Car tyres and fuel efficiency

Looking at new tyres for my car, and quick google results,

I can get a C rated tyre for 60, and an A rated for 80,

I guess that A will be cheaper too run, but any idea what the break even is? Does it actually make any material difference?

Did for a SMax I had a few years ago.  Made about 5% difference as I recall. Given the life of the tyres on that vehicle it was well worth it. But it will depend of your typical drives and speeds. A twenty mile commute on a dual carriageway and motorway run that rarely got much over 60mph during rush hour meant that while stop start wasn’t eating fuel, top speed wasn’t either. At 70-75 (indicated obviously) they might had made less sense.
Quieter though. That was nice.

the figure is pretty marginal, from memory it wont make significant financial sense.

http://www.willis-owen.co.uk/tyre-fuel-efficiency-calculator/ – £20 over the lifespan of a tyre.

I’ve looked into this a fair bit. Each letter is worth 0.1 l/100km apparently. For a van at 40mpg that’s just about 1.5mpg difference.

However A rated tyres aren’t necessarily much more expensive depending on what you’re looking at.

That’s in line with my recollection. I think it was 2-3mph on top of 40mph. Worked out at around £30 extra was worthwhile on the front corners, possibly more of the rears as they lasted longer.

When i changed tyres on my subaru, i went up a size, from 55-65 profile, same rims, same width.
Tyre efficiency went from b down to c. Im probably getting 2mpg less.
But, tyres on my car typically last 45k miles, the new bigger tyres have much deeper treads, so will hopefully last a good bit longer.
The extra life needs to be factored in to any equations.
It’s a minefield.

It was the case that energy saving tyres lasted way longer, but compounds have evolved now so that may not be the case any more.

I just went from really wide sporty tyres to slightly narrower on the rear still sporty tyres with A ratings and gained about 10% in fuel economy

I can’t belive on stw no one has mentioned tyre pressure yet. Maintaining the correct pressure will have a larger impact on fuel efficiency over time.

C’mon… Y’all are slacking. 😀

That calculator uses £116 per litre. Factor in current fuel prices and it’s maybe worth thinking about.

A moot point in my case. Checking all seasons in my size they are all B efficiency rated for known brands apart from the A rated Bridgestone Weather Control.

Unless there was a big price difference I would stick with the Goodyear Vectir 4 Seasons I have on all corners at the moment.

thanks, this is for a current generation 1l petrol polo so c60mpg as a starting point, front tyres are at 20k and just about legal, backs are fine for a while yet. So it sounds like it might be worth considering fuel efficiency ratings .

Can you get A rated for fuel and A rated for grip?
I’ve just got some Michelin Cross Climates, A for grip but only C on fuel.
No noticable difference to the summer tyres which were on it before in terms of fuel, some Hankook ones, but definitely grip better (this may be just because they are new and have loads of tread left🤷‍♂️)

Can you get A rated for fuel and A rated for grip?

Yes, https://www.continental-tyres.co.uk/b2c/car/tyres/ecocontact-6.html

There may be others, these were the first I found, but it does seem to depend a little on tyre size.

Or just pump the tyres up an extra couple of psi.

I can’t belive on stw no one has mentioned tyre pressure yet. Maintaining the correct pressure will have a larger impact on fuel efficiency over time.

C’mon… Y’all are slacking. 😀

When my van goes for a service, I take my tools out of it. They adjust the tyre pressures to suit.
I only noticed as I was struggling to get 50mpg after a service. With the correct pressure back in it’s more like 56mpg on a run.
No idea on the difference in the efficiency ratings though but I gues marginal gains add up

When my van goes for a service, I take my tools out of it. They adjust the tyre pressures to suit.
I only noticed as I was struggling to get 50mpg after a service. With the correct pressure back in it’s more like 56mpg on a run.
No idea on the difference in the efficiency ratings though but I gues marginal gains add up

How are you measuring that though?

Because of you put a substantial weight in it or let some air out of the tyres it would appear that you got higher mpg as the gearing is effectively changed.

E.g. I put winter wheels on my car and got a 5% better economy. I didn’t actually save any money though, it’s just that I was driving 5% slower (or the odometer spun round 5% quicker/more between fillups depending how you looked at it).

Just going by the average readout which roughly matches the miles between fills.
I probably shouldn’t care as I don’t pay for the fuel in the van, but I get bored on long distance drives and try to balance speed Vs economy.
I don’t think it’s too much of a stretch to accept extra weight on the lower tyre pressure will mean poorer fuel consumption. Nicer ride though.

This bothered me for some reason but my googling so far suggests a variation in pressure of 30% only changes tyre circumference by around 1%.

https://www.homeownershub.com/uk-diy/does-a-tyre-change-its-circumference-when-underinflated-1295898-.htm

Something to do with a softer tyre changing shape ftom a circle to more of an ellipse. It has the same circumference.

I’d expect less rolling resistance with more pressure in a tyre.

An underinflated tyre is using more of the sidewall to bear loads and energy is lost as it consequently deflects.

It’s quite apparent on a bike 😀

Maintaining the correct pressure will have a larger impact on fuel efficiency over time.

Only if you compare the correct pressures with seriously too low pressures.

Or just pump the tyres up an extra couple of psi.

No, a couple of PSI won’t do it. It needs a lot more pressure to make a noticeable difference in fuel economy in my experience, and you notice worse ride and road holding long before that.

But how accurate is your pressure gauge? I expect there could be as much as 20% variation across even forecourt gauges, so you could easily be runnign your tyres under / over pressure alot of the time. Remember that the incorrect tyre pressure can subdtantially affect grip, as well as mpg!

But how accurate is your pressure gauge?

All the digital ones I’ve used seem to correlate with each other. In my experience of driving a car with slowly leaking wheels, the effect of low tyre pressure only starts to become slightly noticeable over the effects of weather and traffic once it gets to about 60% of the recommended pressure.

Car (Leon) came with Michelin Energy Savers as standard. In normal motorway and a-road driving, they give me about 5MPG extra over the Conti Wintercontact winter tyres. They’re also still going some 40k miles later

Downsides – the low rolling resistance, wear resistance and fuel efficiency is gained by having zero frictional coefficient, meaning wet roundabouts are to be approached with clenched buttocks.

Anyone use a track pump to inflate their car tyres?

Car (Leon) came with Michelin Energy Savers as standard.

Downsides – the low rolling resistance, wear resistance and fuel efficiency is gained by having zero frictional coefficient

Ok so two things here.

Firstly, they make special versions of tyres with the same names that are really terrible. I have no idea why they do this – people end up with the impression that such-and-such a tyre is rubbish, but the aftermarket ones are good.

Secondly, things have changed since ‘energy saving’ tyres came out. It used to be that you had normal and energy saving as different types, and the energy saving ones have added silica. However now most tyres seem to have some silica in, so now you just get a fuel efficiency rating from A-F. However even the A rated fuel efficiency tyres are now a much more well rounded tyre, so there is no dramatic loss of grip. Which, to be fair, there wasn’t in the first place on aftermarket ones. The big issue is shitty OEM versions.

TL;DR – don’t be put off A rated tyres by stories like this – they are good these days, if you buy aftermarket.

I always buy my tyres based on the wet grip rating, rather than the fuel efficiency rating. I once ended up with B rated tyres that were noticeably worse than the knackered A rated they replaced.

Firstly, they make special versions of tyres with the same names that are really terrible. I have no idea why they do this – people end up with the impression that such-and-such a tyre is rubbish, but the aftermarket ones are good.

That’s really interesting, had no idea this was the case. Thanks for that, due some new tyres soon so may consider energy savers again. I was tempted to sell the winters/winter alloys and replace with Crossclimates or equivalent, but the MPG penalty at the moment makes it more unappealing to run all year round now.

I put some premium brand a rated tires on the wife’s berlingo summer wheels. Wish I hadn’t they are terrible.

Prior to this I had some Michelin primacy’s on there 1 they were equally terrible.

Wet grass. Forget about it. Damp hill- spins up for fun.

Reminded me why we end up keeping the winters on 8 months of the year. Just so much more dependable.

Probably get rid of the eco’s come winter and fit all seasons to the Berlingo also.

Put all seasons on my own car as only one set of wheels and for the extra grip in all situations I’m ok with the couple of mpg it costs me.

Anyone use a track pump to inflate their car tyres?

I use one to top them up.

I always buy my tyres based on the wet grip rating, rather than the fuel efficiency rating

Me too. Having experienced some horrible tyres on new-to-me secondhand purchases, I’ll always seek out wet weather grip over efficiency. I’m also OK with the couple of mpg all-seasons might be costing me – the Pirelli Carrier all-seasons on my van are A-rated wet grip and C-rated for efficiency, the best of the choices at the time I was buying 4.5yrs ago.

That’s really interesting, had no idea this was the case.

My Prius came with Bridgestone Turanzas which were terrible. Like, really bad. The car could wheelspin easily in the dry, and it’s not exactly a powerhouse. Subsequently heard lots of good things about Turanzas, which confused me. It’s apparently not that widely known but it’s out there.

The Hyundai has Michelin Energy Savers on it which are terrible wet or dry. Not to the extent that you fear spinning in the wet, mind, but they don’t stop that quickly. But I’ve bought them before, years ago, for the Prius and they were far better.

I bought Goodyear Eagle F1 Asymmetric 5 for the Merc, they are B rated for fuel IIRC in that size and great tyres with lots of grip. It’s also important to remember that the grades are absolute, and of course narrower tyres are more efficient anyway so it’s harder to find As in larger sizes. You also find OE specifications in the same tyre from different manufacturers, and they are definitely different; but wether or not they are better is a difficult question. They are more tuned for what the manufacturer wanted, which in some cases is fuel efficiency. ISTR BMW versions of a tyre I was looking at had better fuel rating and worse wet grip rating. It’s an utter minefield and I have no idea why they market their tyres like this.

Basically don’t look for things categorised as ‘energy saving’ because they don’t do that so much any more – just some eco branding on some models. Look for tyres with A or B wet grip and the same in fuel efficiency, as close to your price range as you can get!

Followup, i can get a set of Kumho tyres at 60 or Continental at 80, both A rated fuel and wet grip.

I know who conti are, but anyone any idea what Kumho are like, is it a false economy or a worthwhile saving?

Anyone use a track pump to inflate their car tyres?

Ain’t nobody got time for that!
Yes, ive tried it. Got bored long before the tyre was actually up.

wet grip is mostly measuring aquaplaning resistance, which is pretty rare to come across. it doesn’t necessarily equate to general levels of grip on a damp road. That doesn’t mean that the posh tyre is better, just that “grip” is a very particular test.

As far as I know, Kumho are a ‘second tier’ brand meaning they aren’t super fancy (or they don’t make the best most expensive premium tyres) but they are decent quality for normal use. That said, with tyres get the best you can afford. It really could save your life or someone else’s one day.

wet grip is mostly measuring aquaplaning resistance

I thought it was just wet tarmac. It’s detailed a bit here:

https://www.tyrereviews.com/Article/EU-Tire-Label-Current-status-and-challenges.htm

5lab
Free Member

wet grip is mostly measuring aquaplaning resistance

Not sure that is accurate. Google suggests

” water depth shall be 1,0 ± 0,5 mm” which doesn’t look like aquaplaning depth to me.

https://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2011:062:0001:0016:EN:PDF

As for aquaplaning risk. It is why I change tyres well before the legal limit. Below around 3.5mm I can feel the front wheels skipping going through puddles. New tyres and the tyres doesn’t skip.

IMO not running tyres down to 1.6mm is probably as important as wet ratings for aquaplaning.

Kumho is OEM for Kia in the UK and Holden in Australia amongst others. They also supply the TCR Europe Race Series for 2022.

3mm was proven in wet braking tests years ago at MIRA to be up to 44% better than 1.6mm tread

Not sure that is accurate. Google suggests

” water depth shall be 1,0 ± 0,5 mm” which doesn’t look like aquaplaning depth to me.

afaik (happy to be corrected), aquaplaning can happy at any water depth, particularly on a smooth surface (which, according to that doc, it is- less than 1mm of texture is a lot less than our roads). Its much more likely to happen at greater depths as one of the issues in play is the tyres ability to shift water (through its tread pattern).

it seems like the tyre test is at 65kmph so aquaplaning is pretty unlikely, I’d agree that its more about damp grip. I was conflating it with those tests you see on tv to proove how good tyre x is (which is normally faster, and with more water depth).

I always buy my tyres based on the wet grip rating

Grip as per various tyre tests for me.

Scary how energy saving tyres (early ones at least) had poor grip, and how narrow tyres are on some cars (e.g. BMW i3).