My car is lowered with 18" wheels and when sitting on level ground there is roughly 1/2" clearance between the bottom of the bump stop and the axle. This seems like too little clearance to me, so I am trying to determine how much I can trim without having to worry about hitting the tire on the fender well. The car rides really rough over bumps and the rear jars hard when coming off a speed-bump.

So, in order to figure this out, about how much do you think the jounce bumper compresses when hitting a hard bump? That compression distance, plus the clearance will help me determine if I can remove any without the tire hitting. Then again, the bumper should compress less when I remove some of the tip of it, but it will give me a ballpark atleast.

Has anyone lowered with 18's trimmed there jounce bumpers with any success?

 

Cutting the bump stops is a bad idea. The reason why it rides rough is because you have thiner tires. Better shocks and stock springs would help but its not going to ride like a caddy.

 

I don't want it to ride like a Caddy! I just don't want it hitting the bump stops if I can help it.

Is a half an inch clearance between the bottom of the bump stop and the axle normal or too small? If too small what do you think the clearance should be to allow ample suspension travel without hitting the tire on the wheel well?

 

1/2" clearance is definetly not enough.
A full tank of gas and any wieght in the rear, wieght
transfer to the rear plus bumps your going solid on the
axle.
Cut 3/4 to 1" off, put a dab of grease or putty on stop,
full tank, add some wieght in rear and drive it like you
normally do, including bumps, then check to see if it tranfers grease or whatever you use to axle pad.

You should be able to feel if going solid in the rear
anyway
Tire clearance another factor as well as LCA location.
May have to rethink 18' and lowering car and practibility.
I have a lowered show car, but I can drive it like I stold it
and not have to worry about clearance issues and damaging
anything. Planning and checking!
HTH

Later

 

So has anyone trimmed their jounce bumpers, bump stops like explained above and had any success? Better ride quality and no rubbing?

Don't misunderstand me guys, the ride is not that bad and I understand these are the sacrifices you make when you want a lowered car with big wheels. However, if I can make it better without hurting anything, then why not.

 

Jounce bumpers are actually a part of the spring/damping suspension design for the car. It is, in effect, a way of dialing in more spring rate at the extreme end of travel. If you modify the jounce bumper, you modify the suspension spring rate. You will, in effect, delay the point at which the spring rate changes. What will happen is when you do hit the modified (and shorter)bumper, it'll give you a much more abrupt rate of change when you do hit it.

 

But with the hardness of the bumpers it is almost like
going coil bind with the springs. Not good, unless your using it to keep air out from under car while going down
the straight aways ala Nascar. And thats even
not working real good.

Bumpstops on cars and trucks are there to primarily
prevent frame or housing damage.

Later

 

You need to read more books on suspension design. Those bumpers are engineered with a specific durometer, shape, and diameter to not only prevent suspension damage but to compliment the springs at the end of their travel. At least, any car designed after 1980, anyway.

 

I completely agree with you, but the issue becomes what should they be when the car has been lowered, with aftermarket springs and shocks? They are no longer in the same location relative to the axle as they were when it was stock and are no longer working with the same springs and shocks.

It is certainly an interesting issue. Leaving them stock doesn't seem to be the answer as the small clearance means you are contacting them much more often than desired and thus changing the spring rate. But removing them completely could cause other issues, like frame or shock damage. So the questions becomes how much to remove or what bumpers to replace them with.....

 

I suppose, ZZTop, it really comes down to experimentation. Maybe pick up one or two used sets from a junkyard, then grind them down to two different heights and shapes. Try each and qualify them with a good/better/best sort of measurement. Put some chalk, wax, or some other easily removable substance on them and inspect them after a few days to see if you are actually making contact in every day driving.

That's about the only way I can think of to come up with a halfway reasonable solution. Of course, thats the essence of hot rodding and car crafting, isn't it?