# Gear Ratio Calculator

## Effective/New Gear Ratios

Use our gear ratio 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
/R

New Tire Size
/R

Stock Gear Ratio : 1

Calculate

Effective Gear Ratio : 1

New Ratio Needed : 1

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.

## Gear Ratio Chart

Changing tire size will ultimately affect the power and drivability of your vehicle. If you are looking to retain your stock feel or change your gearing to the optimal ratio, then you will need this gear ratio chart to do so.

Using the chart, first cross reference your current gear ratio and tire diameter to find your approximate RPM at 65 MPH. Then reference your new tire diameter with your choice of RPM to find the new gear ratio needed to supply you with that RPM.

This chart is based on a drive gear of 1:1 at 65 MPH using a manual transmission. Automatic transmissions will run a slightly higher RPM do to slippage.

***The diameter column is assuming actual tire roll out mounted on a vehicle, not the calculated diameter. Generally tires squat about 3%. If you are using the calculated diameter, multiply that number by .97 to get a more accurate reading. If you are measuring your tire, measure from flat ground up to the center of the hub and multiply that number by 2.

The color codes indicate:
Highway, Good Fuel Economy
Best Overall Performance
More Power, Reduced Fuel Economy

Diameter Tire 25" 26" 27" 28" 29" 30" 31" 32" 33" 34" 35" 36" 37" 38" 39" 40" 41" 42" 43" 44"
Gear Ratio
2.732.943.073.213.313.423.553.733.914.114.274.564.885.135.295.385.716.17
238525682682280428922988310132593416359037303984426344824621470049885390
229324702579269627802873298231333284345235873830409943094444451947965183
220823782483259726772766287230173163332534543689394741504279435246194991
212922932395250425822668276929093050320633313557380640014126419644544813
205622142312241724932576267428092945309532163434367538633984405243004647
198721402235233724102490258427152846299231093320355337353851391741574492
192320712163226123322409250126282755289630083213343836143727379040234347
186320072095219122592334242325462669280529143112333135013610367238974211
180719462032212421912263234924692588272028263018323033953501356137794083
175418891972206221262197228023962512264027432929313532953398345636683963
170418351916200320652134221523282440256526642845304532013301335735633850
165617841862194720082075215422632372249325902766296131123209326434643743
161117351812189519542019209522022308242625202692288130283123317633703642
156916901764184519021966204021442247236224542621280529483040309232823546
152916461719179818541915198820892190230223912554273328732962301331983455
149116051676175318071867193820372135224423312490266428012888293731183369
145415661635171017631822189119872083218922752492259927332818286630423287
142015291596166917211778184619402033213722202371253826682751279829693208
138714931559163016811737180318941986208721692316247926062687273329003134
135514591524159316431698176218511941204021192263242225452626267028343063