DirtyComanche Posted February 5, 2008 Share Posted February 5, 2008 Given: 4800rpm .78 OD 4.56 gears 31" tire I do: (4800rpm)(60min/hour)(31inchs)(3.14) --------------------------------------- (.78OD)(4.56gears)(12inchs/foot)(5280feet/mile) Giving about 124mph. Out to lunch? Link to comment Share on other sites More sharing options...
Eagle Posted February 5, 2008 Share Posted February 5, 2008 About 120 MPH. Dunno how your formula got there, because it shouldn't have, but you're close. PM me your e-mail if you want my spreadsheet Link to comment Share on other sites More sharing options...
tkgibbs27 Posted February 5, 2008 Share Posted February 5, 2008 what are you trying figure out? Link to comment Share on other sites More sharing options...
DirtyComanche Posted February 5, 2008 Author Share Posted February 5, 2008 About 120 MPH. Dunno how your formula got there, because it shouldn't have, but you're close. PM me your e-mail if you want my spreadsheet 4mph would have been well within my margin of rounding, if you mean it works out to 120. I'd take your spreadsheet but lack excel. What formula do you use? Link to comment Share on other sites More sharing options...
DirtyComanche Posted February 5, 2008 Author Share Posted February 5, 2008 what are you trying figure out? Speed at given rpm in OD with 4.56s and 31s. Link to comment Share on other sites More sharing options...
mfpdm Posted February 5, 2008 Share Posted February 5, 2008 what are you trying figure out? Speed at given rpm in OD with 4.56s and 31s. Your in the ball park. The spreadsheet I used is broken down in 5 mph increments. It came up with at 125 mph you would be at 4823 rpm's. Here's a link CLICK HERE. They may work for you as they have them in different formats. :cheers: Link to comment Share on other sites More sharing options...
Eagle Posted February 5, 2008 Share Posted February 5, 2008 About 120 MPH. Dunno how your formula got there, because it shouldn't have, but you're close. PM me your e-mail if you want my spreadsheet 4mph would have been well within my margin of rounding, if you mean it works out to 120. I'd take your spreadsheet but lack excel. What formula do you use? If you don't have Excel, my spreadsheet ain't gonna help you. I originally developed it in Quattro Pro, but I long since migrated it over to Excel. Your formula isn't based on actual tire rolling radius. When I did up the spreadsheet I spent a lot of time with tire company brochures and web sites, finding the actual revolutions per mile for various tire sizes. Then I factored that in and created a speed-to-RPM chart for just about every tire size from 205/75-15 up through (IIRC) 33". Link to comment Share on other sites More sharing options...
DirtyComanche Posted February 5, 2008 Author Share Posted February 5, 2008 About 120 MPH. Dunno how your formula got there, because it shouldn't have, but you're close. PM me your e-mail if you want my spreadsheet 4mph would have been well within my margin of rounding, if you mean it works out to 120. I'd take your spreadsheet but lack excel. What formula do you use? If you don't have Excel, my spreadsheet ain't gonna help you. I originally developed it in Quattro Pro, but I long since migrated it over to Excel. Your formula isn't based on actual tire rolling radius. When I did up the spreadsheet I spent a lot of time with tire company brochures and web sites, finding the actual revolutions per mile for various tire sizes. Then I factored that in and created a speed-to-RPM chart for just about every tire size from 205/75-15 up through (IIRC) 33". Yeah, I knew I wasn't factoring in actual height or revs per mile. For my purposes it didn't matter. I was just wondering if there was a more fundamental flaw with my formula. Link to comment Share on other sites More sharing options...
Tracker Posted February 6, 2008 Share Posted February 6, 2008 Get one of those circular slide rulers from a hot rod shop and it's pretty easy. Hmmm. I may be dating myself. I was just asked, "What's a slide ruler?" :( Link to comment Share on other sites More sharing options...
DirtyComanche Posted February 7, 2008 Author Share Posted February 7, 2008 Yes, you are... I've never actually seen one in person. Link to comment Share on other sites More sharing options...
Tracker Posted February 7, 2008 Share Posted February 7, 2008 Yes, you are... I've never actually seen one in person. They're fairly low-tech but they work. When I was in high school calculators weren't allowed in chemistry or physics during tests, (yes, they were invented by then) but slide rules were. It beat grinding #'s the hard way. Anyway, several cam companies used to make these promotional circular slide rules for figuring exactly what you were trying to figure. They were for drag racers to know what tire size and / or gear ratio would achieve what speed at a particular RPM. My POS didn't have a speedometer so I used it to know how fast I would be going at different RPM's in different gears- A vain attempt to avoid speeding tickets. Sig Erson and Crane used to make them but they may have gone the way of my long hair. :hmm: Link to comment Share on other sites More sharing options...
jared Posted February 7, 2008 Share Posted February 7, 2008 i don't think 120 mph is wrong. its pretty close, but i doubt you will ever see that much mph :D Link to comment Share on other sites More sharing options...
Eagle Posted February 7, 2008 Share Posted February 7, 2008 Yes, you are... I've never actually seen one in person. They're fairly low-tech but they work. When I was in high school calculators weren't allowed in chemistry or physics during tests, (yes, they were invented by then) but slide rules were. It beat grinding #'s the hard way. I don't mind dating myself -- when I was in high school and even in college, calculators had NOT been invented, so slide rules were all we had. The major gasoline companies used to give out neat circular ones you could use to calculate your gas mileage when you filled up, and there were also scientific slide rules in the circular format. I still have a box full of my old slide rules, somewhere. I saved them for when we run out of electricity and have to go back to a simpler life style. (Not necessarily easier, just simpler.) The thing with sliderules is, you can't get an answer precise to 16 decimal places. You only get two or three significant digits, and beyond that the decimal places are just filled with zeroes. If you don't know how to figure out the number of decimal places your answer should have, you're toast. Link to comment Share on other sites More sharing options...
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