how do you figure your gear ratio if you change the tire size ??? such as I am running 3;73 gears but a very large tire of 255/70/15 I am considering running 255/60/15 tires and want to get an idea of how this will affect my RPM anyone have a guide to figure this out ??? (am I making any sense?)
Good calculators here: http://www.tciauto.com/Products/TechInfo/Calculators.asp You'll need to know the diameters of the tires in question. Good luck! Devon
Pretty simple. 336/tire diameter X rear gear ratio X speed(MPH) =RPM P255/70-15's are 29.05" tall 336/29.05 X 3.73 X 60 = 2588 RPM P255/60-15's are 27.04" tall 336/27.04 X 3.73 X 60 = 2781 RPM so roughly 200 RPM by going to the 2" shorter tires. This is of course with no converter slip figured in.
tire size and gear Simple math guys: ie. 255X70X15 255 = width in millimeters. 70 = the percentage of height to width (70%). 15 = inches of rim. 255 divided by 25.4 (millimeters per inch) = 10.039 (height of 1/2 the tire) 10.039X2 = 20.078 (both halves of the tire upper and lower) 20.078X70% = 14.055 (inches of tire height) 14.055 + 15 (inch rim) = 29.055 tire height. Now plug that into any tire and gear calculator to figure RPM. Mikey
Mikey, You can just stay with millimeters too. A 15" rim is 381mm (15 X 25.4) Even though you got the correct answer, I lost you above. 255 is the section width in mm. 70 represents the aspect ratio, the percentage of height to width (70%), or the height of one sidewall. So, 255 X .70 = 178.5mm. The diameter of the tire = 1 sidewall +rim + 1 sidewall. 178.5 + 381 +178.5 = 738 mm. 25.4 mm = 1 inch, 738/25.4 =29.055"
I don't know why you guys are exercising all this eye glazing over math other then to show everyone how smart you think you are. :grin: :grin: All he needs to do is enter the tire size into the calculator I posted and it will give him the dimensions. Then enter them into the rpm calculator, choose the transmission, pick an rpm and the thing will give you the speeds. :Smarty: Simple!!! :Comp:
Poor guy.. All he wanted to know was how the tire change would affect his RPM's and he gets a lesson in Qualitative Spatial Reasoning. ou: :laugh: :laugh:
Dave, I told him in post #7, 200 RPM or so depending on converter slip. I think we lost him awhile back, or he hasn't bothered to check on his thread. Guess it really isn't important to him to know, or he used your calculator and forgot to thank you. :spank:
...try hangin' with the Pontiac guys. In addition to the above you get the history of the development of Arabic numerals.... :Smarty: ...as well as multiple tire rubber compounding techniques and their affect on rolling radius... :boring:
Tire size What's a calculator? Just kidding, just kidding!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! I should have explained why I did it that way I guess. I have and know how to use all the calculators but some people like me want to know how and why something does what it does. I was just trying to show how the calculator arrived at its findings. Besides a little exercise never hurt anyone. And yes you could do it all in millimeters but you still have to convert to inches somewhere we are still the good ole USA for a little while longer. And no I was not trying to show how really smart I am. If I was really smart I'd be rich and too busy driving my supercharged, intercooled, EFI, alky burning, 455ci, overdriven, 58 Buick Special Convertible (capable of running 8's) instead of here talking to you guys. You know when I took my engineering courses in surveying in college we were not allowed to use calculators, we had to use slide rules or do it long hand. I graduated in 1973. Mikey
Larry....yes I should have said thank you but I was to busy playing with all these great sites people posted I tried all kinds of ideas and the sites listed are GREAT thank you to all of you for your input I found out what my rear wheel horsepower was on one site kind of interesting just plug in the numbers and you get your power mine was 434 1/4 mile horsepower I also see one site says Big Blocks should not rev over 2600 at 60mph (for a street car) again interesting stuff and I could play on the sites for hours I think I need to change my rear gear ratio and tires to use it more for the street but that is later on for now I will just blow the tires off her :laugh: :laugh:
horsepower??? OK one of the sites says that the 1/4 mile horsepower is 434 is this rear wheel horsepower or engine horsepower??? my guess is rear wheel horsepower as the car ran a 12.02 in the 1/4 so that being the case how do I figure the engine horsepower???????? :TU:
calulator sire Here is a site that has just about every calculator you could want. It also has games too. There are three pages of calculators http://www.ajdesigner.com/phphorsepower/horsepower_equation_rotating_horsepower.php Mikey
