CP, COG, weight transfer

[HNORD]

I heard roadsters has issues of spinning, if more than others I can’t say.
Maybe its roadsters more like the street versions with short wheelbase and a high placed heavy engine.
As I’m new into this but I heard of CP and COG.
( from dragracing I’m not new into weight transfer )
But if we look into a gas roadster and say wheelbase at 120” and one try get the engine as low as possible ( FH and dry dump oilpan )
I bougt steel body parts for a 29 and chassie will be dual rail tube and coilovers front/back and plan sit in trunk and sit low so only helmet is over body.
-But how will one plan weight distribution ?
Rules allove wheelbase and engine set back 25% from front axle, but in case of traction and landspeed is there a common idea.

I would not be have allot of power as a NA old school engine under 300 cubic on gas.
Goal is 200 MPH but that might not be possible - but 150 should be realistic so with this factors how to plan CP, COG, weight transfer.

[Paulin adelaide]

I cant answer any of your query's but start with " the purple sage trading post " website Bonneville pages for lots of info.

[Eric Engle]

There's a lot of helpful info on that website. Thanks!

[SPARKY]

study scrub radius and weight jacking when you turn the steering wheel.

[manta22]

Fore & aft weight transfer should not be a problem at Bonneville. A roadster has the aerodynamics of a brick so CG & CP are important. I maintain that suspension geometry is still important at Bonneville. It's a "straight line" race but if a car gets a little out of shape, you don't want the suspension geometry to make it worse. The Ford Mustang II front suspension geometry is very good and a well-located solid rear axle is OK. Keep the roll stiffness high with anti-roll bars.

[Interested Observer]

Further to Manta?s comment on weight transfer due to acceleration, weight transfer due to aerodynamics can be significant at Bonneville, especially for large bluff bodies like roadsters.

[manta22]

Further to Manta?s comment on weight transfer due to acceleration, weight transfer due to aerodynamics can be significant at Bonneville, especially for large bluff bodies like roadsters.

True, especially for tall bricks. However, it transfers to a straight axle so if the spring rates left & right are equal, you'll still go in a straight line. The engine is in the heavy end in a roadster so weight transfer to the rear just improves traction.

[kiwi belly tank]

Most fast roadsters have added ballast weight & are heavy so getting a balance you like isn't a problem. Weight adds to traction & stability on the salt.
  Sid.

[manta22]

I visited a shop of a prominent roadster in Phoenix a few years ago and I noticed a Panhard bar on their rear axle. Unfortunately it was not mounted so that it was horizontal, so as the rear end of the car moved up and down, the rear axle was moved back and forth sideways. Not cool for stability. A Watts linkage would have been a better choice.

[HNORD]

Manta,

I need read more on CP and COG.
So even slimmer/longer GR roadsters are concider as ?bricks?.

Shocks is also s subject.
You was into solid rear axle, is that no dampers etc (?)
Shore less movment but must be a jumpy ride.
Dampening might take some power out.
I note in front one can has a 4-link, coil overs and anti rollbar under hood.
If fronts are more important than rear.

[manta22]

Manta,

I need read more on CP and COG.
So even slimmer/longer GR roadsters are concider as ?bricks?.

Shocks is also s subject.
You was into solid rear axle, is that no dampers etc (?)
Shore less movment but must be a jumpy ride.
Dampening might take some power out.
I note in front one can has a 4-link, coil overs and anti rollbar under hood.
If fronts are more important than rear.

HNORD,
They are "bricks" relative to more aerodynamic shapes such as streamliners, competition coupes, etc. It is a result of the traditional roadster shape that is now written into the rule book.
Nobody in his right mind would run any type of suspension without damping of some kind.
Suspension geometry is a complicated subject and the best approach depends on the type of racing you are going to do.

[Stan Back]

Here're some weight figures that after we added more weight to our only 15% set-back 7 record-setting Street Roadster.  You just gotta put the heavy stuff back and make it sturdy.  We only spun once at Bonneville -- in the Notch.

[Happy Pappy]

Wouldn?t you want a percentage of total front weight versus total rear weight? (1398 & 2212)
Guess  I am confused to the total left side vs. total rear.
I figured this way... Front 1398/3610=38.73% and Rear2212/3610=61.27%

Thank You for the Help.

Chris

[Stan Back]

I think you got it.  We were adding some weight and trying to stay near 40/60 split.  Ended up 1% off or so.

And tried to keep it equal side to side and missed that by 1% or so, too.

The whole car was built to try to get to 40/60 split front to rear and 50-50 side to side.  What you saw were updated specs when weight added.

The chassis is all 1/4-inch steel with rails that tapered in width and depth from back to front.  Car always competed as a street-licensed vehicle.  Could have been faster with channeling and aero improvements now allowed like smoothed fiberglass bodies, silly lens-wrapped headlights, laid-back grille shells, etc.  Sour grapes?  Just made Cabernet out of them.   

[kustombrad]

I see lots of comments about front and back but not a lot of people take into account what's going on under power. Setting up even side to side weight is fine when the car is stopped, but under acceleration that goes right out the window. Watch drag racing with cars who's suspensions aren't set up and you'll understand. Under power the car is trying to twist itself with both the left front and right rear trying to pick themselves off the pavement. On massively high HP cars, the right rear is actually forward (not square) to compensate for the left side pushing harder. On less HP cars they run either a rear "sway" bar with more cross weight put in or just crank up the right spring pressure on a non bar setup. Years ago I started watching videos (both in car and out) of cars spinning out at El Mirage and Bonneville trying to figure it out. The majority of times the car hangs a hard right (left rear tire planted!) or a dance to the left from overcorrecting. Landspeed racing is just a really long drag strip where both tires need to be planted evenly all the way through...