Racing car without swaybars?

[sierra4000]

Hello,

is a good idea?
with low center of gravity 4WD racing car without swaybars? (maybe only small rear bar for balance)

some other reason swaybar for use in racing?(than corner balancing)

thanks for your opinion!


Radek

 

[cibachrome]

NO. The TLLTD does NOT change with lateral g unless you have non-linear springs. Its usually VERY constant unless you have some weird camber changes or a direct acting front bar and high steer angles or very high tire MX/FY action.

 

[GregLocock]

sierra - fantastically good question. everything else is moot until you know this. (a) wag 600mm (b) measure it (c) work it out from your vehicle roll gradient and measured roll stiffness etc (d) build a spreadsheet model.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[sierra4000]

Sorry ,I asked the wrong
What is the typical value of the CoG height for example:
WRC car (asphalt - low version)
WTCC car
DTM car
NASCAR
I know that my calculation will be incorrect,but help understand the connection.

 

[Komodo86]

I know that an MX5 is 18". The rest is just a guess tbh. I would estimate most saloon road cars to be 20-22".

NO. The TLLTD does NOT change with lateral g unless you have non-linear springs. Its usually VERY constant unless you have some weird camber changes or a direct acting front bar and high steer angles or very high tire MX/FY action.

You and I have a very different understanding of FLLTD then. How can it NOT change?

At 0g the FLLTD is 50%. At the point of both wheels lifting, it is also 50%.

At any point between those two extremes, it is dependant on the RSD and the SWD.

In a 50/50 WD vehicle, with a non equal RSD, the stiffer axle will transfer load faster, up until the inside wheel is completely unloaded and lifts off the road, at which point the LT across that axle is 100%. The softer axle will be at less than 100% load transfer as the inside wheel is still loaded, and so the FLTTD at that point is not 50%. Past this point, the softer axle continues to transfer load until it to has transferred 100% of it's static load, at which point the FLLTD is once again 50%.

Please explain how you think it remains constant.

 

[sierra4000]

Thanks, I thought that probably is higher than Mazda

 

[Komodo86]

Yes, RX8 is also in the 18" region, Porsche Cayman and Toyota GT86 are also very low in the 17-18" range. These are all very low CG production vehicles.

Work from those examples and have a think about where the weight is in your car. A saloon car with a high roofline, large glasshouse, upright engine with heavy DOHC head and perhaps high mounted turbocharging equipement is all going to add to that height significantly.

An upright alloy block with heavy DOHC head is going to have a higher CG than a cast iron block V8 with pushrod alloy heads, a lot of sound deadending removed from the floor of the car will move it up, poly windows will move it down, so on so on.

 

[sierra4000]

I understand,
look ,is nothing superfluous

 

[Komodo86]

Rollcage is heavy and high mounted though...

Really, the only way to be sure is to determine it with a tilt test, but it's a bit time consuming as you need to replace the front suspension with rigid links to do it accurately.

 

[Komodo86]

NO. The TLLTD does NOT change with lateral g unless you have non-linear springs. Its usually VERY constant unless you have some weird camber changes or a direct acting front bar and high steer angles or very high tire MX/FY action.

You and I have a very different understanding of FLLTD then. How can it NOT change?

At 0g the FLLTD is 50%. At the point of both wheels lifting, it is also 50%.

At any point between those two extremes, it is dependant on the RSD and the SWD.

In a 50/50 WD vehicle, with a non equal RSD, the stiffer axle will transfer load faster, up until the inside wheel is completely unloaded and lifts off the road, at which point the LT across that axle is 100%. The softer axle will be at less than 100% load transfer as the inside wheel is still loaded, and so the FLTTD at that point is not 50%. Past this point, the softer axle continues to transfer load until it to has transferred 100% of it's static load, at which point the FLLTD is once again 50%.

Please explain how you think it remains constant.

Just to expand on this some more.

At 0g, '0% LT', FLLTD is 50%. At point of both wheels become unloaded, FLLTD is also 50%. Lets call this '100% LT'.

Let's look at 10%, 20% and 30% LT.

2000lb 50/50 SWD, with a 60% front RSD.

At 10% LT there is 200lbs LT, of which 60% is taken by the front.

Front LT is 200 x .6 = 120lbs. The outside front tyre has 500+120 = 620lbs load.
Rear LT is 200 x .4 = 80lbs. The inside fear tyre has 500-80 = 420lbs load.

FLLTD is (620+420)/2000 = 52%

At 20% LT there is 400lbs LT, of which 60% is taken by the front.

Front LT is 400 x .6 = 240lbs. The outside front tyre has 500 + 240 = 740lbs load.
Rear LT is 400 x .4 = 160lbs. The inside fear tyre has 500-160 = 340lbs load.

FLLTD is (740+340)/2000 = 54%

At 30% LT there is 600lbs LT, of which 60% is taken by the front.

Front LT is 600 x .6 = 360lbs. The outside front tyre has 500 + 360 = 860lbs load.
Rear LT is 600 x .4 = 240lbs. The inside fear tyre has 500-240 = 260lbs load.

FLLTD is (860+260)/2000 = 56%.

Thus, FLLTD varies with acceleration.

 

[sierra4000]

not a lot of added weight with rollcage,
but a dramatic increase torsional stiffness!!really

 

[Komodo86]

It might not be a lot in absolute terms, but in relation to the sheet sheets of ally and perspex windows it shares it's space with up there, it will be heavy.

It won't affect the CG greatly, but it will certainly raise it slightly vs having no cage at all.

Given the spartan interior and I'm guessing an iron block DOHC engine, as a total guess I'd probably quote your CG being in the 19-20" region.

 

[sierra4000]

Yes ,
but engine is 4.0 V6 (60 °) SOHC mustang cast-iron block+alu heads

 

[Komodo86]

Er, god knows then! Tilt test would be best for you, shouldn't be too much hassle looking at the work gone in to the build!

 

[NormPeterson]

Crude approximations of vehicle CG height have been given as the height to the camshaft for cars with pushrod (cam in block) V-type engines.

More reliably, there is this NHTSA database (the CG information starts on page 10).

http://www.nhtsa.gov/DOT/NHTSA/NRD/Multimedia/PDFs/VRTC/ca/nhtsa_inertia_database_english.pdf

Norm

 

[NormPeterson]

Front LT is 200 x .6 = 120lbs. The outside front tyre has 500+120 = 620lbs load.
Rear LT is 200 x .4 = 80lbs. The inside fear tyre has 500-80 = 420lbs load.

I think you may be confusing lateral load transfer with the relationships among the resulting wheel loads after the load has transferred.

LLT = Lateral Load Transfer, which is only the 120 and 80 numbers in that particular case.

The only way the distribution of LLT can vary is if there is some nonlinearity involved. The only way that would amount to much would be if said nonlinearity is significant - such as in the case where an inside wheel lifts, or where significantly nonlinear-rate springs are fitted at one end and linear rate springs at the other.


Norm

 

[Komodo86]

I think you may be confusing lateral load transfer with the relationships among the resulting wheel loads after the load has transferred.

FLLTD = Front Lateral Load Transfer Distribution i.e. how much load transfer has happened at the front. It changes with lateral acceleration.

Perhaps it should be called 'Front Diagonal'.

Whatever it is called, the differential between front and rear load transfer is not constant.

 

[NormPeterson]

Of course the load transfer itself changes with lateral acceleration. But the static snapshot of how it is distributed front vs rear is not, assuming that there are no nonlinearities in the geometry or stiffness terms.

You'll note that your 120/80, 240/160, and 360/240 load transfers are all in a 60/40 distribution.

Adding outside front and inside rear cornerweights and expressing that as a percent of total car weight is crossweight or "wedge" in circle track slang, and this will of course vary.


Norm

 

[Komodo86]

Ok, I had the wrong terminology there then, thanks!

 

[sierra4000]

Thank You all for responses!!

Radek