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

I was wondering, I recently got a 3" lift on my 2006 Tacoma 2wd (5lug) and put some 30x950R15 tires. Stock tires were 215/70R15.

I am planning to change gears so I can have more torque acceleration but I don't know if I should first fix or recalibrate the speedometer at a shop or will the new gears fix the speedometer to show actual speed?

So far I know that putting bigger tires makes the car have slower acceleration but the tires run faster than factory OEM. Basically what I want is to have more acceleration (how it used to feel with stock tires or maybe more torque) and adjusting the speedometer to correct 30" tire speed.

 

Speedometer and odometer are fed by a signal generator that counts axle revolutions. Just changing axle gears doesn't affect it. What does throw the speedo/odometer off is the fact you are now traveling a different distance per axle revolution due to the change in tire size.

 

So changing the gear ratio of the axles won't 'fix/re-calibrate' the speedo/odometer? So basically I need to take it to a speedometer auto shop to get it fixed?

 

If you change your gear ratio and tire size by similar percentage it will be pretty close.
Example:
3.73->4.10 = ~10% change
31s->33s = ~7% change

Your speedo will then be off 3% from the factory setting. So when your speedo says 62mph, you are really going about 60mph.

 

This may sound like a lazy question but what would the percentage of mine be. I'm really dumb at math (haha) or can you show me the tools or calculators on how to do it.

I believe my axle ratio is 3.31 (not 100% sure though) on the VIN it says A05A.
My stock factory OEM tires are 215/70R15 and now I have 30x950R15.

I think I want to go with 4.10. Do you think that will bring it back to around stock/factory with 30" tires?

Thanks!

 

Roughly a 24% gearing change and an 10% tire change. So you are still going to be pretty far off. If your numbers are right, that will be overgearing the truck, so you will turn more RPMs for a given speed than you are right now.

4.10/3.31=1.238 ~24%
29.5/26.8 (actual 30 size) = 1.10 ~10%

If you want to gear to maintain power and fuel economy for larger tires, you want these percentages to be close. Overgearing by increasing gearing significantly over tire size will give you more torque, slower crawl speed, but also higher RPMs on the highway and reduced mpg.

 

Ooh ok so the ~24% and the ~10% have to be closer together? Since I already have 30" tires, i need a lower ratio than 4.10? And yes I do drive highways and streets so I definitely want something that wouldn't make me spend too much gas but at the same time give me a little more power (without draining my mpgs).

 

If you now have 30" tires and 3.31 gears, 3.73 will return you to what it was like at stock tire size, since it is about a 13% gear increase.

That being said, most gear shops will tell you it is not worth going up just one size, and will recommend going up 2, so they would likely suggest stepping over the 3.73 and going to 4.10. But this will result in over gearing compared to stock. I've done it in my 90 Toyota pickup. It makes it very different to drive, especially in a manual. Much more low end wheel torque, at the cost of higher cruising RPMs.

 

I don't think regearing will fix your speedo. Regearing will bring your rpms close/back to stock. Your speedo will still be off as much as your tire size difference from stock. Only on the 6 speed, the speedo gets effected from gearing because it gets it's signal from the output shaft, iirc.

 

6 speed manual has speed measured at the tcase versus at the abs sensor with the auto. So, the auto's speedo will not change when regearing since it's getting it's signal from the abs sensor at the wheels.

 

How did you lift a 5 lug 3"?

Tires are part of the gear equation. You can go to 4:10 and run taller tires and get more 'stock like' results.

You might use something like this to correct your speedo once you get it to drive as you want?

Bone up on the math classes. No reason anyone old enough to drive and make substantive changes to their vehicle can't do some rudimentary algebra. It will come in handy for all kinds of things!

 

Tires are definitely part of the equation, but OP's title was asking if regearing would "fix" his speedo being off.

 

OP, regearing will not fix your speedo being off. You will need a speedo recalibrator as @Clearwater Bill posted above to correct it.

 

Oh ok, thanks so much for the information man!! I really appreciate it and I learned a lot today from you!!

 

I have no idea what you just said haha but mine is a 5-speed manual though

 

My speedo always seemed to be within 1-2mph when factory stock. They aren't perfect.

When I put 33's on I was off around 3-4MPH as an average.

Now that I regeared from 3.73 to 4.56 it seems pretty close again. So it can perhaps compensate a little bit.

I used my Ultra Gauge and the GPS on my cell phone to travel a 'known distance' after my re-gear yesterday. In order to get an accurate distance/MPH read my Ultra Gauge is using a multiplier of 1.068 or something like that. So I'm roughly 7% off.

When I was running 33's with the stock 3.73's I think it was off by 9% or so when I calculated it.

 

There are a couple lift kits for my type of truck (ReadyLift and ProComp) and 3" is the max I can do and what I wanted and still be able to fit tires as big as 31".

And I've seen that Speedo calibrator device that you suggested but honestly I don't want to spend over $200 for something I'm going to use one time. I think there are shops that fix the speedometer for less than $100.

And Yea I've always sucked at math, specially algebra! haha

 

I believe that's exactly why @Clearwater Bill provided the OP with a link to the Hypertech speedo calibrator..... ? Since that's the only way to "fix" it properly.

 

Thanks for answering my question. And there are shops that fix it right? Instead of me buying a $200+ device?

 

I have a local shop that offered to buy a Hypertech unit and do it for me. However, each device is tied to ONE vehicle. So you have to buy the device from them before they can use it on your truck.