I bought honda cbr150r 2 month ago, till previous week it reaches 80KM at 5500 rpm, yesterday I drove outside the town I aware that at 5500 rpm it reaches 78KM, first I thought it can be because of wind resistance.So I want to know exactly the problem and I turn back and drove back to the town, it is the same.

There is a another factor take me to consideration of fuel delivery system, my cbr150r is EFI, roughly air and fuel delivery system is control by EFI according to the information provided from CDI. I am wandering why my motorcycle's performance decrease? Now it reaches 80km at 5800 rpm. Any suggestion is greatly appreciated.



3 Answers 3


One possible cause could be the rolling diameter of the tyres change according to the pressure set and ambient pressure and temperature.

Most bike speedos are driven from the front wheel (shorter cables are cheaper and don't have to bend) and the engine is directly connected to the rear wheel via the gearbox.

Without trying to calculate the effects (need the gear ratios and tyre / wheel size and manufacturer's info for speed v engine rpm) the difference could well be down to the changes in both rolling diameters.


You rear tyre tread has worn reducing the effective rolling circumference and causing your gearing ratio to change slightly. Your speed is measured from the front tyre which has not worn as much and so still reading a similar road speed.

The only way for your bikes gearing to change like this is through the change in the effective rolling circumference of the rear tyre either through tyre wear or different tyre pressure

  • I suppose the Op could have a huge amount of tyre wear in 1 week - if he is doing burnouts...
    – Solar Mike
    Commented Jun 7, 2017 at 10:54
  • Hmm.. i guess a 150 isn't going to wear much in a couple of weeks.. I ticked your answer Mike
    – r.anderson
    Commented Jun 7, 2017 at 12:15

It's most likely a change in the traction factor between your driving wheel (Rear) and the speedo wheel (Front). This factor can change with weather, driving conditions, or other ambient conditions from one day to the next. As long as everything seems to be functioning normal, enjoy the ride..

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