I guess that before getting to carried away with doing the sums we should think about how accurate speedometers would have been back then as its probably only since the introduction of speed limiters that operators have been getting them calibrated to make sure they are getting the 56mph out of them. There’s a guy lives close to me tells me his bog standard Yamaha R1 does 200mph!, he might of seen that on the speedo but there’s no way it will of actually been doing more than a real 180.
I would agree, the speedo in my car is 10 mph out @ 110 mph even now compared to the sat nav, when the car follows the truck on the limiter at an actual 56 mph the car speedo reads 61mph, the car is not that old on a 07 plate with 50,000 miles on the clock
i know in the past of some double drive fodens from this area which would touch 90mph, a mate of mine had an erf es6 4 wheeler with the steyr cab that would do 85mph, Longsons also had some very fast erf’s, i dont thik they were pulling tanks i am sure they were rocket boosters of the space shuttle! never seen owt doing over the ton before running out of revs though!
got to agree with you moose , my present car shows 60mph when i am following a truck on the limiter , so not very accurate . i did have a 1979 foden unit with the 290 big cam which did 67 mph at 2050 revs . when it was retrofitted with an overdrive box , it went off the clock at 1600 rpm , but there was no way of checking its actual top speed (no gps then ) it would leave longsons for dead on the motorway though . cheers , dave
Car speedos are, I think, allowed by law to read +10% but not under-read at all. They will fit the cheapest mechanism they can get away with, so the tolerance on car clocks will be +5% ±5%, if the manufacturer has got it right. IE at the magic ton, the average car will show 105mph but some may be accurate and some may read 110.
Are tachos and speed limiters calibrated to within ±2%?
Lorry tyres are 3% smaller when the tread is worn down, but still just about legal. If you want to go a bit faster, get your speed limiter calibrated on tyres with the bare minimum of tread- ones which have already been recut. Same with the tacho, if you want it to record a lower speed and distance. Then fit brand new ones. Those ERF Fuel Duel vehicles had this done, but the other way round, so that the lorry would be limited to a lower speed and use less fuel. I made that last bit up, but it is true. 
newmercman:
Riverstick, my 379 is very stable at speed, it holds the road very well too, a bit unnerving at first as there’s not much lean compared to a cabover, it does lean but instead of feeling like I’m going to fall out of the chair, the biggest tell tale is the ting ting ting from the chrome weights on the bottom of the mudflaps scraping along the road
Now that rings a bell alright…The chrome weights scraping off the road as you pushed it on the corners…What a fantastic truck to make up time on a motorway…I reckon the Pete has the edge on the Kenworth…just a personal feeling.
Riverstick:
newmercman:
Riverstick, my 379 is very stable at speed, it holds the road very well too, a bit unnerving at first as there’s not much lean compared to a cabover, it does lean but instead of feeling like I’m going to fall out of the chair, the biggest tell tale is the ting ting ting from the chrome weights on the bottom of the mudflaps scraping along the roadNow that rings a bell alright…The chrome weights scraping off the road as you pushed it on the corners…What a fantastic truck to make up time on a motorway…I reckon the Pete has the edge on the Kenworth…just a personal feeling.
hi,
agree with you both 100% 
regards andrew.
I agree, the Pete has the edge over the KW, the rear suspension on the KW uses an eight bag set up and kicks you in the arse all day long, the KW I had was the worst riding truck I’ve ever driven and that includes empty eight wheeler tippers and hydraulic tag axle Scanias, come to think of it the parabolic springs on a 111 gave a better ride and the old Scania had better brakes than the KW too 
I was chatting to driver today who drove a Renault Magnum 520bhp V8 in the early~mid 1990’sand reckoned it was good for 114mph…Can anyone confirm or deny?
newmercman:
I agree, the Pete has the edge over the KW, the rear suspension on the KW uses an eight bag set up and kicks you in the arse all day long, the KW I had was the worst riding truck I’ve ever driven and that includes empty eight wheeler tippers and hydraulic tag axle Scanias, come to think of it the parabolic springs on a 111 gave a better ride and the old Scania had better brakes than the KW too
Kenworth 8bag air…often used to wonder if it was “concrete” air in there!! Pete air leaf was a lot kinder, but the real “bumper and banger” had to be Reyco springs…I learned the hard way with American iron.
Thinking about velocity, I imported a Marmon conventional, V8 Cat, 15speed double overdrive, and a 6speed spicer behind that, riding on Newway air. So fast, really fast, when you (bravely) put her into o.d. and 5th behind, it was like riding a Gold Star, and motorway bends became quite sharp! She rode so smooth, and the cab did not rattle. and the windows worked, even the bed was leather, and two chrome straight thro`s . Oh happy memories Cheerio for now.
I have just fitted a fuller 13speed double overdrive (rtox) to a foden to give it better economy on the motorways.
the young boy on the fleet was handed a 06 Mack Vision 460 13sp fuller ,eaton back ends. (had been breathed on as was an ex o/o truck) and was running only 1 trailer and was doing some impresive times (depot-quarry).
Well i had it for 1 day as my old girl had been reveresed into…honest 
well it was 7 in the morning and i let her go (empty) fme i was off the clock (over 160kmph)…flipped the jake on to slow down as i remembered we had remoulds on trailer… very smooth …well for a Mack 
.jimmy