Fuel Consuption Fatties V Skinnies

Lower pressures in any tyre will cause this, but the 265's are a lot better in their handling and comfort. At least now you won't get flats from tube rub thru.

10% is pretty dramatic. Up the pressure all round a bit and see what happens. Check the handling and watch for poor wear, but that should bring back the economy a bit.

Gday Dennis,
You now have more grip, but unfortunately more rolling resistance which means more fuel.

It also depends on the tyres too - the Goodyear MTRs and BFG ATKOs that I ran in the past had good grip, but got poor fuel consumption. I run the Bridgestone 694s now which are less aggressive and fuel consumption seems a bit better.

In general terms, wider tyres have poorer fuel economy, and poorer off-road ability (including mud and sand). Don't believe the common misconception that wider tyres have better flotation ability; it's worse, in particular if they are also low profile, as they can't be deflated as much as high profile tyres before risking damage to the tyre or the rim (esp if the rims are alloys), and often have softer side walls. The only reason to go for wide tyres (apart from looks) is if you need the speed rating which is generally related to width of tyre, as wider tyres are often lower profile and in any event provide better lateral stability at high speed and usually better on-road traction as they run at lower pressures (and hence have larger footprint or contact area with the road for the same axle loads). If you don't need the speed rating, one option is to just go back to a narrower tyre, providing it has the load and speed rating, and tread pattern, you are after. That's my take on it, anyway!

G'day Dennis,

In addition to the earlier comments, it may also be worth checking the circumference of each tyre type to ensure your speedo readings are apples for apples.

Always interesting to see how seemingly simple changes have such an effect.

Regards,

Rob.

i'll think i will stick with my cheese cutters. they seem to get me to where i am going.

thanks for the info.

Do the new ones feel rubbery through the steering wheel? My D694 B/stones did along with increased fuel consumption.
Seemed to improve as the tyres aged and hardened up.

Can I put forward a few points in favour of my own arguments? I realise everybody takes their choice of rims and tyres very personally, so try to avoid taking offence! At the end of the day, these are opinions only!
• At any given tyre pressure, a narrower tyre will have a longer footprint than a wider one. When driving through sand, a narrow tyre means pushing a smaller “bow wave” of sand in front of the tyre compared to a fat tyre, assuming both are running at the same pressure. Have a look at what the tour operators do on Fraser Island and elsewhere; they all run with the narrowest practical tyre for the load rating they need. A similar situation applies in mud.
• If “fats” were better than narrow tyres, why are cross-country (and even downhill) skis long and thin, rather than short and fat? You can get the same surface area either way but a long surface area in the direction of travel is far more important than a wide surface area in the direction of travel!
• A high profile tyre means the tyres can be deflated much lower than (lower profile) fats before there is potential rim damage. Rim damage is perhaps not such an issue on sand, but certainly is on hard or rocky surfaces. I run 255/100R16 tyres on my EarthCruiser and I've successfully lowered these to 14 psi (hot). At that pressure, the footprint is huge and it is mainly the length that increases, rather than width. Like the cross-country skis, it is then easier to cross soft surfaces.
• Road bicycles run with narrow tyres and high pressures. This reduces frontal area on the tyre and hence wind resistance, and also reduces contact area with the road and hence rolling resistance (resulting in less effort to pedal, similar to better fuel economy).
• The military run with narrow tyres on off-road vehicles. If wider tyres were better off-road, surely they would have figured this out by now!
• Most outback tyre repairers that I’ve spoken to say that the main problem with punctures is:
o People not using light truck tyres, and
o People running with too high tyre pressures
• I can’t see how split versus single piece rims would have anything to do with tyre punctures? One refers to rims, the other to tyres??
• I certainly DO accept that “fats” look better, and (since they normally operate at lower pressure than narrow tyres on road) also provide better traction, steering stability, and braking for ON-ROAD conditions. Fats (esp if low profile) can also run with thinner side walls due to less flex, which is important for heat dissipation which in turn is critical for high speed driving. But it’s a totally different story off-road. This assumes, of course, comparable tread pattern between the narrow and wider tyres.
In summary, my take on this (also reflected in my experience driving off-road trucks in the Army reserve, and as someone who has also been across the Simpson Desert 4 times, Cape York 8 times, the CSR, driven up to the Arctic circle, and basically expedition driving much of my time) is that wide, low profile tyres are the best choice for high speed on-road driving, but narrow, high profile tyres are the best choice for off-road work, no matter what it is.
Have a look at what is said about this on the Expeditions forum & elsewhere:
http://expeditionportal.com/forum/showthread.php?t=31096
and also http://www.team-bhp.com/forum/tyre-alloy-wheel-section/90524-off-roading-tires-wide-narrow-better.html

Thanks to every one for their contribution.
It’s basically what my tyre supplier predicted - the skinny 7.50’s are more economical on the bitumen whilst the 265's ride softer on bitumen and handle better in soft sand.
Just for the record - I didn't have a flat in 60,000ks with the skinnies and for me they handled sharp rocks well but in very soft sand they tended to dig in more than the 265's. I haven't tested them on sharp rocky surfaces but I expect they will suffer a bit compared to the skinnies - its all a matter of compromise.
Regards Dennis