Weight distribution / CG what is ideal

[Salty Nuts]

What is preferred as far as weight distribution is concerned (roadster)?

[jl222]

What is preferred as far as weight distribution is concerned (roadster)?

    Talk to Wilson and Waters or Chuck Salmen both are record holders over 250mph and run suspension and i don't think a lot of weight. Formula 1 cars run around 65% on rear tires not counting downforce from wing.
    Some roadster run more weight than the above cars weigh.
   Depends also how much hp and how fast you go.
   Also if you add weight its better to keep it from being to far back and keep low.

                       Good luck JL222
         
     

[panic]

This is a dilemma, since good high speed handling (viz. sports cars, F1 etc.) is very different from LSR.
Too much weight in the rear is (always, assuming RWD) good for traction, but not necessarily for handling unless the suspension rates, tire width differentials, etc. are on track or oversteer results. You don't really want to run tires that wide in the back - too much rolling resistance, too much width, more unsprung weight.

The 2 (main) methods of increasing tractive effort are weight and aerodynamics.
Weight is predictable, linear (more is better in direct ratio), reversible, cheap (comparatively), and easily adjustable. Downside: it reduces acceleration, and changes center of gravity location.

If rules permit, downforce is preferred over weight for traction. It doesn't reduce acceleration (i.e., mass is constant), and the amount of added traction can be very large.
The problem is that it's not legal in all classes, expensive to make or buy, not very adjustable as to location (position & height), and very difficult to anticipate the exact effect it will have. It also changes the car's angle of attack (relative nose height) as speed increases, and may unload the front wheels and permit air under the car. Higher downforce generally requires higher drag (larger surface, greater angle of attack), which eats power at high speed (but need not be a problem if the car is traction limited). It also stops working if the car yaws more than a bit, and lifts the tail if the car spins, so handling in an incident becomes scary.

Both load the suspension and structure in proportion to their location, exactly above the rear wheels = 100%, but cantilevered behind the rear wheels = more than 100% (and removes some weight from the front wheels). It can even be added directly to the axle (illegal for aero devices in some racing), within reasonable limits (or bending results, plus unsprung weight penalty).
Whatever method is used, the aero center of pressure (in elevation or side view) should be behind the center of gravity for stability. When you add weight or downforce to the rear wheels, the center of gravity may move back too close to (or even behind) the aero center, which is an unstable condition.

There's more, but look at the rules 1st, then figure how "do-able" hiding weight is vs. adding a wing.

[sockjohn]

Too much weight in the rear is (always, assuming RWD) good for traction, but not necessarily for handling unless the suspension rates, tire width differentials, etc. are on track or oversteer results. You don't really want to run tires that wide in the back - too much rolling resistance, too much width, more unsprung weight.

Can you run a FWD roadster?  Seems to have worked to advantage on a lakester before.  I wonder how wide tires in front, skinny in back would work out in the wind tunnel, easy enough to try without fully committing.

Just a bike guy that will have to run OneWD   

[maguromic]

No more 4Wd roadsters.

[roadsterman]

They killed the 4WD roadster because the powers to be did not want to see a 4WD roadster go over 300 before a normal fuel/gas roadster did. 

[RichFox]

FWD might mean Front Wheel Drive. There is at least one of those running and doing well. But it's ugly I think

[kip305]

Salty: I believe that there is at least one discussion of this topic in the archives.  It was quite extensive. Some of those people are still on the forum.
Kip

[jl222]

  Salty
  I agree with panic about land speed racing being different than sports car or other types of racing but most of high speed handling has come from road racing when it was discovered that high speed oversteer was caused by aero lift resulting in tires with little contack with track. Jim Hall ''Chaparral'' were one of the first to use spoilers and then wings to spoil lift and get downforce. 4 link and latter bars came from drag racing and high boost and hp came from formula 1. Also Hall used an adjustable spoiler before the wing came along which landracers can still do ''wings also''.
 We need to look at pro racing they have a lot that we can use.
 In landspeed racing to little weight on rear as in road racing-oval track -grand national-drag racing, results in wheel spin and oversteer.
 Get ''Tune to Win'' by Carroll Smith which explains handling problems and what to do.

                                Good luck JL222

[GH]

John, if you were going to build a new car with a smaller, less hp engine, would you build it as light as possible and add weight later if needed, or build it heavy to start with??

[jl222]

John, if you were going to build a new car with a smaller, less hp engine, would you build it as light as possible and add weight later if needed, or build it heavy to start with??

  Hi Gary

 I would go light as possible with engine set back as far as rules allow and as much weight on rear tires as possible with out getting to much behind rear axle centerline but some. Try to get down force from spoiler or wing and low pressure under car and add weight later if needed. Well you no me always preaching light springs and 4 link suspension.
 Roadsters are at a disadvantage with out spoilers or wings.
 What are you putting that 6 cyl in?

                                        JL222


 PS. I'm not saying light as possible, i like funny car cages in coupes and midplates for engines and strong frames.
      Weight is not as much of a penalty in LSR as other types of racing but some [unless you need it for traction as a last resort]

[sockjohn]

FWD might mean Front Wheel Drive. There is at least one of those running and doing well. But it's ugly I think

Yes, I meant front wheel drive.

Ugly?  I think that sort of thing is an abonimnation of all that is holy!   

But if it's in the rules, and makes life easier/better, why not?

Lots of engine choices in 2.0 liters and under in FWD, and no so many in RWD.  Many of the FWD platforms are well proven in drag racing and have many off the shelf parts available to boot.

BWDIK

[Joe Timney]

Think of an arrow...the weight is on the nose, with tail feathers to guide it straight. I believe that for a door car, 51 or 52 percent on the nose helps. Keep all liquids and ballast between the wheelbase ( avoiding the barbell effect), mounted low. Long cars have drag to aid in keeping them straight.

Just an old chassis guy with all the scars to prove it,
joe

[jl222]

  I asked Les Leggitt how much weight they had in the 333+mph Lindsley-Leggitt Firebird and he said ''more than you would believe'' this in altered class with roots blown hemi with max engine setback.

                                        JL222

[bvillercr]

Think of an arrow...the weight is on the nose, with tail feathers to guide it straight. I believe that for a door car, 51 or 52 percent on the nose helps. Keep all liquids and ballast between the wheelbase ( avoiding the barbell effect), mounted low. Long cars have drag to aid in keeping them straight.

Just an old chassis guy with all the scars to prove it,
joe

An arrow doesn't have wheels trying to drive it.  Also if you have too much weight on the front you limit the amount of traction on the rear wheel.