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      10-31-2008, 06:54 PM   #1
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Arrow More Findings & Discussions About Lowering the M3

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. (Dinan claims 1/2")

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

Stock Bumpstop Facts:
Front: 2.25" (my measurement); 2.375" (Dinan's claim)

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 (claimed) 1/8" according to my measurement; 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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Last edited by rzm3; 11-04-2008 at 01:26 AM.
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      10-31-2008, 07:08 PM   #2
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Quote:
Originally Posted by rldzhao View Post
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)
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.
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      10-31-2008, 07:10 PM   #3
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Quote:
Originally Posted by HIS4 View Post
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.
I agree. That's why I think we need a side-by-side comparison of two M3s (one with H&R and one with Dinan).
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      10-31-2008, 09:24 PM   #4
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nice work man. Now I don't know what to do
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      11-03-2008, 11:32 PM   #5
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Good work. Looks like H&R designed their springs to be used with the stock dampers, while Dinan want's you to buy their system since you'll need new dampers in order to compensate for the stiffer springs since the bump stops are stiffer.
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Let me get this straight... You are swapping out parts designed by some of the top engineers in the world because some guys sponsored by a company told you it's "better??" But when you ask the same guy about tracking, "oh no, I have a kid now" or "I just detailed my car." or "i just got new tires."
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      11-04-2008, 12:44 AM   #6
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So in conclusion, what would u guys say is the best way to go? Dinan or H&R? I deff wanna buy something to lower this.
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      11-04-2008, 01:23 AM   #7
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It depends on your personal preference. If you like more lowering, go with H&R. If you like less lowering and like to play it safe, go for Dinan.
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      11-04-2008, 01:24 AM   #8
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Quote:
Originally Posted by aus View Post
Good work. Looks like H&R designed their springs to be used with the stock dampers, while Dinan want's you to buy their system since you'll need new dampers in order to compensate for the stiffer springs since the bump stops are stiffer.
Well, both are designed to be used with stock dampers. The only difference is that Dinan provides more travel before contacting the bumpstop.
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      11-04-2008, 03:17 AM   #9
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Some H&R's are designed to be used with the stock dampers, but obviously can be used with aftermarket dampers.

I wonder what happens with the suspension travel if you install coil overs?
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Let me get this straight... You are swapping out parts designed by some of the top engineers in the world because some guys sponsored by a company told you it's "better??" But when you ask the same guy about tracking, "oh no, I have a kid now" or "I just detailed my car." or "i just got new tires."
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      11-04-2008, 08:19 AM   #10
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good info!
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      11-09-2008, 08:33 PM   #11
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Can u run dinan bump stops with h and r springs or that would be wrong for h and r designs
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      11-09-2008, 09:01 PM   #12
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Quote:
Originally Posted by rawedge2 View Post
Can u run dinan bump stops with h and r springs or that would be wrong for h and r designs
1. dinan wouldn't let you only buy the bumpstops

2. it won't make it a difference since it's only 1/8" shorter than stock according to my measurement.
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      11-10-2008, 12:23 AM   #13
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What about the Eibach Pro springs... Almost seems like best of both worlds... the price like the H&R but a drop that is similar to Dinan?? (IE not as agressive drop as H&R)
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      11-10-2008, 12:48 AM   #14
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I'm installing RDsports springs on Wednesday, anyone on here try them yet?
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      11-10-2008, 01:08 AM   #15
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Quote:
Originally Posted by tmntmn View Post
I'm installing RDsports springs on Wednesday, anyone on here try them yet?
What did they set you back, the Eibachs cost around $265?
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      11-10-2008, 04:03 AM   #16
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I believe that the RDsports springs have the most aggressive drop of them all (greater than Dinan, Eibach or H&R)
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      11-10-2008, 11:34 PM   #17
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nice writeup. Thanks. I have been having the same dilema about which setup to go with. I am interested to see how this develops.

Im really surprised that we havent seen anyone with the dinan setup yet.

Also surprised that I have not heard of any EDC issues with any of these springs. Encouraging for sure.
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      11-10-2008, 11:44 PM   #18
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Quote:
Originally Posted by spectrumphoto View Post
I believe that the RDsports springs have the most aggressive drop of them all (greater than Dinan, Eibach or H&R)
Not true, I had them before I got the KW v3. I loved them they rode nice and best of all they made the car level. To me the H&R springs make the front end lower than the rear and it looks funny. I think its a 3/4 drop all around but I could be wrong. RDs springs dont sit lower than the H&R springs.

I dont know anyone crazy enough to spend $900 on springs(&bump stops) that dont even drop your car so I cant say how they stack up to Dinans

Great post rldzhao!
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      11-12-2008, 01:50 PM   #19
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How long to install the springs? My dealership quoted 9 hours for the Dinan springs including alignment. Does that sound right?
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      11-12-2008, 02:14 PM   #20
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9 hrs!! absurd.
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      11-12-2008, 02:18 PM   #21
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How long to install? What can I expect to pay for alignment afterwards?
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      11-12-2008, 02:28 PM   #22
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Quote:
Originally Posted by TXM32B View Post
How long to install the springs? My dealership quoted 9 hours for the Dinan springs including alignment. Does that sound right?
no. 3 hours max including alignment. should be 30 min per corner
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