After doing some poking around into tyres, I’m still largely unclear on which of the low rolling resistance tyres are going to deliver results, and what kind of results to expect.
I understand the key concept – a tyre with a lower rolling resistance takes less power to get moving, and keep moving, and thus will be more efficient. Simple.
Finding exactly which tyre has the lowest rolling resistance, in theory, isn’t hard. Grab some low rolling resistance tyres, let them roll, the one that rolls the furthest wins.
Finding a tyre shop that has that kind of space, and isn’t affected by wind, and will let you take some tyres, fit them to some rims, inflate them to 40 PSI and roll them down the road by applying the same force to all, is not easy.
And I would have thought the manufacturers looking to pimp their black tyres with green advertising involving kids, clouds and nature (as if tyres are somehow environmentally sustainable!), would show that data.
“When subjected to a force of X kg, the tyre fitted to a rim, inflated to x PSI, rolled x metres before finally coming to a stop”.
Then, for the customer shopping around, it’s easy to say “That tyre costs $20 more, but only rolls an extra 1 metre”. It’s not.
So you have to troll through all the ‘green’ advertising for the Michelin Energy XM2, Pirelli Cinturato P6, Bridgestone Ecopia, Goodyear’s whatever the heck it was, and the like and see if there’s a hint of a number of how ‘low’ is the rolling resistance.
We came across Choice’s article online, but I dismissed that because I remember finding that new tyres will have a coating from the manufacturing process on them still and that needs to be worn off first.
Nitrogen was another to check into, but dismissed because the car is never on the race track, the likely result will be a slightly higher than is already in air content of nitrogen in the tyre.
The prices on them are variable too, I get that some are likely to last longer than others – that’s a quality thing, what really would help them sell one tyre over another (except for those lured by green advertising), would be to show the real world numbers on them.
For now, Michelin’s XM2 is the likely candidate – Pirelli’s website doesn’t leave much to work with, Bridgestone’s website doesn’t do a great deal with a Planet Ark logo and ‘green’ Ecopia logo – but no data to really say exactly what the tyre is capable of.
Pirelli and Bridgestone are cheaper than the Michelin tyres, but there’s nothing there to make a purchase decision on, more simply put – I might as well just put Budget tyres on as they were at least $120 cheaper.
Michelin’s got some information in Google from others who have used them, and a website fit to sell them – it’s easy to see:
– “20% Extra Mileage”, cool, so the tyres cost 40% more yet last 20% longer.
– “10% less rolling resistance”, ok, so that’s not going to translate to much in fuel economy.
Looking at the US Dept of Energy’s website they have numbers on percentage reduction in fuel consumption per percentage decrease of rolling resistance. The best number is 0.19. That is, for every 1% decrease in rolling resistance, you get 0.19% reduction in fuel consumption.
Michelin made that easy, 1.9% reduction in fuel consumption by using their tyres.
They last around 50,000kM according to my Googling (maybe longer, maybe shorter). I know my current car is supposed to get around 6L/100kM. So, to travel 50,000kM, I need to use 3000L (around there, say 3500L if we were getting 7L on average). At 1.9%, we’ll save 66.5L a corner, 4 corners is 266L. At today’s rough price of $1.41 (I use 95RON min, Ethanol is actually worse off for our food supply and the planet) – 266L is $375. Not a bad result at all. I might be confused and the result doesn’t need to be multiplied by 4, in which case the savings in fuel come to $93.
If the result is $93, and is divided by 4 for the 4 tyres, it reduces the price per tyre down to $109, and counting the extra life of the tyre, that’s easily worth it (it’s around $20 extra from ‘budget’ tyres, and these last 20% longer for an 18% increase in price after fuel savings subtracted).
That of course, assumes a few things, like, Michelin’s website contains no misleading or incorrect marketing statements, and the promised benefits are actually realised. I’d like to have been able to check that against the other possible candidates. The Planet Ark logo isn’t enough to sell me some tyres. A splash of ‘green’ tells me nothing about the product.