# Community Forum

## differential

Forum Overview >> Farming Simulator 22

 Category Farming Simulator 22 Created 25.01.2022 16:11

Patton_M47 25.01.2022 16:11
Hi how do I calculate what my torqueRatio and maxSpeedRatio should be for my differential?

Fredrick Fox (moogle4u) 01.02.2022 05:50
TL;DR- As I understand it, from when I started working with mods back in FS17, torqueRatio is the the difference in torque, or power, sent to each axle connected to that differential. maxSpeedRatio is the amount of overrun, or difference allowed between the connected axles.

Using a basic 4WD tractor or truck or other vehicle with two axles as an example:

<differentialConfigurations>
<differentialConfiguration>
<differentials>
<differential torqueRatio="0.5" maxSpeedRatio="1.5" wheelIndex1="1" wheelIndex2="2"/>
<differential torqueRatio="0.5" maxSpeedRatio="1.6" wheelIndex1="3" wheelIndex2="4"/>
<differential torqueRatio="0.5" maxSpeedRatio="1.3" differentialIndex1="1" differentialIndex2="2"/>
</differentials>
</differentialConfiguration>
</differentialConfigurations>

The tractor above has 2 axles, front and rear, and a "differential" that connects them. It is easier to think of this "differential" as a transfer case or power divider, since most people associate differentials as the component that connects two wheels, not two axles.

In both the axle differential and the center differential (inter-axle differential) the values work in similar fashion, the only difference is what components they provide torque, or power to.

Rule of thumb: For every 2x axles you want to connect, you will need 1x center differential (inter-axle differential) between them.

2x (1,2)Axles + 1x (+)Connecting Diffs = 4x4 (1+2)
3x (1,2,3)Axles + 2x (+)Connecting Diffs = 6x6 (1+2, 2+3)
4x (1,2,3,4)Axles + 3x (+)Connecting Diffs = 8x8 (1+2, 2+3, 3+4)

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torqueRatio
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torqueRatio is power bias. How much torque, or power, is being split between each end or each side of the differential. This is a decimal percentage, so a value of "0.5" is 50%, "0.6" is 60%, "0.8" is 80% and so forth. As a ratio, this would look like 50/50, 60/40, 80/20, respectively.

For axle differentials this determines how much torque, or power, is split between the two WHEELS.

Using our example, differentialIndex="1", the front axle, has a torqueRatio of "0.5" or 50%, which means each wheel receives 50% of the torque, or power, also called a 50/50 split.

This is the same for differentialIndex="2", the rear axle. It has a torqueRatio of "0.5" or 50%, so it is 50/50 split as well.

This is an equal/even split and ideal for most vehicles and powered equipment, since having the left wheel being driven with more power than the right wheel, or vice versa, would create an undesirable and potentially unstable driving experience; one side would want to "pull" harder than the other.

Rule of thumb: Unless there is a specific need for one side to have more power than the other, a setting of "0.5" is ideal for axles.

For the inter-axle differential or center differential or power divider, this determines how much torque, or power, is sent to each connected AXLE.

In our example, the torqueRatio is "0.5" or 50% between differentialIndex1="1" (front axle) and differentialIndex2="2" (rear axle). This means that as a 50/50 split, 50% of the power is going to each axle.

This is where you will sometimes find a torque bias necessary, in the real world, either due to mechanical limitations or nature of the equipment. For game purposes, it may or may not make a difference on what you are creating/modifying, since there aren't the same types of physics, like having a drive or axle shaft break due to excessive torque, in the game.

Real world examples of torque biasing are most of the US made AWD cars and compact SUV's utilize a front bias AWD system. These vehicles have a 60/40 to 80/20 split, providing the majority of the engine power to the front wheels with the rear wheels providing supplemental tractive force. They are not 50/50 splits. The reason for this is that there is more weight over the front axle of the vehicle, due to the transverse mounted engine, transmission, and other powertrain components, and less over the rear since this is typically open cargo space or passenger seating. The increased weight equates to increased traction/stability in adverse conditions compared to the "light" weight of the rear. This is also the reason a FWD vehicle is typically more capable in the snow or on slick terrain than a RWD vehicle.

Performance AWD systems like the ones you find in M-series BMW's and AMG Mercedes and other higher end vehicles with multi-mode AWD systems provide the ability to switch this bias for racing purposes (and just flat out fun), since hard cornering and turning and other track oriented maneuvers are better performed with rear bias, not front.

A more useful real work example is also a tractor with smaller steer and larger drive or multiple drive tires. Some even have less aggressive tread tires on the front as well. In this circumstance, having a rear bias is useful for traction purposes. Having the majority of the power going to the rear drive axle where the implement is and where you want the most traction is a good thing. Having a small portion going to the steer or front axle helps keep the tractor from getting bogged down by letting the front axle help pull everything along.

There are many reasons to want to adjust the bias between the front and rear axles, depending on the application or nature of the equipment, so it is something to experiment with! Otherwise, you really can't go wrong with a "0.5" torqueRatio. The 50/50 split is a good starting point and will work for most vehicles or powered equipment.

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maxSpeedRatio
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maxSpeedRatio is the amount of overrun, or difference, between the two ends or sides of the differential.

This is usually the least understandable of the two, since it is sometimes hard to grasp the concept and how it all fits together.

If you a driving in a straight line and all 4 tires are the same size, overrun does not exist. Everything is turning at equal speeds, one side isn't turning faster than the other, life is good!

However, that is rarely ever the case. You are turning, your tires are different sizes, traction causes one wheel to slip, you are crossing uneven terrain, you are stuck in the mud or snow or in a field ... and the list goes on.

When working on the maxSpeedRatio on axles, it is usually good to have some level of overrun unless you have a need otherwise.

A quick overview of differentials:

If you make a sharp left turn, the inside tire, or left tire, basically makes a short path or pivots left while the outside tire, or right tire, has to travel a longer distance in an arc to make the turn. This equates to a speed difference between the two tires meaning the outside tire overruns the inside tire.

If the differential did not allow this to happen, the outside tire would be dragged along at the same speed as the inside tire making it difficult to make the turn and wearing out the tire and other components from the stress of not being allowed to freely turn at different speeds.

The downside to this is if you are off-road on slick terrain and one tire gets stuck in soft mud or ends up off the ground, the openness of the differential will cause the wheel with the least traction to spin while the other tire doesn't spin at all or very little.

Under normal driving conditions, a completely open differential is great as it allows the easiest turning and maneuvering, but it is the worst when it comes to traction in adverse conditions. A completely locked differential, where both wheels turn at the same speed at all times, you get the best traction in off-road and uneven terrain, but it makes normal driving less than ideal due to the inability to turn, even small turns, easily since the wheels will not smoothly travel in an arc due to the inability for the outer wheel to turn faster than the inner wheel.

This is where limited-slip differentials come in. This limits the amount of overrun before connecting the two wheels, causing them to no longer spin freely of each other. This allows for increased traction in adverse or off-road conditions as well as good driving manners under normal conditions.

How does this all come together in game?

maxSpeedRatio is the value that determines overrun. It's been a while since I've adjusted the values here, but if memory serves, a maxSpeedRatio="1" would mean that both ends turn at the same speed. In our example of "1.5" means one side is able to turn 50% faster than the other, or at 150%.

An example is if both wheels are turning at 100 revs and you lose traction or make a turn, one wheel will be able to spin at up to 150 revs while the other is spinning at 100 revs. This is the "limited" slip scenario where it allows for some speed difference between both sides, but it doesn't allow one side to just free spin as fast as it can.

There is definitely some experimentation that goes into what is "ideal" for your particular vehicle or application, but "1.5" is a good starting point and will usually work well for general purposes.

Here's where we get into a little more complexity. What if you had different size tires on the front and rear axles? A lot of tractors do. They have smaller tires on the front than they do on the rear.

This means that the center or inter-axle differential is always in a state of overrun. If you are moving at 15 km/h and the front tires are spinning 130 revs and the rear ones are only 100 revs because they are larger, if you don't have the differential set to a value that allows at least that much overrun the axles will bind and the tractor will not drive correctly.

The front tires need to turn 30 revs faster than the rear tires to go 15 km/h. This means if they were locked to the rear tires and not able to, the rear tires would be turning at a rate to travel 15 km/h but the front tires would only be traveling at 11.5 km/h so they would causing a bind in the drivetrain.

This equates to some undesirable behavior in the game and potentially a completely undriveable vehicle or piece of equipment.

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If you've made it this far, I hope you at least have a better understanding of how differentials work, if you didn't already know.

If you did already know, I hope you have a better understanding of what these values do and how it relates to how differentials work.

If I didn't answer your question or I didn't explain it in a way that makes sense, I apologize. I'm a technician and engineer who does modding on the side because I like to break stuff and design stuff, so I understand that I'm not always the best when it comes to explaining things in a simple way that is easy to understand.

Whatever the case, if I am able to help, feel free to reach out!

-Fred

Colin Smith (WrinkleysRule) 01.02.2022 22:27