New tyres, increased fuel consumption. Grounds for complaint?

all vehicles use more fuel in winter

Immediately following a tyre change? The weather here hasn't changed that much and my fuel consumption has never increased by this much before in any winter.

Tim

Some tyres are optimised for low rolling resistance and fuel efficiency. The Ventus Prime2 makes no such claim. If you had, say, the Hankook Kinergy eco tyres on before, you *should* be seeing a reduction in fuel economy - if the manufacturers claims are to be believed.

Also, note that a new tyre of typical car size has a circumference approx 2% greater than a worn-out tyre. Thus a notional 2% "reduction" in fuel economy is to be expected, as each "mile" recorded by the odometer is now 2% longer than it was before the tyre switch...

Ian

2% I wouldn't mind whether it was a "counting" error due to circumference or just because it was a stickier compound. A 10% increase potentially for the next 20,000 miles I do mind.

Tim

Did the tyre fitters adjust the tracking?

Chris

Nope.

Tim

You simply can't achieve that much change in rolling resistance with different make tyres to affect fuel comsumption by 10%. Even the best low rolling resistance brands only change fuel consumption by the odd percent or so. You clearly have a coincidental effect going on here with something else that changed at the same time - either that or you aren't working your fuel consumption out properly.

Don't think any of the energy saving tyres claim 10%, so I'd be looking for another reason.

,

I have to agree, 10% just seems too much to blame on the tyres but I stuck for a plausible alternative explanation. The car's running fine and fuel consumption went up immediately after the tyres were fitted. It feels to be rolling freely with no brakes dragging.

Tim

,

someone dipped the tank?

My Touran was delivered 95k ago with Conti's. Since then it's had a set of Bridgestone Turanza and is now running with Michelin Primacy on the front and Goodyear EfficientGrip on the back.

My use pattern and annual mileage has not changed and I have never noticed a measurable change in fuel consumption. Wear rates on the tyres, that's another matter!

,

Nope, I'm going by the computer. Not exact I'm sure but it's always been consistent.

Tim

Hmmm. There's a clue. Are you sure the tyres are the same size as the old ones? If the rolling radius is different the computer will think the car is covering a different mileage plus the speedo calibration will alter. The computer has no idea how far or fast you are really going. It only knows wheel revolutions per unit time and in total.

That did occur to me but I'd be surprised if they've fitted the wrong section tyres or if same section tyres of the same brand would be significantly different. I'll need to rtfm and check what's on it. ;-)

Tim

also worth doing a comparison of your speedo with a gps unit over a few miles and see whether they differ significantly.

Now that's a good idea. Easy to do too.

Tim

But how did it compare previous, to the new tyres?

Our car the speedo is 4kms fast compared to the GPS and always has been through two new sets of tyres.

I have tried three different GPS devices at the same time, and they were not consistent with each other, especially when cornering and going up and down inclines. They could be an 8mph difference in their displays (one from another) at the same moment.

David

Well I've checked it against GPS and the speedometer is exactly as inaccurate as it's always been

The good news is that the consumption seems to be gradually improving which makes me think that the tyres just need "running in".

I've never changed all four tyres before so it's conceivable that when only changing two, the increase in consumption is less noticeable.

Tim