Good Idea or Bad Idea To Trim?

[2006gtmike]

Here's a pic of my stock bump stops.

There's about enough room from the top of the bump stop to the frame for one finger to fit or barely a 1/2 inch room.

I figure it COULD help ride quality but it MIGHT mess with the performance of the bump stop because it was manufactured a certain length to work with the stock springs/ride height.

Is it allright to trim one nub off or will it compromise the integrity of the bump stop and/or cause the inner cell to degrade?

OR do it the right way and just buy the Ford Racing bump stops?

 

[danbev07]

Since it's purely compression, I highly doubt you'll see any fatigue worth worrying about as a result of cutting these. They are fairly firm, especially closest to the rear-end.

4 years ago I trimmed my bumpstops when I purchase some Eibach Pro-Kit springs. 2 full suspension setups later (and a big accident involving the rear-end) I am still running the same bump-stops I trimmed that day.

I cut the bumpstop down to about an inch in height (just looks like a cylinder).

 

[2006gtmike]

I wasn't sure if the material inside the bump stop would degrade faster since the outer layer was cut exposing whatever is inside to any elements.

From what I understand, the bump stop acts as a spring, so if you cut part of it the initial action and reaction I think would change.

 

[Norm Peterson]

When you cut a bump stop you also change the shape of its spring rate. Bump stops are progressive springs, meaning that the initial compression is relatively soft, followed by resistance that continually increases as it is further compressed.

Translated, that means that if you're going to cut them down - where you really need to be cutting is off the base end so that you'll still be leaving the soft initial rate intact.

The free end is the soft end, so if you cut from that end the initial contact will be harsher. You'll feel it more, as will the bump stop, whatever the bump stop is attached to, and whatever is hitting it.

There might be a small advantage in cutting only mostly off the base and a tiny amount off the free end. But I won't even attempt to guess how much from each would be optimum beyond commenting that taking half of your total shortening off of the free end would be way too much.


Norm

 

[2006gtmike]

So in other words replace the stock rear bump stops with the Ford Racing M-5570-A bump stops?

The front KONI Yellow Struts have bump stops inside the strut assembly because there are no external ones?

All the pairs of KONI Yellow struts I've seen for these cars don't come with new bump stops

 

[Whiskey11]

So in other words replace the stock rear bump stops with the Ford Racing M-5570-A bump stops?

The front KONI Yellow Struts have bump stops inside the strut assembly because there are no external ones?

All the pairs of KONI Yellow struts I've seen for these cars don't come with new bump stops

I don't think they do, I reused my stock stops in front when I installed my d-specs last november and they didn't come with any either.

I'm interested in this thread though, specifically about the FRPP stops as they are so inexpensive to swap the rears.

 

[2006gtmike]

I know the FRPP bump stops are cheap but maybe a vendor would do a group buy if there was enough interest.

 

[steveespo]

Just a note, the FRPP bumpstops are the same height as the Brembo package cars, ask me how I know?
Steve

 

[2006gtmike]

Just a note, the FRPP bumpstops are the same height as the Brembo package cars, ask me how I know?
Steve

You car has the Brembo package?

So are these bump stops shorter in height versus a stock bump stop?

 

[frank s]

In the earlier days I remember an article with photos showing the bump-stop cutting procedure. It appears they tried several different contours (profile shapes?) to add a little tuning to the action of the bump stops. I don't recall which cars they were working on, but it might have been road-racing MGBs.

I guess there might be some concern about distortion on a non-symmetrical cut. For my money, bump stop replacement with a proven shape, length, and material would be best. What do the factory racing cars use?

 

[JEWC_Motorsports]

The 11-12 cars come with the shorter bump stops from the factory the 05-09 cars do not. I thought I went over this already.

 

[Sharad]

I cut the top nub off of the bump stops on my '06 a couple days ago. No problems, and it rides a little nicer.

On UPR Pro Series springs (same as Eibach Pro Kit) the snubbers were hitting the brackets enough to wear through the paint.

 

[908ssp]

When you cut a bump stop you also change the shape of its spring rate. Bump stops are progressive springs, meaning that the initial compression is relatively soft, followed by resistance that continually increases as it is further compressed.

Translated, that means that if you're going to cut them down - where you really need to be cutting is off the base end so that you'll still be leaving the soft initial rate intact.

The free end is the soft end, so if you cut from that end the initial contact will be harsher. You'll feel it more, as will the bump stop, whatever the bump stop is attached to, and whatever is hitting it.

There might be a small advantage in cutting only mostly off the base and a tiny amount off the free end. But I won't even attempt to guess how much from each would be optimum beyond commenting that taking half of your total shortening off of the free end would be way too much.


Norm

What you're saying is right on the money. While I am sure people can get by hacking the tops off it is not a proper solution. The real pity is it is all for looks. A car lowered so much that the pump stops need cutting probably doesn't handle very well as the limiting suspension travel is not a good thing. When the suspension bottoms out the loads that were on the springs are transferred to the tires and when done all at once it causes the tires to lose traction for the overload shock. You want loads to be transferred gradually which is what a progressive bump stop does. If looks are more important than handling then you probably don't care.

 

[2006gtmike]

What you're saying is right on the money. While I am sure people can get by hacking the tops off it is not a proper solution. The real pity is it is all for looks. A car lowered so much that the pump stops need cutting probably doesn't handle very well as the limiting suspension travel is not a good thing. When the suspension bottoms out the loads that were on the springs are transferred to the tires and when done all at once it causes the tires to lose traction for the overload shock. You want loads to be transferred gradually which is what a progressive bump stop does. If looks are more important than handling then you probably don't care.

I have the Steeda Sport Springs so I didn't think my car was "lowered so much."

I had the Vogtland lowering springs which were less of a drop but I was told the Steeda's would perform better.

Pretty much everything modified on my car was intended for upgrades in the power and handling department.

Looks are not more important to me and I do care about the handling otherwise I wouldn't be on these damn forums trying to find the proper solution.

 

[danbev07]

I cut the bumpstops for more travel. My drop is about 1/4" lower than the Eibach Pro-Kit drop.

As a side note, I noticed my Roush Trak Pak shocks came with their own bumpstops as well. No, they are not true rear coilovers like griggs or other setups use - they are the separated shock and springs just like the OEM setup. The bumpstops slip over the shock piston rod, similar to those on the OEM front shocks.

Based on the logic presented in this thread, I should run both?

I guess I tried to recreate the same technique used in proper lowering techniques, such as spindle-drops. Since I have a solid rear axle, there's nothing I can do to raise the hub relative to the bumpstop, but I can modify the bumpstop to recover some of the vertical travel I would have otherwise lost from a result of lowering the car...