Racecar Engineering Vol 9 No 4 - Ortiz on Dynamic Load Transfer

[e043656]

I'm beating my brains out trying to decide if the "Asymmetrical Racecar Part 2" article has an error or not.

Page 44: "The basic rule is that the stiffer end gets the greater load transfer. Load transfer at the softer end is correspondingly reduced. This increases cornering power at the softer end and reduces cornering power at the stiffer end."

(I agree)

Page 48: "If we have a tight-on-slick condition, we can improve the car by creating a setup that produces less wedge when cornering forces are modest, with a greater wedge gain as cornering force increases. To obtain this, we would decrease static wedge, and make overall roll resistance distribution more front-stiff.

For a loose-on-slick car, we would do the opposite: more satic wedge, with a more rear-stiff roll distribution"

I would think tight-on-stick would require LESS front-stiff (not more) and that loose-on-stick would require LESS rear-stiff (not more).

Or is Mr. Ortix saying that the static wedge dominates the "modest cornering force" situtation and the roll resistance dominates the "more than modest cornering force" situtation.


Any thoughts?

[GordonG]

I think he is saying that the wedge is more dominant on less grippy conditions. Imagine driving on ice (normal tyres) - there is virtually no dynamic load transfer so the corner weights will be more or less as per static, ie totally dominated by the degree of wedge applied. So if you wedge the car with 50lbs more on the RHF than the LHF then you have 50 LBS more on the LHF in cornering.

When you go to a grippy surface with sticky tyres, there will be more load transfer from the cornering forces, so the relative stiffness of the front and rear becomes more relevant. If there is 500lbs of laod transfer to be shared between the front and rear, you could easily cancel out (and then some) the wedge.

So you wedge the car for slick condition balance, and tune the ARBs /springs/roll centres so the car remains balanced as the grip improves.

Glad I race on proper circuits with left and right corners and dont have to worry about all that asymetric stuff...

G

[phoenix]

I am guessing that the "wedging" would be on the right rear corner on an anti-clockwise oval. If this is the case, reducing the wedging would give the rear outside tyre less load and therefore reduce the oversteer or "tight on slick" situation. Without knowing that as a fact what follows is purely conjecture:

I agree with you that having made this adjustment to the wedging it would seem that increasing the front roll resistance would have the same effect as de-wedging the outside rear tyre, so the two adjustments would appear to be in the same direction.

Not being an oval racer I have never used wedging, so I don't know if the effect of wedging reduces with cornering speed and load - but I imagine it wouldn't.

However, if the effect of wedging does reduce with speed, then stiffer front roll resistance, which transfers more load in proportion to speed, would add understeer/kill oversteer as cornering speeds got higher.

I haven't read the article yet, but it appears from what you have written that maybe Mr Ortiz could explain his thinking in a slightly clearer way, or provide some additional explanation.

[e043656]

Ah, I don't race ovals either, but we have some road courses that are so dominant in one direction that we still use wedge

[glenn22481]

someone please define 'wedging'......I dont have the funny handshake that racecar engineering readers have

is this 'wedging' the same as a 'controlled jacking effect' eg: preloading a corner of the car as oval racers would?

sorry for not being clued up but i would like to stay on track of this thread..

[ubrben]

Originally Posted by GordonG

I think he is saying that the wedge is more dominant on less grippy conditions. Imagine driving on ice (normal tyres) - there is virtually no dynamic load transfer so the corner weights will be more or less as per static, ie totally dominated by the degree of wedge applied. So if you wedge the car with 50lbs more on the RHF than the LHF then you have 50 LBS more on the LHF in cornering.

When you go to a grippy surface with sticky tyres, there will be more load transfer from the cornering forces, so the relative stiffness of the front and rear becomes more relevant. If there is 500lbs of laod transfer to be shared between the front and rear, you could easily cancel out (and then some) the wedge.

So you wedge the car for slick condition balance, and tune the ARBs /springs/roll centres so the car remains balanced as the grip improves.

Glad I race on proper circuits with left and right corners and dont have to worry about all that asymetric stuff...

G

Unless you're racing at Suzuka you'll always do 360 degrees more cornering in one direction.

Snetterton, Donington, and Thruxton are all very biased to the right. If you bias the corner weights to the inside front wheel you'll probably be able to brake a bit later, worth having...?

Ben

[ss_collins]

I don't think our readers have a funny handshake - mind you we do have one Tony Tobias on the staff so anything is possible