TreadIndex — Tire sizes converted, compared, and checked against your fenders.

Sections	Latest
Size Conversion	8
Speedometer Error	6
Fitment & Clearance	6
Plus Sizing	120
Load & Speed Ratings	5
Load index and speed ratingLoad index and speed rating — one page per exact question.	280
Tire Size ReferenceEvery metric tire size worked out — overall diameter, sidewall height, circumference and revolutions per mile.	576
Tire Size ComparisonWhat changes when you swap one tire size for another — speedometer error, ground clearance, section width and revolutions per mile, worked from geometry alone.	946
Axle Ratio After a Tire ChangeWhat axle ratio restores stock gearing after fitting bigger tires — with the engine rpm before and after, and the nearest ratio you can actually buy.	210

Speedometer Error From Tire Size — One Ratio, and It Runs Both WaysSpeedometer Error · 3 min read
A one-inch increase in diameter on a 30-inch tire is a 3.3% error. At an indicated 70 you are doing a bit over 72.
Load Index and Speed Rating — The Two Codes at the End of the SizeLoad & Speed Ratings · 4 min read
Everyone reads the size and stops. The two characters after it are the ones with a safety consequence.
Will 33s Fit Without a Lift? Often Yes — the Rubbing Happens Where You Are Not LookingFitment & Clearance · 3 min read
Most stock trucks clear a 33-inch tire driving in a straight line. Fitment is decided at full lock over a bump, which is the one condition nobody tests in the parking lot.
Plus Sizing Chart: Wider Tire, Shorter Sidewall, Same Rolling DiameterFitment & Clearance · 3 min read
Plus sizing trades sidewall for wheel and keeps the overall diameter where it was. Done properly nothing on the vehicle notices — which is the entire point.
Recalibrating a Speedometer After a Tire Change: Four Routes, and How to Verify It WorkedSpeedometer Error · 3 min read
On most modern vehicles the tire size is a stored number, not a mechanical ratio. Where that is true, correcting it takes minutes; where it is not, the options get physical.
Bigger Tires Change Your Gearing — Here Is How Much, and What to Re-Gear ToSpeedometer Error · 3 min read
A larger tire is a gear change nobody installed. The effect is the same as swapping the differential for a taller one, and the arithmetic is a single ratio.
Tire Load Index Chart: What Each Number Carries, and Why Four Tires Is Not the SumLoad & Speed Ratings · 4 min read
The load index is a code, not a weight, and the table is not linear. Reading it correctly also means understanding why the four numbers do not simply add up to your vehicle's weight.
Does Tire Size Affect the Odometer? Yes — and It Costs You Warranty MilesSpeedometer Error · 3 min read
The speedometer error gets all the attention because you can see it. The odometer runs on the same signal and quietly accumulates the same error over every mile.
Reading a Tire Sidewall: Every Marking, and Which Ones MatterSize Conversion · 2 min read
A sidewall carries a dozen markings and most buying decisions come down to three of them. One of the three is a date.
Plus Sizing: Bigger Wheels, Same Diameter, and What It CostsFitment & Clearance · 2 min read
Plus sizing keeps the tire the same overall height while making the wheel bigger and the sidewall shorter. Everything good and everything bad about it follows from that shorter sidewall.
How Tire Size Changes Your Speedometer — and What Else Reads WrongSpeedometer Error · 2 min read
The speedometer is the error people notice. It is not the only one, and on some vehicles it is not the most important one.
Why Tire Pressure Is Always Checked ColdSpeedometer Error · 2 min read
A tire gains several psi within a few miles of driving. Every pressure specification in the world assumes you have not driven.
Reading Tire Wear: Five Patterns and What Each One MeansFitment & Clearance · 2 min read
A worn tire is a record of everything that has been wrong with the car. Five patterns cover almost all of it, and each has one main cause.

Plus-sizing a wheel

120 calculations · Plus Sizing · browse all

Axle ratio for a tire change

210 calculations · Axle Ratio After a Tire Change · browse all

Load index and speed rating

280 calculations · Load index and speed rating · browse all