Betty and Gene
Bill: Betty & Gene, I've heard about your homemade tire spinner and this is a fascinating hot rod story. How did this come about?
Betty & Gene: Bill, we've been spinning tires since back in the '80s and it all comes out of the desire for SAFETY! We want to run fast at Bonneville and we DON'T want anybody to get hurt. Nor do we want to get our equipment torn up in a crash if we can help it.
(Tom Burkland comments: Tire failures at the speeds routinely achieved in land speed racing are definitely not a matter of pulling over to the side of the road and replacing the flat tire! The resulting vehicle damage from the decompression and dynamic disintegration of a tire at speed WILL be substantial. Then the driver is faced with bringing this damaged vehicle to a safe stop without all of the ground contact points and keeping it upright during the process.)
Tires have a lot to do with safety and we were okay with our competition coupes because we were operating in the speed range the Firestone tires of that era were designed for. The engineers of the tire companies are dead serious about their products and if they say they are rated for 300 mph, you can take it to the bank.
Now you know the classical tire spinner the tire companies use runs the tire at a certain speed, but it also applies a certain load to the tire at the same time to simulate the weight it carries on the car or truck.
We talked to many tire company engineers at the 1992 Specialty Equipment Manufacturers Association show in Las Vegas when we were looking for tires for our streamliner, as we'll detail later. We were rebuffed by all of them, EXCEPT Gene McMannis of Mickey Thompson. We had long conversations on the phone with Marv Rifchin of M&H , who had tremendous experience with racing tires. He's gone now, but you can look him up on the Internet at http://www.nhra.com/blog/nhra-notebook/2009/6/3/mh-tire-founder-marv-rifchin-dies/ . Marv said the load on the tire from the car weight was a negligible factor and could be disregarded at the high speeds being run. The centrifugal load on the tire spinning at high rpm on a car over 300 was the overwhelming factor in whether it would hold up or not..
Well, we were glad to hear this because we could build our own tire spinner without too much trouble, but there was no practical way for us to add a load to it as well.
It doesn't really take that much power to spin a tire on a shaft at any rpm you want. Our first spinner was powered with a snowmobile engine.
Okay, back to the mid '80s, our team decided to build our streamliner and we were still running our Datsun. We were looking for streamliner speeds up to at least 450 mph, and there's no use whatsoever in starting to design and build your car (or a motorcycle streamliner) unless you KNOW that proven tires are available. This is no place for trial and error, the stakes are too high!
First thing we said is, what wheels and tires can we use? We looked around, and saw that the F-16 Air Force fighter plane had some small wheels and tires with a very high speed and load rating, and these were available in the aircraft salvage industry.
But let's back up a minute to say that in the design of our streamliner, Tom started with the basic fundamentals of aircraft fuselage design from his engineering training. Frontal aspect is the first consideration, since that has so much to do with the air drag of the body irregardless how slick the shape is. And the drag increases as the square of the speed. At 400 mph each additional square inch needs around 45 more horsepower to push it through the air.
In our case, this meant the frontal aspect had to be big enough to contain the complete blown Donovan, and besides that as little as possible extra. Meaning the smallest practical tires and wheels that would work. The Donovan is 34" high and 33-1/2" across the heads, and the body was designed to fit as tightly as possible around that, plus the smallest air intake scoop on top that would do the job. As it ended up, the Donovan heads only clear the body panels by 1/4 inch.
The size of the Donovan did have an extra advantage for us, however, since it allowed a fairly comfortable position for the driver, in fact he is only reclined in the rollcage about 15 degrees from vertical. This helps his ergonomics, control and confidence quite a bit compared with a lie-flat position. And Tom is six feet and 210 pounds, not a small man.
But as you can see from the frontal photos of the streamliner, the front tires are as small as possible on the car, and 24" between the tread centers. The rear ones involve even less air drag since they are only at 13" between the tread centers with the "tricycle configuration", and buried in the body. Needless to say, the wheel wells have to be large enough to allow for tire growth at speed. The MT tires we used on the streamliner grew a total of 2-1/2" and we allowed 1-1/4" clearance in the wheel wells for that.
Okay, back to the F-16 tires. These are about the same size as the Mickey Thompson 24.5 x 7.50 x 16 tires we ended up with as we will tell you later.
We started off before doing any detail design and long before cutting any metal on the streamliner by getting two of these F-16 wheels and tires and testing them on our tire spinner. The tread rubber thickness was shaved down to minimum levels and the inflation pressures adjusted for the much lighter axle weights of the car before running them right up to 500 mph and they were just fine. No failures whatsoever. So we thought, "Great, end of tire problem, we can use these when we get ready to run the streamliner."
As a quick description of the streamliner design and build process, Tom started out with computer modeling for the body shape, the way all aircraft are designed now. Came up with something that seemed right, and the next step was that he built a 1/8 scale model of wood and had a friend test it in the wind tunnel of a famous aircraft company, using means to simulate the ground effect, since running at high speed over the surface is a different situation than that of a plane in the air.
The model passed its tests with flying colors, showing the downforce you wanted and that the center of pressure behind the center of gravity would give desirable steering into a crosswind, and the very important characteristic that if some unthinkable bump on the course made the car jump six inches into the air, it would still never blow over. Part of his design criteria was for the body to be stable in the air without the need for any vertical stabilizer, as it later proved to be at Bonneville. Tom will describe everything about the design and engineering of the car later on in this story.
At this point Tom sat down at his drafting board where he spent some 1200-1500 hours designing each and every component
for the chassis, powertrain, and body panels to start construction. Next, we all set to work to build the car. Near the time it was almost finished, we sourced 12 more F-16 wheels and 30 tires in a Houston aircraft salvage yard. History unknown, but a couple of the tires were brand new and all of them appeared to be in good condition.
Well, we said, we want to have 12 complete tires and wheels to have spares to swap quickly at Bonneville after a pass, and especially at turnaround for FIA record attempts.
Next, we thought we maybe had better mount and balance 12 sets and spin-test them, to be sure that all of them were okay. And right here is when the fun started, and before we knew it we were in trouble up to our NECKS!!!!
The brand new tires we had (we paid $14.95 each for all of them as a joblot, mind you) could not be balanced at all because they were so far out of balance. So that was why they were brand new. That was one thing, but the next thing you know our other F-16 tires were BLOWING UP LEFT AND RIGHT ON SPIN TEST, AT SPEEDS AS LOW AS 350 MPH!!!!! There was no way Tom could risk his neck with these things. They were unpredictable.
Why the first two had been fine at 500 mph, we do not know and probably never will.
Now we're really stumped, our streamliner almost completed with a huge investment of design and build time, a considerable amount of money in it, and NO PROVEN TIRES AVAILABLE!
It happened to be a period, you see, when Mickey Thompson company, which had made and sold plenty of good Bonneville tires for years, had changed hands and was in transition with new ownership.
By now it's November 1992, and we all went to the SEMA show to talk to some tire companies and see what we could do.
We ended up having some casual discussion with Gene McMannis and John Barguary of Mickey Thompson and it slowly developed over a few months that we could do something for each other. MT did not have a tire spinner of their own, but we did. We could not make Bonneville tires, but they could, and we could spin test and prove their tires for them.
We never signed a contract with them, everything was just done on a verbal basis, but beginning in August '93 we started in to test tires for them. There was an understanding that we would help them develop 500+ mph tires, and when they got to a proven reliable design, they would give us twelve of the size we wanted, noted above. And we tested tires for them for two years before we came up with the tires we needed, and we are STILL testing tires for them.
This has been a good working relationship, and we got reliable tires that carried us to the world record. You understand what a critical element of the car this is, because a tire failure at high speed would absolutely result in a disastrous crash! You can design the car as scientifically as you want in every detail, but there are a couple of risks you cannot ever fully control. One is a tire running over a sharp piece of metal, or even a sharp hard chunk of salt on the course, causing a puncture; the other is the random failure of some car component. So there are these risks, but you want to reduce them to the absolute minimum by testing and proving everything you can.
Bill: I can see all that. Describe your tire spinner for us and then let's go into what the failure modes of the tires were at first.
B&G: Bill, we're almost embarrassed to show you our tire spinner but I guess we HAVE to (laughing)! We sent you a couple of shots of it. Actually, as noted the first spinner was snowmobile engine-powered and the one we have used ever since the beginning of the MT period, we made out of an old Dodge Ramcharger with a 318 V-8 and four-wheel drive.
We removed most of the body for convenience and kept the transfer case and drive to the front wheels so we could drive the rig out to the farmland where it is safe to operate.
The rear axle driveshaft was removed and the output from the automatic transmission for it was diverted to the output shaft of a pickup stick gearbox which has a 4 to 1 gear in it, and we mounted this in the frame. We use that gear to run the original input shaft in the stick gearbox four times the speed of the automatic transmission. A shaft and bearing mount for the tire spinner shaft is mounted to the original input shaft (can you follow all this?) so the tire spinner can support a wheel and tire between the original rear frame horns of our Dodge pickup.
Bill: How did the auxiliary gearbox hold up in this improvisation, spinning two or three times the original rpm that it was designed for in its truck application?
B&G: Good question, Bill. The answer is that at first it didn't hold up well. The normal gear oil didn't provide sufficient lubrication protection and the gears wore out and stripped. But when we changed over to synthetic gear oil, the wear stopped and the gearbox could stand the high rpms applied to its internals and its original clutch shaft.
Now, when we run the 318 V-8 at 2000 rpm with the automatic transmission in top gear (and the front wheel drive of the Dodge disengaged, of course) our tire spinner shaft runs at 8000 rpm. 2000 rpm is just a cruising speed for the V-8 and it takes very little power to spin the tire. We have a very accurate digital tachometer on our spinner shaft so we know exactly what mph we are running our tire at.
Long story short, 8500 rpm on our spinner equals 680 to 700 mph, depending on tire growth, on our streamliner tires and every tire we have used on the car at Bonneville has been tested up to this speed before we passed it for use. These tires are run at 90 psi filled with nitrogen to minimize the pressure increase as their heat builds up, and to prevent moisture accumulation.
Might add that we have used telescopic video cameras focused on the tires, and white boards with 1/4" markings behind them, so that we can scientifically measure the tire growth at various speeds, and know just exactly what we've got. The cameras record both slimming and growing as the rpm increases by aiming at the tires in two directions.
At the beginning we had tires blowing up, and it was spectacular. A tremendous amount of force involved, and the departing rubber ripped the steel frame horns right off the pickup. Nothing you want to get in the way of. So our crews would operate the engine and equipment well back out of the way of any flying debris.
Bill: FANTASTIC! This is hot rod ingenuity at its best! I can see it all. Okay, what were the failure modes of the tires at first, did the treads separate from the bodies?
B&G: No, the tread rubber on the 'slick' tires is only about .090" thick and it did not come off. The failure point was the bead wires. They would break from the tremendous centrifugal force and the tire would explode.
You understand, Bill, that a tire bead wire is made of seven wire groups woven together into a cable configuration and laid in the rubber around the area that seats on the rim. The early tires were six of these groups per bead and that was not quite strong enough. Known in the industry as a 6 x 7. MT had to go up to a 7 x 7 with seven of the bead wire groups per bead to achieve the strength needed for this size of tire. And when they did, it proved to be sufficient for a sustained 700 mph, figured using growth at top rpms, without failure. So far we have spun a total of 61 tires for MT.
Bill: VERY impressive. While we're talking about the tires, would you describe the wheels you use.
B&G: Sure, the 16" steel rims are 4.5" wide and originate as some kind of implement rim that is 1/32" thicker than normal car standard for strength. Delbert "Hoppy" Hopkins at American Racing Wheels made them for us. The center sections are five-bolt for 9/16" studs on a 7-3/8" circle. The wheels run true within .060" wobble and .040" out of round, and the tires are better than this. We selectively mount them to compensate for their runouts and the complete wheel and tire assemblies vary from .010" to .040" runout measured on the tire.
Naturally, we balanced all the wheels by themselves first, with welded-on weights. And then the mounted tires are balanced with extreme precision. The final balance weights for the assemblies are epoxied in place, with the epoxy ramped up to improve air flow.
Since it is a principle of four-wheel-drive that the front wheels should have a slightly higher gear ratio than the rear, so that the front wheels pull slightly more than the rear wheels push, we select the mounted tires that have the largest measured circumferences for the front end when we make up the three sets of four we take with the car to race. The difference might be only a quarter to a half inch but it should make a difference in the vehicle's stability.
Bill: Why do you need to change them at the Salt Flats?
B&G: We change them after every pass on the course because it's quicker than taking the time to clean and inspect them carefully. We've never lost one during a pass, but on later inspection a few of them have shown damage from running over either metal junk on the course, Dzus fasteners, nuts and bolts or what have you, or it is known that even a hard chunk of salt can hurt a tire at 400 mph. So we have replaced a few of our original dozen from MT, but most of them are still serviceable. When Tom had that crash in 2001, the wheels were not bent, but we decided the tires had been overstressed and were discarded.
Bill: Okay, this leads into the streamliner itself so let's take a look at that next.
Copyright © 2009 Bill Hoddinott