With the growing number of mechanical front wheel drive MFWD tractors, the rolling circumference of the tires play an important role in determining the correct setup for your tractor. In MFWD tractors, both the front and rear tires do the work. Too much positive slippage, or leading, can cause the front tires to do too much work and become less efficient. Too much negative slippage, or lagging, can have a braking effect on the front tires and reduce your steering ability.

Since the front tires are smaller than the rear tires, the front tires have to rotate faster to cover the same distance as the rear. The mechanical gearbox in the tractor accomplishes this task. When selecting tires for your MFWD tractors, you want to make sure to maintain the proper ratio of rolling circumference for your tractor.

Lead Lag Calculator With the growing number of mechanical front wheel drive MFWD tractors, the rolling circumference of the tires play an important role in determining the correct setup for your tractor. Front Tire Rolling Circumference in inches :. Rear Tire Rolling Circumference in inches :. Calculate Lead - Lag. Mechanical Ratio:. Calculate Front Size. Calculate Rear Size. Find Tires. Search all tires in: Agriculture. Enter Keyword or Tire Size:.An axle is a central shaft for a rotating wheel or gear.

Majority of semi-trucks are equipped with one front steer axle and two rear axles combined as a tandem axle.

Semi Truck Axle Ratio Overview

The number of rear axles will usually determine what axle truck it is. For example, two rear axles is called a tandem truck and three rear axles is called a tridem truck. The axles transfer driving torque to the wheel. They must be able to withstand the weight of the commercial vehicle and any added cargo in the trailer. The axles allow the truck to carry more weight and assist in propelling the truck. A two rear-axle truck is commonly paired with a tandem axle trailer which can be identified with two pairs of wheels near the end and a kingpin at the front that connects to the hitch.

Axles are also responsible to locking in the wheels to the specific direction the other wheels are positioned in. The semi-truck axles are also called the drive axles. The basic metric to gauge to understand the affect a drive axle will have on your truck is the axle ratio. The axle ratio represents the comparison between the driveshaft which is a component responsible for transferring torque power and the drive axle rotations or revolutions. The axle ratio represents the relationship between the number of spikes on the ring gear of the tandem axles to the number of spikes on the pinion gear on the driveshaft.

For example, a 3. This means the driveshaft must turn 3. In simple terms, the higher the ratio the greater the towing capacity but lower the speed and fuel economy.

Medium duty trucks will require a lower semi-truck axle ratio while heavy-haul trucks will need one that is on the higher end of the scale.

tractor gear ratio

Speed, Grade-ability, Load type and weight, Towing, Aerodynamics, Tire Size, Torque Converter are all factors to take into consideration when assessing which axle ratio will best fit your fleet whether that consists of only a few to a large number of trucks.

On-highway trucks will generally travel at significant speeds for long durations with consistent load weights. Therefore, it may be suitable for your truck s to have a axle ratio that strikes a balance between towing capacity and speed. If the route s your truck s take to transport goods have steep slopes then a higher ratio is required.

tractor gear ratio

Majority of on-highway over-the-road trucks will have a relatively constant load weight throughout its journey. Therefore, you will want to assess the axle ratio to provides a strong balance while maintaining reasonable fuel efficiency rates.

Speaking in terms of towing capacity, you want to understand what percentage of the time your vehicle will be travelling at its gross vehicle weight rating GVWR.

For instance, does the transport of freight for your company mainly consist of LTL Less-Than-Truckload or TL Truck-Load If majority of the time the truck is at or close to its max GVWR then you will want to sacrifice some road speed for towing capacity and lean toward a higher ratio. The smaller the tire circumference, the drive axle operates as if it was classified at a lower ratio compared to if the tire had a larger circumference.

Therefore, smaller tires will increase the speeds at which the truck may travel at. There are also 6X2 tandem axle configurations in which power is only supplied to one rear axle in an attempt to reduce vehicle weight and increase fuel economy.

For off road? What is an axle? Alcee Templet says: November 9, at pm. Hatem Elhaj says: August 26, at pm. Leave a Reply Cancel reply Your email address will not be published.Use our gear ratio calculator to find the changes to gear ratio when going to a different tire size. Both the effective and new gear ratios are calculated. Use our gear ratio calculator to find the effective gear ratio your vehicle will have with a new tire size.

Also calculated is the new gearing you would need in order to return back to your original gear ratio when going to a bigger or smaller tire. Input your stock and new tires sizes along with your original gear ratio.

Click "Calculate" to find your new effective gear ratio and the gear ratio needed to return your vehicle back to stock gearing. Changing tire size will ultimately affect the power and drivability of your vehicle. If you are looking to retain your stock feel or change your gearing to the optimal ratio, then you will need this gear ratio chart to do so.

Using the chart, first cross reference your current gear ratio and tire diameter to find your approximate RPM at 65 MPH. Then reference your new tire diameter with your choice of RPM to find the new gear ratio needed to supply you with that RPM. This chart is based on a drive gear of at 65 MPH using a manual transmission. Automatic transmissions will run a slightly higher RPM do to slippage.

If you are using the calculated diameter, multiply that number by. If you are measuring your tire, measure from flat ground up to the center of the hub and multiply that number by 2.

Tractor Gearbox operation Collor shift

Gear Ratio 2. Tire Size Tools. Tire Categories. Popular Sizes.Most older farm tractors use a manual transmission. They have several gear ratios, typically 3 to 6, sometimes multiplied into 2 or 3 ranges.

Slow, controllable speeds are necessary for most operations that are performed with a tractor. They help give the farmer a larger degree of control in certain situations, such as field work. However, when travelling on public roads, the slow operating speeds can cause problems, such as long queues or tailbacks, which can delay or annoy motorists in cars and trucks.

Tractor Transmission

These motorists are responsible for being duly careful around farm tractors and sharing the road with them, but many shirk this responsibility, so various ways to minimize the interaction or minimize the speed differential are employed where feasible.

Some countries for example the Netherlands employ a road sign on some roads that means "no farm tractors". An older model European farm tractor. These types of tractors are still common in Eastern Europe Older tractors usually have unsynchronized transmission design, which often requires that the operator stop the tractor in order to shift between gears.

This mode of use is inherently unsuited to some of the work that tractors do, and has been circumvented in various ways over the years. For existing unsynchronized tractors, the methods of circumvention are double clutching or power-shifting, both of which require the operator to rely on skill to speed-match the gears while shifting.

Both of these solutions are undesirable from a risk-mitigation standpoint because of what can go wrong if the operator makes a mistake — transmission damage is possible, and loss of vehicle control can occur if the tractor is towing a heavy load either uphill or downhill — something that tractors often do.

Therefore, operator's manuals for most of these tractors state that one must always stop the tractor before shifting, and they do not even mention the alternatives. As already said, that mode of use is inherently unsuited to some of the work that tractors do, so better options were pursued for newer tractor designs. Cutaway of modern tractor In these, unsynchronized transmission designs were replaced with synchronization or with a continuously variable transmission CVT.

Either a synchronized manual transmission with enough available gear ratios often achieved with dual ranges, high and low or a CVT allow the engine speed to be matched to the desired final-drive speed while keeping engine speed within the appropriate rpm range for power generation the working range whereas throttling back to achieve the desired final-drive speed is a trade-off that leaves the working range.

The problems, solutions, and developments described here also describe the history of transmission evolution in semi-trailer trucks. The biggest difference is fleet turnover; whereas most of the old road tractors have long since been scrapped, many of the old farm tractors are still in use. Therefore, old transmission design and operation is primarily just of historical interest in trucking, whereas in farming it still often affects daily life.

News News Technic. Contact Us E-mail: sales wheeltractor.Log in or Sign up. Find Trucking Jobs. What Rear Ratio Poll closed Aug 12, Aug 5, 1. Hey guys, I am looking at trucks Tomorrow and Wed. What is a good rear ratio for fuel fuel mileage and overall hill climbing?

tractor gear ratio

Detroit hp, 10 spd. GazooAug 5, WB and Road Killer Thank this. Yes, let employers and TruckersReport text me with new opportunities, job alerts and other career information to the number I provided. There is no charge for this service, but standard message and data rates may apply. Aug 5, 2. It depends really on what you are going to use the truck for and where you will be driving. If you are going to pull a lot of heavy loads over mountains then you want a higher number.

If you expect to be running the flatlands then a lower number would serve you better.

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Aug 5, 3. The dealer should have a computer program to input all your requirements and make recommendations from there. BrickmanAug 5, Road Killer Thanks this. Aug 5, 4.

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Aug 6, 5. Like other have said it depends on where you will run most of the time and what you will be pulling most of the time. The dealer can put it all into his computer and figure out where to gear it for you and you can always have the pumpkins changed later if things change its a little expensive but it can be done pretty easy. The best ratio is to have your engine run at the sweet spot RPM at the speed you will be running most of the time.

If you run the east coast mainly then 65 if you run out west allot the 70 or 75 in the sweet spot. Usually the Detroit's like it around or so is a good range. I personally don't like the 10 speed but if thats what they offer so be it a 13 or 15 over will give you better fuel millage over all because you can keep it in the sweet spot allot easier.

Aug 6, 6. I have a XL running a 60 series linked to a 13spd direct with 2. MPG is good around 6. When I pulled refers at 78, to 80, all the time I got 5. I would def go with a 13 direct over the 10spd for the simple fact that it is better for climbing the hills. As far as the pull goes it climbs fine I can hold my own just fine.

Also the nice thing is at 65 mph I run about rpm. So it helps the mpg for sure. And while running in Ca at 60 mph im about rpm. Socal Xpress and Captredbeard Thank this.This is often a detailed process so being familiar and knowledgeable about different truck components and metrics is vital to ensuring you choose a truck that will bring the most benefit for your business. In previous articles we have covered engines, transmissions, and drive axles in detail.

This guide will provide brief information on the different factors to be considered when understanding how to spec a semi truck. The type of engine you select will have a direct effect on your bottom line especially when it comes to fuel consumption. Fleets are steadily increasing the use of LNG engines for their trucks.

However, the vast majority of engines being used in semi-tractors, continues to be of the diesel variety. Diesel engines have come a long way in terms of fuel economy over the years, especially as government agencies such as the EPA have lobbied for stricter emission standards.

Some primary factors to consider when choosing a diesel engine for an over-the-road truck is to look at the horsepower. The horsepower directly reflects the power of an engine. Ideal horsepower range for heavy-duty diesel truck engines are between Anywhere from will provide excellent horsepower to haul less-than-truckload and most full-truck-load freight. Torque range represented in lb-ft is a detriment of the rate at which the truck can pull a load from a stop.

Torque range generally starts at lb-ft and go up to about lb.

Gear ratio

Engine displacement is another metric to assess because higher a displacement volume is suitable for heavier loads. The miles per gallon is a metric that can vary depending upon route, payload weight etc. It is important to not over spec but to understand the overall performance capability of the engine.

For example, for most over-the-road semi tractors horsepower will be more important than a high torque rating. The transmission is another important part of the powertrain. The first step is to choose the type of transmission suitable for your trucking operation.

tractor gear ratio

If the driver is highly skilled, a traditional manual transmission may be of interest. However, for the majority an automated manual transmission will work best. Next, choose the number of speeds which will suit your needs. The greater number of speeds means greater versatility. Aim to find a balance. The different gear modes such as skip-shift and power-takeoff are important things to consider.

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Moreover, the transmission should have the option to switch between operating modes such as manual and automated manual. The drive axle configuration is another feature to assess. Tandem axles are more common in semi-tractors. While, this may help reduce fuel consumption there are drawbacks for long-haul commercial vehicles. Axle ratio is a specification that will help you determine the towing abilities of a truck.

A higher ratio means greater hauling ability but slower speeds while vice versa is true for lower ratios. The Gross Combined Weight Rating will have an impact on your payloads.

The axles should be able to withstand enough weight to haul the specific freight.

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To calculate this, add the weight ratings of the steer, rear, and trailer axles. Therefore, consider choosing a truck with more aerodynamic exterior features such as fairings, side skirts, and low rolling resistance super single tires.The gear ratio of a gear trainalso known as its speed ratiois the ratio of the angular velocity of the input gear to the angular velocity of the output gear.

The torque ratio of the gear train, also known as its mechanical advantageis determined by the gear ratio.

In a gear train, the input gearor drive geartransmits power to the output gearalso known as the driven gear. The input gear, which is usually connected to a power source, such as a motor or engine, transmits power through any other gears that may be in the gear train to the output gear.

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The simplest gear train is a pair of meshing gears in which the input gear drives the output gear. The gear teeth are designed so that the pitch circles of the two gears roll on each other without slipping. The velocity, represented by vof the points of contact of the two pitch circles are the same. The number of teeth on a gear is proportional to the radius of its pitch circle, which means that the ratios of the gears' angular velocities, radii, and number of teeth are equal.

Where N A is the number of teeth on the input gear and N B is the number of teeth on the output gear, the following equation is formed:.

This equation shows that if the number of teeth on the output gear G B is larger than the number of teeth on the input gear G Athen the input gear G A must rotate faster than the output gear G B. Gear teeth are distributed along the circumference of the pitch circle so that the thickness t of each tooth and the space between neighboring teeth are the same.

The pitch p of a gear, which is the distance between equivalent points on neighboring teeth along the pitch circle, is equal to twice the thickness of a tooth. The pitch of a gear G A can be computed from the number of teeth N A and the radius r A of its pitch circle. In order to mesh smoothly two gears G A and G B must have the same sized teeth and therefore they must have the same pitch pwhich means.

This equation shows that the ratio of the circumference, the diameters and the radii of two meshing gears is equal to the ratio of their number of teeth. In other words, the gear ratio, or speed ratio, is inversely proportional to the radius of the pitch circle and the number of teeth of the input gear.

A gear train can be analyzed using the principle of virtual work to show that its torque ratio, which is the ratio of its output torque to its input torque, is equal to the gear ratio, or speed ratio, of the gear train. The torque ratio of a gear train is also known as its mechanical advantagethus.

In a sequence of gears chained together, the ratio depends only on the number of teeth on the first and last gear. The intermediate gears, regardless of their size, do not alter the overall gear ratio of the chain. However, the addition of each intermediate gear reverses the direction of rotation of the final gear.


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