Hello all,
Here is an e mail from Brian Savage to the Land Speed mailing list in 2002. I asked Tom Burkland if it was OK to post it here. Especialy note the part about bead strength.
Jim,
The data contained in this response to Brian from back in 2002
is still accurate. All of our tire testing information from the very
beginning of our program all the way back into the late '80s has been
available to anyone that wants data. There may be some new input from
Goodyear now that they have the "high speed" front runners in addition
to the land speed eagles mentioned in my note. The physics and load
distribution in high speed tires still works the same as it did then.
Feel free to distribute the information across as much of the land speed
community as you can.
If you have any other specific questions on tires they can be
forwarded to me at this address and I'll try to answer them with what I
know.
See you at the salt.
Tom Burkland
From: Bryan A. Savage Jr <basavage@earthlink.net>
To: List Land Speed <land-speed@autox.team.net>
Subject: LSR tire information
Date: Saturday, September 07, 2002 1:29 AM
List,
I've asked Tom Burkland some questions about high speed tires. Tom
agreed with my request to put them on the Land speed List. I hope
you folks fund Tom's answer as educational as I did.
Bryan
My question:
If a given Goodyear is good for 300 MPH at 1700 pounds as a drive wheel,
what might be a safe speed on a non driven wheel (front) with only 250
pounds load?
Tom's reply:
You raise a good question as to the amount of speed rating increase
available through drive torque and load reduction on a given tire. This
is a similar line of thought to using F-16 main gear tires that were
originally rated at 250 MPH with almost 25,000 lbs per tire load. Even
with the tread rubber shaved off to reduce the centrifugal force on
the casing these tires > only went about 350 MPH with no applied load on
our spinning machine. The bottom line is that the centrifugal loads on
the casing far overshadow the drive torque loads and the weight. For
light casings such as the Goodyear or > M/T the weight may have a
slight influence as the casing deflection and resulting heat generation
are increased as the weights go up. Drive torque distributed over the
area of both side walls in the tire really does not add significantly
to the stresses seen by the casing (remember that LSR cars don't hit the
tire with inertia and the friction coefficients are roughly half of a good
drag strip). Since centrifugal loads are the driving design factors in
these tires it is obvious that high strength-to-weight materials and
thin tread rubber are essential to a good high speed tire design. Just
making the tire stronger does not necessarily help the speed rating
(the F-16 tire referenced above was a 20 ply casing with two bead wires
and a tread belt reinforcement) unless the strength is achieved without
adding too much additional weight. All of the material in the tire
produces centrifugal loads that are applied to the load path (tread belt,
if used, to the casing cord then on to the bead wire in hoop tension).
These high speed tires need to reduce the load generated by limiting
tread thickness and casing weight while increasing the strength of the
load bearing portions of the tire.
The Front Runner tires, in my opinion, have way too much tread rubber
thickness > with all of the break-on-the-dotted-line patterns molded in
and the casings are not strong enough for real high speed use. We have
run some of them in free spin conditions on our spinner in the 325 MPH
range, so the best case answer to your question would be at zero load and
drive torque the speed rating would raise to 325. The casing construction
is also not concentric enough to allow the excess rubber to be shaved
off safely without cutting into the cord structure.
Hope this helps you. Let me know if there is anything else you need.
Tom Burkland
--------------------------
Bryan's note:
That's 325 MPH at ->ZERO LOAD<- !!!
--------------------------
My question:
I've tried to convince folks for a long time to use dry nitrogen
instead of air in LSR tires to reduce aging. No one's been interested.
Am I wrong?
Tom's reply:
All of our spin testing and racing applications use only nitrogen
inflation. We have even gone so far as to spin one of the early M/T tires
back-to-back with shop air, nitrogen, and helium. The theory was that the
inflation gas being lighter would put less centrifugal load on the tire
casing and produce less diameter growth since the casing stiffness was
constant throughout the test. We were unable to measure a difference in the
tire response or diameter at speed except to note that the helium is very
difficult to keep inside of any container (leakage rates are about five
times the other gases). This result was not entirely surprising considering
that the weight of the total inflation charge was only decreased by a few
ounces (roughly equivalent to 0.005 inches of tread wear over the outside
diameter of the tire). One of the other side benefits of the nitrogen
inflation is its thermal coefficients are significantly lower than shop air
so the tire pressures do not vary as much with temperature changes (ambient
and operational). The lack of moisture and the ozone component of shop air
will increase tire life as you mention. Keep trying to convince all of your
high speed friends, they deserve the benefit of your wise advice.
Let me know if there are any other ideas I can help you with.
Tom Burkland
Gene Burkland chimes in;
Wes:
We never had anything to do with Mickey Thompson's 5-year plan or the
speed rating that they put on their tires.
The thing we did for them was to spin each of the 5 sizes they produce and
record the growth amounts at various rpms from 3,500 to 8,500. These were
all no-load, free spins. We were most interested in the growth of the
tires, as weight is not a problem in our car (1,000 lbs. to 1,100 lbs. per
wheel).
Marv Rifkin (of M&H Tire Co., who actually built the tires for M/T) told
us early on that if we spun the tires fast enough their growth would lift
the Empire State Building. He didn't believe it was possible to build a
ground plane or other surface that would stop tire growth.
In the end, our tests showed that bead wires were the key factor in
holding a high-speed tire together. The aircraft tire we originally
designed our car around had 20 plies and actually self-destructed because of
the weight of those plies. The M/T tire we are now running has 4 plies and
a 7x7 bead wire -- and we have spin-tested it up to 700+mph.
I'm not sure this answers the questions posed, but might be interesting to
someone out there.
See you at the salt!
Gene
