Gearing question (1 Viewer)

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I have a 2.7 with a 5 speed. If I'm traveling at exactly 70 mph(speedometer reading) it has exactly 2500 RPMs.

What is my gearing? Just trying not to have to jack it up to see what it is.
 
Tire size?

There's a code on your door tag that can be deciphered using a chart on ttora.

don't 'mud and drive
 
I've got 33s, but regardless of tire size the speedo will read the same. I've checked that chart, and my year and model had a variety of gearing. 70 on speedo, and Tom Tom says 74ish.
 
I've got 33s, but regardless of tire size the speedo will read the same. I've checked that chart, and my year and model had a variety of gearing. 70 on speedo, and Tom Tom says 74ish.

Ummm....tire size does indeed affect what your speedo reads. 4mph over seems about right for 33's at highway speeds.

Didn't the 4cyl trucks come with 4.10 gearing?
 
Jacket said:
Ummm....tire size does indeed affect what your speedo reads. 4mph over seems about right for 33's at highway speeds.

Didn't the 4cyl trucks come with 4.10 gearing?

Negative. If I had the same 15s with a set of low profiles, it's read the same on the speedo with the same RPMs. Actual speed would vary, though. It pulls about the same as when I had some wide 325/60-15s. Doesn't handle as good, which was expected. I was thinking of a front locker and just googling some prices.
 
What kind of vehicle is this?

If it's a 4runner there is no good way to find out the axle gear ratio without counting turns or teeth. The tag has been wrong many times.
The tacomas seem to be reliable from the axle code on the door jamb tag.

Unless your previous tires were the exact same diameter overall, the mph reading will change a bit. It might not be perceptible on the analog gauge, but it will change a touch.
 
Negative. If I had a set of 28s or a set of 38s, one revolution of the tire is one revolution of the tire. That's all that the speedo reads. It doesn't have a GPS.

I was just curious if anyone with a 2.7 and a 5 speed knew their gearing and what their RPMs read at 70 mph according to their speedo. It's a simple concept and I don't understand why no one has gathered up enough info to make a chart of this. If I were to check it like everything I've found has said to check it manually, it still doesn't matter what the tire size is.

I'm 3 hours from home at a hotel and figured I could source a locker for S&Gs. I'll just put it on jakstands when I get home. I wouldn't order one until I physically checked it myself anyway. No biggie.
 
Unless Toyota designed a workaround, a change in tire diameter will change your speed at a given RPM.

When I went from 30'' stock tires to 31.8'' BFGs, that would mean my speedometer is now ~6% slow, and my odometer is ~6% slow.

For example, when I want to go 60mph, I need to go 63.6mph according to my speedometer.

AFAIK, most 2.7L 4wd Tacos with manual transmissions come with 3.88 gears. I think that gear ratio is a bit low, personally, but that's what I know.
 
This is the silliest confusion I have seen for a while. No, one revolution does NOT equal the same speed regardless of tire size! An increase in tire size equates to an increase in circumference which directly translates to a further distance traveled for each revolution. So for a given RPM, which has a time element, you travel further in the same time, which means you are going faster (speed = distance divided by time)
 
The SPEEDOMETER reads tire revolutions regardless of tire size. The ACTUAL speed traveled changes. If I had some 44s and checked my gear ratio it wouldn't matter if the tire was mounted or if I just marked the brake drum. One revolution=one revolution.

//end thread
 
The SPEEDOMETER reads tire revolutions regardless of tire size. The ACTUAL speed traveled changes. If I had some 44s and checked my gear ratio it wouldn't matter if the tire was mounted or if I just marked the brake drum. One revolution=one revolution.

//end thread

How does it read tire revolutions from the rear of the transfer case?
 
Picking on the new member? Or can y'all really not grasp the concept?

An unmolested speedometer will read the same speed at the same rpm regardless of tire size. The actual ground speed will increase with a larger than OEM diameter tire, decrease with a smaller tire. Meanwhile, the rpm and speedometer will read the same.
 
No, we don't pick on new members.

It actually reads the revolutions of your rear output shaft. :flipoff2:

Now, there is a mathmatical formuler that will answer your questions, the problem is I have no clue what gear you are in, what your tranny ratio is, and if you were judging an adjusted speedimeter or what.

Do some research, Google it, lift it up, but asking what's my gear ratio with no other information on trans ratios, or selected gear leaves us with guess work.

don't 'mud and drive
 
I have a 2.7 with a 5 speed. If I'm traveling at exactly 70 mph(speedometer reading) it has exactly 2500 RPMs.

What is my gearing? Just trying not to have to jack it up to see what it is.

Original post^. Sorry for the confusion. I was just thing, 'someone may have a similar truck, and know their gearing...and maybe next time went for a drive they could look at the speedo when in 5th gear at 2500 RPMs and could state their gear ratio'
 
I think we're having some confusion in terminology here.

What Brake is saying is the speedometer and engine are essentially linked.
For example, the speedo will always read 15mph in second gear at 2000 rpm, regardless of tire size (random numbers pulled from ass). HOWEVER, your ACTUAL road speed will differ from what the speedo is saying based on your tire size.

If you want to calculate the difference once you change tire sizes, you can do it by percents.

Example, my truck came with 30'' tires. I went to 31.8'' tires.

31.8 - 30 = 1.8
1.8/x% = 30/100%

x= approx 6%

So your speedo will read 6% slower than your actual speed, your odometer will be 6% lower than your actual distance traveled.



I'd call a dealership service dept. with you VIN number in hand to find out your exact gearing.
 
RiverRat gets it.

I bought it used in '01 and had Classic IIs on it with different tires and from what I've googled you cant trust what it says in the door jamb. They were 30.8" if your do the math, and the speedo was off a few mph. So it could've been those originally.
 
Check this out, it says I have 3.38:1 gears.... but I'm not sure if it should be 3.58:1 because my speedo is 6% slow.

Put in your #s and see what you get.
 

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