gearing for a loaded tourer, unless the load is very light.
Willem

 

[RecordAceFromNew]

Assuming and according to this the OP has a 11-32T cassette.

To answer the OP's original question, the road shifter and front mech (a Sora FD3403 or similar road triple) should work with e.g. a Shimano 44/32/22 mtb chainset as long as he ensures his chainline being close to 45mm is maintained, and doesn't clash with the frame. The profile of that front mech is designed for a 50T large ring, but the shift with a 44/32/22 won't be worse than running e.g. a 48/38/22T chainset, because the mech can now be positioned 8mm lower, which also makes the cage correspondingly closer to the small ring.

If he keeps the current chainset and 48T large ring and just swapping the inner ring for a 22T e.g., then there are three potential issues:
a) the mech's cage will be a long way behind the small ring making it even more difficult shifting from the small to the middle (which is always the toughest shift for a triple anyway),
b) the chain might drag on the mech's tail for some rear sprockets when he is on the 22T (because he would be exceeding the front mech's range of 20T by 6T), and
c) requiring a 47T wrap range he might run into wrap range problem with the rear mech too even if his rear mech is a long cage mtb model (with 43T limit).

If he wishes to consider changing the chainset, unless he is changing the bb at the same time it is important to find out which bb he has - Truvativ Isoflow chainsets come in either their proprietary Powerspline or normal jis square tapered form. If the latter the recommended bb length is 118mm delivering a 46.5mm chainline according to this, meaning an mtb chainset e.g. the FC-M311 or FC-M411 (which normally requiring a 123mm square tapered bb delivering 50mm chainline) should work, and delivering a 47mm chainline I believe, assuming there is enough clearance with the frame of course.

A compromise between decent shift and achieving for the lowest gear could also involve changing all 3 rings to mimic a mtb chainset, e.g. a 44/32/22 respecting the front mech's 11T large/middle minimum difference constraint, but this could end up costing more than a new mtb chainset/bb.

Certainly not the most straightforward decision, hopefully Spa will also be able to advice.

 

[frank9755]

I think you've got a couple of bits wrong there. It's really not a big problem. It's a very common request on a touring bike and changing one chainring is the obvious thing to do. The other thing worth considering would be to change the 11-32 cassette for an 11-34.

- It won't shift as well with a 44T outer ring. You can certainly drop the mech down but because the curvature of the mech will be substantially different from that of the smaller chainring it's not a good idea to try. Best to stick with the existing 48 / 38.

- The thing that dictates how well the small-to-middle shift works is the size of the middle ring. The size of the small ring doesn't make much, if any, difference. So this is not a reason to avoid a small inner ring.

- A touring bike with long chain stays will make a large chainset range more likely. On the OPs bike I would be 99% certain that 24/38/48 will work fine in all gears, and 22 would probably work as well. If there was a problem it would only be a theoretical one affecting a gear which the OP would never use (small ring / small sprocket)

To the OP - if you talk to Spa you will be in good hands!

 

[willem]

The simplest package of solutions consists of three parts:
1 fit a 24t inner chainring. Officially 22t is the maximum between outer and inner, but almost always 24 t works just as well. A steel chainwheel will last longer and will only cost a couple of pounds. It is a cheap experiment.
2 if you have an mtb rear mech, fit a 34 t cassette (I am not sure if there are already 8 speed 36t cassettes) and a new chain. You can easily do this yourself. Keep the existing cassette (with a new chain while you are at it) for when you will be fitter. This is more expensive for less immediate result. However, since you are not actually throwing the 32 t cassette away, it is still cheap in the long run.
3 take less luggage. This will have by far the largest impact (climbing is a fight against gravity). I am all in favour of 15 kg max in two rear pannniers and a bar bag, or even less, depending on circumstances.
Willem