using the values from the site i linked to would have given you an answer to this but i suspect your interpretation would depend on your need to win your argument.
You know, I came across that website when I was doing my own research. I didn't realize that I could click the button to get detailed specifications at the time. Now I see that the information is there.
5th gear on a 1965 850 is shown to be a ratio of 0.806 which by your definition is an overdriven gear with 4th speed being 1:1
Exactly. 4th gear is direct drive. 5th gear is overdrive.
however the true definition of an Overdrive is a gear to allow lower RPM at a higher speed but a being only able to attain top vehicle speed in a lower gear so theoretically you can go faster in 4th than in 5th and that 5th gear is really only there for the long haul cruse and economy
Exactly. The discussion (it wasn't an argument) I was having with my buddy is that the 5-speed gearbox would have contained an overdrive gear (5th) for lower RPM at high speeds, therefore helping fuel economy. That's really the purpose of an overdrive gear in any transmission.
however the theoretical top speed of that same car in 4th gear is 86-mph based on max engine revs etc
the top speed of the car although not considerably higher is rated at 87-mph. so the 5th gear does allow the car to go faster than is possible with a 4 speed gear box.
There are very few cars that can attain top speed in their top gear. Most cars reach top speed in a lower gear. There are only 3 different ways that any car reaches its top speed: 1- electronic governor (this is typical on a lot of today's cars), 2- Aerodynamic drag (when a car is unable to overcome the drag and reaches a top speed plateau), or 3- gear limited (this is when a car has enough power to run all the way to redline in its top gear. Like I said, very few cars are capable of reaching redline in top gear. Most cars simply don't have nearly enough power to do that, so of course their top speed is usually attained in the next lower gear.
what I would assume however is given the prevalence of 'Over drive' gearing on british cars in the 60s and 70s (some early 80s) the guy you know is referring to the actual presence of a 5th cog built into the box unlike many of the cars at the time which used an 'over drive' unit as an extra overdrive gear external to the original main gearbox. around the time 5 speeds became more common some where actually advertised as having an 'overdrive' when by todays standards they simply had a 5 speed gear box
Well, he claims that the 5-speed gearbox used 5 underdriven gears, which seemed unlikely to me. Simply looking at the individual ratios of each gear clearly shows that 5th gear is indeed an overdrive ratio.
using your argument and definition virtually every single 5 speed gearbox ever made contains a 5th speed which is an overdrive ratio.
Exactly. I've seen plenty of 4-speed gearboxes that didn't have an overdrive gear in them, but I've never seen a 5-speed gearbox that didn't have 5th gear as an overdrive gear. That's not to say it is impossible...just that I've never seen it.
BTW, there are some 6-speed manual gearboxes out today that have the top three gears (4th, 5th, and 6th) all overdriven ratios.
i am inclined to side with 'guy' because i believe he is arguing that the 5th gear was in the box and not an external overdrive unit, although i would like to add that you are technically correct (just)
Well, the discussion really had nothing to do with external overdrive units. He simply said that 5th gear was underdriven, just like the other four gears. I still haven't seen anything to support his claim.
