The Donut In The Trunk

[RidingOnRailz]

Originally Posted by CapriRacer

Thanks for the clarification. A part of me wondered if you were asking me to compare a 40 year old tire to a 10 year old tires - and
that was going to be difficult! Im glad its current tires.

OK, on to the question. What's different? Actually not much.

First, the steel belt consists of 2 layers of rubber coated steel wire, with the wires running parallel to each other in each layer.
If you were to look through the 2 layers, it would look like a cross hatch pattern.

But those are the same to each tire, the only difference is that the wider tire has wider belts - and within each tire, the belts are the same
underneath the treadface, except for the ends - meaning the strength of the belts are the same throughout either tire except at the ends -
no difference.

But there is a difference in that the wider tire has wider belts so each individual wire wraps further around the circumference of the tire.
I don't think that makes a difference in how the tire behaves, but it is a difference, but probably in the wrong direction for your theory.

So let's look at your assertion that lower profile tires get more pressure. According to Tire Guides, 2010 Honda Accord. It came with
P215/60R16 94H at 30 psi and P225/50R17 93V at 32 psi. If I do the math, the load carrying capacity of each is the same - which
would explain why there's a difference in specified pressure. But the Accord also came with P235/45R16 94V at 34 psi. That seems
to be the odd man out, but I note that Tire Guides says this was only for the EX-L Coupe V-6, and that for the 2011 and 2012 model
year, that same entry is listed as 32 psi. That's doubly odd. Can't tell what is going on there.

Maybe we could get some insight if we looked at the Civic. In 2010 it came with P195/65R15 89 S &H at 32 psi, P205/55R16 89H
at 32 psi, and P215/45R17 87V at 32 psi. Huh?

What about the Accord in 2013? 205/55R16 95H at 32/32, 215/55R17 94V at 33/33, 235/45R18at 33/32. That doesn't seem to
follow any pattern at all!

So I don't think your theory holds up.

For the wider tire, with wider belts, are the belts beefed up with additional 'windings', or strands of wires? In other words, are the belts scaled up in size along with the size of a given tire section?

IE: The size record-breaking Olympic Trio of ocean liners were originally designed with scaled up hull and deck plating in mind: Two inch thick steel hull plating, for example, in place of time-honored 1 inch steel plating. Ultimately, they were built with 1 inch, but I'm sure their framing was beefed up by some percentage over that of the Cunarders they were built to out-class.

Does such scaling up of interior elements of tires occur with tires of greater width, diameter, and overall size?

[CapriRacer]

Originally Posted by RidingOnRailz

For the wider tire, with wider belts, are the belts beefed up with additional 'windings', or strands of wires? In other words, are the belts scaled up in size along with the size of a given tire section? .....

No.

While this is something I've wondered about - that is, why doesn't this happen - manufacturing complexity is the reason. There has to be a certain level of standardization within the plant for the plant to remain efficient.

Originally Posted by RidingOnRailz

.....IE: The size record-breaking Olympic Trio of ocean liners were originally designed with scaled up hull and deck plating in mind: Two inch thick steel hull plating, for example, in place of time-honored 1 inch steel plating. Ultimately, they were built with 1 inch, but I'm sure their framing was beefed up by some percentage over that of the Cunarders they were built to out-class.

Does such scaling up of interior elements of tires occur with tires of greater width, diameter, and overall size?

There is a certain amount of scaling up just due to the bigger dimensions - that is, wider tires have wider belts and that means more wires across the tread width. Larger diameter tires obviously get more belt material.

But also consider that the purpose of the belt is stiffness, not strength. It's sort of like how they size the smoke stacks on a cruise ship so they look in proportion to the size of the ship and not because they need to be bigger.

[RidingOnRailz]

Originally Posted by CapriRacer

No.

While this is something I've wondered about - that is, why doesn't this happen - manufacturing complexity is the reason.
There has to be a certain level of standardization within the plant for the plant to remain efficient.



There is a certain amount of scaling up just due to the bigger dimensions - that is, wider tires have wider belts and that
means more wires across the tread width. Larger diameter tires obviously get more belt material.

But also consider that the purpose of the belt is stiffness, not strength. It's sort of like how they size the smoke stacks
on a cruise ship so they look in proportion to the size of the ship and not because they need to be bigger.

So in theory, if I divide my heavier gross axle weight of the two in half, and find out that my tire size and load designation satisfies that capacity at a lower pressure, IE, in my case 30psi instead of 32, can I run my Accord's wider, lower profile tires at that?


Your analogy of the tire belts and ocean liner(by the way!) smoke stacks is not exactly correct. Scaling up the radial tire belts is being done for a physical property. Scaling up the funnels on the liner was done for looks. Two different goals.

[CapriRacer]

Originally Posted by RidingOnRailz

So in theory, if I divide my heavier gross axle weight of the two in half, and find out that my tire size and load designation satisfies that capacity at a lower pressure, IE, in my case 30psi instead of 32, can I run my Accord's wider, lower profile tires at that? .......

You and I have had this discussion before.

The spring rate of a tire varies according to the inflation pressure. Vehicle engineers set the springs, shocks and sway bars at the target inflation pressure, so following the vehicle tire placard is the correct way to do this.

[RidingOnRailz]

Originally Posted by CapriRacer

You and I have had this discussion before.

The spring rate of a tire varies according to the
inflation pressure. Vehicle engineers set the springs,
shocks and sway bars at the target inflation pressure,
so following the vehicle tire placard is the
correct way to do this.

This should be on a placque on every garage wall - and on its own page in the drivers/owners manual!

Thank you - point well taken!

Now how do I get all the naysayers and know-it-alls - even those with 'ASE' embroidered on their shirt - on board?

[CapriRacer]

Originally Posted by RidingOnRailz

This should be on a placque on every garage wall - and on its own page in the drivers/owners manual!

Thank you - point well taken!

Now how do I get all the naysayers and know-it-alls - even those with 'ASE' embroidered on their shirt - on board?

I have taken to certain tactics:

1) Repeating it whenever I get a chance. I always include the explanation as well as the advice.

2) Recognize that some folks are resistant to new information. I had a friend who called this "First Learnings" - that is the first time some folks hear some bit of information, is the last time they learn.

3) Also recognize that some people (and in this case, I mean you) aren't going to be able to pass on this information successfully. Not because of any personal flaw, but because the recipient isn't going to be receptive of information from certain sources.

[RidingOnRailz]

Originally Posted by CapriRacer

I have taken to certain tactics:

1) Repeating it whenever I get a chance. I always include the explanation as well as the advice.

2) Recognize that some folks are resistant to new information. I had a friend who called this "First Learnings" -
that is the first time some folks hear some bit of information, is the last time they learn.

3) Also recognize that some people (and in this case, I mean you) aren't going to be able to pass on this information
successfully. Not because of any personal flaw, but because the recipient isn't going to be receptive of information
from certain sources.

Well, I use the following art analogy:

The tire is the 'canvas' and the vehicle is the 'art form'

IE: You have a 51" or 44" canvas to paint on, but that doesn't mean you have to use every square inch of that surface for your painting. That 51" is just the maximum dimension of that canvas.

They sort of get where I'm going, after that explanation.


This question popped into my mind while I was typing that:

On vehicles where there is a tire pressure split/offset of the recommended cold pressures: Front=34, Rear=40, for instance.

How does a car's TPMS and other body control systems reconcile that difference?

I'm sure the axle with the lower pressure will accumulate several dozen more revolutions per mile.

[CapriRacer]

Originally Posted by RidingOnRailz

........ This question popped into my mind while I was typing that:

On vehicles where there is a tire pressure split/offset of the recommended cold pressures: Front=34, Rear=40, for instance.

How does a car's TPMS and other body control systems reconcile that difference?

I'm sure the axle with the lower pressure will accumulate several dozen more revolutions per mile.

First, the revs per mile statement:

RPM is a function of inflation pressure AND load. On a tire with a light load, the rpm's will lower.

Plus, on ABS based braking systems, the computer notices the DIFFERENCE in revs. I am sure computers can be programmed to ignore steady, but different RPM's.

But ABS systems is not my area of expertise, so what I just said is a guess.

[RidingOnRailz]

Originally Posted by CapriRacer

First, the revs per mile statement:

RPM is a function of inflation pressure AND load. On a tire with a light load, the rpm's will lower.

Plus, on ABS based braking systems, the computer notices the DIFFERENCE in revs. I am sure computers
can be programmed to ignore steady, but different RPM's.

But ABS systems is not my area of expertise, so what I just said is a guess.

So for vehicles that do recommend disparate front and rear cold tire pressures, this has(in theory at least) been accounted for by the engineers, with regards to sensors, TPMS, transmission ratios(in AWD cars), etc.?

Several 9th generation(2013-17) Accord trims specified, IE, 33 Front 32 Rear cold. That also was accounted for during design of those machines?

[CapriRacer]

Originally Posted by RidingOnRailz

So for vehicles that do recommend disparate front and rear cold tire pressures, this has(in theory at least) been accounted for by the engineers, with regards to sensors, TPMS, transmission ratios(in AWD cars), etc.?

Several 9th generation(2013-17) Accord trims specified, IE, 33 Front 32 Rear cold. That also was accounted for during design of those machines?

Vehicle engineers are responsible for the entire package as presented - and that includes the tire inflation pressures specified on the vehicle tire placard. If it doesn't work, THEY are responsible - and if that leads to a recall, then that's what it does. The engineers - in the form of the manufacturing company - are responsible for addressing anything recallable.

That made for an interesting dynamic in the Ford/Firestone situation. While The tire manufacturer was responsible for the issue, the fact that the vehicle manufacturer approved that tire for their vehicle pot the vehicle manufacturer in an interesting position. Eventually, Ford recalled those tires - and I can't remember how they did it without issuing an official (as in recorded by the Federal government) recall notice. I suppose I could look it up and figure it out, but I know the situation was complex.

[RidingOnRailz]

Originally Posted by CapriRacer

Vehicle engineers are responsible for the entire package as presented - and that includes the tire inflation pressures
specified on the vehicle tire placard. If it doesn't work, THEY are responsible - and if that leads to a recall, then that's
what it does. The engineers - in the form of the manufacturing company - are responsible for addressing anything
recallable.

That made for an interesting dynamic in the Ford/Firestone situation. While The tire manufacturer was responsible
for the issue, the fact that the vehicle manufacturer approved that tire for their vehicle pot the vehicle manufacturer
in an interesting position. Eventually, Ford recalled those tires - and I can't remember how they did it without
issuing an official (as in recorded by the Federal government) recall notice. I suppose I could look it up and figure
it out, but I know the situation was complex.

Along this pattern of thought:

Some vehicles' TPMS systems use a rudimentary RPM(iles)-based system of monitoring, where if one tire's pressure drops enough to increase it's revs-per-mile/km indication by enough of a difference from the other three, it will trigger a light on the drivers instrument panel.

My 2010 Accord might be one such vehicle. So if I do experiment with different front/rear tire pressures, enough of a difference could trigger such a light on my dash - albeit inadvertantly! Best for me to keep them all evenly inflated, if that's what's on the door placard and in the manual.

On vehicles where a different front/rear axle pressure is specified, Barry, I would assume the TPMS system(which ever type is used) is factory calibrated to account for the difference in rolling revs-per-mile caused by a two - or more - psi inflation offset between rear and front axles.will

More sophisticated RF(radio frequency) TPMS units transmit the actual PSI/kPa/Bar to the BCM(body control) or whatevever receptacle receives this info. If any/all tires are more than below a specified threshold, IE: 75% of door-placard pressure, regardless of differencs in specified front/rear pressures, an indication will occur for those tires - the excessive low pressures on each tire on the dash may be displayed in amber or red, for instance, instead of normal color.