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Need Advice on Motor Upgrade (Razor Dirt Quad)


I have a Razor Dirt Quad that needs more "Oomph".  I tried installing a YK43B speed controller and going to 36v but that just destroyed the stock 350w motor (2 of them actually).  The stock gear reduction motor had good torque and speed with that setup but it only lasted about 5 minutes before dropping speed/power with a burning smell!  So, I am considering installing the 750w (non gear reduced) motor available at TNC OR the 36v 600w gear reduced motor.  Given the YK43B I already own, what would you recommend on the dirt quad.  It's not really a matter of fit as I will custom fab whatever brackets I need.  It's really a matter of what's going to give me the best performance.  We need more torque for our yard which has some moderate inclines and a little more speed than the 24v 350w stocker can provide.  Another option would be to start over with the 1000w 36v "kit" available at TNC (matched speed controller and throttle).  I've already spent way too much on batteries, chargers, burned up motors, speed controllers, etc. so I'd like to hear from someone who can recommend a good 36v setup that will perform well and last a long time!

Thanks in advance for the help.


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I did some gear ratio calculations and found that with the original 47 tooth rear sprocket a 3000 RPM motor with 11 tooth sprocket would give the Dirt Quad a top speed of around 30 MPH, which is too high of a gear ratio for an offroad vehicle with a 750-1000 Watt motor. This 30 MPH gear ratio would lug and overheat the motor when going uphill or through dirt, mud, or sand. I think that 30 MPH is also a little too fast to safely ride the Dirt Quad because it only has rear brakes which are not designed for that high of a speed.

I ran gear ratio calculations with the 36 Volt 600 Watt gear motor that has a 480 RPM output speed with the original 47 tooth rear sprocket and found that the top speed would only be around 4 MPH which is way too slow.

I ran some gear ratio calculations for a 2800 and 3000 RPM motor with 11 tooth sprocket running with an 80 tooth rear sprocket, such as our item # SPR-2580, and found that it would have a top speed of 15-16 MPH. This is a good gear ratio and top speed for a 750-1000 Watt motor to have and would be a good choice in my opinion. Our 80 tooth rear sprocket is for #25 chain, and our 36V 750W motor has a #25 sprocket on it, however our 36V 1000W motor has an 8mm sprocket on it which can be replaced with a #25 sprocket (item # SPR-2511C) to make it compatible with the 80 tooth rear sprocket.

The 750 Watt motor has over twice the power of the original 350 Watt motor and would definitely give it more "Oomph".

Here are my gear ratio calculations for both the 36 Volt 750 Watt and 1000 Watt motors:

Please let me know if you have any questions. are awesome.  That's exactly what I needed to know.  Could I go with the 9 tooth front sprocket and a smaller rear sprocket (I think I saw a 72 tooth or something like that) which would keep around the same gear ratio but have a smaller diameter on the axle sprocket.  I ask because that big rear sprocket reduces the ground clearage on the Razor dirt quad quite a bit.  It's probably not a big issue in my yard but if it's all the same, more ground clearance is better.  I measured the diameter of the tires at 12.25 for whatever that's worth.

Thanks again.


I checked and the 9 tooth sprocket fits a 7mm x 8mm shaft, and the 750 and 1000 Watt motors have an 8mm x 10mm shaft, so unfortunately it would not fit. The 11 tooth sprockets are the smallest ones we have that would fit those motors. I ran the gear ratio calculation for the 750 Watt motor with a 12.25" tire and found that compared to a 13" tire the top speed is 14.08 MPH which is not much of a difference from 14.94 MPH but is a lower gear ratio which is usually what is wanted for an off road vehicle.

I ran a gear ratio calculation with a 65 tooth rear sprocket which is the next size smaller than the 80 tooth that would fit the Dirt Quad, and the top speed with 750 Watt motor was 17.32 MPH. This might work alright if the ATV is not climbing any hills or going through mud or sand but I would recommend going with the 14.08 MPG gear ratio to give it better acceleration and uphill power, and also more importantly too keep the motor running cooler. The 80 tooth sprocket has a 6.5" diameter, so with a 12.25" wheel it would have 2.875" of ground clearance, which is not a lot however the rear sprocket is right in between the two rear wheels which would most likely hop over anything in the way that would hit the rear sprocket.
I want to put all of the parts together for the upgrade with the 32V 750W motor. Can you put a list together of everything I need to upgrade from a stock dirt quad and on a difficulty scale, where would you put this project? I am pretty mechanical but don't necessarily want to purchase special tools just for the upgrade. Thanks!!
Hi Erik, I can help with that. I have not personally installed a 36V 750 Watt motor on a Dirt Quad so I do not know everything involved, however I have see other install different motors and it looked fairly straightforward. Let me check to see if the 36V 750 watt motor can be geared for your requirements. What is the top speed that you want the Dirt Quad to go and will it be used to go up any hills?
The speed isn't that important, it would be nice to get 15 mph but we go up some big hills and would prefer something with more torque and power. It struggles to get over anything more than a mound of dirt. Thanks!!

I ran a gear ratio calculation for the Dirt Quad using our 36 Volt 750 Watt motor and an 80 tooth axle sprocket. Here are the results.

The top speed is 14.37 MPH with this setup which is fairly high gearing for a 750 Watt motor to be a hill climber. It would go pretty fast on flat ground, and be able to climb hills but lug slowly up the steeper ones and not be able to climb the steepest hills at all. Using a 1000 Watt motor would provide 25% more power than a 750 Watt motor though so that might be something to consider.

To make a steep hill climber with a lower top speed but that would climb anything with ease, a gear motor such as our MOT-36600G would be needed. I ran some calculations with this motor and a 34 tooth axle sprocket.

I would have hoped for a top speed of around 7 or 8 MPH however with the only sprocket we have that works with this motor and fits the Dirt Quad axle the top speed winds up being 5.27 MPH. At this speed it will have a tremendous amount of torque though and could climb the steepest hills with ease.

If you are looking for a low speed high torque setup like this but want a slightly faster top speed then we custom make sprockets and could make practically any size axle sprocket that you need for any top speed that you want. Here is a link to our custom-made sprocket order form page:

Thanks for the response. The 750w with at top speed of 15 would work better for us. Can you put a complete list of parts from your website together to modify the stock dirt quad. I want to put everything together in one order to ensure I have all of the parts when I start the modification. Thanks!
Sure that is no problem. Here is a parts list:
  • MOT-36750B 36 Volt 750 Watt motor with mounting base.
  • SPR-2580 or SPR-2589 axle sprocket.
  • CHN-HD25 heavy duty #25 chain sold by the link, includes master link.
  • SPD-36800B 36 Volt 800 Watt controller.
  • HNS-156 power switch to controller adapter:
  • CNX-51 connector to make existing brake switch wire connect to the new controller.
  • CNX-51 and CNX-52 to connect the throttle to the controller.
  • THR-86 twist throttle with 36 Volt battery meter.
  • GRP-54 matching grips for THR-86 throttle.
  • Three 12 Volt batteries, any size 12Ah or larger.
  • HNS-105 36 Volt battery pack wiring harness.
  • FUS-360 ATO fuse holder with 1/4" push-on connectors to go between two of the batteries.
  • FUS-ATO35 35 Amp ATO fuse.
  • One 36 Volt battery charger with 3P Inline plug, 1.6 Amp recommended for 12Ah or 15Ah batteries, 2.5 or 3 Amp recommended for 18Ah or 22Ah batteries.

That is pretty much it. I would expect as with all custom projects that there might be something needed which is missing from this list, but these are definitely all of the major parts that will be needed for the job.

I notice that the red and black wires in the Dirt Quad's charger port connector will need to be reversed to match the wire colors of the controller.

It will be easier to get a little more chain than is needed and cut the chain to the required size after the motor and axle sprocket are installed than to try to figure out what size chain is needed before installing these parts.

I could make a kit out of these parts with matching and labeled connectors so everything would plug together right out of the box. I would just need to know what size batteries, sprocket, and chain you want to use.

Please let us know if you have any questions.

Hi I'm looking to do something similar as mentioned above, I have a razor dirt quad 500 that runs a 36v 500w stock with a integral gear reduction on the motor. I'm looking for a little more speed and a ton more power. Like burn the tires pull the front off the ground whenever power. Any thoughts on what components I would need to pull this off.
To modify the Razor Dirt Quad 500 to have a higher top speed and to also have enough power to burn rubber would require a lot more power than it has in its stock form. We have 1000 Watt motors which could increase the top speed or torque by two times compared to the original motor. A 1000 Watt motor with low gearing could burn the tires if the Dirt Quad had front brakes so it could do a brake stand. In order to burn the tires without using brakes would require a lot more than 1000 Watts of power though, probably something in the five or ten thousand Watt range. With a 1000 Watt motor and fairly low gearing the front wheel could be pulled off the ground on acceleration with the help of the rider, however I do not think that it would pull up the front wheels unassisted.
Yea not keeping it stock at all double wishbone front suspension in front with 4 inch width addition for stability has new seat installed and working on 8 inch lengthening of rear swing arm and looking at splitting axle and making it an independent setup with 2 motors. I have a friend that willing to donate 2 60v 58 ah lifepo4 batteries and the chargers if that's a good start. I just don't know how much power I need or what components to use. I'm looking for equivalent power to an 18 hp gas engine. And somewhere under 30 mph but over 15mph
If it would help i could spring for another set of 60v batteries we could fit them I just measured. That way we could run a total of 240v dc At 58 ah or any iteration that would work best. But I think if we up the volts that high it may be hard to find components to work with that many volts if not and we can make more power lay it on me.

i have dirt quad v#3- and would like to know if these 48v 1800w kits would work

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