tyre rating dilemma

2nd_Time_Lucky

I have a 10 yr old 4x4 that I've had for 8 years and 180 k miles so I'm running it til it dies as doesn't owe me anything, would cost loads to replace with another that will tow. Plus I now only work locally so do 8k miles a year . Car does 22 to gallon.So it needs new tyres, tried black circle , national, just tyres etc all online. Most have the Yokohama tyres I always have had plus most of the other brands also rate at an F or G fuel economy. I've found Kumho tyres which are a C rating - will I actually notice a difference in fuel economy? They are £5 cheaper to buy !

Grateful for any replies :beer:

Netwizard

The best way to make sure you are getting the best fuel economy in terms of the tyres is to make sure they are pumped up to the correct pressure.

In terms of different brands of tyre and fuel economy, You won't notice any difference. As I say, tyre pressures make more of a difference to fuel economy than anything else.

There are too many variables that affect fuel economy. It would be impossible to tell if your fuel economy was better or worse over a week purely down to the tyres.

force_ten

the new tyre rating label is not very well explained and the figure i tend to look for on my tyres is wet grip over fuel economy, my car runs quite wide low profile tyres and like your 4x4 tyres you are never going to achieve a low rolling resistance due to the nature of the tyre

I did read that the difference between A rated tyres and G rated tyres is something like 17 gallons a year on an average of 10,000 miles which sounds like a good saving over the year

as i said your 4x4 tyre is never going to have a low rolling resistance so i dont know what saving if any you would notice between an F rated and a C rated tyre

if you got a quarter of the saving quoted above then you are looking at 4.5 gallons saving over one year and 10,000 miles plus your £20.00 saving on the four tyres, not a fortune but every penny helps

tberry6686

Iv'e been running Kumho tyres on my cars for a couple of years now (not 4x4) and they've been great so if their 4x4 tyres are a similar quality to their car tyres I would get them.

Joe_Horner

The more or less standard example given is a saving of 6 litres per 1000km between A and G ratings. There are problems with that.

It assumes an "average" fuel consmption of about 35mpg, which is low. Rolling resistance also plays an increasingly small part in fuel consumption as speed increases. Although the rolling resistance increases with speed, air resistance increases much faster. So, while around 1/3 of fuel consumption is due to the tyres at 50mph, by the time you get to 70 it's dropped to about 1/4.

That means that "A" rated tyres will benefit you in slow, town, driving far more than it will on the open road (although, to be fair, there will still be a benefit at speed).

Finally, the fairly common claims that "A" rated tyres can pay for themselves over the life of the tyre generally assume a life of around 35k miles, which lots of people won't get close to.

As with many such things (premium fuels, outrageous "book" economy figures etc), there's an awful lot of marketing hype mixed in with just enough science to justify it under carefully specified (and likely unrealistic) conditions.

All that being said, if the more efficient tyres are cheaper than the less efficient then it certainly won't hurt to have them!

forgotmyname

I wouldnt trust the ratings at all. Just buy the tyres you want.

I have Khumo on my car. They grip well in the wet. Depends on the tread pattern though.

takethatfan1978

I had to order two tyres yesterday and I couldn't believe how flipping difficult it was.

All those ratings were very confusing! Anyway our mechanic recommended camskill. Found the tyres I wanted and they were cheaper than black circles plus a couple of others

Ended up getting some rated b for fuel efficiency and a for grip. Waiting for them to be delivered and fitted at weekend hopefully.

Joe_Horner

Further to my earlier post, just had a pair of fronts put on my workhorse this afternoon.

Local tyre shop was cheaper than any of the chains, and anything I could find online apart from remoulds and Asda. Asda could beat them by £1.15 per tyre but would have involved an extra 40 miles round-trip to their nearest fitter.

Being a tight git and a driving God, I went for the cheapest available, which happened to be Landsail LS388 all-seasons at £41.20 each (fully fitted etc). Just checked online and their official rating in 175/70/14 size is:

Fuel C
Wet grip C
Noise 71dB

Now, assuming that the scores (whether meaningful or not) are at least arrived at by standard testing, that's interesting because the first "brand name" tyre to match these budgets appears to be Avon ZT5 at around £42 each from Camskill, so around £57 by the time your friendly local has fitted and balanced them.

To actually improve on their wet grip you have to go to Uniroyal Rainexperts at £45 delivered / around £60 fitted. Many of the tyres from "premium" brands are well below the ratings at considerably above the price.

The worst on Camskill appears to be the Pirelli P4 Cinturato at fuel F / wet grip E / noise 71dB and costing £63 each delivered / £78 ish fitted.

The moral of that little rambling? Either the ratings are completely screwed or (a) Premiums are not always more capable than budgets, at least within what's scored

In either case, don't automatically run online for "best deals" - your local tyre shop might just surprise you on price!

Ultrasonic

Joe_Horner wrote: »

Rolling resistance also plays an increasingly small part in fuel consumption as speed increases. Although the rolling resistance increases with speed, air resistance increases much faster. So, while around 1/3 of fuel consumption is due to the tyres at 50mph, by the time you get to 70 it's dropped to about 1/4.

That means that "A" rated tyres will benefit you in slow, town, driving far more than it will on the open road (although, to be fair, there will still be a benefit at speed).

Interesting points. I think it is true that the percentage change in mpg from improved rolling resistance will be greatest for constant slow speed drving compared to constant high speed driving due to the air resistance effect. In terms of the absolute fuel saving (i.e. litres of fuel per mile or equivalent) I'm not sure it is clear cut, is it? Thinking about it quickly this seems a difficult question to answer since the force taken to overcome the rolling resistance will vary with speed, and the engine efficiency will also vary. The tyre label categories specify difference in absolute fuel saving, and I'm not sure whether or not it is reasonable to assume this is approximately independent of speed. It might be...

Edit: looking into this a little, what would seem more obviously to affect the fuel saving would be the weight of the vehicle and the efficiency of the engine. Lighter, more economical vehicles will see a smaller absolute fuel saving I think. For vehicles like the OP's 4x4 I suspect the savings may be bigger.

goonarmy

For a 4x4 id recon on getting the tires you need be it road, AT or MT. ECONOMY AND4x4 arent good bed fellows.

Hintza

The tyre companies could make all tyres AA rated but buyers wouldn't be too keen when they need to be replaced after 5,000 miles.

There are more to tyres than the official rating.