indy roadster builders
building a badass
Building a BadAss Part 1 A Watson roadster with a twist
By Tom McGriff Proprietor of mac miller’s garage INDY
In January 2012, I was contacted by Florida racers, David Johnston, Jerry Carbone and Bill Wendt about building a new Indy roadster. Not unusual, as I get several calls a month about building new roadsters. The difference was that these guys were serious and they wanted something out of the ordinary. They wanted to build an Indy roadster specially to run at the August 2012 Bonneville Salt Flats Land Speed event.
The primary goal is to set a class record for vintage oval track race cars. The class is XXO/VOT and the current record is held by a vintage Kuzma Indy roadster at 176.5 MPH. The secondary goal is to run over 200 MPH.
The original plan was to build an A.J. Watson style car with a, Bonneville legal, roll cage, coil spring suspension and powered by a 270 c.i. OFFENHAUSER Indy engine.
Following some very tedious and time consuming “back and forth” with the Bonneville safety and rules people, it became obvious that the car was going to be a bit more complex than a standard Watson chassis design.
Current Bonneville requirements include 1 5/8 “dragster style” roll cage, 1 5/8” tubing structure surrounding the driver from seat back to motor plate and full metal paneling enclosing the cockpit area. The material specified for this frame construction is 120 thou. DOM mild steel tubing.
In addition to building a “rules & safety” compliant car, the design had to maximize all areas of development relevant to high speed, straight line running.
Aero – At Bonneville, “aero” means streamlining and minimum frontal area. The Watson body has a fairly good shape with a smooth round nose and a long rounded tapering tail.
One potential problem is that the bottom surface of the nose curves upward at the front. To minimize the oncoming air from compressing under this curved surface and lifting the nose off the ground, it is essential to tilt the nose down at the front, so that the bottom surface is as parallel to the ground as possible. A small spoiler across the bottom surface, if legal, would also kill some of the “lift”.
Streamlining also includes fully enclosed side panels, bottom pans, inner and outer wheel discs covers and some small clearance fairings on the nose and hood.
One final pre “run” aero tweek is to clear tape all bodywork seams for as clean airflow as possible.
Frontal Area – Certainly, the amount of air that must be displaced as this car moves forward has a huge effect on the ultimate top speed.
The size of the standard Watson chassis and bodywork “is what it is” so not much can be improved in this area.
The second biggest forward facing surface on this car is the exposed wheels & tires. Not only does their actual size add to the total frontal area but the fact that they are spinning multiplies the amount of turbulence and aero drag that is created. To minimize the “drag” effect of the open wheels, the narrowest possible rims & tires will be used ….. 4 inch wide X 28 inch diam. Goodyear Land Speed tires mounted on 4.5 inch wide X 15 inch wheels.
The third factor is the suspension & steering links, the springs & shocks and the axles. Each piece doesn’t add much to the frontal area but, collectively, it adds up to a notable percentage. The real problem with exposed suspension is additional turbulence and drag it creates.
The initial plan was to locate all of the steering & suspension links and the spring & shock units inboard, out of the airstream. After more, slow moving, discussion with the Bonneville rules guys, they agreed to the inboard steering & suspension links but required that 50% of the shock absorber had to stick out past the side of the frame. Because the springs were mounted on the shocks, that also meant that part of the spring would also be out in the airstream…. Not good!
At this point, it may have been better to switch from coil springs to torsion bars because the torsion bars could have been located totally inboard leaving only part of the shocks “in the wind”, but the design was far enough along that it would have required major time consuming modification to switch springs.
One final comment on frontal area, turbulence and drag. The driver cockpit & roll cage is one of the biggest generators of turbulence and drag on the whole car. This makes the windscreen very important. Its size adds to the frontal area but its shape can greatly improve the streamlining around the cockpit and rollcage.
Stability – Equally important to aerodynamic stability is mechanical stability. This, mostly, has to do with suspension design, steering design and Newtonian physics.
As a life long oval track and road racer, I have a very difficult time understanding that everything I know about racing car design does not matter at Bonneville. This car does not have to accelerate rapidly, decelerate in a short distance or change directions….. all it has to do is go in a straight line, so everything is set to do that with minimal drama for the driver.
Steering - The usual steering gear for the Indy roadster chassis is a Halibrand or Schroeder with the pitman arm and drag link mounted on the outside of the frame, in the airstream. Another characteristic of this type of steering is its fast, twitchy 8 to1 steering ratio….. not the best combination for stable straight line running.
The steering gear selected for this car is the Saginaw 140 “vega”. It can be mounted totally within the bodywork for better streamlining and it has a slower reacting 20 to1 ratio for more straight line stability.
The final key to steering stability is the front axle castor angle. The usual castor for an Indy roadster is 6 to 7 degrees but this car will use 15 degrees to make sure the front tires always want to point straight ahead.
Wheel Dynamics - Although the spinning wheels & tires are the biggest cause of turbulence and drag, they are also the most important factor in directional stability.(Here is where the Newtonian physics happens)
Spinning wheels & tires generate great gyroscopic forces. This means, when the wheels are spinning, it is very difficult to change their attitude and direction. The heavier the wheels and the faster they spin increase the amount of force generated .
This high gyroscopic force is exactly what we need to keep this car going straight down the track.
Weight - I am constantly reminded that in Bonneville Land Speed Racing, weight doesn’t matter. In my usual world of oval track and road racing, where the cars must accelerate fast, change directions quickly and stop in short distances, light vehicle weight & rotating component weight is very important.
Extra weight designed into the structure and components of the Bonneville car can add greatly to the safety margin and directional stability.
The “track cars” and Bonneville cars have one very important thing in common. They both must stay in total contact with the track surface. A major concern of all drivers and car designers is high speed aero lift.
The “track car” adds “weight” with air pressure generated by wings or spoilers. The amount of “weight” generated is proportionate to the speed of the car.
Bonneville cars do not use wings because of the unacceptable amount of drag & turbulence, adversely effecting top speed & stability.
This Bonneville Indy roadster uses a combination of heavy duty materials in design & construction combined with heavy metal ballast, located toward the front to discourage front end aero lift.
The car must always weigh just a little more than the amount of aero forces trying to lift it……….. especially at top speed….
The elusive perfect setup up at Bonneville must be the exact combination of streamlining and weight to minimize drag & turbulence while keeping the car from lifting off of the ground.
Other misc. factors –
There is another little known bit of Newtonian physics that applies in racing. It is called “polar moment of inertia”.
Cars with the their major weight masses(fuel & oil tanks, battery, radiator, etc) closer to the “center of gravity” are easier to turn or maneuver. This is known as “low polar moment of inertia”. Good for road racing.
Moving these weight masses to the extreme ends of the car makes the car much more difficult to deviate from its straight line direction This is called “high polar moment of inertia”. It is great for straight line stability.
The Indy roadster, by its standard design, is a “high polar moment” car, with its extreme rear mounted fuel tank and extreme forward mounted radiator.
The Bonneville roadster will have additional forward weight with the battery and engine oil tank mounted on the forward frame.
Wheelbase – The standard wheelbase for the Indy roadsters was between 96 and 99 inches. The longer wheelbase improves straight line stability. This car will use a 101 inch wheelbase. This extra length will be added to the driver cockpit area for a little extra driver comfort.
Tires and traction - We have already discussed the importance of the wheel & tire dynamics. but the tires also must do their job as the cars only contact with the ground.
The Bonneville salt surface is loose and slippery but with no real urgency for fast acceleration, ultimate traction is not the most important factor. Ideally, you need just enough forward traction to keep the car accelerating down the course and, hopefully, you will never need lateral traction.
The tires, particularly for an open wheel class, should be narrow to cut frontal area & drag and have low rolling resistance.
The correct tires for the Bonneville Indy car are the special Goodyear Land Speed Tires. The size is 28 x 4.5 x 15. They use 70 p.s.i. for stability & minimum rolling resistance. They are rated for 300 MPH giving a good margin of safety above the 200 MPH goal.
Horsepower - Not much to say here. As much as you can get!
Don’t worry about torque, put the power at the top end. When approaching top speed, the amount of needed horsepower goes up at an exponential rate to any increase in speed. At top speeds it doesn’t take a little more HP to go a little faster, it takes a lot more HP to go a little faster because drag also goes up at an exponential rate with speed. Terminal speed is when air resistance, rolling resistance and drag equals the amount of power available.
This car will use a 1950s era 270 c.i, twin cam, 4 cyl. OFFENHAUSER engine with around 420 HP, which was the standard power plant for the Indy roadsters. This engine should turn between 5400 and 5600 RPM.
Final Drive Gear Ratio - One more variable that must be calculated is the final drive gear ratio. The class record for this car is 176.5 MPH, so a reasonable speed ambition to break this record would be around 180 MPH.
A common formula using wheel diam, engine RPM and rear axle ratio will calculate the top speed of the car.
With the 270 OFFY turning 5400 RPM driving 28”diameter tires, a top speed
of 180 MPH can be reached with a final drive gear ratio of 2.50 to 1.
This top speed and RPM should be reached just before the official timing zone. If the car reaches its terminal speed well before the timing zone, a few more MPH may be possible by using a higher final drive ratio closer to 2.40 to 1.
The secondary goal of this car is to run 200+ MPH. To do this would mean winding the OFFY to 5600 RPM with a final drive gear ratio of 2.30 to1.
Other features of this car include:
It will use a Winters V8 quick change axle with no differential.
It will also use a Winters Phoenix 2 speed transmission.
It will be equipped with Wilwood brakes on the rear wheels only.
Primary and emergency braking will be done by a drag chute.
After a lot of computer hours, designing and integrating all of these factors, as purely as possible, the chassis and body drawings were ready to be turned into steel and fiberglass. Construction began Feb 1.
By the middle of May, the frame, bodywork, axles, suspension and steering were reaching completion. The Florida “crew” moved into my shop and began installing the driveline, steering linkage, interior paneling, radiator etc. while I finished fitting the bodywork and installing the roll cage.
June 6, the rolling chassis and body rolled out of my shop for the trip to its new home in Miami Fla. where many more hours of finish and detail work remain installing engine, electrical, plumbing & hydraulic systems, fuel & oil tanks, paint & polish and careful final assembly.
“The Setup” - When the car left my shop, it did not have the real engine. wheels & tires, drive line and many other systems and pieces, so it was not possible to determine an accurate final weight and suspension setup.
New car...Zero setup data…Keep it simple!... Stick to basics!
I reckoned the weight of the finished car would be between 2000 and 2200 lbs. so 500 lb/in coil springs were mounted over 50% compression/50% rebound, 70% resistance shock absorbers on all four corners with 3 inch ground clearance, front and rear . The springs are mounted at a 30 degree angle, so, with the correction factor of 75%, the 500 lb/in springs have an effective rate of 375 lb/in. Ya gotta start somewhere!
Lead Ballast – The final key to chassis setup at Bonneville is the addition of lead ballast to the frame for downforce and stability. This ballast can amount to 250 / 300 lb. The amount and location of the ballast has a major effect on the handling of the car.
Final decision on spring rates and ride heights will be set with the ballast in place.
When the car is finished, it is very important for the Florida crew to get total weight, corner weights, RS/LS weight distribution and front to rear weight distribution.
Well! My part of the project is finished and the Florida team is doing the final assembly and finish in their Miami shop. A few final thoughts on the design & build of this car.
* It doesn’t get any better than Indy roadsters and Bonneville “specials”. Building both of them as one car is a great opportunity and challenge…. But, what really puts this car “above and beyond” is the awesome 270 OFFENHAUSER “thumper”.
* Breaking records at Bonneville is hard!.. Breaking a record at Bonneville by 25MPH is really hard! …… but this project has good ingredients, a good owners group willing to commit whatever resources and effort is necessary and good bits & pieces throughout the car.
* We were honored that “the man” himself, A.J. Watson, made several visits to the shop to oversee the construction of the car. It was interesting that A.J. said, even as a young California hot rodder, he had never run a car at Bonneville.
If you “google” the word “BadAss” , you might find a picture of Darth Vader, maybe John Wayne, Clint Eastwood or Chuck Norris…….. or you might get a picture of this car!
Building a BadAss Part 2 “On the Salt”
By Tom McGriff
Proprietor of mac miller’s garage INDY
After six weeks of intensive work at the Florida shop, installing plumbing, electrical & hydraulic systems, fuel tank, radiator, engine & driveline, safety stuff, paint & plating and final assembly, the Johnston-Carbone-Wendt roadster is ready for Bonneville.
The high level of preparation and finish of this car is stunning, from its 1959 vintage “Roger Ward”, red & white paint job to its, very cool, Halibrand wheel decals on the flat aluminum aero wheel covers.
The finished weight of the car, without ballast, is 2150 lb.
RR 590 lb
LR 590 lb
RF 485 lb
LF 485 lb
Front to rear weight bias F45% R55%
Right to Left weight bias R50% L50%
For their “starting setup” the team decided to use the same 500 lb/in springs & shock absorbers that were installed when the car left Indy. They set the rear ride height at 3in. and the front ride height at 1in. for some added aero dow nforce.
The Lead Ballast Conundrum
The main concern of the crew is rear wheel traction. With 400+ HP, 4 in. wide tires and a slick, loose track surface they, definitely, have a legitimate worry, so they decided to locate 300 lb of lead, aft of the rear axle for maximum rear wheel weight. My unreasonable paranoia about front end lift, tells me to put that 300 lb in the nose It is probable that the amount, location and F/R distribution of this ballast is the most important factor for maximizing tire traction under acceleration and stability at top speed. A better understanding of ballast could definitely improve the potential of this car…. I will be thinking a lot more about this.
Painting the car - One detail in final preparation, that is kind of overlooked, but is important is “surface drag”. As the oncoming air rubs along the surfaces of the car, it creates “surface drag”. Much of this drag is generated by protruding or irregular stuff such as bolt heads, Dzus buttons and adjoining bodywork seams. Of course, these things should be as flush with the surface as possible, but also, the paint surface should be as smooth and polished as possible. Some people take this so seriously that they have all of the decals and graphics installed before the final clear coat layers are applied so, even, the thin edges of the decals do not affect the air flowing along the body surface. These same people clear tape over all of the bodywork seams before a run, I think that careful attention to “surface drag” is important.
Bonneville – The Florida team arrived at Bonneville with a great car, great enthusiasm and great expectations. David Johnston and Jerry Carbone are rookies but Bill Wendt is a Bonneville veteran with a “vintage oval track midget” class record to his credit.
A couple of things to consider about Bonneville, besides the vastness of the place and the unusual track surface. * The Salt Flats are over 4200 ft above sea level. This is good and bad. It is good because, aerodynamically, the thin air means less air resistance for better top speed. It is bad because the thin air makes it harder for the engine to “breath” meaning less power. …. Gain a little ….. lose a little….
* Bonneville is a rather tight knit little society and they do not hand out ”free passes” to new teams and new cars. There are definitely protocols and initiations before being allowed on their track surface.
The first order of business is to submit the roadster for technical inspection by the Southern California Timing Association, who sanctions and manages the event.
The car would be scrutinized by “the safety” technoids, the “class rules” technoids, and, I guess, any other SCTA officials who wanted to have a look.
In my opinion, for a new team and new car, the technical inspection is the most important challenge of the entire meet.
During the inspection the roadster was picked at, poked at, examined, dismantled, questioned, commented, measured and eyeballed to the smallest detail.
After two hours, the scrutineers could find no technical concerns with the car and issued the “tech sticker”.
I believe that getting through tech, first time, without any major issues, is the best way for the new car & team to earn the respect of the officials and veteran Bonneville racers. These guys can help you, if they like you.
All three of the team principals intended to drive the car, so, most of the available opportunities to run would be used up with rookie tests and speed qualification runs. They will run the 5 mile short course for speeds under 175 MPH.
During Sunday and Monday runs, both Carbone and Wendt spun the car at just over 140 MPH. Fortunately, with the hard, slick, grainy surface and nothing out there to hit, spins are, normally, just spins and a big thrill for the driver.
These spins were caused by front end aero lift because there was not enough forward ballast. The crew moved 250lb from the rear to the front .
With the revised forward weight distribution, the car was stable and true down the course.
During five days, the team made a total of nine runs, including rookie tests, speed qualifying runs, “the spins” and speed runs of 147.7, 174.9 and181 MPH.
During the 181 run, the engine started to tighten up a bit so they shut it off to avoid damaging the Offenhauser. The problem turned out to be a scuffed piston.
The XXO/VOT class record, they are shooting for, is 176.5 so the car is fast enough to do the job. With a new car and rookie drivers, it is almost impossible to make a record attempt the first year but they should be well prepared for a serious attempt at their next meet.
The team had a purty good week. They have a great car, had a few thrills, learned a lot about car setup for Bonneville, established some good credibility for themselves and their car, made some valuable new friends among Bonneville officials and veteran Bonneville racers, found some speed by the end of the week and had a great time.
I’m very proud of the team and proud of my first Bonneville car.
A few final comments…….
So? What to do now??? The car is good…. No major changes or redesign is needed.
* The main area of potential development is the “setup”. Now with some Bonneville experience, the team will evaluate their baseline spring rates, shock rates, ride height and front/rear ballast setup for possible improvements.
* It seems that there would be something to be gained with a knowledge of the atmospherics at the Salt Flats, stuff like air density & humidity, barometric pressure, air temp, wind speed & direction. I think I would include one of those little modular weather stations as part of my pit equipment and learn how to interpret it. HA! I’ll bet some of those “salt flats oldtimers” know the perfect time of day and weather conditions for an optimum run.
* The car is equipped with a GPS device, giving “real time” MPH during the run. If this GPS was hooked up to a recorder and superimposed over a course diagram, it could be quite helpful with final drive ratios, etc. I’m sure this would be no problem for some smarter guys than me…… HA! While they’re at it, it would be nice to have some shock travel and ride height sensors.
* With 400 HP, 4” tires and a slick, loose surface, traction and wheel spin is a definite concern, not only off the starting line but, also, at high speed, down the course. With a 2.50 final drive ratio and a mile of acceleration distance before the first timing zone, there is no real urgency for a wheel spinning “burnout”. An orderly departure from the starting line is the responsibility of the driver. The real problem is wheel spin at high speed. At best, it will hurt acceleration and top speed. ……..at worst, it could cause the car to spin off course. During the past 20 years, there have been a lot of traction control systems tried in all areas of racing. Maybe one of these systems would be useful on a Bonneville car.. ???
After considering all of the above weather stations, data acquisition computers and traction control gizmos, the reality is, sometimes the driver & crew experience, knowledge and intuition is as good as any of these scientific gadgets. The fact is, Bonneville is the only major motorsports event left in the world where a racer can build a car from scratch and drive it by the “seat of his pants”, sometimes at speeds faster than NASCAR, IndyCars and F1.
The Johnston-Carbone-Wendt roadster was built in a small back yard shop with minimal equipment……… not a laboratory, a special factory or a wind tunnel. It was designed and built by experienced racers……… not scientists and engineers. And, it was built from steel, aluminum and fiberglass……. not titanium, magnesium and carbon fiber. By avoiding all of the stuff that has purty much ruined most other top level racing, Bonneville has remained the greatest bastion of genuine “old school” racers, drivers and builders, on the planet. Maybe it should stay that way.
The Johnston-Carbone-Wendt Watson 270 Offy is the latest in a long history of modified Indy cars to run land speed courses. In 1924, Tommy Milton drove a 183c.i. 8cyl. Miller to 151MPH at Muroc Dry Lake in In 1927, Frank Lockhart drove a supercharged 91 c.i. 8cyl Miller to 171MPH at Muroc Dry Lake. In 1928, Wilbur Shaw drove a 151c.i. 4cyl. Miller to 135MPH on the sand at Daytona Beach Fla. In 1930, Shorty Cantlon drove a 183c.i. 4cyl Miller to 145MPH on the Muroc Dry Lake. In 1930, Cliff Woodbury drove a front drive, supercharged 91c.i. 8cyl Miller to 181MPH on the sand at Daytona Beach Fla. In 1932, Wilbur Shaw drove a 220c.i. 4cyl. Miller to 137MPH at the Muroc Dry Lake. In 1940, George Barringer drove the rear engine 4WD Miller to 157.5MPH at the Bonneville Salt Flats. In 1947, Marvin Jenkins tested the supercharged front wheel drive Kurtis NOVI at Muroc Dry Lake before taking it to the 10 mile circular course at the Bonneville Salt Flats, where he ran 179.5 MPH In 2008, the current XXO/VOT class record was set, by the Lattin-Gillette 1959 Kuzma laydown 255c.i. OFFENHAUSER, at 176.5.
It is amazing how different the historically classic America land speed surfaces are.
Muroc Dry Lake, Cal. dirt surface, 2300ft above sea level.
Daytona Beach, Fla. sand surface, less than 12ft above sea level
Bonneville Salt Flats, Utah salt surface, 4200ft above sea level
The Johnston-Carbone-Wendt car is an excellent project and I am very proud of my part in making it happen!
Proprietor of “mac miller’s garage” in INDY