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I just upgraded my wheels and tires in my 2015 JKUS. I went from the OEM Bridgestone Dueler A/T 255/70R18 tires to Goodyear Wrangler Duratrac LT 285/70R17 tires. The diameter increased from 32.1' to 32.8' and the revolutions per mile decreased from 649 to 635. The weight of each tire increased from 42 lbs to 54 lbs (including the spare). The data came from Tire Rack's website.

My concern is whether or not I should use a Superchips Flashcal to calibrate my speedometer for the upgraded tires? Will this void my factory warranty? I haven't noticed any change in shifting (I have an auto trans) or gas mileage.

My questions are: Do I need to calibrate using a Flashcal for a change in tire diameter of .7'? If I do will this void my factory warranty? If I use the Flashcal is there anything else that needs to be calibrated using the device? Here is the one I purchased: Superchips 3570 - Superchips® Flashcal Programmer for 07-15 Jeep® Wrangler & Wrangler Unlimited JK - Quadratec

Any help and advice is greatly appreciated. This is my first Wrangler so I'm new to all of this. THANKS!
 

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I would, otherwise your speedometer (and odometer) is going to read slow.

Oddly, you need to set the flashcal about 1/2" smaller than your actual measured diameter (not what the tire specs out at) in order to get it bang on. Superchips has a small buffer since they don't want the speedo showing too slow, so to get it bang on you need to set it a bit small.

You'll have no warranty issues either way most likely, your dealer may try to blame larger tires on ball joints going or something like that, but very unlikely they would ever bring up the odometer being slightly out.
 

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I don't think it's worth it for less than an inch difference. People jump up to larger tires on all different types of vehicles and don't use a module. If you feel a big difference then go for it but I wouldn't worry about it.
 

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I don't think it's worth it for less than an inch difference. People jump up to larger tires on all different types of vehicles and don't use a module. If you feel a big difference then go for it but I wouldn't worry about it.
Thanks all for the input. Carlton you are correct, I do not need the Flashcal. I downloaded a speedo app on my iPhone and my speed is still 100% accurate. I tested the app in my wife's car last night to make sure it is accurate with her speedo. I'll be returning the Flashcal and will buy a new one when/if I get 35 inch tires in the future. Thanks again!

:iamhappy:
 

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It's not the Flashcal that makes the speedo read fast when set to the "correct" size... it's the factory speedo programming. It will always read fast with the correct size set, but the odo will be right on.

To get it to read right, I had to set mine at 30.75" with the same 32.1" tires you had before. So now my speedo is bang on but the odometer may be racking up miles a little more slowly than it should, who knows. I didn't test that.

So I'd say 33" tires with stock 32" tire programming should be pretty much perfect. :)
 

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No problem. You will see maybe a 1 mph difference at 60mph below that even less. You should be good to go!
 

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Either way I'd get a flashpaq. It does everything a flashcal will do but will make a huge in difference in performance, even on a stock jeep. Better throttle response and shift points, especially in the 93 octane tune. There is crawl mode for Wheelin as. Off all the things I've done to my jeep that's probably the best money spent IMHO

**update**Sorry my bad I just saw you had a 2015, the flashpaq isn't out yet for it.
 

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I just measured my tires from ground to top. I got 35x12.5x17 Yokohama that are actually only 34.6. I set mine to that and my speedo is dead on.
 

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Thanks all for the input. Carlton you are correct, I do not need the Flashcal. I downloaded a speedo app on my iPhone and my speed is still 100% accurate. I tested the app in my wife's car last night to make sure it is accurate with her speedo. I'll be returning the Flashcal and will buy a new one when/if I get 35 inch tires in the future. Thanks again!

:iamhappy:
That's because it read fast from the factory, not because the new tires didn't affect it.
 
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