Bump and rebound
08-04-2009, 07:45 PM
#1
Nordschleife Master
Thread Starter
Bump and rebound
I've enjoyed the honeymoon period with the new KW V3 suspension but now I want to experiment and learn more about how the two way adjustment can enhance the performance of the car. Especially on track.
The car was initially set up for 'fast road' and if I were to drive it just on the road there wouldn't really be any need to change the settings. These are currently:
Front rebound = 1.5 turns open
Front bump = 1 turn open
Rear rebound = 1 turn open
Rear bump = 0.75 turns open
'turns open' refers to how far they are away from full hard (1/4 turns are the smallest adjustments). Full soft would be 3 turns open for rebound and 2 turns open for bump.
While I accept that whatever I do, everything will be a compromise at one end of the car or the other, what I would like to know is...is there a general principle for setting bump and rebound for track work?
I guess that getting everything near to full hard would provide stability at high speed but might be detrimental to what happens in the braking and acceleration zones. In particular, I've already noticed that the rear loses some grip during hard braking - the back gets a bit squirmy. If I understand the principles of bump and rebound correctly this could mean that the rear shocks are not rebounding quickly enough. Therefore if I soften the rebound at the rear (and maybe firm it up at the front) this should allow the tyres to maintain grip?
For information I run Toyo R888s on 17 inch rims on the track and adjust the pressures so that they are 36 psi all round when hot.
Looking forward to some education on both bump and rebound and how that they can influence what the car does.
The car was initially set up for 'fast road' and if I were to drive it just on the road there wouldn't really be any need to change the settings. These are currently:
Front rebound = 1.5 turns open
Front bump = 1 turn open
Rear rebound = 1 turn open
Rear bump = 0.75 turns open
'turns open' refers to how far they are away from full hard (1/4 turns are the smallest adjustments). Full soft would be 3 turns open for rebound and 2 turns open for bump.
While I accept that whatever I do, everything will be a compromise at one end of the car or the other, what I would like to know is...is there a general principle for setting bump and rebound for track work?
I guess that getting everything near to full hard would provide stability at high speed but might be detrimental to what happens in the braking and acceleration zones. In particular, I've already noticed that the rear loses some grip during hard braking - the back gets a bit squirmy. If I understand the principles of bump and rebound correctly this could mean that the rear shocks are not rebounding quickly enough. Therefore if I soften the rebound at the rear (and maybe firm it up at the front) this should allow the tyres to maintain grip?
For information I run Toyo R888s on 17 inch rims on the track and adjust the pressures so that they are 36 psi all round when hot.
Looking forward to some education on both bump and rebound and how that they can influence what the car does.
08-05-2009, 12:35 AM
#3
Addict
Rennlist Member
Rennlist Member
Good suggestion.
General guidelines:
- Koni recommends that you start soft, keeping stiffening until handling deteriorates and then back off to the previous setting
- Compression should not be so stiff as to cause your car to skip across the rumble strips on exit.
- Rebound should be stiff enough to eliminate floating
- Make one change at a time, e.g. front shocks or rear shocks but not fronts and rears
- Fix the end which isn't handling properly, e.g. oversteer => soften the rear; understeer => soften the front
- Optimize handling for the most important corners. There will be compromises but, for best lap times, your car needs to handle well in the important turns. Prioritize.
As for your braking question, a squirrely back end means either the front compression is too soft or the rear rebound is too stiff. You might also consider adjusting your braking technique since stiffer shocks increase the rate of weight transfer, i.e. inputs are realized much quicker. And always use a lap timer to evaluate changes. Often, what feels fast is anything but. so use a clock to measure progress objectively.
General guidelines:
- Koni recommends that you start soft, keeping stiffening until handling deteriorates and then back off to the previous setting
- Compression should not be so stiff as to cause your car to skip across the rumble strips on exit.
- Rebound should be stiff enough to eliminate floating
- Make one change at a time, e.g. front shocks or rear shocks but not fronts and rears
- Fix the end which isn't handling properly, e.g. oversteer => soften the rear; understeer => soften the front
- Optimize handling for the most important corners. There will be compromises but, for best lap times, your car needs to handle well in the important turns. Prioritize.
As for your braking question, a squirrely back end means either the front compression is too soft or the rear rebound is too stiff. You might also consider adjusting your braking technique since stiffer shocks increase the rate of weight transfer, i.e. inputs are realized much quicker. And always use a lap timer to evaluate changes. Often, what feels fast is anything but. so use a clock to measure progress objectively.
08-05-2009, 03:26 AM
#4
Nordschleife Master
Thread Starter
Thanks for the suggestion guys. Searching the Racing section I came up with this....
https://rennlist.com/forums/racing-a...hlight=rebound
....which seems to have most of my questions covered. It too mentions that the squirmy back end could mean that I'm over-braking and therefore need to work on my technique which should in turn improve my corner entry speed.
https://rennlist.com/forums/racing-a...hlight=rebound
....which seems to have most of my questions covered. It too mentions that the squirmy back end could mean that I'm over-braking and therefore need to work on my technique which should in turn improve my corner entry speed.
