New Rear Gears

[Rocketir]

I was getting ready to have the stock rear gears changed from 3.31 to 4.10. Currently I do not have a tune on the car. From what I gather, there is no way to fix my speedo to account for the change until I get a tune. Are there any consequences to having the rear end gears changed and then getting a tune later? Or do they need to be done at the same time.
Jesse

 

[Willie]

Speedos are nowadays controlled through the tune unlike old school with (plastic) gears and cables. Obviously you do not tune yourself, and I do so I took the liberty to screenshoot this from my stock tune:

This is where you change the ratio. Super simple, takes longer to open and save the file than to make the change.

If you physically change the gears without changing this value in the tune, your speedo will not be accurate. Example: Tune stays at 3.31, gears changed to 4.10.

3.31 / 4.10 = 0.8073

Let's say you're driving down the road and your speedo reads 45 mph. Your actual speed is:

45 * 0.8073 = 36 mph

The consequences of this are not that significant other than the incorrect speedo reading, but worth mentioning. You're actually going only 81 percent of what your PCM thinks (in this example). All the output PCM parameters, i.e. air fuel ratio, timing, fan control.... anything that's related to the speed of the vehicle, will be slightly in error because it does not know the speed you are really traveling. Is this error significant? Not really. All you will know is when you're on the highway going 70 mph (on your speedo), everyone will be passing you because you're actually going only 56 mph.

Ironic because I just posted a related question very recently. I want to take my 3.73's out and go with 3.31's....

 

[biminiLX]

Do them together.
I only had 4.10s, Lund pump 93 tune and 315/35/20 Nitto DRs (on 20” Alcoa’s) and ran 11.07@129 back in the day.
Great plan good luck.
-J

 

[Rocketir]

Do them together.
I only had 4.10s, Lund pump 93 tune and 315/35/20 Nitto DRs (on 20” Alcoa’s) and ran 11.07@129 back in the day.
Great plan good luck.
-J

Thanks, Your posts were the inspiration for the 4.10's. Was considering 3.73's but the plan is to go with 315/35/20's as well. I plan on a tune, just not the same day. I'm in California so no 93 for me! Was going to go with an AED tune on 91.

 

[me32]

Thanks, Your posts were the inspiration for the 4.10's. Was considering 3.73's but the plan is to go with 315/35/20's as well. I plan on a tune, just not the same day. I'm in California so no 93 for me! Was going to go with an AED tune on 91.

Definitely contact

@Shaun@AED​

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