UnSubRocky wrote on Oct 4
th, 2026 at 11:39am:
Setanta wrote on Oct 3
rd, 2026 at 11:19pm:
UnSubRocky wrote on Sep 29
th, 2026 at 10:23pm:
I changed my front tyres and had a wheel alignment on my car. The fuel efficiency must have improved 25%, and my speedometer matches my actual speed.
Impossible, your speedo is either mechanichally driven if your car is old or read via magnetic pulses on the the axles/driveshaft, i.e. off mechanical moving parts. Nothing changed, it's your imagination which has been shown to be very active.
I don't know how they measure speed to display on the speedometers. However, upon getting new tyres and a wheel alignment, the fuel efficiency improved remarkably. And I was shown to have my speedometer nearly match the speed display sign I drove passed in Parkhurst fairly recently.
Why would there be a differential of 5kmh between my speedometer and what is displayed on the speed detector sign, but be about 2kmh different after the wheel alignment? And why would my fuel consumption improve considerably, even though I do the same amount of driving? I would fuel up every week, about 2 months ago. Now, it is once every 10 days.
I put new Michelin Pilot Sport 5 tyres on my car the shop asked me if i wanted a wheel alignment like Maccas ask if you want fries with that.
My car tracks straight ahead if i take hands off wheel it doesn't pull left or right so it didn't need toe in or out adjustmenton front wheels. Tyre wear was even inside and out so didn't need camber adjustment.
The car turns in wheel self centres coming out of corners co castor didn't need looking at.
My car didn't need a wheel alignment they tried to sell me one.
New tyres might explain some speed reading difference it could also be the roadside thing might not be calibrated.
How often do you check tyre pressures answer this question honestly and tell us what pressure you run front and back?
We have just come out of winter pressure volume and temperature are related since tyre volume doen't change pressure does change with temps in winter pressure will drop with colder weather.
My bet is like most people you don't check pressure unless tyre looks flat you have no idea of what pressure works best.
This does make a difference with rolling circumference which can impact speed readings.
You also mentioned new tyres if you add 5mm top and 5mm bottom which gives you 10mm difference in diameter which will also impact speed reading.
A wheel alignment and new tyres isn't going to give you 25% better fuel economy even if car is pulling hard left or right and has half flat tyres
What is year make and model of your car? manual or auto?