[4banger]

As a quick experiment, I went out and measured the amount of compression on my tires. These are my winter tires and I have lowering springs, but it should be a ballpark number. I measured 1" of compression of the tire radius. That means the spring rate at this weight is around 900lbf/in. If anyone is out there running the stock tires, can you take some measurments and post up?

[BigSky]

yeah I was comparing your guys #'s on unsprung weight w/ the STi and they are close- as you point out there are places are where there are some savings, others that add- overall very close

do you have the link for the article you ran across?

I've been scouring this site to look for "clues" on the inclusion or exclusion of the swaybars- nothing yet (some interesting reading though on some other subjects )

Automotive suspension engineering Forum - Eng-Tips

[4banger]

Originally Posted by BigSky

yeah I was comparing your guys #'s on unsprung weight w/ the STi and they are close- as you point out there are places are where there are some savings, others that add- overall very close

The change in unsprung mass has such a small effect that it is barely worth mentioning. I just thought it was interesting. The real differnce is in the 33% vs the 99% of the strut/spring weight.

Originally Posted by BigSky

I've been scouring this site to look for "clues" on the inclusion or exclusion of the swaybars- nothing yet (some interesting reading though on some other subjects )

I have seen articles with levels of analysis ranging from the simplest approximations all the way to 7 post shaker rig analysis and none of them mention an ARB. I think there are 2 reasons they are not mentioned. 1-The rest of the world uses ARBs as tuning devices and not band aids, so they just leave it out. 2-They are adding it to the Kspring and assuming that anyone reading their article will just figure it out. Not that I've written any technical articles published by the SAE, but if I had, I would definately mention how I calculated Kspring if it was something other than just the spring. I am leaning towards #1.

Originally Posted by BigSky

Automotive suspension engineering Forum - Eng-Tips

Good website. THat is where I got one of the estimates for Ktire listed in a post above.

[4banger]

Originally Posted by BigSky

yeah I was comparing your guys #'s on unsprung weight w/ the STi and they are close- as you point out there are places are where there are some savings, others that add- overall very close

I've been able to find numbers for almost all the STi parts, and with the change to the factor for the strut/spring assembly I've come up with:

130 Front
120 Rear

Stretch is going to take some measurements on his stock tires. Once I have that number, I should have everything I need to repost the graphs.

[DuncanG]

Originally Posted by 4banger

I've been able to find numbers for almost all the STi parts, and with the change to the factor for the strut/spring assembly I've come up with:

130 Front
120 Rear

Hopefully that is both sides, or is that per side?

[BigSky]

that would be per side I''m guessing, the WRX is roughly 100 front/90 rear per side- the 05+ STi has a beefier knuckle, larger calipers/larger rotors, heavier tires/wheels- so that would make sense- we're talking oe not any aftermarket

[4banger]

The main difference is this. In Fred Puhn's book How to Make Your Car Handle, he states that for the strut/spring combo, that you take the average of the the motion ratios at each end of the sturt/spring and multiply that by the weight of the strut/spring combo. For us, this is essentially one times the weight (vice 1/3 times the weight) I used 1/2 of the weight of the axles, control arms, later and trailing links. I will post up a list of the weights that I used later tonight.

[stretch]

You still cut the weight of the spring and strut in half since part of it is sprung. In an inverted strut like on the STI, the part of the strut containing the oil is all sprung weight- it's the outer sleeve that is unsprung. I think it's is a pretty even weight split since the sleeves are made of heavy metal (surprising, as one point of an inverted strut is to save unsprung weight).

Likewise the spring is half sprung since the top hat sits mounted against the sprung chassis.

Control arms are probably more like 1/3 because they're fatter (heavier) towards the chassis, not that that's a huge deal.

I'd be really surprised if unsprung weight is 130lbs, that's a LOT! I know the brakes are heavy, but the wheels are pretty light. Please post up the list, I'm curious.

[BigSky]

here's the list for a oe WRX wagon

FRONT

tires- 22 lbs
wheels- 16.5
lugs- .5
dust shields- .5
rotor- 14
caliper- 13
knuckle/hub 16.8
axle-12
control arm-10
strut assembly 19

REAR

tires-22
wheel-16.5
lugs- .5
knuckle/hub 18.4
rotor- 9.5
caliper-6.8
lateral links-7 (both)
trailing link 4
axle 12.2
strut assembly 17.5

I took the full weight of the wheels/lugs/knuckle-hub/rotors/calipers and half the weight of the axle, arm(s), and a 1/3 of the weight of the strut assembly.

101 lbs front/ 91.5 rear

The RE070's are heavy 28 ish lbs? the 17x8 rims while relatively light for their size are still heavier than the oe 16x6.5 WRX rims, I'd be curious to see what the front knuckle/hub weighs- it's going to more than the WRX (the rear should be the same), the Brembos aren't exactly light either- nor the rotors.

[4banger]

Here are the numbers that I used.
Front:
Tire - 27
Wheel - 17
Lugs - 0.5
Dust Shield - 0.5
Rotor - 22
Caliper/Pad - 10.8
Knuckle/Hub - 22.5
Axle - 12 (0.5)
Control Arm - 9.5 (0.5)
Strut Assembly - 20 (0.985)
Weighted Total: 130.7lbs

Rear:
Tire - 27
Wheel - 17
Lugs -0.5
Knuckle/hub - 22.5
Rotor - 18
Caliper/Pad 4.6
Lateral Link (both)- 4 (0.5)
Trailing Link - 4 (0.5)
Axle -12.2 (0.5)
Strut Assembly - 20 (0.995)
Weighted Total: 119.6

Note: AnorexicSTi posted that the rear knuckle/Hub was 22.5 lbs. I used this also for the front knuckle since I could not find any measurement for the front. Axles I kept the same as the WRX since I couldn't find any info on them. The various links I found estimates from Nasioc and I think they all came fom BigSky (thanks!). The axles are probaly heavier, but I wasn't going to guess at how much.

If I change the weighting of the strut/spring assembly to 0.5, it comes out to 120.9/109.7 F/R.

[4banger]

In the above post, everything with a (#), the # is the weighting factor. If no number is listed, then the weighting factor is one.

[4banger]

I have reposted the origional graphs using the new unsprung weights. Even though you see a cell for the tire spring rate, it is NOT being used at this time. BigSky - I need to do some more work on the WRX dampers before I repost them. I fell bad that you are one of the few who posted about one of these setups and I ended up having to take your graph down.

[BigSky]

no problem if I can help w/ something let me know

[twiSTies]

I need to dyno the BCs when I take them off the car and upgrade.

On full soft, the steering response noticeably slows, the car rolls a lot more and the ride becomes like a cream puff except over the biggest bumps.

At setting 5, the ride firms up noticeably and the steering is more reactive. Bumps are felt a bit more but it is not harsh at all.

At setting 10, ride firms up more, but not as noticeably.

At setting 15, ride firms up more, noticeably over bumps. Reacts very well to steering input, little roll.

At setting 20, its a go kart. Next to no roll, quick steering input, bumps start to hurt.

At setting 25, same as 20 but the bumps hurt more.

On full hard, its very stiff. I say punishing, but I don't remember it being as bad as the Swifts on stock struts driving into the bump stops. I haven't ridden on full hard in a very long time, even to autocross. I do remember the rebound being very strong and the car bouncing back one time from a hard bump very strongly. I couldn't stomach that on the street.

[import111]

As has been said by a couple other people.....I am not as much into the whole mathematical calculations. However this thread has been a great read. There is 1 thing that was said in this thread that I strongly believe in. Someone mentioned that the smoother the surface, the less suspension travel you need (probably wasn't those exact words but close to it). There is 1 main reason why I have modified the suspension on every car I have owned......reduce body roll to keep the car as planted and stable as possible through twisties. I have learned that vehicle weight plays a HUGE roll in this. My last car (2001 2.5RS-T) weighed 2800 with me in it. It had JIC FLT-A2 coilovers with 8k/6k F/R spring rates, and 18x7.5 wheels with 215/40/18 rubber. That car felt more nimble and almost as stiff as my current car (2005 STi weighing around 3250lbs with me in it, with 255/40/17 tires on 17x8.5 wheels, Tein Flex coilovers 10k/8k F/R rates, Cobb 25mm hollow F/R swaybars rear set to middle setting). I hear a lot of people complain about how Flex's are over damped. For a very bumpy road this would be true, but for those smooth roads and smooth sections on a road course, I feel like they could be even stiffer. I guess I think there is no perfect suspension set up for every situation. There are gonna be times you want it softer, there are gonna be times you want it stiffer. I guess you gotta find that balance for the situations your car sees.

Wow, that was a lot of ranting, lol. Looking at the plot for the Flex's on full stiff, I am not shocked at all. I run mine 1 notch from full stiff always, and I know there is almost no suspension travel at all in both bump and rebound. For daily driving, small bumps are not a big deal and I didn't notice much of a difference going from stock to Espelir GT springs to Flex's. For big, or abrupt bumps, the Flex's hit them VERY hard and there is a huge difference from stock and Espelir GT's to the Flex's.

I don't have any "hard" data to add, but I thought I would share my thoughts and experiences with this type of thing.