did you or did you not say that 'the radius has no bearing on this?'
and you don't need to know the circumference..............where S = smaller tire and L = larger:
circumference L / circumference S = diameter L / diameter S = radius L / radius S
they are in EXACTLY the same ratios since circumference = 3.1416 diameter =
6.2832 radius
Because the tire is 2 * PI radians around. And the circumference is
2 * PI * R.
Punch some buttons on your calculator. For percent changed the radius works exactly as well as the diameter which works exactly as well as the circumference when comparing speedometer/odometer errors.
A high school student in algebra class should be able to explain why. Because we are lacking HS algebra graduates I'll explain.
The only difference between circumference and diameter is that diameter is multiplied by PI to get circumference. When comparing two tires the constant PI can be factored out from both sides of the equation.
Same applies for radius and 2 * PI.
Ouch, ok.... I give up. LOL!
I like simple stuff......
You know, the 'KISS' principal.
If I put a BFG P235/75 against a wall and a BFG P215/75 against a wall I have a 1.2" height difference.
In my mind that makes one tire taller than the other. 'Lots taller'.
The chart at BFG tells me this.
WHY THE HECK SHOULD I DO ANY FANCY MATH CONVERSIONS WHEN THE FORMULA IS SO SIMPLE! (or even need to know more than basic, which I happen to anyway)
Excuse me for shouting, but this thread is getting totally silly....
PI times the diameter works for me......
Radius does not come into the equation when figuring out a speedometer like the original poster asked about!!!!
The tire makers don't give you radius on the tire charts, they give diameter!
Crap guys....
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT'sDavid Kelly wrote:
Mike, determining tire height with radius suits better for those who want more academic conversation and more "convincing" formula. They have the joy of multiplying the radius by two to get what we know without multiplying, "how tall the tire is", diameter.
You're the one that admitted you dont get. rofl.
Boy I am glad someone else here understands 7th grade math. I was begining to wonder!
Which equals the radius, which in his example, equates to just over one half inch (.6). phew. Perhaps he understands a non mathematical explanation.
actually, you should use the 'loaded radius', from the center of the axle to the fround, with the truck's weight resting on the tire(s)
then compare and divide to get differences
'to the Ground'.........damn arthritis
Approximately 11/26/03 16:16, Mike Romain uttered for posterity:
Eggshually if Jason could *accurately* talk in circles, you wouldn't be so frustrated with his ignorance.
"Lon Stowell" wrote
nice one. How accurate a circle is a tire with weight on it tho?
rhys
Approximately 11/27/03 14:11, rnf2 uttered for posterity:
Depends on how fast it is turning and the load. However given two tires from the same manufacturer and model differing only in size, isn't too much of a stretch to presume that these would be more or less equal, allowing the larger diameter to be a reasonable WAG for speedometer effect. With the disclaimer that at higher speeds the circumference grows depending on construction etc. etc. and that even the tire measurements given by a manufacturer have a disclaimer that they are averages and apply only in reference to the rim width noted, etc. etc. etc. Or more simply, either a change in radius or diameter may be used to calculate the percent of speedometer nominal effect given that the other factors all cancel out. Except for amount of air. And atmospheric pressure. And pizzas consumed by the driver and passengers. And fuel load. And speed. And temperature. And fudge factors. etc.
Funny, I have been 100% accurate. Why some people are so threatened by intelligence is beyond me.
Approximately 11/27/03 18:07, Jason Cothran uttered for posterity:
Tsk, sad how a minimal level of intellect is required to even be able to be aware that you have none. Sad.
Still waiting for anything I have been wrong on instead of childish, unfounded name calling. Of course that's what those with inferiority complexes about ignorance do, I have found in my travels. Feel free to relay any example to email, as I will not be returning to this board, since knowledge seems to make some people upset (read as jealous?) here.
Lon
Don't feel bad about upsetting Jason.. this is a quote of his from alt.trucks.chevy..
"I must travel on to more intelligent places, as some fools here are intimidated by knowledge, and I so despise people getting bent out of shape when they read actualities. I prefer everyone to just get along. Best of luck, all with of your trucks, and keeps those tires turning!"
This was as a result of a discussion in the aforementioned newsgroup.. that discussion was about tires too.. worst part is that he may end up in one of the two Jeep newsgroups..
-- History is only the past if we choose to do nothing about it..
75% percent of 235 is more than 75% of 215.
I work at a tire shop and can say that for Example, you have a 235/75R15, and a 215/75R15, that the 235 will be TALLER!!! It would in fact be quite a bit taller, by a couple Inches. Your moving up
2 sizes, since you skipped a 225/75R15. If you had a 215/75/R15 before and wanted to keep the SAME Height but get a little wider, then a 225/70R15 would be the tire to get. Or Wider yet with a 235/65 or 60 R15 Depending on the Brand of tire since they do very from different Manufactures.I have P275/45R20 on my own truck. The Height is quite close to the Stock Chevy P245/75R16" wheels that were on in. Much Wider tire but not a whole lot of sidewall. Ignoring the Wheel Diameter or either 16" or 20", you can see that the first number is going up and the Second Number is going down. So while the height is the same, the tire is wider by quite a bit. If I needed to replace the stock 245 tires, but want to keep the height but a little wider, again I'd go with a P255/70R16. The height the same, the Width a bit wider.
If someone says there want to go up from a 215 to a 235 and don't give the second # then I and anyone else will assume that the second number is the SAME. In which case the tire WILL BE A LOT TALLER! A couple inches is a lot. Your jumping up 2 tire sizes.
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