Tyre Size & Economy

[Blacktemplar]

Apologies if this has been discussed elsewhere, but I'm interested to know other owners' experiences with 255x19x35 Conti Sport Contact 3 tyres...

I've recently bought a 35K-mile 2010 A6 Avant Le Mans 2.0 TDi running these (fairly new boots all round), and have noticed my indicated fuel economy has dropped significantly from my 2005-plate A6 Saloon with the older 138bhp PD engine. I was under the impression the CR diesels were 'more efficient' but on like-for-like journeys, driven with a fairly light right foot I'm seeng anything from 15 to 20mpg different. For example, on a long run at a fairly steady 55-60mph, I was getting an indicated 60mpg-plus on the old car, but only 44-46mpg on the new one.

Is this all down to the width of the tyres & increased rolling resistance? The old car was running 195x16x55's

If the drop in mpg is simply down to the tyres, are there better choices for the 19" Le Mans wheel that help? Or should I just MTFU? ;)

Thanks!

[discobarry]

Well first things first, your old tyre size doesn't exist and if you have the numbers the wrong way round (ie:195/55/16 instead of what you said) then that tyre size again wasn't on the 05 plate a6, maybe 205-55-16 however. On your newer A6 likely hood is that you are now on bigger tyres which can be less efficient, I know 225-50-17s can be as efficient as 205-55-16.

The thing with your new tyre size is your fuel economy will suffer due to what the fuel efficiency of the current tyres on sales is, so it will certainly contribute to your poorer fuel economy however i doubt tyres are the soul solution.

[JimC64]

Hi there, different tyre makes and sizes will certainly play a part in fuel economy.............especially such a big change.

I'm sure it's not the sole reason though to be fair.

As an indicator, my 2.0 Tdi ( 07 ) remapped with 255x35x19 tyres on recently covered 795.5 miles on a single tank ( economy run )
You might find this post a useful indicator......
Economy Runs - What's the best you've had? (http://www.vwaudiforum.co.uk/forum/showthread.php?145755-Economy-Runs-What-s-the-best-you-ve-had)

I did at one point see 64.1mpg although generally it will be around 44mpg unless on a long run and driven conservatively IMO

[aldfort]

Apologies if this has been discussed elsewhere, but I'm interested to know other owners' experiences with 255x19x35 Conti Sport Contact 3 tyres...

I've recently bought a 35K-mile 2010 A6 Avant Le Mans 2.0 TDi running these (fairly new boots all round), and have noticed my indicated fuel economy has dropped significantly from my 2005-plate A6 Saloon with the older 138bhp PD engine. I was under the impression the CR diesels were 'more efficient' but on like-for-like journeys, driven with a fairly light right foot I'm seeng anything from 15 to 20mpg different. For example, on a long run at a fairly steady 55-60mph, I was getting an indicated 60mpg-plus on the old car, but only 44-46mpg on the new one.

Is this all down to the width of the tyres & increased rolling resistance? The old car was running 195x16x55's

If the drop in mpg is simply down to the tyres, are there better choices for the 19" Le Mans wheel that help? Or should I just MTFU? ;)

Thanks!

I assume you've checked the pressures are correct for your tyres? Other than that you can get an idea of the rolling resistance of your tyres by checking the traction and tread-wear ratings. Generally tyres designed for longer life have lower rolling resistance and lower traction ratings. (for tread-wear the higher the number for your tyre the lower the tread-wear or longer the life. For traction AA is the best and C is the worst for traction but C is probably best for fuel economy if you see what I mean). Other than that you need to factor in the current emission regulations which impose a significant burden in terms of absolute fuel economy.

[discobarry]

Thats the second time i've come across tread wear ratings today, it's for the American market really, not European so all the Manufacturers I deal with tell me.

[aldfort]

Thats the second time i've come across tread wear ratings today, it's for the American market really, not European so all the Manufacturers I deal with tell me.
It's normally on the tyre sidewall - the problem is that you need to know what it means. I think it's mandatory in the USA as you have suggested but it is normally on the sidewall of European tyres. If not it's almost always on the tyre makers web site.

[JimC64]

Treadwear ratings may or may not be mandatory, but they give a good indication of expected wear life of the tyre.

For example my Conti CS3 had a treadwear rating of 240......offered AA traction, so really grippy but perhaps didn't last as long s others.
My Barum Bravuris 2 had a treadwear rating of 360....offered A traction, so grippy too but not as good as the CS3's but you can expect them to last around 1/3rd longer