• Shimano Dyna-Sys (which are marketed only as “10-speed”)
• SRAM E.S.P (which are marketed only as “9-speed”

Both take 35mm of cable to go over the whole cassette. Picture shows SRAM X.9 and Shimano XT, but any other derailleurs of the mentioned types would be interchangeable.

This means that either one can be replaced with another (provided that it can handle your biggest cog). I have not verified this myself. Remember that “SRAM 10-speed” deraileurs have different mechanical advantage, as do “Shimano 9-speed” ones, and there are no other pairs which are not designed for each other but work.

Maybe not a really useful finding in practice, but certainly an interesting one.

Report with photos here. I’m wondering how is it possible that I’ve been to that region already three times and I’m ready to select it for my vacation trip once again.

Recently I traveled with my MTB, and Pendolino was the only feasible option (it was the first morning train, the next one arrived already too late). The only way was to partially disassemble and pack the bike so that it becomes normal luggage.

Packed bike in the room

I did the following:

• Removed wheels and bound them firmly to the rear triangle
• Unscrewed the rear derailler and fixed it inside the rear triangle together with the sloppy chain
• Removed the handlebar from the stem and fixed it to the frame
• Turned the fork backwards and fixed it to everything else
• Removed the saddle with the post and bound it to the inside
• Put the rack on top of the frame

Resulting package could stand firmly on the fork blades and the wheels on the rear. It was also easy to carry it holding by the frame. The final wrapping was done with the tent, as I did not want to carry anything extra.

Disassembled bike in Pendolino train

The train was pretty full, but fortunately there was free space at the place for wheelchairs. I’m not sure whether my package would have fit to the top rack shelf.

Assembling back at the arrival station

Assembly took about half an hour. I forgot to calculate how much did I spend for the disassembly. Fortunately I did not need to do it on the way back, there was a regular InterCity train.

Other riders carry water bottles in their jersey back pockets, but my jacket has pockets which are not really suitable for it. So I decided to try a camelbak. Unfortunately models in the store make my digestive tract to work in the opposite direction. Such simple thing as bag for the plastic water bladder is made of tens of various colorful cloth pieces, contains plastic foam padding everywhere, several strips and bindings all over the body, and weighs up to 500g! I’m not much of a weightweenie, but half-kilo for such appliance is really ridiculous. All this plastic foam and nylon base becomes completely wet during the ride, I’d have to carry half kilogram more of own sweat each time, and wash it each time at home. And for these rides, grams actually matter for me: it can easily mean keeping up with the group until the end or dropping out somewhere in the middle.

I realized that I do not want to take any of these fancy ready camelbaks even for free. I bought just the plastic water bladder (was marked “Platypus”, weighted 120 g.) and quickly sew an ultra-simple nylon cover for it together with two thin, minimally padded shoulder straps. The latter attach directly to the top handle of the bladder. This creature weighs 20 grams and does not collect more sweat than the inner lining of the jacket.

Last weekend this masterpiece was successfully tested. I didn’t drop out of the ride. Here is the map.

View in a larger map

It worked! It takes 2l of fluid, which seems to be just enough for me for a 6-hour ride. It weighs less than 2 x 1l. standard water bottles with holders. I’m taking it next time.

See you on the ride!

• There are two planet carrierrs. Call “first” the one which is closer to the sprocket.
• Both rings have two suns, two gears on the planets, and only one ring gear. The ring gear meshes with the smaller gear of the planets.
• In lower gears 1 and 2, power input applies to the ring of the first planet carrier. This carrier lowers down the transmission ratio, depending on which sun is locked to the axle by a pawl. The second carrier is not involved.
• In higher gears 6 and 7, the first carrier is not involved. Power is applied to the planet ring of the second carrier. Depending on which sun is locked to the axle by a pawl, two step-up ratios are obtained.
• In middle gears 3, 4 and 5, both planet carriers are involved.

The table explains which exactly rings are engaged, and gives tooth numbers:

Note that in the step-up ring (Ring2), 30+19+14=63, while the ring has 66 teeth. Also, 36+14+14=64. I saw one tooth differences between sums of sun and planets and the ring, but at the moment I do not understand how so big difference (3 teeth) can make working combination.

I found the service instruction in German, explaining which planet rings are transmitting the torque in which gear. This, plus the transmission ratios with three decimal digit precision, plus some general theory proved to be sufficient. Update: No! The numbers below are wrong. You may think, how this can be seen from them. See the real counts from the disassembled hub for correct counts.

To understand the numbers below, you must know that Nexus-7 has two planet carriers; each has planets with two bound gears. One of them meshes with the ring gear. Each of planet gears meshes with corresponding sun gear. The latter can be rotating freely, or fixed to the immobile axle with pawls, activated by the shifter. In gears 1 and 2, only the first step-down ring is engaged. In gears 6 and 7, only the second step-up gear is engaged. Read the service instruction linked above for further information.

I give values for the active sun, planet meshed with the sun, planet meshed with the ring, and the ring. Next, the exact fractional ratio is shown, and it’s decimal value with 5 digits. Last in the line is the 3-digit decimal value from the manuals. We see the rounding errors (and sometimes inconsistencies).

First ring, step-down:
Gear 1: 31, 17, 22, 69. Ratio: 69 * 17 / ( 69 * 17 + 31 * 22) = 1173 / 1855 ~ 0.63234 ~ 0.632
Gear 2: 24, 22, 22, 69. Ratio: 69 / (24 + 69) = 23 / 31 ~ 0.74193 ~ 0.741

Both rings engaged:
Gear 3: G1*G6. Ratio: (1173 / 1855) * (617 / 462) = (17 * 23 * 617) / (2 * 5 * 7^2 * 11 * 53) = 241247 / 285670 ~ 0.84449 ~ 0.843
Gear 4: G2 * G6. Ratio: (23 / 31) * (617 / 462) = (23 * 617) / (31 * 2 * 3 * 7 * 11) ~ 0.99085 ~ 0.991
Gear 5: G2 * G7. Ratio: (17 / 11) * (23 / 31) = 391 / 341 ~ 1.14663 ~ 1.145

Second ring, step-up:
Gear 6: 31, 21, 15, 66. Ratio: 1 + (31 * 15) / (21 * 66) = 617 / 462 ~1.33549 ~1.335
Gear 7: 36, 15, 15, 66. Ratio: 1 + 36/66 = 17 / 11 ~1.54545 ~1.545

The inspiration for this feat was John Allen’s table of tooth counts for various hubs. John did this by some guessing-and-trial-and-error, putting numbers in a spreadsheet with the formulas. Unfortunately his data does not include the two hubs I have, Nexus-7 and Nexus-8. I decided to leave the guessing to the computer and wrote a script, which does exhaustive search over all reasonable combinations. There are two restrictions on numbers of teeth in a working planetary gear (diameters should add up in a known way, and some counts must be divisible by number of the planets for them to be equally spaced; ask me if you want to get techy). Allowing the precision of the resulting ratio down to the last decimal number given in the documentation, the search returned just one result for both planet rings of the Nexus! I was so delighted to get such a consistent answer.

Update once again: this “consistent answer” is wrong. Here is the right one.

So I made my own from a 2mm thick rubber sheet. It is heavy and non-aerodynamic. It is heavy-duty! It makes difference when riding in the rain. It is tested. Highly recommended for bike commuters.

What to expect there? A sporty ride for 2-3 hours; this time we rode 87km in 2:40h, which makes 32.8km/h average.

View in a larger map

Almost 33km/h average speed may sound too sporty for many. But it’s a group ride, and the power for 33km/h in draught is comparable to maybe 27.5-28km/h average alone. Also, the group motivates! I’m unlikely to pedal the same distance even at 27.5km/h average because of my lack of motivation – I need a reason to push myself. When there are 15 persons hanging around, I need a reason to drop out. Sometimes there is one (too fast! ), but now I holded until the end. Of course there is absolutely no problem if anyone wants to stop or continue own way – just inform somebody in the head so that others do not think that you have some technical problem and do not stop to wait.

It was sunny, dry, and a bit over +20°C. We do not have that good cycling weather too often in Finland, so it must be used effectively!

Cycling in Himachal Pradesh: practical issues

My next plan is to publish the daybook with facts and impressions. Stay tuned.