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speedo recalibration after new tires and regear

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Old 07-11-2013, 10:35 PM   #1
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speedo recalibration after new tires and regear

Hey everyone,
So I just upgraded the stock 27's to 32's and am planning to regear from 3.58 to 4.10. After the tire change my speedo and odo are obviously way off (by about 20%), but once I regear to 4.10's it should make them more accurate since I'm gearing the truck closer to stock ratios right? If that's the case, does anyone know how to factor in the regear when calculating speedo and odo discrepancies? Or does anyone know of calculators that take both tire change and gear ratio change into consideration?
If it's still too far off after the regear, i might consider buying a recalibrator like the hypertech http://www.autoanything.com/performa...0&AID=10561927 mainly to fix the odometer. My main concern with this particular unit is I've heard it doesn't actually plug into the OBDII and instead plugs straight into the gauge cluster. Has anyone used this unit and if so, how hard was the install and do you think it was worth the money?
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Old 07-11-2013, 10:58 PM   #3
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Quote:
Originally Posted by 503TRD View Post
Hopefully someone chimes in on that tool...I'm gonna buy that if it works...just wish it went to OBD2?
Yah it would definitely be more convenient if that were the case, but on the other hand I already have an ultragauge plugged into the OBDII and would rather not have to buy an OBD splitter.

Also, just to add to the ultragauge thing, I know you can calibrate the ultragauge to the correct speed and whatnot, but i'd like to have the odo recalibrated as well just to make it a little easier when maintenance times roll around

So I think I got the calculation but I'm not sure if it's right. To factor in the tire changes it's just multiply the speed/additional speedo mileage by 1.192 (tire diameters ratio). And to factor in the gear change it's just 4.10/3.58= 1.14
So to factor in both tire change and gear ratio change, it's just 1.192/1.14= 1.045 so the correct speed is the speed on the speedometer times 1.045, which is pretty negligible until you get into highway speeds. Can someone confirm this?
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Old 07-14-2013, 01:11 AM   #4
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I had a box that allowed you to change the signal to the ECU on another vehicle I had. It worked well to correct for tire size. I'll try to find a link to it.

Unfortunately it threw a code too and the dealer pulled it. Then they reported possible odometer tampering to DMV. It printed on the title, and the resale value was trashed.

Hopefully this isn't the case now. Just my experience.

I pay more attention to my mobile device now for speed than my speedometer since it's more accurate and mounted right there at the vent to the right.
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Old 07-14-2013, 01:15 AM   #5
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Gear ratio has nothing to do with your speedometer. Going to a 33 inch tire actually gets the speedometer closer to correct than what it is stock. Use a gps to compair.
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Old 10-02-2013, 03:34 AM   #6
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Quote:
Originally Posted by jacobigindi View Post
Hey everyone,
So I just upgraded the stock 27's to 32's and am planning to regear from 3.58 to 4.10. After the tire change my speedo and odo are obviously way off (by about 20%), but once I regear to 4.10's it should make them more accurate since I'm gearing the truck closer to stock ratios right? If that's the case, does anyone know how to factor in the regear when calculating speedo and odo discrepancies? Or does anyone know of calculators that take both tire change and gear ratio change into consideration?
If it's still too far off after the regear, i might consider buying a recalibrator like the hypertech http://www.autoanything.com/performa...0&AID=10561927 mainly to fix the odometer. My main concern with this particular unit is I've heard it doesn't actually plug into the OBDII and instead plugs straight into the gauge cluster. Has anyone used this unit and if so, how hard was the install and do you think it was worth the money?
I added the Hypertech last week. It's worth it to me not to have to keep thinking about my speed, I have enough other things I'd rather be dreaming of than worrying about my speed. I installed it in about 20 min., super easy & plug n play..
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Old 01-11-2014, 10:49 AM   #7
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Quote:
Originally Posted by TrdSurgie View Post
Gear ratio has nothing to do with your speedometer. Going to a 33 inch tire actually gets the speedometer closer to correct than what it is stock. Use a gps to compair.
Not really sure where this thinking is from... (yeah, I know it's an old post, but deserves attention).

I have worked in Automotive Electronics for over 25 years. Specifically in Factory Speedometer repair and troubleshooting. I cannot think of a vehicle on the road, that the above statement applie to, that is less than 5 years old, and I'm not certain of the later models, as some may be using GPS for speed readings... but None for all the years I worked in it, were independent of gear ratios in both the transmission and Rearend. (in vehicles with rear wheel drive for sure)

I used to actually do Speedometer accuracy tests on a Dyno and the Speed and the Odo are both affected by all of the final drive gearing. Back in the day, our adaptations required a small gear box called a ratio adapter. Nowadays, with all the electronic speedos (which I was dealing with on their initial application in consumer vehicles), the same still applies, yet you adapt it using electronic signal modification and correction. In GM (where most of my dealings were), The DRAC (Digital Ratio Adapter circuits) were first introduced in a separate box and mounted remotely from the EM and Instrument Cluster. WE got the gear ratio from the glove box tag (or wherever it was located) and did a Tire roll-out for circumference, and had charts that gave us the circuit modifications for THAT application, to make it read correctly. This had to be done anytime there was a tire Size change, and if someone changed their rear end gears, we had them supply the Gear Ratio. All of that applies to both Speedo and Odo on ALL vehicles. The odometer uses the speedometer to determine how much to add to the mileage... There is no disconnect at all. There cannot be unless you are modifying the circuitry in the instrumentation and ECM Separately. The only thing Many of the Adapters and correctors provide, truly, is a Speed signal modification, based on what you input. It corrects both readings, by modifying ONE signal set. That set is ONLY the SPEED SIGNAL inputs. On the more Schmancy ones, it can also change the shift points per RPM/Speed and other things, but the stuff that talks to your speedo is still the same info that controls your ODO. I believe the Hypertech does the Trans info as well from what I understand of it.

I'm an old guy... I see tons of things done on these trucks (Tacomas) that are not very well understood. Some of them I can ignore simply because I know it doesn't matter much, and it really doesn't affect many people. But the Speedo info like the quoted one above, and some of the wheel change info, can be very misleading and get some undesirable results.
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Old 01-11-2014, 11:06 AM   #8
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Quote:
Originally Posted by SCOTTRODS View Post
Not really sure where this thinking is from... (yeah, I know it's an old post, but deserves attention).

I have worked in Automotive Electronics for over 25 years. Specifically in Factory Speedometer repair and troubleshooting. I cannot think of a vehicle on the road, that the above statement applie to, that is less than 5 years old, and I'm not certain of the later models, as some may be using GPS for speed readings... but None for all the years I worked in it, were independent of gear ratios in both the transmission and Rearend. (in vehicles with rear wheel drive for sure)

I used to actually do Speedometer accuracy tests on a Dyno and the Speed and the Odo are both affected by all of the final drive gearing. Back in the day, our adaptations required a small gear box called a ratio adapter. Nowadays, with all the electronic speedos (which I was dealing with on their initial application in consumer vehicles), the same still applies, yet you adapt it using electronic signal modification and correction. In GM (where most of my dealings were), The DRAC (Digital Ratio Adapter circuits) were first introduced in a separate box and mounted remotely from the EM and Instrument Cluster. WE got the gear ratio from the glove box tag (or wherever it was located) and did a Tire roll-out for circumference, and had charts that gave us the circuit modifications for THAT application, to make it read correctly. This had to be done anytime there was a tire Size change, and if someone changed their rear end gears, we had them supply the Gear Ratio. All of that applies to both Speedo and Odo on ALL vehicles. The odometer uses the speedometer to determine how much to add to the mileage... There is no disconnect at all. There cannot be unless you are modifying the circuitry in the instrumentation and ECM Separately. The only thing Many of the Adapters and correctors provide, truly, is a Speed signal modification, based on what you input. It corrects both readings, by modifying ONE signal set. That set is ONLY the SPEED SIGNAL inputs. On the more Schmancy ones, it can also change the shift points per RPM/Speed and other things, but the stuff that talks to your speedo is still the same info that controls your ODO. I believe the Hypertech does the Trans info as well from what I understand of it.

I'm an old guy... I see tons of things done on these trucks (Tacomas) that are not very well understood. Some of them I can ignore simply because I know it doesn't matter much, and it really doesn't affect many people. But the Speedo info like the quoted one above, and some of the wheel change info, can be very misleading and get some undesirable results.
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