9+ MPG Class 8 5 Axel Trucks with Trailers

It makes total sense what you experienced running the two R620's side by side.....a 6 x 4 is driving through three differentials.....a 6 x 2 or a 4 x 2 is only dring through one....The mechanical losses are noramlly responsible for up to 2MPG....0.8MPG is very reasonable

 

I have to say the lad driving the 6*2 says she is harder than it should be, he reckons another one he sometimes runs with is better than his one, 2 mpg, that's serious! I don't doubt it though cos it only done 7.01 mpg with a load of dumper wheels on a lowloader and returned with a load of farm machinery , my 580 does almost 9 mpg and that's a 4*2 and that's fridges to Italy , the lowloader was only to holland

 

Should have also stated we were pretty heavy but the terrain to holland is pretty easy, it's hard to judge it unless you got the trucks working side by side but the 6*4 is definately harder on fuel, I never took much notice until I read these threads and seen it for myself

 

this is good result for 6x4

here we count 6x4 use 5L more /100km than single axle

i am confused with this 1300rpm at 90

do you know which tires they use

and are they with hypoid axles or hub reduction

i guess hypoid

 

Drives run on 315/80r22.5, just hypoid axles, the gearing isn't the standard ratios like the ordinary r620, they cruise about 1200 rpm, this r620 is plated for 80 tons, I don't know the ratios he specced on it

If the second drive axle makes that much difference is it worth it for me to micro blue my rear end as it's just single drive, would microblueing the wheel bearings be enough since as riverstick pointed out ive got two differentials less than a 6*4 so I don't think I'd get the same savings as dice did.

 

with my calculations rb662+r660 with 3.8 diff ratio, overdrive grso905 gearbox and 315/80 should be 1333rpm at 89kmh

btw i know for one r620 with 3.8 diff ratio ( 4x2 tractor) overdrive gearbox and 315/70 have 1450rpm at 89

 

It's actually just a shade below 1400 but not much, how good is the 3.8 diff? I actually find the ordinary 620 you have to split top gear all the time, there's a huge gap between 12th and 11 th also the gap is so big when you lose speed on a hill then split top gear it actually accelerates back up to top speed or maybe I'm just not used to overdrive gearbox my habits may not suit it, this 620 is better there's more power going into the hill, can the 620 be specced without the overdrive box?

 

My apologies, that should be 1400 rpm not 1300

 

Customer service, home time (otherwise known as maintenance time) and the FMSCA is why speed is(can be) a big factor. I didn't say I run 75 or 80 or what ever "hammer down is". The difference between 65 and 55 can make a big difference sometimes at the end of the week.
I guess if you're fortunate enough to have the kind of run you have then more power to yah. Hell take her down to 53 or so if thats how you make your money.
I'm still not sure about your math on the fuel savings but it's your story....tell it like you want. $960 a week would be a 3mpg improvement or there abouts. And i don't know where you buy fuel but mine aint 4 bucks.

 

I still think Dice is onto something by Microblueing the rear end....jack up the rear axle of your truck some day and try and rotate the wheels by hand....and you'll soon realise the horsepower that is absorbed in the drivetrain....I would like to try the rear end,rear axle wheel bearings and driveshaft universal joints and centre bearing(s)and see the results. I think the universal joints would be worth doing from a durability point alone.