Suspension travel.... use more on the street or track?
08-04-2015, 04:04 AM
#1
Suspension travel.... use more on the street or track?
So here is a question for you street and track guys, where do you typically use more suspension travel, fast street driving or on the track? I am doing some bump stop tuning with my GC/Koni setup. As delivered with 500lb springs and a 13.5" ride height there is about 5/8" clear piston travel (rear) before the shock body will engage a 2" progressive bump stop. This is the bump stop provided by GC with their upper mount. Driving the car on the street it feels like I am getting into the bump stops pretty fast. Especially going fast over rough pavement. So I am working on increasing the bump travel before hitting the bump stops, but before I go crazy with modifications, what can I expect at the track?
I am on a stock weight 00 with factory bars and a near stock alignment. Rubber is BFG Rivals in factory AP2 sizes.
I am on a stock weight 00 with factory bars and a near stock alignment. Rubber is BFG Rivals in factory AP2 sizes.
08-04-2015, 06:28 AM
#3
Why not give Ground Control a call and see what they think?
On a street car, bump stops should only come into play over severe bumps where the car might otherwise bottom out the shocks.
On a race car the bump stops are sometimes used to give what is in effect a variable rate spring. They tend to be used when normal spring travel is used up in a way that in intended: aero or soft springs leveraging brake dive. In those applications they are usually tuned to come into play just for the last 1/4" or 1/2" of wheel travel on the race track. The bump rubbers are available in different heights and stiffnesses; they act as a progressive spring but on a race track they are usually kept in a relatively linear section of their compression curve. For some applications they have been replaced by bump springs which provide a consistent rate. To have them work just where needed there position is adjusted with 1/4" and 1/8" spacers. There is even a machine to precisely set this: https://www.youtube.com/watch?v=c0CyYoIM0s4
Many lowered S2000s end up with excessive droop travel; to prevent this from happening they add helper springs that are in coil bind at normal operating ranges but if a large droop occurs they prevent the spring from becoming unseated.
There are used to be dual rate spring setups. In these two springs are used in series with the rate (k[sub]1[/sub] * k[sub]2[/sub])/( k[sub]1 [/sub]+ k[sub]2[/sub]). One spring, k[sub]2[/sub] is designed to go into coil bind leaving the rate as k[sub]1[/sub] . I don't think anyone does this anymore.
On a street car, bump stops should only come into play over severe bumps where the car might otherwise bottom out the shocks.
On a race car the bump stops are sometimes used to give what is in effect a variable rate spring. They tend to be used when normal spring travel is used up in a way that in intended: aero or soft springs leveraging brake dive. In those applications they are usually tuned to come into play just for the last 1/4" or 1/2" of wheel travel on the race track. The bump rubbers are available in different heights and stiffnesses; they act as a progressive spring but on a race track they are usually kept in a relatively linear section of their compression curve. For some applications they have been replaced by bump springs which provide a consistent rate. To have them work just where needed there position is adjusted with 1/4" and 1/8" spacers. There is even a machine to precisely set this: https://www.youtube.com/watch?v=c0CyYoIM0s4
Many lowered S2000s end up with excessive droop travel; to prevent this from happening they add helper springs that are in coil bind at normal operating ranges but if a large droop occurs they prevent the spring from becoming unseated.
There are used to be dual rate spring setups. In these two springs are used in series with the rate (k[sub]1[/sub] * k[sub]2[/sub])/( k[sub]1 [/sub]+ k[sub]2[/sub]). One spring, k[sub]2[/sub] is designed to go into coil bind leaving the rate as k[sub]1[/sub] . I don't think anyone does this anymore.
08-04-2015, 07:51 AM
#4
I called GC, and they recommended cutting the bump stop and getting rid of the dust cap. See pic
Koni did not recommend losing the dust cap because the bump stop may seal to the top of the shock body under compression. This could put pressure on the shock seals.
Koni did not recommend losing the dust cap because the bump stop may seal to the top of the shock body under compression. This could put pressure on the shock seals.
08-04-2015, 08:14 AM
#5
So bump stop aside, if I pull the cap off, the shock body will go up into the mount. The issue then is the first thing to bottom is the shock piston...not good. Instead I think I will machine the top ridge of the cap so it will slide up into the mount. However with this configuration the cap will hit the upper mount just before the shock piston hits bottom. I am guessing that would be better. This is without the bump stop, obviously adding that will prevent harsh bottoming.
How much bump stop and how progressive? Also how much travel should I expect to use on the track? More or less than on the street?
How much bump stop and how progressive? Also how much travel should I expect to use on the track? More or less than on the street?
08-04-2015, 08:40 AM
#6
No more or no less on the street or track, there is equal opportunity for both depending on the circumstance, however on the track, when your riding that limit of adhesion, this could cause you to spin out. Id leave the dust cover alone and just cut off the bump stop, either where you have it high lighted, or even the next section up to leave the larger single bump. Ideally you should have a good 1.5-2" of piston rod movement before any contact is made with a bump stop, and as long as the bump stop is substantial enough to do its job of preventing total bind/collapse then your golden. As long as you are running the appropriate spring rate for your car, you shouldn’t have to play around with limiting free travel on progresses rubber sponges.
08-04-2015, 10:02 AM
#7
If I have to I can bump the ride height a little. I think stock was 14.5 or so, I could go up to 13.75 rear 13.5 front.
So as far as bump stop tuning, is the goal just to have something to cushion mechanical bottoming while maximizing free shock travel? Or do you want the bump stop to contact sooner and deliver more progressively. I would think not the second, because then you are just adding to the spring rate exponentially.
So as far as bump stop tuning, is the goal just to have something to cushion mechanical bottoming while maximizing free shock travel? Or do you want the bump stop to contact sooner and deliver more progressively. I would think not the second, because then you are just adding to the spring rate exponentially.
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08-05-2015, 07:01 PM
#9
Agreed. Use the shortest bump stop possible. You can check your damper travel by using a zip tie around the damper shaft. Secure it snuggly around the damper shaft just above the bumpstop. Run your session as you normally would, and inspect the distance between the zip tie and the top mount. Should give you an idea of how close you are to actually hitting the bump rubbers.
08-06-2015, 08:49 AM
#10
Community Organizer
Are the rear Koni bodies too tall for the application? (I haven't seen a pictures comparing the front and back for Koni Yellows.) I have Swifts on CR shocks and ride at 13" front and back and I still have a decent amount of travel before I hit the rear stops (I have only done it once that was of significance).