# Gear reduction equation (new Q)

Discussion in 'The Garage' started by big94gmc, Jun 1, 2005.

1. ### big94gmc1/2 ton status

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Can some please teach me the gear reduction equation??? You know, what you use to find out your final crawl ratio.

Also, can someone please tell me the granny low ratio in an SM465?

What about an NV4500??? Can someone please tell me the first gear ratio of that tranny?

And while we're on the topic of ratios and equations, can someone teach me about all those different equations that have to do with tire size, desired road speed, r&p ratio, etc etc etc.... I've always wanted to memorize all the different equations for figuring out crap having to do with these trucks.... Any I'm missin'??

Last edited: Jun 1, 2005
2. ### Leper1/2 ton status

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3. ### resurrected_jimmy1/2 ton status

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This list could get long depending on how far you take it.

crawl ratio = 1st gear (x) t -case low range (x) axle gear
SM 465 low gear is 6.55:1
rpm = mph x axle ratio x 336/tire diameter (in)
gear ratio = rpm x tire diameter/mph x 336

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there are a couple of calculators on 4lo.com too.

5. ### big94gmc1/2 ton status

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So.... 6.55 x 4 x 4.56.... I get 119, but, too little to bicker about. Even if I went to 5.13's, I'd still only have 134 to 1.... I thought I was higher then that. Damn. Oh well....

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The 203 ratio is straight 2.0 but the 205 ratio is 1.96, that's where the difference in calculations comes from.

Either way the crawl ratio is very nice. If you want more you could swap in a D70 and go for more axle gear. Another option is the WMS 3:1 for the 203 but it's a little pricey. Or... you could hold your breath and get a 3:1 205 in about 5 more years.

7. ### big94gmc1/2 ton status

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Too expensive for me for the 3:1.... I'll stick what I have.

TTT for new question.

8. ### tarussell1/2 ton status

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The 4500 first gear could be one of two different ratio's depending on what year the tranny is , 6.34 or 5.61
Tom

9. ### big94gmc1/2 ton status

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So what about an NV4500 from an early/mid 90's GM one ton???

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That's the 6.34 version I believe.

Chris, if you decide not to use the NV4500 let me know I'm looking for one for my crew cab.

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