Mpg suddenly changed

[Jeffyjazz]

I do the same journey to and from work on a motorway and always had the dash reading 48-54mpg each time I reset it after a tank fill

But this week it's at 38mpg 
Drove in today and didn't exceed 60mph and it still wouldn't  go up

I know it's not always accurate but anyone know what might cause a drop like this the only thing that has changed is my front tires I went from bridgestones to some random make

Surely tires can't make that much difference

[guest5355]

It might be that the random tyres that you have put on are made from a Soft Compound and this will cause the tyre to give more resistance.
 I have Michelin tyres fitted for the summer months and  these have a hard compound and our average mpg is, when using as a shopping/run around,  is between 45-50 mpg. and when on the open roads it returns up to 60 mpg.
   I fit the winter tyres, Goodyear Ultra Grip 9, in early December to late March, when the softer tread not only sticks like s*** to the road but the fuel consumption drops down  to apx.  30-40mpg.
   I always buy my tyres from: Oponeo (on line) as their price is good and even paying £10. per wheel for fitting at our local tyre shops, the overall price is about 25% less.
   The best thing is when changing back to  summer tyres,  the ride is so much smoother plus the extra MPG

[Jeffyjazz]

I normally buy them online
But I need two front ones urgently and had no choice but to get them from local tire place
They are made by sonar thy said they were midrange but I get a feeling they are budget

I normally get Bridgestone or continental

[monkeydave]

might be the tires or binding rear brakes

[guest4324]

I can't imagine the tyres would have that much effect, maybe upto 5% which would be around 3 mpg in your case. Are they inflated correctly and the same size as the old ones?

[Jeffyjazz]

Right I've used my tank of fuel this week and managed 208miles

I normally get 350

Has my little Jazz finally given up the ghost

[edam]

What about pressures

[guest5589]

Right I've used my tank of fuel this week and managed 208miles

I normally get 350

Has my little Jazz finally given up the ghost

Not like that. Mpg depends a lot of factors. Choked air filter, bad spark plug or maybe just that the car didn't like the fuel. Get some from somewhere else and keep an eye

[guest5505]

I have this problem, in that my mpg went from 50 to 40 for no apparent reason. I looked into it and thought it could be the EGR valve at fault, so I took it off and cleaned it, but no difference. So if you find a solution, let me know !

[guest1521]

Binding brake caliper? Easily found if a wheel feels warmer than its counterpart on the same axle after a run.

[Jeffyjazz]

Hmmmmmm.  Filled up this morning got to work and it was back up at 48
That was with out resetting the counter as well so it climbed from 39 to 48

If I had reset it I probably would have seen 55

Must  have been dodgy fuel

[trebor1652]

I put some "better" fuel into my mk1 once thinking the car would perform/run better but had the same experience with the mpg nosediving.
There must be a moral there!?!?

Sent from my XT1039 using Tapatalk

[edam]

Same problem as well
I put some better quality petrol in it and the mpg fell. I complained to the petrol company but got fobbed off.
I went back to my normal supermarket petrol and my mpg went up

[degzi]

I always run on cheapo tyres, at about 60mph I can just about squeak 58mpg on a long run.
I keep them at about 38psi. I have found in past experience, sometimes you get a puncture you don't realise and it really effects mpg.
Also oil change helps if it's due, and defiantly worth spark plug change or check the gap. Keep basics in tip top condition and it puts less stress on other things.

One thing I did notice is that, the little jazz really likes it if you get in a decent slipstream of a high lorry, BUT it takes a hell of a battering with stonechips  I once got on-board mpg to a solid 64mpg on a chilled out holiday run
It was a bit of a effort keep dropping off accelerator pedal instead of feathering it and dropping into neutral on slopes.
Anyhow I'm rambling.


Strangely looking at the dates I did notice a drop in my own mpg roughly 2 weeks ago which is back to normal now. Using Morrison's petrol, would be interesting if it was a dodgy batch of fuel, I put it down to lots of small journeys.

[culzean]

I always run on cheapo tyres, at about 60mph I can just about squeak 58mpg on a long run.
I keep them at about 38psi. I have found in past experience, sometimes you get a puncture you don't realise and it really effects mpg.
Also oil change helps if it's due, and defiantly worth spark plug change or check the gap. Keep basics in tip top condition and it puts less stress on other things.

One thing I did notice is that, the little jazz really likes it if you get in a decent slipstream of a high lorry, BUT it takes a hell of a battering with stonechips  I once got on-board mpg to a solid 64mpg on a chilled out holiday run
It was a bit of a effort keep dropping off accelerator pedal instead of feathering it and dropping into neutral on slopes.
Anyhow I'm rambling.


Strangely looking at the dates I did notice a drop in my own mpg roughly 2 weeks ago which is back to normal now. Using Morrison's petrol, would be interesting if it was a dodgy batch of fuel, I put it down to lots of small journeys.

its pretty dangerous to run tyres that much over recommended pressure as it reduces the area of contact patch (in doing this it does lower rolling resistance of wheel which is why mpg gets better) - which reduces the tyres grip on the road, making aquaplaning more likely,  increases braking distance and makes wheelspin more likely as well as increasing the chances that car will lose traction in a bend and slide.  may also cause tyre to bulge in centre of tread and wear the middle of tread out earlier,  increased pressure makes the ride harder and gives car suspension a hammering.

Tailgating close enough to get pulled along not a good idea either as if the lorry brakes hard you could be in big trouble,  IMHO not worth the risks for saving a few quid on fuel.

http://www.hybridcars.com/forums/showthread.php?101213-Dangers-of-Over-Inflating-Tires