Bump stops - To trim or not to trim

[Hammersticks]

I get this question from time to time based on the spring install reference guide I put out so I wanted to bring this up here and I'll add the link to the other thread.

I have typically done what the install instructions say to do on different applications (cut or not), but I know not all instructions include that info leaving people sometimes scratching their heads as they are neck deep in the install.

H&R offers this information on how bump stops impact spring rates: http://www.hrsprings.com/technical/spring-rate-101

Their general guidance is NOT to cut unless instructed to do so; however, if you watch the Emmanuel Design video they trim them when installing their ED springs which aren't ultra low themselves. I have also heard to trim front and rear regardless if you are lowering. Specifically: trim 50-75% of the TOP coil on the rears and 1/4-1/2" of the TOP coil on the fronts...at least on the GTI. (assume about the same for golf variations)

Back when I did my initial lowering install of neuspeed sports, I trimmed them based on the feedback above, despite the lack of instructions from Neuspeed to do so.

Cutting the bump stops seemed to work fine with the Neuspeed sports. I only had the setup for about 5k miles so TBD if there would be any long-term impacts.

The only other thing is that not all shocks/dampers require bump stops. For example, the Bilstein B8 fronts have their own internal ones, so read up on what you have before you dig into it.

So, what did you do for yours?

Cheers.



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[Hammersticks]

Nobody eh? Lol. Again, doing for research sake.

Cheers!




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[Sandman GTI]

Nobody eh? Lol. Again, doing for research sake.

Cheers!




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I will add that on My Eibach Pro Kit (1 inch lower) install the dealer Mechanic did not cut mine. I talked to him about it and he felt it would not be an issue. The stop might help protect the shock and keep it from stroking too far. I have DCC so worth the cost to protect. I sometimes wonder if it would help ride on larger bumps but for now mine are not cut.

 

[breaking badly]

Interesting question. It isn't trivial. First you'd need to look for the remaining travel.

 

[jacincm]

The DAP install video said to not trim them for these springs since the drop isnt that significant.

 

[Hammersticks]

The DAP install video said to not trim them for these springs since the drop isnt that significant.

Yes. Now watch the Emmanuel Design video and see them cut the bump stops.


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[breaking badly]

The DAP install video said to not trim them for these springs since the drop isnt that significant.

DAP (or any other vendor) isn't god.

 

[Hammersticks]

Sandman, thanks for your input!

BB, agreed.

Regarding the DAP video, you also hear guys complain about VWR ride quality deteriorating over time. Perhaps partially due to not trimming the bump stops? Back when I had my neuspeed springs another member had reached out to me and said his car had become bouncy over time. He then trimmed the rear bump stops the problem went away. One case I know, but a data point nonetheless.


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[jacincm]

I trust Paul from DAP when it comes to these cars. Will trimming it help out with ride quality? Probably. Is it necessary? Probably not. Different people will do different things and have different results. Unless there's a controlled test with a measurable metric to use, it doesn't really matter.

 

[breaking badly]

Regarding the DAP video, you also hear guys complain about VWR ride quality deteriorating over time. Perhaps partially due to not trimming the bump stops?

At least that isn't unlikely.

IF total positive travel (bump) is, say, 65 mm and the bump stop is 35 mm,
then you'd have 30 mm remaining without the vastly increased spring rate
of the bump stop.
Now, when your car settles just for, say, 10 mm within a year, only 20 mm
will remain, which is a significant decrease of 30 % of your precious travel.
I'm conviced this is clearly noticeable.
That being said, I wouldn't even wonder if the positive wheel travel on many
lowered GTIs would actually be even less than that mentioned number.

Will trimming it help out with ride quality? Probably. Is it necessary? Probably not. Different people will do different things and have different results. Unless there's a controlled test with a measurable metric to use, it doesn't really matter.

I don't get that. It doesn't matter if trimming helps, since it isn't (easily)
measurable?
Anyway, it isn't too hard measuring wheel travel. I'd highly recommend
doing this.

 

[Petey T]

I'm having my Eibach sportlines installed tomorrow. 1.7/1.6" drop, sounds right to have the fronts trimmed down a bit? Eibach includes new rear bump stops

 

[Sandman GTI]

Sandman, thanks for your input!

BB, agreed.

Regarding the DAP video, you also hear guys complain about VWR ride quality deteriorating over time. Perhaps partially due to not trimming the bump stops? Back when I had my neuspeed springs another member had reached out to me and said his car had become bouncy over time. He then trimmed the rear bump stops the problem went away. One case I know, but a data point nonetheless.


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I am not a Spring Expert but the issue you mentioned above is why I picked Eibach Pro Kit Springs. I also heard that the OE winding like VWR uses can settle over time as they age. Many feel the OE type winding is best as it matches OE ride, but what I read is that the Eibach Springs with the dual winding use the tighter springs to control the lowering part, they actually touch when the car is loaded and sitting still. This winding is a better way to control the lowering and over time will sag less. Then the lower wider spaced winding will handle the ride control. So if this design does not sag then you have the same ride consistently over time. I might be wrong but this is why I think the Eibach Pro Kit is a better Spring. Few people choose them, but I tend to keep cars for a while and want the parts to hold up. Eibach has also been doing this a long time and over time has likely made springs for these other named companies. I also read the dual winding springs are harder to make so this is a sign of a good company.

My thoughts.
Now if Eibach would make a spring bearing just for our cars!!!!!!

Pic below of the Pro Kit Spring - should be for a GTI MK7.

My build thread has more info - go to first page and use link. FYI.
Enjoy the lowered life - the good and bad.

The rear springs below are actually upside down.
The tighter coils are mounted at the top of the spring when installed.

 

[snobrdrdan]

I just buy the shortest OEM ones possible.

On the MK6, it came with 70mm on the front from the factory but there was a OEM 55mm one: 1K0412303F

After looking up the MK7 parts, it's the same 55mm front bump stop on cars without the Performance Package. So it shouldn't need any trimming, IMO, it's pretty short.

PP cars get a different front bump stop, 1K0412303AE, but I'm not sure of the length on it.
It looks exactly the same though, but just has a rubber "band" around it between the last section:

 

[Sportwagen SEL]

PP cars get a different front bump stop, 1K0412303AE, but I'm not sure of the length on it. It looks exactly the same though, but just has a rubber "band" around it between the last section:

That's strange I don't have that bump stop at all (at least on the rear, haven't checked the front yet) on my '17 GTI and I always bottom out horribly on larger potholes. Could it be that somehow they "forgot" to put one on all of my springs??

 

[breaking badly]

NEVER RUN WITHOUT BUMP STOPS !!

NEVER
RUN
WITHOUT
BUMP STOPS

Seriously, NEVER !!