Can someone help me understand torque sensor PAS?
 

I currently have a rear hub motor with cadence PAS. With a 52t chainring (recumbent trike) I mostly use my 13t cog on the flats. The assist is dialed down in the software so that I have a decent amount of resistance. This is consistent no matter what. So if I want to work hard or go faster I shift to my 11t cog, if I am tired or going up an incline i shift to my 15t cog to make it easier. The amount of assist stays the same since I'm in level 1. Now if I change to a mid drive system, I don't understand how that works. As I ride the flats and get some speed up, I use less pressure on the pedals so would i slow down if I wanted to spin at my typical rpm of 55? Would I experience ups and downs as i ride using the same cog because I push harder as I start out and then spin more lightly as I get going? I find this confusing. I am trying to figure it out because I have myasthenia gravis which affects my muscles the more I ride so I'm trying to see if a torque sensor system would or would not work for me. Would I want a smaller chain ring with a torque sensor or the same size I have now? Does the gear inch preference stay the same? Say I am cruising at 55-60rpm and then shift to a lower gear to go up an incline, well that lower gear would mean I'd spin faster with less pressure on the pedals, so would i get less help up the incline? Seems kinda backwards to me so i'm pretty sure i don't understand how it plays out in real use. Any explanations would be greatly appreciated. thx.
Edited to add; i am not going up big hills but want a mid-drive to make rear flats easier on my trike as well as improve chain line.

your spinning is pretty slow so your not going to get the most out of a mid drive. a torque sensing mid drive feels like a regular bike but it takes less effort. the harder you peddle the more the motor will help. your speed is from the gear choice and your cadence just like a normal bike. How much effort it takes is from the level of assistance you choose. so you would change the assist level to meet the level f effort you want to put out. on my bikes I have 4 levels. so I can go 20mph putting out 90 watts on the highest assist to close to 200 watts on the lowest level but I am still peddling the same speed and in the same gear.

For DIY the most popular systems with a torque sensor are Tongsheng (too many problems for me) and CYC, while Bafang makes the BBS02 and BBSHD which are RPM based. FME, AFICT (and I could be mistaken), the torque based ones provide assist based on the pressure you exert on the pedals, while RPM based on the speed you're pedaling. The great feature of the DIY systems is the amount of assist for each level can be programmed specifically for each individual.

I'm not looking to get "the most" out of the mid drive. Tbh i rarely go over 15mph. But changing a flat on a recumbent trike with a rear hub motor is a gigantic pita!!! It is worth the swap just for that, but also the chain line will be improved - recumbent trikes have long chains and a mid drive will help with it. I don't change the assist level on my cadence PAS system, I leave it in level 1 all the time, and change the effort required thru gear selection. Would that be the same on a mid drive torque system? Because the other option is the Bafang which is a cadence sensor mid drive, instead of the Tongsheng torque mid drive. i'm looking at a 36v. 250w for either, I don't want or need much power.

when I mean the most out of it I mean the most efficient. mid drives work best with a higher cadence then they are the most effort. Plus you are too it's easier to put out 400 watts if you're spinning 80 rpms then 40 rpms.
You would have to go to the biggest Bafang to get torque sensing. the 1000 or is it the 1200 watt? but their newest one has it. if you can live with the chainlink maybe putting a good sealant in the rear trie or going tubeless would be far easier and cheaper. There is torquer sensing for some Bafang hubs.
but torque sensing is going to be like riding your bike like you did without a motor. I shift all the time to keep my cadence even and I choose the assist level on how my energy level is that day. so I can work harder or easier in the same gear.

Ok, so I think i get it. With a torque system, if I ride with a 55 rpm cadence pretty much all the time, then going up hills or against wind, I would have to increase the PAS level to a higher multiplier. Dropping down one cog wouldn't do it like it does with the cadence sensor.
Is that right?
So the difference is whether I change the pas levels or not, which then makes me wonder about the effect on range. Since I stay in level 1 with my cadence system, i get great range. But supposedly torque sensor systems are even better on range - would that be true
even if one is going up and down in assistance levels? i am not about speed, I am all about range and consistency. if I went with a torque system it would be the TongSheng; if I go with a cadence system it will be the basic Bafang BBs01. Anything else would be beyond overkill for my needs.

Right now the torque sense system worries you because you have no experience with it. If you got one you would figure it out just like you did the one you have. I have a TongShen motor on a cargo bike project that has stalled. David Hall has put a lot of time in designing systems that work well for a lot of people. I don't think you can get 250W even if that's all you want. Go big, or go home they say. Overkill is rarely a problem. You usually get a better built product and since you aren't pushing it to it's limits you get excellent performance and longevity.
Edit: I have heard it from too many different sources to continue arguing with it: torque systems are very easy to use. 'Natural' for want of a better word. You just ride like you always have. Start off with a low level of assist like you like to do and if it isn't enough you will know. It will probably be fine. To go faster you gear up. If your speed drops (going uphill) then gear down like you would (should) add more power. It will do that automatically anyway but there will be times when that won't be enough and you don't want to bog the motor. That's another reason to get the 500W motor. It can take some bogging at low speeds. Edit 2: Flats? Flats have not crossed my mind in a very long time. I don't carry tubes, patches or pumps on commute or errand rides because I have invested in tires known to be highly flat resistant. With a motor you shouldn't have to worry about the ride performance of tires like Schwalbe Marathon Pluses and if you wanted to put Rhynodillo or Mr. Tuffy tire liners in a Continental Gatorskin tire you would have an essentially flat proof tire. FWIW.

My trike has a mid drive Shimano torque based pedal assist, 250W and 36v. It has three assist levels, a 44T front chain ring and a 11-36 ten speed cassette. To my perception, it feels like a regular bike. I use the lowest level of assistance MOST of the time, and I feel like it basically compensates for the extra weight of the trike, battery and motor at that low level assist. I regularly use all ten of the cogs on the cassette, and also use my cadence readout to stay at my optimum pedaling pace of 65-70. Changing the power level because I'm going up a hill is not something I do. I gear down to lower gears on the cassette, try to maintain my cadence and light pedal pressure, just like I used to do on my regular bike.

I seem to get the best range by pedaling with a light pedal pressure, low assist, and whichever gear is appropriate. To increase my speed, I pedal faster until I can shift comfortably in the next higher gear, then repeat until it takes too much effort to go faster. I average 12-14 mph, depending on how much I want to work at it, the wind, etc. At the end of a 48 mile ride, I feel like I used to feel after riding my regular bike for the same distance: pretty tired.

If I turn the assist OFF, I can still pedal, but it feels like I'm pedaling a fully loaded touring rig, maybe 50-60 pounds, which is a lot when you're used to a 25 pound DF bike. I ran my battery out of power one day and pedaled the last four miles with no assist. I think I averaged 9-10 mph on that section.

I have no experience on a cadence based system, but I think I have the best, most natural feeling pedaling experience with the torque based assist.

its the same with our bosch powered tandem. but usually when we clip hills I turn assist up but I don't have super low gearing till I just put the 11-42 on we did it with 11-32. but we can climb 18% grades. but we ride and shift like a regular bike.

Ok that really helps a lot! Regarding the chain ring, in order to feel any resistance and get exercise with my current system I need the gear inches provided by my 52t/11-13t combo. Some of the mid drive torque systems I've looked at offer a 52t but some top out at 44t. Do you think the torque sensor system is so much more tuned to effort that i would want to go with the 44t rather than a 52t? With my hub motor turned off and no assist, I can still easily ride with the 52t and my 15t cog at 10mph. I've ridden a number of e-assists where the gearing just isn't high enough so you basically "ghost pedal" and I don't want that. But it sounds like that can't happen with a torque system, so I'm wondering about whether to drop down the chain ring size. What do you think? Also, you said you are pretty tired at the end of your ride.....since i have a medical issue that makes my muscles deteriorate while I ride, would upping the PAS level towards the end of my ride compensate for that do you think? Does upping the PAS level mean you can put in less effort to achieve the same speed?

you would use more of your gears. I doubt you would need a 52 but it depends on your cadence. like on my commuter I have a 46t and 11-32 and if I had enough energy I could get it up to 28. but I also try to keep my cadence at 80 or so rpms. since your peddling slower the 52 may be what you need. or you will just use some of the smaller cogs. but yes if your feeling tired you can crank it up. the ni was so sick I could not put any effort into peddling in turbo I could go 20mph and keep my heart ride around 90 so like walking. I can go 20 and get a hard workout or no workout.

Lol, regarding flats....I have a marathon plus on my rear tire and have gotten 2 flats. just bad luck and too much construction crap in the streets. i have rhinodillos on my two front tires now, after a bunch of flats, but front tire flats are a 2 minute fix so no big deal. On a tadpole trike they are super easy. The rear is a pita however and not fun at all and my muscle weakness makes remounting the wheel challenging sometimes.
i am probably being super cautious because this is my only means of transportation, my car basically, and that coupled with my medical situation means I can't get it wrong. With a cadence based hub system, getting a too powerful system makes it impossible to reduce the assist enough to get real resistance and exercise - it becomes more like a moped. i'm getting from what you said that this would not apply to a torque system? i'm looking at this one:

Eco+ TSDZ2B with Open Source Firmware (250w-750w+)

cant you turn down the power a bit? I know you're kinda stuck with speed being the limit. I tired a cadence system and it was like no way it feels so unnatural.
I have not tried this in a tubed tire. I did not have any luck with a sealant over 50psi. but when I went tubeless on our tandem (dropped the marathons because of the harsh ride) I used this sealant and it works well at 70 psi.
https://shop.flatouttire.com/collect...mall-tire-16oz

I'm reading that with something like the Bafang BBSxx I can set 9 levels of PAS (cadence) and input the exact amount of assist for each level with their programming cable. I'm beginning to think this might be the better choice for me. I don't spin fast. I also use the throttle
for a quick blip to start off from stops (bad knee - i am old) and don't really want to have to down shift and upshift riding on city streets. 90% of my riding is on flats, city streets and the occasional pathway, and i used to ride a single speed just fine when I could ride 2 wheelers
and loved the simplicity. i do very little shifting with my hub motor, just one cog up or down, period. With a torque system it sounds like i would need to shift a lot? I think the torque systems sound great for folks who ride varying terrain.

Respectfully, you are overthinking this. Go re-read the Dead Grandpa's post again. I think it is a succinct summation of what you can expect from a torque sensing system. The only people they don't work for are folks who need pavement ripping power from 1000W systems that are very hard on the plastic final drive gears of the stock TSDZ2. I had the option of getting a metal final drive but if that breaks ... $$$$. Shifting should not be that much of a chore that you avoid it. You may not have to do any shifting at all with a TSDZ2, I don't know where you ride. I do know that the TSDZ2 is available with a very neat torque arm that the Bafang Systems do not have. If you specify that your kit is for a recumbent the torque arm will be supplied and it grabs the boom in such a way that the motor cannot rotate to the top of the bottom bracket.

It seems that you and I pedal very differently. I live in Coastal Carolina, where the terrain is incredibly flat, yet I routinely start off in my lowest gear to get the trike moving, and then move progressively to higher gears until I'm going at a comfortable pace. I shift gears often, just as I did when riding non electric two wheeled bikes. (Incidentally, I rarely, if ever, used to stand on my pedals.) I find that mashing at low rpm and high effort depletes my muscles more quickly than higher rpm and lower effort.

With a torque based assist, I can pedal with a weak or strong effort, but if I slack off to "ghost" pedaling, the motor will cut out. Since my goal is to gain endurance, rather than build peak muscle strength, I change gears to gain speed while I maintain a relatively constant effort. I've been working harder for the past couple of months and my average speed has increased measurably. However, the battery doesn't last for as many miles as it used to when I pedaled with lighter effort. As long as I put more effort in, the motor also seemed to match my increase in effort. But again, I'm shifting a good bit. I round a curve and get a strong burst of headwind, and I downshift one gear to keep the same rpm and pedaling effort, even though I may slow 1 mph or more.

And although I have "bone on bone" in one hip and walking is a painful chore, pedaling with my light effort methodology is not uncomfortable in the slightest. I regularly ride 42 miles, and 50-60 milers are not uncommon.

I ride the Bay Trail and it is mostly flat but a great deal of my riding is city streets since this is also my car. So it is one or two blocks and stop kind of riding. With my non-motorized 2 wheelers i found it easiest to just find a gear i could take off from a stop in and also pedal the flat in without shifting every block; I ended up using my geared bikes like a single speed. Watching for cars is more than enough to focus on, lol. I also am not riding for endurance because that's not an issue for me, but due to my medical condition i DO need to push myself for as much of my ride to build muscle strength (until i get too tired). So it is different. Spinning lightly is what I do towards the end of my rides when i am tired, but I need to push against resistance at the front end of rides to maintain muscle tone and build what i can. And I'm just not sure the torque system is right for that kind of riding. I really appreciate your input and perspective - any more thoughts you have would be great, thanks!

Yes I am probably overthinking this, but it's not something i can reverse if i get the wrong thing; my budget will allow just one conversion. I use very little power, I rarely go over 15 mph, I have a slow cadence around 50rpm because i need to use my bike to keep and build my leg muscles due to my medical condition (i'll save the long explanation). Much of my riding is stop and go city street riding since it is my car as well - one or two blocks, stop, take off, rinse and repeat. As a result, I found picking one gear and riding like a single speed worked well for me on my 2 wheelers - easy enough to take off from a stop and strong enough to get some resistance while pedaling. Speed didn't matter because i was stopping so often. Shifting up and down was just an annoyance every couple hundred feet. Now I also do ride the Bay Trail for fun and exercise but my city riding is the priority because i have to be able to run all my errands and get places. The Trail rides are optional. i may have freaked myself out a bit when reading an article about mid-drives: How To Ride a Mid Drive Ebike Without Breaking It – Tales On Two Wheels

I read every post again. Seriously, the best thing for you is work with the system you have already invested money in. If rear flats are a pain then make your rear tire flat proof. It is possible. The use protocol you describe for your riding cannot be as effective as a systematic program of weight training in a fitness facility. Then when you ride you can focus on riding as transportation period. A 52T times anything is an immense gear. You say you don't use much power. Have you ever tried to take off with no power at all? I wouldn't be able to do it in a 52 x 13 gear! And your cadence cannot be 55rpm much of the time. Quite a bit of the time you are probably barely pedaling. I am curious as to how you got here. Did a medical professional tell you to buy this e-assist trike? Seems to me you could do a couple of things to make you life a lot easier. You could (like I already said) use a gym for ALL of your fitness, muscle building and health maintenance needs, and use a non-powered bike for transportation, maybe a folding design to use in tandem with Mass Transit for longer trips. You could probably get an electric scooter for local transportation, and it might not cost anything. No flats. No exercise either, but I really don't think you get much from the system you have at present. Besides that is what the gym is for.

I'm not going to explain my entire medical situation to you except to say you are incorrect in your assumptions, very much so. Thanks anyway.

I did not intend to offend and I made no assumptions. I've asked questions, but not about your medical condition.I do think you are best served not spending ~$500 (minimum) on either a Bafang or TongShen mid-drive system simply because it will make rear wheel removal easier. I'll leave it there. Best.

I'm just saying your suggestions about a gym do not apply, for reasons I won't go into. And i also want a mid drive because there are issues with the current chain line. My mechanic has done what he can to address them but there are issues that cannot be remedied. A mid drive would fix all that, make flats easier, and let me get rid of the marathon plus on the back and put another big ben on which really helps with suspension comfort, so several reasons, lol. All good though, thanks.

I agree with you, now understanding better just how you ride. Based on what little I know of how the cadence based system, it might fit your needs. I should stress that I have tried to explain how the torque system works for me, but I'm not an authority by any means. Good luck and keep us posted.