RPMs @ 55 MPH
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RPMs @ 55 MPH
at 55 mile per hour what should the rpms be for a 88 f 150 2wd with the 300 inline six 3.55 gears and 235 75 r 15 tires. mine is at almost 2100 at 55 mph and someone told me that this is way to high.
just wondering.
just wondering.
Cargo Master
Joined: Oct 2004
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From: Seneca, SC
ok, I'm assuming you have an overdrive tranny, so yes that's fine. Here's the math I did if you (or somebody else) wants to check it.
235mm wide tire, 75% of that is 176.25 mm, is 6.93898'' total sidewall, is 21.939'' total tire height
21.939*pie gives us circumference (roughly as tread is a factor here) which is 68.9233'', so every revolution of the tire traverses 69'', or 5.74361'.
So you're going 55MPH, or 290400ft/hr, so divide that by the ft/rev, and you get 505060.5rev/hr. Divide this by 60 and you get 842.676 rev/min. Now your final drive gear. 842.676*3.55 is 2991.5 RPM.
This assumes a final drive out of the tranny of 1:1, but still seems a bit high to me. Anyways, you've got overdrive if I'm right, and you're fine.
235mm wide tire, 75% of that is 176.25 mm, is 6.93898'' total sidewall, is 21.939'' total tire height
21.939*pie gives us circumference (roughly as tread is a factor here) which is 68.9233'', so every revolution of the tire traverses 69'', or 5.74361'.
So you're going 55MPH, or 290400ft/hr, so divide that by the ft/rev, and you get 505060.5rev/hr. Divide this by 60 and you get 842.676 rev/min. Now your final drive gear. 842.676*3.55 is 2991.5 RPM.
This assumes a final drive out of the tranny of 1:1, but still seems a bit high to me. Anyways, you've got overdrive if I'm right, and you're fine.
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Cargo Master
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From: Seneca, SC
oh, and your overdrive would have about a .7 to one drive ratio, which also seems right as far as trannies go.
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I've got the same tranny, gearing and tires on my Bronco, and now that I think about it I believe I'm turning about 2800 or so at 75 mph. If that's right (my memory for things like this isn't as good as it used to be, or maybe I just don't pay that much attention anymore) then you're in the right range. The overdrive on the M5OD is .8, at least on mine.
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From: Western PA
Originally Posted by amish77
235mm wide tire, 75% of that is 176.25 mm, is 6.93898'' total sidewall, is 21.939'' total tire height
1:1 transmission ratio output puts engine RPM's at 2278.
5th gear (using 0.8 to 1) is 1822 RPM's.
Last edited by Mauler; Feb 24, 2006 at 07:35 AM.
Cargo Master
Joined: Oct 2004
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From: Seneca, SC
ah, and therein lies mine being high. Thanks mauler. I thought I might be a little off. It just seemed high.
But then again 7'' of sidewall seemed a bit much for me so that's why I thought it was total sidewall. thanks again.
But then again 7'' of sidewall seemed a bit much for me so that's why I thought it was total sidewall. thanks again.
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