RE: Rear-end gear ratios

[mikelj@xxxxxxx]

Wow, this is cool.  Let me do the math:  

My 26.3 inch 225R14 tire rolls 82.6 inches per revolution. or 6.882 feet.
50 MPH is 50 X 5280 which is 264000 feet per hour divided by 60 which is 4400 feet per minute. 
The tire rolls 6.882 feet per revolution and 50MP is 4400 feet per minute then 4400/6.882= 639.4 Axle RPM 

If the engine is turning 2000 RPM at 50 (GPS checked) then 2000/639.4= 3.13 gear ratio. Since the nearest possible gear ratio is 3.23 then we know this car has 3.23s.   Great, thanks Butch and Don.  This brings back memories of my college physics courses!

Mike in New Mexico



 



 

> To: 1962to1965mopars@xxxxxxxxxx
> From: waedison@xxxxxxxxxxx
> Subject: Re: Rear-end gear ratios
> Date: Wed, 25 Feb 2009 16:36:56 +0000
> 
> 
> 
> 
> 
> Thanks Don! This is a great topic for a lot of us. If you have a gps unit in your car, even a portable one like mine, it shows mph and seems to be really close. Eliminates having to have two vehicles involved and having to work the variances on two speedos. /Butch/ Ferndale, WA 
> 
> 
> 
> 
> ----- Original Message ----- 
> From: "Don Dulmage" <big-d@xxxxxxxxxxxx> 
> To: 1962to1965mopars@xxxxxxxxxx 
> Sent: Wednesday, February 25, 2009 5:42:54 AM GMT -08:00 US/Canada Pacific 
> Subject: Re: Rear-end gear ratios 
> 
> 
> Why not go for a drive. take the RPM and the MPh and just do the math. I 
> would have someone veryiythe speedo witha neewer car. I get My wife to check 
> ine with her PT cruiser. I tell her to drive at 50 MPH which she will do 
> exactly and then follow and check mine. I correct my speedo error mentaly 
> After that read the tach . Do the math for the rear tire rollout. Work that 
> back into the fifty MPH which will give you axle rpm per hour . divide that 
> by sixty for axel RPM per minute. Divide that into engine RPM and Bingo! 
> minus a tu iny bit of torqueconverter slip you will have the number. Since 
> gear ratios are only available in steps it is a simple matter then to figure 
> out which one you have. 
> I know it seems like a bigdeal since we mostlyhate math but in fact a matter 
> of minutes will do it. Certainly less time than to jack up the car. 
> Don 
> ie 28 inch tire rolls 87.92 inches per revolution. or 7.3266 feet 
> 50 MPH is 50 X 5280 which is 264000 feet per hour divided by 60 which is 
> 4400 feet per minute. 
> sincethetire rolls 7.3266 feet per revolution and 50MP is 4400 feet per 
> minute then 4400/7.3266= 600Axle RPM 
> if the engine is turning 2500 RPM at 50 then  2500/600= 4.1666666666666666 
> gear ratio. Since the nearestpossible gearratio is 4.30 then we know this 
> car has 4.30s. It could not be 4.10s because you cannont invent speedonly 
> ose a bit to driveline inefficiency. 
> Now i have only had one coffee today so my math may need correction but the 
> idea is right. It is based on the same way we figure Gear ratio and speed 
> for racing except just working from the other end. 
> ----- Original Message ----- 
> Don 
> From: "SB" <polecat2@xxxxxxxx> 
> To: <1962to1965mopars@xxxxxxxxxx> 
> Sent: Tuesday, February 24, 2009 11:24 PM 
> Subject: RE: Rear-end gear ratios 
> 
> 
> > 
> > I'm working on an all-original '64 Dodge Polara 500, 383 2 barrel car 
> > right now.  It has its original 3:23 sure grip. 
> > 
> > 
> > mikelj@xxxxxxx wrote: 
> >> 
> >> 
> >> 
> >> I am curious what the gear ratio is for the rear-end of my '64 Dodge 
> >> Polara 500.  I can't find anything about that on the window sticker, 
> >> build-sheet, tag, etc.  It seems like it is around 3:00, and I am sure 
> >> they didn't have many choices in the mundane 383 2 bbl. TorqueFlight 
> >> setup.  Anyone know? 
> > 
> > 
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> 
> ---- 
> Please address private mail -- mail of interest to only one person -- directly to that person.  I.e., send parts/car transactions and negotiations as well as other personal messages only to the intended recipient, not to the Clubhouse public address. This practice will protect your privacy, reduce the total volume of mail and fine tune the content signal to Mopar topic.  Thanks! 
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> '62 to '65 Mopar Clubhouse Discussion Guidelines: 
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> [Non-text portions of this message have been removed]
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> ----
> Please address private mail -- mail of interest to only one person -- directly to that person. I.e., send parts/car transactions and negotiations as well as other personal messages only to the intended recipient, not to the Clubhouse public address. This practice will protect your privacy, reduce the total volume of mail and fine tune the content signal to Mopar topic. Thanks!
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> '62 to '65 Mopar Clubhouse Discussion Guidelines:
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--
[Non-text portions of this message have been removed]


----
Please address private mail -- mail of interest to only one person -- directly to that person.  I.e., send parts/car transactions and negotiations as well as other personal messages only to the intended recipient, not to the Clubhouse public address. This practice will protect your privacy, reduce the total volume of mail and fine tune the content signal to Mopar topic.  Thanks!

'62 to '65 Mopar Clubhouse Discussion Guidelines:
http://www.1962to1965mopar.ornocar.org/mletiq.html.