Monday, November 19, 2012

Shimano Alfine 11

           As anyone who knows me will tell you, I am a big fan of internally geared hubs, from the old Sturmy Archer systems through to the new crop from Shimano, I think they are the best option for anyone who is a recreational rider, they are hassle free, need very little adjustment and are easy to keep clean. Another plus for people that transport bikes in the back of a car or pick-up is that there is no derailleur hanger to bend. Nothing screws up the shifting quite as quickly as a bent derailleur hanger.
          However, as much as I am a fan of internals for Recreational riding I have never recommended them for aggressive mountain bike applications. Except for one model, The Rohloff 14 speed internal hub. These hubs are in a completely different league and that goes for price as well, a Rohloff setup usually runs around $1400.
          Recently though Shimano has stepped up the game a little, the new Alfine 11 speed hub, although looking similar on the outside to the 7 and 8 that preceded it, are completely re-vamped internally. The 11s are even running an oil bath system just like the Rohloff. A sign that things have changed somewhat is the emergence of some cyclo-x rigs running the new Alfine 11. The hubs are also compatible with the new Gates belt drive setup. It is a bit soon to tell if these hubs have the durability required but initial feedback seems quite positive. We have a couple of projects in the workshop at the moment, which will feature a little later here on the blog, and an Alfine 11 is definitely on the short list as the drive choice.
Alfine 11. Total gear ratio of 409%.

Wednesday, November 14, 2012

Bottom Bracket Conversion

          A common problem that arises nowadays, with the influx of new bottom bracket standards is what, why and how to move from one system to another. With the threaded bottom brackets of old there was not many issues with a change to the newer outboard bearing systems but, with the move to frame specific systems, the switch is no longer as simple or, in some cases even possible.
          One of the most common issues is the press fit systems more specifically the PF30 and BB30 standard. Whilst both these systems are good and make for a solid crank interface often the issue arises because the frame has been purchased as an upgrade for a specific build kit already owned and the owner needs to convert the bottom bracket over to a threaded external system. There have always been a couple of options for this however, the good folk at Praxis Works, makers of our favorite chain-rings, have come up with a superb new conversion kit for the purpose.
         One of the biggest problems with conversions and even the press fit systems as a whole is that they tend to creak and groan. This is because the adaptors are, like the bearings, seperate from each other. With the Praxis system the cups are actually conected to each other by means of a threaded sleeve. This sleeve is very tightly machined but also as it is installed it flares out and takes care of any wiggle that may cause problems.
          If you are thinking of doing a conversion or have already performed a conversion with another product take a look at the Praxis system. It is the only way I will go in future. If you want more information or need a kit just let us know as we are Praxis dealers and use the full range of their products.

Thursday, November 8, 2012

Airless Tires in our Future

A Colorado engineer has come up with a new tire design. Not just another new tread pattern but a whole new approach. Instead of the usual threads encapsulated in rubber he has gone for the latest in carbon nano-tube technology. Result is a tire that mounts directly to the rim and requires no tube or air pressure to give it shape. The nano-tubes can be adjusted to give different ride characteristics, much like adjusting air pressure, and are covered in the rubber coating with the tread pattern. Not available as of yet but I am sure it will not be long before they are filtering through into the bike shops. In the meantime have a look at the video. If nothing else they look cool.

Sunday, November 4, 2012

Park Tool Goes For Gold

           Anyone who wrenches on a bike knows Park Tool Company. Venture into the back of any bicycle workshop and it will be a sea of blue handled devices as far as the eye can see. Our workshop is no different. Well the good folk at Park will be celebrating their golden anniversary in 2013 and to celebrate the fifty year milestone they are releasing a limited edition gold plated Y wrench, or as it is called in our workshop the "3 pronger." This tool is never far from my hand or pocket and is used more than any tool on the bench. Anyone looking to honor their favorite bike mech should look no further...
The mainstay of all bike mechanics...

Friday, November 2, 2012

Watts to Horsepower

A good friend of mine recently posed a follow on question to the watts article that appeared here some time ago. He had recently read about a new small car that had an engine power output of 6.5hp. Now, Tom is keen to know if that kind of output could be supplied by pedals and a couple of willing and fit passengers. So this post is for you Tom.
            A good place to start is by looking at the definition of horsepower. Basically the answer is in the name. Back when the steam engine had just been invented there was born a need to be able to measure power. What was this boiler shaped thing, puffing steam capable of? It was all very well turning up at a mine with one in hand but unless you could say to the mine owner that this had the power of something that they already knew, it was always going to be a tough sell. Thus horsepower was born. A guy named Thomas Savery came up with the horse comparison around 1702. He used it to good effect and sold many a steam unit by saying how it did the work of 15 horses. A problem arose quite quickly however, with competing manufacturers adding an extra horse on the figures here and there. All I can fathom is either some out and out monstrous sized horses were around back in the day or the figures were being fudged a little. So along came a standardized measurement of an average horse's potential, devised by Mr. James Watt the Scottish engineer. Using a gathering of fit dray horses, a mill wheel and a measured weight they ended up with the following. It is still the standard today. They fathomed that the average horse could produce 33,000 foot pounds per minute. Anyone that knows horses will tell you that those figures are a little optimistic, especially for a longer, period but those are the numbers.
              So that is the horsepower figure and Toms little car is producing about six and a half cart horses worth. The more astute of you are probably seeing a problem already, but I will continue. How does a human stack up with a horse? And can we fit them all in the car?
              There is a basic conversion for watts into hp., I won’t bore you with it, suffice to say that 1hp is equivalent to roughly 745.5watts, sustained, therefore the 6.5hp car is equivalent to 4845.75 watts. Going back to the original post we can see that a guy of reasonable recreational rider fitness, weighing in around 185lbs will be able to sustain approximately 196.8 watts over a period of an hour or so. Looking at these figures we can see that the car will need to be the size of a school bus to accommodate our human engine. The figures look a lot better if we can convince a dozen or so tour guys to be the engine but even then it is going to get cramped and gas, although expensive, is still cheaper than steroids.
              Tom had already fathomed this out and his main question is. Would it be possible to power batteries by pedal power that in turn powers the car with the necessary wattage and equivalent hp? Answer; yes, hooray. Not so fast, yes it would be possible for pedals to charge the battery bank but it would take a long time.
Using Ohm's law (amps=power divided by voltage) we can see that the average person could quite reasonably produce a 10amp charge rate, requiring about 120watts output, this is about the same as your average car battery charger. So, looking around at some electric motors it seems that the average requirement for a 1hp output motor is around 1000 watts. I know I said that 1hp = 745 watts but there is no such thing as a 100percent efficient motor.  
Watts ÷ volts = amps. Therefore the above example would mean 1000 ÷ 12 =83.3. Your average car battery can supply about 50 to 80 amp hours of capacity each battery would then require 5 to 8 hours of charge time at your pedal power 10 amp charge rate (divide battery capacity in amp hours by the charge rate).
Our 6.5 hp car would need approximately 8 batteries. I will leave you to work out your charge routine… Now I shall go and lay down, all this math has given me a headache.