Re: Math

[Simon Favre <simon@domain.elided>]

Try this:

New_RPM = ( New_gear_ratio / Current_gear_ratio ) * Current_RPM

For example, if your current gear is 3rd, and the ratio is 2:1 (very
artificial example), and you want to shift to 2nd with a ratio of 3:1,
your RPMs will rise from 3000 to 4500. Actual ratios may be quite
illuminating. Take the difference of ratios between 1-2, 2-3, 3-4, and
4-5. You'll see that the differences in gear ratios get smaller as you go
to higher gears. As mentioned before, it's the large gap in the ratios
between 2nd and 3rd that aggravates 2nd gear synchro wear.

Here's a VERY approximate way to estimate speed from RPM for the top 3
gears: In 3rd, the RPM reading from the tach, in hundreds, is pretty
close to actual MPH. In 4th, multiply tach by 3/2. In 5th, multiply
RPM by 2. A reading of "40" from the tach in 5th means 80 MPH. This may
no longer apply to more modern cars with tall rear ends. It worked fairly
well with the old 4.56:1 rear ends.

If you use Km, sorry, all bets are off. ;=)

Quentin Bourke wrote:

>if I know gear ratios can I calculate what engine speed I need to attain
>if I am changing to a lower gear?
>
>eg If I am travelling in fourth at 3,000 rpm what rpm would I need to
>maintain the same road speed in third

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