Gear Ratio Calculator for Tire Size Changes

Use this calculator to find the changes to gear ratio when going to a different tire size. Both the effective and new gear ratios are calculated.

Stock Tire Size

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R

New Tire Size

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R

Stock Gear Ratio

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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.

For more detailed tire sizing information and to visualize the differences between tire sizes, try ourTire Size Comparison Calculator.

Gear Ratio & Tire Size RPM Chart

Find the optimal gear ratio for your tire size based on engine RPM at highway speeds.

This chart shows actual engine RPM at 65 MPH assuming a 1:1 drive gear in high gear. The diameter calculations account for 3% tire squatting when mounted on a vehicle.

Engine RPM at 65 MPH

Tire Size2.73:12.94:13.07:13.21:13.31:13.42:13.55:13.73:13.91:14.11:14.27:14.56:14.88:15.13:15.29:15.38:15.71:16.17:1
25"783843880920949980101810691121117812241307139914711517154216371769
26"75381084688591294397910281078113311771257134514141458148315741701
27"7257808158528799089429901038109111331210129513621404142815161638
28"6997537868228478759099551001105210931167124913131354137714621579
29"675727759793818845877922966101610551127120612681307133014111525
30"65270273376779181784889193498210201089116612261264128513641474
31"6316807107427657918218629049509871054112811861223124413201426
32"6116586887197417667958358769209561021109311491185120512791382
33"593639667697719743771810849893927990106011141149116812401340
34"575620647677698721748786824866900961102910811115113412041301
35"55960262965767870072776480184287493499910501083110211691263
36"54358561163965968170774377881885090897210211053107111371228
37"5295695956226416626887237577968278839459941025104211061195
38"515554579605624645670703737775805860920968998101510771164
39"50254056459060862865268571975578583889794397298910491134
40"48952755057559361363666870173676581787491994896410231105
41"4775145375615795986216526837187467978538979259409981079
42"4665025245485655846066366677017297788338759039189741053
43"4554905125355525705926226526857127608138558828979521028
44"4454795005235395575786086376696967437958368628769301005
Highway Cruise, Good Fuel Economy (675-785 RPM)
Best Overall Performance (785-895 RPM)
More Power, Reduced Fuel Economy (895-1000 RPM)
Too Low - Engine Lugging (below 675 RPM)
Too High - Engine Strain (above 1000 RPM)

Understanding Gear Ratio Changes

Changing your vehicle's tire size affects more than just ground clearance and appearance—it directly impacts your effective gear ratio. Larger tires effectively increase the distance traveled per engine revolution, which is equivalent to having a numerically lower (or "taller") gear ratio.

This change can result in reduced acceleration, altered shift points, and potential strain on your drivetrain components. Smaller tires have the opposite effect, causing your engine to run at higher RPMs at any given speed, potentially improving acceleration but possibly reducing fuel economy.

Our gear ratio calculator helps you understand these changes and provides you with the information needed to maintain your vehicle's optimal performance. If you're upgrading your tires, this tool will show you both your new effective gear ratio and what physical gear ratio change would be required to restore your original driving characteristics.

Frequently Asked Questions

How does tire size affect gear ratio?

Tire size directly impacts your vehicle's effective gear ratio. Larger tires increase the distance traveled per wheel rotation, creating the effect of a taller (numerically lower) gear ratio. This typically results in lower RPMs at highway speeds but reduced acceleration. Smaller tires have the opposite effect, causing higher RPMs but improved acceleration. The change is proportional to the difference in tire circumference.

How do I know if I need to re-gear after changing tire size?

You should consider re-gearing if:

  1. Your effective gear ratio has changed by more than 5%
  2. You notice significant loss of acceleration or towing capability
  3. Your engine struggles to maintain power in its optimal RPM range
  4. You experience poor fuel economy or transmission shifting issues after the tire change

Our calculator can help determine both your new effective ratio and what gearing would restore your original performance.

What happens if I don't change my gear ratio with bigger tires?

Without changing your gear ratio when installing significantly larger tires, you may experience:

  1. Reduced acceleration and hill-climbing ability
  2. Engine lugging (straining at low RPMs)
  3. Transmission shifting issues, as the vehicle may struggle to find the right gear
  4. Potential drivetrain stress over time
  5. Reduced fuel economy in some vehicles

The impact depends on the percentage change in tire size and your driving conditions.

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