# Taller tires - computer recalibration

This is on an 88 correct? If so there is no reprogramming needed. The speedo reading from the 215 to the 235 will be off by 3 mph low. So if it says 65 your running 68,
not a big deal.

was right

That is the

determines how

line,
side.
total
rim
rimdiameter), so yes

but
215/75.
inches per

it
P215's
get
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It isn't 'my' tires in question here, someone else's, I didn't start this thread.
And as it turns out, I am now running 'exact' to my GPS with the oversized tires on it.
The factory speedo gear was giving me a 'safe' speedo reading, which was low compared to 'reality'.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
"Steve W." wrote:

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the radius has EVERYTHING to do with it 'being taller'
the RADIUS is half of the DIAMETER

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ROTFLMAO!!!!
Man, so why would I want to divide the diameter in half to figure out the circumference?
I don't want the area of the sucker, I want the circumference to figure the % difference from the smaller tire to the larger.
The speedo will be off by that percent....
Mike
Gary Glaenzer wrote:

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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

it
P215's
get
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On Wed, 26 Nov 2003 20:39:26 -0500, Mike Romain wrote:

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.
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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.
So I have a 'diameter' given to me from the tire maker, no radius mentioned there....
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's
David Kelly wrote:

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Well, Mike, you are right about the thread getting silly. I also don't care about radius or diameter or circumference or any mathematical shit. So here's the only way for you to get it. Stand the tires against the wall. One tire is 2 inches taller than the other one. The taller tire will raise the truck by ONE INCH!!! The other inch is at the top of the tire. Holy shit, this is getting to be some boring reading! However much taller the one tire is, divide by 2. It bolts on in the middle!!!! .

the
figure
is
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care
raise
Which equals the radius, which in his example, equates to just over one half inch (.6). phew. Perhaps he understands a non mathematical explanation.
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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

the
figure
is
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'to the Ground'.........damn arthritis

out
the
diameter
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the
Boy I am glad someone else here understands 7th grade math. I was begining to wonder! <wink>
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right
the
how
line,
side.
yes
215/75.
per
You're the one that admitted you dont get. rofl.
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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.
--
Still a Raiders fan, but no longer sure why.

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nice one. How accurate a circle is a tire with weight on it tho?
rhys
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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.
--
Still a Raiders fan, but no longer sure why.

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Funny, I have been 100% accurate. Why some people are so threatened by intelligence is beyond me.
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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.
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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.
--

Remove the words 'NO' and 'SPAM' to reply

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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..

relay
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