Published by Colorado Axle and Gear | Denver, Colorado
If you have lifted your Jeep or truck and installed larger tires, you have probably noticed the performance is not quite what you expected. The rig feels sluggish off the line, fuel economy has dropped noticeably, and at highway speeds the engine seems to be working harder than it should. The culprit is almost always the gear ratio — and a regear is the fix.
This guide explains what a regear is, why it matters after a tire size increase, how to choose the right gear ratio for your specific setup, and what to expect from the regear process. We have been doing regears in Denver for over 30 years, and this is the information we give every customer who comes in with a lifted truck or Jeep.
What Is a Regear?
A regear is the process of replacing the ring and pinion gear set inside your front and rear differentials with a new set that has a different gear ratio. The ring gear is the large gear bolted to the differential carrier. The pinion gear is the smaller gear that meshes with the ring gear and connects to the driveshaft. Together, they multiply torque from the driveshaft to the axle shafts.
The gear ratio describes how many times the driveshaft rotates for every one rotation of the axle. A 4.10 ratio means the driveshaft turns 4.10 times for every one wheel rotation. A 4.88 ratio means the driveshaft turns 4.88 times. A numerically higher ratio multiplies torque more aggressively — the engine does not have to work as hard to turn the wheels, and acceleration is stronger.
Why Bigger Tires Require a Regear
When your truck left the factory, the gear ratios in the differentials were chosen by the engineers to work optimally with a specific tire diameter. When you install larger tires, two things happen:
1. Your effective gear ratio gets taller (numerically lower). A larger tire has a bigger circumference, so each rotation of the wheel covers more ground. This has the same effect as installing a numerically lower gear ratio. If your factory ratio is 3.73 and you go from stock 265/70R17 tires (about 31.6 inches) to 35-inch tires, your effective gear ratio drops to roughly 3.32. That is a meaningful change in how the drivetrain feels and functions.
2. The engine has to work harder to turn the bigger tires. Larger tires are heavier and have more rotational mass. The engine has to produce more torque to accelerate the same amount, but the taller effective gear ratio means it receives less mechanical advantage to do so. The result is sluggish performance and reduced fuel economy.
A regear corrects this by installing a numerically higher ratio that compensates for the tire size increase and restores the effective gear ratio to something close to factory.
Choosing the Right Gear Ratio
The most common question we hear is: “What gear ratio do I need for my tire size?” Here is a general guide for popular tire and truck combinations:
| Tire Size | Recommended Ratio (Auto) | Recommended Ratio (Manual) |
|---|---|---|
| 33 inch | 4.10 | 4.10 |
| 35 inch | 4.56 | 4.56 |
| 37 inch | 4.88 or 5.13 | 4.88 |
| 40 inch | 5.13 or 5.38 | 5.13 |
These are general guidelines. The right ratio for your specific vehicle also depends on your transmission type and gear count, your transfer case low range ratio, how you use the vehicle (daily driver vs. dedicated off-road), and your engine’s power and RPM characteristics. We calculate the optimal ratio for your exact combination when you bring the vehicle in.
Do You Need to Regear the Front and Rear?
Yes, if your vehicle has four-wheel drive, you should always regear both the front and the rear differentials to the same ratio. If you only regear one axle, the front and rear will be spinning at different speeds when in four-wheel drive, causing drivetrain binding, accelerated wear on the transfer case, and potentially catastrophic damage on hard surfaces. Always do both.
The Regear Process: What to Expect
Drop-off: You bring the vehicle in. We confirm your tire size, check current gear ratios if unknown, and discuss your use case and budget. We provide an estimate and parts timeline.
Parts: We order quality ring and pinion sets from our preferred suppliers (Dana/Spicer, Yukon Gear, Revolution Gear and Axle) if they are not in stock. Lead time is typically 1–3 business days for most common ratios.
Installation: Each differential is disassembled, old gears are removed, and the new ring and pinion set is installed. Setting pinion depth and backlash correctly is the critical step that separates a quality regear from a poor one. We use precision measurement tools and take the time to get it right. The differential is then reassembled with new bearings and seals.
Break-in: After the regear, we recommend a 500-mile break-in period. During this time, avoid sustained highway speeds, heavy towing, and extreme off-road loads. After the break-in, change the differential fluid — this removes metal particles generated as the new gears seat in.
Noise check: A properly performed regear should be quiet. If you hear a whine after a regear, it typically indicates a setup issue with pinion depth or backlash. We stand behind our work.
Typical Cost of a Regear
Regear costs vary based on the vehicle platform, the gear ratio, and whether additional components like bearings and seals are replaced (they should always be replaced on a quality regear). Call us at (303) 286-0338 for a current estimate on your specific vehicle. We will give you honest, upfront pricing with no hidden charges.
Ready to Regear Your Truck or Jeep?
Colorado Axle and Gear is located at 2611 W. 64th Ave Suite A, Denver, CO 80221. We serve customers throughout the Denver metro area, including Westminster, Arvada, Lakewood, Aurora, Boulder, Fort Collins, and beyond. Hours are Monday–Friday, 8AM–5PM. Call us at (303) 286-0338 or email Al@axlengear.com to discuss your regear.