Jazzer The Cat

Well, I just hopped over to MM and peped their CO spring rates and was amazed at what I found. The rears range from 175#~700# and fronts from 200#~500# and is incredible to me that much range comes into play. I found my 300#/200# quite comfortable on the street, but cannot imagine what a 500#/700# CO would be like!

I know that CO spring rates can run a lot lower and especially up front. Springs are not my strong suite, as you know, but those numbers seem VERY high in comparison to my own car and cannot imagine them to be near stock comfort.

Jazzer

Aereon

I run 325/525lb's and love it on the street.

Talking about IRS woes, my pass side shock is blown and leaking=/ won't be able to replace till next month.

Jazzer The Cat

Wow....

Well, I don't know what to say, but sure seems high to me. You would know, as I am aware of why you went with IRS and scrapped the SRA.

Jazzer

teej281

Jazzer, have you ever riden in an IRS car? Stock the springs in the rear are 600lb springs and the ride is gorgeous compared to the sra. So would going with a 600 kb rear coilover spring not give the same ride quality?

Jazzer The Cat

The reason being is the location of the spring relative to the pivot point of "A" ams. I just did TONS of searching and cannot believe there is not better pic I can find, but take a lookie hee...


Note the location of the bolt that holds the "A" arm and the OEM spring location. Now.... look at where the strut connects directly above the ball joint. This moves the spring outward about 2/3 more distance from the "A" bolt. This means the tire will respond more quickly to a shock (bump in the road) and need less spring rate to support the car. This is why a front CO is a MUCH nicer ride and improved handling all else being equal.

Imagine you have a teeter-totter and the plank is 20' long. If you put the pivot in the middle, you can have a 200 lb. person on each end and will balance so both pepes are off the ground. NOW.... move that pivot point 5' closer to one side. What will happen at this point? The 200 lb person will EASILY lift the other up until he himself is sitting on the ground and the other guy is way up in the air. This is due to the increase in leverage and a good person at math (maybe CliffyK will chime in here!) can describe it in numbers. I am guessing here, but I would figure you could maybe have a 150 lb. guy on the short end and would balance (Cliffster? )

The rears are the same way, but not sure why there is differing opinion as to ride quality on rear CO's when nobody disputes the improved ride of fronts?

Jazzer

teej281

I dont know what you were getting at there Jazzer. lol could you explain to me what that explanation is for? Im familiar with the CO setup as i've read about it and talked with you about it a bunch. I'm guessing that the reason why the rear springs have to be that stiff is just because each side is independent of eachother like the front suspension, it just is not as well designed. Im just trying to throw ideas out there to see if we can come up with an answer.

teej281

I just posted something up on SVTP about the difference in SRA and IRS spring rates and the reasoning for it so we'll see where that gets me.

Jazzer The Cat

***HERE*** is a link with a more detailed description. Pay close attention to Norm Petersons posts, as this guy knows his sheet and VERY knowledgeable on suspension geometry. I have read a bit and is quite technical, so I will keep looking... hold on...

[elevator music here]

I have an animated .gif image, but from another site that is usually blocked by MF's. I will try it now, but may "vanish" into a red-x later today. If so, I will put it up on my Photobucket page and re-link it:

Here you can see the CO on the LH side and OEM located spring on the RH side. The CO spring is farther outward and hence can be much lighter rate to do the same job. This also allows the wheel to repond more quickly to a bump in the road so the ride is nicer. The spring has more travel for the exact same amount of movement of "A" arm to compress, so can be MUCH more exact in its calculation for rate.

This puts the spring VERY close to the wheel/tire and can actually rub, in some cases. For this reason, you want to consider a 2.25" diameter spring over a 2.5" one offered at MM. On a side note, I am able to run a 10" wheel up front as my shock/spring is inbetween the two locations above and tiled farther inward to a point just along side the frame. The original "cups" that hold the upper ends of the OEM located springs, are actually part of the OEM "K" member and no longer exist on my car, so I have additional clearance here in which to lean my CO shock inbetween the twin-A arms of my SLA

Jazzer

teej281

The front coilovers are 2.5" springs and the rear are 2.25" springs, is that what you were talking about? Or were you saying that it would be wise to use 2.25" springs in the front as well to improve clearance? Have you read anything about how IRS's can get away with running 600lb springs and still ride better than an SRA with 200lb springs?

Jazzer The Cat

teej.... I spoke with John Griggs yesterday about the vast differences between CO's on the IRS vs. SRA. The pivot location differs vastly between the two and why a 200# CO on my ride would be nearer to a 400# on on yours to get approx. the same ride quality.

Hey... what is up with like 4 threads on your IRS? I couldn't find this one, so I peped your CP and searched your threads *OMG*

Jazzer thinks teej needs a hug