The Ultimate Guide to Riding Lawn Mower Transmissions
Best Mower Transmissions for Traction
Imagine walking or driving during an icy winter. You'll probably tread more carefully trying not to lose your grip so that you don't fall or run off the road.
The same applies when you're mowing in wet, muddy conditions. You need a riding lawn mower that can get you through obstacles rather than just spinning the wheels, or leaving you stuck on an incline. You need a lot of power and torque to get moving while maintaining grip for traction. But, as you speed up you need less torque to keep going.
A lawn mower transmission is what transmits the power from the engine to the wheels and is responsible for managing the vehicle's speed by altering its torque depending on the conditions.
You might see the various kinds of transmissions available and wonder which one you need for your riding mower. This guide is here to help.
What is Transmission?
Because the transmission plays such an important role in handling speed, it’s also an important part of making sure that your mower has the right amount of torque to handle the most challenging backyard conditions:
- Wet grass
- Muddy ground
- Hills and inclines (we recommend never using a riding mower on inclines greater than 15 degrees)
- Obstacles like tight corners, tree roots, and trees
Lower gears might provide more tractions but can't go fast, and vice versa. Plus, different transmissions have different gear reduction ratios and different numbers of gears.
A gear ratio is simply how many revolutions a driven gear will turn in relation to the main drive gear. In a low gear ratio of 3:1, for example, the driven gear will turn three times as much as the main gear providing increased torque but since it's spinning three times as fast, the engine's speed (RPM) will quickly max out.
Oppositely a 1:3 gear ratio will turn at a third of revolutions of the input gear, thus providing less torque, but increasing the ability of the engine to spin slower to maintain a higher rate of speed.
There are four basic types of transmissions:
- Manual Transmissions are found on sports cars and older lawn tractors. The gears are manually selected using a lever and clutch. Users report a responsive, more immediate feeling of power.
- Hydrostatic Tranmissions (also known as automatic transmissions) use hydraulic fluid to shift gears automatically. These are the most common type of transmission on the market. They are relatively easy to maintain and provide a good mix of responsiveness and ease-of-use.
- Friction-Disc Transmissions are mainly used on small power equipment. They have a spinning disc with a movable wheel on top. Just like a record player, as the wheel moves across the disc from the center, it creates varying degrees of speed and torque. They're inexpensive but require more maintenance. Users sometimes report lurching and jerky-ness while operating the shifters.
- CVT Transmissions, or continuously-variable transmissions, are becoming more common. They employ a metal band sandwiched between two cone-shaped pullies that alter their diameters and thus their gear ratios. Users often report a 'rubber-band' effect after revving the engine, in which the power sent to the wheels feels delayed. The chief benefit is that the transmission is always in the 'best' gear ratio for the given power demand.
Riding Mower Transmissions: The Basics
In the past, riding mowers and vehicles such as lawn and garden tractors used manual gear drive transmissions to change the mower’s ground speed. If you’ve ever driven a stick shift or seen someone do it, you have the basic picture. By engaging a clutch and manually moving a gearstick, a user would change the gear ratio and vary the mower’s speed.
Manual transmission mowers still exist and can be incredibly helpful for users who are more comfortable using a gearstick with their hands than pressing pedals with their feet.
However, automatic transmissions have been the default on riding mowers for some time. The most common type of automatic transmission currently available is a hydrostatic lawn mower transmission.
Hydrostatic transmissions allow for greater variability in the mower’s forward speed. The “jump” between gears often felt on manual transmission vehicles is absent in hydrostatic lawn mowers. All a user feels when the pedal is pressed is a gradual change in speed.
Several manufacturers produce hydrostatic lawn mower transmissions for different types of riding mowers. However, when it comes to transmissions for residential and semi-pro lawn mowers, there are two big names to know:
- Tuff Torq Transmissions
- Hydro-Gear Transmissions
Garden and Lawn Tractor Transmissions
If you see a lawn mower transmission identified with a code that begins with the letter K, you’re looking at a Tuff Torq transmission.
Tuff Torqs are standard in garden and lawn tractors – the riding mowers designed to pull various kinds of attachments:
The names of Tuff Torq’s models follow a straightforward convention: the higher the number, the greater the potential power and durability the transmission offers.
Starting with the K46, which is Tuff Torq’s most popular basic transmission, each model with a higher number offers more improvements over the K46:
- Heavier axles
- Larger hydraulic pumps
- Strong motor systems
- Greater responsiveness
The tradeoff for this improved performance is an increase in price. So, if you’re looking for a low-cost, lightweight transmission made for flat lawns or slightly hilly lawns where the traction tends to be good, your best bet is to look for the K46, which is found in lawn tractors. The K58, a Tuff Torq K46 upgrade that’s common in lightweight garden tractors, will be slightly more responsive and better for towing heavier loads.
More robust transmissions such as the K66 will be available in heavy-duty garden tractors as one of the parts that makes them well suited for heavy workloads.
Zero Turn and Rear Engine Rider Transmissions
Not every rear engine riding mower uses a hydrostatic transmission; some brands still produce rear-engine riders with gear-based transmission systems. However, most rear engine riders these days are outfitted with Hydro-Gear transmissions, as are the vast majority of zero turn radius (ZTR) mowers.
Hydro-Gear has a line of models, the ZT line, designed specifically with ZTRs in mind. As with the Tuff Torq transmissions, the higher the model number of a ZT transmission, the stronger the construction will be on its features – and the more expensive the mower will be.
So, transmission models like the ZT-2200 (EZT) and the ZT-2800 will be able to handle minimally challenging conditions and as a result will be found in lightweight, residential-grade or mid-grade zero turn mowers. Models like the ZT-3100 and the ZT-3400 will have upgraded axles and bearings and will be better suited for long hours of commercial use.
Hydro-Gear also offers larger and more productive commercial models including the ZT-5400 that offers two-speed operation up to 18 miles per hour for transporting.
Being able to change speeds is undeniably helpful for getting your riding mower out of a slippery patch of mud or grass. Unlike zero-turn mowers that have two independent transaxles, riding mowers have another feature that works with the transmission to create even more traction: the locking differential.
What does a locking differential do? Simply put, it prevents the wheels from slipping. This kind of differential will "lock" the left and right axles together so that they rotate as a single axle. Contrast that with an open differential, in which the left and right axles can rotate at different speeds.
The idea with a locking differential is that, instead of having one wheel spin wildly while the other sits stuck in the mud, the differential gets the wheels to turn at the same speed and helps the mower regain traction on the side that slipped.
Locking differentials are becoming more common on mowers from the commercial level to the residential level and all the mowers that fall in between those two categories. They can be found on garden and lawn tractors.
And of course, you’ll see different types of locking differentials available. They can be categorized by location on the mower:
- Rear-locking differentials affect only the rear axle
- Front-locking differentials affect only the front axle
- Full-locking differentials affect both the front and rear axles (AWD)
They also can be categorized by the way they’re activated:
- Manual or selectable differentials require the user to press a button, step on a pedal, or use a hand lever when a tire slips
- Automatic-locking differentials respond automatically when the mower senses uneven rotation in the wheels
As you can imagine, the more convenient a locking differential is to use and the more traction it provides, the more it raises the cost of your mower. However, no matter which kind you prefer, shopping for a lawn mower with locking differential is a great way to improve your chances of being able to mow almost any terrain.
The Right Transmission for a Smooth Ride
Realistically, when you’re shopping for a riding lawn mower, the transmission won’t be the first factor you consider. Instead, you’ll be thinking about details like engine power and weight capacity, and you’ll be looking at specific kinds of mowers such as tractors or zero turns as a result.
But the transmission is a component that helps distinguish the different types of mowers available and makes each one better suited for certain jobs. Knowing what kinds of transmissions are commonly available will help you understand what your mower is capable of.
So, when shopping for any type of riding mower, think about the terrain you’ll be working on – how slippery it tends to be and how steep the ground inclines are. The type of transmission is one factor that will help you determine which riding lawn mower will give you a nice, smooth ride.
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