• 26th June 2006 - By greg

    June 26

    June 26, 2006

    162 speed M5 and Critical Power Streetliner doors and foot holes.

    My trusty M5 has been upgraded to a 162 speed with the installation of a Shimano XT 9 speed mid drive (jack shaft, intermediary drive, intermediate drive, or a whateveryouwanttocallit drive). The reason is mostly because with the standard gearing set-up and when the Streetliner fairing is on, I was in my fastest gear and spinning like nuts.

    There are easier ways to add gear inches starting with simply adding a larger chain ring in the front. The first problem with this idea, is that the Shimano XT mountain bike rear derailleur only has enough capacity for the 53 tooth front ring. If the front ring was any bigger, I would need to build a custom cage for the rear derailleur to take up the excess chain when using the larger cogs on the rear. I could go smaller with my rear cassette range, but I would lose my mountain climbing 34 tooth cog, and since this is a ‘street’-liner, and intended to be used on the average roads around here, I will need to climb hills. In fact, I’ll need an easier hill climbing gear due to the fact that the bike will now weighs much more with the fairing on.

    The other idea was to replace the rear hub with a geared hub – a planetary gear system like a Shimano Nexus or a Rohloff The problem with that idea is that I would not be able to put my Zipp disc wheel on because it has a hub bonded into the carbon.

    A third idea was to go with a geared bottom bracket, but then I would lose my SRM, so that wasn’t an option.

    A 9 speed mid drive has many advantages. The long floppy chain is now gone – it’s a nice, tight compact system. I have WAY more gears to choose from. I can achieve any cadence I want for any kind of road grade and speed – a nice feature. I have PLENTY of upper end gearing. Way more than I would ever need even on the steepest down hills. And lastly, a mid drive could offer easier mountain climbing gears – larger range on BOTH the upper and lower end.

    The disadvantage to a mid drive is the loss in mechanical efficiency due to all the extra chain routing and gears. Using the SRM, I was able to measure that it took 6 watts just to turn the whole system over – not including the wheel. That is, when I am freely coasting down a hill, and the SRM is zeroed out by spinning BACKWARDS, I require 6 watts just to spin the peddles around. That’s not really as high as it seems because zeroing by peddling backwards tends to set the SRM to about 2 to 3 watts higher than actual. The typical way I set the zero offset is by zeroing it while spinning forward freely (while coasting down a hill). The proper way to do this (and I will try it within the next couple of days) would be to set the zero offset with the long chain (no mid drive) while spinning forward. This would set the measurement at ZERO watts when freely spinning. Then I would replace the long chain with the mid drive and freely spin the cranks and watch to see how many additional watts were required just to move the mid drive around. This would give me the additional ‘cost’ in watts to turn the mid drive system compared to the standard M5 long chain drive. I am thinking it will probably be about 4 watts – not too bad.

    I considered many possible locations for the mid drive and selected a spot just under the seat back. The best place for it would be to take the place of the two chain pulleys that route the M5 chain under the seat to the rear wheel. Since one of these chain pulleys is on the tension side of the chain, this is already contributing to a mechanical efficiency loss, so replacing it with a mid drive would make sense. After considering this option, I decided that I couldn’t do it because the derailleur would hand down too far below the bottom of the streetliner fairing shell and interfere with my right foot getting in and out.

    The mod to the M5 frame was simple – a rectangular tube notched and tig welded to the M5 main mono tube. I had an old Shimano free hub that I had removed the palls from so that it rotates both directions. An axle through the hub and through the rect tube secured the gear cluster to the frame.

    Then I made a derailleur hanger from an old rear chain stay. This bolts to the axle. It was originally my intention to secure the front end of the axle with a ‘fork’ that was welded to the frame, but after a few test rides, the mid drive seems pretty secure with a mono axle support.

    After a good 3 hour test drive, everything seemed to work fine except for the chain kept coming off the large cog on the mid drive when the chain was on the largest cog on the rear wheel. The reason is the chain angle in that gear wants to pull the chain off the mid drive. The other issue was I didn’t have a granny gear for climbing. I have this huge freaking hill called Springbank hill that I need to climb on every ride, and climbing that steep grade with 2 gears LESS than what I typically use had me going about 8 kph and 30 rpm and way over 200 watts. Too much mashing and I knew it would only be worse with the weight of the streetliner fairing on. So, back to the shop I went and figured out a totally IDEAL gearing solution!

    I found an old Shimano Ultegra 11-21 road cassette and removed the riveted gears off of the main large cog assembly. Then I cut away all of the excess aluminum and ground it smooth and flat. This slips right onto my mid drive free hub and is 10 teeth SMALLER than the largest gear on the mid drive which is 32. In fact, it’s a few teeth smaller than the second largest gear on the mid drive also.

    I couldn’t get all of the other gears onto the free hub, so I put on a good selection of smaller gears so I wouldn’t lose my high speed gearing. So now I have TWO easier hill climbing gears 5 additional speed gears – the perfect set-up for a streetliner! My gearing is now as follows:

    Front: 39 – 53

    Mid (in): 12 – 34

    Mid (out): 21

    Rear: 12-34

    If the Critical Power fairing shell was on the M5 (CdA .03) then I would have the gearing to go 100 kph at 100 rpm and still be able to spin up the steepest grade.

    The other problem that I fixed was to stop the chain from coming off the mid drive with the addition of a UHMV plastic chain guide.

    To complete the streetliner, I reinforced the fiberglass shells around the door and foot hole cut-outs, then made some neoprene covers for them.

    I contact cemented corrugated cardboard patterns to the areas I wanted to reinforce on both shell halves. Then I painted epoxy over them and waited for the epoxy resin to get sticky, then I players some carbon fabric over them and completed the wet-out. In theory, this is a good way to get your composite fabric to stick to your form without having to use a vacuum bag. In reality, it is very tricky because when the quick-set epoxy starts to kick, it kicks FAST! In fact, I left my shop for 20 minutes and when I returned, the epoxy that was exposed to sun shining in through my shop window was as hard as a rock.

    To make the doors, I stretched some neoprene over the door openings and traced the door shape. Then I ironed on some velcro to the perimeter of the neoprene, and contact cemented the mate velcro strips to the inside of the door.

    The neoprene stretches over the opening on both sides of the shell nicely and is pretty easy to cover or open a bit while riding.

    I also bonded some neoprene covers for the foot holes (not shown). And finally, I formed a structure to hold my windshield from flopping around. It’s a strip of SINTRA plastic that is cut to the same general shape as the back edge of the windshield and then heat formed to curve around and glued to the PETG windshield.

    Today or tomorrow I am planning on taking the Streetliner with it’s NEW gears out to highway 22 and getting some watts / speed / CdA data.

    Less than a month away!!!

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