Transmission with 2 speeds but without change
At the beginning of the twentieth century, French inventor Paul de Martin de Viviés patented a transmission system that allowed two speeds and one pedaling that could be performed both to the right and to the reverse (back and forth). He put the name retro-direct, or what is the same, back and forth.
A first version of two chains was patented in 1869 by Barberon and Meunier, while in 1903 came a new model with a single chain by the bicycle manufacturer Hirondelle.
There are different variants when running the Retro-direct system, but the most common is that consisting of two sprockets, one larger than the other that are connected to the plate through a path that allows the first pinion (the most Boy) when we pedal in a natural sense (to the right), the largest sprocket being in charge of performing the transmission of the rider when he pedals in reverse.
At the rear, the chain runs through a small pulley that is responsible for joining both chain sections, the upper (pedaling to the right), and the lower (reverse pedaling).
In this way we have the option of having two gears but without having to install any type of change, either the internal in the bushing or the external one used modernly in the systems of cassette.
With this chain system, the rider pedals right on the stretches on plain, while pedaling in reverse when facing any uphill slope.
With this configuration the cyclist should only pedal right or reverse to handle both gears. There is no need for any kind of shift system that selects one or the other gear.
Some amateurs modify the route of the chain so that the system works the other way around, that is to say, to pedal to the right when we face some rise, since that is this way with which the cyclist can develop more force on the bicycle.
By means of a pivoting spring sheave, the system allows the use of a change of plates within certain margins.
Advantages of the Retro-direct system
First, there are some clear advantages to the pure retro-direct bicycle (ie, without front derailleur that some aficionados implement as an additional gearshift system): it does not allow the chain to have any clearances or paths that allow it to exit or to hook.
The pinions mounted on the rear hub do not need any type of auxiliary system that produces the change of the transmission between one or another pinion. The rider only needs to change the direction of rotation to choose between one or the other.
It is therefore an elegant system of selection of gear in a very simple and simple.
But above all, the retro-direct bicycle is different: pedaling back to select the second gear produces a pedaling a bit rare and unusual. The musculature of the rider manages muscles different from those used in conventional pedaling.
If you decide to install a retro-direct system on your bike, you will notice that the reverse-pedaling sensations are quite different from those experienced in conventional pedaling.
We use different muscles and we use them differently in both form and form.
Disadvantages of Retro-direct system
When we pedal forward or reverse, there is always a free-wheeling pion (which does not use traction), so we always hear the ratchet noise from the drive that we do not use. It is a sensation somewhat different from that of a conventional gearshift, but it is easy to get used to.
Some people feel very strange when performing reverse pedaling. The system requires a certain learning curve, since many people have a tendency to pedal in reverse mode when what they really want is to use the freewheel, just as they would with a conventional bicycle.
It is not possible to place the pedals in a certain position to support the bicycle and prevent it from falling when we decide to leave it. However, it is a matter of becoming accustomed to a somewhat peculiar type of transmission.
Retro-direct mounting kits
There are many enthusiasts and fans of the world of the bike who choose to install for themselves this great unknown transmission system. The good news is, this is not a task too difficult or complicated to perform by any fan of the mechanics and DIY of the bicycle.
These are some of the tasks that we must carry out in a conventional bicycle with external change:
- We must install a double pinion in the hub of the rear wheel.
- Installation of a crazy wheel (pulley) on the right strap of the frame.
- We need an extra long chain. Two new chain sections are recommended to avoid asymmetries.
Apart from that, the work involves removing the devices, cables and shirts involved in the rear and forward shift for a pure Retro-direct.
My big concern was to have to modify the frame in order to install the idler pulley. I have found another solution that does not imply having to solder on the frame any type of device.
The installation of two free wheels (pinions) on the bushing is not complicated. We need the bushing to be screwed, that is, it does not carry the traditional core system for the cassette.
Screwing two free wheels into a hub is not very difficult: as it happens, free wheels and lower brackets share the same thread (1,370 “x 24 TPI, with 60-degree threads It is an ISO thread, you know …) Ross. Harrop is simply screwed to the big free wheel in the bucket, bowl on the leftover threads of the big free wheel, and the small free wheel in the BB cup. Personally, I do not feel that bowl confidence would be enough to withstand the lateral pressure free wheels have to endure, so they resorted to a special adapter on the winch with a BB wire in the shop, but made of steel and much Thicker than the bowl. But in essence it is the idea itself. If you are lighter than I am, the bowl solution will probably work fine.
Finally, installing a crazy wheel (or two crazy wheels, if you choose my retro-direct variant) is left to your imagination. If it can be soldered, it will be easy to do. If you can not do it, creative reuse of collars, composite metal rods and bicycle parts will probably lead to a solution. I did this last about a Sunday in my garage, away from the shop, without even a thumbscrew, with only things from the home improvement store location, bow saw, drill and other basic tools, so it is definitely possible.