Neil Perry

Hi
Regarding 993 Carrera,

Has anyone measured the suspension motion ratio of a 993, front and rear?

Can you share these measurements?

Thanks,

Bill Verburg

???

ToSi

Haven't measured yet but have been using the following approximations:

Front is a strut, KPI is listed as 19.5 deg so start with ~0.94?

Rear is a bit more difficult to eyeball - the 'spring/damper ratio' is provided as 0.9 which seems a reasonable starting point considering the mounting location & angle of the shock.

Working on something interesting?

Neil Perry

Hi ToSi,
Thanks for the information.
I have a mate that is an engineer on one of the V8 Supercars in Australia and we are looking at the suspension of my 993 and considering spring rates and so on.

If anyone has actually measured the suspension and has the measurements that would be great.

Thanks,

ToSi

I worked out the ride frequencies using the above assumptions. Base suspension is ~1.5hz, m030 is ~1.6, & RS is ~2hz. Pss10 is in between.

changing the motion ratio by .05 changes the freq by ~.1 so likely close enough to pick a decent starting point.

Luftd993

Are you chaps getting bored with searching for the Higgs boson particle?
Wish I could help you.
No.
I really wish I could help you.

flyingchappy

This is the Wiki definition. Interesting comparisons can be made between p-car models.
"Motion ratio in suspension of a vehicle describes the amount of shock travel for a given amount of wheel travel. Mathematically it is the ratio of shock travel and wheel travel. The amount of force transmitted to the vehicle chassis reduces with increase in motion ratio. A motion ratio close to one is desired in vehicle for better ride and comfort. One should know the desired wheel travel of the vehicle before calculating motion ratio which depends much on the type of track the vehicle will run upon.
How to decide the motion ratio?
It basically depends on 3 factors
a)Bending Moment: To reduce the bending moment the strut point should be near to the wheel.
b)Suspension Stiffness: The suspension tends to get stiff when its inclination of the shock absorber to horizontal tends to 90 deg.
c)Half Shafts: In Rear suspension the wheel travel is constrained by the angle limitations of the universal joints of the half shafts. Design the motion ratio such that at maximum bounce and rebound shocks are the first components that bottom out by hitting bump stops."

Neil Perry

Hi David, you watch way too much "Big Bang Theory"

although, this is my favorite show

ToSi, I will speak to my mate and see what we can work out, thanks for your help.

Thanks,

chris walrod

Measuring the MR isnt difficult, just time consuming. Just need to remove the spring, then reassemble. Two dial indicators, one at the spindle, one at the damper. I would think both front and rear would have a MR of 1.

ToSi

Would be if the springs were perfectly vertical. Need to account for the angle of the spring, multiply by the cosine of the installed angle.

chris walrod

Exactly, but without rocker arm construction, the MR isn't going to be that great of a number. The rear will be a greater number than the front.

David Borden

For the guys that quoted guesstimates of the MR above, are you refering to the measured motion ratio, or the calculated motion ratio?

The measured MR needs to be squared to get the ratio that actually impacts the wheel rate/spring ratio. So a .80 measured MR would have a .64 calced MR. For example a 100lb spring would have an effective wheel rate of 64lbs.

Does anyone have some of the spring rates of the different springs M030, M033, stock, etc?

I like to geek out on suspension geometry, shock valving, etc on cars Ive raced, just havent measured out our 911's as of yet.

David

Neil Perry

Hi
There were some spring ratings posted by Steve Weiner Rensport Systems some time ago, as below.

Porsche M030 150-200 Front and 225-275 Rear
H&R Sports 240-260 Front and 280-310 Rear
PSS10 225-250 Front and 280-310 Rear

The PSS10's use a unconventional main-tender package so it's not directly comparable unless one understands the relationship and crossover points between mains and tender springs.

Hope this helps,

Thanks,

Beverly393

I worked out the ride frequencies using the above assumptions. Base suspension is ~1.5hz, m030 is ~1.6, & RS is ~2hz. Pss10 is in between.

changing the motion ratio by .05 changes the freq by ~.1 so likely close enough to pick a decent starting point.

ToSi

my estimates are of the measured values, i.e. not squared.

re: rates,

Porsche published values in lbs/in - F/R:
M032 (base) 145/217
M030 165/285
RS 245/456

I measured PSS10 mains @ 220 / 380.

I have no idea where the other #'s that have been quoted in the past come from.