Tyre size Vs Speedo Meter vs Milage Meter Questions

[Spiderman302]

Dear Experts here,

I have 2 questions hopefully someone can help clarify.

 

Say as our tyre size gets smaller due to wear and tear :

 

1. Will the speedo meter show higher or lower speed compared to when tyre is new ?

2. Will the milage meter shows more or less km travelled than the car actually travelled ?

 

Thks

 

[Expertz]

your speedometer is directly tied to your mileage meter, if your speedo is affected your mileage meter will be affected too

however you don't have to worry because the difference in circumference of your new vs old tire will be off by only 1 or 2 cm, so both won't be affected

 

[Stiener]

Hmm...so only if there is an increase in rim size that is bigger than the stock wil I get an error in speedo and odometer readings? Still very confused with this area.

 

As the rim size increases, the reported mileage is lesser than the real mileage travelled?

[Spiderman302]

Thats what i am trying to findout. As tyres wear out if the milage meter shows lesser km we may mistaken our fuel consumption goes up. And viceversal.

 

[SimonTan]

Very correct.

People who buy smaller diameter tyres will see good fuel economy.

The mileage is fixed by the revolution of the shaft. The manufacturer fixed the factory tyre diameter and set the computer to multiple the circumference of wheels with the revolution speed.

So if you use smaller diameter tyres, you will actually travel lesser actual distance than what the computer thought.

So if you travel lesser actual distance for the same amount of fuel, the computer will display a false good economy.

 

 

[Russ]

TECHNICALLY, there will be a difference.

 

A 205/55R16 tyre is about 630mm diameter

When worn down to the legal limit, it will reduce to 620mm

Difference = 1.5%

 

So if you are doing 100km/h, and the speedo says 105 km/h, when worn down, the speedo will say 107 (rounded up) km/h.

 

The odometer is tied to your speedometer. If you do 200km, and it showed 202km when new, it sill show 205km.

 

PRACTICALLY, 1.5% is not a lot. The normal speedo error is usually 5% or more. Also, the 1.5% is when we wear down 5mm of tread, which means you are left with precious 2mm which is very dangerous in the wet. Most tyre treads are 7-8mm deep, and once you wear down 3-4mm, and you are left with 3mm, the tyre should be changed. No problem in dry weather, but in our tropical rainy weather, not very wise.

 

So, in the end, a insignificant 1% is what you are looking at.

 

 

 

[Stiener]

So if the recommended stock tyres for my 05 civic is 185/60r15 while I changed it to 205/45r16. It would mean that my real mileage is above what was recorded on my odometer.

 

I tried to use this calculator

Tire size

 

It shows that the speedometer and the real speed is the same. So there should not be any difference between my real and displayed mileage.

[5936]

If I drive a taxi, i will love smaller tyres $$$