Speedo Accuracy

[Unfazed]

Hi Friends here,

 

Juz for knowledge sake.

 

Do we cause our seedo reading to be inaccurate when we change to bigger rims? I understand that the wall of the tires becomes shallower when switch to bigger rims.

 

Is there a formula that we should based on in terms of incremental of rim size vs decrease in the side wall of the tires?

 

My wira was formerly on 175/70R13, to 195/50R15 currently. If my next set of tires becomes 195/55R15, does that mean that my speedo will become inaccurate?

 

Or can we conclude that any increase in rim sizes will cause the speedo to be inaccurate?

 

Thanks for the lessons here.

 

Cheers!

[Gadgeter]

based on the data from:

 

http://ejelta.com/tiresize/index.html?ws15...&maxdelta=2

 

+0.14% difference.

[Redplanet]

Hi Friends here,

 

Juz for knowledge sake.

 

Do we cause our seedo reading to be inaccurate when we change to bigger rims? I understand that the wall of the tires becomes shallower when switch to bigger rims.

 

Is there a formula that we should based on in terms of incremental of rim size vs decrease in the side wall of the tires?

 

My wira was formerly on 175/70R13, to 195/50R15 currently. If my next set of tires becomes 195/55R15, does that mean that my speedo will become inaccurate?

 

Or can we conclude that any increase in rim sizes will cause the speedo to be inaccurate?

 

Thanks for the lessons here.

 

Cheers!

 

Do a practical test. Compare your speedometer to a GPS speedo readout. For both my old and current car, original rims upgrade 2" both showing faster speed of 5 kmh compared to GPS.

 

[Tkseah]

how accurate is GPS speed reading? maybe speedo more accurate than GPS?

[Watwheels]

I think you and many ppl got it wrong. Many ppl think speed on the speedo is predetermine by the diameter of the wheel. As a matter of fact the speed is determine by a pulse sensor in your transmission(aka gearbox). A computer will calculate and convert the no. of pulses during rotation to determine the speed.

 

The speedo is not 100% accurate. There's a tolerance of + - 10% due to factors like wear on tires, tire temperature and such. As long as your wheels overall diameter is within stock specifications your speedo will still be consider accurate.

[Unfazed]

I think you and many ppl got it wrong. Many ppl think speed on the speedo is predetermine by the diameter of the wheel. As a matter of fact the speed is determine by a pulse sensor in your transmission(aka gearbox). A computer will calculate and convert the no. of pulses during rotation to determine the speed.

 

The speedo is not 100% accurate. There's a tolerance of + - 10% due to factors like wear on tires, tire temperature and such. As long as your wheels overall diameter is within stock specifications your speedo will still be consider accurate.

Stock specs ah? siao liao...how to know my stock specs? I only know original rim n tire size, then my current rim n tire size leh. How?

[Unfazed]

I think you and many ppl got it wrong. Many ppl think speed on the speedo is predetermine by the diameter of the wheel. As a matter of fact the speed is determine by a pulse sensor in your transmission(aka gearbox). A computer will calculate and convert the no. of pulses during rotation to determine the speed.

 

The speedo is not 100% accurate. There's a tolerance of + - 10% due to factors like wear on tires, tire temperature and such. As long as your wheels overall diameter is within stock specifications your speedo will still be consider accurate.

On the tolerance part I m aware...I wanted to find out more is bcos for my next set of tires, i intend to change to either 195/55 or 185/55, as my current 195/50 is abit harsh on the comfort. I know i m getting gd cornering on my current set but i feel there's a fair bit of compensation on the pickup power n fuel consumption. Well its not really much of a prob for me as my wira is a opc but being someone curious, i always wanted to find out more. Nevertheless, thanks for the great explanation.