Thread: For Don Shilady

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34-40 The driving tests are fun but I hate to give up the 16.2 mpg with many more tire tests. My son and I are taking a lot of photos of both side rear tires in a large parking space at a nearby mall. I'll show just three photos that indicate 30 psi rear and 32 front is not far off for the weight of my car and the tire size. We see that with 30 psi on the rear the three middle ridges wear off the most but after a full run across the parking lot of about 250 feet the line is worn off all across the tire. I'll try 25 rear with 30 front next because the steering was easier with higher pressure in the front and a bit of work when I tried the front pressure down at 20 psi; especially on my gravel driveway. I'll humor Jerry in deference to his expertise but I expect that 25 psi in the rear will be too fat and I will end up with something like 28 rear and 30 front. Since the ride is pretty harsh anyway I will favor better mpg. For some reason when I select the photo option my list of old photos is full and was not cleared out after one hour as the page says. I will go out and have some more fun but I need to have my photo gallery cleared out before I can send any new pictures.

Don Shillady
Retired Scientist/teen rodder

Originally Posted by Don Shillady

Since the ride is pretty harsh anyway I will favor better mpg....

..... and accept faster tire wear and reduced performance.

First to answer Dave take a look at the specs for a much better streamlined
1977 Z28 Camaro which has a similar driveline to my roadster:

1977 Camaro data - Statistics, facts, decoding, figures & reference information

Even the better streamlined body of the Z28 only got 17 mpg on the highway.

Next to answer Roger I did the chalk line test again with 28 psi in the rear and 30 psi in the front. This time I used only 3.704 gallons on the usual 63 mile circuit to and from Bowling Green VA. (63 miles/3.704 gal) = 17.00864 mpg! I guess that is all I can expect since the better streamlined Z28 body only got 17 mpg with a similar driveline to my SBC 350, 700R4 and 3.55 rear gear so I plan to keep using the 30/28 tire pressures from now on. I note the ride is better at 55 mph and keeping the speed at or below 60 mph probably helps increase the mpg as well as the improved tire pressures.

Can anyone please tell me how to flush the 20 pictures I have accumulated in "Manage Attachments"? At present I am unable to submit pictures since the buffer is limited to 20.

Don Shillady
Retired Scientist/teen rodder

Originally Posted by Don Shillady

First to answer Dave take a look at the specs for a much better streamlined
1977 Z28 Camaro which has a similar driveline to my roadster:

1977 Camaro data - Statistics, facts, decoding, figures & reference information

Even the better streamlined body of the Z28 only got 17 mpg on the highway.


Don Shillady
Retired Scientist/teen rodder

You can't compare apples to oranges, Don!! The '77 Z outweighed your roadster by at least 1,000 lbs, and was loaded with ineffective and poorly designed emissions equipment!!!!!

Don,
On the tire pressure discussion you continue to ignore the proven steps of driving a nominal 100' across pavement, checking the chalk line and adjusting tire pressure accordingly until the line scrubs evenly, showing an even contact patch. You state that you checked at about 100', saw the middle scrubbed clean with the outside still showing chalk, then drove to about 250' which scrubbed most of the line off at which point you assumed it was OK. NO!! You violated a basic instruction, and of course you're going to scrub off more chalk if you drive farther. The point is you're still riding on the center 1/3 of your tire. It's not rocket science, but it appears that you're in the paralysis by analysis mode evidenced by your continued comparisons to totally different vehicles for mileage comparisons, so I'll not mention it further. Enjoy the ride at 30 pounds, and we'll look forward to the post wondering why your tires wore out at 20,000 miles....

Originally Posted by Don Shillady

Can anyone please tell me how to flush the 20 pictures I have accumulated in "Manage Attachments"? At present I am unable to submit pictures since the buffer is limited to 20.
Don Shillady
Retired Scientist/teen rodder

I am not aware of any limit on the number of files that appear in the "Manage Attachments" "buffer". Mine shows thirty (30) pages with a total of 583 image files that I've attached at one time or another over the years, and I just uploaded another one this morning and attached it without problem. I've never seen any message telling me that I've exceeded a limit in the attachments area, only messages telling me that the file is too large.

Most of the time I get 12 to 15 mpg out of mine, and occasionally I get 17 mpg when cruising, which makes me more than happy.
But to be honest, I didn't get mine for the gas milage and I find it does considerably better when my fat foot isn't stuck to the floor.

.

Roger, just for the sake of conversation I will mention that the tires were marked and pictures were taken of the extent of scrub at 5,10,15,20,30,40 and 50 wheel revolutions. It is true that eventually the whole line was scrubbed and that 100 feet should be around 13.25 wheel revolutions (roughly). I admit the outer four ribs scrubbed first but I do not know why the innermost rib did not scrub at 20 revolutions except that the only available large surface we have access to is not totally flat. Since I could not submit pictures I gave a verbal account. Thanks for your suggestions I was not previously aware of this procedure but please don't take a fit if I don't do exactly what you envision when you are not here. See my next message to Dave. I am satisfied I am close to optimum and can break even with a 1977 Z28 for reasons given in the next message.

Since you are the only one to respond to my question about the picture limitation I can ask again if anyone knows how to delete the old pictures? I did get a memory address overflow on my PC after the 20th picture that leads me to think that the limitation is in my system and you say you have some 583 or more saved in your buffer file. Even so the question is how to delete the old pictures because obviously those pictures are not deleted after one hour!

Don Shillady
Retired Scientist/teen rodder

Dave in my comments above to Roger I have tried to carry out the chalk-line procedure as best I could with the only available surface as a semi-flat (one month old) black top parking lot at a nearby Mall. Maybe the mpg can still be improved further while reducing the tire wear to a minimum but I was really pleased to get 17 mpg today for two reasons. First, I was really upset when my first mpg test was barely 15 and LESS than the mpg obtained by the heavier Z28. However and second, 17 = 17 ! As a teacher of Physical Chemistry that means to me that the energy in 1 gallon of fuel could move the heavier Z28 17 miles (on average) against the inertia of the vehicle weight and whatever friction + air resistance there is. By comparison my roadster is of course lighter and less aerodynamic but evidently the results indicate that the total energy needed to move the Z28 17 miles is equal to the energy to move my roadster 17 miles against the forces opposing it. Breaking even is not much of a victory but it was terrible when the roadster got LESS mpg than the heavier Z28! Thus I am pleased that I can at least break even. Since I do not have a roll bar it is unlikely I can get an official 1/4 mile comparison to what was a rather mediocre time for the Z28 at a little over 16 seconds but perhaps I will be able to record my own 0-60 time which just might be quicker than for the Z28 due to the light weight of the roadster. Even so, my training leads me to consider balancing the energy in one gallon of fuel as the break even point. My comparison to the 1977 Z28 is due to my engine being a 1976 Corvette and the old GM claim that the Z28 had a Corvette engine and the fact that I used Z28 specs to emulate the Z28, especially the cam.

Don Shillady
Retired Scientist/teen rodder

36 Sedan and 34-40, I agree that the over view of a hot rod is to use a more powerful engine than the stock version and apparently that has a price in terms of the amount of fuel needed. I had dreams of 20 mpg based on the idea of the 700R4 overdrive gear but apparently you still have to feed the baby! I was impressed that my little 4 cyl Pontiac Sunfire gets almost exactly twice the mpg of the SBC V8 which is close to the ratio of the engine displacements. Anyway 36sedan put it clearly that the mpg of the larger more modern engines produce more power but burn more fuel and if we want more power we should not be surprised that mpg is lower. The lesson for me is that over 55 mph my "flying brick" will require more fuel to overcome the increasing air resistance. 36sedan congratulations for saying it so well in so few words!

Don Shillady
Retired Scientist/teen rodder

Just to keep in touch I note that in the last two weeks our family 2008 Impala has twice signaled low tires via the dash digital readout. Checking the pressure showed the first case had a pressure of about 14 psi and again today another tire registered 19 psi compared to the recommended 30 psi. I say this in view of the discussion above about tire pressure. It occurred to me that the temperature dropped from mid 70s last week to 40 F when I checked the latest low pressure. Let's convert those temperatures so we can use the Charles-Gay Lussac pressure equation to estimate the pressure change due to seasons.

75 F = 23.89 C = 297.03 Kelvin, approximately 297 K
40 F = 4.44 C = 277.59 Kelvin, approximately 278 K
Temperature difference Difference = 19 K

The Ideal Gas Law is generally good up to about 10 atmospheres (147 psi) so we can use

(P1)(V1)/T1 = (P2)(V2)/T2

and if we assume that the volume of the interior of the tire remains essentially the same we can cancel V1 = V2 and use (P1/T1)=(P2/T2). Thus if the pressure was 28 psi at 75 F we can calculate the pressure at 40 F as P2 = P1(T2/T1) so we find

Pressure at 40 F = (28 psi)(278 K/297 K) = 26.2 F for a difference of about 1.8 psi

The same sort of reasoning applies for the case of tires heating up upon use. Of course in a race situation small corrections are made for air temperature as well as altitude above sea level so in that case a car would be set up right at the time of the race. Now add to that the common experience of slow leakage of tubeless tires on older rims and it is my claim that unless I set the pressure of my tires exactly every day for the ambient conditions I can easily see a variation of +/- 1 psi at least and in particular the tendency without inner tubes will be to go to lower pressure when starting out cold and then an increase in pressure during the run of the trip. Thus I think I will still start out at 28 psi and allow for tubeless tire leakage and compensation for increasing psi during travel. Perhaps a future investment of inner tubes could reduce this variation but for now if I am within a degree F or two the exact psi value will mush out due to temperature variations. In the case of our 2008 Impala I think the larger effect is probably due to old rims because the tires are less than a year old while for my roadster the rims are circa 2005 so the same slow leakage is probably occurring. Even if I get inner tubes for both cars we see that the temperature variation will make an accurate pressure setting no better than to about 2 psi.

Now to another important topic, I have not received any suggestions as to how to reduce the size of the temporary file with pictures I have previous put on this forum. The posting procedure says they will be deleted after a short time but maybe the problem is that I am running out of memory on my laptop? If so I should delete some of the 25 that are on there now but how to do it??

Don Shillady
Retired Scientist/teen rodder

Aaaah, english translation, colder temperatures = lower pressures...............

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Originally Posted by Don Shillady

Now to another important topic, I have not received any suggestions as to how to reduce the size of the temporary file with pictures I have previous put on this forum.

Go to your settings at the top of the this page, scroll down to attachments, check the box at the right side of the attachment(s) you want to delete, scroll down to the bottom of the page and on the right side hit delete selected.

The posting procedure says they will be deleted after a short time

I believe you have confused this, I believe it says if the attachment is NOT used it will be deleted after 30 minutes.

Don Shillady
Retired Scientist/teen rodder

However, I believe you maybe right, it may be your laptop giving you trouble.

.

Glad to hear you're happy! Keep an eye on the tire wear and drive the heck out of it!

I drive the heck out of mine, it's what makes me happy. Most of the time I can afford a little extra gas, happiness, well that's priceless!

Gotta go, gas pedal is beckoning.

.

You've got leaks. You can expect 1 to 2psig drop for each 10F drop in temperature, or between 3 a 6 psig for your 32F delta - Goodyear Corporate | Newsroom | News Releases | As Temperature Drops, So Does Tire Inflation

As far as re-sizing pictures.. a lot of computers come with the software already loaded that'll re-size most any picture.

I use the one that comes with Microsoft Office.. but you can do it with the "Paint" program also, even the program that I have for the printer can change picture size and shape.

But there are free programs available also, just google / Bing "picture resize software"...