GT Sprint Cup - Season 2, Round 6, Spa - Jan 17

[mo]

Generally set up the bump first and then tune the rebound afterwards.

The ratio of bump:rebound in reallife racecars is about 1:3 or 1:4
This is a fairly constant ratio and does not change from track to track, even though the actual bump value wil be different at each track.

Dont really know how realistic GTR is in this area though.

[popabawa]

The ratio of bump:rebound in reallife racecars is about 1:3 or 1:4
This is a fairly constant ratio and does not change from track to track

Sorry Mo, don't quite understand what you mean by "the ratio" 

That implies (to me) that the rebound setting is always larger than the bump setting by a factor of 3-4 

I'm sure that's not what you were saying though!

[fozzmeister]

The ratio of bump:rebound in reallife racecars is about 1:3 or 1:4
This is a fairly constant ratio and does not change from track to track

Sorry Mo, don't quite understand what you mean by "the ratio" 

That implies (to me) that the rebound setting is always larger than the bump setting by a factor of 3-4 

I'm sure that's not what you were saying though!

I'm sure that's what he was saying.

Its time based remember :-)

[mo]

I'm sure that's what he was saying.

Its time based remember :-)

Well I think that's what I'm saying LOL
I think the scales in GTR only allow for a 2:1 ratio (from memory) when both bump and rebound are at max so the 4:1 ratio may be extreme and apply only to ovals.
The greater the ratio the more oversteer at corner entry and exit (handy entering turn 1 at eg Michigan where the turn in speed is about 230mph!!!!)
I do however run the car often with max rebound and bump at about 6  -- a 3:1 ratio more or less.

You can melt your brains here

http://www.smithees-racetech.com.au/theory/shocktune.html

and if the heasdache hasn't got too bad check this too

http://www.smithees-racetech.com.au/theory/shocktune1.html

[popabawa]

I do however run the car often with max rebound and bump at about 6  -- a 3:1 ratio more or less.

OK, I clearly had NO idea what you were talking about 

If rebound and bump are both at 6, how is that a 3:1 ratio, surely that's 1:1

[mo]

running the car at max rebound (which is 18 I think) and bump at 6.............

3:1

[Dave 'Gizmo' Gymer]

I think the scales in GTR only allow for a 2:1 ratio (from memory) when both bump and rebound are at max so the 4:1 ratio may be extreme and apply only to ovals.
The greater the ratio the more oversteer at corner entry and exit (handy entering turn 1 at eg Michigan where the turn in speed is about 230mph!!!!)

Now I'm confused again. Surely it would give oversteer or understeer only if the ends (front & back) of the car were set up as opposites?

[fozzmeister]

mo your swapping your numbers around,

The ratio of bump:rebound in reallife racecars is about 1:3 or 1:4

running the car at max rebound (which is 18 I think) and bump at 6.............

3:1

Which makes it hard to read.

bump of 3, rebound of 9 = 1:3
rebound of 9, bump of 3 = 3:1

Lol

Anyway Rebound is always bigger, at least I cannot think of a reason why it should not be.

Fozz

[popabawa]

Thanks for your patience Fozz & Mo, I understand what you were saying now 

I'm definately lacking in any understanding of this stuff!

[mo]

I think the scales in GTR only allow for a 2:1 ratio (from memory) when both bump and rebound are at max so the 4:1 ratio may be extreme and apply only to ovals.
The greater the ratio the more oversteer at corner entry and exit (handy entering turn 1 at eg Michigan where the turn in speed is about 230mph!!!!)

Now I'm confused again. Surely it would give oversteer or understeer only if the ends (front & back) of the car were set up as opposites?

Yeah not clearly written sorry, you're absolutely correct Dave - I was only thinking about the rear of car.
Any adjustments to all four wheels should retain the car balance, increasing the rear will cause oversteer at corner entry and exit.
Increasing the front will cause the opposite.

mo your swapping your numbers around,
Which makes it hard to read.

bump of 3, rebound of 9 = 1:3
rebound of 9, bump of 3 = 3:1

Lol

Anyway Rebound is always bigger, at least I cannot think of a reason why it should not be.

Fozz

I'm not trying to make it confusing - it just is LOL, but yep its the other way round as you point out

[Truetom]

I remember from somewhere that the ratio should allways be at least 1:2 and I was really confused with Sharks setups where bump was sometimes of higher value than the rebound...

But I don't know much about this and so I google setups and try them all to find which one suits me best. I then fuddle with it until the car behaves as I want it, though that's not allways the fastest setup, but I try to make it stable (for me) at the highest available speed (for me). With this I at least (mostly) finish my races now. 

[Rich_A]

The dampers are in clicks but 1 for bump is not same as 1 for rebound. You know this already right?

Look in .plr and find this line...

Damper Units="0" // Show damper settings as (0)clicks or (1)actual force units

Set to 1 gives actual n/m/s newton's per meter per second I assume. So if it's set to 4000 n/m/s then the damper when under a load of 4000 newtons, would move one meter [if it was allowed to move a meter but of course it isn't] in exactly one second. So they are purely all about, weight, distance and time..

This probably why you find some guys using 5 for bump and 1 for rebound cause in actual force units rebound is still higher than bump, so it's a much norrower ratio 1:1.5 or something. This ratio is important, I tend to think of it as launchieness vs bunny hoppyness lol. You can either launch a car over a bump or curb and hope it lands ok but it usually won't because tyres lift more easily off track. Or you can bunny hop over it and weight longer for car to settle but at least tyres stay on track better. What you say mo about before and after is very good, I think about that one more..

For this strange lack of low speed grip. This is very difficult to judge especially in 911 RSR cause the rear is heavy and tends to be a bit sluggish so once it does something it takes a while to get it to change again. The brakes change the balance of the car the most at lower speed because there is less forward momentum, so as you get further into braking zone the cars balance will change more and more quickly. And it's same for accelerating, low speed acceleration disturbs balance more easily than when accelerating at a higher speed - so the slowest part of the track is where things will be most difficult.

What can happen is the front dips too far and the rear gets very light. It's no problem the rear going light braking in a straight line but as soon as you want to turn rear will want to overtake front and also the engine revs will drop more quickly because the rear tyres have very little resistance. So many things going on it's not easy knowing what actually happening!!
 
An increased rear slow rebound will keep the tyres closer to the chasis on braking. This means that the chasis requires more 'upward' weight before the rear tyres lift off the track. So stiffer rebound keeps weight on the rear therefore keeping tyres on track for longer. But what then can happen is very sudden loss of weight, there's more weight for longer but also it will go more suddenly. A softer slow rear rebound allows chasis to rise in relation to tyres and so keeps the tyres on the track better and is less likely to lift tyres off track but there is less overall weight because the chasis is more in the air as opposed to on the tyre.

Also stiffening front slow dampers or springs can help keep the rear down under braking!! It's good idea to make setup for slowest turn.. so then I know if I can brake hard and confidently into slowest turn, all other turns it's only matter of figuring out braking points and handling. But if I get good handling and grip through slowest turn it gives me good confidence for all other turns.

[Jamera]

Excellent Rich!!!

Very good explanation of things there

[mo]

Good stuff Rich -  think I';ll try setting that in the .plr file