Axle Ratio To Tire Size Chart | Match Gears To Diameter

A taller tire acts like a lower numerical gear, so bigger diameters usually need deeper axle gears to keep the same feel.

An axle ratio to tire size chart is one of the handiest tools you can use before buying bigger tires. When tire diameter goes up, the tire rolls farther with each turn of the axle. That drops engine rpm at any road speed and changes how the vehicle leaves a stop, climbs a grade, and holds overdrive on the highway.

That can feel fine on a light street truck with a strong engine. On a heavier rig, it can make the whole setup feel sleepy. You press the pedal harder, the transmission downshifts more often, and towing gets less pleasant. The fix is not guessing. The fix is matching the new tire height to a ratio that puts the gearing back where it belongs.

This chart does that job. It gives you a clean starting point for common tire diameters and shows what axle ratio you’d need to keep the same overall feel you had with a 28-inch tire. If your stock setup already feels right, the numbers below help you stay close after a jump to 31s, 33s, 35s, or 37s.

Why Bigger Tires Change The Way A Vehicle Drives

Think of tire diameter as part of the final drive. A taller tire covers more ground per rotation, so it acts like a taller gear. That trims cruise rpm, which sounds nice at first. But it also blunts launch feel and can pull the engine farther away from its sweet spot.

The effect gets bigger as tire height grows. A move from 28 inches to 30 inches is mild. A move from 31 inches to 35 inches is a different story. Add extra tire weight, steel wheels, bumpers, tools, passengers, or a trailer, and the gap gets easier to feel from the driver’s seat.

Use This Math Before You Buy Gears

If you like the way the vehicle drives now, use your current setup as the baseline. Then scale the axle ratio to the new tire diameter.

• New axle ratio needed = old axle ratio × new tire diameter ÷ old tire diameter
• Lower numerical ratios like 3.31 or 3.55 cut rpm more
• Higher numerical ratios like 4.56 or 4.88 bring back punch and towing feel

Say your truck has 3.73 gears and a 28-inch tire, and you want 35-inch tires. The math lands near 4.66. Since gears come in real-world steps, that usually pushes you toward 4.56 or 4.88. A light daily driver may be happy with 4.56. A heavy 4×4 or tow rig often feels better with 4.88.

How To Turn A Tire Size Into Diameter

The sidewall gives you the numbers you need. In 265/70R17, the 265 is width in millimeters, the 70 is the aspect ratio, and the 17 is wheel diameter in inches. Goodyear’s tire size calculator uses those same three numbers to work out tire height.

The rough math is simple: sidewall height times two, then add wheel diameter. So 265/70R17 comes out to about 31.6 inches. That means you should use the 32-inch row in the chart, not the 31-inch row. One inch can change the ratio choice, so don’t skip this step.

Pick The Nearest Real Gear Set

You won’t find every decimal ratio on the shelf. That’s normal. Use the chart to find the target, then round to the closest real gear set. If the vehicle is heavy, sees hills, or tows often, leaning one step deeper usually feels better than going one step taller.

Street use on flat roads gives you more room to stay near the middle. Off-road crawling, big mud tires, and soft overdrive transmissions push the choice upward. The chart gets you into the right zone. The final pick still needs a little common sense.

Axle Ratio To Tire Size Chart For Common Diameters

This chart uses a 28-inch tire as the baseline. The middle column shows the ratio needed to keep the same feel as 3.55 gears on a 28-inch tire. The right column does the same for 3.73 gears on a 28-inch tire.

Tire Diameter	Keeps The Feel Of 3.55 On 28″	Keeps The Feel Of 3.73 On 28″
26″	3.30	3.46
27″	3.42	3.60
28″	3.55	3.73
29″	3.68	3.86
30″	3.81	4.00
31″	3.93	4.13
32″	4.06	4.26
33″	4.18	4.40
34″	4.31	4.53
35″	4.44	4.66
36″	4.56	4.80
37″	4.69	4.93

Read across the row that matches your new tire height. If your current truck feels right with 3.55 gears and you’re moving to 33-inch tires, the chart lands near 4.18. Since 4.18 is not a common set, 4.10 or 4.30 becomes the real choice. Light street use leans toward 4.10. Weight, hills, and towing lean toward 4.30.

The same pattern shows up with 3.73 gears. Move from a 28-inch tire to a 35-inch tire and the chart points at 4.66. That puts you right between 4.56 and 4.88. If you hate hunting between gears on the highway, the deeper pick often feels better than the taller one.

What The Common Gear Choices Usually Mean

• 4.10: a mild jump that works well with 31s and some 33-inch setups
• 4.56: a strong all-around pick for many 33s and 35s
• 4.88: often a sweet spot for heavy 35-inch rigs and many 37-inch builds
• 5.13 and up: more common when 37s, towing, low-range trail work, or a small engine are in the mix

Common Tire Jumps And The Ratios They Tend To Like

From Stock Tires To 33s

A jump to 33-inch tires is where many owners first feel the stock gearing soften. If you started with 3.55 gears, 4.10 often wakes the vehicle back up. If you started with 3.73s, 4.10 stays close, while 4.30 can feel nicer on a heavier SUV or pickup.

On a manual transmission, driver style matters a lot. On an automatic, overdrive behavior matters more. If the transmission already liked to downshift on grades, bigger tires will usually make that habit worse.

From 31s To 35s

This is the change that catches people out. A truck that felt fine on 31s with 3.73s can feel flat on 35s without deeper gears. Many builds in this range land on 4.56 or 4.88, based on weight and highway use. That is why so many 35-inch builds end up re-geared after the tire swap.

The tire itself also matters. A heavy mud tire hits harder than a lighter all-terrain of the same stamped size. The chart only sees diameter. Your right foot will feel the extra rotating mass too.

From 35s To 37s

At 37 inches, the margin gets tight. A 3.73 gear that once felt normal can now behave like a much taller ratio. That is why 4.88 and 5.13 show up so often on 37-inch builds. With a small engine, a soft overdrive, or regular towing, the deeper pick is usually the safer bet.

If you’re still unsure, run your actual numbers through TREMEC’s gear ratio calculator. It lets you change axle ratio and tire height so you can see what road speed and rpm look like in each gear before you order parts.

Common Tire Sizes And The Chart Row To Use

Many people shop by tire size code, not by inches. This table gives you a quick bridge from common metric sizes to the chart rows above. Actual mounted height can vary a bit by tire model, wheel width, and load, so treat these as good working numbers.

Tire Size	Diameter In Inches	Use This Chart Row
235/75R15	28.9″	29″
255/70R16	30.1″	30″
245/75R16	30.5″	31″
265/70R17	31.6″	32″
285/70R17	32.7″	33″
275/70R18	33.2″	33″
295/70R18	34.3″	34″
315/70R17	34.4″	34″

What Can Throw The Chart Off

The chart is solid, but it is still a chart. It does not know your engine’s torque curve, the transmission’s first gear and overdrive ratios, the weight of the vehicle, or how often you tow. It also does not know whether your “35-inch” tire measures 34.4 inches on the truck. Those little gaps matter.

Speedometer and shift behavior can change too. Some vehicles let you correct for tire size in software. Some need a tuner. Some still want deeper gears even after the speedometer is fixed, because calibration does not put mechanical advantage back into the axle.

If your build has one or more of the items below, lean toward the deeper gear when you’re between two choices:

• Frequent towing or hauling
• Steep grades or mountain driving
• Heavy all-terrain or mud-terrain tires
• Armor, winch, racks, camping load, or other extra weight
• Small-displacement engine or a tall overdrive gear

Use The Chart As Your Starting Point

If you want the shortest version, here it is: taller tires call for deeper gears if you want to keep the same feel. Work out the true tire diameter, match it to the chart, then round to the nearest real gear set based on how the vehicle is used. That one step can save you from a tire upgrade that looks right but drives wrong.