QUITE SIMPLE

NZ Truth, Issue 1194, 18 October 1928, Page 21

QUITE SIMPLE

That Is— When You Know How

Owners who ' are interested, m the -performance, of their cars also will be interested m the formula from which they will be able* to work:. out their engine revolutions . at any speed m a simple manner. THE first thing to do is to pump the rear tyres to the correct working pressure^ A chalk mark is then made on the tyre/, corresponding with a similar mark on the road. ': : The;car, is then' moved aue. revolution of the wheel,! and a second mark made on' ithe ro&d.. . : - . v \ '.'-'-i ';: ; ■ v : v / : ' ' ; ;: -;' : :.: The distance bet\v;een ' these two marks' jnustjbe measured Jn millimetres. This ..can be done- by/ multiplying the number 4 of inches by 25.4. V' •■ 'Thus.riifv-the wheel' moved) 'say, 70 inches, the distance m millimetres would be 1778. .; .■: ... . ! ; ;.^This number of millimetres is ; thin divided by 31-7, that is multiplied by 7 and divided' by. 22, thus ; : giyirtg the diameter- of the- wheel. : • The formula is as follows :4— ' ; .Meauals miles per hour. JD—diameter of wheel m millimetres, • G-^r-gear ratio, -R4-revolutlons per minute,'-. and C is a constant, 8540 per cent. ' The revolutions equal C divided by D, multiplied -by G, multiplied by M.', therefore,' taking the distance mentioned,. 1778' divided by 3 1-7 . (equal to 566 m round figures) and a gear ratio of four .to -one, the revolution rate of a car travelling -30- m.p;h. would be 8540 divided by 566, multiplied by 4, multiplied by 30.. -^ - ■• -'■ : ••• This works outsat about 1810. j ■..'"■.''' •:'■■.''. ■■'••.