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.
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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.