I'm thinking I will take a middle ground approach and pump them up to 40...

 

That's as good a plan as any......just another good thing about America: no one can force you to run your air at 58 PSI !!!

 

Hi ElanC:

___Please do not assume so much … High pressures can shorten your stopping distances … It will be up to you to find out of this is the same in your car or not? Here is one of those great older threads that you might be interested in?

Tire pressure does effect MPG - How much is too much?

___Make sure you read the GY based - real world data on page 2 - post 2 of the thread in particular

___NASAginner, don’t saddle your HCH-II with snow boots when she wants running shoes for the run of a lifetime …

___Good Luck

___Wayne R. Gerdes

 

I'm not assuming much at all. I just pointed out what was initially my gut feel, which I found in a quick Google search was supported by others. That is, your braking distance may be reduced by over-inflation. I don't know how much it's reduced. All I know is I would inflate exactly to the ideal pressure for braking distance, if I knew what it was, and let FE be what it may.

The GY numbers you graciously provided, which I also saw in my Google search, address the issue of under-inflation. Under-inflation is bad from practically every aspect. I haven't found any hard numbers for braking distance as a function of pressure in the over-inflation range.

And there's no way I can find the optimal inflation for braking distance myself. An emergency stop is rare in real life driving situations. I'm not going to take my vehicle through a series of measured emergency stops from high speed, at various inflation pressures, surfaces, and temperatures, to find out for myself.

Following this discussion I actually went out and inflated the tires on my Accord to 3 lbs above the recommended pressure. I'd love to make a more informed decision on inflation, for maxiumum safety not maximum FE. Do you know of any way to make such a decision?

 

Hi ElanC:

___Here was your assumption:
___The GY study was done at max sidewall of 35 #’s on those particular tires. Max sidewall gave a shorter stopping distance in 16 of 18 dry/wet/differing wear tests on two different automobiles and usually by a significant margin!

#############################

Dry Macadam Surface
(Stopping Distance in Feet)

2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi
Full Depth Tread with ABS_________75.5____76.2____75.8
1/2 Depth Tread with ABS__________69.9____68.1____66.3
Full Depth Tread without ABS______98.3____95.9____91.6

1997 Ford Ranger
Full Depth Tread with ABS_________80.8____78.2____77.6
1/2 Depth Tread with ABS__________79.0____74.8____71.4
Full Depth Tread without ABS______97.8____96.5____94.1

#############################

0.02 Inch Wet Macadam Surface
(Stopping Distance in Feet)

2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi
Full Depth Tread with ABS_________79.8____78.5____77.1
1/2 Depth Tread with ABS__________84.7____73.7____81.4
Full Depth Tread without ABS_____111.1___110.2___108.6

1997 Ford Ranger
Full Depth Tread with ABS_________83.8____81.5____79.8
1/2 Depth Tread with ABS__________91.5____89.4____84.6
Full Depth Tread without ABS_____131.9___126.0___118.4

#############################

0.05 Inch Wet Macadam Surface
(Stopping Distance in Feet)

2001 Dodge Grand Caravan Sport__20 psi__28 psi__35 psi
Full Depth Tread with ABS_________80.0____81.1____82.7
1/2 Depth Tread with ABS_________103.7____99.7____92.2
Full Depth Tread without ABS_____118.0___112.2___111.7

1997 Ford Ranger
Full Depth Tread with ABS_________89.7____86.0____81.5
1/2 Depth Tread with ABS_________125.7___118.5___104.5
Full Depth Tread without ABS_____142.9___134.8___125.7

#############################

___Personally, do what you feel is absolutely safe for your own situation. With an HCH-I or II with their relatively low profile shoes, I would be running 55 #’s myself but that is just my own setup … For an all out Max FE segment or tank run, I would and have run 60 + #’s in the Insight. Look up the thread entitled “The Attempt” for more details … 50 + is only worth 2 - 3 mpg over and above 35 or so but to me, that extra amount of FE adds up pretty quickly over a years time …

___Good Luck

___Wayne R. Gerdes

 

Wayne, you'll be (somewhat) happy to know that I pumped up my tires to 40# today. I know it's not 55, but it's a start So far the handling doesn't seem to be any different, but I haven't had it on the freeway yet...

 

Hi NASAgineer:

___God Bless You!

___The bad part is that you will have to do all your experiments all over again And again at 44 #’s, and again at 50 #’s, and again with the Mobil1 0W-20 change out, and again at 5,000 miles, and again at 10,000 miles and … Yes, it is a continuously improving process

___How did the 80 mph in cruise test go today?

___Good Luck

___Wayne R. Gerdes

 

From a scientist's point of view, that's a good thing!

I was foiled by holiday traffic, so I wasn't able to maintain 80 for the whole trip. From the data I did get, I'm guessing that I would have gotten 41-42 if I had been able to hold 80.

After I got home, I reset the trip and went out again to try some P&G. I tried varying between 45-55 on the high side to 30-35 on the low side. Still only got 52 MPG after 15 miles It's the pulse phase that gets me every time. I can't seem to do better than 2-3 blocks (9-14 MPG) on the instant during accel, regardless of how gently I do it. So, while I can coast a ways at zero fuel flow, I eat up the gains on the pulse. Any ideas?

 

Hey,

Have any of you new '06 HCH owners tried neutral coasting yet? I'd like to know if neutral inhibits regeneration during off-throttle coasts, and will the ICE go into fuel-stop mode?

 

You can inhibit regen simply by using a bit of pressure on the throttle and still remain in zero fuel flow (valves sealed) mode, no need to go into neutral. See the rest of this thread for more details.