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Discussion Starter #1
I just upgraded my stock 16" wheels and 29" tires
with aev pintlers 17" and 265/70r17 Duratracs (31.7")

how far off will my speedometer read?

Thanks!
 

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That's pretty close to what I got too, but my math teachers always taught me to show my work... Plus, we want him to be able to calculate this for himself in the future, right?

29/31.7=0.9148
that means that 29" is 91.48% of 31.7"
100-91.48= 8.52%

However, I got your 9.3% figure when I divide 31.7/29=1.0931
that means 31.7 is 109.31% of 29
That's where the 9.3% came from

And, just like in math class, I've confused myself further.
 

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Speedo is calculated off stock size, so 29"

difference in size from 29" to 31.7" is 2.7"

2.7 / 29 = .093

=9.3%

Yeah, he was right. Disregard my rambling above, I often confuse myself when I try to overthink math.
 

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You can fix the speedo with an AEV Procal module.. Way better than trying to do that math when flying down the highway.
x2 that's definitely the best way to do it.


The Superchips FlashCal and FlashPaq also do it. I have a FlashPaq and it corrected the speedo, let me keep fogs on with brights, increased throttle sensitivity, and tuned the engine for 91 octane for a little hp/tq boost. It's even more useful if you have an auto transmission, because it can set shift points and let you get way more of the power band for larger tires so you can go bigger before a regear is needed for street driving.
 

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Discussion Starter #7
Thanks for the info and explaining the math
At least now I have an idea how fast i am going
Don't want to get pulled over
I'll look into the pro cal and flash cal too
 

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Big fan of the Procal. Took me longer to measure my tires than it did to set the switches and actually update the computer.
 

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That's pretty close to what I got too, but my math teachers always taught me to show my work... Plus, we want him to be able to calculate this for himself in the future, right?

29/31.7=0.9148
that means that 29" is 91.48% of 31.7"
100-91.48= 8.52%

However, I got your 9.3% figure when I divide 31.7/29=1.0931
that means 31.7 is 109.31% of 29
That's where the 9.3% came from

And, just like in math class, I've confused myself further.
Since he didn't ask how to figure it out and just asked for the answer, I assumed he wasn't interested in the process and just wanted the work done for him. I gave exactly what he asked for.
 

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Since he didn't ask how to figure it out and just asked for the answer, I assumed he wasn't interested in the process and just wanted the work done for him. I gave exactly what he asked for.
Haha, sorry man, I wasn't knocking you- I was just contributing! If you hadn't given your answer, I might have messed up the math! Some people like having the explanation, some just want a quick answer- being able to get both types is one of the reasons this forum is so great!
I totally wasn't meaning to come off as confrontational, so no worries!
 

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You could also sweet talk your dealer into setting your tire size. 31.7 is close enough to stock Rubicon size they will be able to do it.

Even if they charge you, it would be cheaper than an aftermarket programer, especially if you dont think you will ever use any of the added features of the programers.
 

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Discussion Starter #14
Hey TurkTTR I do appreciate the explenation
Now know how to calculate it. Thanks!

I took you guys advice and picked up a Procal today from Quadratec
so easy to use, definitely worth it

Here's my JKU in front of Quadratec today with the new wheels/tires

 
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