Our lot are changing 85 to 70 size tyres on all the fleet,conti has said they are better on fuel etc and are sorting the contract out,how can a tyre a touch smaller save fuel 
i see merc come new with them fitted standard…
they will also have to get the tachos recalibrated as the tyre size is programmed in to the tacho head
norb:
they will also have to get the tachos recalibrated as the tyre size is programmed in to the tacho head
yea they on with it,wont the engine run quicker with smaller tyres norb
I know owner drivers like to put worn tyres on for calibration as that gives them an advantage when they then put their new tyres back on…as that will upset the L factor,which is the measurement of the tyre circumfrance ,hence you have that reflective tape on your tyre…I may be wrong but I don’t think you will notice any difference
I dont understand how a smaller tyre can save fuel 
,conti are certain that they get better results ,all our work is motorway driving…
they probably have a lower rolling resistanceif if you go on to their website it may expain how the tyre works
norb:
I know owner drivers like to put worn tyres on for calibration as that gives them an advantage when they then put their new tyres back on…
No it doesn’t as the tyre wear is taken into account when the calibration checks are done. I once took one in for its test with 50% worn tyres and it was half a km/h out. The difference between worn and new isn’t as much as they think in their heads, maybe a couple of percent difference in speed.
norb:
I may be wrong but I don’t think you will notice any difference
the difference between a new tyre and a worn-out one can be as much as 2mph. I’ve tried that trick myself but sadly they also measured the circumference of the drive tyres, then compared to that of a new tyre and then calibrated the lorry to run at 89kph only after I put the new tyres on 
haven’t seen 80-series tyres on euro-spec trucks for ages, must be the overall height.
Conor:
norb:
I know owner drivers like to put worn tyres on for calibration as that gives them an advantage when they then put their new tyres back on…No it doesn’t as the tyre wear is taken into account when the calibration checks are done. I once took one in for its test with 50% worn tyres and it was half a km/h out. The difference between worn and new isn’t as much as they think in their heads, maybe a couple of percent difference in speed.
I know what your saying ,but owner drivers see it as a big issue ,had one complain as due to it needing a new sender I had to do a recal,and he moaned about his speed and how I must have done X Y &Z to his truck and how it was slower ,and he wanted another free recal ,surprisingly it now had old worn tyres on it …Doesn’t bother what they believe ,unless they are saying I have done something wrong…
Obviously a worn tyre will complete a revoloution quicker that a new tyre ,is there any real benefit in that couple of mm
I had 4 new boots fitted to drive axle, Magnam, and it went, on limiter, from 54 to 56. Sat nav speed 
SWEDISH BLUE:
I had 4 new boots fitted to drive axle, Magnam, and it went, on limiter, from 54 to 56. Sat nav speed
nice 