Math help for drivetrain please - Defender Source
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  #1  
Old September 17th, 2008, 11:44 PM
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Math help for drivetrain please

I know there are a couple math studs on here that can help me with this. I need to calculate top speed based on gear ratios. So assuming that the useable top speed on a 300TDi is 75mph stock, the numbers would go:

3.73 gears, (??) 1.4 t-case, 31in tires = 75 mph at a decent rpm about 3200-3500 I think.

So what would be the top speed of:

6.20 gears, 1.4 t-case, 40in tires = what at 3500rpm

Also, that would it be for:

6.20 gears, 1.2 t-case, 40in tires =??

Last:

6.20 1.0 t-case, 40in tires = ??

Standard r380 transmission in this. If that matters. This is only for gear ratio purpose. Thanks in advance!!
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  #2  
Old September 18th, 2008, 01:10 AM
madcowdungbeetle
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If no one has replied to this with some numbers, I'll run the calculations sometime in the morning when I get to work.
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Old September 18th, 2008, 08:26 AM
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Quote:
Originally Posted by Buckon37s
3.73 gears, (??) 1.4 t-case, 31in tires = 75 mph at a decent rpm about 3200-3500 I think.
6.20 gears, 1.4 t-case, 40in tires = what at 3500rpm
6.20 gears, 1.2 t-case, 40in tires =??
6.20 1.0 t-case, 40in tires = ??
6.2/3.73 * 31/40 = 1.29 i.e. engine will run 1.29 times faster for the same speed.
6.2/3.73 * 1.2/1.4 * 31/40 = 1.10
6.2/3.73 * 1.0/1.4 * 31/40 = 0.92

I estimate 3350 rpm for your base case.

So 3500 rpm for each case is:
78 mph
60
71
85
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Old September 18th, 2008, 09:56 AM
madcowdungbeetle
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Assuming you're running in 5th gear with an R380 for a TDI with a 0.77 5th gear:

@ 3500 RPM assuming an ACTUAL tire height of ~38"

1.4/6.2 - 59mph
1.2/6.2 - 69mph
1.0/6.2 - 83mph

I made an Excel spreadsheet I can post up if you like for your own person tweaking.
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Old September 18th, 2008, 10:02 AM
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Guys, thanks a ton, I really appreciate it.

Follow-up Post:

Quote:
Originally Posted by madcowdungbeetle
I made an Excel spreadsheet I can post up if you like for your own person tweaking.
Yes please!
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