Gear ratio vs axle ratio

BillTheCat · Jan 13, 2015

Received and installed my new Superchips Traildash. As denoted in my signature, I have a stock JKUR with a 3.5' lift and 315/70/R17 Duratracs. I reprogrammed the axle ration from 3.73 to 4.10 and the check engine light came on with an error. Apparently, I'm unclear as to the definitions of gear and axle ratios.

Canvas JK · Jan 13, 2015

Do you have an automatic? If so you have 3.73 gears not 4.10's unless you just had it regeared. This is probably why your check engine light is on.

Axles do not have ratio's only gears do.

R/
Will

wayoflife · Jan 13, 2015

BillTheCat said:
Received and installed my new Superchips Traildash. As denoted in my signature, I have a stock JKUR with a 3.5' lift and 315/70/R17 Duratracs. I reprogrammed the axle ration from 3.73 to 4.10 and the check engine light came on with an error. Apparently, I'm unclear as to the definitions of gear and axle ratios.

Why did you change your axle ratio? Your check engine light came on and you're most likely in limp mode now because of it. The only thing you want to do is input the correct tire size as measured from the center of your wheel to the ground x2.

jfallon1 · Jan 13, 2015

BillTheCat said:
Received and installed my new Superchips Traildash. As denoted in my signature, I have a stock JKUR with a 3.5' lift and 315/70/R17 Duratracs. I reprogrammed the axle ration from 3.73 to 4.10 and the check engine light came on with an error. Apparently, I'm unclear as to the definitions of gear and axle ratios.

You only change the axle ratio on the programmer if you've changed them in your axles.

BillTheCat · Jan 13, 2015

Canvas JK said:
Do you have an automatic? If so you have 3.73 gears not 4.10's unless you just had it regeared. This is probably why your check engine light is on.

Axles do not have ratio's only gears do.

R/
Will

Yes, an automatic.

BillTheCat · Jan 13, 2015

wayoflife said:
Why did you change your axle ratio? Your check engine light came on and you're most likely in limp mode now because of it. The only thing you want to do is input the correct tire size as measured from the center of your wheel to the ground x2.

I reset it back to 3.73 as soon as it came on. Engine light is gone. Tire height I set to 34.5 since they are 315/70/R17's.

OverlanderJK · Jan 13, 2015

BillTheCat said:
Yes, an automatic.

Doesn't matter. Read above.

OverlanderJK · Jan 13, 2015

BillTheCat said:
I reset it back to 3.73 as soon as it came on. Engine light is gone. Tire height I set to 34.5 since they are 315/70/R17's.

Did you measure your tires or just guess?

BillTheCat · Jan 13, 2015

OverlanderJK said:
Did you measure your tires or just guess?

I use a tire conversion program that indicated 315 metric was 34.5. I will measure to verify.

seanb123 · Jan 13, 2015

You need to actually measure with a tape measure

NV375 · Jan 13, 2015

wayoflife said:
........input the correct tire size as measured from the center of your wheel to the ground x2.

This should get you dead on. Worked for me the first time. :thumb:

bsimon187 · Jan 13, 2015

My old duratracs were the same size as yours and measured out to 33.5. That is what I used in my pro cal for calibration.

AncientTrail · Jan 14, 2015

I measured from the middle of the axle to the top of the tire x 2. The weight of the jeep will cause a bulge in the tire. Think about it

Good Luck with it!

OverlanderJK · Jan 14, 2015

AncientTrail said:
I measured from the middle of the axle to the top of the tire x 2. The weight of the jeep will cause a bulge in the tire. Think about it

Good Luck with it!

That isn't the correct way to do it.

jnabird333 · Jan 14, 2015

OverlanderJK said:
That isn't the correct way to do it.

Agreed. The reason you measure from the center down is to get an actual radius for a circumference calculation. Center to top would be unloaded and cause the measured speed to be high.

Edit - Sorry I left out the X2 to get the diameter for a usable number.... but it's covered later anyway

frenchjk · Jan 14, 2015

AncientTrail said:
I measured from the middle of the axle to the top of the tire x 2. The weight of the jeep will cause a bulge in the tire. Think about it

Good Luck with it!

wrong as said above measure with a good tape measure and a level on top of the wheel to get an accurate reading.....and check the tire pressures before (get your mean pressure!!!)

H8ROADS · Jan 14, 2015

jfallon1 said:
You only change the axle ratio on the programmer if you've changed them in your axles.

I'm still not seeing a response to this - sounds to me like you're just trying to change the ratio without changing the actual axle.

wayoflife · Jan 14, 2015

frenchjk said:
wrong as said above measure with a good tape measure and a level on top of the wheel to get an accurate reading.....and check the tire pressures before (get your mean pressure!!!)

Sorry but, putting a level on top of your tire and using that point to measure will give you a WRONG measurement. You NEED to measure from the center of the wheel to the ground and x2. This is the only thing your speed sensor will care about and you only x2 because your computer can only take a diameter size.

jnabird333 · Jan 14, 2015

I edited my reply because I was idiot and left out the X2 to get a diameter part... My bad. :doh:

AncientTrail · Jan 14, 2015

OverlanderJK said:
That isn't the correct way to do it.

My thinking is this, if you took your tire off with no load and measured it, you would get the same reading regardless if you measured from top or bottom. No change in diameter from load. Round is round. Once you put a load on the tire (bulge) you will get a different reading from the bottom as you would the top ( no bulge ) think of a ball that is round then you add pressure and it's no longer round, correct?

What am I missing?

Willing to learn....

:beer:

Gear ratio vs axle ratio

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