315/70/17 without calibrating speedo?

[SG19JLUR]

I just bought a '21 Rubicon and put 315/70/17's (basically 35's) on it today. I ordered a Tazer but it's not here yet. In the meantime I wanted to check my speed against GPS to see how far off the speedo was and to make sure I knew how fast I was going. With the cruise set at 72 I pulled up Waze on my phone and it was also reading 72. Then I downloaded an app called Speedometer and it also confirmed my speed at 72. Am I missing something here? If the speedometer is spot on with the new tires that means it was reading too fast with the stock tires. Either that or both GPS apps on my phone are inaccurate.

Are most people having to recalibrate when changing to 35's?

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[aldo98229]

My Sahara came from the factory with the speedo off by about 1.5 MPH. It was spot-on after I mounted 275/70R18 tires, which are 1.1 inches taller than OE.

 

[MtCamper]

I put the 315 KO2s on my JLUR and when I go thru the roadside speed checkers my spedo shows 2 MPH slow. Not sure how accurate the radar is, but I haven't recalibrated. I think stock I was showing 1-2 MPH faster than reality.

 

[Spdu4ia]

i found that after i had mine calibrated for 35's not only was the speedo more accurate, but also the MPG, and shift points seemed smoother so the benefits where worth it to me

 

[Jeepsmashin]

I just put some 35s MT on my JLUR and noticed that at slower speeds its 2 mph off and around 65 mph its 3 mph off

 

[Jeepsmashin]

OP what brand/model tires are they?

 

[SG19JLUR]

OP what brand/model tires are they?

They’re BFG KO2’s in load range C. I’m pretty sure these are the Raptor tires that a lot of Jeep’s are running

 

[SG19JLUR]

i found that after i had mine calibrated for 35's not only was the speedo more accurate, but also the MPG, and shift points seemed smoother so the benefits where worth it to me

I’ve got a Tazer on the way and I was planning to recalibrate. But it seems to me if I change anything it will make my Speedo worse instead of better.

 

[SG19JLUR]

Ok I figured out what was causing my confusion...when my iPhone is plugged in to CarPlay the speed reading in Waze and in the 3rd party app called Speedometer both sync with the actual speedometer in the Jeep. But when I unplug the phone (but still paired to bluetooth) the speed in both apps changes to read higher than the Jeep speedometer. Cruise set at 60mph...with the phone unplugged it reads 64-65mph, but when I plug in the phone it syncs to the built-in speedometer and starts reading 60mph. I have no idea why this happens, but I was able to repeat the test several times with the cruise set and it happens every time.

Can anyone else confirm if this happens for them?

 

[Uhdinator]

don't plug your phone in when checking speedometer vs GPS apps.

 

[SG19JLUR]

don't plug your phone in when checking speedometer vs GPS apps.

Oh great idea, why didn't I think of that ?

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