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Suspension and Chassis Trimming bump stop

Nomad17

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Dec 21, 2018
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The Eibach pro-kit instructions mention trimming the front bump stops by the same amount as the drop (and includes replacements for the rear). I'm sure this is to maintain suspension travel but has anyone run into problems doing this? I assume the struts are ok with this and nothing will bottom out?
 
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s55b30

New Member
Apr 26, 2019
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New England
So, while I've never modified a car with electric dampers, I've probably done aftermarket suspension in at least a dozen cars and I haven't had (properly) trimmed bumpstops become an issue in the past.
 
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RameusJH

Member
Mar 12, 2019
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As long as you keep the stiffer end on the car you should fine (should be the fatter end). This is to ensure that the bumpstops provide enough force to resist impacts without letting the strut/shock bottom out internally (which can damage them). I would be careful not to trim more than what Eibach recommends...

Trimming bumpstops means that the change in stiffness upon impacting the stops will be more abrupt, but, the benefit of maintaining the suspension travel before hitting the bumpstops is usually worth that trade-off. Otherwise you would be often or possibly constantly riding the bumpstops, which are usually quite stiffer than springs. This is one reason why extreme lowering via springs (without corresponding changes to struts/shocks) can be really bad for ride and handling despite the fact that lower CofG = better handling (to be more specific, lower CofG means less lateral load transfer, which translates to higher overall grip capacity).
 

Piro Fyre

New Member
Feb 5, 2019
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Milwaukee, WI
Lower center of gravity is one thing. But when it comes to lowering a car, roll center needs to also be considered. Especially when you're cutting up and replacing bump stops with shorter ones. Most manufactures usually develop these types of performance cars so that the bump stop is the absolute limit of the car's roll center. Surpassing these limits can yield some weird handling characteristics like a lot more understeer than OEM.
 
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Nomad17

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Dec 21, 2018
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Best option of course is to not lower the car at all unless the entire suspension is reworked. Eibach's testing says to trim if you lower the vn but would you say riding on the bump stops fulltime is a better option? I assume this is what h&r, whiteline, etc is suggesting.
 

Piro Fyre

New Member
Feb 5, 2019
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Milwaukee, WI
H&R and Whiteline springs were made specifically for the N models and are stiffer to accommodate for the drop. With that being said, I don't have their instructions so who knows what they want you to do with the bump stops. Although previously having experience with installing H&R lowering springs in a CT9A Evo, their instructions also told me to cut bump stops so it could be the same story with the N.

Eibach doesn't really have an official spring for the N and a few people found out the Spec-R lowering springs fit the N. So naturally, people have been putting these springs in the N. The spring rates are done specifically for the R-Spec so they are softer than the other 2 springs. The spring rate might be similar to the stock N springs, which is probably why they want you to cut the bump stops on the N.

But really, it's your car. You do what you want.
 

Nomad17

Well-Known Member
Dec 21, 2018
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I would like the car to sit slightly lower but admittedly it's just for looks. I wouldn't expect to be able to improve the handling of the car with springs alone but if I can do so without noticeably reducing performance I would like to.

If I can't then I will leave it alone.

Previously I've only ever swapped complete coilovers and trimming bumpstops was never suggested. I like that Whiteline references their spring rates but I can't seem to find this info from the other manufacturers (or Hyundai for that matter) but it does seem that Whiteline uses the same springs for the elantra gt and veloster n. H&R seems to similarly have the same part # for the i30n and vn.

I am unsure if the R-spec eibach kit is the same they've had for the i30n for a while now but would be surprised if they separated them (would prefer they did but would be surprised). To top it off Eibach has pictures of this kit on a vn on their site but even there it is referred to as being for the R-spec.

I don't know the weight difference between the 2.0t and the 1.6t, not to mention other beefed up components on the N, but either way it looks like I should wait a bit longer and see what other options may be released.
 

R Veloster N

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Mar 5, 2019
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Best option of course is to not lower the car at all unless the entire suspension is reworked. Eibach's testing says to trim if you lower the vn but would you say riding on the bump stops fulltime is a better option? I assume this is what h&r, whiteline, etc is suggesting.
No, you don't trim the bump stops with the Whitlines. Their springs set only drops the VN .25. I'm utilizing everything from Whiteline but I have not installed the springs as of yet. I'll do so when I deem it necessary.

Suspension tuning to me is, a bit of a methodical process. I don't like making to many changes, until I have an opportunity to test each of the adjustments. I'm also utilizing a Mando ECS 10 so it's a bit more complicated.
 

RameusJH

Member
Mar 12, 2019
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Agreed that roll centre height is important, particularly for performance driving. As long as the stiffer end is left on the car though, trimming approximately .5" off a bumpstop does not mean that the bumpstop allows bump travel 0.5" deeper at end of travel. It would be somewhat less than that because the less stiff end is trimmed off and the stiff end is kept on the car.

Another way to look at roll centre in this situation is by how much impact a "too low" roll centre height at deep bump travel would have. If not driving on track or autocross, a too low roll centre height doesn't really matter, and only comes into play when reaching deep into bump travel (which only happens on big impacts maybe a few times a day, and usually when driving in a straight line).

If one does not trim the bumpstops, the stops would engage earlier in bump travel and therefore more often during normal driving. The stiffness of bumpstops is progressive and ramps up to higher values than the springs, to the point where the dampers don't control the bounce well anymore. If the goal is primarily to lower the car, trimming the bumpstops per Eibach's instructions should be more comfortable, still protect from bottoming out, and I don't believe roll centre effects will have a serious impact in the OP's application. Remember as well that Eibach is a really big name in suspension and spring engineering.

I very much agree with @R Veloster N about a methodical approach to suspension. Make one change, allow lots of time to feel the effect, and only then decide the next change.
 
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