How do Artics go so fast

magnet on the gearbox for digi tacho, crease in the paper with analog tacho,

fuse 17 for rev limiter and if you are lucky, the smallest set of tyres on it to the station where they set the rev limiter to it's max then bigger wheels on when you are back to base.

my instructor hated me for knowing that stuff

Ahhh thats what I wanted to know, so gearboxes only go as far as direct in top gear 1:1 so the ability to do say 100 MPH is only down to diff ratio and tyre dia although these are almost all the same size these days arnt they ?

 

This has interested me due to my GMC that has the engine governed to 2750 RPM, top (5th ) is slightly overdrive and rear axle is 6.6:1 only does 45 MPH.

I believe the GMC has a reduction ratio in high box and well as low box........so not really a overdrive effect so to speak.

I believe the GMC has a reduction ratio in high box and well as low box........so not really a overdrive effect so to speak.

Yep did know that but its only slight, My interest was regarding the larger modern trucks, I assume the large diesels are fairly low reving so how do they achieve the high speeds must be a low ratio diff ?

Indeed. Those high cube rigs (any relation??) you see run on smaller diameter wheels to reduce height. So they have a much lower ratio (= much faster) diff to compensate for wheel size and give comparable speed.

So if one were to order a tractor unit with low ratio diff but with standard size wheels - one might be able to do well over 70mph…….:cool2: