Rear-Engined Modified Roadsters

[Stan Back]

I'm wondering if the rules makers and the Board considered just including (by changing the rules) the rear-engined roadsters in with the other modified roadsters.  A hundred years ago in drag racing they were lumped together.  And Tony Waters won more races than Speed Sport, as I recall.  Are rear-engined modifieds faster at Bonneville?  Are front-engined lakesters faster?  Does engine placement insure a better weight distribution, or is it just how you build the car?  Comments?

[JackD]

When they removed the requirement for the tread to be the percentage of the wheel base, they got way away from the roadster tradition.
 Does anyone remember how the Sports Racing Class evolved into Gas Streamliner?
 Are they safer? Are they faster? Are they a logical evolution or do
 they obsolete the older configuration?
 There is a basic law of aerodynamics, weight, center of pressure and center of balance that never changes. Are we stepping past that or will it be considered in the rules?
 I know the aero laws are not universally understood but they never change.

[RichFox]

I would tend to agree with Stan. Seith Hammonds lakester showed that it dosn't require a rear engine lakester to work, even if almost all are. I fail to see how a rear engine would make my car faster.  Rich Fox V4F/GMR

[Rex Schimmer]

I think that I agree with Rich that engine placement probably doesn't make much difference when it comes to ultimate speed, although most front engine modified roadsters have the driver offset to one side which then adds the frontal area of the engine scoop, which most of them run, and the frontal area of the driver/roll cage, where as with a rear engine car these two items can be put in line, which is probably better.
 
 I think it was back in 1953 or 54 that 3 or 4 rear engined roadsters got sideways and flipped and there were some deaths. The next year rear engined roadsters were outlawed. I do think that we have probably progressed past that era, especially from the safty aspect, but it is interesting that Seth Hammond had a lot of problems in the 240 mph area and the red rear engine roadster, that ran as a "time only"  car this year, ran very close to the same speeds and seemed to have no trouble. 27 T bodies at 250 mph now there is an aero challenge!
 Rex

[Dynoroom]

Rex, the only question I have is why can Chavin & Jim Howe run over 300 in there cars? Seth is a racer and will get his handling issues figured out. As far as rear engine modifieds go I know they used to run but to add a bunch more classes (to go along with all the classic classes we needed) just takes away from the achievement if the records are only 1/2 of a gas/fuel roadster. Speaking of that lets let 4 wheel drive roadsters in, have 1 crash, grandfather them, then decide that they might go 300 first so outlaw them. 20 years from now build 2 or 3 and get your own class! IMHO BS.
 Mike

[Rex Schimmer]

Mike,
 I remember that Chavin's car had a really big wing mounted over the rear wheels. And in standart Chavin's manner it was a really well engineered and fabricated installation. Does Howe's car have a wing? I know that Chavin had a ton of HP so pulling the wing at 300+ was not a problem plus it probably moved the aero center of pressure back behind the CG and this helps high speed stability. Maybe Seth needs to add a tail fin?
 
 Rex

[Bob Drury]

Rex, a properly designed wing has very little drag, so you don't need big horsepower to "pull one".  A spoiler, on the other hand, adds to the aero drag on the vehicle.

[Ken Walkey]

Rex-"the aero center of pressure back behind the CG and this helps high speed stability"...
 Think of a high speed vehicle as a dart, or an arrow. Would you put the weight and the driving force both in the rear? What happends when you take the weight off of an arrow or a dart, and thro it? Not too much stability. With the mas weight forward it will go straight. Think about it.

[jacksoni]

Rex is correct.  CP behind CG gives stability.  That is exactly what a dart,arrow or airplane has.  CP in front is an unstable disaster looking for a spin.  Driving force has nothing to do with the aerodynamic stability, but if the rear tires are spinning.........

[ddahlgren]

What would make you think that the CP stays in one place? What effect does downforce play in your 'arrow' model? Why would a car be like an arrow when everything else about them is different. Have you ever shot an arrow in a crosswind? I personally just love the hammer analogy as well. It has even less to do with vehicle dynamics..
 Dave

[Rex Schimmer]

CP, as related to stability in traveling in a straight line at high speed,(kind of sounds like Bonneville doesn't it!)is a function of the car shape in the elevation (side) view and is defined as the point on the car that all of the aero forces acting on the car, in side view,can be summed and that resultant force acts at the CP. So if you add a big tail fin on the back of your car, you move the CP rearward and hopefully behind the CG which increases straight line stability. There, of course, is also a CP for the vertical force generated by the cars shape, and these forces it can be up or down, preferably down. This CP is really defined by the cars shape and any aero appendages that it may have and I don't believe that it would move much without a change in the cars attitude as related to the ground and air flow. Cars with full and flat belly pans, when set at a proper ride height and angle can certainly generate some down force and if at speed the attitude of the car changes such that the relationship between the belly pan and the ground changes it can certainly change the CP for the downforce generated by the flat bottom. If it gets to low it can effectively block off air flow and halt any down force generation which usually results in the car then raising back up to a height that allows air flow and then the the down force is re-established and the cycle starts again. This can happen at a fairly rapid rate, several hertz, and in the old days of F1 with gound effects and side skirts, they called it "porposing".
 
 Rex

[Stan Back]

Yaa -- but why dint they just include them together?  Weight distribution is not an issue covered by the Rule Book and they're all rear-wheel drive.

[John Burk]

In 58 or 59 Jim Culbert ran a front wheel drive roadster at bonneville - It probably didn't handle well because it lacked negative offset front wheels so it didn't start a trend - A roadster with front drive gains traction and stability.

[jimmy six]

There are currently 2 front wheel drive modified roadsters running that I know of..Both are under the "G" size engine