dvaid852456

I have searched through the on-road section and could not find a discussion directly about droop. Only regarding specific settings for specific cars.

I wondered if anyone can help or give their experiences, specifically regarding front droop settings on touring cars.

I understand the theory, that more front droop increases weight transfer to the rear on acceleration and more rear droop increases weight transfer to the front under braking and vice versa.

BUT...

I always find that reducing front droop helps to add on power push and calm down an over-steering car, especially on carpet.

Shouldn't the opposite be true? If you increase front droop, thus increasing weight transfer to the rear on power, shouldn't this cause under-steer on power as the rear wheels have more grip?

Or is it a case that more weight on the rear wheels under acceleration in high grip situations actually pushes the car round more and as the nose of the car is in the air and has less grip?

dvaid852456

One theory I have is that altering weight transfer with droop also affects the roll at the end of the car that you alter droop.

Is it a case that reducing droop at the front reduces roll at that end and gives a little less lateral grip, thus creating on power push?

dvaid852456

I just found this which ties in with my theory. If my car is over-steering on carpet I usually go with stiffer springs in the front, a thicker front roll bar and a small decrease in front droop. This seems to help calm the car by reducing the front grip.

Antimullet

iTrader: (65)

Things reverse themselves past a certain threshold.

Do a test. Zero out droop, drive car.
Then add only front droop, drive car.
Then zero front and add only rear droop drive car.
Then add droop front and rear and drive car.

Record handling traits of each test. Then you have a baseline idea for each chassis.

dvaid852456

A sound plan, I just need to set aside a club night and get some testing under my belt. I do find on carpet the track changes each round so you can be fooled into thinking a setup change has given you more grip when it is actually just the track rubbering in.

I have found cranking things to the max and then the min can give false feedback as you mention, over a certain point a setting can have the opposite effect. Best as you say, to try it from 0 and add a bit at one end to observe the effect.

slotracer577

Don't confuse body roll or movement with weight transfer. They are often exactly opposite. Usually softer has more body movement and less transfer of weight. A stiff chassis has effectively infinite transfer of weight and potentially no body movement.
Trophy trucks are a great example. They have huge body movement on soft springs to reduce weight transfer since they race on low traction surfaces. Put them on a high traction surface and they almost roll over.
Look at how anti roll bars work, they stiffen up the vehicle in roll, increasing weight transfer and reducing roll. Usually they result in a net reduction of traction due to the increased weight transfer. That is ok since they are usually used on high traction surfaces to control body movement.

snuvet75

iTrader: (16)

Great point.

To OP, once weight transfer has taken a set in with more droop F, it should push the car on power. But b4 it takes a set in, the rear traction is actually lower compared w less F droop which can make the rear step out. It is only a brief moment tho. If ur car is loose rear with more droop F, it could be due to something else. E.g. rear chassis bottoming, u turn ur car too hard on power,etc.

dvaid852456

So if roll increases it doesn't automatically mean the weight transfer does. If I increased front droop and created more body roll towards the rear I may have to increase the rear spring rate to push back against the body roll and thus increase weight transfer at the rear and ADD grip?

Does roll increase grip or is it weight transfer? Or neither or both

"a net reduction of traction due to the increased weight transfer" - I always thought an increase in weight transfer was putting more weight over say the rear wheels and giving them more grip. I also thought body roll was the action that added that extra weight. If body roll doesn't add the weight over the wheel and is the opposite to weight transfer why does body roll increase traction such as in the example of the trophy truck?

I am struggling to wrap my head around this but thanks for the replies so far. I just think if I can understand it a little better my setup skills will improve.

dvaid852456

If anyone is struggling to get to sleep this site has a VERY in depth explanation of load transfer Weight Transfer: how it works and how to use it in setup

All this has done is confuse me further as to exactly what we mean when we use the term roll centre

You have the centre of gravity of the car and an imaginary point called roll centre. Years ago I thought raising the roll centre reduced roll as you were putting the RC point nearer the COG. Then it seemed from reading other guides lowering the RC reduced roll as the "roll point" of the car was lower.

So are we using the wrong term when we talk about roll centre in model cars?

Does lowering or raising the roll centre reduce roll?

According to this website Raising the RC decreases roll and lowering the RC increases roll, https://balancemotorsport.co.uk/suspension-geometry

The Hudy Setup guide says:

Weight transfer is the key to car handling. Consider that a car has a certain amount of
“weight” on various parts of the car, and on each wheel. By transferring weight to one
end of the car (front or rear), to one side (left or right), those tires will be forced onto the
racing surface more, and will have more grip or traction.
Weight transfer is affected by the car’s set-up and by the way that you drive.

A “roll center” is a theoretical point around which the chassis rolls, and is determined
by the design of the suspension. Front and rear suspensions normally have different roll
centers. The “roll axis” is the imaginary line between the front and rear roll centers.
The amount that a chassis rolls in a corner depends on the position of the roll axis relative
to the car’s center-of-gravity (CG). The closer the roll axis is to the center of gravity, the
less the chassis will roll in a corner. A lower roll center will generally produce more grip
due to the chassis rolling, and the outer wheel “digging in” more.
Roll-centers have an immediate effect on a car’s handling, whereas anti-roll bars, shocks
and springs require the car to roll before they produce an effect.

So it seems my original thought is correct. Raising RC decreases roll and lowering RC increases roll. Roll generally increases grip. But when I reduce front droop it results in a more angled wishbone (higher at outside, wheel edge and lower at inside,pivot edge). This gives a lower RC and thus more roll. This should give more grip to the front in terms of RC left to right and yet it seems to have the effect of less front grip.

So I'm still stuck as to the basic relationship between roll and weight transfer and why reducing front droop reduces over-steer for me? I have tried reducing front droop more and more and with every reduction the car starts to under-steer more and more. It seems to definitely promote under-steer when all the theory says it should increase front grip and make an over-steering car over-steer more?

two shoes

iTrader: (21)

If I have it straight in my head... (unlikely, but plausible) when there is a greater distance between CG and RC (moment) the larger effect on body roll is seen for the same weight... Like a cheater bar on a wrench, it has more leverage. Where the RC is in relationship to the rest of the car is how that leverage will impact what the car does. If the RC is below the chassis as apposed to above the axles, the effect will be different. This page is one I am digesting now: ROLL CENTER

theproffesor

iTrader: (66)

Changing droop should not effect the angle of the suspension arm while car is it rest.

If it does then you are going to alter ride hight as well. There should always be a difference (1-3mm) between where the chassis sits at rest and if you lift it, how much before the tires come off the ground.

Also if there is no uptravel of the chassis, that means little to no weight transfer.

ixlr8nz

I believe what you have found is 100% correct — less front droop = less front grip. This is just simply down to the fact your inner front wheel is in the air.

Droop only makes a difference when your suspension arm hits the stop. At that point it will lift a wheel if you keep the load on. Basically the car will roll regardless of your droop setting.

snuvet75

iTrader: (16)

The term "Roll" is usually only for between left and right. Use the term "weight transfer" for front vs rear. This might have confused you when you read some articles.

Weight transfer from F to R or vice versa gives that end more grip like you said.
But weight transfer in general decreases overall grip. Think you can't really drive your car when cornering as fast as when you go straight. e.g. static overall grip is 200lb. when it's rolling, it becomes 180lb. Hence less overall grip.
Body roll increases traction. But what you're missing here is that the statement is talking about "relative" traction. e.g. more roll in F than R. Then more traction in F. Vice versa. Yet again, overall available grip decreases because of weight transfer.
All in all, the less weight transfer the better. Amount of weight transfer is determined by CG height, track width, and weight of the car. Proportional to CG height and car's weight. Inversely proportional to track width. This is why you try to make the car as light as possible, as low as possible and as wide as possible. To add another note on this account, the less droop decreases weight transfer between F and R. This prevents horribly (or unexpectedly) pushing or over rotating car on and off throttle respectively. Generally speaking, because of this, with acceptable grip on road surface, less droop is almost always better. The "less" droop is relative term though

BadSign

iTrader: (15)

overall traction across the front or rear axis does reduce with weight transfer. That's because the grip generated at the tire is not linear, it's a curve. The amount of traction on the laden/ outside tire does not make up for the traction lost on the inside/ unladen tire

Obviously, losing traction is not good. To reduce the amount of weight (and traction loss) that transfers, you'd need to reduce the overall weight at the axle, lower the center of gravity, widen the track, or just slow down

Body roll is a result of weight transfer. You can limit body roll with springs, swaybars, roll center, and droop

So you have two cars going through the corner at the same speed. The car that weighs less, has a lower cg, or a wider track will transfer less weight and therefore roll less.

Swaybars, springs, shocks, droop and roll center don't affect how much weight transfers, just how quickly it transfers and how much the car will roll

snuvet75

iTrader: (16)

Maybe this is the most important aspect we never listen to