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  #1  
Old 07-09-2016, 11:19 AM
bquindawl bquindawl is offline
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Default Tire Size, Gear Ratio, Speedo Question....

Hello all,

Here is my situation. 2005 Ford Ranger. It has 3:73 gears in it. The truck originally had 225/70/15 tires on it.

I recently lifted the truck (2WD) and put 31x10.5x15 on it.

Of course performance has suffered.

I was looking at putting 4:56 gears in the truck.

I am concerned about the Speedometer, and how much it will be off.

I talked to a Ford Dealer, and they said all they could "flash" was what came on a Ranger from the Factory. Neither the 31" tires, not 4:56 gears came on Rangers from the factory obviously.

So my questions are:

1.) Is there an easy way to get the speedometer right? I know I could try and get it programmed with an aftermarket programmer, but It doesn't even look like a lot of "programmers" on the market even work with a Ranger.

2.) Is there an online calculator somewhere where I could input tire size and gear ratio and see the speedometer output?

I know the Tire Change would make it show slower than I'm going in reality, and I know the gears would have the opposite effect, so I'm curious what the NET effect of these changes would be?

Thanks a lot.
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  #2  
Old 07-09-2016, 11:36 AM
ford4thot ford4thot is offline
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Default Re: Tire Size, Gear Ratio, Speedo Question....

If all you're concerned about is staying under the speed limit, just download a GPS speed app and check it against your speedometer. Then you will know what speed to stay at to follow the speed limit laws

4.56 seems pretty steep for 31s, however I noticed you have a four-cylinder.

Someone will come along that knows better than me
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  #3  
Old 07-09-2016, 11:40 AM
bquindawl bquindawl is offline
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Default Re: Tire Size, Gear Ratio, Speedo Question....

Quote:
Originally Posted by ford4thot View Post
If all you're concerned about is staying under the speed limit, just download a GPS speed app and check it against your speedometer. Then you will know what speed to stay at to follow the speed limit laws

4.56 seems pretty steep for 31s, however I noticed you have a four-cylinder.

Someone will come along that knows better than me

My main concern honestly is the fact that it would be showing I was going faster than what I was, and that would artificially put miles on my truck.
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  #4  
Old 07-09-2016, 11:50 AM
cowboybilly9mile cowboybilly9mile is offline
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Default Re: Tire Size, Gear Ratio, Speedo Question....

Just use the calculator on your phone to determine the percentage change between the old tire size and the new (result is, vehicle speed change as a percentage), then then repeat this again using your current and a proposed axle ratio to see what it will take to a least get back to where you were, and then go from there. As for adjusting the vehicles current tire size to what you installed, you might be able to do this using FORscan. Might because, there could be a max/min range in your PCM. One way to find out.
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Last edited by cowboybilly9mile; 07-09-2016 at 11:55 AM.
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  #5  
Old 07-09-2016, 11:56 AM
ford4thot ford4thot is offline
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Default Re: Tire Size, Gear Ratio, Speedo Question....

Quote:
Originally Posted by bquindawl View Post
My main concern honestly is the fact that it would be showing I was going faster than what I was, and that would artificially put miles on my truck.
Actually if I understand correctly, it would show less miles on your truck with the larger tires and uncorrect speedo. Because you are traveling further per rotation than OE
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  #6  
Old 07-09-2016, 11:58 AM
rangeredge2014 rangeredge2014 is offline
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Default Re: Tire Size, Gear Ratio, Speedo Question....

The only im aware of to correct for the gear swap would be with a tuner like an sct
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  #7  
Old 07-09-2016, 02:37 PM
bquindawl bquindawl is offline
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Default Re: Tire Size, Gear Ratio, Speedo Question....

Larger tires would effect the odometer as less miles being logged for miles driven. Whereas the speedo is showing slower than I'm actually going.

Lower Gears would do he opposite. It would adverse the speedo in the other way. It would cause the speedo to show that going faster than what I really was.

Now figuring out the effect of those two things, and how those would coincide is in question (at least until I figure it out )

Quote:
Originally Posted by ford4thot View Post
Actually if I understand correctly, it would show less miles on your truck with the larger tires and uncorrect speedo. Because you are traveling further per rotation than OE
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  #8  
Old 07-09-2016, 02:43 PM
ford4thot ford4thot is offline
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Default Re: Tire Size, Gear Ratio, Speedo Question....

Quote:
Originally Posted by bquindawl View Post
Larger tires would effect the odometer as less miles being logged for miles driven. Whereas the speedo is showing slower than I'm actually going.

Lower Gears would do he opposite. It would adverse the speedo in the other way. It would cause the speedo to show that going faster than what I really was.

Now figuring out the effect of those two things, and how those would coincide is in question (at least until I figure it out )
I said without a corrected Speedo

I know that was part of your original question, that is why I said someone here who knows more than me should hopefully contribute to your thread soon
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  #9  
Old 07-09-2016, 05:39 PM
bquindawl bquindawl is offline
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Default Re: Tire Size, Gear Ratio, Speedo Question....

Quote:
Originally Posted by ford4thot View Post
I said without a corrected Speedo

I know that was part of your original question, that is why I said someone here who knows more than me should hopefully contribute to your thread soon
Ok, gotcha. Sorry about that.
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  #10  
Old 07-09-2016, 08:43 PM
ford4thot ford4thot is offline
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Default Re: Tire Size, Gear Ratio, Speedo Question....

Quote:
Originally Posted by bquindawl View Post
Ok, gotcha. Sorry about that.
No apology necessary for this
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