Vehicle Gears & Torque

Basically, I have been trying to build a vehicle with a friend for a while now and I am having a bit of trouble trying to understand how gearing and torque should be done. I understand the basics of gear ratios and how they effect torque, but haven’t had any luck with it in Gmod. What I am trying to do is pretty simple. My engine is just a motor wheel that will try to run at the same rpm at all times, and I simply want to have a gear for torque, and a second gear for speed. Perhaps even a third gear between. I know how to do this in the game, but I have had no luck with any of my results. For testing purposes, I have created a few vehicles with a single motor giving power to each wheel and tested how far they can make it up an incline. After, I would attach a small gear for input, then a large gear (at least 3:1) as output that would turn the wheels. I noticed no real difference in how far it could get up the same incline. I could give the motor wheel more torque, but that would not help either as it would just increase wheel spinning out or front end of vehicle popping wheelies. I’m really not sure if I am doing this right or if I am missing something.

Heres a poor illustration of what I was testing with. A 500kg 24" motor wheel with 100,000 torque pulling 4 120inch monster truck tires through a bsocket differential and 2000kg body weight. With no gears, I could get around 25mph and 1/4th up an incline. With a 3:1 gear ratio with same setup, I was accelerating faster but I was still only making it about 1/4th up an incline that was not very steep. Any modification of weight for motor/gears or more motor torque just made the vehicle do wheelies or spin out.

Any help at all would be appreciated!


In layman terms… Horse Power can tell you how fast you can go while Torque defines how fast you get to that top-speed… that’s how it was described to me many years ago anyways…

100k Torque is a lot depending on the unit of measurement… so the reason you’re doing wheelies is because your torque is so high that your engine is able to turn the wheel faster than gravity can pull the vehicle back down. With it not able to make it all the way up the hill is because you’re probably causing very little weight to be applied to the wheels with that torque because of the torque lifting the front or spinning the wheels ( think of it like a pickup truck or van; there’s very little weight on the rear wheels unless you’re carrying cargo so rear wheels are much easier to lock up or spin )…

For in-game units: 4/3 units = 1 inch which means 16 in game units = 1 foot. You may want to recalculate your torque value.

Thanks for the response. I admittedly switched torque and horsepower around a bit and thinking about it should have realized the high torque/gravity issue. I had such a high torque for my motor wheel since even at 500kg, that high of torque was still barely able to move even 2000kg of weight. My confusion is why increasing the motor weight increases the power a bit, and why increasing the size of the motor wheel drastically increases the power. Does the diameter of the motor wheel function the same way a longer wrench would apply more torque around a nut? If that is the case, how exactly does the weight of the motor wheel factor into it all?

Torque = Force x Distance, so to move 2000kg 10 meters/sec my force would be 20,000N. Not sure if distance would be 10 meters, or 1 foot? This all confuses me from here since I don’t know if I am supposed to measure torque in foot pounds or newton meters in gmod.


If something is rotating at the same speed regardless of diameter, then a speck on the side of an eraser on a pencil spinning at 1 revolution per second is WAY slower than say a 10" rim spinning at 1 revolution per second.

By increasing your wheel-size you are increasing the speed even if the rpm stays the same.

As for increasing the weight of the engine… There may be a behind-the-scenes calculation to determine true horsepower based on the size / weight of engine ( determine weight / size of pistons, chamber capacity, crank-shaft, etc )… I know that HL2 Vehicles do go through a pretty realistic measure of calculations to determine acceleration, etc… so it isn’t a huge stretch to see it also implemented into engines that can be spawned…

I’m actually not using an engine, rather just a simple motor at a set torque with a wheel attached to it that remotely spins a gear, which the other gear spins the differential/wheels. So that is why I am a bit confused as to how weight plays a factor into it all. A larger wheel spinning at the same rpm as a smaller wheel and having more speed makes sense as you said, just not sure why I am only gaining acceleration and top speed, but not the ability to climb elevation. I can use a larger motor wheel or higher torque and a 3:1 gear ratio, but I will only gain speed. It isn’t a traction issue or my 4 wheels sizes either, as I will simply speed up to a hill at 20-30mph, then the wheels just stop moving completely. I know it should have enough power, because increasing it further just makes it flip which as you said means it has too much power. Without the 3:1 gear, I am much slower, but I still make it the same distance up the hill albeit slower. This makes no sense to me. I’m just really confused and sorry if I sound stupid with all this, lol.


Speaking to this, I’m the prime guy you’d want to consult when dealing with vehicle physics.

Before I explain my opinion on torque and it’s application. I’ll first start off by saying: I’ve been working on a vehicle physics-engine inside the source engine for almost a year and a half. All of it is written in lua, however the calculations and math are very much applicable in any language.

Not familiar with my work, look here.

Now, I have proved I’m worthy to answer your question, let me begin.

Torque and it’s physical application to my vehicles is a little odd. It’s not so much what you’d expect rather it’s a very different way of accomplishing it.
To reinvent the wheel, so to speak means you have to think outside the box. ( That was a tasteless joke, I know… But my words have a lot of salt!! )

My cars have no physical wheels.
Torque can be one big math formula. Math that can be predicted and predetermined by our code of coarse.
No physical wheels means essentially it is a block that hoovers over thin air.

Still not satisfied? Stay with me a moment.
The current source-engine’s physics engine relies on a lot of unreliable things: gravity(mass), wheel patterns, and other unreliable vehicle-script variables.

Too much gravity causes the vehicles to bug out. Too little gravtity causes it to bug out. Torque is affected by this balance.
This is because the wheels are physical. Under heavy weight, imagine it like a *spring* being pushed down by gravity.

ISSAC NEWTON’S Gravity Formula:

I use it, source engine vehicles use it, our reality to some degree uses it.

What does this have to do with torque? Answer is: Everything. ( In source engine’s vehicle physics engine. )

I hope this helps you understand a bit more about exactly what goes on beyond the end result.

If you got questions about more, feel free to add me on steam. NOT before you send me a private message on facepunch first. Chances are, I’ll ignore the invite like all the rest. D:

Not sure if this is helpful, however to make a vehicle you should account for this sort of thing.

And also, friction.

That’s a pretty interesting way to do driving, fixes all that wheel friction bullshit too. Cool videos, hitting really high speeds too! Your map seemed huge somehow as well, lol. That’s all over my head though, but I appreciate the post, thanks. I’m mostly just trying to keep it simple. I sort of figured out the torque I need, but have trouble with my transmission gearbox. Doesn’t seem like any of my gear ratios are doing much. Feel like maybe my gear sizes are all wrong. A low gear definitely has more acceleration, but a high gear just gets really slow. After I change into the high gear at 30mph, the car just slows down.

I don’t mean to bump this, rather I’d like to clarify exactly what my question was before. Basically, I just need help with what gear setups would do what. I have a screenshot here of some different possible gear setups but not exactly sure which ones would be most effective for torque or for top speed. The left gear is spun by the motor wheel, while the right gear spins the differential/wheels. I thought (1) would give me plenty of torque and acceleration, while (2) would give me top speed and prevent my wheels from spinning out of control.