changing dampers

[pete g]

Right.. adjusting dampers.
I am right in saying you can only unpin front... yes?

So you can only adj front, this will change balance of car, which is why Ren pin em in the first place, it is unheard of to sell a prod car that you can only adj at one end.
Might be practically il-legal TUV SVA etc...

But dont worry too much.... if you soften front a bit it will reduce the front roll stiffness that will reduce understeer, which asuming you have no other wild mods is prob what you want for a track visit. All this 'will ruin handling' is load of rubbish.

Just be aware on the road what u have done ... and you will have better ride ... at the front only mind, the back will still shake your teeth out however..!

Pete G.

 

[George K]

Pete G

At the risk of being contraversial - softening the front will not reduce roll stiffness, but it will reduce the amount of roll damping. This will have the effect of making turn-in more sluggish, which normally ends up with more forward weight transfer and hence understeer. The important thing is to divide a corner into several elements, the first of which is the initial change of direction - a transient condition. Mid corner is when the springs and arbs are loaded up and then is roughylysteady state - then too stiff a front end, in spring terms, will cause understeer. The other anomally is that in some conditions a stiffer front arb will reduce roll and hence keep the wheel more upright - more grip and thus less understeer.

The Trophy is very stiff in bounce, but actually not that stiff in roll, the consequence of being a top heavy saloon with low roll centres. This is why negative camber is such an important mod.

It is quite reasonable only to adjust the front dampers, as this is where most of the weight is and thus they will control most of the transients. The other reason for not playing with the rear is that the set up is a brilliant compromise between taut handling and avoiding snap over steer - which is why it is so quick in the wet (as iIhave said many times i am not a brave driver, but in the wet it (rather than me) is ultra competitive).

Admittedly hill climbing requires a relatively soft set up (many single seaters probably run 40% of a high speed circuit settings - springs, bars and dampers). I am sure that for high speed circuits the Trophy will feel quite soft, and this is where the Mark Fish set-up of springs and rear dampers will pay off. The Challenge racers run springs about 5 times stiffer than the Trophy, but then they also have very different tyres.

The most interesting thing about set up is that few of us mere mortlals have time to anaylyse what is going on detail - that is why data logging is so important. In most porfessional racing it is now possible to make a mathemtical prediction of how the car should behave all around the circuit and then overlay what actually happens - this very quickly pin points the areas to work on and to predict the effect of any changes.

Incidentally the road car industry use a similar package, the best known of which used to be ADAMS. The way it is used is farily conistent, which is why most ordinary road cars have the same fail safe (unsdersteer) characteristics.

Sorry about the lecture - actually totally over the top, but it is a subject about which I feel passionate and that has fascinated me for a very long time.

 

[trophyfan]

Found the ride on mine harsh after the 182 and 197 before it then I discovered that the tyre pressures were 35 all round. Changed them to 31F and 29R and now it is precise without being too harsh.

 

[__CA__]

Pete G

At the risk of being contraversial - softening the front will not reduce roll stiffness, but it will reduce the amount of roll damping. This will have the effect of making turn-in more sluggish, which normally ends up with more forward weight transfer and hence understeer. The important thing is to divide a corner into several elements, the first of which is the initial change of direction - a transient condition. Mid corner is when the springs and arbs are loaded up and then is roughylysteady state - then too stiff a front end, in spring terms, will cause understeer. The other anomally is that in some conditions a stiffer front arb will reduce roll and hence keep the wheel more upright - more grip and thus less understeer.

The Trophy is very stiff in bounce, but actually not that stiff in roll, the consequence of being a top heavy saloon with low roll centres. This is why negative camber is such an important mod.

It is quite reasonable only to adjust the front dampers, as this is where most of the weight is and thus they will control most of the transients. The other reason for not playing with the rear is that the set up is a brilliant compromise between taut handling and avoiding snap over steer - which is why it is so quick in the wet (as iIhave said many times i am not a brave driver, but in the wet it (rather than me) is ultra competitive).

Admittedly hill climbing requires a relatively soft set up (many single seaters probably run 40% of a high speed circuit settings - springs, bars and dampers). I am sure that for high speed circuits the Trophy will feel quite soft, and this is where the Mark Fish set-up of springs and rear dampers will pay off. The Challenge racers run springs about 5 times stiffer than the Trophy, but then they also have very different tyres.

The most interesting thing about set up is that few of us mere mortlals have time to anaylyse what is going on detail - that is why data logging is so important. In most porfessional racing it is now possible to make a mathemtical prediction of how the car should behave all around the circuit and then overlay what actually happens - this very quickly pin points the areas to work on and to predict the effect of any changes.

Incidentally the road car industry use a similar package, the best known of which used to be ADAMS. The way it is used is farily conistent, which is why most ordinary road cars have the same fail safe (unsdersteer) characteristics.

Sorry about the lecture - actually totally over the top, but it is a subject about which I feel passionate and that has fascinated me for a very long time.

Agree 100%. Evidence that it's soft in roll:



:wink:

 

[pete g]

That is evidence the front springs are soft, not the damping!

 

[George K]

BTW just look how little droop there is at the rear - which I am convinced is one of the great Trophy secrets.

Whether it is the springs or arb that is too soft is another debate. As the Challenge racers run much stiffer springs, it would be quite safe ot run much stiffer springs for circuit use (with appropriately stiffer damping) - just beware of a trade off in the wet.

 

[hoolio]

BTW just look how little droop there is at the rear - which I am convinced is one of the great Trophy secrets.

George, that's a bit enigmatic, can you explain (probably for the n'th time) to us numpties why you think this is so important to the handling.

Also when i was at Mark Fish he was of the strong opinion that if you stiffen the front damping it was advantageous to stiffen the rears as well which he considers very soft.

 

[George K]

Hoolio, To be honest it is hard to explain, becuase it is multi-dimensional, waffle for I know it works, but I have never come up with a water tight scientific explanation. Roughly it moves the roll centre sideways, to where the tyre meets the ground, which increases the the self righting effect and at the same time increases the roll stiffness becuase the inside spring has nothing to push down against.

Mark is correct if stiffer springs are fitted, but then there are varying schools of thought and for FWD I belong to that of preferring softer damping at the rear as there is so little load on the rear wheels - makes it much better on bumpy surfaces and in the wet and in sudden lift off.

BTW now that my front dampers have been rebuilt and run a bit to get them fully bedded in, I have tried the 'push down' test and it is almost solid even at 22 clicks. It certainly felt great at the last event. In comparison the back just moves a bit, with a suprisingly even stiffness going down (bump) and returning back up (rebound). I would have expected down to be relatively softer. This is the usual situation for road cars - again a sign of how good the Sachs are. Bilsteins with equal bump and rebound are incredibly harsh, but as that is a more common setting for track use, comfort is further down the list!

On a totally different subject, any progress re IK and re-map?

 

[hoolio]

I had a long chat with Mark and is it to my shame that i've forgotten more than i remember considering he was so nice to share his valuable time, in mitigation i was so cold i think my brain had shut down, but your first paragraph pretty much contains the elements of the point of view i had at the time.
As to the re-map etc i'm just waiting for the funds to build again, i had to insure both cars last month, very bad planning, but i was hoping to get it sorted end of this/early next month, i'll let you know.

 

[vamos]

This is a very interesting debate, I have a couple of related questions that have been nagging me for some time:

1) Does anyone know what the adjuster on the Sachs adjustables actually adjusts? Bump, rebound, low speed, high speed, a combination? I would assume that it is either low speed rebound or a combination of low speed bump and rebound, but it would be good to know for sure, as it does have a bearing on the impact of stiffening fronts up relative to the rear with regards to handling.

2) I would also dearly love to know the front and rear spring rates, so if anyone has that nugget of info, let's be having it

 

[pete g]

Vamos..

Dont know 100% but would expect it to adjust bump and rebound in the set ratio the dampers are factory set at, prob 3:1 ish.
Dont know spring rates as it basically my road car and would not change as we all accept not bad anyway/do well to improve, I have a stiff Elise for the track!
Renaultsport may tell you, or Fish or Yozzer etc etc...

 

[George K]

Adjustment - will try to find out

Front springs - circa 200 iirc