How Tyres Affect Fuel Consumption?

[Blisteringblue]

Calling all boffins!  I'm probably after a bit of a physics lesson?

Since moving from my SE to the new Sport and 16" to 18" wheels I've lost 7mpg.   I got metronome 52mpg in the SE but now barely 45mpg in the Sport. Identical driving styles, nothing flash and steady 75 on the motorway, but a lot of motorway.

I know this doesn't seem a lot, but its 100 miles less from a tank of petrol.   Tight northerner and all that?  This is summer too, will loose another couple of mpg in the winter.

Anybody care to explain the physics?

[Spacewagon52]

I do not have the physics knowledge to explain what is happening but I changed from ALL-TERRAIN tyres on my Grand Jeep Cherokee, to MUD tyres which were much larger. The fuel consumption went from 20 mpg to 13 mpg! It may be the make of tyres and their rolling resistance as well as the size. Would be interested in other peeps comments.

[Farqui]

This is a complex subject with many factors to consider but in general you can expect larger wheels to give around 10% less mpg.

Did you also change the tyre widths?  Thinner is better for mpg.

Were the 18" alloys heavier or lighter than the 16"? Lighter is better for mpg.

Did you move from an eco/hard wearing tyre to a performance/softer compound tyre?  Harder is better for mpg.

Are you running the same tyre pressures?  They may need adjusting to take into account the lower tyre profile.

How many tank to tank fills and mpg calc's have you performed on the new wheels?  More are better and will help to average out temperature differences, traffic, terrain driven, etc.

I'm sure there are many more contributing factors that the masses are sure to chime in with.

 

[Britprius]

As "Farqui" says there are a number of factors that come into play. However the actual tyres you are using can make a big difference to your MPG figures

What tyres were fitted to your previous vehicle, and what tyres are fitted to your new vehicle? Looking these up for rolling resistance may give a clue as to what is going on.

If you are uncertain let us know the details of the tyres, and I will put the figures up for you. The difference between an "A" rated tyre, and an "F" rated tyre is substantial. If you can put up with the harder ride increasing tyre pressures by  2 PSI can make a noticeable difference, and can often improve tyre life.

The simple fact is the right tyres can pay for themselves in fuel saved over there life time.

John.

[rayaans]

Simply down to the tyre being wider causing more friction - other factors play a part as well including the tyre compound itself. 

Its very possible that the car isn't fully run in yet? Ive found MPG gets much better when a car has atleast 10-15k miles on it.

[tanimbar]

As others have said it's due largely to increased tyre width, i.e. more rolling resistance.

You've gone from 205 width on all four wheels of the SE giving 52 mpg (matches my SE exactly) to 45 mpg in the Sport on 225 fronts and 255 rears. The width difference between the two models is +10% fronts, +24% rears (rounded); the difference in fuel use is c. +15%. That is what you would expect; no surprise; Sport is fine.

[Ben1001]

In my experience fuel economy increases after the first 10k miles and a service.

daft question but you're definitely running in eco mode? Makes a huge difference in my 250.

[Blisteringblue]

As others have said it's due largely to increased tyre width, i.e. more rolling resistance.

You've gone from 205 width on all four wheels of the SE giving 52 mpg (matches my SE exactly) to 45 mpg in the Sport on 225 fronts and 255 rears. The width difference between the two models is +10% fronts, +24% rears (rounded); the difference in fuel use is c. +15%. That is what you would expect; no surprise; Sport is fine.

Cheers, sums it up perfectly thanks.

 

I was just curious, only done 2000 miles so it should improve after the first service.

 

Sent from my SM-T810 using Tapatalk

 

 

[wh05apk]

My premier on the same tyres averages about 46mpg, to me 18 inch wheels on these ruins the car, the noise levels and ride are ruined by them.

[Blisteringblue]

I'm going to try a week on ECO and see if its any better, but boy does it knock back the performance.   It's going to have to be a massive improvement to make me stay on it.

[dutchie01]

I never drive in ECO. It's like towing a lorry.

[Blisteringblue]

41 minutes ago, dutchie01 said:

I never drive in ECO. It's like towing a lorry.

Tell me about it  It's like driving the wife's 1.1 Hyundai , just want to see what it does for consumption to satisfy my curiosity.

[Carl1983]

Hi

to put your mind at ease, i have an F Sport with 18inch wheels. I have michelins pilot sport 3's all around and I'm averaging around 51mpg mainly motorway/main roads in eco mode. I'm sure after a few thousand miles and a service it will improve 

carl

[Blisteringblue]

Thanks, yes I got it up to 48/49 on Eco this week without even trying hard so it will make the difference, but I put it back to normal it's just too lethargic, you might as well call is SLUG rather then ECO , will take the hit on normal.

[rayaans]

Eco makes the car feel slower than a 1.0l Polo. I really don't see the point of it. If you want outright  economy get a diesel or plug in passat

[Ben1001]

Interesting, I drive my Gen 3 IS250 in eco 99% of the time, I find it quite punchy. Left it in normal by mistake a few times and wondered what was going on with my mpg. Eco makes a huge difference.

[michaelH]

I moved from a luxury on 17" wheels to a premier on 18s, and was initially concerned as to whether this would Impact on ride quality, which is important to me because my wife has spinal injuries and travels badly. But we have noticed no deterioration at all.  We both feel that, for whatever reason, the ride is marginally better and the noise levels are no different. When the time comes to replace them, the tyres will however be more expensive.  MPG seems slightly worse, but the difference is so slight (1 mpg or so) as to be insignificant.