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VWR Spring/Damper kit Install- Trim Bumpstops?

SouthFL_Mk7.5

Drag Racing Champion
Location
South Florida
Car(s)
2019 GTI S
I’ve searched and have found mixed results. Some have trimmed, others no.

I’ve got all the strut assembly install parts, new Febi/Bilatein strut tops, hardware, etc. ready to go for installation this coming Monday- just not sure as to what to do with the bumpstops. Trim yay or nay?
 

El_bigote_AJ

Autocross Champion
Location
Las Vegas
Car(s)
2019 GTI bunny
Just trim a quarter inch while they are easily accessible. may not need it, but 1/4” won’t hurt anything if it did bottom out, and they is gains some head room to avoid hitting the stops on and getting the fun thud! Lol.
 

ZERO815

Go Kart Champion
Location
Köln Germany
Car(s)
NA '17 GTI SE DSG
Was never a fan of cutting bump stops until recently. My '17 is on Bilstein B16 damptronic coilovers and my daily/family car. My commute is ~50 miles one way mostly German Autobahn A1 with many unrestricted miles. During install I used bump stops 1K0 412 303 F in the front and bump stops 5Q0 511 357 J in the rear. I leveled the vehicle at 340mm center of the wheels to the fenders. That is 28mm lower than the designed ride height.

The car felt planted and very direct, but also very nervous/bumpy on higher vehicle speeds especially from the rear.
- 1. Step I removed the plastic ring from the rear bump stop. It made it better in town and more driveable on the Autobahn. But still I wasn't happy and WAF (Women Acceptance Factor) was negative.
- 2. Step I raised my coils by 5mm. What are great effect on the "searching around ride height" (low amplitude inputs) in the front and the rear, still the rear bumpiness was present. A very good indicator that the bump stop riding is mainly my ride concern.
- 3. Step I cut 13mm from the top of the rear bump stops off. On our next family trip my wife commented without being asked: "I don't know what you have done to the car but now it feels great!".
- 4. Step is going to be to cut 5mm off the front bump stops soon. The rear is really good now, only the front keeps pushing a little bit here and there.

Bump_Stop_Mod.jpg


Why was I so hesitant on doing this? W/ trimmed bump stops you change the jounce travel. But by how much and why is that important?

- Designing a car VW uses a wheel envelope to model all positions a wheel and tire combo may be expected during driving. The maximum jounce allowed by the suspension system and the maximum turn and tilt allowed by the steering mechanism are taking into account. Tire inflation changes and wear conditions may also be considered when generating the envelope. During an interference/collision analysis the envelope is compared to the wheel wells and other components in the package. The wheel/tire combo shouldn't get in contact w/ other components under normal driving conditions. Personally I have been in many expensive (and quick) vehicles on the Nürburgring for suspension testing. What can I say, on most cars the tires get in contact with the wheel wells at "Fuchsröhre". Is it normal driving conditions? For some test drivers maybe, not for me.
- The front jounce bumper is 55mm long and at 5kN load it's compressed to 16,5mm. Now if I remove 5mm off the front jounce bumpers I will gain about 2mm more travel in jounce
- The rear jounce bumper is 112mm long and at 5kN load it's compressed to 47mm (with POM ring). For the rears I haven't tested the jounce bumpers compessed length without the POM ring yet. All I can tell is w/ factory 18" wheels, 3 buddies in the car, 200km/h through the "bumpy balls curve" on the A1 and there was no rubbing or anything weird.
- I noticed that the planted feel got a little bit reduced with every step I took. No regrets here.
 

SouthFL_Mk7.5

Drag Racing Champion
Location
South Florida
Car(s)
2019 GTI S
Great information.

I’ve ordered front bumpstops in both 70mm and 55mm lengths. And the 110mm rear.

I have not pulled out the factory US market assembly, so I’m figuring that we may have the 70mm front bumpstops, while the 55mm set may be European market spec? I wonder why the difference in length. I ordered both just to have them available.

I’ve read posts from Emmanuel Design saying to cut 1/2” off the top
for their spring install. That’s very close to the difference between the 70mm and 55mm front bumpstops.

Emmanuel also recommends cutting 1/3” to 3/4” off the rear bumpstops.1/2” is close to the 13mm posted by ZERO815 above.

87451C09-B72D-424C-8C62-D98BBFC46581.jpeg


7EF3361B-AC22-4D45-8FCE-05F0BD315F40.jpeg


3D9860B0-02DE-41AE-93DB-C37A175C930C.jpeg


Based on reading that some end users don’t cut their bumpstops with this kit and have good results and the 1/2” recommendations from EMD and the detailed information posted above by ZERO 815, Perhaps the 1/4” figure is a good intermediate estimate?
 
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victorofhavoc

Autocross Newbie
Location
Kansas City
Was never a fan of cutting bump stops until recently. My '17 is on Bilstein B16 damptronic coilovers and my daily/family car. My commute is ~50 miles one way mostly German Autobahn A1 with many unrestricted miles. During install I used bump stops 1K0 412 303 F in the front and bump stops 5Q0 511 357 J in the rear. I leveled the vehicle at 340mm center of the wheels to the fenders. That is 28mm lower than the designed ride height.

The car felt planted and very direct, but also very nervous/bumpy on higher vehicle speeds especially from the rear.
- 1. Step I removed the plastic ring from the rear bump stop. It made it better in town and more driveable on the Autobahn. But still I wasn't happy and WAF (Women Acceptance Factor) was negative.
- 2. Step I raised my coils by 5mm. What are great effect on the "searching around ride height" (low amplitude inputs) in the front and the rear, still the rear bumpiness was present. A very good indicator that the bump stop riding is mainly my ride concern.
- 3. Step I cut 13mm from the top of the rear bump stops off. On our next family trip my wife commented without being asked: "I don't know what you have done to the car but now it feels great!".
- 4. Step is going to be to cut 5mm off the front bump stops soon. The rear is really good now, only the front keeps pushing a little bit here and there.

View attachment 198785

Why was I so hesitant on doing this? W/ trimmed bump stops you change the jounce travel. But by how much and why is that important?

- Designing a car VW uses a wheel envelope to model all positions a wheel and tire combo may be expected during driving. The maximum jounce allowed by the suspension system and the maximum turn and tilt allowed by the steering mechanism are taking into account. Tire inflation changes and wear conditions may also be considered when generating the envelope. During an interference/collision analysis the envelope is compared to the wheel wells and other components in the package. The wheel/tire combo shouldn't get in contact w/ other components under normal driving conditions. Personally I have been in many expensive (and quick) vehicles on the Nürburgring for suspension testing. What can I say, on most cars the tires get in contact with the wheel wells at "Fuchsröhre". Is it normal driving conditions? For some test drivers maybe, not for me.
- The front jounce bumper is 55mm long and at 5kN load it's compressed to 16,5mm. Now if I remove 5mm off the front jounce bumpers I will gain about 2mm more travel in jounce
- The rear jounce bumper is 112mm long and at 5kN load it's compressed to 47mm (with POM ring). For the rears I haven't tested the jounce bumpers compessed length without the POM ring yet. All I can tell is w/ factory 18" wheels, 3 buddies in the car, 200km/h through the "bumpy balls curve" on the A1 and there was no rubbing or anything weird.
- I noticed that the planted feel got a little bit reduced with every step I took. No regrets here.

Why are you adding bumpstops to bilsteins? They have internal bump stops built in...
 

ZERO815

Go Kart Champion
Location
Köln Germany
Car(s)
NA '17 GTI SE DSG
Just lift one front wheel and slide the dust boot away
Why are you adding bumpstops to bilsteins? They have internal bump stops built in...
Not the Damptronics
 

ZERO815

Go Kart Champion
Location
Köln Germany
Car(s)
NA '17 GTI SE DSG
I’ve ordered front bumpstops in both 70mm and 55mm lengths.
Just lift one front wheel and slide the dust boot up. Should be able to see part number then. In the rear remove zip-tie of dust boot and slide dust boot down, bump stop is accessible now. That's how I trimmed my rear bump stops w/o removing the shocks.
 

snobrdrdan

former GTI owner
I'd cut or trim the bottom/lower part of the bumper, not the top.
If you cut too much off the top, there might not be enough material left for it to fit snuggly in the mount anymore & it'll just fall down

my 2 cents
 

SouthFL_Mk7.5

Drag Racing Champion
Location
South Florida
Car(s)
2019 GTI S
Just picked up the car from the install.
We used the 55mm Front, trimmed 1/8”
And trimmed the 110mm Rear 1/4”

All is good. After driving around the city running errands...
 
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