but higher tire pressure = less friction during from a stop and more coasting time!

just avoid the potholes and cracks, if you can't then just coast along with it at rather than still trying to cruise along with it. I'm sure with the tires only worrying about "rolling" rather than "pushing" through the bad road would reduce the risk of a blowout.

 

Terry

Thank you for wise (as ever) words. That is how I see it as well. There will have been several round table conferences in the Honda design lab arguing this very point. It will not have been decided on the whim of a single individual.

BTW. The current edition of Business Week on p.6 has a full page Honda advert for a design feature that I was unaware of, namely Advanced Compatibility Engineering (ACE) and it "comes standard on the all-new Civic". "It's a unique design that helps spread the energy of a frontal collision throughout the body. In the future ACE will become standard on many of our models as they evolve."

Another first and highly important but invisible reason for selecting the HCHII !!

Nigel

 

You guys have some CRAZY ideas about tires and their proper pressures, and how they react/wear/perform under different pressures, so much so that I e-mailed BOTH Bridgestone AND Dunlop about it. I will post their e-mail responses as soon as I get them....

 

There are government studies showing that from 15-35 PSI
pretty much everything gets better, a nice smooth curve in most cases.
Stopping distance (wet and dry), hydroplaning, wear, reduced chances of blowout,
and performance when half the tread is worn down all improve as PSI increases
through 35 PSI. So at least within those pressure ranges the claims we are making
are well established.

Here is one of the good studies:
http://www.nhtsa.dot.gov/cars/rules/...FEA/TPMS3.html
It quotes the Goodyear data that people will often refer to.

What we don't have is solid data going past 35 PSI. The anecdotal
evidence in these groups tends to suggest that the handling curve
levels out and begins to fall off slightly at some point (stopping distances increase
by a few percent as you approach 50 PSI). What is significant about that
is that a large falloff in traction is not evident (there is a prevailing myth
about this).

Hydroplaning is different, it will decrease with PSI period, although diminishing
returns may occur. I can testify that I never drove a car that resisted hydroplaning
like mine did at 48 PSI but without a solid study to back that up it is just heresay.

So in all honesty, 35-40 psi is probably the best all around pressure
given the data we have. If you want to go for mpg and/or really hate
hydroplaning (and don't mind a stiffer ride), a little higher is not unreasonable.

Frankly, rain performance has always been my first concern for a tire's
handling, most tires are ok on dry, it is the wet that you care about.
That alone is enough for me to go to 40 PSI, but I admit we don't have
solid proof of benefits beyond that level.

It will be interesting to see if the tire manufacturers are willing to share
anything new.

The pessimist in me is expecting a pre-recorded lecture along the lines of
"inflate to manufacturers recommended pressures".

In the case of manufacturer recommendations under 35 PSI,
we at least have the NHTSA to back us up when we say please
inflate to at least 35 PSI.

 

Hi guys; I have been trying to drive for maximum FE since 1980. I have put more than 1.3 million miles on a Rabbit Diesel, Honda CRX HF, and 3 Insights. Tires have been a special interest. Learning all about tire sizes, compounds, pressures. Here is what I know: The owners manual recommends a certain pressure, intended for a fairly soft, cushy ride for the majority of people. The car manufacturer does NOT want complaints about the ride being rough. Higher pressure greatly increases FE; you must think of it this way: 10 extra lbs each tire, x 4 tires, that is 40 lbs of air. That makes a huge difference in rolling resistance! So I tell people to read closely on the sidewall, and inflate tires to the stated maximum. Yes, there is a large safety margin above that, but also serious liability issues. No tire store will ever tell you to inflate them above the maximum. So, if you dont mind feeling the bumps more, put more air in your tires, and enjoy the fuel savings! Billy............

 

I hope you're not thinking there is an extra 40 pounds of air in the tires. When we talk about lbs in this context we're talking about pressure. It's lbs per square inch. The total weight of the air inside a tire is probably less than one pound.

The reason a tire has less rolling resistance when we inflate it more is that it keeps its round shape more. It has a smaller footprint on the road. Imagine rolling two objects on a road. One is a steel drum. The other is a sack of corn. The drum would be much easier to roll because it stays round. The sack flattens at the bottom and hugs the road, and is thus very hard to roll.

 

Most smaller cars today use "P" series radials. Radial tires are very sensitive to proper inflation. Underinflated radials run hot and wear prematurely. Overinflated, they can cause unstable handling and will wear only along the center circumference. Ideally, P series should be operated at their rated pressures year around. However, because most of these tires have a relatively small air capacity, changes in outdoor temperatures can create tire pressure changes that could exceed the rated capacity very quickly (in hot weather). Therefore, 40 psi is a good number (assuming a rating of 44), which allows the radial to run cool, yet has some capacity to absorb rising temperatures. As a rule of thumb, every 10 degrees F in temperature will cause a 2-3 psi change in tire pressures (increasing as temperatures go up, and decreasing as they go down).

 

According to this link it's more like 26 grams of mass, or about 13 grams of weight. There's 28.3 grams in an ounce, so the mass of air in a tire is closer to 1 ounce actually.

 

Still waiting on those e-mail replies....thats good customer service for you....

In any case, I noticed something weird today: I went to go back down my tires from 50 PSI (the ride is just too rough, I can feel those little bumps) to 40 PSI, and I noticed that my back tires were down to about 44 PSI. I KNOW for a fact that I pressed them all up to 50 PSI at the same time. I thought maybe it was because the tire didn't have a valve cap, but only the left side didn't, the right side did....and they were still less than 50. The fronts were at 50 though....weird.

Anyway, I might have to agree with an earlier post that the rolling resistance seems to be SIGNIFICANTLY decreased when at high speeds. For many of you, that isn't that big of a deal. But for someone who's trying to stay at a minimum 60, max of 70 or 80 where allowed, it helps with the gas mileage. I want to see what kind of impact dropping 10 mpg's does to my rolling resistance. I just don't like the bumps. For 24K, I want a smoother ride, I'll give up the 1 or 2 mpg, I have 50 or so of them anyway....

 

Nigel,
If I remember it right, the ACE feature is discussed with photos in the HCH 2 buyer's brochure handed out by the Honda dealers. This also contributed to the car's rating as the only '06 Compact car given a "GOLD" rating by the Institute for Highway Safety (or something like that).
Regards,