Cornering Analysis

[TT205 42]

If you welded the suspension solid you would not get any transfer at all .

 

 

peach!! lmfao

[Rippthrough 98]

If you welded the suspension solid you would not get any transfer at all .

 

 

In that case - why do go-karts load up the outside wheel and lift the inside ones?

 

Chassis roll only accounts for a very small portion of the amount of load transfer when cornering, hence the stiffer springs will mean more imbalance between the front wheels and less effective use of the tyres.

If the geometery is ideal in either case you always generate more grip with soft springs compared to hard springs, because the tyre loadings are more consistant.

It's just that we don't live in a ideal world and the body roll buggers the geo. up.

 

 

Sometimes those textbooks are right you know

Edited May 28, 2010 by Rippthrough

[crf450 0 1 Cars]

In that case - why do go-karts load up the outside wheel and lift the inside ones?

 

Chassis roll only accounts for a very small portion of the amount of load transfer when cornering, hence the stiffer springs will mean more imbalance between the front wheels and less effective use of the tyres.

If the geometery is ideal in either case you always generate more grip with soft springs compared to hard springs, because the tyre loadings are more consistant.

It's just that we don't live in a ideal world and the body roll buggers the geo. up.

 

 

Sometimes those textbooks are right you know

 

Yep sorry I wrote that in a bit of a rush and it would have been clearer if it had read "If you welded the suspension solid you would not get any of the additional weight transfer associated with chassis roll.

 

I agree going too hard with your springs is gonna create problems but at the end of the day the flatter you can get your car cornering that better and the only way of doing this if your not going uprate your front ARB is to up the spring rates. That's why they run up to 750lb springs on the previous model of Clio cup car which is comparable to a 205 as it has macpherson struts and is a similar weight.

[Rippthrough 98]

Depends if the roll points and CoG are comparible too though, but you're going to be somewhere in that region for a car that's scraping the tarmac and track-only.

[Cameron 16]

Harder front springs reduce weight transfer which seems pretty obvious too me.

 

Nein! You increase the roll stiffness at an axle then you also increase the weight transfer at that axle accordingly.

[Cameron 16]

Yep sorry I wrote that in a bit of a rush and it would have been clearer if it had read "If you welded the suspension solid you would not get any of the additional weight transfer associated with chassis roll.

 

I agree going too hard with your springs is gonna create problems but at the end of the day the flatter you can get your car cornering that better and the only way of doing this if your not going uprate your front ARB is to up the spring rates. That's why they run up to 750lb springs on the previous model of Clio cup car which is comparable to a 205 as it has macpherson struts and is a similar weight.

 

Yeah but at the end of the day the single biggest variable affecting weight transfer is the roll stiffness, which can be attributed to springs and anti-roll bars. The total amount of weight transferred can only be changed by either reducing the weight of the vehicle or lowering the CG height. By changing the roll stiffness front and rear you're altering the roll stiffness distribution and also altering the load transfer distribution, which therefore affects the distribution of grip AKA the handling balance. I'll explain why:

 

When you're cornering, the "centrifugal" force acts on the centre of gravity. Since the centre of gravity is a certain height above the ground you will generate a torque (roll moment (moment = fancy word for torque)) equivalent to the force acting on the CG multiplied by the height above ground. This roll moment then produces a change in vertical tyre force equal to the roll moment divided by half the track width, to turn torque back to a force. This change in vertical force (normal load) is called the load transfer. This can be used to find the total load transfer, and you can hopefully see that the only way to alter it would be to either reduce the mass or the GC height, or increase the track width.

 

Unfortunately if you want to calculate things for both axles it becomes a bit more complicated as you then have to account for the different roll stiffness front and rear, and the weight distribution. To work this out you have to use the roll stiffness to find the front and rear theoretical roll angles, which is the body roll angle at each axle assuming that they aren't connected by the chassis. You work this out by multiplying the roll stiffness (Nm per degree) by the roll moment (Nm) to give a roll angle. If the front and rear roll stiffnesses are different, you'll get a different theoretical roll angle! The effect of roll stiffness distribution then becomes clear when you join the two ends of the chassis back together. Since the front and rear theoretical roll angles are different, the actual body roll angle must be half way between the two (assuming the chassis is perfectly rigid). Say the front roll angle was 2 degrees and the rear 4 degrees, the body roll angle would be 3 degrees, meaning the front will actually be experiencing a greater roll angle than it should, and the rear experiences a smaller roll angle. This means the front end will have a greater amount of load transfer because the "spring" that is the front roll stiffness will have been "compressed" more!

 

So basically, this means if you increase the front roll stiffness you will increase the front load transfer!

 

Of course this all assumes that the chassis is perfectly rigid, which it isn't! When the chassis is flexible, the roll stiffness distribution has a smaller effect on the load transfer distribution. A very stiff chassis will be very sensitive to adjustments to spring and anti roll bar rates, whereas a floppy chassis will not.

 

You're right about increasing the spring rates having a positive effect on handling if they're changed as a whole front and rear, but you won't have reduced the load transfer. You will benefit from keeping your geometry through minimal body roll, but you'll lose out on rougher surfaces as you'll be relying on the tyres to absorb small bumps rather than the springs. This is bad because the tyres are essentially undamped springs, so you could find yourself losing grip.

[edbar 6]

So in lamens terms is a bigger ARB with standard TB's the best way to go?

[Cameron 16]

No.

 

Then you'll have a back end that is too soft on bumps and you may bottom out. You should really match the spring rate increase front and rear to maintain the balance. ARB's should only be used to fine tune the handling, so a thicker one is only necessary if you think the car needs it. For example if it tends to understeer a lot then providing the problem isn't down to your throttle control fitting a stiffer rear ARB will balance the handling out. Go too thick and you'll be going everywhere sideways or backwards.

Edited May 29, 2010 by Cameron

[edbar 6]

Thats what i thought but got a bit lost along the thread. Hear so many differant views on this topic hard to know what to belive but that is what make ssense to me.

[j_turnell 137 3 Cars]

Getting it corner weighted and 4 wheel alligned is always a good start.

[edbar 6]

Having the tracking done on mine was one of the biggest improvements I've ever done, the front was toeing in 5 degrees each side, was a real hedge finder and was always wheel spinning and weaving under acceleration. Set the toe to parrallel and its a differant car!

[Cameron 16]

It's amazing how much difference tracking makes actually, considering it's such an unexplored modification. Seems funny that people will go to great lengths and expense to modify their suspension and not think to deviate from the factory toe settings.

[edbar 6]

Couldn,t agree more, just like an engine the chassis will only be good with a good set up. On my car it really was like night and day, and you only have to look at my build thread to realise I renewed and bettered everything as I went along (new arms, rear beam, drop links,shocks, top mounts) it only started to handle after the tracking was done. I want adjustable front camber next and coilovers so i can get a decent set up and see what benefits that yields!

[nick 3]

I've read and re-read this topic numerous times now and still can't get my head round how stiffening the front springs will INCREASE weight transfer.

 

Can someone please explain in plain english (including crayon drawings if need be..) how this works.... it seems to go against basic physics....

 

When you want to reduce weight transfer under braking on a motorbike, you stiffen the front springs or increase preload, this reduces w/transfer to the front and keeps the back wheel on the deck increasing stability, why does this differ on a car?

 

On an even more basic level, if I was sitting in a chair with soft springs on each leg, if I leant forward a lot of weight would "transfer" that way.... If I put stiffer springs on the front legs and then leant forward by the same amount less of my weight would transfer.... or am I missing something fundamental here!!??!!

 

Why do drag racing cars run the SOFTEST rear springs (talking rwd here...) as possible to increase the weight transfer on launch to aid traction? Is that not just a reversal to what we are talking about in this thread??

 

Nick

[oz. 2]

From what I understand the same amount of weight is transfered on soft or hard springs as there is still pressure pushing that way. Having a stiffer spring would stop the car from moving about above the wheels.

 

Drag cars have soft suspension at the rear because they're trying to maintain the highest amount of grip possible. As they're not cornering they don't need the stiffer springs to counteract bodyroll.

[Cameron 16]

You're confusing roll angle with weight transfer basically. Think about it, if you have a very stiffly sprung front end then you're resisting body roll more at the front than the rear. This must mean that you're then getting more load transferred at the front end in order to satisfy the basic laws of physics (equal and opposite reactions etc).

 

If you want a really good explaination with pictures and diagrams, see if you can get hold of a copy of Millikens' Race Car Vehicle Dynamics from a library or something. It's probably one of the best books on the subject and has everything you need to know worded in a way that isn't over-techy and confusing.

Edited May 30, 2010 by Cameron

[oz. 2]

I'm fine. I was just trying to make sense an type it up in simple speak for others. Looks like I failed though!

[Henry 1.9GTi 36]

I actually typed it without the use of a text book.....

 

So heres a passage from a piece of paper.

 

"By adjusting the roll stiffness at each end of the car, it is possible to alter the distribution of weight transfer front to rear and so alter the vertical load on the tyres. Since the lateral force that a tyre can develop depends on the vertical load, doing so alters the amount of lateral force generated front to rear changing the yawing moment and so affecting the understeer gradient. Total weight transfer can never change but its distribution can."

 

"If the same lateral cornering force is applied to a body with unequal spring stiffness (roll stiffness), and the weight transfer must remain the same scince the same lateral force is applied, then the end with a higher spring rate will exert a much larger force."

 

Read, F=kx (spring stiffness x displacement) If the the amount of roll front to rear differs, the car is twisting.

 

moving a spring that is softer than another the same amount as a stiffer spring will require less force. So you can imagine you have to compress both front and rear left of the car the same amount, the stiffer end requires more force and therefore the force applied by the tarmac to the tyre is higher.

 

anyway what was the OP??