Anyone know what Jounce Bumpers are?

Was reading some old archives on lowering. Anyone want to comment on this?:
'From Ken Brown:

If you lower your car and want to autocross or compete in SCCA roadracing with it make sure you change the heights of the front and rear (especially the rear) jounce bumpers or you could be in for a big surprise. The jounce bumpers are designed to increase the ride rate when when the wheel goes into compression a certain amount. When you lower the car you hit the jounce bumpers after only a small amount of wheel travel. This can cause the car to become very loose on corner entry if the rear jounce bumpers engage before the fronts.

To shorten the jounce bumpers, remove the shock from the car and remove the dust cover. The yellow hard foam cone that looks like 4 donuts stacked on top each other is the jounce bumper. it can be cut shorter using as tile knife. Trial and error is the best way to determine the length of the jounce bumper. Good luck!'

 

bump stops.

David
'with trimmed jounce bumpers'

 

Yes!! I did some research on this very thing.
I found that with my Z51 car w/Bilstein Sports, lowered about 2"( 26"to front fender), I only had 1/2" of travel before hitting the "jounce bumper".
I trimmed 1/2" off of the "type B" Bumper, I now have 1" of travel.
I noticed a difference when hitting bumps in the road, it's not as harsh as before.

Talked to a Bilstein Tech and "under the table" he agreed with this.


As you can see in the pic, Being lowered with the factory shocks you would be hitting the Jounce bumpers all the time :eek: And they are a lot stiffer than either of the Bilstein Bumpers.

I say get the bilsteins and trim the Bumpers if you are lowered alot:D



I haven't got to the rear yet ;)


[Modified by Flyin'Brian, 2:11 AM 12/9/2001]

 

This is from the "Lowering 1"" thread in this same area, call any Koni distributor, the Z06 bumpstop is 1" thick and extremely hard, when the shock bumps it, suspension compression stops and your spring rate becomes infinite:

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My experience is that lowering a C5 causes the front end to toe-in and the rear end to toe-out; the difference between the two is because of the fore and aft tierod positions on each end of the car. Realigning after the car has settled is IMO highly recommended. Note that the factory's nominal rear toe spec is -0.01 (negative is toe-out). Also, soft shocks with lowering will result in hitting the bumpstops without much provocation, which will upset the car if it does so in the corner. Stiffer shocks are IMO highly recommended, especially if you have base equipment and are otherwise stock suspension. I would also seriously consider replacing the hard factory bumpstops with an aftermarket progressive bumpstop, which will reduce shocking the tires. Koni and others sell them in a variety of stiffness and lengths, see any distributor.

The lower rear shock mount is rather long too; it can be modified to be about 1" shorter by any good fabricator. CAUTION: DO NOT WELD ON SHOCK BODY - HIGH GAS PRESSURE!!! By doing this you change the travel range position to provide 1" more shock compression travel before hitting the bumpstop. I do not recall the motion ratio for the C5, but the wheel will travel further for a given amount of shock travel. I have not yet checked to see if there is enough upper wheel well clearance to accomodate that much extra wheel travel. 1" of extra shock compression travel by modifying the lower rear shock mount is what's readily available, but you may need to use less due to other restrictions. Should have an answer on that situation soon.

Unfortunately you don't have this luxury on the front shock. Accomplishing the same requires more money than is worth investing in an OE shock and unlike the rear what you gain in compression travel you lose in overall stroke. Basically you would have to machine the top of the front shock shaft to be shorter.

Otherwise you can run a variety of custom-aftermarket shocks that can achieve all that and more; Penske, Moton, JRZ, Koni, etc.

Mark
TeamZ06

 

Brian, that car is low!!!! :eek:

 

How much travel is in the stock Z51 setup?
I plan to stay Z51. Final lowering should be about 1.5"
Should 1" travel be the goal?

What is the best way to reach 1" travel? Trimming the stock bumpers down or replacing the bumbers with another type? If so, where can I find other bumpers?

HEYYY, The Z06 Jounce Bumpers are 1/2" shorter. Maybe that would be enough? What do y'all think??

Thx!


[Modified by MelloYellow, 10:50 AM 12/9/2001]

 

keeping the stock Z51 shocks they need to be cut by the same amount you are lowering.
btw, imho, lowering her 2 full inches all around is too much for daily driver duty, makes it impossible to go over any bumps. I'm as low as practical. you need at least 3.5 inches of ground clearance to the lowest point of the body (ie behind the front wheels). I occasionally run 3 inches, and them I'm slamming over everything...

 

Thx. I guess I'm about 3/4 lower than stock now and will go down another .5 to .75

I'll measure the existing shock travel now, cuz it's been great. At the stock travel I had too much wheelhop. 3/4" lower seems perfect travel. Hmm, or maybe my logic is wrong. Would more travel or less help launching hard off the line? More, eh?

I'll check the existing travel to compare. Think I should target 3/4" or 1" travel? Will call around for aftermarket bump stops.

Anyone know stock or Z06 bump stop specs?

 

some people just don't get it ... but I already wasted too much time here.

geesh :rolleyes:

TeamZ06

 

The thread is to learn. Katech, Wheel to Wheel and my local race shop will be doing the work.