My copy of techstream does not allow for that
4.88 gear question... How to calibrate the speedometer? (1 Viewer)
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kcjaz
SILVER Star
So I know the speedo is based on wheel speed sensors and when I moved up to 285/70/R17 it displayed a higher speed relative to actual speed than with stock tires. It actually made the speedo dead nuts on compared to gps. But the odometer was now off by about the rev/mile ratio of the OEM to larger tire.
I thought the reason the stock speedo read hi was due to some Japanese law and JDM vehicles were calibrated this way but the odometer would need to be correct so I thought they used a transmission input/output sensor and calibrated that one without any bias.
I just got 4.88s installed and was expecting to have to do something to recalibrate the odometer but the odometer is not affected with the new gears so that must mean both speedo and OD are based of wheel speed and just must have different correction factors applied to the same wheel speed input.
The error is only 3.9% so it isn’t really a big deal to me but I’m curious if anyone has installed one of the correction devices. I think it may not be possible to fix both the speedo and OD if the same speed sensor input is used for both speedo and OD without getting into the ECU logic and changing something downstream of the wheel speed input.
I thought the reason the stock speedo read hi was due to some Japanese law and JDM vehicles were calibrated this way but the odometer would need to be correct so I thought they used a transmission input/output sensor and calibrated that one without any bias.
I just got 4.88s installed and was expecting to have to do something to recalibrate the odometer but the odometer is not affected with the new gears so that must mean both speedo and OD are based of wheel speed and just must have different correction factors applied to the same wheel speed input.
The error is only 3.9% so it isn’t really a big deal to me but I’m curious if anyone has installed one of the correction devices. I think it may not be possible to fix both the speedo and OD if the same speed sensor input is used for both speedo and OD without getting into the ECU logic and changing something downstream of the wheel speed input.
bloc
SILVER Star
When I dug into this years ago that was my takeaway.
Anyone ever try this? It makes total sense in my mind. As far as I know, the LX uses the same setup of gathering speed info from the sensors at the actual wheel. The yellow box says it works with all of the modern type of sensor signals like hall effect, reed switch, and inductive coil. If I'm not mistaking ours is a 2 wire hall effect based sensor.
It seems like this is the best option on the lx if it works, as it would affect all downstream systems too. We would simply be intercepting the signal wire off the sensor at each wheel, passing it through the yellow box for modification, and send it back on its way to whatever controller those signals go to get parsed and converted into canbus language.
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bloc
SILVER Star
Those wheel sensors handle signaling for the ABS though. Personally I wouldn’t want to do anything to interrupt or alter their signal.
Yeah, I've investigated this based on the same response in another thread (maybe you posted the same reply?). However, there's nothing special going on here at the sensor. It's not a 2way communication system. Its a simple one way signal being sent. It's single purpose is to detect wheel speed, thats all. I'd argue that right now, on 35s, the abs system on my lx won't operate like it's supposed to because of the tires. In fact, I've had two occasions where I've had to emergency brake on the highway, and the result was an overly aggressive ABS system action that continued to apply braking for me even after I got off the brake. The only way I can express the feeling is like a runaway brake application. Smash the brakes due to someone cutting you off, for example, and within a split second you are already taking your foot off the brake but by then the abs system took over and is still braking for you. It's a really odd feeling because it turns into a much harder brake maneuver than you intended it to be.
Anyways, these sensors are simply reporting wheel speed to the computers via a signal that then gets parsed into digital language. Providing the computers with accurate wheel speed data via signal manipulation seems to me like the correct path forward. Im.just trying to suss out the wiring side of things at this point.
bloc
SILVER Star
I forget the 3 letter system name but that is “normal” behavior for this platform independent of tire size. Mine has done it a couple of times in six years for emergency braking on stock rubber.
But yeah it sounds like you’ve wrapped your head around what these systems do. If you’re comfortable with putting aftermarket hardware with their level of build quality in-line for such a system go ahead, but IMO there’s a risk that’s worth mentioning to people that don’t understand the nuts and bolts as well.
And there's the rub: reliability. That's really the only thing holding me back on trying this out. Who knows how long these little devices will hold up to being exposed to the elements. One thing I thought of is following the wiring to see how it's routed and maybe intercept the wiring for each sensor wherever they converge, which is hopefully inside the vehicle somewhere.
Thanks for the info about the braking situation being normal even on factory size tires. If that's the case, man that sucks lol
I did upgrade my 14 to the 16+ calipers and rotors up front. Made a huge difference in braking performance on 35s and the added weight of mods. I went with the same factory branded stuff toyota uses, Advics.
bloc
SILVER Star
I’m also really happy with my 16+ brakes even on stock diameter rubber. And yes it’s odd.. on mine it typically even pretensions the seatbelts. It’s a really intrusive system.. but I do feel like it may help some drivers avoid a front-end collision. But then it probably increases the odds of being rear-ended.
And yes that’s exactly my concern with these.. reliability. As for converging, from memory the rears converge near the upper control arms. The fronts probably don’t until close to the ABS computer, but I’d have to dig around in the EWD to be sure. I also can’t remember whether these wires are shielded or not, but I do know Toyota takes extra steps to maintain function and durability like molding both conductors into a single rubber wire, presumably to eliminate chafing. Which makes sense as they probably consider this a safety critical circuit.
Awesome, yeah. Thanks for the chat and info! I'm going to be in the garage working on the regear for the lx next week. I'm going to trace the wiring as best I can since I'll be under the vehicle.
VF Tuner map edit has a feature which allows for entry of tire diameter. Currently mine is set to factory whereas my tires are approx 33” diameter. Not sure exactly what features are affected by this setting; at least the fuel economy/range, possibly the speedometer. Will confirm here if/when I test.
It doesn't affect or correct the speedometer. I've tried both vf and hptuners, both of which have this tire diameter setting you can change. Neither has any effect on the speedometer.
Huh, interesting. As I understand it, regearing has zero impact on how the speedo reads, since the speed is measured at the wheels and not the transmission output shaft on the 200 series (LC/LX).
4.88 and 34.5” 35s my Speedometer is about 8 percent slow.
61 is about 65.
69 is about 75
61 is about 65.
69 is about 75
Those are my exact numbers, essentially, on my 14 on stock gears and 35s (skinny kenda klever rt 35x10.5). At 65 indicated I'm right at 70 on gps. Which confirms what everyone says about gearing having no effect on speedo.
Nope, not on the 200
Speed is calculated by taking the average wheel speed sensor. Gearing has no impact on the Speedo. It might have some bearing on the odometer as I think I read that is calculated differently, but I can 100% confirm it had no impact on the speedometer.
32.5” tire size will get you pretty close to accurate though as the 31” factory size run a bit high on the speedometer.
VFTuner has settings for both the tire size and axle ratios.
I am not sure if those would affect the speedometer or not. I find it odd that Toyota wouldnt have a global tire size and gear ratio adjustment either in the BCM or PCM. My F150 used the BCM tire and gear ratios for all modules in the truck, and within the PCM there was a selection to use the BCM value, or use the values in the PCM. So most people would adjust the tire size in the BCM and then the PCM would just accept that as the correct value unless you exceeded at 35" tire(the Raptors stock tire size)
I am not sure if those would affect the speedometer or not. I find it odd that Toyota wouldnt have a global tire size and gear ratio adjustment either in the BCM or PCM. My F150 used the BCM tire and gear ratios for all modules in the truck, and within the PCM there was a selection to use the BCM value, or use the values in the PCM. So most people would adjust the tire size in the BCM and then the PCM would just accept that as the correct value unless you exceeded at 35" tire(the Raptors stock tire size)
How does lower gearing not change the wheel speed?
I get you cannot re-program the computer, but if you match the re-gear to the tire size to return the wheel speed to the original wheel speed, it should be correct?
Lower gearing only changes the engine speed relative to the tire speed. If the computer is taking the wheel speed measurement from the ends of the axle, then the gears have no effect on the calculation. At any given speed the axle shafts will rotate at the same speed regardless of the gears.
