Need HELP with speedometer
I just put 31x10.50-15 on my 93 s-10 blazer. it had 235-75-15 on it.
how far is my speedo going to be out ??? please help 93 s10 blazer 4.3 4x4 96grand AM 3.1 |
RE: Need HELP with speedometer
A 235/75R15 tire equates to about a 28.9" diameter tire with a rev/mile of ~697.8 revs/mile.
235 is the width in mm. 235mm = 9.25". 75 is the sidewall height as a percentage of tread width. 75% of 9.25" = 6.94" sidewall height. Now double that and add it to the rim size to get the overall diameter. 15" + 6.94" + 6.94" = 28.875" or ~28.9" 5280 ft/mile * 12 in/ft / (28.9 in * 3.14159) = 697.8 revs/mile Now your 31x10.5-15 tire has a 31" diameter and 650.5 revs/mile. 5280 ft/mile * 12 in/ft / (31 in * 3.14159) = 650.5 revs/mile The speedo will be reading slow by ~7.25%. So at a speedo reading of 60mph, you will be travelling ~64.4mph. |
RE: Need HELP with speedometer
thanks swartlkk I didnot know those faxs thay helped lots. I will have pic soon
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RE: Need HELP with speedometer
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RE: Need HELP with speedometer
ORIGINAL: blazingsadle http://www.miata.net/garage/tirecalc.html Go to above link. No hard work needed. |
RE: Need HELP with speedometer
so what would be the speed differance between 235/70/15 and 245/35/20...and can i fit any bigger tire on that size rims with out rubbing....wouldnt mind a thicker sidewall
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RE: Need HELP with speedometer
235/70R15 ==> 722 rev/mile
245/35R20 ==> 754 rev/mile So at a speedo reading of 60mph, you will actually be travelling at 57.4mph. You will be going 4.3% slower than the speedo reading. I believe that others have ran 30" overall diameter tires without problems. 235/70R15 is a 28" overall diameter. So you should be able to go up to a 255/50R20 tire depending on if that would fit on your 20" rims. That would give you a 30" tall tire, but would result in a speedo reading that is 7.5% slow or at a 60mph speedo reading, you would be travelling at 64.5mph. If you wanted to stick closer to the 235/70R15 tire size (~28" tall), then you should go with a 255/40R20 which would be 719 rev/mile or 0.3% slow speedo or at 60mph speedo reading, you would be travelling 60.2mph. Again, this is dependant on the availability of the tires and if they would fit on your rims. |
RE: Need HELP with speedometer
so do u think 255/45/20 would fit and how much does it cost to recalibrate your speedo at a tire and rims place
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RE: Need HELP with speedometer
Not sure that tire/wheel places have the capability to recalibrate the speedo for different tire sizes.
I know that 255 width tires fit on my 17x7.5 rims on my Bonneville so I would think that if your 20's are atleast 7.5" wide, they should hold the tire just fine. Now the diameter, well... I am just going by the writeup that Hanr3 has created stating that 30" diameter tires fit with little to no rubbing. A safe bet would be to stick with 29" or smaller overall diameter. I'm going to be checking out the tire size recalibration here in a little bit. I have a friend that has the full blown Snap-On scanner/reprogrammer and I'm going to see if we can get in and change the tire size / gear ratio with it. If we can, that should open the door for more options to get it done. |
RE: Need HELP with speedometer
ok cuz thats what littledan911 has and he said they dont rub, he has 20s. I want the biggest sidewall without rubbing that i can get because i like the look of 20s but want the smoothest ride possible...im used to my michelins :D...so the 245/35/20 tire would be how many inches in diameter??....and stock is 28 in. diameter right
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RE: Need HELP with speedometer
Go look at the tire manufactures website. Every tire is different. Just becuase it says its a 31" tires doesn't mean it measures 31". Each tire is different. You have to check with the tire manufacture to get the tire specs.
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RE: Need HELP with speedometer
ok sorry about all this but one last question whats the differance between 245/45/20 and 255/45/20 and will the 245/45/20 fit
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RE: Need HELP with speedometer
Ok... Now to type this again (stupid firefox crash)...
I agree with Hanr3 on the tire size. These numbers are nominal numbers and they vary manufacturer to manufacturer. Anyway, a 245/45R20 will be a ~28.7" diameter tire with 703 rev/mile while the 255/45R20 tire having a 29" diameter with 695rev/mile. The 255 tire is also 10mm (~0.4') wider than the 245 tire. To break down the metric nomenclature for you: Lets examine the 245/45R20 tire... The first number, 245, is the tread width in millimeters. 245mm = ~9.645inches The second number is the percentage of sidewall height to treadwidth. So for a 45 series tire, the sidewall height would be 245 (treadwidth) * 45 / 100 = 110.25mm (~4.34inches). The third number is the rim diameter. To get the overall diameter of the tire, you have to add up all of the heights. So double the sidewall height and add in the rim diameter and you'll get the overall height. Again for the 245/45R20, the overall height would be 4.34+4.34+20 or ~28.7" Good luck and any more questions, just post away. |
RE: Need HELP with speedometer
ok ahha so i can find another question to ask u ho big is the sidewall on a 245/35/20 tire
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RE: Need HELP with speedometer
245*35/100 = 85.75mm (3.38in)
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RE: Need HELP with speedometer
thanks for the help...so in your eyes is there a very noticeable size in sidewall increase that a normal eye would see because i want to fill the wheelwell as best as i can without dropping it
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