Although I bought a new bike with the idea to upgrade my old mountain bike for more multi-day outings, fact that it is with Nexus 7 and designed for urban cycling, appear no small problem. I was in love with the frame design, but as I felt on Velorodopi 2016 – going and returning to Chatama with these gears I had no chance and on the smallest hill. And as much as was profitable and good bike, I began to regret that I bought it.
That is why after I returned from the Rhodopes I asked in an international Cyclists Facebook group, is someone have impressions and what would recommend.
In the west these bicycle gears are very popular, unfortunately here in Bulgaria are not yet known. Group members say pretty good recommendations about Nexus models, mostly about closed-type, little maintenance and their large coefficient of speed. But despite this great odds, especially at 3 and 7-speed models to be relevant high speed is taken from the low turnover on small speeds. Which in city is not a problem because there is no steep or long hills. But for touring this for me was drama. I found gears calculator and looked at what had like configuration on the bike.
That is in front 42 teeth and rear 7-speed internal crown with 18 teeth. Which gave ratio of 1.47 for first speed, 2.3 for fourth to 3.60 for seventh and rotating movement of the meter by 3.20 meters at first to nearly 8 meters of seventh speed. With single rotation of the pedals passed eight meters at a speed of 42 km / h. But on the hill a bike with 21 speeds at low speeds has a rotating movement of 1.5-1.7 meters per revolution of the pedals, allowing normal pedaling at a speed of 6-8 km / h. For me the lowest rate was twice as difficult. One of the options mentioned by participants in the Facebook group was to put additional smaller chainring at the front and so do bike with 14 speeds. This idea is most liked because with a chainring 29-30 tooth movement would fall by 1 meter, and the gear ratio of 1.00 to 3.60 to Little Venice and the big step from 0.17 to 0.48.
Inspired started to circle around shops and repairers of parts and mechanics to make the installation. But every time I received a negative answer – or no place to mount derailleur or additional chainring. It was such a model, they said, and I saw that no one was confronted with such a modification, and there is no vision of how this can happen. Once again, regretted I’m not a cyclist in the Netherlands. Hit a stone. I returned to the group and again reread all posts. Then I saw idea number two – experiment with the teeth of the rear chainring.
Changing the rear chainring is easy (in theory) and solves the problem partially. The wheel stays with 7 speeds, but raising the number of teeth at the back, reduction gear ratio and consequently the effort, speed, etc. Again calculator showed that it is not a bad idea to try a 21 tooth. And I ordered.
The first attempt at change was not successful, not because the chainring did not it fit, but because it turned out to be wide. It turned out that Shimano rear sprockets manufactured for internal speeds is up to 18 or 19 teeth. Those with more teeth are other models, including BMX and hence different chains. It writes on the package of the chainring that is 1/8 chain, but when I do not understand…
I decided that unless the chain must change and front chainring which and started looking. But this proved problematic and complicated. However impatient I tested how fit a piece of 1/8 chain on front and took to fit in all the teeth. So it had only new chain! I went to the store and took one BMX type. Again put the 21 tooth, flung new chain, which proved that must be shortened with very little (actually can with at least one or two units, but left to have if break) and hop, I think I was ready.
In theory, the transmission ratio should be from 1.26 to 3.09, and the rotation of the pedal correspond to 2.74 meters for the first speed to 6.71 on the 7th. And if the low speed difference is only 50 centimeters, it went down a lot on high speed. I fell down one speed. Whether I had won searched low speed for hills and what was lost. Surely now the hills were easier to climb, I think that with this method, it was optimum down. In practice, the feeling was like more than one speed down and around town already starts from the 3rd or 4 th speed as most of the time I drove a sixth and seventh. But not looking for high speed but constant one. Now as a happy medium is the sixth speed of 5.8 meters per spin and hypothetical constant speed of 30 km/h on flat. What I liked most is that acceleration of speed feels better. I guess I’m reduced rates range. Original range that total reaches 244%, it is now less like as a Nexus 5, but separated seven times. This combined with my favorite advantage of internal gearswhich is to switching on standing, gives me starting and acceleration as a “sports car”.
However, this combination is not “original” and shows discrepancies in gear. Especially common type of idling appears in sixth speed, not sure if it is set well the cable or I missed the moment to switch gears.
However, from modification I drove only once a long distance. And I was pleased both from distance and from input effort.