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Can one go too big?

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    Can one go too big?

    Hello. new member here. I was wondering what the disadvantages would be with going with a motor that may be a little large. I've read plenty of articles discussing picking a motor size, but all basically say the disadvantage of a larger motor, is a larger battery/ more consumption.
    To me this only sounds true if you use the motor to its max. Minus a little more drag with a slightly heavier motor, could you not regulate a 1000w motor with 500 watts to get close to the range/speed/ efficiency of a 500w motor? Still leaving that extra 500w potential if need be?
    I am planning out a build on a bike I will use for commuting and fun. I live in a fairly rural area, so there are some distances I would like to get this thing up to some decent speed. Not to mention I am a gearhead who is constantly building performance cars and bikes, so I dont think I'd be too content with a little 250w bike.
    I guess what I'm asking is, how much is efficiency compromised with a big kit? Apples to apples, does a bike kitted with a 1kw motor vs a bike with a 500w motor goung the same distance/ speed terrain, use the same watt hours as each other (again, figuring a little weight drag of a heavier motor)
    Last edited by offalot; 10-06-2016, 08:28 AM.

    I hesitate saying this, being very much a newbie myself, but at least with BBS02 versus BBSHD, I think right now you have more chain/belt line & gearing flexibility with the older BBS02 (if you are limited to using off the shelf parts).
    Last edited by ncmired; 10-06-2016, 09:04 AM.
    BBSHD / BBS02: Nexus / Alfine 8: 1 2 3 4 5 6, Rohloff: 1 | PHOTON: Alfine 8: 1 2


      You can calculate that stuff with the motor simulator on the site.


        Get the largest motor that you can afford in the first place and then enjoy it.

        I have Cromotors that I turned down (to 72V/30A) and I get all the torque and speed that I want without any heat issues. It is very fun!


          My only experience is with the BBSHD. I am using 5 PAS levels. Level one 4-6 amps, two 9-12, three 14-19. You are in total control especially if the control switch is within reach of one of your thumbs. If you have a long ride and/or you are trying to save battery use level 1. If you come to a hill and you didn't down shift fast enough jab that + button a couple of times and you will fly up the hill but only if you bought the larger motor.

          So do yourself a favor and get the largest motor and battery you can afford.


            For the $170 difference in price I would also suggest you go with the biggest you can afford. I just use mine for commuting but the extra power does get utilised for some steep hills, especially when the bike is fairly heavily loaded. For a comparison, my partners admittedly lighter bbs02 gets about 6wh per km compared to my bbshd mid 7-8 wh per km. Both get similar range from 20ah batteries


              You will lose range with the bigger motor, because you will accelerate faster, cruise faster, take the long way home looking for hills to climb, and have a bigger grin on your face. Get the big motor and the big battery.


                Well, here is how I look at it ... you can have a motor that is being wrung out at max out-put, or you can have a larger motor not doing much more than it's continuous rating just cruising.

                TL : DR

                IMHO, better to have a little more motor & battery than you need so it lasts longer since it won't be working as hard.

                Different motors like to perform in different ways, but generally speaking, if you're needing to climb a lot of hills and/or go fast (averaging above 15 MPH) you would want to go a size bigger than the minimum required so that the motor & battery doesn't have to work as hard.

                The harder a motor has to work, the more waste heat is produced, which is why many of the cheap hub motor kits from Ebay with 80% or worse efficiency (and are just less efficient being stuck and the low RPM of the wheel) need a much larger battery to do the same work of a good mid-drive such as the BBS02 or BBSHD.

                Good efficiency is very important too, so you need to properly gear the motor in the form of the chain ring on the BBSX (02 or HD) motor so that the motor is never bogged down, always able to spin at high RPM especially with these smaller geared motors, or you are going to wear them out faster. (not just motors, but the gears, chain and sprockets of the bicycle drive train too .. in a really hilly area, consider a smaller chain ring than stock)

                Lots of factors to consider:

                - Total Gross Weight (Bike + Rider & Cargo)

                - Grade of hills to include length, i.e. a long 2 mile + hill doesn't have to be terribly steep to generate some stress/waste heat of motor & battery.

                - Speed which you need to travel, i.e. anything above about 20mph starts to really factor in drag so that you have to use a LOT more wattage at speeds of 30+ (like 3x the wattage for a typical up-right bicycle) where as if you average below 20 MPH, you're not having to deal too much with drag.

                I would say that if you are above the 180 lb average rider weight, and plan on going above 30 MPH or hauling a considerable amount of cargo, go with the BBSHD.

                If you are in that 180 lb average weight and lower, but want to go high speed a lot, I would still say BBSHD as it will perform more efficiently and with less stress than the BBS02.

                If you'r fine going more average bicycle speeds, and plan on building up a relatively light road bike or are a fairly light rider or you like to pedal as much as use the throttle, the BBS02 might be just fine.

                I am thinking since you live in a rural area, you might need to go at higher speeds to be safe and keep up with traffic assuming there aren't as many alternative low traffic routes or bike paths available, then you're probably going to want to be cruising closer to 30 MPH + at times, and although the BBS02 will hit that speed, it will be working much harder than the BBSHD.

                The idea that having a larger motor = need of a larger battery isn't necessarily the case.

                However, when I have more power, I tend to use it, so yes, having a larger motor would tend to mean larger battery, but if you're content with more of a "pedal assist" and add lots of the power with your legs, you can just leave the assist level low and do fine.

                If you're going to use the throttle a ton, and go fast most of the time, and barely pedal at all, THAT is what is going to hurt efficiency more than anything.


                  Thanks guys! I guess it seems pretty unanimous, Go Big! So will take all your advice. I do want to peddle assist as much as possible, as I ride my bike fairly often now and don't want to get lazy, so I'll have to play with gearing a bit so I can keep up. The main road to my work is probably 10 miles with a 50/55 mph speed limit. So it would be great to cruise around 30.
                  I am in the midst of building my own battery pack, so the sky's the limit as to how big I can make it. I guess it's just limited by my wallet at this point.
                  I am going to have to research BBSHD and BBS02, as these two options are new to me just since I started looking around this site. So far, it sounds like, if I can afford it, BBS02 is the way to go. I was set on going with a rear hub motor. I'm sure there is enough info out there for me to read up on out there on this subject so as not to let this topic get off on a tangent.


                  • Peter Halt
                    Peter Halt commented
                    Editing a comment
                    BBSHD is the larger of the two commonly available mid drive motors. A hub motor is en entirely different animal. Pros and cons of each have been well documented in this forum and endless sphere.