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-   Diesel Discussion (http://www.peachparts.com/shopforum/diesel-discussion/)
-   -   Diff Ratio and Gearing Analysis (http://www.peachparts.com/shopforum/diesel-discussion/321636-diff-ratio-gearing-analysis.html)

Brian Carlton 07-19-2012 09:59 PM
Quote:
Originally Posted by t walgamuth (Post 2976710)
Actually I have an excellent understanding of the two.
Of course you do. That's why you refer to torque as a parameter in top speed results.

vstech 07-19-2012 10:28 PM
Quote:
Originally Posted by Brian Carlton (Post 2976361)
"Higher" could be "taller" or it could be "numerically higher". Both are opposite.

So, the correct terms are "taller" and "shorter". The 3.46 is "taller" than the 3.92.

Those that use "higher" and "lower" are guaranteed to cause confusion, as evidenced on here all the time.
the term "higher" is due to those used to dealing with transmission shifts...
4th gear is "higher" than 2nd gear...

the diff and or transmission gear RATIO's should use the term "taller" or "shorter"

the "higher" gear ratio is a "shorter" GEAR
the "taller" gear ratio is a "lower" GEAR numerically... this is why it's not good to discuss higher or lower when talking about gear ratio's... cause it's confusing...

so, in short... :D
higher and lower are terms you should only use when counting shifts in a transmission, and taller and shorter are terms you should use with gears...
and the word ratio should be left out of the conversation altogether...
whiew!


of course, you could use bigger and smaller... but that will bring up an totally different confusion and bragging and such...

charmalu 07-19-2012 11:51 PM
Quote:
Originally Posted by vstech (Post 2976736)
the term "higher" is due to those used to dealing with transmission shifts...
4th gear is "higher" than 2nd gear...

the diff and or transmission gear RATIO's should use the term "taller" or "shorter"

the "higher" gear ratio is a "shorter" GEAR
the "taller" gear ratio is a "lower" GEAR numerically... this is why it's not good to discuss higher or lower when talking about gear ratio's... cause it's confusing...

so, in short... :D
higher and lower are terms you should only use when counting shifts in a transmission, and taller and shorter are terms you should use with gears...
and the word ratio should be left out of the conversation altogether...
whiew!


of course, you could use bigger and smaller... but that will bring up an totally different confusion and bragging and such...
:confused: HMMM.................Ok.


Charlie

Shortsguy1 07-20-2012 12:12 AM
Excel Program is available (but just not here)
 
Hi-
I really appreciate all your thoughts on my analysis. I was about to attach the excel file that I cleaned up a bit, but I just realized that I cannot attach a .xls file. Wish I had noticed that before I spent the last few hours tidying it up. Oh well. Anyway, I think Army was the only person who asked for it, so I will send it to him directly.

Andrew

Stretch 07-20-2012 12:34 AM
Quote:
Originally Posted by Shortsguy1 (Post 2976790)
Hi-
I really appreciate all your thoughts on my analysis. I was about to attach the excel file that I cleaned up a bit, but I just realized that I cannot attach a .xls file. Wish I had noticed that before I spent the last few hours tidying it up. Oh well. Anyway, I think Army was the only person who asked for it, so I will send it to him directly.

Andrew
And I'm looking forward to it. I reckon there's still some mileage in doing these types of calculations!

t walgamuth 07-20-2012 08:09 AM
To the OP......I would not hesitate to change the diff but not to increase fuel economy. I would expect little gain there. It would make the motor quieter on the highway.

t walgamuth 07-20-2012 08:10 AM
Quote:
Originally Posted by Brian Carlton (Post 2976680)
I already explained that I got about one-half of that amount, as predicted.
Yes, but you thought that 288 divided by 307 was a 9.6% od effect.

Brian Carlton 07-20-2012 09:10 AM
Quote:
Originally Posted by t walgamuth (Post 2976832)
Yes, but you thought that 288 divided by 307 was a 9.6% od effect.
Calculation error...........since corrected.

The fuel benefit was 1 mpg.........about 1/2 of your predicted 1.7 mpg based upon the ratio.

This benefit holds true for most vehicles that undergo the diff change...........except yours. You manage to violate all laws of physics by getting the exact fuel economy percentage as the ratio change. Magically, the force required to dispel the air has also been reduced by the same differential percentage on your vehicles. Additionally, the work required to accelerate the vehicle around town is also reduced by the same differential percentage on your vehicles.

Brian Carlton 07-20-2012 09:13 AM
Quote:
Originally Posted by t walgamuth (Post 2976831)
To the OP......I would not hesitate to change the diff but not to increase fuel economy. I would expect little gain there.
Quote:
Originally Posted by t walgamuth (Post 2976610)

In these MB diesels and in my suburban diesels if you drop the engine speed 20% you realize nearly an exactly corresponding increase in fuel economy.....20%.

Consistency in thought is a wonderful attribute.

t walgamuth 07-20-2012 10:14 AM
Quote:
Originally Posted by Brian Carlton (Post 2976857)
Consistency in thought is a wonderful attribute.
Unless I had a bad diff, I would never have changed from a 307 to 288. Not enough benefit there.

I'd be happy to share the log books from before and after diff swaps in my cars with you. And the before and after results from the five speed od swap into the 83 240/300D. I don't claim all the answers but I have documented results and over multiple vehicles.

The correlation is not exactly 20% but close enough for rules of thumb, in my experience.

It is not possible to control every variable so rules of thumb are close enough for me.

kerry 07-20-2012 12:01 PM
Quote:
Originally Posted by Brian Carlton (Post 2976361)
Those that use "higher" and "lower" are guaranteed to cause confusion, as evidenced on here all the time.
'Higher' and 'lower' are used all the time in regard to transmission gears so the meaning can easily be transferred to different differential ratios.

t walgamuth 07-20-2012 01:18 PM
Quote:
Originally Posted by Brian Carlton (Post 2976857)
Consistency in thought is a wonderful attribute.
In order to benefit from a taller gear ratio you have to have some available power to exploit. There is not much to work with with the 220D.

vstech 07-20-2012 02:35 PM
Quote:
Originally Posted by kerry (Post 2976982)
'Higher' and 'lower' are used all the time in regard to transmission gears so the meaning can easily be transferred to different differential ratios.
with gear ratios in diffs, think of it like climbing stairs.

a 6' incline is harder to climb with 2 steps than with 4 steps... so a 2:1 ratio is TALLER than a 4:1 ratio...;)

t walgamuth 07-20-2012 02:50 PM
Quote:
Originally Posted by vstech (Post 2977111)
with gear ratios in diffs, think of it like climbing stairs.

a 6' incline is harder to climb with 2 steps than with 4 steps... so a 2:1 ratio is TALLER than a 4:1 ratio...;)
Good one!;)

vstech 07-20-2012 03:00 PM
thanks, it just came to me driving down the road thinking on this thread...
I'm sure it's been stated elsewhere before though...


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