Moe Zhoost

I'm thinking about adding a mid-drive system to my recumbent trike and was wondering what changes I'd want to make with my gearing. Currently I have a 3x9 system with a range of 19-100 gear inches. The mid-drive conversion will replace the triple crank with a single ring (probably 42t), which if I keep the rear as it is will give me a range of 32-92 gear inches. I'm not concerned about the high being reduced, but wonder if I'll be ok with the not-so-low gear, given the e-assist. I know that there are many variables, but with with something like a 750w Bafang motor could I expect enough assist to easily compensate for losing the lower range I have now. If so, would it be possible to go to a closer range cassette (say with a low of 35-40 gear inches) so I can get rid of my long cage derailleur (which sits about 2 inches above the road)?

Comments, opinions, and advice are welcome.

DeadGrandpa

You don't mention how hilly the terrain is where you ride, but assuming you aren't talking about mountain grades, you should be fine. My e-assist trike came with a 44T front chain ring and an 11-36 ten speed cassette. I get along fine on rolling hills and, of course, the flatlands. If you are in the mountains, you might want to get a 38T front chain ring or possibly smaller, depending. My mid drive is 250 watts, and I wouldn't want a more powerful motor. From what I read, over dependency on the motor when a lower gear is not available leads to motor burn out. I use the motor to assist my pedaling, not in place of pedaling, so I'm working pretty hard on the climbs.

If you haven't tried a motor with torque based assist, such as the Shimano eSteps, I strongly recommend you do so before buying a cadence based electric assist. My system has no throttle and none is needed. --- Hope that helps.

Edit -- The clearance of the derailleur isn't a factor when I'm on pavement. Off pavement, single track trails might be an issue, so an IGH such as Rohloff is probably the way to go for rougher terrain.

fooferdoggie 

our Bosch is 250 watts on our tandem and we have a 46-32 and can climb 16% grades and short 18% grades. a mid drive will do a lot for you.

Leisesturm

There are not many of them but 2x mid-drive systems exist. I am building one. But the 32 - 92 inch drivetrain sounds pretty workable. I've never worried about derailleur cages and 20" wheels. Maybe on a Delta where it is just hanging in the breeze but tucked up alongside the rear wheel it should be just fine.

2old

I have both BBS02-equipped (cadence sensor) and Yamaha (cadence and torque sensors) hardtails, and the cadence works fine for me, and usually is the bike of choice. Tong Sheng has a mid-drive for DIY (TSDZ2), but I've avoided this system because there have been many reports of failures. For extreme off road conditions I've used a 30T front and 11-28 rear.

Moe Zhoost

I agree completely about the torque sensing systems. I used Bafang as an example because folks seem more familiar with it. The one I plan to use is the TSDZ2 with torque sensor. I installed one on my wife's bike 3-4 years ago and it's worked out great. Re: the DR clearance - I've never snagged it roughly so probably not an issue. It does tend to collect a lot of pine straw on some of the trails that I ride.

I saw an account of where someone added a granny chainring up front just to have available in the rare occasions when standard gearing is not low enough. He ran it without a front derailleur and shifted by moving the chain tube by hand. Sounds like it would work; however I'd like to stick to a 1x arrangement if at all possible.

The TSDZ2 on my wife's bike has worked beautifully over the last 3-4 years. It's the stock system, not the open-source firmware version so, perhaps that's a plus for reliability. The common failure I've heard of are related to the plastic drive gear stripping. The newer motors come with a sturdier composite gear that was designed to eliminate the stripping. One may also install a metal gear that is bomb-proof, though noisier. The other failure is over heating. This is mostly caused by tweaking an OSF system to use higher voltages and amperages. Hotrodders will always push the envelope.

I didn't add in my first post that I'm limited to a 26t big cog. My trike (ICE Sprint) had a Shimano Capreo hub with a 9-26 cassette - It's days are numbered, though since replacements are hard to find for this discontinued product. The future will bring a new wheel with maybe a Rohloff, but probably an Alfine 8 or 11. I'm a Sturmey fan so I've also been looking at their 3 speed hub that accepts a 9-10 cog cassette.

Anyhow, while crafting this post, I had the light bulb go off: I can do some experimenting on my wife's bike to gain some knowledge about low gearing at different levels of assist. Don't know why I didn't realize this before.

Thanks all.

linberl

If you have a lot of flat ground you may find yourself spinning out at 92 gear inches depending on how much assist you dial in. It can create "ghost pedaling" where you spin a little and stop and spin again to keep the motor going but there is zero resistance so you can't spin fast enough evenly. I've had to increase the high on each bike I have added assist. And I'm not a strong rider. A torque sensor would possibly negate this issue, I've only had cadence sensors, but I'm not entirely sure about that. Just fyi if you ride flats a lot.

Calsun

I replaced the 11-44T cassette on my e-bike for a 11-34T that provided closer gear spacing. I also replaced the rear derailleur for a Shimano 105 one that has a medium length cage that handles up to 34 teeth. I made the change after a month of riding and realizing that I did not the ultra low gears with the pedal assist.

Moe Zhoost

So I thought I had posted a followup but it's not here so I guess I forgot to hit the post button. My experiment with my wife's bike (with TSDZ2 motor) was enlightening. On my test hill a 30 inch low was challenging but with assist set at 3 of five I had the same level of challenge with a 50" gear. I am now convinced that I should indeed focus on the high range and not worry so much about the low. My 9-26 cassette will serve for now with the right front chainring (tbd). After I've had some miles on the conversion I'll have a better idea about which way to go.

Thanks all

tds101 

Post pics please,... Visuals are something I totally look forward to seeing.

Moe Zhoost

I'm still wavering about whether to spend the money on the conversion, but if I do, I'll do a post about the process.

fooferdoggie 

ya my trek came with the same gearing. I have debated on putting a medium cage on it as it can get clunky compered to my bulls with the same gearing. but I put that 11-44 on our e tandem there it shines.