Terrible fuel economy on 20"

[DizzyNinja]

Hi, I've just fitted my 20" wheels on the van, and while they look awesome my fuel economy has gone absolutely shocking.

Before I was happy to see 40mpg+ on long motorway and extra-urban trips. The new tyres are 275/40 Uniroyals - I am aware they are both wider and greater rolling radius. However, even taking this into account I cannot accept that now the van is only indicating 25mpg at best, on similar journeys and driving style. Total range has gone from over 500 miles to barely 300. There's got to be something wrong here.

Something I've noticed is there is a sound (not really a vibration) at speeds say 40+, it's very low frequency, like 'vrrrrrrrrr....... vrrrrrrrrrr.......' - I'm pretty sure it wasn't there before.

Has anyone else seen a similar issue, or do you have any advice please as to what to look at?

Everyone I have talked to so far just shrugs and says it's going to be lower with bigger wheels - but by *this much*? It's costing me almost double to get anywhere now.

 

[Loz]

Has the fuel economy gone wrong, or are the calculations now different because the overall rolling circumference has changed compared to what you had before?

 

[Bav]

Have you actually calculated the impact made by the increased wheel circumference? It's easy to dismiss this as trivial, but a small increase in circumference makes a big difference in the number of wheel rotations required to travel a given distance.

 

[DXX]

Big wheels kill MPG?

Hello, first time posting here. Proud owner of a new 6.1 150 DSG Highline panel van since January So naturally first thing I did was replace the 16in wheels with 20in wheels on 275mm wide tyres. However I really noticed the MPG drop and that's been highlight by going back to the stock wheels...

www.t6forum.com

 

[DizzyNinja]

Have you actually calculated the impact made by the increased wheel circumference? It's easy to dismiss this as trivial, but a small increase in circumference makes a big difference in the number of wheel rotations required to travel a given distance.

Hello, yes the difference is basically 10% if you go by rolling radius / gps vs speedo / tracker distance vs odo - they all give the same result. But my fuel economy has gone down by 40%.

 

[Andpopse]

The extra weight of the 20in wheel / tyre combo. The extra rolling resistance of the 275 wide tyre. Tyre pressure, and of course extra circumference of the tyre all affect the Mpg reading. Probably best to brim the tank and travel a known distance, then top tank back up. This will give a fairly real Mpg.
But of course 20s look cool and looking cool costs £s

 

[Andpopse]

I meant to add, when I recently changed from 275/40/20 on the front to 245/45/20, my mpg improved. Less resistance caused this I assume.

 

[PB-T6]

Hi
confirm was it just wheels you changed or did you change suspension and hence ride height?

 

[Andpopse]

It was just the tyres. I am changing Suspension and lowering by 60mm next week, so will see what effect that has

 

[Gavinda]

Has your actual expenditure on fuel gone up by 40% though?

 

[mmi]

Odometer reads 10% less.
Possibly still driven by speedo indicated speed? Thus 10% higher speed would add aerodynamic drag by 21% (relative speed difference squared 1.1²)
Possibly difference in air temperature, e.g. at 0C air is 8% more dense than at +20C (=8% more drag)
This worst case scenario would have an influence of 44%.
Just by calibrating speedometer could eliminate the two first factors.