I am wondering if anyone would know how the Driven Wheel Pulses Per Rev (H0152) and Non Driven Wheel Pulses Per Rev (H0153) are calculated? The new tire size will be 39.8".
Thanks,
dave w
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I am wondering if anyone would know how the Driven Wheel Pulses Per Rev (H0152) and Non Driven Wheel Pulses Per Rev (H0153) are calculated? The new tire size will be 39.8".
Thanks,
dave w
This is just an educated guess based on your screenshot and experience. But, the driven wheel pulses per rev is based on the final drive ratio & number of teeth on the VSS reluctor. I am assuming that the non-driven wheel pulses per rev is based on an input from the wheel speed sensor via the EBCM in an OE application. Given the info you have, calculating the driven wheel pulses per rev is just a matter of mathematics. You would simply multiply the VSS pulses per rev (36) by the final drive ratio. The tire size is irrelevant for THAT calculation because the number of VSS teeth is a constant and regardless of tire size the driveshaft is still only going to rotate x (insert final drive ratio here) number of times for every rotation of the wheel. The speedometer calibration is then based on this calculation and the tire circumference. I believe that the only reason for having a non-driven wheel pulse constant is for torque/traction management.
Additionally, Transmission Output Shaft Revolutions per mile = 5280 / tire rolling circ (in feet) * final drive ratio.
pi * dia = 3.1415 * x 39.8" = 125.0" circumference.
125.0"/12" = 10.417'
5280/10.417 = 506.88 revs / mile
506.88 * fdr = TOS revs/mile
Rolling circumference is by far the most accurate method to obtain the revolutions / mile figure.
The final gear ratio is 3.42, which is not in the screen shot.
I'll work some math, and see if I can figure it out.
dave w
That part of the calculation was where I was a little uncertain about my answer thus my leaving it out of my reply. Your answer actually raises two questions for me though. They are related, but may be a little OT so if you want to move this reply to a new thread or delete it and answer in a PM I understand.Quote:
Originally Posted by 1project2many
First, am I correct in assuming that you are in agreement with my original reply ? I ask because lately I find myself second-guessing everything I say and do, lol.
Second, your terminology "rolling circumference" leads me to ask the question about "true" rolling circumference vs. "static" circumference in terms of speedo calculations. I am using the terms "true" rolling circumference and "static" circumference because that is the best terminology I can think of at the moment. But, it is a given that the "true" rolling circumference of a given tire size will be different than the "static" circumference due to the flexing of the sidewall as the tire is loaded. I know that when OE manufacturers are setting up speedo calibrations that the engineers aren't going to the length of measuring the actual rolling circumference of the tires. It just isn't practical because there is a variance between different types and brands of tires as well as tire pressure and load, and most vehicles have more than one tire option when new. So, the question is, does anyone ever take into account this variance and if so how do you determine that figure and how much difference does it make in accuracy ? I ask this out of curiosity because in my experience with owning sport bikes I have often changed sprocket sizes and tire sizes which requires a correction to the speedo through the use of a signal altering box. The manufacturers website for these boxes has a calculator that you use to obtain the correction factor. This calculator is setup to be so precise so as to account for the factory error that is purposely built in as well as accounting for rear tire wear. The tire wear portion always intrigued me just because I wondered if there was really enough of a difference to matter. Back to my question though, I would think that the difference in circumference on a car/truck tire would cause more of a variation in speedo readings than the amount of tread wear on a motorcycle tire would.
BTW, I do agree that circumference is the most accurate way to calculate the speedo. And in response to Dave's last reply, the TOS revs per mile would be 1733.5296 and given that there are 36 teeth on the reluctor that would equate into a VSS value of 62407.0656 pulses per mile.
Understood. Your theory sounds reasonable but the values in the screenshot do not agree with it. 36 for pulses per TOS revolution vs 32 for driven wheel pulses per rev while fdr is 3.42. More investigation is in order imo. These values may be for two different inputs where there are separate speed sensors on each wheel and a speed sensor at the trans. Or, is this controller responsible for providing ABS functions or providing signals to the ABS computer?Quote:
First, am I correct in assuming that you are in agreement with my original reply ? I ask because lately I find myself second-guessing everything I say and do, lol.
Yes, someone does take that into account. In the '80s and early '90s when GM techs were still allowed to make repairs to instrument clusters, one of the steps for calibrating the dash of trucks, and later for ordering calibrated DRACS, was to roll the truck through one complete turn of the tire to measure rolling circumference. In fact, we spent about 15 minutes in one of my training classes discussing how much different published tire size can be from actual due to wear and pressure variations.Quote:
I know that when OE manufacturers are setting up speedo calibrations that the engineers aren't going to the length of measuring the actual rolling circumference of the tires. It just isn't practical because there is a variance between different types and brands of tires as well as tire pressure and load, and most vehicles have more than one tire option when new. So, the question is, does anyone ever take into account this variance and if so how do you determine that figure and how much difference does it make in accuracy ?
The standards for speedometer accuracy are wide. OE speedometer accuracy errs on the high side and tends to read higher above 65 mph. I'm not a conspiracy theorist but I've always wondered about that one. Odometers are generally fairly close, though. There are standards to tires that should keep tires of the same size roughly within a certain diameter. 225/75 16 puts the ID at 16" and the OD at 16" plus 225 * .75 mm plus tread depth. Tread depth is the greatest variable. I can't tell you how the speedometer calibration decision is arrived at but after years of playing with cars and tires we all know it's never exact. I also know that police vehicles with "certified" speedometers are (or were... do they certify speedos any more?) only supposed to use the make and model tire the speedo was certified with... suggesting some extra care goes into making those specific tires consistent in size.
If you ever look at tire maker's specs, when they publish a revs/mile figure it's not equal to the number of revs you calculate using the published diameter. These are for a Goodyear Wrangler ST - P225/75R16 104S
Diameter: 29.3"
Revs/mile: 714
By calculation, the revs/mile at 29.3" dia is 688. 714 revs/mile represents a 4% smaller diameter tire which seems like an accurate representation of rolling circumference.
We can also estimate the change due to wear. New tire spec is 10/32" tread depth. Worn tires are 2/32". For this tire, 1/4" change in OD creates a 1% change in the number of tire revolutions per mile. For smaller diameter tires the percentage difference is less. This is a smaller difference than an 8 psi reduction in air pressure.
What are typical tread depths new and worn for a motorcycle tire? What's a typical tire diameter?
There is a lot of interesting info there Shannen. I knew that if anyone had a decent answer it would be you. I was hoping that although slightly OT, my question might yield answers containing valuable info like that.Quote:
Originally Posted by 1project2many
I noticed the value of 32 for driven wheel pulses per rev and thought it seemed funny at the time, but I thought that perhaps Dave had begun to make changes already. After reading your reply and studying the screenshot again I do have some more info to add. I confused myself by looking at the speedo calculations to the right of the screenshot and based my answer off of that. There are in fact individual wheel speed sensors at all 4 wheels as well as an output shaft sensor on the transfer case on the donor vehicle. The wheel speed sensors are still wired directly to the EBCM and the VSS is wired to the ECM. The ECM does not provide ABS functions or wheel speed signals to the EBCM, but does reference the wheel speed sensor data from the EBCM for reasons that I cannot recall. So, the true answer to Dave's question would be that those values are based off of the reluctor tooth count on the wheel speed sensors. What he needs to do with those values depends on how you eliminate the EBCM in standalone drivetrain transplants which is beyond my realm of expertise. The calculations that I provided would be correct for speedometer calibration though.Quote:
Originally Posted by 1project2many
Typical sport bike rear tires are right at 25 inches in diameter and average tread depths are ~7/32 new & 1/32 at the wear indicators.Quote:
Originally Posted by 1project2many
It is well known in the biker community that the speedometers consistently read on the high side. Funny thing is that I just checked the site where the online calculator was for making speedo adjustments and they have removed the option to compensate for tire wear but the factory speedo error option is still there which is set at a fairly generous 5.5%. What makes this error seem so deliberate is that there are confirmed instances of the odometer being accurate despite the speedometer error. Once the error was corrected with a signal modifier the speedo was then correct, but the odometer was then incorrect.Quote:
Originally Posted by 1project2many
BTW, I based all of my answers under the assumption that this screenshot was taken while trying to calculate the speedometer for the drivetrain transplant that Dave is assisting with currently.
You're saying it's something like a snapshot taken between no changes and job complete? Interesting. Dave??Quote:
BTW, I based all of my answers under the assumption that this screenshot was taken while trying to calculate the speedometer for the drivetrain transplant that Dave is assisting with currently.
Quote:
Originally Posted by 1project2many
No, I meant that I was assuming that this question was regarding the drivetrain swap he was working on and that the technical info I gave would pertain to the particular vehicle that the drivetrain was out of (2012 Chevy 1500 4x4). Since the E38 ecm is used in several applications some of my statements might not be correct for a different type of vehicle. That was why I stated that my reply was based on an assumption so as to avoid confusion. I did, however, originally think that the wheel pulses per rev value of 32 in the screenshot might have been where he had begun to make changes to correct the speedo because I had confused myself while making my first reply as stated above.
The screen shot is from the stock .ctz file (2012 project I'm involved with). My question for parameters (H0152) & (H0153) was to understand if (H0152) & (H0153) needed to be changed for a larger tire. I was hoping to learn and understand the conversions for (H0152) & (H0153). The other parameters in the screen shot I have a good understanding on how those parameters are calculated. I was thinking, maybe someone would share their experience calibrating a similar vehicle (stock) with larger tires. Seems logical to me, someone owning a 2012 vehicle would change tire sizes and require speedometer calibration.
I don't have the 2012 vehicle, which limits the available information I would like. It seems logical to me that (H0152) & (H0153) are from the wheel speed sensors. It seems logical to me the ECM and BCM would have some communication back and forth about the wheel speed sensors. The E38 is about 1.7 Meg in size, which might have programming not fully understood, except for a few GM engineers. I might be years from now, if ever, that all the programming in the E38 is fully understood. I would have liked better comments from EFI Live about (H0152) & (H0153)! As an EFI Live customer, I feel EFI Live has ample room for improvement with the E38!
dave w
I can explain to you with confidence how the vehicle is configured which will answer most of your questions as I have intimate knowledge of those vehicles. I have no knowledge of EFI Live, but can make a logical assumption based on my knowledge of the vehicle and interpretation of the screenshot. I got a little too carried away in my original reply and overcomplicated the answer as well as making it wrong. The simple answer is yes H0152 and H0153 should be from the wheel speed sensors based on the screenshot you provided. But, no those values should not be effected by tire size as 1 revolution is still 1 revolution regardless of the tire circumference.
I'll delve further into the technical workings of these systems as I know that you like to know how things operate. Those two values are simple and based on the tooth count of the reluctor and I don't see any purpose for needing to change them unless you have a situation where the wheel speed sensors and reluctors are not OE. An example would be if you were utilizing the drivetrain and EBCM from the donor and utilizing the new vehicle's existing wheel speed sensors. I don't know exactly how the ecm behaves in a transplant situation like yours where you are not using an EBCM. But the way modules on the high speed lan network are designed to communicate is that if a module is not detected then the remaining modules would operate properly unless they were not receiving critical data which wheel speed sensors would not be considered critical data for the ecm. On the donor vehicle the front wheel speed sensors and reluctors are contained within the front hub assembly. The rear wheel speed sensors mount on the axle tubes and the reluctor is on the axle shaft a couple inches behind the wheel bearing. As I stated in my last reply the wheel speed sensors are wired to the EBCM for ABS and Stability Control functions (if equipped with stability control). The VSS, or what is labeled in the screenshot as the TOS, should be wired to the ECM. The EBCM and ECM communicate directly on the high speed lan network and work closely together to control traction (and stability if equipped with stability control) and possibly other functions. The speedometer calibration should not be effected by these two values.
I hope that I made some sense of this for you,
Phil
Exactly. Values that represent pulses per revolution are tied to the configuration of the sensors and do not change with tire size or gear ratio. Values that contain or reflect distance will change with tire size or gear ratio.Quote:
The simple answer is yes H0152 and H0153 should be from the wheel speed sensors based on the screenshot you provided. But, no those values should not be effected by tire size as 1 revolution is still 1 revolution regardless of the tire circumference.