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KMX Tadpole Trike

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    KMX Tadpole Trike

    Hi I am new to the forum but did a bunch of reading before posting. Interestingly trying to search for the term "kmx" is difficult because the forum software says it would return to many results. I suspect that this is because it is a 3 letter word.

    Bottom line:
    Budget: $1300
    Expected usage - suburb streets, maybe some hard-packed bike trails
    Expected miles per month: <100
    Bike experience: Novice
    Handy: yes


    I am a 45y/male/200lbs/southern calfornia - I ride the trike for in the suburbs but find it very difficult to do any types of inclines and off-road the rear wheel spins freely if there is even a bit of gravel on the ground (I suspect that it needs more weight over the back tire). My kid and I go riding all the time on pretty flat surface streets and I would like to convert to electric.

    I have seen two major options for this bike and it seems like the rear hub, the mid-drive motor, and the Bafang front-mounted motors. But most of the information that I have seen is about 4 years old. I wanted to get the community perspective.

    I will probably put &lt;100 miles per month, I might use it for shopping but there is no commuting or real city driving. I am comfortable with a wrench, I just want to see how others have approached this conversion. And suggestions on the best path for about $1300. I am pretty handy.

    With the BBHSD it looks like I lose the 3 gears in the front and it becomes a single large gear - which is probably ok as I spend most of my time in the larger gear.

    I have included some pictures for those who are unfamiliar with the configuration.

    and a link to the KMX site

    I have read some older posts about KMX bikes

    Thanks in advance.

    Is yours the 2 front wheel version? Some of the clicks with the link seemed to be stopped by my popup blocker so I wasn't able to get too many details. You mention back wheel so I assume its the 2 front version. I think a BBSHD should be a good fit for that from what I can see in the photos. Looks like a fairly standard bottom bracket on there so the BBSHD should just slide on in there.

    Unlike conventional bikes you should not be limited by chain ring size and clearance issues or even chain line issues. Your bottom bracket appears to just be sticking out there on a straight piece of tubing so no clearance issues at all. On most bikes the chainstay (part of the frame that goes to the back wheel) kicks out fairly quickly after the BB to clear ever wider tires and this creates clearance issues with chain rings and the BBS systems. Since the chain ring and sprocket are not that far away from each other we can't just space out the chain ring to clear because the chain angle becomes too great the chain won't track or wear well. On yours there is no kick out so even if you went with a small 30 ring you should not have had to use any spacers so you won't be that far out from normal to start with and even if you were out it should not matter much because of how long your chain is. Worst case you may have to slightly space out the first idler to make it an easier transition.

    The HD's from most suppliers ship with a cheapo offset 46t ring. If you don't use any spacers that puts the chain ring at about the same place a 2x or 3x large ring would have been. People like Luna and Lekkie make down to a 42 that has a similar or greater in the case of the Luna Eclipse ring. Lekkie makes a offset 40 but its expensive because it also replaces the gear cover. Generally the smaller than 42 rings have to sit outside the gear box. Most of them are offset to get the chain right up against the box but in some cases that is too far especially when used with a derailer/cassette setup that has to get to the lower gears. They also make adapters to take regular 130mm chain rings. These only have the slight offset but may give you more options including using existing ones if they are 130 mm spacing.

    I would say start out with the stock ring and see how it feels before spending money on something else. Since you have the single back wheel that I assume uses conventional cassettes you also have the option to upgrade to a wider range so if you do stay with a larger front ring for top speed you may be able to get a 40 or larger on the rear to still get some reasonable hill climbing. The BBSHD can spin significantly faster than most people so top speed may be less of a concern than hill climbing. You pedaling plus the motor will be able to climb in higher gears than you could alone but if you are going to do it very often it can be very hard on everything. That's why I suggest starting with the stock one and ride a bit and see where you are at. I both my builds are now getting lower gears. When I started I was worried that top speed was going to be the issue but its really not. Also helps that I'm old enough now where speed isn't everything.

    Your budget of $1300 is going to be close. I would research the displays carefully especially with your layout. Some are larger center mount with a remote button unit and others are much smaller like the 500c/mighty mini and have the buttons built in. There is also the eggrider 2 that is newer and very small plus does bluetooth to your phone for advanced features which seems interesting. Different displays can add $20-150 to your build. ALso not with a vendor like Luna you get a discount on those options if you order with the kit. You also have things like brake cutots and gear sensors that many of us really like to have. The big expense is the battery. I have Luna Wolf's and me being a fatish older guy on regular bicycle can typically do around 20 miles with power to spare. I think in general trikes have a little more drag so if you are lighter maybe that will even out. The Wolf packs are around $550 I think. You can find similar spec packs for as low as $300 but you have to question their build quality and safety. Also need to consider the form factor and mounting options. With a trike I can see wanting or easily being able to have multiple batteries just because you are not restricted on width like bikes can be.

    Let us know what you are thinking and we will do our best to further confuse you but hopefully end up with a better ride in the end.


      Here are the actual images from my bike if this helps to clarify while I continue to read your post.

      I was not really even aware of the considerations of the front ring. Looks like Utah Trikes has some options - and when chatting to support just now they mentioned that the 750 is quite popular.

      I as looking at the 750 because it has the newer motor - a little steeper than expected but as it kit it should just work.

      Do you know if Luna does something similar and what do you think of the 1000 kit from UT ?
      Last edited by bks; 1 week ago.


        Ya you should have no problems dealing with spacers or issues picking any size chain ring you want. Most bikes have issues because the frame kicks out right away but yours doesn't. You can even keep the derailer there as a chain guide for extra protection, just lock it into position with the adjusting screws.

        Another thing you may need to add to your budget is extension wires since these are designed for bicycles. You may need a longer main harness or extension as well as extending others. Not like those things will cost as much as a better battery but do tend to add up.

        The BBSxx has 3 cables hanging out of the main unit. The are in the 18" range I think. One is for the gear sensor. One is the dual fatter cable for the battery and has an anderson red/black connector from the factory. The 3rd is the main harness which has a multi pin plug on it. The main harness cable plugs into that which is maybe another 18" long before it breaks out into maybe 6" tails for the various usually bar mounted dodads. Lengths are from memory so don't quote me on those. The bar mounted dodads are 2 brake levers, throttle, and display. With your layout the stock lengths won't likely work.

        If you get the package from a vendor like Luna they supply a pre made 8" or so cable to go between their battery and the motor, even a piece of shrink tube if you don't ever plan to unplug the anderson plug. Luna uses X-60 for charger and X-90 for the main on their BBS kits. The X connectors are commonly use on RC cars and such so are not too hard to find parts to make your own as well as various extensions and adapters and such. Vendors like Luna also sell various bits too. The main harness and other connectors appear to be somewhat unique to Bafang stuff so unless you want to cut and splice yourself you are stuck with getting them from a supplier but there does appear to be plenty of options since people do cargo bikes, trikes, and tandems al the time.

        Got pics of your brake levers and bars? Maybe that will help with suggestions for the display, throttle, and cutouts.


 - updated with brakes levers and bars.


            Hmmm..... IF you don't find yourself accidentally shifting while turning maybe you could do a left half twist throttle since you would be getting rid of the front derailer anyway. Full and half twist doesn't have to do with how much twist there is its does it take up the whole grip or just half. Since I assume you do some twisting to steer I would think you would not want a full one. I don't know how ergonomic the standard throttle would be mounted on the top of the bar would be. I'm thinking not very and not having your thumb around the bar may not be good for steering. I wonder if one the 'deluxe' throttles mounted to the top of the bar would let you do it with your index finger? That would still leave a good grip on the bar. I have a left one somewhere, maybe if I ever get off the couch today I will grab it and stick it on the end of a bar and see how it fits.

            For brakes looks like they are cable discs with a parking lock. To be safe and keep the lock I think I would get the 'hydraulic' cutouts. Those are a small sensor you glue onto the body then a small round magnet you glue or zip tie to the base of the lever. The Bafang levers have worked for some and are a little cleaner but on my bike with Avid BB7's I was not happy with the amount of travel I got out of the Bafang levers so I went back to the stockers with the hydraulic sensors. My antique cantilever bike is fine with the Bafangs as is my wally world bike with no name discs. I have not seen any E levers for sale that have the parking brake option so if you use that you may not have any choice.

            For a display not sure. Bars are already pretty cluttered and don't look that easy to access other than what you are gripping on. How far away is the KMC decal and those crank adjusting knobs? I wonder if a self contained display there may be reasonable? The display or its control button unit is where you turn it on and off and select the pedal assist levels. Also where you can toggle through the display stuff like elapsed time, trip miles, total miles, and max speed sort of things so it can be handy to have reasonable access to the buttons and in a place its easy to look at. Not sure what you would do for a mount. Have or know someone with a 3d printer?

            Have to see more of it for battery ideas. You could always put a BBSHD into that Tesla and make the performance scale to the full size version. Is there a full size Tesla nearby too? I saw one of those cars on a ride last week. No idea how many people make those or if they are fast at all. Unless Tesla had something to do with them I assume they are pretty slow and just begging for mods unless you actually got it for a little kid to drive and they are having fun as is.


              no full size tesla, this will be my first electric for me. I got that one for my kiddo from an auction supporting a charity. They are actually pretty fast, I think it goes to about 7 mph. I actually did not know that my bike had a parking brake option - I have a rubber band that I use to pull the brakes when I am off the bike to keep it from moving.

              Utah seems to have a mounting bracket that goes above the left grip for mounting of the display. I had not tought about the need to use the handles for both turning and for accelleration - its something that I'll need to research a little more to see wht the optimal position is and how to activate the power.

              It seems like I'll need to consider two more sensors - brakes and then a shifting sensor to ensure that the motor is not under load as I change gears. So from your perspective is the route the BBSHD with some longer cables a reasonable option?


                oh man! just made an adjustment so that the parking brake actually engages - wow what a difference in stopping distance. If for nothing else - THANK YOU.


                  Based on very little BBSHD experience and almost zero trike experience I would think its a reasonable way to go. The chain line is pretty wacky anyway and those chain guide rollers look to have pretty tall flanges on em so I would not think the chain line will be an issue.

                  If there is room to scooch things down a bit on the bars without effecting things the left deluxe throttle mounted on the right looks workable or a Right on the Left. In my fuzzy photo its at the top of the bar and you can see that my hand is down a bit from the top. The tape is just there because mine is missing part of the mount. Feels like it could work but I have not ridden a trike like that so don't know for sure.


                    I wonder if you could do a 'bar end'? Get the style that clamp on the end of the bar and are the size of a bar? Maybe then you could use the regular universal throttle trigger style and get the display on it? Not sure if that would have clearance issues with anything tho. Would not be good if it limits your steering or is always in the way getting on and off.


                      Have you been on Utah Trikes YouTube channel. I know they did a BBSxx install on a trike. It looked like a straight forward install, other than their questionable decision to zip tie wires to the tie rod.


                        I wonder if we scared him away? Maybe the parking brake is stuck on now and he can't ride at all? Or maybe his system is on the way? He should have it by now since all the vendors seem to be west coast ish.... Not like me that has to wait at least 4 days for any E bike related part. Feel really bad for the east coast guys, guessing coast to coast ground shipping catches both weekends so you either have to pay for fast shipping or really plan ahead.

                        I was hoping he maybe worked at SpaceX or Tesla and was going to be the first to do a BBSHD with a Tesla battery module. Trike would be the way to do it too since you have more space and less balance issues.


                          Funny - not scared but sorry for not responding. I did contact Utah and they gave me some great pointers as well as a link to their products that have been validated and tested on the KMX platform. I expect to be going with the 1000 when budget improves. And I'll post pics when I have them.



                            That's cool that they have it as a kit with most of the tricky stuff like the mounts. 17ah battery should give you decent range.