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Old 10-15-2010, 03:37 PM
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Hello from ND & Tire size / speedo reading?

Good Day fellow Car Nuts. I collect Old Cars in ND, so I know it's probably a little "off" from what you guys do. I collect things that no one else wants, like Hudson, Packard, Nash, Studebaker, Jeep, Kaiser, Mercury Turnpike Cruisers, Dodge Chargers & the like.
I currently have a 57 Merc TPC that the speedo is off by 10% - when it reads 70, the car is doing about 63.
I have P215 tires on it; which are about 26" tall. I can put the "More Correct" size tire on it; P225 which is supposed to be about 27.6" tall.
So, I need someone smarter than me in mathematics; to tell me how many more inches down the road it will go per revolution; or how I can figure how much closer the speedo would be. The height would be 6% more; would that equate to 10% larger tire & hence 10% more ground distance per axle revolution???????
Thanks, Dan Caswell, Minot, ND 701-839-5820

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Old 10-15-2010, 04:20 PM
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Old 10-15-2010, 04:41 PM
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I was just thinking what rear gears do you have now and what ride are you talking about anyway. what trans do you have also and how is it setup also.
And have you considered changing the speedometer gear in the trans to make it all come together ? Just a thought. Oh and do you really want you info like phone# and things out for everyone to see?


Cole
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Old 10-16-2010, 08:27 AM
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Quote:
Originally Posted by forklift2
Good Day fellow Car Nuts. I collect Old Cars in ND, so I know it's probably a little "off" from what you guys do. I collect things that no one else wants, like Hudson, Packard, Nash, Studebaker, Jeep, Kaiser, Mercury Turnpike Cruisers, Dodge Chargers & the like.
I currently have a 57 Merc TPC that the speedo is off by 10% - when it reads 70, the car is doing about 63.
I have P215 tires on it; which are about 26" tall. I can put the "More Correct" size tire on it; P225 which is supposed to be about 27.6" tall.
So, I need someone smarter than me in mathematics; to tell me how many more inches down the road it will go per revolution; or how I can figure how much closer the speedo would be. The height would be 6% more; would that equate to 10% larger tire & hence 10% more ground distance per axle revolution???????
Thanks, Dan Caswell, Minot, ND 701-839-5820
Using a CALCULATOR (click on "Tech Articles" then click on "Useful Math Calculators" on the Left side)- there are many other calculators like this on the web, if you are going 63 MPH w/26" tires, you need 29" tires to go 70 mph, all else being equal- but the speedo will still be in error.

What you need to do is change the speedo gears. If you know how many teeth are on one of the two speedo gears, the rear tire diameter and the final drive ratio, you can use THIS to determine how many teeth the other gear should have.

THIS site has some FoMoCo speedo gears, I'm sure there are other, possibly better places also.

Good luck.

Oh, another thing- Measuring the tire height will not be as accurate for getting the diameter. You should do a circumference check on the diameter of the tires, mark both the tire and pavement, roll out at least two full revolutions, measure this distance and divide to get the circumference, then divide that by 3.1416 (Pi) to get the diameter.

Changing the tire diameter will raise the ride height by 1/2 of the diameter.
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Old 10-16-2010, 01:42 PM
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Quote:
Originally Posted by forklift2
Good Day fellow Car Nuts. I collect Old Cars in ND, so I know it's probably a little "off" from what you guys do. I collect things that no one else wants, like Hudson, Packard, Nash, Studebaker, Jeep, Kaiser, Mercury Turnpike Cruisers, Dodge Chargers & the like.


Not really, a LOT of us here have different tastes and like different vehicles.

I drove 1835 miles one way to get a 1949 Mercury M-47 pickup.



I drove from the Carolinas to Baldur, Manitoba Canada to buy the above truck. Then we went WEST on over the western parts of the US States sight seeing ... 4,800 plus miles in all ... to get a pooey, rusty, ratty old truck. My wife says it is the UGLIEST thing to ever sit on our driveway.

BUT ... I like it
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Old 10-16-2010, 03:59 PM
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I though MS Deuce had better visionary talent than that. I see a lot of potential for a neat tow truck for a Deuce!!!

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Old 10-16-2010, 07:36 PM
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Originally Posted by trees
I though MS Deuce had better visionary talent than that.

Trees
She has that dreaded disease ... DEUCE FEVER ... and just about only likes 32 Fords and of course ... her Cadillac DTS.
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