Does your speedometer get fixed when you change gear ratio on your truck?

Oh shiznet i didn't know that. So spending $200 on the device is pretty much inevitable then if I want to fix the speedometer?

 

Fun fact, a 30/950R15 tire would be:

1.18" wide, ~15.5" tall.

You running bike tires on that truck?

 

Thanks! But it doesn't say which new gear ratio I would need to bring it back to factory power with the new tires? Wait it says factory ratios are 3.73, 3.91, 4.11 . Are those the ratios I would need with the new tires? Do they even sell those gear ratios?

 

I think I'm going to stick with my $70 Ultra Gauge. I can calibrate it to my heart's content and just look at the speed reading on it instead of my dashboard. Then I'm not messing with the Speedo or ECU on the truck at all.

 

They 30x950R15 not 30/950R15 idk if the x and / are important

 

So it's like the "real" speedometer rather than the actual speedometer? haha gotcha!

 

30" tall by 950" wide on a 15" wheel?

 

30 inches diameter
9 1/2 inches width
15 inches of wheel length and 6 inches of rim width

 

See post #13

 

Your regear did not change how much your speedo was off. Your speedo is measuring at your abs sensors (doesn't care what gearing you have). Unless you have a 6 speed, then a regear will throw the speedo off along with larger tires.

 

It's not 'one time'. It's installed in the truck. You calibrate it to your need. You can recalibrate it if you change something again. It corrects both the speedo and Odo.

Currently both are wrong. You don't even know how many miles you are driving, have nothing to base simple things like maintenance intervals and MPG calculations on.

When I spoke of tires/gears before, I was trying to point out your goal was to be 'feeling' close to stock and retain MPG.

To accomplish that via bigger tires + regearing, you have to do the math so it compares closely to the OE setup. The easy gear choices you have available, as @crashnburn80 pointed out, 'skip' the ratio you need. That's because of the tire you have selected. Pick a tire compatible with an available gear ratio, and you'll meet your goal.

Once you have that settled, THEN you correct the speedo/odo.

These things are all part of the cost of admission for upgrading the looks of your vehicle. It's always good to think through all the impacts any change will make so there are no surprises, it drives like you want it and everything works as it should.

 

Neither does the manual 6sp - either at driveshaft or wheel it is basically the same thing, converting what is actually wheel revolutions, with the manual having to account for effect of the ring/pinion.

 

Wrong, If you regear with a 6-speed your driveshaft is spinning more revolutions per tire revolution than before.

 

Correct, my bad. But excluding ring/pinion change, it doesn't matter where the speedo/odometer picks up its signal. In the old days, there was a gear on either the transfer case or transmission with speedo/odometer connected by a cable to the dashboard. If a given model used more than 1 ring/pinion say on a v6 versus a v8, a different gear was specified. On our trucks, a tire diameter change (no gearing change) affects the manual and automatic the same way.

 

Yup, I was just trying to let the OP know that regearing would not bring his speedo back to normal. He has an auto. So basically, the only way to totally fix your speedo is to use a speedo recalibrator.

 

No, I have a manual transmission but thanks for the detailed info!

 

Yea I actually have done the math with the correct numbers already.

My truck has a 3.15 gear ratio and was running stock 26.8" tires (215/70R15).
The stock RPM at 65MPH on 4th gear were 2567 rpm and on 5th gear were 2054 rpm.

Now I am running 30" tires with the 3.15 gear and my new RPM at 65MPH on 4th gear is 2301 rpm and on 5th gear is 1841 rpm. So as you can see, it has lost its power.

Doing the math, I basically need a 3.55 gear ratio. 3.55/3.15 (new gear ratio/stock gear ratio) =1.1269 ~13%
And 30/26.8 (new tires/stock tires)=1.1194 ~12%

The RPM with the 3.55 gear ratio would now be (at 65MPH) in 4th gear=2593 rpm and 5th gear=2074 rpm.
As you can see, the RPM are pretty close to the original stock RPM.

I don't know if I am wrong or if it will correct/bring back stock power and MPG to my truck but this is the closest and best ratio I found out.

 

Someone correct me if I'm wrong, but I thought 4 cyl came stock with 4.10 gear ratio.

 

I think that may be only in Pre-runners but I am not sure. Mine is a base SR5, 5-speed manual (4cyl-2.7L) and it has 3.15. Pretty freaking weak IMO

 

Okay, must be a 5-lug gear ratio thing.