Thread: For Don Shilady

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Tire pressure might help a bit Don, but you've got to remember that the car is about as aerodynamic as a barn door!!!!! Unless it's going through the air smoothly, which a 20's and 30's car (with a few exceptions) were designed as a low speed rig, and aero was never a concern......

Don,
Just to be sure that you understand, the chalk process is not to see the pattern on the floor, but to see what's left on the tire after driving a short distance. Your floor pattern really doesn't tell you anything. For the process, a large parking lot on a Sunday when the store is closed, or a big church parking lot during the week work well, and you'll likely need an air "bubble" tank to add air during the process. With the tires warmed up, check your pressure with an accurate gauge for a reference point - I only use a digital gauge that has 0.5 psig resolution. The old mechanical gauges are useless for this - not repeatable, and not accurate enough. Draw a chalk line across the tread, not necessary to "paint" the tire, a 1/2" wide line is good, side to side across the tire. Drive about 100' or so and stop, check the line and see what part is scrubbed clean. If the center is gone but the edges remain you're over inflated, and would let out 1/2 pound of air and try again. Repeat the process until the nominal 100' drive scrubs the chalk clean, or leaves an even pattern across the tire. If you're lucky you'll hit it without going too low, where the outer edges are cleaner but the center has more chalk remaining. I'd bet a cookie that your 30psig is still at least five pounds too high.

let it down 5 lbs at a time til too much then reverse and add a set amount ( 2 or 3 lbs) til too fat that way and then reverse with smaller increment---should be able to do it in 4 trys-----called bracketing in artillery

I used the 'chalk trick' to get the optimum tyre pressures for the Cobra.
Finished up at 22 psi for the front, and 18 psi for the rear.
With the pressures set by this method handling improved markedly.

Thanks for the pics Don! Best part of your write up... you were having fun!

Keep playing with the tire pressures to find the best balance between ride / economy / handling.

But most important, keep having fun!

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

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.

.

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