[Jase007]

I know that some here (besides me) run konis on their track and street cars (and trucks). I thought those that did might find this short instruction on setting bump (1st) and then rebound (2nd) on their struts / shocks helpful. Yes, I know that most Koni sports / specials / classics are single adjustable (SA) for rebound only.

From koniracing.com site:

Road Racing Setup
Adjusting bump

Bump damping controls the unsprung weight of the vehicle (wheels, axles, etc.). It controls the upward movement of the suspension as when hitting a bump in the track. It should not be used to control the downward movement of the vehicle when it encounters dips. Also, it should not be used to control roll or bottoming. [edit]this is why you increase T-bar rate[end edit]

Depending on the vehicle, the ideal bump setting can occur at any point within the adjustment range. This setting will be reached when “side-hop” or “walking” in a bumpy turn is minimal and the ride is not uncomfortably harsh. At any point other than this ideal setting, the “side-hopping” condition will be more pronounced and the ride may be too harsh.



STEP 1: Set all four dampers on minimum bump and minimum rebound
settings.

STEP 2: Drive one or two laps to get the feel of the car. NOTE: When
driving the car during the bump adjustment phase, disregard
body lean or roll and concentrate solely on how the car feels
over bumps. Also, try to notice if the car “walks” or “side-hops”
on a rough turn.

STEP 3: Increase bump adjustment clockwise 3 clicks on all four
dampers. Drive the car one or two laps. Repeat Step 3 until
a point is reached where the car starts to feel hard over bumpy
surfaces.

STEP 4: Back off the bump adjustment two clicks. The bump control is
now set. NOTE: The back off point will probably be reached
sooner on one end of the vehicle than the other. If this occurs,
keep increasing the bump on the soft end until it, too, feels
hard. Then back it off 2 clicks. The bump control is now set.




Adjusting rebound
Once you have found what you feel to be the best bump setting on all four wheels, you are now ready to proceed with adjusting the rebound. The rebound damping controls the transitional roll (lean) as when entering a turn. It does not limit the total amount of roll; it does limit how fast this total roll angle is achieved. How much the vehicle actually leans is deter-mined by other things such as spring rate, sway bars, roll center heights, etc. [edit] again here is where t-bars and upgraded sways have to act in concert with dampening[end edit]

It should be noted that too much rebound on either end of the vehicle will cause an initial loss of lateral acceleration (cornering power) at that end which will cause the vehicle to oversteer or understeer excessively when entering a turn. Too much rebound control in relation to spring rate will cause a condition known as “jacking down.” This is a condition where, after hitting a bump and compressing the spring, the damper does not allow the spring to return to a neutral position before the next bump is encountered. This repeats with each subsequent bump until the car is actually lowered onto the bump stops. Contact with the bump stops causes a drastic increase in roll stiffness. If this condition occurs on the front, the car will understeer; if it occurs on the rear, the car will oversteer.



STEP 1: With rebound set on full soft and the bump control set from
your testing, drive the car one or two laps, paying attention to
how the car rolls when entering a turn.

STEP 2: Increase rebound damping three sweeps on all four dampers
and drive the car one or two laps. Repeat Step 2 until the car
enters the turns smoothly (no drastic attitude changes) and
without leaning excessively. Any increase in the rebound stiffness beyond this point is unnecessary and may in fact be detrimental.

EXCEPTION: It may be desirable to have a car that assumes an over-steering or understeering attitude when entering a turn.
This preference, of course, will vary from one driver to
another depending on individual driving style.

[end clip]

Couple things to note without getting WAY into the details (volumes can be written on this):

Stiffer struts / shocks control the rate of bump / rebound. MATCH, MATCH, MATCH the dampers and spring rates (t-bars).

If you upgrade struts and shocks and DON'T upgrade the T-bars you will over dampen the car (OK to a point e.g. adding koni classics to a 356). If you upgrade the T-bars and NOT the struts / shocks you will go "boing-boing-boing" over the bumps b/c the T-bars can't be sufficiently dampened. Suspend the car's weight with T-bars applicable to the task and then dampen them accordingly. Fine tune with sways.

FWIW

Jase

[BlackTalon]

I just read some info about Konis in an autocross newsgroup the other night. One of the members runs in SCCA ProSolo events (and Nationals), and recently went to work at an engineering shop. He put two adjustable Konis on a shock dyno, and said the match between shocks was quite poor. He also indictaed the majority of the 'tuning' occurs within the first half-turn, and there was very little change after that.

In the end, he suggested getting Konis revalved in order to ensure you get what you want/ need. I know this may sound a little extreme for street/ DE use, but it may be worthwhile for a serious racer.

[Jase007]

Here is what Koni says is their "force-velocity" graph with range of rebound adjustment.




Most adjustment may come from initial adjustment (one click or half turn). Knowing this, (b/c you are slowly adjusting as you dial-in on the track) you can account for it accordingly as you manipulate the externally adjustable types or compress and rotate the non-externally adjustable types.

FWIW: we have the remote reservoirs on our IROC and RSR set differently F to B and R to L for each track. Keep a log and adjust accordingly when running practice (or in a DE, multiple sessions). The tuning is fun Definitely something you "might" like to futz with progressing up the DE ladder. 8)

Jase

[BlackTalon]

I think Dennis's main point was that your two front Konis may not be at the same point on the 'curve' when their knobs are in similar positions. Mis-matched compression or rebound settings will result in inconsistant handling characteristics. He is supposed to post the dyno charts; when he does, I will try to post a link to the thread.

[Jase007]

He ought to shoot an email to Koni-na and let them know about poor QC. I know I would.

Jase