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-   -   Different rear gear ratios = ?? (http://www.hotrodders.com/forum/different-rear-gear-ratios-42125.html)

84Z 06-23-2004 12:31 AM

Different rear gear ratios = ??
 
I've seen a lot of odd explanations for different rear gear ratios and decided just to ask some experts. If I have a 3.23 gear ratio and go to a 4.11. Then I'll have less acceleration and more top end? Please let me know, these websites are confusing me. Thanks.

87442lover 06-23-2004 04:09 AM

No, it the oppisite.

If you have a 3 speed (transmission ending in 1.0:1) than with a 3:23 rear end your top speed is gonna be around 120-130 with a typical V8.

If you have a 3 speed and a 4.11:1 rear end than your top speed will be around 95MPH (roughly 5000RPM).

M&M CUSTOM 06-23-2004 06:06 AM

The above post is only a vague response to your question, not explaining much and giving no REAL explanation.

So here goes.

Assume you have the following:

Any engine no matter the manufacturer, or size.
Any transmission, manual OR automatic with a final gear ratio of 1:1.
A tire size of 235/60/15. (This tire has a diameter of 26.1 inches)
Lets compare this information to a gear change.

gear ratio-...................3.23........4.11
engine RPM at 60 MPH-..2504........3186 (slightly above most engines' peak output, this does NOT include automatic transmission slippage factors)

top speed at 5000 RPM-..119 MPH....94 MPH (assuming engine is at peak performance at this RPM only, a lower peak WILL lower this number)

Torque at rear wheels assuming 200 foot pounds at pinion-
-.................................646'#........822' #

Changing nothing else, your vehicle will slow down with a higher ratio gear set.

jimfulco 06-24-2004 01:19 AM

With a 3.23 gear ratio, your driveshaft will turn 3.23 turns for every one turn of the axles.

Centerline 06-24-2004 05:38 AM

Quote:

Originally posted by M&M CUSTOM
Changing nothing else, your vehicle will slow down with a higher ratio gear set.
Very true. But to clarify a bit... all things being equal a higher gear ratio will also increase acceleration but only to the limits of the engine's ability to rev to a particular RPM. In other words, with a higher gear ratio acceleration will be increased but your top speed will come down, unless your engine is modified to increase it's power band and usable RPM range.

To state it another way, with the higher gear ratio (4:11) you will get to 95 mph quicker than with the lower gear ratio but... the lower gear ratio will allow you go ultimately go faster. If the engine is modified to increase it's usable RPM then top speed will be increased with the higher gears and you will get to that higher speed faster than with the lower gear ratio. It's ultimately a trade-off and the trick is to match the engine's ability to rev to the gear ratio so that your top speed and max RPM come together at the end of the quarter mile.

Hope I didn't muddy the water even more...

Centerline

84Z 06-24-2004 01:14 PM

makes perfect sense now, thanks


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