chainglider for rohloff...finally

[hendrich]

I now have a hebie chainglider for the rohloff on our tandem. The chainglider is difficult to buy in the US, I finally found both components (front/rear) from Spain for a decent price with low shipping fee. Our timing and rear chains are on the same side of bike, using a double chainring at the stoker. Thorn tandems are also of this design. I was concerned the chainglider might not fit onto a double chainring. After a new chainring, addition of chainring spacers, some adjustment, and a bit of oil, the whole thing works great. No interference with the timing chain. We often ride on dusty trails, so looking forward to a longer life from the rear chain. We go through 3 or 4 rear chains (~2500 mi) for every timing chain (~9,000 mi) replaced. The whole contraption also looks great. Thanks to this forum for showing the way.

[Matt2matt2002]

I'm sure you will be happy with your chainglider.
Welcome to the club.

[Andre Jute]

This poster described chain wear on a tandem before fitting a Chainglider:

We go through 3 or 4 rear chains (~2500 mi) for every timing chain (~9,000 mi) replaced.

Anybody wonder why two chains operated under precisely the same ambient conditions should wear so hugely differently?

Hendrich, I wish you luck with your Chainglider.

I, for one, would appreciate a follow-up report the next time you replace the rear chain.

[martinf]

Anybody wonder why two chains operated under precisely the same ambient conditions should wear so hugely differently?

Seems obvious to me, though I might be wrong.

The timing chain transmits the pedalling force from just the person on the front, the rear chain the force from both persons.

[Andre Jute]

Anybody wonder why two chains operated under precisely the same ambient conditions should wear so hugely differently?

Seems obvious to me, though I might be wrong.

The timing chain transmits the pedalling force from just the person on the front, the rear chain the force from both persons.

I did wonder about differential loads on the two chains but the wear ratio is 9000/2500 or 3.6, while the pedalling force ratio back to front is likely less than 2/1 which is 2. Since I don't know anything tandems, is there another contributing factor I'm overlooking, perhaps a multiplier in the transmission string which affects only the rear chain?

[PH]

Since I don't know anything tandems, is there another contributing factor I'm overlooking, perhaps a multiplier in the transmission string which affects only the rear chain?

I don't know anything about tandems either, though I've read a few similar threads, the wear difference is well reported.  The couple who recently tandem'd around the World in 180 days*, used belts for the timing transmission and chain for the final derailleur drive, 2 belts, 7 chains.
I've seen explanations for the wear on the timing transmission and it's complicated, it's two drivers rather than a driver and driven, it's argued that the wear will be proportional to the difference between the drivers.  Then there's the difference in chainwheel/sprocket sizes, even on a solo, increasing the size of a sprocket reduces wear, having both rings the same size must be ideal.  Then, where the chainglider comes in,  I think the rear chain is always going to attract more muck than the timing chain. 

*There's a website and a book - https://www.stelatandem.com/
 

[Danneaux]

As the owner of a (derailleur) tandem with crossover timing chain, I have also noticed a generous disparity in chain wear, though mine is more pronounced because of the lateral chain deflection due to the rear derailleurs and resultant offset chainlines vs the inline drive of the timing chain or an IGH.

That aside, I have found greater wear at the rear is due not only to increased drive loads as Martin noted, but also due to the proximity to the driven rear wheel, made worse in wet or dusty conditions. The debris literally showers the drive chain, whereas the timing chain is clear of all that and I have come to think contamination is -- not surprisingly -- a big factor in increased chain wear. We know how dirt and debris makes the grinding paste you often reference.

You know I prefer my bicycles and their drivetrains be kept clean and my tandem gets no less care, but the cleaning differential between my tandem's two chains is next-level, on the order of 6:1, drive vs timing. To give some idea why, I'll reach back and reference my photos and posts detailing my homemade half-chainguard for my Fixie. See...
https://thorncyclesforum.co.uk/index.php?topic=13951.msg110999#msg110999
...and...
https://thorncyclesforum.co.uk/index.php?topic=13951.msg111000#msg111000

Though the chainline is straight (as with an IGH), you can see the glop thrown on the chainguard by the rear wheel (and the clean chain beneath it). Now, imagine a timing chain running with no deflection between two equal-size chainrings located well ahead of the wheelspray and the difference becomes clear.

You can bet if I had a Rohloff-equipped tandem (I have the hub for it already in hand; just need to narrow the dropouts and braze on a locator for an extended torque-reaction arm), I'd equip it with a Hebie Chainglider at the rear...and probably no need to cobble one for the front where the difference in benefit would be much less profound!

One last issue Paul alluded to, and that is the size of the timing-chain gears. It is a balance between too large and risked foldover under extreme torque (seen by myself in the local tandem races that used to be held yearly) and too small, which incurs excess friction. I settled on 40t for each as the best compromise and I think the reduced articulation compared to, say, a 38 x 16 (or smaller cog) combination often seen in Rohloff final drivetrains is bound to contribute to the wear differential. Anecdotally, I've seen vastly increased bottom bracket wear on tandems I've serviced with the once-standard 26 x 26 timing chains that were default in many T/A tandem drivetrain kits back in the day. The standard address was to size-up the timing 'rings.

As an aside for overall parts life, crossover (CO) vs same-side (SS) timing chains further muddy the mix, with some folks feeling the CO evens out pedaling forces at the rear BB as both sides are loaded, while others prefer the full load to go into the right-side bearing.

FWIW, I think muck thrown from the rear wheel and larger timing rings account for most of the wear differential.

All the best, Dan.

[Andre Jute]

Thanks, Martin, Paul, Dan for info and insights. Here are some apparently agreed preliminary conclusions:

1. Differential chain wear is a fact of tandem operation, with the rear chain wearing much faster than the timing chain (and associated parts).

2. There are a number of other factors widely considered to have some influence besides the c2:1 power input between the rear and the timing chains.

3. It is likely that the muck sprayed on the rear chain, a far greater serving than on the timing chain, will have a dominant role in the differential wear.

4. Personally, I don't think the differential wear, even if we have some gross overall ratios that are pretty close (3.9 and 3.5), is one of those cycling facts that one can make into even a rough algorithm. There are too few tandems for statistical respectability, just the influences already identified are enough to make isolating cause and effect of each bothersome, and too much depends on individual riding conditions.

5. If muck on the rear chain is indeed the major determinant of chain wear, Hendrich is in for a pleasant surprise in rear chain longevity now that he has clad the rear chain on his tandem in a Chainglider.

In the light of all this, I'll bet a cautious half-guinea that Hendrich's Chainglider sets the record for relative chain mileage improvement of its chain, relative defined as mileage after it was fitted divided by mileage before.

[hendrich]

Thanks all for the conversation. My observation over many years is that our rear chain always has more grime than the timing chain. This was true for our older derailleur tandem and has been true for our rohloff tandem. The chain proximity to the rear wheel is apparently more significant for grime than the closer to the ground derailleur chain position.

I have wondered if the rear chain has significantly more that twice the load of the front chain, since the stoker's force may tend to reduce timing chain force from the captain. Seems to be a physics question, anyone know? Thanks.