More Findings & Discussions About Lowering the M3

[doba_s]

Originally Posted by spyderco10

How about a 300lb woman in the passenger seat?

300lb woman= frame damage

[rzm3]

Originally Posted by lucid

Hi guys. I just checked the specs on the machine and it can easily handle the forces and the displacements we are talking about. I just need the dimension of the stock springs to make sure I can mount them properly. Diameter and uncompressed length? Also, can someone post a pic of stock and aftermarket springs? Once I get this info and verify that we are good to go, I'll start another thread on this.

i will do that sometime next week, lucid.

[lucid]

Originally Posted by rldzhao

i will do that sometime next week, lucid.

OK, thanks. Whenever you get a chance.

[Blip Bavarian]

Originally Posted by AutoTalent

Lowering height is one thing but spring rates is another. Just because one is lower doesn't mean that it will ride worse if using a lower spring rate. Oddly, RD springs ride better with the lower stance than H&R. I have not installed Eibach springs yet so can't provide any real input.

The proper way is to have springs matched to shocks like the KW Coilovers

would you elaborate a bit on what you mean when you say that they ride better?

I am stumped and cant decide which company to go with. Thanks

[Blip Bavarian]

Originally Posted by lucid

You can ship one of your front springs to me if you'd like, and I'll ship it back after I get the data. We can split the shipping costs. Shouldn't be much. Or we can meet up if you are ever in the area. I have access to equipment that will yield accurate force vs. displacement data. Just an offer.

would only performming the test on the front springs be enough info? wouldnt you need to do the rears too?
Thanks for all the great info guys. Keep it coming.

[rzm3]

Front spring length: ~11 inches
Rear spring length: ~12 inches

[Orb]

Spring Rates:

F: 160 lb/in
R: 550 lb/in

System Frequency (about):

F: 1.3Hz
R: 1.5Hz

Orb

[rzm3]

Thanks. Do you have Dinan's spring rates?

[Orb]

Originally Posted by rldzhao

Thanks. Do you have Dinan's spring rates?

I only have the spring rated KW v3 and Clubsport. Both will induce under steer without bar change. The motion ratio for the rear is about 0.35 after being squared. The OEM frequency between front and rear is dead perfect (not surprising) and one should aim for about 10% higher frequency in the rear than the front.

If someone wants to measure one coil at time on the Dinan front spring I can calculate the spring rate. The rear is same method but much easier.

I am still curious what the supposed outcome of the Dinan bump stop investigation is…a purpose to an end. The shorting is just in proportion to bump travel….it is fairly straight forward and expected with increased spring stiffness. I would just phone them and ask.

Orb

[rzm3]

Originally Posted by Orb

I only have the spring rated KW v3 and Clubsport. Both will induce under steer without bar change. The motion ratio for the rear is about 0.35 after being squared. The OEM frequency between front and rear is dead perfect (not surprising) and one should aim for about 10% higher frequency in the rear than the front.

Could you explain why the frequency should be 10% higher frequency in the rear than the front?

Lucid, I ran a few hand calcs and the spring rates make sense. I guess we just need to test the aftermarket springs now?

[Orb]

Originally Posted by rldzhao

Could you explain why the frequency should be 10% higher frequency in the rear than the front?

Also by frequency you mean sqrt(k/m)?

You can start with this page but I would generally read the whole series. It is a bit technical for most but getting the basic of it is all that is required (There is a few math errors in the calc as well). Be careful reading this as they will suggest higher frequency on the front when you have down force but it doesn’t apply for a street car but there are other cases when the rules change. The second site give you better overview on many subjects on suspension and very well written in laymen terms.

http://www.optimumg.com/documents/te...Tech_Tip_1.pdf

http://www.fromsteve.net/

Orb

[rzm3]

Originally Posted by Orb

You can start with this page but I would generally read the whole series. It is a bit technical for most but getting the basic of it is all that is required (There is a few math errors in the calc as well). Be careful reading this as they will suggest higher frequency on the front when you have down force but it doesn’t apply for a street car but there are other cases when the rules change. The second site give you better overview on many subjects on suspension and very well written in laymen terms.

http://www.optimumg.com/documents/te...Tech_Tip_1.pdf

http://www.fromsteve.net/

Orb

Thanks for the links. They are very helpful.

[lucid]

Originally Posted by rldzhao

Lucid, I ran a few hand calcs and the spring rates make sense. I guess we just need to test the aftermarket springs now?

Thanks for posting the pics. Do you know what the diameters are? I can estimate from the pics based on your length figures I guess...

As you know, spring rate is a function of displacement. To completely characterize the behaviour of the spring+bump stop, I'd like to take data on the entire operational displacement range. I doubt that the springs will be perfectly linear, and then there are the effects of travel on the bump stop. My goal is to come up with a complete effective force displacement graph including the part of the displacement that is on the bumpstops. I should call the dealer to see how much the bumpstops cost. As you said earlier, they should be fairly inexpensive.

I checked with my friend and he says he has a way of keeping the springs stable, but I'll run the dimensions by him to make sure we are OK.

[William Blake]

Will installing Eibach springs induce more understeer than fully stock?

Yes/No

[gthirtyfizle]

I dont think so

[rzm3]

Originally Posted by lucid

Thanks for posting the pics. Do you know what the diameters are? I can estimate from the pics based on your length figures I guess...

As you know, spring rate is a function of displacement. To completely characterize the behaviour of the spring+bump stop, I'd like to take data on the entire operational displacement range. I doubt that the springs will be perfectly linear, and then there are the effects of travel on the bump stop. My goal is to come up with a complete effective force displacement graph including the part of the displacement that is on the bumpstops. I should call the dealer to see how much the bumpstops cost. As you said earlier, they should be fairly inexpensive.

I checked with my friend and he says he has a way of keeping the springs stable, but I'll run the dimensions by him to make sure we are OK.

I will measure after the holiday. Bump stops are like $11.54 a piece. Check mileoneparts.com part number 31302283444

[rzm3]

Ends of the front coil spring have about 4" dia.

[Blip Bavarian]

Originally Posted by William Blake

Will installing Eibach springs induce more understeer than fully stock?

Yes/No

+1 ?

[e46e92love]

Updates on the testing?

[MrHarris]

any updates on testing?

[aajami]

Another bump for any updates

[William Blake]

Originally Posted by Blip Bavarian

+1 ?

On my Mini it actually killed some of the understeer.

So probably it will be the same for the M3.