Spinning Street Roadster

[CobraBall]

I am familiar with a Bonneville STR class '27 Ford/ 32 Chassis w/ a small block V8.  The roadster had a nasty habit of spinning above 170mph .  Here are some of my observations, thoughts & ideas regarding this racecar. 

The trunk was completely filled with a water tank, fuel tank, 3 batteries and lead ballast.  The ballast & batteries were over or aft the rear axle.

The front suspension was an off-the-shelf aftermarket street rod traverse leaf sold axle.  Most street rod steering arms are designed to provide front tire clearance resulting in a negative Ackerman. About 20 degrees caster.  Scrub radius unknown.

The required rear fenders had been trimmed/shortened on the front edge.

Besides using a body that was designed for 50 mph tops, IMHO several other problems contributed to the tendency to spin.

•  The CP was forward of the CG.
•  Too much added weight aft of the rear axle.
•  Negative Ackerman caused outside front tire to skid.
•  Open rear end

Possible fixes:
- Mount a Moon style water tank in front of the grille.
- One battery
- No added weight behind the rear axle
- Locked rear end.
- Go to a no Ackerman setup.
- Extend the front of the rear fender down to the original stock shape/position

These are my observations and ideas.  Please criticize, suggest, correct, ignore, etc....

[Glen]

Whats the vehicle number so I can look up it's history. We record every spin plus all unusual runs at the lakes and on the salt. We have a history of repeat vehicles

[thundersalt]

Geez Louise Glen, you mean to tell me there's a spin police? Man I hope I don't get on that list any more.

[Glen]

Some vehicles have bad habits as do some drivers.

[bvillercr]

Geez Louise Glen, you mean to tell me there's a spin police? Man I hope I don't get on that list any more.

You didn't spin, you just got really sideways.

[Roadsters.com]

In 1997, when I asked former Breedlove aerodynamicist Don Baumea to explain why some cars spun out on the salt, here's the essence of how he explained it:

It's not a matter of horsepower, torque, or pounds of ballast. It's pounds of thrust versus pounds of drag. A vehicle has a certain amount of pounds of aerodynamic drag holding it back, and it is propelled forward by a given amount of pounds of thrust that is applied at the contact patch of the tires on the driven wheels.

As the vehicle's speed increases, and its aerodynamic drag increases exponentially, it is at the point where the amount of drag exceeds the amount of thrust that you have instability. You reach a point where the air is simply preventing the vehicle from accelerating.

In itself, adding more power will not help unless the power reaches the ground as thrust at the contact patch of the tires on the driven wheels, and that calls for a corresponding increase in ballast to keep the tires planted and hooked up.

There's more to it of course, and my understanding of all this is quite limited, but I wanted to share what I could.

Dave
http://www.roadsters.com/

[willieworld]

are you saying----you get up against it and spin the tires     willie

[Sumner]

In 1997, when I asked former Breedlove aerodynamicist Don Baumea to explain why some cars spun out on the salt, here's the essence of how he explained it:

It's not a matter of horsepower, torque, or pounds of ballast. It's pounds of thrust versus pounds of drag. A vehicle has a certain amount of pounds of aerodynamic drag holding it back, and it is propelled forward by a given amount of pounds of thrust that is applied at the contact patch of the tires on the driven wheels.

As the vehicle's speed increases, and its aerodynamic drag increases exponentially, it is at the point where the amount of drag exceeds the amount of thrust that you have instability. You reach a point where the air is simply preventing the vehicle from accelerating.

In itself, adding more power will not help unless the power reaches the ground as thrust at the contact patch of the tires on the driven wheels, and that calls for a corresponding increase in ballast to keep the tires planted and hooked up.

There's more to it of course, and my understanding of all this is quite limited, but I wanted to share what I could.

Dave
http://www.roadsters.com/

You pretty much nailed it and once the tires spin and you have that weight in the back like was mentioned it can want to act like a pendulum and swing the car around and of course once the weight gets in the front it now has a spinning momentum and will go past the front back to the back again, and again.

Under ideal conditions what was described will result in the spinning tires that starts the whole thing off, but if anything upsets the car and unloads a tire it can happen sooner than when it should.

I have a spread sheet on my site that will give you a good idea of how much weight you need on the tires.....

http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html

..... the "Drag Force-HP-Thrust-Weight" one.  Also using that spread sheet if you know the frontal area of your car/bike and the HP it took to run a speed from previous runs you can narrow in on the Cd of your vehicle by figuring backwards through the spread sheet.

Likewise if you use the know the HP it took you to run a certain speed you can use the "Horsepower Needed" to figure the HP you will need to run a new speed.  Then you can go back to the "Drag Force-HP-Thrust-Weight" one and using the new HP figure figure how much weight you will now need on the rear tires.

If you don't have figures from running already don't let that stop you.  You can go to Dr. Mayfield's site....

http://www.mayfco.com/tbls.htm

........................ and see if he has the Cd of your vehicle.  Then go back to the spreadsheet and plug in the Cd, frontal area and HP you think you can make at the rear wheels and see what speed you should be able to run.  Plug in the Cd, frontal area and then different mph until the HP figure comes close to what you think you have.  Then go down the spread sheet again and look for the weight you will need.

Clear as mud  ,

Sum

[Sumner]

are you saying----you get up against it and spin the tires     willie

That is what he is saying, just like putting your front tire against a building and some water under the back tire,

Sum

[desotoman]

are you saying----you get up against it and spin the tires     willie

That is what he is saying, just like putting your front tire against a building and some water under the back tire,

Sum

That is when you find out who the really good drivers are. LOL

Tom G.

[SPARKY]

I know I am capable of flunking---but to day on the dyno----my eng jumps over 100'# just above where it falls back to after the shift.. explains why I am subject to getting really busy shortly after it settles down after the shif...

[jl222]

I am familiar with a Bonneville STR class '27 Ford/ 32 Chassis w/ a small block V8.  The roadster had a nasty habit of spinning above 170mph .  Here are some of my observations, thoughts & ideas regarding this racecar. 

The trunk was completely filled with a water tank, fuel tank, 3 batteries and lead ballast.  The ballast & batteries were over or aft the rear axle.

The front suspension was an off-the-shelf aftermarket street rod traverse leaf sold axle.  Most street rod steering arms are designed to provide front tire clearance resulting in a negative Ackerman. About 20 degrees caster.  Scrub radius unknown.

The required rear fenders had been trimmed/shortened on the front edge.

Besides using a body that was designed for 50 mph tops, IMHO several other problems contributed to the tendency to spin.

•  The CP was forward of the CG.
•  Too much added weight aft of the rear axle.
•  Negative Ackerman caused outside front tire to skid.
•  Open rear end

Possible fixes:
- Mount a Moon style water tank in front of the grille.
- One battery
- No added weight behind the rear axle
- Locked rear end.
- Go to a no Ackerman setup.
- Extend the front of the rear fender down to the original stock shape/position

These are my observations and ideas.  Please criticize, suggest, correct, ignore, etc....

 CobraBall
 Don't forget about aerodynamic lift as one of your problems. Years ago Jim Hall (Chaparrals) and chev, figured out the high speed instability they were having (and all others) was aero lift causing the suppension to go into droop and unloading the tires
and voila! the spoiler was born, then the adjustable spoiler then the wing and adjustable wing. Of couse you can't have a spoiler in roadster class. Make sure that your rear end is square with the chassis and is not toed in our out,same with front but
make sure you have a little toe in.We run 1/8''. Talk to the record holders in roadster class,i know a couple that have gone 255 and 260 with out a bunch of weight and they run suspension. A few blown roadsters have gone 285 to almost 300, but i'm not sure on the weight but suspect a bunch.
 Back to aero lift, even though this was figured out in the mid 1960s a lot of coupes and sedans don't do anything to combat it even though they could. Some just do not know.
  What kind of suspension do you have.The wrong type of setting can cause problems.
 I have a book from Alston Chassis-( Door Slammers: The Chassis Book by Dave Morgan) and Tune To Win by Carroll Smith.
 Smiths book has all the different handling problems and how to deal with them. These books will give you a lot of knowledge
about setting up a race car.
  Also what kind of tires are you running ,not to wide i hope.
                                 Good luck JL222

[jl222]

Geez Louise Glen, you mean to tell me there's a spin police? Man I hope I don't get on that list any more.

    But you could belong to the Spin Out Club and get a spin out hat pin. Is anybody still giving those out?

                          JL222

[dwarner]

El Mirage Ladies Aux, EMLA, the pin is yours for a small donation. Ask at the sales trailer at any meet.

DW

[Richard Thomason]

There is also a cute little sticker (or at least there used to be) that you can put on your car.