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False Speedometer Reading       #: 2017
 Moderated by: NoPower, Mike69, MaDMaXX,
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 Posted: Sat Feb 29th, 2020 06:05 am
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eegle1
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 I just purchased a 2004 Ranger XLT Super Cab FX4.  The only problem I've come across is a false reading on the speedometer.  For example, at 40 mph it reads 45 mph.  The truck is supposed to ride on 245 75R16 tires, but someone has put 235 70R16s on it.  So here's the question.  Will the combined difference in the tread width and sidewall percentage be enough to change the tire circumference and cause this?  If not, what do I look at next?

Thanks in advance.

2004 Ranger XLT FX4 Offroad
4.0L V6, Automatic
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 Posted: Sat Feb 29th, 2020 08:47 am
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JAMMAN

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 Absolutely yes. AND I believe there is a way to adjust it, didn't they include this in one of the recent releases of Forscan?

Someone summon Anthony he's the forscan expert.

It boils down to the amount of pulses per rev and I'm pretty sure you can scale that with the right software.

I bet it is worse at higher speeds until you change it be careful of getting pulled over.



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 Posted: Sat Feb 29th, 2020 09:41 am
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410customs

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 yes when a speedo is off, it is off by a percentage, so at low speeds it will be slightly off as you go faster it will be off more and more



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 Posted: Sat Feb 29th, 2020 09:41 am
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mhoward
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 Yes, tire size CAN affect the speedometer accuracy.  My "summer" tires are 235 70R 15 and that throws it off by 3-4 MPH.  This is based on the GPS MPH compared to the speedometer.  Right now, I have my OEM "winter" wheels and tires installed that are 235 75R 15.  Speedometer agrees with the GPS.  That being said, there IS a way to adjust for different tire sizes using ForScan software and an ELM 327 OBDII connector.  Unfortunately, I don't know how to do that, as I don't bother to change it.  I think our member Anthony (SheltonFilms) made a post about that once.



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2003 Ranger Edge / Extended Cab / Flareside / 3.0L FLEX / 5r44e Auto / 2WD / 8.8 LS 4:10 / Sonic Blue Pearl

So many mods... so little time...
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 Posted: Sat Feb 29th, 2020 10:08 am
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JAMMAN

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 mhoward wrote:
Yes, tire size CAN affect the speedometer accuracy.  My "summer" tires are 235 70R 15 and that throws it off by 3-4 MPH.  This is based on the GPS MPH compared to the speedometer.  Right now, I have my OEM "winter" wheels and tires installed that are 235 75R 15.  Speedometer agrees with the GPS.  That being said, there IS a way to adjust for different tire sizes using ForScan software and an ELM 327 OBDII connector.  Unfortunately, I don't know how to do that, as I don't bother to change it.  I think our member Anthony (SheltonFilms) made a post about that once.
I tried it once and could not get it to stick, just a lack of experience. One of us has to get off our *** and start hacking ECM's and related modules.



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 Posted: Sat Feb 29th, 2020 12:07 pm
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mhoward
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 When I installed my keyless entry door pad, I had to play around in there with ForScan Pro.  Happily, with Bob Wenzing's help and a little dumb luck, I was able to make that all work.



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2003 Ranger Edge / Extended Cab / Flareside / 3.0L FLEX / 5r44e Auto / 2WD / 8.8 LS 4:10 / Sonic Blue Pearl

So many mods... so little time...
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 Posted: Sat Feb 29th, 2020 02:13 pm
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 The Speed-O in the '03 is off by 4 mph high.
I thought more than that but I saw one of those MPH Tell All Signs on the side of the road, it said I was going 4 mph under what my speed-o said.
65 = 61, at least it will keep me under the speed limits around here.

33" tires and 4.56 gears are my changes.

4 mph is not too bad for those changes.

Is a "235 70R16s tire" larger or smaller in OD than the "245 75R16" ?  My guess smaller !



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 Posted: Sat Feb 29th, 2020 03:15 pm
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 I LOVE this site for tire planning:

Tire Size Calculator



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 Posted: Sat Feb 29th, 2020 05:38 pm
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Scrambler82
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 OK thx, the new tire is 1.5" larger in diameter.
Slightly more revolutions per mile... appears faster to the computer.
Could display a faster speed, point A to point B.
Not enough to throw much of anything off.



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Ltr,
2003 EDGE, Std Cab, Steppie, E4 Red, 5sp, 4x
5" SuperLift, 33" x 12.50 x 15"
Hurst Shifter
Mod'd Backrack to fit Steppie
Front and Rear Bumpers by Custom 4x4 Fabrication, OK; now Mike's Welding and Fabrication.
Working on more Mods, just need more time, longer days would work !
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 Posted: Sat Feb 29th, 2020 05:52 pm
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eegle1
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 Thanks everyone.  I suppose the best solution is the correct tire size when I go to something a little more aggressive this summer.

Again, Many thanks for confirming my suspicion.
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 Posted: Sat Feb 29th, 2020 06:59 pm
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JAMMAN

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 You are welcome, come back any time you need!



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01 XLT 2WD RC Steppie 3.0 auto Silver
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 Posted: Sat Feb 29th, 2020 10:04 pm
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Tsquare
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 LOL, I put undersized tires on my son's truck so it would read faster on the speedometer. When the spedo read 63 he was going 55. He didn't get a ticket until he was in college and needed to change the tires. He put on the correct size and started racking up speeding tickets.



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 Posted: Sun Mar 1st, 2020 04:09 am
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eegle1
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 :-)
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 Posted: Sun Mar 1st, 2020 08:23 am
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mhoward
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 Tsquare wrote:
LOL, I put undersized tires on my son's truck so it would read faster on the speedometer. When the spedo read 63 he was going 55. He didn't get a ticket until he was in college and needed to change the tires. He put on the correct size and started racking up speeding tickets.
LMAO :cool:



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2003 Ranger Edge / Extended Cab / Flareside / 3.0L FLEX / 5r44e Auto / 2WD / 8.8 LS 4:10 / Sonic Blue Pearl

So many mods... so little time...
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 Posted: Mon Mar 2nd, 2020 08:07 pm
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eegle1
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 UPDATE:  I put a new set of 245 75R16s on the truck and the speedometer is now spot on.

Thanks for all the help!
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 Posted: Mon Mar 2nd, 2020 09:24 pm
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JAMMAN

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 That's one way to do it, speedometer correction by tire size! Glad it worked out.



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01 XLT 2WD RC Steppie 3.0 auto Silver
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 Posted: Tue Mar 3rd, 2020 11:43 am
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 Good to hear you got it done.



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Ltr,
2003 EDGE, Std Cab, Steppie, E4 Red, 5sp, 4x
5" SuperLift, 33" x 12.50 x 15"
Hurst Shifter
Mod'd Backrack to fit Steppie
Front and Rear Bumpers by Custom 4x4 Fabrication, OK; now Mike's Welding and Fabrication.
Working on more Mods, just need more time, longer days would work !
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