A couple of weeks after picking up my new car I decided to check the tyre pressures. All four were different and they were all over inflated, both rear tyres set to well over 40psi… Given that I normally travel alone, unloaded and only use a relatively short stretch of motorway, I reset all four tyres to the recommended 32psi.

 

I immediately noticed a consistent drop in mpg (the ‘since start’ reading dropped to 50 – 51mpg). Weekend before last I reset all four tyres to 34psi, no noticeable difference in ride but mpg immediately improved (again using the ‘since start’ reading as my guide it’s back up to 54 – 55mpg). I do the same journeys at pretty much the same times every day, so the only thing that’s changed here is the tyre pressures.

 

I’m sure everyone reading this appreciates that tyre pressures have an impact on mpg but I was/am genuinely amazed that 2psi as made a difference of approx. 4mpg.!

 

I know that this isn’t a very scientific test by any stretch but, clearly there is a difference….. just need to keep an eye on tyre wear now.

 

It’s also clear the supplying dealer didn’t check the tyre pressures when doing the PDI….

Wow that's quite a difference for a small change in pressure !

 

Have not experienced that in mine but do agree that dealers never check the pressures properly for pdi. Mine were all over the place as well !

 

Don't get me stared on tyre pressures - oh I have ...

 

I often ask myself why tyre pressures are not higher up the priority list when it comes to active safety systems in the car - uneven or wrong pressures give bad handling and braking distances are increased especially in the wet.

 

I bet if a car was allowed out from a garage with loose break calipers there would be a massive punch up

Ambient temperature can have a big effect on mpg !

But I agree that dealers are not good at checking tyre pressures.

10 minutes ago, YS53 said:

Ambient temperature can have a big effect on mpg !

But I agree that dealers are not good at checking tyre pressures.

 

This ^

 

The weather has warmed so this is where you'll be getting the mpg improvement plus we've just had Easter with less traffic on the roads. I wouldn't expect much difference with just an additional 2lbs of air in the tyres.  

If you want an accurate measure do the same route back to back, setting off with a full tank with the different tyre pressures. If you're average speed is consistent I wouldn't expect much difference. 

Edited 2 May, 20179 yr by CWARD

YS53 & CWARD, you've both made some very fair points there and it has been a couple of degrees warmer (especially in the morning) this past week or so. However, I got the car at the end of March and ran it for about 10 days with very over inflated tyres, typically my 'since start' reading was around 54 - 55mpg. When I dropped the pressures to 32psi the 'since start' reading also dropped to around 50 - 51mpg as I said before, but the temperatures didn't drop during this period, if anything it got warmer....

 

Like I said, in no way was this a scientific test, merely an observation based on a relatively short period (and based on the on-board computer). I do appreciate that many things can affect fuel consumption as you've suggested and in my case, it may be sheer coincidence that the mpg figures have changed around the same time that I've adjusted my tyre pressures?

 

In truth I don't get too bogged down with actual mpg readings. When I got the car I hoped to get 50mpg + and according to my refills I am achieving that so I'm happy enough.

 

Still think the tyre pressures made 'some' difference though.... ha ha.!

 

Terry     

Over inflated tyres do give better MPG but not very good for tyre life or grip. When you reduced the tyre pressure the MPG dropped too due to more rolling resistance. You then increased the tyre pressures slightly, which coincides with generally warmer weather and you had a moderate increase in MPG which is what you would expect. 

Tyre pressures do make a difference but trying to keep your average speed up will benefit more. If you a resetting the MPG after each tank then do the average speed to and note it against your MPG for that tank and a picture will soon form.

 

Pleased you're getting over 50mpg regularly, my Octavia Mk2 with the same engine and gearbox but lighter than your car would struggle do over 50mpg and that's with lots of coaxing on near empty roads. New car does it easily regardless of how I drive.   

Wet roads are also a big factor, think about how much water the tyres are pumping away.

 

The TPS helps a lot, VAG (AFAIK) still use the speed sensors so it only senses changes, my wife's Mokka has pressure sensors in the valves. and can be set at normal/full load/eco and each has a set of pressures in memory that the tyres must match within 1psi or the system gives a warning - no chance of setting them a little low/high.

 

Must check the pressures on mine.