Standard Suspension Bump Travel

[u/Josh]

Originally Posted by Racecomp Engineering

to be super CLEAR…our bump stops are MUCH shorter and firmer ( progressive 3 stage) than stock. So you gain travel technically. Not to mention the spring RATE is increased and there is less travel USED in most situations.

Small detail many forget.

NOTE: not said in a defensive way, just trying to explain better !

Myles

Have you measured the stock bumpstops force vs. deflection? I'd be interested in a plot.

The reason I ask is that a lot of people compare their new springs or coil over spring rates with the stock spring rates, but if we are constantly on the bumpstops then the bump stop rate needs to be included if you want to make a fair comparison.

[bfrank1972]

Originally Posted by u/Josh

Have you measured the stock bumpstops force vs. deflection? I'd be interested in a plot.

The reason I ask is that a lot of people compare their new springs or coil over spring rates with the stock spring rates, but if we are constantly on the bumpstops then the bump stop rate needs to be included if you want to make a fair comparison.

I'd be interested to see that as well. Also plot transition from spring to bump stop (I imagine it's fairly abrupt). You make a good point about it though, especially if our cars are very "bump stop active". I was kind of joking about custom bump stops before, but maybe something like that (tuned for transition from different spring rates, and suspension travel) would be beneficial?


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[7thgear]

Originally Posted by bfrank1972

I'd be interested to see that as well. Also plot transition from spring to bump stop (I imagine it's fairly abrupt).

it's not abrupt at all, the rate is progressive.. it starts out low and goes up..


none of this is new, the same conversation has been taken place on all the boards where cars are predominantly MacStrut.


it's simply part of the balanced and economic system that car manufacturers decided to use. Our duty is to understand it and upgrade our properly knowing the dynamics and designs.

[bfrank1972]

Originally Posted by 7thgear

it's not abrupt at all, the rate is progressive.. it starts out low and goes up..


none of this is new, the same conversation has been taken place on all the boards where cars are predominantly MacStrut.


it's simply part of the balanced and economic system that car manufacturers decided to use. Our duty is to understand it and upgrade our properly knowing the dynamics and designs.

Well I guess I'm learning about it here, gotta start somewhere right? I've read elsewhere here about people feeling the transition when the "hit the bump stops", they say the car changes character pretty quickly - nose plows when front bump stops, rear destabilizes on rear bump stops. I guess it depends on what you do, maybe it's people installing lowering springs with stock bump stops? It's just clear to me that this topic probably needs a bit of a spotlight for the "lesser informed", at least on this forum. Up to this point I haven't read much at all regarding progressive rate bump stops - the general consensus was to cut them with lowering springs to make sure you stay off them. In context of this thread, that concept seems a little lacking.


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[u/Josh]

Originally Posted by 7thgear

Our duty is to understand it and upgrade our properly knowing the dynamics and designs.

For that we need the force vs. displacement curves for at least the stock bumpstops. If we really want to make an informed decision about a lowering spring, we would also need to know the amount of travel before they are into their bumpstops and the force vs. displacement curves of those bumpstops.

[bfrank1972]

For those learning about this like me, check out this youtube playlist,

http://m.youtube.com/playlist?list=P...DC8BAD62876251


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[Wepeel]

Originally Posted by Suberman

So I'm looking at pictures of this suspension and I don't see any bump stops. There have to be some. Are these inside the shock bellows?

I do see a toe control link that has me suspicious that rear toe is manipulated through the compression arc to induce the oversteer I am experiencing during sharp turns.

That toe link makes the lower "wishbone" into a parallel arm setup, but I'm sure the travel arc of the toe control arm is shorter than that of the main transverse link. The outside rear wheel will toe in under compression while the inside rear wheel will toe out under droop if this is in fact the case.

I'm looking at Edmunds walk around here:

http://www.edmunds.com/car-reviews/t...alkaround.html

Yes, the "bump stops" are on the damper shaft under the dust boot/covers, you wont' see them unless you disassemble the coilover assembly.

Yes the toe link is designed to modify the toe as the rear suspension articulates. I haven't looked at the BRZ rear suspension specifically but I know on the GR Imprezas that the suspension is shared with the suspension is configured to make the rear wheels toe in under droop and compression (i.e. the toe arm is at it's 'maximum' radius at nominal ride height).

[Suberman]

Originally Posted by bfrank1972

I'd be interested to see that as well. Also plot transition from spring to bump stop (I imagine it's fairly abrupt). You make a good point about it though, especially if our cars are very "bump stop active". I was kind of joking about custom bump stops before, but maybe something like that (tuned for transition from different spring rates, and suspension travel) would be beneficial?


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Well it won't be abrupt because you'd feel the car step out immediately it started riding the bump stops if the effective combined rate weren't progressive. All of the spring rates are additive: air in the tire, road spring, roll bar and bump stop. If you have high pressure gas shocks they also have a rising rate spring rate, one of their distinct advantages for sharpening up soft road springs. If the bump stop is to be safe it would have to be progressive in compression.

[Racecomp Engineering]

When people say they are "hitting the bumpstops" and it's abrupt and jarring, it's usually the shock almost bottoming out.

- Andy

[bfrank1972]

So are coilover systems typically designed the same way, or do they include enough travel so contact with the bump stop doesn't happen often during compressiion from hard cornering?


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[Suberman]

Originally Posted by bfrank1972

I'd be interested to see that as well. Also plot transition from spring to bump stop (I imagine it's fairly abrupt). You make a good point about it though, especially if our cars are very "bump stop active". I was kind of joking about custom bump stops before, but maybe something like that (tuned for transition from different spring rates, and suspension travel) would be beneficial?


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Remember that although the bump stop is made from specific compression rate "foam" that the shape of the bump stop also determines how it compresses under load. By moulding in those wider and narrower sections the bump stop will have a progressive rate even though the foam has a fixed compression rate. The narrower parts will compress first and resist compression less until they "bottom out" against the wider sections which will then progressively stiffen up the spring rate. The driver will not be aware of the bump stop effect unless the spring is compressed rapidly, then you'll feel the jolt just as in the old days when bump stops were small and constant rate, just buffers to prevent metal to metal contact and damage.

What we're being told now is that properly designed bump stops actually augment the road springs. This means you need to ensure your coilover supplier also supplies properly designed bump stops, not just shorter or stiffer springs. Also, the shock needs to be able to handle the bump stop compression (jounce) and decompression (rebound) characteristics in conjunction with the spring rate loads.

[86•BRZ]

Originally Posted by bfrank1972

So are coilover systems typically designed the same way, or do they include enough travel so contact with the bump stop doesn't happen often during compressiion from hard cornering?


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Coilovers typically have more travel and I would suggest that when done properly wouldn't bottom out but for bumps. No hard and fast rule though and there are plenty of coilovers available that give no regard for travel, be it bump or droop.

[fatoni]

im pretty sure this is why you can buy coilovers with spring rates 5x that of stock and also have a better ride quality.

[Dezoris]

This is a good thread for sure!

I just torched my springs, the good thing is you heat them up enough it also shrinks the bump stops and you get a great drop and fix the size of the bump stops without cutting.