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With diff ratios less is more...
Page 28
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I AGREE THAT the AEC Mammoth Major Mk1II should be considered as one of the century's great trucks and hope it will be included in those that we can vote for —as should be its successor,the MkV, which started the trend towards improving the driver's lot.
It gave an easy-entry cab as standard and good performance from the standard AV590 engine, which was rendered superlative when the optionalAV690 was installed with the six-speed overdrive gearbox. Even these were even surpassed when the Ergomatic version replaced it.
I remember drivers telling me how much less tired they were at the end of the day when driving these compared with competitors' products. However, in the write up on the MkII1 (CM26 May) the author made the common mistake that a lot of writers do when referring to diff ratios.
He said the highest ratio was 6.25:1 but a lower ratio of 7:1 was available for drawbar work,when he meant exactly the opposite: 6.25:1 is a lower ratio than 7:1.The ratio gives the number of turns the prop shaft (or cardan shaft' in AEC terminology) makes to turn the road wheel one revolution.
Thus with a 6.25:1 ratio, the road wheel turns 288 times a minute at the maximum governed speed of 1,80Grpin, while the 7:1 diff turns the wheel 257 times a minute.Thus the lower ratio gives a higher road speed, whilst the higher ratio gives a lower road speed but better climbing ability, and is therefore better for the drawbar application.
I hope this will be of interest to your readers and lead to a better understanding of the term diff ratio.
Robin Hannay Goostrey, Crewe Editor's response Oops!We apologise for our mechanical confusion. The author has now been made to revise the intricacies oldifferential ratios and other engine related terminology until he can recite it in his sleep. Meanwhile, to vote in CM's Greatest CV of aniline poll visit www.cm100.co.uk