chart to show what gear ratio change with taller tires

| How-To - Transmission

Getting the Ratio Right; Correcting the Axle Gear Ratio for Oversized Tires

RATIOnale

Photographers: John Lehenbauer and Steve Flores

For part two of our series about transforming Jared Lehenbauer's new-to-him '01 Ford F-250 into a truck that's better suited to his needs, we're detailing how to select the right gear ratio for two- and 4-bicycle-drive trucks with large tires.

There are probably thousands of reasons why people don't install the correct rearend gears to compensate for larger tire sizes. Some may not want to spend the money (easily more than than $i,000 including labor) while others may experience a diesel truck has an abundance of ability and torque and so it volition non be affected by the tire-size increase. We admit non irresolute the gears does not have a huge effect on a truck that's only driven to the store and around town. However, if it tows or hauls heavy loads, in that location may be a noticeable difference.

Jared purchased the truck with an inherent gear trouble. The previous owner lifted the rig and installed 37-inch tires but left the stock 3.73 gears intact. The ratio is fine with the original (approximately) 32-inch tires, equally Ford engineers developed this combination (tire size and gear ratio) along with the transmission gearing to establish a drive ratio that provides the best power, economy, and driveability. Fifty-fifty though the 5-inch size difference doesn't seem like much, a 37-inch tire reduces the 3.73 gear ratio down to about a 3.19.

When we arrived at Steve Flores' place, he wasted no fourth dimension getting the rear of Jared Lehenbauer's '01 Ford F-250 upwardly on jack stands and removing the tires. You may be curious about the F-350 bluecoat on the tailgate. No, nosotros did not make a mistake; the truck is definitely an F-250 (the Dana 50 front beam is a giveaway). Somewhere along the line, the badge got switched.

From the factory, a truck's engine and drivetrain are engineered to piece of work together to provide the maximum amount of ability in the most efficient mode. The engine revs to the correct rpm and the transmission shifts to the right gear at the proper speed, ultimately providing the nearly power and economy bachelor. When an incorrect tire-and-gear combination is used, information technology throws that balance off. Engine rpm and gearshifts will not coincide correctly with the vehicle's speed on the highway (as originally engineered). The engine'south rpm will be lower, possibly taking the engine out of its prime number power range. At present, fueling must be increased and the engine has to be pushed harder to brand the same power information technology made at the previous speed. Information technology can likewise require a driver or the transmission to downshift in club to get back into the power range (simply at a slower speed). Information technology is also possible to observe the manual "betwixt gears" and hunting for the correct i, which tin exist hard on the gearbox if it happens too frequently.

Correcting the gear ratio for compatibility with tire size allows engine speed to return to the proper rpm range and the transmission into the correct gear for the speed being traveled (like stock). This is critical when hauling or towing heavy loads that can put even more strain on the engine and transmission when not in the correct power range.

It is not always piece of cake to know the right gear ratio to employ with a particular tire size, so we went to the Internet and searched for a "gear-ratio calculator." The search brought upward a number of different charts posted by manufacturers and businesses, which allow you to figure out the best ratio for the tires you lot are using. Also, most shops that install gears are good sources of information regarding the proper setup.

In one case we understood what was needed, we gave Nitro Gear & Axle a telephone call and ordered a set of four.xxx gears for the Dana 50 front and 10.five-inch Sterling rear axles (too as new bearings and seals) that will bring the '01 Ford'southward drivetrain as close to stock every bit possible. Magazine-Hytec's differential covers are being added to give the upgrade a clean terminate.

We contacted our buddy Steve Flores (who has been setting up axles for years) for aid with the installation. Later a trivial blackmail of food and drink, Steve agreed to aid us out and give us his proficient insight on the proper fashion to set up front and rear axles with new bearings, seals, and ring and pinion gears.

The left and right axleshafts are popped out so the differential can be removed.

Steve makes alignment marks on the bearing caps and axlehousing before removing the caps to ensure they are correctly oriented during reassembly.

The carrier comes out with an easy tug. Usually, a large prybar and some grunting are involved in getting extracting one. Steve says when carrier bearings become worn, they lose the preload that's exerted on them by the housing and shims. While the centersection is in good overall shape, components such as bearings, gears, and such are just fatigued.

The stock limited-slip differential is in good shape, but the ring gear has seen better days. There is a lot of pitting and some rust on the teeth. When Jared got the truck, he serviced both differentials and found the gear oil in the rear resembled chocolate milk. The oil was contaminated with water, which accounts for the pitting and rust establish on the gears.

Steve removes the pinion nut and and so uses a puller to separate the yoke from the pinion. With the yoke removed, he uses a expressionless-blow hammer to tap the pinion gratuitous from the bearings.

The pinion seal and front end begetting are removed from the centersection.

The bearing races are removed from the housing with a hammer and punch. Some metallic shrapnel is found in the front cavity of the housing between the races. Upon inspection of the pinion and bearings, we encounter the rear bearing (nearest the gear) has spun on the pinion shaft and eaten the bearing shims. This explains the play Steve institute on his initial inspection of the yoke/pinion.

Normally, when replacing the pinion gear and bearings with new pieces, there is no need to remove the sometime begetting. In this case, Steve is using the old bearing as a setup bearing (to properly shim the new pinion before pressing on the new bearing). He opens up the inner race with a barrel sander, enabling it to slide on and off the pinion for changing shims hands and not dissentious the new bearings.

A bearing puller is used to remove the carrier bearings. The begetting on the band-gear side did not want to come up off with only the puller, so Steve heated the inner race before reinstalling the puller.

All the new pieces are unboxed for installation.

After removing the bearings and ring gear from the carrier, Steve begins the assembly process. Kickoff, he installs the new ring gear with the supplied bolts, making certain to use thread-locking compound on each one. Once the bolts are installed, Steve torques them to specifications.

New bearing races are installed in the differential housing.

Steve measures shim thickness to determine what he will utilise on the pinion. The same-thickness shims are used under the crush-sleeve eliminator. Once Steve gets the test bundle close to a fitment he thinks might piece of work, he installs the pinion and bearings in the make clean axle centersection.

The differential is lifted into the housing so tapped into identify with a brass punch and hammer. Steve installs approximately the same number of shims on the exterior (betwixt begetting and housing) to go the ring gear and pinion gear mesh shut. The bearing caps are so installed.

The ring gear is painted with a marking compound before the differential is spun to see what the mesh blueprint between the ring and pinion looks similar. And so, a dial indicator is positioned to determine how much backfire there is so Steve knows what adjustments he needs to make.

The carrier and pinion are removed and installed two or three more times as Steve tries to determine the right shimming for all the bearings to centre the gears and accomplish the mesh pattern he wants.

When Steve finally gets the gears centered with a good mesh design and .007 inches backfire, the carrier and pinion are pulled out 1 last time.

Once the proper shimming is adamant, the setup bearing is removed from the pinion, and the new bearing is pressed on with the shims.

Before installing the pinion gear, Steve smears grease on the bearings to ensure they take some lube and will non dry out out before gear oil gets to them. The pinion with bearings, shims, and oil slinger is installed with the yoke (and nut), but no seal. An inch-pound torque wrench is used to make up one's mind the bearing preload on the pinion and too helps verify all the shimming is correct. The new bearings are set at 30 lb-in. No seal is installed at this time because it adds extra drag to the yoke/pinion and Steve wants an exact measurement of preload.

The carrier is installed in the housing with the correct shims, begetting caps, and thread-locking-chemical compound-coated bolts. Bolts are torqued to specification.

A new pinion seal is installed along with the yoke, pinion nut, and washer. Thread-locking compound is used on the pinion nut to make sure it stays in place. Steve taps the yoke with a expressionless-blow hammer to make sure everything is seated properly. The final step before installing the driveshaft is to torque stripe the pinion nut.

We put the stock Sterling ten.5 differential cover and the Mag-Hytec replacement next for a comparison. The aluminum Mag-Hytec piece holds more fluid and has ports for temperature sensors, a dipstick, and a magnetic drain plug that is definitely a plus when it's time to service the differentials.

Before installing the Mag-Hytec cover, the O-ring is installed with a dab of silicone spread over it. Stainless steel hex-head bolts and washers that come with the cover are used.

The axleshafts are reinstalled with the bolts torqued to specification. After the driveshaft is set in identify, the tires and wheels are put back on and the differential is filled with the proper gear oil.

With the rear differential at present sporting 4.30 gears, it's fourth dimension to pull the forepart apart. The forepart-axle steering knuckles make this disassembly a flake more complicated.

Steve begins taking the Dana 50 forepart axle apart by removing the driver-side tie-rod end, then he tin can access the differential cover (to drain the oil and remove it). He then removes the locking hub and axleshaft C-prune, which facilitates removing the unit-bearing hub from the knuckle. The axleshaft is then removed. We discovered the outer seal that supports the stub shaft in the knuckle and the thrust washer were worn out, so we had to rails down new parts before putting information technology back together. Nosotros also replaced the outer axle seal on the rider side.

A dead-blow hammer, a prybar, and a piece of foursquare metal tubing (to protect the sealing surface of the differential housing from impairment and provide a better prying angle) are used to remove the forepart differential.

With the differential out, Steve begins removing the bearings and ring gear.

Reassembling the carrier for the front end Dana 50 axle is the same bones process every bit the rear, with a couple of steps slightly altered. The new ring gear is heated with a torch (to expand the metal slightly for easier fitment) before beingness installed on the carrier. Another difference is the carrier-bearing shims are under the bearings, which makes them difficult to interchange for setup when the bearing is pressed on. Then, the old bearings are opened with a barrel sander and so they tin can be used as setup bearings.

On Dana forepart axles, the shaft seals are pressed into the centersection to keep oil out of the axle tubes. The seals, forth with the sometime pinion-bearing races, are removed and the housing is cleaned of any old oil and droppings. With everything cleaned up, Steve taps new axle seals into place with a seal commuter. Note: Brand sure to use the proper tools to install the axle seals. They are prone to leaking if they're installed improperly.

The ring gear is painted with marking compound to check the mesh pattern to see what adjustments need to be made. The carrier and pinion come out several times for shimming until the pattern is right.

One time the correct shims for the carrier and pinion are plant, Steve removes the setup bearings and presses on the new ones. Like the front pinion, a crush sleeve is not used with the pinion bearings—an eliminator is used instead.

Before installing the differential, grease is applied to the axleshaft seals.

The carrier is installed with the begetting caps and bolts (with thread-locking compound applied). The backlash and preloads are rechecked.

After installing the yoke and pinion nut, the differential cover is installed. The larger Mag-Hytec cover is designed so it does non interfere with the necktie rods when the steering is turned total left or right.

Finally, the axleshafts, (care is taken not to damage the seals), unit-bearing hubs, locking hubs, and brakes along with the wheels and tires are reinstalled.

What Deviation Did the Gears Make?

Before we installed the gears in the '01 Ford F-250, we hooked up Jared Lehenbauer's 30-foot toy hauler loaded with off-road machines, firewood, fuel, and all the essentials for a couple of days away. Our towing route took the states on a department of California Superhighway 14, which has a couple of adept hills that would requite usa a feel for how well or poorly the truck will climb a grade. On the road, the Banks iDash 5-inch monitor we installed in office one of our series was used to tape information during the trip to see how the truck performed. This also gave us an opportunity to look for any other problems the truck may take that might need to exist addressed.

The run with the stock three.73 gears had the truck working hard to get up to speed on the highway. Once at that place, EGT ranged betwixt 800 and one,000 degrees Fahrenheit, transmission temperature was around 180 degrees, and engine-oil temp was 208, with an average of near 60 pct load on the engine in 3rd gear at threescore mph. When we hit the biggest loma on the highway, the transmission had to be dropped into Second gear with 100 pct engine load at 2,800 rpm to keep the truck shut to 50 mph. The turbocharger'south boost shot upwards from 10 psi to 20 psi and the EGT tipped 1,200 degrees F. The manual temperature but went up slightly, while the oil temp crept up to 220 degrees.

Later on installing the 4.30 gears in the truck's axles, we hooked up the trailer once again and took the same route to see what type of improvements the gears made. The truck definitely got up to speed quicker and easier. We also noticed accelerating to pass was easier. The readings going down the highway were in the aforementioned ballpark equally before, even with outside temperatures a bit warmer. Only the biggest divergence was seen on the hills. On the largest grade, the truck was able to climb in 3rd gear at 2,600 rpm going more than than 50 mph with some pedal left. The EGT was slightly higher at 1,300 degrees F while the transmission, engine, and heave but crept up a fraction.

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Source: https://www.motortrend.com/how-to/1902-getting-right-correcting-the-axle-gear-ratio-for-oversized-tires/