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Old 20th September 2008, 11:15   #1
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Default Guide on gear ratios

hope this article helps many of you there -
Gear Ratio Guide

When ever you change tire size from the original size to another there will be a direct effect on power and drivability. We have developed this chart to help you select the optimum gear ratio to put your performance back where you want it.
Using the chart below, first determine your original gear ratio and tire size and follow to the intersection that should be your approximate RPM at 65 MPH. Next find your new tire size and follow that across to the closest RPM to your original and that will be first choice.
If you are interested in a change that will give more power or better fuel mileage use the color coding as a guide.
Highway Driving, Good Fuel Economy Daily Driver, Best Overall Performance Most Power and Towing, Reduced Fuel Economy
This chart is based on 65 MPH and a gear ratio of 1:1, on a manual transmission in 4th gear. Please NOTE: If you have an automatic transmission your RPM will higher due to slippage in the transmission and the torque converter. With an overdrive transmission your RPM in overdrive will be 15% to 30% less than indicated.
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Last edited by Rehaan : 28th September 2008 at 01:42. Reason: bmp image replaced with gif
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Old 20th September 2008, 11:26   #2
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Can't make out a thing from this chart.

What does this chart help calculate, exactly? And when you say "gear ratio" which gear are you refering to?

Shan2nu

Last edited by Shan2nu : 20th September 2008 at 11:31.
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Old 20th September 2008, 11:30   #3
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Originally Posted by Shan2nu View Post
Can't make out a thing from this chart.

What does this chart help calculate, exactly? And when you say "gear ratio" which gear are you refering to?

Shan2nu

direct paste didnt work, i have attached the chart now; this article is about the ring and pinion ratio required for a particular tire size.
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Old 20th September 2008, 11:37   #4
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Ok so this is basically altering the final drive ratio to maintain the "engine rpm : wheel rpm" ratio after the wheel diameter has changed.

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Old 20th September 2008, 11:50   #5
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I think even this works :

new wheel dimeter x old final drive / old wheel diameter = new final drive

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Old 20th September 2008, 15:49   #6
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Originally Posted by vikid View Post
Gear Ratio Guide

If you are interested in a change that will give more power or better fuel mileage use the color coding as a guide.
Which color is used for what application ? Of course the experts can understand it by looking at the figures itself but I need some help here.

As far as I can the "same engine rpm : same wheel rpm " configuration, we still need to calibrate our speedometers and odometers but dont you think the characteristic of the engine will change. Say, at X rpm the engine turned 25 size tire then now at the same rpm its turning the 27 tire at same wheel rpm or speed dont you think its strain !!

Last edited by rranjith_kum : 20th September 2008 at 16:04.
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Old 20th September 2008, 16:48   #7
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Quote:
As far as I can the "same engine rpm : same wheel rpm " configuration, we still need to calibrate our speedometers and odometers but dont you think the characteristic of the engine will change. Say, at X rpm the engine turned 25 size tire then now at the same rpm its turning the 27 tire at same wheel rpm or speed dont you think its strain !!
Can't really say, it depends on the weight of the bigger wheel. If the weight remains the same, it doesn't matter but if the weight increases the strain on the engine will increase. Morover, when you alter the final drive (in this case it will have to be shortened), the resulting torque at the wheel also increases. This can help improve acceleration.

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Old 20th September 2008, 17:46   #8
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How do you change the Final drive ratio in a car
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Old 20th September 2008, 17:58   #9
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You can buy them - http://www.hmotorsonline.com/shop/sc...age&item=10006

But you have to make sure the final drive you're buying matches your transmision.

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Old 21st September 2008, 00:24   #10
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Quote:
Originally Posted by rranjith_kum View Post
Which color is used for what application ?
the yellow is for more torque, less gas milage; light blue is for moderate power; dark blue is for highway driving and better milage.

we go to the yellow as we need more torque while offroading with bigger tires.
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Old 18th November 2009, 11:03   #11
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How does high gear ratio in first gear provide more available torque to pulll off the vehicle at low speeds ? Why can't low gear ratio provide sufficient torque ?
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Old 6th December 2009, 14:28   #12
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Originally Posted by taurian2804 View Post
How does high gear ratio in first gear provide more available torque to pulll off the vehicle at low speeds ? Why can't low gear ratio provide sufficient torque ?
http://www.vettenet.org/torquehp.html
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Old 6th May 2010, 00:06   #13
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guys, whats the stock ring and pinion ratio of the MM540? and are there aftermarket r&p with different ratios available in india for the 540..thanks.
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Old 6th May 2010, 07:06   #14
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Originally Posted by vikid View Post
guys, whats the stock ring and pinion ratio of the MM540? and are there aftermarket r&p with different ratios available in india for the 540..thanks.
Answer to Part 1: 4.88
Answer to Part 2: YES.
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Old 6th May 2010, 15:41   #15
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Thanks a lot Red Liner. Does MM540 have a D27 in the front and D44 at the rear?
Will i get a numerically higher ratio than 4.88 in India for these diffs if i had to run tires bigger than 33"..

Thanks..

Last edited by Rehaan : 7th May 2010 at 15:53. Reason: Removing formatting tags.
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