No Such Thing As A Dumb Question

[ksagis]

The fact remains that my original presumption was that the radial ply steel belts were in-compressible in the tangential direction. Thus creating a perfectly inelastic compressive member.

So My base assumption in the hypothesis is that you have a FIXED length perimeter.

I think the key assumption is that a tire is inelastic (maybe I missed that in a previous post), want to poke at that one a bit. Any material is elastic, even metal.

Perhaps radial tires due to their construction manifest stress induced deformation much less than bias plies? If so, that would corner out.

To answer @DirtDonk question, seems to me the easiest thing to do measure circumference of a tire at various pressues.

This and been enjoyable @jamesroney, thanks for the banter!

 

[Slowleak]

If the distance traveled/revolution does not change with pressure, then I don’t understand how an indirect TPMS system could work. Wheel speed is monitored by the ABS sensors. When pressure drops in a tire, that wheel spins faster relative to the others in order to cover the same distance. That difference in speed is used to calculate the pressure loss.
For all that to work, the circumference of the tire would have to decrease when pressure decreases. It doesn’t decrease enough to notice by sticking tape on your driveway like in the YouTube video, but it changes enough that an ABS system can detect a change in wheel speed after a certain distance or amount of time.

From Bridgestone: “Based on the rate of revolution of each wheel, the computer can interpret the relative size of the tires on your vehicle. When a wheel starts spinning faster than expected, the computer calculates that the tire is underinflated and alert the driver accordingly.”

 

[Wild horse 75]

If the distance traveled/revolution does not change with pressure, then I don’t understand how an indirect TPMS system could work. Wheel speed is monitored by the ABS sensors. When pressure drops in a tire, that wheel spins faster relative to the others in order to cover the same distance. That difference in speed is used to calculate the pressure loss.
For all that to work, the circumference of the tire would have to decrease when pressure decreases. It doesn’t decrease enough to notice by sticking tape on your driveway like in the YouTube video, but it changes enough that an ABS system can detect a change in wheel speed after a certain distance or amount of time.

From Bridgestone: “Based on the rate of revolution of each wheel, the computer can interpret the relative size of the tires on your vehicle. When a wheel starts spinning faster than expected, the computer calculates that the tire is underinflated and alert the driver accordingly.”

TPMS systems use pressure sensors in each wheel. They don’t need rotation to work. That’s why you can get away with putting them inside sealed pvc pipe to fool you system if you want to run low pressure in a drag radial or offroad tire.

 

[Slowleak]

TPMS systems use pressure sensors in each wheel. They don’t need rotation to work. That’s why you can get away with putting them inside sealed pvc pipe to fool you system if you want to run low pressure in a drag radial or offroad tire.

That’s direct TPMS. I’m referring to indirect TPMS .


Sent from my iPhone using Tapatalk

 

[jamesroney]

That’s direct TPMS. I’m referring to indirect TPMS .


Sent from my iPhone using Tapatalk

This is good.

I am intrigued by the notion that the relative pulse width of the Wheel tone ring would be able to discern the tire pressure. That runs contrary to my initial statement that the inflation pressure was not proportional to the revolutions per mile.

To be more precise, I asserted that wheel hub height was not proportional to revolutions per mile. And I maintain that is true. But now I need to figure out if inflation pressure is proportional to revolutions per mile. I suspect that there is some level of pressure, hub height, and tire design where the revolutions per mile IS proportional...but I expect it to be a very small window and certainly not linear within the range of 0-50 psi tire pressures.

Given that a modern run-flat tire can maintain a relatively normal revolutions per mile with zero pressure, I am skeptical of the indirect TPMS validity. I think we are going to find out that the guy that applied for the patent for indirect TPMS via differential Wheel Speed Sensor, developed the principle of operation withing the paradigm that a tire is a balloon, and pressure was proportional to revolutions per mile. And I expect that we will learn that the technology has not been adopted because it is inadequate. I find it somewhat coincidental, and more than a little humorous that your username is @Slowleak

 

[jamesroney]

I think the key assumption is that a tire is inelastic (maybe I missed that in a previous post), want to poke at that one a bit. Any material is elastic, even metal.

Perhaps radial tires due to their construction manifest stress induced deformation much less than bias plies? If so, that would corner out.

To answer @DirtDonk question, seems to me the easiest thing to do measure circumference of a tire at various pressues.

This and been enjoyable @jamesroney, thanks for the banter!

I only used elastic in the context of a casual user reading the post. If it were a group of Engineering students, I would have said "anisentropic incompressible solid" Of course the proper engineering definition of elasticity and permanent plastic deformation are not in scope as we discuss the mechanical characteristics of a steel and Kevlar reinforced radial tire carcass.

I do know that radial tire construction results in some very impressive hoop strength and I am often impressed at how a 35 series or 40 series tire can inflate and remain mostly square to the road. If a radial tire was a "balloon" it should crown with increasing pressure. I don't even know if you can make a bias ply tire in a 35 series?

Gotta be careful about measuring circumference. It's easy to measure when the tire is unconstrained. But as soon as you load it...the math gets crazy. I would say it is indeterminate using graphical or explicit equations. It might be able to be modeled in 3D. But I wouldn't want to do it. Normally I would give it to an Intern as an assignment. Being retired has some disadvantages.

But the empirical solution is the easy one. Just mark off 1320 feet at your local drag strip. Put a camera on your tire. count the number of rotations to achieve the distance. Change the pressure. Measure again. Then say: "wow, that's pretty cool."

Nice chatting with you. Are you an Engineer?

James Roney BSME, BSMgE, Six Sigma Black Belt. My LinkedIn profile is accurate.

 

[Yeller]

The indirect TPMS intrigues me as well. Just spit balling theory but a low tire has more resistance to rolling than a fully inflated one. I have measured the circumference radials at different pressures. I have gotten on some tires that had slightly more in the center versus the shoulder and others that the margin of error was well within the difference, most 1/8” in circumference, these were in changes from 10psi to 30psi.

1/8” in circumference could just be getting the tape crooked somewhere.

 

[ksagis]

@Slowleak, thanks for sharing about indirect TPMS, I wasn’t aware of it. Glad to see my engineering intuition may be okay!

@jamesroney, looks like from a quick literature review that several OEMs have actually implemented indirect TPMS so more than theory (as long as its actually working in the field). As expected, literature indicates its less accurate than direct TPMS. Yup, engineer by trade, wrench turner by passion Often get to comingle those which makes life even better.

Back to no dumb questions, what data feeds the annotation on our forum handles? May not be a Guru, but I’m better than a Newbie, as currently marked. Anybody know where that is set?

 

[Speedrdr]

@Slowleak, thanks for sharing about indirect TPMS, I wasn’t aware of it. Glad to see my engineering intuition may be okay!

@jamesroney, looks like from a quick literature review that several OEMs have actually implemented indirect TPMS so more than theory (as long as its actually working in the field). As expected, literature indicates its less accurate than direct TPMS. Yup, engineer by trade, wrench turner by passion Often get to comingle those which makes life even better.

Back to no dumb questions, what data feeds the annotation on our forum handles? May not be a Guru, but I’m better than a Newbie, as currently marked. Anybody know where that is set?

Don’t know what the # is, but it’s related to the # of posts made. I seem to remember in the usr profile a place where the “handle “ can be altered.

Randy

 

[Slowleak]

@Slowleak, thanks for sharing about indirect TPMS, I wasn’t aware of it. Glad to see my engineering intuition may be okay!

It has been used by a lot of manufacturers. BMW, Ford, GM, Honda, Mazda, Toyota…and others. Honda actually switched from direct to indirect and used it as recently as 2020, don’t know if they still do.
I’m not an engineer, I don’t know for sure how it works, I have owned several vehicles that used it, and everything I hear about it says it functions by measuring wheel speed. It’s limitations are that has to be recalibrated and cannot provide actual tire pressure. It can only indicate that a tire is low.

https://www.hondainfocenter.com/2018/Civic-Coupe/How-To-Videos/LX/Notable-Features/Indirect-TPMS/

 

[Speedrdr]

Go to the top line (just below the advertisers block) and click your avatar/screen name) and there’s a line called “account details” that you scroll down to “custom title” and put in what you want for a title.

Randy

 

[ksagis]

Go to the top line (just below the advertisers block) and click your avatar/screen name) and there’s a line called “account details” that you scroll down to “custom title” and put in what you want for a title.

Randy

Thanks!

 

[ksagis]

It has been used by a lot of manufacturers. BMW, Ford, GM, Honda, Mazda, Toyota…and others. Honda actually switched from direct to indirect and used it as recently as 2020, don’t know if they still do.
I’m not an engineer, I don’t know for sure how it works, I have owned several vehicles that used it, and everything I hear about it says it functions by measuring wheel speed. It’s limitations are that has to be recalibrated and cannot provide actual tire pressure. It can only indicate that a tire is low.

http://[URL]https://www.hondainfoce...-To-Videos/LX/Notable-Features/Indirect-TPMS/

[/URL]

Another limitation of the system is if all four tires are slowly losing air, it won’t know.

Regardless of some of the limitations, I love when you can repurpose data from one system for another one, and delete a part along with its failure point.

Good stuff, and seconding James’ comment on the irony of your forum handle as related to this topic!

 

[Slowleak]

Good stuff, and seconding James’ comment on the irony of your forum handle as related to this topic!

Yeah, I have seen way more than my share of leaky tires. I’m just glad we are not discussing urological issues.

 

[Speedrdr]

Yeah, I have seen way more than my share of leaky tires. I’m just glad we are not discussing urological issues.

Second that, @Slowleak! I’m having to retrain post surgery.

Randy

 

[jamesroney]

Back to no dumb questions, what data feeds the annotation on our forum handles? May not be a Guru, but I’m better than a Newbie, as currently marked. Anybody know where that is set?

The data set for your "newbie" designation is based solely on the number of posts. I once went in and deleted a bunch of posts, and returned my status to newbie.

The location data field is populated by the profile information that you enter when you originally sign up. About 2 years ago the site hosting was updated, and the location field data source was deleted. This is why you have no location listed under your Avatar.

 

[DirtDonk]

In the early days, some vehicles had the sensors only for the rear wheels. Sometimes they had them for all four.
Sometimes it was a tone ring in the differential, sometimes a tone ring out at the wheel/rotor, and sometimes, as was the case with my 2004 Buick, the sensors were in the wheel bearings.
Or unit bearings I should say.
Each one had a simple two or three wire connector, and other than that, the R&R procedure was the same as any other hub bearing.

Unlike a direct reading pressure sensor in the tire, these would only show a low or flat tire after you had driven for a little while and above a certain speed.
Probably the resolution of the things didn’t allow it to accurately sense at slow speeds or perhaps they were tuned that way, so as to not take into account the usual twists and turns of driving around the city.
In my case they actually worked pretty good a couple of times that I had low pressure.
Just glad I never started off with a flat tire!

 

[ba123]

Maybe, but switching the bucket seat mounts for the one's with 3 inches more legroom certainly does. I'm 6'-3" and appreciate the extra legroom.

These Tom’s seat seem to slide for days…anyone who needs more room might wanna check those out.

 

[Wild horse 75]

These Tom’s seat seem to slide for days…anyone who needs more room might wanna check those out.

Good to know. I was already looking at those seats and I know leg and gut room are going to be at a premium.

 

[NickC24]

Good to know. I was already looking at those seats and I know leg and gut room are going to be at a premium.

6'-2" here and I'm thinking I might install these.

https://www.agasooutdoor.com/parts-and-gear/p/driver-seat-extension-brackets