Quote:
Originally Posted by rldzhao
Suspension Travel Before Loading Bumpstop
So amid the discussion of how much suspension travel is in the front before the progressive bumpstop is contacted, I went to my car and measured. I basically pushed the bumpstop downwards as much as I can and measured the gap using a piece of paper. The result - 3/4 inches. (see picture)
H&R Responses to Dinan's Design
The H&R springs would drop the front by 1 inch, so basically the car would be riding on the bumpstop before any loads. So I called a technical manager at H&R and asked him about the effect of riding on the bumpstop prematurely, and here is his answer (paraphrase):
The bumpstops in modern day vehicles aren't really a bumpstop in the traditional sense, because in the past bumpstops are basically firm rubbers that prevented the car from bottoming out. On modern vehicles, the "bumpstops" are engineered foamy elastomers, and are part of the suspension system, making the compression progressive.
So I mentioned that a competitor is offering a design with a shortened bumpstop and guide support to avoid premature bump stop contact, and he said:
Shortened bumpstops are made to be stiffer than stock to work properly, which means that there will be a drastic change in the stiffness of the suspension system when compression reaches a certain level. This means rougher stops when the spring is near full compression. That's why H&R kept the factory bumpstop.
Here's an H&R article: http://www.hrsprings.com/technical/m..._jounce_bumper
H&R M3 Springs Facts:
Front lowering: 1"
Rear lowering: 1/2"
Front will compress bumpstop by 1/4" when stationary
Dinan Springs/Bumpstop/Guide Support Facts:
Front lowering: 1/2"
Rear lowering: 1/2"
Front bumpstop 1/4" shorter than stock; guide support 0.3" shorter than stock
Front will have 0.55" travel (0.5" factory travel + 0.3" guide + 0.25" bumpstop - 0.5" lowering) before loading bumpstop
Front full compression travel will increase by 0.3" into fenders (assuming Dinan bumpstop has same full compression height as stock)
So, hope this helps. Just trying to offer the story from both sides. Both Dinan's and H&R's stories make sense, and I guess the best way to compare the two is to have a side-by-side track test. Any one planning on getting a Dinan system soon?
(If there are any mistakes in my calculations please let me know  )
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It is true that the bumpstop is considered a small progressive spring and it acts as part of the whole suspension system. What H&R is doing is not wrong it's just a different approach to the problem from what Dinan has decided to do. I'm sure part of the motivation for doing what H&R is doing is cost. No one can really say which is better without actually testing it. Even then, I'm sure the results would differ based on the application.
One other thing. That 3/4" you meaured would be decreased significantly with a passenger and when the car is in motion just because of the load exerted on the suspension by the engine. So it is possible that you'd be very close to the buumpstop before you even hit a bump causing suspension compression.