If you've put bigger tires on your Jeep, or you're about to, one question always comes up on the trail and in every Jeep forum out there: do I need to regear? The honest answer is it depends on your tire size, your current axle ratio, and how you drive. This calculator does the math for you in seconds, and the regear chart below it shows the answer for the most common Jeep combinations. Enter your numbers, and we'll show you the effective gear ratio your Jeep is running with the new tires, plus the nearest common ring and pinion ratio to bring it back to where it should be. It also shows how far off your speedometer and odometer read on the new tires. Jeep Decal Store does not sell gears and does not install them, so we have no reason to talk you into a job you do not need.
Why Bigger Tires Throw Off Your Gear Ratio
Your Jeep's axle ratio and tire size work as a pair. A taller tire has a bigger circumference, so it takes fewer wheel rotations to cover the same ground. That sounds like a win until you remember the engine still has to spin the driveshaft the same number of times to make it happen. The right way to think about it is leverage at the contact patch. The tire is a lever arm, and its length is the tire's radius, not its diameter and not its diameter compared to the axle shaft. Going from a 33-inch tire to a 35-inch tire lengthens that lever by one inch of radius, which is about six percent. That is the whole penalty, and six percent is enough to matter, but it is a modest number, not a dramatic one. You will occasionally see the claim that a 30-inch tire means applying thirty times more force to the axle. That figure comes from dividing tire diameter by axle shaft diameter, and it does not describe a real leverage relationship. Torque at the wheel scales with tire radius, and the comparison that actually tells you anything is between the tire you had and the tire you are putting on.
Installing a numerically higher gear ratio restores the mechanical advantage your Jeep's engine was tuned around, so it gets back into its powerband instead of lugging everywhere you drive. That is also why acceleration goes soft, and fuel economy drops after a tire upgrade, and why the speedometer starts reading low.
Jeep Gear Ratio Calculator
Enter your current gear ratio and tire sizes below. If you know your tire's overall diameter in inches, use that field. If all you have is a metric size like 285/70R17, switch to the metric tab and we'll convert it for you. Along with the gear ratio, the results show your true speed at common speedometer readings, your odometer error, and how far engine RPM moves at the same road speed.
Not sure? See "How to Find Your Jeep's Current Gear Ratio" below.
Stock tire diameter used: "
New tire diameter used: "
Your calculated effective ratio:
Nearest common ring & pinion ratio:
Speedometer and odometer on the new tires
Actual speed and distance compared with what the dash shows:
| Speedometer reads | Actual speed |
|---|---|
| 25 mph | mph |
| 35 mph | mph |
| 45 mph | mph |
| 55 mph | mph |
| 65 mph | mph |
| 75 mph | mph |
Every 1,000 miles on the odometer: miles actually driven
Engine RPM at the same road speed
New tires on your current gears:
New tires with gears:
These numbers are a math estimate, not a recommendation to buy a specific gear set. They show the ratio that comes closest to your Jeep's original mechanical advantage on the new tire size. Read the caveat below, and talk to a gear shop, before you order anything.
The speed and odometer figures apply until the speedometer is recalibrated for the new tires. They come straight from the two tire diameters you entered, so measure your mounted tires if you want them exact. The RPM comparison assumes the same transmission gear and the same road speed.
How this works: your new effective ratio equals your stock ratio multiplied by the new tire diameter divided by the original tire diameter. That is the same formula axle shops and gear manufacturers use to figure out what a tire change does to your effective gearing. Revolution Gear & Axle describes the same relationship in its own regearing primer, linked in the sources at the end.
Jeep Gear Ratio Chart by Tire Size
Here is the same math worked out for the combinations Jeep owners actually run. Every cell below was calculated with the formula above, using a 32 inch stock tire as the baseline, which is close to what most Jeeps leave the factory with. The first number in each cell is your effective ratio on the new tire. The second is the nearest common ring and pinion set, chosen from the same list the calculator uses.
| Stock axle ratio | 33 in tires | 35 in tires | 37 in tires | 40 in tires |
|---|---|---|---|---|
| 3.21 | 3.31 → 3.21 | 3.51 → 3.55 | 3.71 → 3.73 | 4.01 → 4.10 |
| 3.55 | 3.66 → 3.73 | 3.88 → 3.73 | 4.10 → 4.10 | 4.44 → 4.56 |
| 3.73 | 3.85 → 3.73 | 4.08 → 4.10 | 4.31 → 4.10 | 4.66 → 4.56 |
| 4.10 | 4.23 → 4.10 | 4.48 → 4.56 | 4.74 → 4.88 | 5.13 → 5.13 |
| 4.56 | 4.70 → 4.56 | 4.99 → 4.88 | 5.27 → 5.38 | 5.70 → 5.86 |
Two things jump out of that chart. First, a lot of tire upgrades do not need a regear at all. A 3.73 Jeep on 33s comes out at 3.85, and the nearest common set is the 3.73 it already has. Second, the popular internet answer that 37s want 4.56 or 4.88 is only true if you started at 4.10. A 3.73 Jeep going to 37s lands at 4.31, and the nearest common set is 4.10, not 4.88. If your stock tire was taller or shorter than 32 inches, run your own numbers through the calculator, because the baseline moves the whole row.
How to Find Your Jeep's Current Gear Ratio
You need your stock ratio before this calculator, or anyone else, can tell you what to change it to. The easiest reliable method needs no tools at all.
Count the driveshaft turns. Chock the front wheels, safely lift one rear wheel clear of the ground, put the transmission in neutral, then mark the driveshaft and the tire with a piece of tape. Turn the tire one full revolution and count how many turns the driveshaft makes. Music City 4x4 publishes this conversion:
| Driveshaft turns | Gear ratio |
|---|---|
| About 3.25 | 3.21 |
| About 3.5 | 3.55 |
| About 3.75 | 3.73 |
| 4 | 4.10 |
| About 4.5 | 4.56 |
| About 4.75 | 4.88 |
If the differential is open, or you are already in there, the other methods are:
- The ring gear stamping. Ring gears are usually stamped with the tooth count, and sometimes with the ratio itself. Divide the ring gear teeth by the pinion teeth. A Motive Gear Dana 35 set sold as 3.73, for example, is specified as a 41 tooth ring gear and an 11 tooth pinion, and 41 divided by 11 is 3.727, which is what gets printed on the box as 3.73. That is how ratios are actually built, in whole tooth counts that rarely land on a round number.
- The axle tube tag or sticker. Older Jeeps often have a small metal tag under two of the differential cover bolts. Newer ones use a sticker or a stamped code on the axle tube, and it does not always spell the ratio out in plain numbers.
- Call a dealer parts department with your VIN. A Jeep dealer can pull the original build sheet and read the factory axle ratio off it. This is the quickest option if you bought the Jeep used and want to know what it left the factory with.
What not to bother with: the door jamb sticker. On JL Wranglers and JT Gladiators, that label carries tire size and inflation pressure, not the axle ratio. And if two methods disagree, trust the tooth count or the driveshaft count over any sticker. Axles get swapped on used Jeeps more often than people expect.
Crawl Ratio, and How to Calculate Yours
Axle ratio on its own does not tell you how your Jeep will behave on a rock ledge. The number that does is crawl ratio, and almost nobody works it out for you. The formula is simple:
Crawl ratio = transmission first gear ratio × transfer case low range ratio × axle ratio
Work it for an automatic JL Wrangler Rubicon. Its eight-speed first gear is 4.71:1, the Rock-Trac transfer case low range is 4:1, and the factory axle ratio is 4.10. Multiply them: 4.71 times 4 times 4.10 equals 77.2. That matches the 77.2:1 crawl ratio Jeep publishes for the automatic Rubicon, which is a useful sanity check that the formula is right and the inputs are right.
Now see what a regear does. Leave first gear and the transfer case alone, swap 4.10 for 4.88, and the crawl ratio goes to 4.71 times 4 times 4.88, or 92.0:1. That is a nineteen percent increase in torque multiplication in low range, and it is the actual reason a rock crawler regears, more than the highway drivability everyone talks about.
To do this for your own Jeep, you need two numbers we cannot look up for you: your transmission's first gear ratio and your transfer case low range ratio. Both are in the owner's manual specifications section. A non-Rubicon Wrangler does not have the 4:1 Rock-Trac case, so its low range multiplier is smaller, and its crawl ratio will come out well below a Rubicon's on the same axle gears. Do not borrow a Rubicon's numbers for a Sport.
Axle Models and the Carrier Break
Here is the cost surprise that catches people. A ring gear can only get so large for a given differential carrier. Push past a certain ratio, and the ring gear no longer fits the carrier you have, so you need a new carrier too. Gear suppliers call that dividing line the carrier break, or case break, and Revolution Gear & Axle puts it plainly: many differentials have a carrier break, which can increase the cost of a gear job.
Two breaks are published clearly enough to quote. On the Dana 30 front axle common to XJ, TJ, and JK Wranglers, Motive Gear lists the case break at 3.54/3.73, meaning a 3.73 or numerically higher set wants the taller carrier. On the Dana 44, Yukon lists the carrier break at 3.73/4.10, and offers thick cut gears marked with a T that let you keep the original carrier when moving to 4.10. Dana 35 rear axles have a break as well, with 3.73 sets specified for a 3.54 or higher carrier.
For the JL and JT generation, the axles are named for ring gear size in millimeters. A Sport or Sahara typically runs an M186 front with an M200 rear, and a Rubicon runs the wider Dana M210 front with an M220 rear, which is why a Rubicon has more room in the housing to begin with. We could not find a manufacturer-published carrier break figure for the M series axles that we are willing to quote as fact, so we are not going to invent one. Ask your gear supplier which of their sets for your specific axle require a carrier and which do not, and get that answered before you accept a quote. It is the single biggest swing factor in the price.
Front and Rear Have to Match
This is not a preference. In Four Wheel Drive, the transfer case ties the front and rear driveshafts together, and it expects both axles to turn their wheels at the same speed for a given driveshaft speed. That only happens if front and rear axle ratios are identical. Run 4.10 in front and 4.56 in the rear, and the two halves of the drivetrain fight each other every time you engage Four Wheel Drive, and the transfer case is where that fight gets resolved. It will not survive it. If you regear one axle, you regear both, to the same ratio, and that is why shops quote the job as a pair.
Speedometer Recalibration and Why the Tuner Is Not Optional
The speedometer error from a tire change is proportional to the diameter change, not a fixed few miles per hour. Multiply your indicated speed by the new diameter divided by the old one. Go from 32-inch tires to 35s and an indicated 65 mph is really about 71. Go from 32s to 37s and an indicated 65 is closer to 75. That is not a rounding error, and your odometer is off by the same percentage, so it records fewer miles than you actually drive and pushes your service intervals later than they should be. The calculator above works this out for your exact tire sizes, with your true speed at six common speedometer readings and the real miles behind every 1,000 on the odometer.
Regearing changes that relationship again, and on a modern Jeep the vehicle has to be told. Music City 4x4, which does this work daily, publishes the split by year: on a 2007 to 2011 Wrangler, a tuner is optional, but on a 2012 and newer Wrangler or a Gladiator it is required, because otherwise the vehicle will not recognize the difference in gear ratio and think something is wrong, putting it in limp mode. The shop uses Superchips tuners on JKs and a Tazer Mini on JL and JT.
The part worth understanding is that on those Jeeps, the tuner is the recalibration. It is not an accessory bolted on afterward to make the needle read right. You enter the new tire size and the new axle ratio, and the vehicle's computer starts doing its math correctly again. Skip it and the odometer, the transmission shift points, the ABS and traction control speed references, and the trip computer all keep working off numbers that are no longer true. Budget for the tuner as part of the regear, not as a maybe.
What a Regear Actually Costs
Nobody publishes one honest number, so here are real quotes from named shops rather than an average that would hide the spread.
- ExtremeTerrain publishes a gear overhaul kit at $600 to $1,200, a differential carrier at about $700 to $1,000, and labor at approximately $500 to $700 per axle.
- Rebel Off Road advertises a flat $1,899.99 installed for both axles, parts and labor included, on JK, JL and JT, using Revolution Gear & Axle components. Their JL and JT package offers 4.56, 4.88 and 5.13, and includes a complimentary gear oil change for both differentials 500 miles after the regear.
Two costs get left out of almost every quote you will read. The first is the tuner, which is required on a 2012 and newer Jeep as described above. The second is the gear oil service at 500 miles, which some shops include and some do not. Ask about both by name. And ask specifically whether a carrier is included or excluded, because a carrier is the difference between a job that lands near the flat rate and one that runs several hundred dollars past it.
Break-In and the 500 Mile Gear Oil Service
A new ring and pinion is not finished when the cover goes back on. The gear faces have to wear into each other, and that wear puts metal into the oil. Music City 4x4 drives 15 miles as an initial break-in before handing the Jeep back, then asks for a 500-mile break-in with no heavy acceleration, no towing, and no off-roading, followed by a differential drain and fill at 500 miles to get the metal fragments out. Rebel Off Road builds the same 500-mile gear oil change into its package. When two shops that do nothing but this converge on the same number, treat it as the standard, not a suggestion. Towing a trailer home on fresh gears is a good way to pay for the job twice.
Signs You're Due for a Regear
Already running bigger tires and skipped the math? Watch for these:
- Sluggish acceleration, especially off the line or merging onto the highway
- Fuel economy that dropped more than the extra tire weight and rolling resistance would explain on their own
- A speedometer and odometer that read slower than your actual speed and mileage
- The transmission hunting between gears, or the engine feeling like it is working harder than it used to at normal cruising speed
Any one of these on its own might just be normal wear or driving conditions. All of them together, right after a tire upgrade, is your Jeep telling you the gearing and tire size are no longer talking to each other.
When You Should Not Regear
Every shop that writes about regearing sells regearing. We do not, so here are the cases where the right answer is to keep your money.
- The diameter change is small. Look at the chart again. A one- or two-inch bump often lands on the ratio you already have. Paying two thousand dollars to go from 3.73 to 3.73 is not a modification; it is a donation.
- You are a Rubicon already on 4.10. A Rubicon has deeper factory gears and a 4:1 low range doing a lot of the work. On 35s, a 4.10 Rubicon calculates to 4.48, and while 4.56 is technically nearer, the gap is small enough that plenty of owners run 35s on stock gears without complaint. Drive it first.
- The money has a better job to do. If your Jeep needs tires, brakes, a steering box, or a death wobble diagnosis, those come first. Gears make a well-sorted Jeep nicer to drive. They do not fix a Jeep that is not well sorted.
- You mostly drive highway. Numerically higher gears raise cruising rpm. If the Jeep spends its life at 70 mph and rarely sees a trail, a deep regear can trade a quiet commute for low-end punch you will not use, and it will not necessarily give you the fuel economy back either.
A Word on Warranty
Regearing is a driveline modification, and a driveline modification can affect how a powertrain warranty claim is handled on a Jeep that is still covered. We are not going to characterize anyone's warranty policy for them. If your Jeep is under factory warranty, call your dealer's service department before the job and ask directly how they treat an axle ratio change, and get the answer from them rather than from a forum.
One Honest Caveat
This calculator gives you the mathematically ideal ratio for your tire size. It is not mechanical advice, and it cannot account for everything on your Jeep. Real-world gear selection also depends on your engine (a torquey V8 or diesel tolerates a taller tire better than a four-cylinder), your transmission, how much you tow or wheel, and plain personal preference. Treat the number this tool gives you as a strong starting point for a conversation with a gear shop, not gospel, and never as a guarantee of how your Jeep will drive afterward. Regearing itself, pulling the axles apart and setting pinion depth and backlash correctly, is precision work. It is worth having a shop that does this every day handle the install rather than turning it into a driveway project.
After the Tires: Sorting Out the Spare
Once you have settled on a new tire size, the spare on the back has to match it, and so does the cover over it. Our guide to choosing a spare tire cover covers material and fit for the new setup. If you are running a matching full-size spare now, our 5-tire rotation guide covers working it into the rotation so all five wear evenly. New wheels usually come along with new tires, so it is worth checking our Jeep wheel bolt patterns and lug nut torque specs by generation before you install anything. And bigger tires change how the front end behaves, so read up on what causes death wobble and how to fix it before you go chasing a new vibration.
Covers that fit the new spare
Covers are made to order, so allow 10 to 14 business days for manufacturing. Free shipping on orders over $59.99.
Frequently Asked Questions
How do I find my Jeep's current gear ratio?
The fastest no-tools method is to count driveshaft turns. Chock the front wheels, lift one rear wheel off the ground, put the transmission in neutral, mark the driveshaft and the tire, then turn the tire one full revolution and count how many turns the driveshaft makes. Roughly 3.5 turns means 3.55, 3.75 means 3.73, 4 turns means 4.10. You can also read the ratio off a stamping on the ring gear, off a tag on the axle tube, or by calling a Jeep dealer parts department with your VIN. Skip the door jamb sticker on a JL or JT, it carries tire and pressure information, not the axle ratio.
Do I need to regear for 35-inch tires?
It depends on your stock ratio and stock tire diameter, there's no single answer for every Jeep. As an example, a Jeep running a 3.21 stock ratio on 32-inch stock tires that moves up to 35s comes out to an effective ratio of about 3.51, close to the common 3.55 ratio. That shift is usually enough that owners feel it in acceleration and fuel economy. A Jeep with taller stock gears already might land close enough to a common ratio to skip regearing. Run your own numbers through the calculator above.
What gear ratio is best for 37-inch tires?
There is no single best ratio for 37s, and the popular answer of 4.56 or 4.88 only applies to Jeeps that started out fairly deep. Run the formula. A Jeep with 4.10 gears on 32-inch stock tires going to 37s works out to 4.10 times 37 divided by 32, which is 4.74, so 4.88 is the nearest common set. That same Jeep with 3.73 gears works out to 4.31, and the nearest common set is 4.10. Engine torque, transmission and how much you tow move the answer around that number.
Does every tire size upgrade require a regear?
No. Small tire upgrades, roughly an inch or two of diameter, often land close enough to a common ratio that a regear isn't necessary, especially with an automatic transmission or a torquey engine that can absorb the difference. Bigger jumps, like moving from stock tires to 35s or 37s, usually push the effective ratio far enough from stock that most owners notice the difference and choose to regear.
Will regearing fix my speedometer after a tire upgrade?
Not by itself. On a 2007 to 2011 Wrangler a tuner is optional. On a 2012 and newer Wrangler or a Gladiator, Music City 4x4 says the recalibration is required, because otherwise the vehicle will not recognize the new gear ratio and can drop into limp mode. The shop uses Superchips tuners on JKs and a Tazer Mini on JL and JT. On those Jeeps the tuner is the recalibration, and skipping it leaves the odometer, shift points, ABS and trip computer all working off the wrong numbers.
How much does it cost to regear a Jeep?
Quotes vary by shop and by how much has to be replaced. ExtremeTerrain publishes a gear overhaul kit at 600 to 1,200 dollars, a differential carrier at about 700 to 1,000 dollars, and labor at approximately 500 to 700 dollars per axle. Rebel Off Road advertises a flat 1,899.99 dollars installed for both axles on JK, JL and JT, parts and labor included. Budget on top of that for a tuner and for the gear oil service at 500 miles.
Can I use this calculator for a tire size listed as a metric size, like 285/70R17?
Yes. Switch either tire field to the metric option and enter the section width in millimeters, the aspect ratio, and the wheel diameter in inches. The calculator converts it to an overall diameter in inches automatically. A 285/70R17 works out to a nominal 32.7 inches. Real tires usually measure a fraction of an inch under the nominal figure, so if you want the exact number, use the overall diameter the tire manufacturer publishes for that specific tire.
Sources: Music City 4x4, Regears: Why Would You Want To Regear Your Vehicle? (driveshaft turn conversion table, tuner requirement by model year, 15 mile and 500 mile break-in, 500 mile differential drain and fill) · Revolution Gear & Axle, Re-Gearing Your Vehicle (carrier break increases the cost of a gear job) · ExtremeTerrain, When and Why You Should Regear Your Wrangler (gear kit, carrier and labor pricing) · Rebel Off Road, Regear My Jeep (flat installed price, ratios offered, included 500 mile gear oil change) · Yukon Dana 44 4.10 thick ring and pinion listing (Dana 44 carrier break 3.73/4.10, thick cut gears marked T) · Motive Gear Dana 30 ring and pinion listing (Dana 30 case break 3.54/3.73) · Motive Gear Dana 35 3.73 ring and pinion kit (41 tooth ring, 11 tooth pinion, 3.54 or higher carrier)
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