Tyre Pressures: fully laden pressures recommended for fuel economy by Skoda UK (&VW)

Ultrasonic

The Skoda UK website makes the following recommendation to improve fuel econonmy (see here):

For more savings, you can use the higher tyre pressure recommended for full load, even if you're on your own and without luggage. It may reduce comfort slightly, but the difference should be minor.

For my Octavia this would be a change from 2.1 bar at the front and 2.0 bar at the rear, to 2.4 bar at the front and 3.1 bar at the rear. So at the rear at least this would be a big change.

The idea of increased tyre pressures to reduce rolling resistance and therefore improve fuel economy is well known. Many drivers run very high pressures for precisely this reason but I have always avoided this due to concerns of it reducing grip (and therefore being less safe), and possible issues with the police and/or insurance companies if I had an accident with pressures much higher than recommended for the car. Does the fact that car manufacturers are now making this sort of recommendation mean that I should reconsider this?

Surely increasing my rear tyre pressures by over 50% would reduce the contact patch on the road to some extent, and therefore reduce grip? Or is the change so minor that it's irrelevent?

(For information, the same advice is aslo given on page 7 of this VW economic driving booklet.)

neilmcl

Generally there is a trade-off between lower rolling resistance and wet grip, which is why these newer "Eco" tyres from the big manufacturers are a bit of a compromise and don't tend to fair well in tests compared to their standard siblings. Personally I'd prefer safety over (marginal) economy gains any day of the week.

Ultrasonic

neilmcl wrote: »

Personally I'd prefer safety over (marginal) economy gains any day of the week.

Me too, which is why I've always kept my tyres at the recommended pressures in the past. It was seeing car manufacturers actually making this sort of suggestion that made me think again: would they be making this sort of recommendation if they thought it would make their cars less safe? I would have thought their legal departments would be rather twitchy about such advice...

I've e-mailed Skoda UK to see if they have any comments on this, though I won't be at all surprised if I never get a reply.

Gloomendoom

There is also a comfort compromise too. I increased they tyre pressures on my wife's car last week from 33 psi to 39 psi as we were towing with it. Unladen, the ride was noticeably much more harsh. Quite unpleasant actually.

Ultrasonic

Gloomendoom wrote: »

There is also a comfort compromise too. I increased they tyre pressures on my wife's car last week from 33 psi to 39 psi as we were towing with it. Unladen, the ride was noticeably much more harsh. Quite unpleasant actually.

Interesting. I understand that ride would be compromised, though I was perhaps underestimating how much difference it would make going by your comments. For ride I'd happily simply try it and see what it's like and if I'd be OK with it or not though. Any safety implications are something I wouldn't like to end up in the position where I'd have to test it out though, so it's rather harder to judge.

mad_rich

Thanks for posting that VW leaflet. It's actually a lot more useful than most of the generic advice I've seen (slow down, service your car, dejunk) because it gives numbers. (I like numbers.)

Particularly interested in the graph on page 6 which indicates that, despite all the doom-and-gloom over short journeys, you can expect to reach very close to max fuel efficiency within 6-7km. (In summer, at least.) In my head, I'd imagined a much slower warm up over 20 miles or so, so that's good news.

I've always added a couple of PSI to my tyres just for good measure (on the advice of my driving instructor, believe it or not). Like you, I would be a little hesitant putting 44 PSI in my Fabia.

Also, surprised to see just how much fuel the accessories use. An extra 0.5 l/100km just for turning the fan on? That's 10% on a motorway run. :eek:

Ultrasonic

mad_rich wrote: »

Also, surprised to see just how much fuel the accessories use. An extra 0.5 l/100km just for turning the fan on? That's 10% on a motorway run. :eek:

Now that you mention it that does seem a lot. I haven't been in a new Golf - didn't realised they'd installed a wind tunnel!

forgotmyname

I would rather have that bit more grip than to try and get .01 extra mpg.

As long as your within the manufacturers limits and within the tyres limits then there shouldnt be any insurance issues.

But increasing the pressure may also cause eneven wear. It will wear the central band faster than the shoulders. The extra wear could cost more in tyres than the fuel you save.

Ultrasonic

Ultrasonic wrote: »

I've e-mailed Skoda UK to see if they have any comments on this, though I won't be at all surprised if I never get a reply.

In case anyone is interested I'll just mention that I have had a reply from Skoda. The important part said:

I have checked with one of our ŠKODA Technicians regarding the tyre pressure, he has advised the following. The offset in grip
with increased tyre pressures will be marginal; the level of grip will be more dependants on the road surface, weather
conditions and general condition of the vehicle and its tyres.

He advises that the tyre pressures are set as per the manufacturer's instructions.

Not exactly clear-cut advice given the last sentence...

Out of curiousity I did try increasing the front and rear tyre pressures to 2.4 bar for a short trip. The steering felt noticeably lighter than normal, I assume due to reduced front grip. So I'll be sticking to the standard recommended pressures.

I do think there may be an interesting legal case if a driver does follow the advice on the Skoda website of running max. laden pressures all of the time and then has an accident where loss of grip may have been a factor though.

oldagetraveller

"He advises that the tyre pressures are set as per the manufacturer's instructions."
Which is not the same as "The Skoda UK website makes the following recommendation to improve fuel econonmy"
The difference being a recommendation compared to an instruction?
I'd be guided by the vehicle handbook or any stickers on the vehicle and not something posted on Skoda's website. They also say to refer to the handbook anyway in the first sentence before going on to advise increasing the pressures to the fully laden figure.

Ultrasonic

oldagetraveller wrote: »

I'd be guided by the vehicle handbook or any stickers on the vehicle and not something posted on Skoda's website.

That is definitely what I'm going to do.

What concerns me slightly is that the advice on the website implies that the only compromise resulting in increasing the pressures is one of comfort, whilst I'm far from convinced there aren't potentially safety trade-offs as well. They may be small but not non-existent. Fuel savings will similarly be small.