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Why don't we have a longer 5th gear?

Posted by Earendil 
January 15, 2010 03:15PM
On my car, 4th gear reaches up to somewhere around 120mph.
Why then isn't 5th geared a lot lower? In other words, why doesn't a cruising speed of 70mph sit closer to 2500 rpm instead of 3000+ ?

The only explanation I can come up with is that that stupid physics velocity-squared bit means that at those higher cruising speeds our car needs to be revving that high to pull the needed horsepower out of the engine. But even though that's the only explanation I can think of, it's not an explanation that I particularly think is true. 5th gear pulls far better than it needs to going 70, or even 80.

Thoughts or ideas from the peanut gallery?

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1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

January 15, 2010 03:50PM
well, i have a super tall 5th in my 190E and it sucks when you really gotta mash the throttle on long grades on the highway...

'93 190E 2.6 » days
'92 318ic » weekends
'85 280TE » resto
January 15, 2010 03:58PM
Quote
ducatipaso
well, i have a super tall 5th in my 190E and it sucks when you really gotta mash the throttle on long grades on the highway...

Perhaps it would be more trouble that I think. But as it is, if I want to accelerate fast I just downshift to 4th. If I need to adjust my speed 5mph I rarely care if it takes 3 seconds or 7 seconds.

-----------------------------------------------------------------------------------
1989 - E30 - M20 - Manual. Approximately 270,000 miles
2000 - E46 - M52TUB28 - Manual. Approximately 110,000 miles

January 16, 2010 10:41AM
If you cruise at higher speeds, say 150-160 kms/hr, with others on the road at about the same speed (read autobahns), then you will see that the 5 th gear ratio is just right.:wink:

salut, Bob P.
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