Am I Being Thick?

[Steveski]

I have just had fitted some wolfrace wheels with general grabber tyres along with a few other bits and bobs and my MPG has plummeted!!

I’m a proper fairy foot and was getting 43-47mpg on a run, now I struggle to get past 33-34mpg?

Can this be purely down to the tyres/wheels?

 

[True Romance]

Have you measure fill to fill or just using the onboard trip computer? Do the new wheels/tyres have a bigger circumference?

 

[Steveski]

I’ve gone by the computer to be honest?
They are bigger 18” as opposed to 17s previously.
Does the trip computer tell porkies? Should I just do a fill to fill?
Thanks for the reply.

 

[Pete C]

The trip computer goes by what size wheels/tyres it thinks you have fitted. It doesn’t know you have changed them to a different circumference.
Try fill-to-fill measurement.

Pete

 

[Steveski]

Thanks all I was thinking of getting rid when I saw that reduction!

 

[Dellmassive]

bit more info >

Mpg + Fuel Economy - What Mine Does -

 

[Salty Spuds]

Try fill-to-fill measurement.

Pete

But won’t that be out too, as the odometer will be reading under due to the tyre size being incorrect??

 

[dubber36]

Tyres with an overall larger diameter will rotate less times over a given distance. It's a good way of keeping your recorded mileage down, but your speedo will read too low as well. Plucking figures from thin air, if you drive an actual 10 miles, the van may only record 9 miles. If you would normally use a litre of fuel for those 10 miles, the computer thinks you've used one litre to drive just 9 miles.

What size tyres did you have before and have now? Put the sizes in this link and see what results you get https://www.willtheyfit.com/

 

[chriscroft]

View attachment 49602 I have just had fitted some wolfrace wheels with general grabber tyres along with a few other bits and bobs and my MPG has plummeted!!

I’m a proper fairy foot and was getting 43-47mpg on a run, now I struggle to get past 33-34mpg?

Can this be purely down to the tyres/wheels?

That is a huge difference
What size tyres are you now running?

I run 235/60/17 which are around 3.5% larger rolling radius; so roughly speaking when my van say I'm getting 30mpg, it's actually 31mpg - all other things being equal.
The biggest tyres people run on this forum (mostly) are 255/55/18 (or similar) these are 7.5% larger rolling radius s0 30mpg indicated is around 32-33 mpg actual.
If you do the fill-up to fill-up method (ignoring the fuel computer), you still need to adjust (increase) the recorded milage by 3.5% or 7.5%, or the calculation will be wrong.
It's not the wheel size that makes the difference it's the tyre size (rolling radius) when adjusted to your actual mpg.
But you are showing a circa 30+% difference...... MASSIVE

Are you constantly getting this reduction??

In terms of actual economy then all of the below will reduce your economy in my experience.
A tyre with a higher fuel economy rating (friction)
A wider tyre (friction)
A tyre with a different rolling radius (our vans are optimised by VW for the stock tyre size), especially a DSG gear box left in auto (the change points are now slightly out)
Ant wheel/tyre combo which is heavier than stock; and/or has its centre of mass further away from the hub (2nd moment of inertia)
Low tyre inflation pressure
Tracking/balancing issues
Load/Speed/Aerodynamics
Towing
Engine/Transmission issues or alterations/settings
Terrain type and undulation/twist
Driving style

If you combined all of the above you I think you would struggle to get a 30% shift in fuel economy under normal world conditions.mmmmm.

 

[Dannyb6467]

View attachment 49602 I have just had fitted some wolfrace wheels with general grabber tyres along with a few other bits and bobs and my MPG has plummeted!!

I’m a proper fairy foot and was getting 43-47mpg on a run, now I struggle to get past 33-34mpg?

Can this be purely down to the tyres/wheels?

What van are you driving?

 

[Salty Spuds]

That is a huge difference
What size tyres are you now running?

I run 235/60/17 which are around 3.5% larger rolling radius; so roughly speaking when my van say I'm getting 30mpg, it's actually 31mpg - all other things being equal.
The biggest tyres people run on this forum (mostly) are 255/55/18 (or similar) these are 7.5% larger rolling radius s0 30mpg indicated is around 32-33 mpg actual.
If you do the fill-up to fill-up method (ignoring the fuel computer), you still need to adjust (increase) the recorded milage by 3.5% or 7.5%, or the calculation will be wrong.
It's not the wheel size that makes the difference it's the tyre size (rolling radius) when adjusted to your actual mpg.
But you are showing a circa 30+% difference...... MASSIVE

Are you constantly getting this reduction??

In terms of actual economy then all of the below will reduce your economy in my experience.
A tyre with a higher fuel economy rating (friction)
A wider tyre (friction)
A tyre with a different rolling radius (our vans are optimised by VW for the stock tyre size), especially a DSG gear box left in auto (the change points are now slightly out)
Ant wheel/tyre combo which is heavier than stock; and/or has its centre of mass further away from the hub (2nd moment of inertia)
Low tyre inflation pressure
Tracking/balancing issues
Load/Speed/Aerodynamics
Towing
Engine/Transmission issues or alterations/settings
Terrain type and undulation/twist
Driving style

If you combined all of the above you I think you would struggle to get a 30% shift in fuel economy under normal world conditions.mmmmm.

Another factor is that the larger diameter will reduce the acceleration, so more right foot will be required when pulling away.