The Mark Ortiz Automotive

CHASSIS NEWSLETTER

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March 2008

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WELCOME

 

Mark Ortiz Automotive is a chassis consulting service primarily serving oval track and road racers. This newsletter is a free service intended to benefit racers and enthusiasts by offering useful insights into chassis engineering and answers to questions.  Readers may mail questions to: 155 Wankel Dr., Kannapolis, NC 28083-8200; submit questions by phone at 704-933-8876; or submit questions by    e-mail to: mortiz49@earthlink.net.  Readers are invited to subscribe to this newsletter by e-mail.  Just e-mail me and request to be added to the list.

 

 

ANOTHER EXOTIC CAR LAYOUT

 

A reader sent this link, with the following brief comment:

 

http://sitepalace.com/donmichael/reece/reece.html
 
Don't know what magazine this came from.  If it's Racecar, you've probably seen it.  Interesting chapter in circle track history!

 

The article is from Open Wheel, which was a companion publication to Stock Car Racing.  What tipped me off was the mention of Doug Gore being the technical editor.  I remember him being technical editor for both of those titles.  He is now in a similar position at Speedway Illustrated.  I asked Doug if he remembered the article and he said he did.  Open Wheel ceased publication eight years ago.

 

The car shown is a supermodified with three right wheels and one left wheel.  It was called a 3-to-1 car.  It was built in 1979 by Kenny Reece.  It was tested, but was outlawed before it ever got a chance to race.

 

The left wheel and the center right wheel were connected by a beam axle, and driven by the engine, which was an aluminum big-block Chevy.  The front and rear right wheels steered.  The rear one steered out when the front one steered in, but by a lesser amount.

 

This idea could be regarded as an oval-track variant of the Scalabroni diamond layout discussed in the March 2007 newsletter.  The end wheels are just offset all the way to the right.

 

Tim Richmond drove the car in testing.  The lateral forces generated were so great that his helmet strap broke.  (I can't tell if this refers to the one under his chin, or an extra one to the side to keep his head upright, which some drivers used at the time.)  The thin-walled fuel tank began to bulge laterally on the right side.

 

 

This is on a flat, half-mile, fully round skidpad, at Honda's Marysville, Ohio transportation research center.  The car had no wing of any kind.  It didn't even have a rear spoiler.  It had a rounded tail with a tailfin, reminiscent of an Indianapolis car or a Detroit styling exercise of twenty years earlier. 

There can't have been any aerodynamic downforce at all.  The tires were all twenty inches wide, and the total car weight was 1,315 pounds.  According to the article, 75% of the weight was on the single left wheel, in static condition.

 

Even considering the engine being almost half of the mass, I'm a bit skeptical of the 75% left figure.  Also, I'm sure all the weights are without driver.  The driver is a bit to the right of center.  I'd guess the car might have as much as 65% left, with driver.  Supermodifieds have been built with 75% left, but they have wider tracks and the right wheels hang out considerably further from the main structure than in this car.

 

The big worry I'd have about such a layout is, what happens if you have to suddenly slow down and turn right at the same time?  You don't have to do that to turn a fast lap on an oval, but there are times while racing when you have to turn right and slow suddenly to avoid a wreck.  This is worrisome enough in a conventional supermodified with two left wheels.

 

I would also expect the car to veer rightward pretty heavily in hard braking.  The article does not explicitly say this, but most supers run spools, so any braking on the drive axle slows both of those wheels.  Then we have the other two wheels, acting entirely on the right side.  In straight-line braking, the left wheel has to contend with about 65% of the inertia, but it only has something like 25% of the braking power.  Even with two left wheels, it is difficult to keep a supermodified straight while braking hard, or make it turn left while trailbraking.  The heavy side wants to keep going.

 

As with the diamond layout, trying to tune the handling properties by adjusting the wheel loads and spring rates presents some interesting quandaries.  In the pictures, it looks like the three right wheels are not perfectly in line; the middle one appears to be set inboard slightly.  But let's imagine that the right wheels are all in line, for simplicity.

 

In such a car, raising or lowering the left wheel suspension wouldn't change any of the wheel loads.  Raising or lowering all three of the rights the same amount also wouldn't change any of the loads.

 

A conventional car has percentages for the ends, the sides, and the diagonals.  The 3-to-1 car has side perccntages, a middle percentage, an end percentage (front and rear right combined), and separate front and rear right percentages.

 

If we raise just the right front, we increase the end percentage and decrease the middle percentage.  All the load comes off the right middle wheel.  No load comes off the left wheel, although its ride height might change a little bit, depending on exactly where we measure.

 

 

 

What does this do to the handling?  Does it do anything?  It probably changes it some, at least with the car in the article.  It might not, if the car's center of gravity were right on the axle.  However, the

Reece car appears to have its c.g. well forward of the axle.  The axle is somewhat aft of the wheelbase midpoint, and both the engine and the driver are forward of it.  The only major mass aft of the axle is the fuel load.

 

If the car had very little end percentage, and a lot of middle percentage, we would expect it to push, or understeer.  The centrifugal inertia would act forward of the tires with most of the load, and the front tire would have little ability to resist this.

 

Conversely, if there is less load on the axle, tire stagger has less influence.  Usually, oval track cars with spools are over-staggered, compared to the stagger theoretically required for the turn radius of the racetrack.  Consequently, anything that unloads the middle wheels tightens the car by reducing stagger-induced oversteer.

 

This could get tricky.

 

And then there's the steering on the rear wheel to play with.

 

Of course, this is all largely academic, since there is no place to race such a car.  This case illustrates a point I have made in the past regarding highly visible or radical innovation: you have to think not only about whether your idea is legal under existing rules, but also how the rule-makers are likely to react when they see what you've come up with.

 

I do think there might be a role for really unusual cars like this as exhibition acts between races for legal cars, sort of the way jet cars have been used in drag racing.  I'd probably turn out if I knew my local short track was going to let a car with three right wheels do some laps and see how fast it could go.

 

 

Now, if we wanted to build a no-holds-barred exhibition car that would break track records on any oval short track it showed up at,  might we want to use more than two right tires?  I think so.  But I think we'd also want at least two lefts.  Additionally, we'd want powered ground effects some form of sucker car.  If you're going to throw away the rule book, throw it all away!

 

Some readers will remember the Chaparral sucker car.  It had two big exhaust fans in the tail, driven by their own two-stroke engine, sucking air from under the car and blowing it out the back.  It had vertical Lexan skirts that dragged on the ground, to help exclude air from the underside.  The skirts had slots where they attached to the body, so they could slide up and down.  Their own weight was all that held them down.  The skirts on the Chaparral were clear.  I think if you had multiple right wheels, you'd want opaque skirts, so nobody could see how many wheels there were.  Black would be good.  In fact, it would be good theater to paint the whole car black, for that extra aura of

 

 

mystery.  And keep it under a cover whenever it wasn't actually running.  People would go nuts trying to figure out what was underneath.

 

An exhibition car doesn't need a number, but you could put something on the side.  An infinity symbol perhaps?  Or maybe 666?

 

If the car only has to do a few quick laps, electric power starts to look really attractive.  The batteries could be fairly light, and all to the left.  All or most of the wheels could be driven by individual motors.  The sucker fans could also be electric.  The car would obliterate lap records, almost silently.

 

It might also be pretty good at drying and cleaning the track.  That could be its job, once more advanced exhibition cars put it out to pasture.

 

My guess is that pretty quickly we'd reach a point where the driver's ability to withstand the accelerations would become the limiting factor.  Also, if large numbers of people started building

outlaw exhibition cars, the market for between-races exhibitions might become saturated.  But at least in the US, there are a lot of short tracks that need a draw.  I think a lot of people could have lots of fun before one factor or another called a halt to the party.