Hi, I have converted a kettcar using a 24v 250w motor (2750 rpm) controller setup. The motor has 11 teeth and I am using a 47 tooth sprocket from a Razor e100, bolted to the original. The tires are original at 10.5". I am using a 3 wire thumb throttle. There is a bit of play in the axle which caused the chain to slip off. I placed a zip tie in between a washer and the wheel, it helps keep the chain on but I can hear it rubbing. The wheels are attached like power wheels so once you get the ring off it's a pain to get it back on. I may have to just do it to get a washer or two in there. According to the gear ratio, it should be getting around 20.18 mph having a 4.27:1 gear ratio. From what I have read on here that may be too high and not allowing the motor to run at the full rpm. It's definitely not hitting 20 mph or even close to that, maybe 5 but I haven't tested it on an open road. When the lighter kids ride it goes ok but when my 10 year old gets on it slows significantly. Today, I noticed the motor quite warm and we put it away. I am new at this but decided to venture out any advice would be greatly appreciated. Thank you.
Gearing for a top speed of 20.18 mph is too high for a 250 Watt motor, which is why the Kettcar is going slow and the motor is overheating. A 10 or 12 mph top speed gearing would be more appropriate for a 250 Watt motor and should work good for average riding conditions like you described. If the car is driven with the 20.18 mph top speed gearing the 250W motor and controller will not last very long and will probably burn out fairly quickly.
Increasing the size of the axle sprocket is definitely the way to go. The distance between the motor sprocket and axle sprocket does not matter as far as functionality goes, however the shorter the chain is the less likely it will be to fall off so I would mount the motor as close to the axle as possible to help the chain from falling off.
The Razor E100 scooter has a 100 Watt motor which would be a big downgrade from the 250 Watt motor, so I would continue to use the 250 Watt motor.
Hope I have answered all of your questions. Please let us know if we missed any questions or if you have any new ones.
The right gear ratio can be determined by using our online gear ratio calculator at this link: https://www.electricscooterparts.com/motorwheelgearratio.html
The top speed that a motor should be geared for is typically around 10 mph for a 250 Watt motor, 20 mph for a 500 Watt motor, 30 mph for a 1000 Watt motor (air resistance kicks in at 30 mph so the top speed is not proportional once the top speed increases over 20 mph), and 35 mph for a 1500 watt motor.
The gear ratio and top speed should be around the same for electric scooters, dirt bikes, and go karts because they are all around the same weight and size.
I don't know anyway to attach a chain sprocket to a Kettcar wheel however the most common way to attach a sprocket to the axle is by mounting it to the original sprocket with nuts and bolts, or by welding it onto the old sprocket. I prefer nuts and bolts because then the sprocket can be replaced easier. If you do not have the original axle sprocket to mount a larger one onto then an original sprocket might be able to be found from Kettler USA at this link: https://www.kettlerusa.com/parts
Please let us know if you have any questions.