Ride height - sense check

[Glenfield]

Team,

Wrapping up suspension refresh. Replacing Bilstein struts and 7 and 9x16 Fuchs with MCS 1WNRs and 7 and 8x15 Fuchs.

I was running Yoko A008 205/55 and 245/45. I’m now running Avon 215/60 and 225/60. Believe tire OD is roughly same in front and 1” more in rear.

Doing a baseline measure of ride height before tweaking and #s surprise me. Would appreciate a sense check.

Front - Floor to arch = 25 5/8”. Measured WC to TC it’s a whopping 160mm. Less 16mm raised spindles yields a WC-TC of ~149mm and 142mm respectively.

Am I right in thinking that larger wheel OD is making the arch to floor measurement “ball park” Euro with the car actually running very low using factory measurements?

The rears are +10 and +5 respectively. If I don’t change fronts, I’d have to lower by 22 and 27mm respectively to be on the factory chart for setup.

Have I done my math wrong?

[Glenfield]

There’s about 3/4” from tire to fender at the front and 1.5” gap at the rear.

If I left fronts alone, and dropped the 22mm or ~1” at the rear passenger say, rear would measure -122mm on factory measurement and 25 3/4” floor to fender.

[David Inc.]

If the tires are about the same OD, and they should be, then they shouldn't have an impact on the ride height.

You sure you're measuring WC-TC right? at 145mm I'd expect the control arm to be horizontal or going up towards the wheel pretty significantly, and your wheel arch would be hugging the top of the tire.

[Glenfield]

See below for photos of control arm. It’s at a negative angle to the road.

Thinking more on it, I think it’s got something to do with the shorter strut body also. I measured 165mm and then subtracted the 16mm raised spindle to get to ~ 149mm. What I didn’t account for is how much shorted the strut body is vs the Bilstein it replaced.

I don’t have that measurement but looking at the attached photo, it’s reasonable to think it’s considerably shorter which puts me well below 149.

* I lowered rear from 26 3/4 to 25 3/4 which would move it from +10 to -15mm on factory method. If strut body is ~1.5” shorter than Bilstein, then my 149 is actually 149-38 or 111. Measure of 111 front and 15mm rear is “Euro height” and yields a rake of ~1 degrees which is what it was when I swapped wheels. May explain why the car is looking close to correct now.

[76FJ55]

the overall strut length has nothing to do with it. it will only determine how much droop you get when the car is lifted off the ground. at any given ride height, the strut sits somewhere within the compressible range.

[Glenfield]

I don’t know the compressible range of MCS vs Bilstein shock inserts. Assuming those are equal for a moment, won’t a shorter strut position the wheel hub higher relative to torsion bar ie. Have same impact as raising spindle height?

[LJ851]

Originally Posted by Glenfield

I don’t know the compressible range of MCS vs Bilstein shock inserts. Assuming those are equal, won’t a shorter strut position the wheel hub higher relative to torsion bar ie. Have same impact as raising spindle height?

The wheel hub position won't change, 76FJ55 is correct.

The only ride height effect a strut insert can make is from gas pressure.

[David Inc.]

Originally Posted by Glenfield

I don’t know the compressible range of MCS vs Bilstein shock inserts. Assuming those are equal for a moment, won’t a shorter strut position the wheel hub higher relative to torsion bar ie. Have same impact as raising spindle height?

The only thing that matters for ride height is the distance from ball joint to spindle.

[Bill Verburg]

Originally Posted by Glenfield

Team,

Wrapping up suspension refresh. Replacing Bilstein struts and 7 and 9x16 Fuchs with MCS 1WNRs and 7 and 8x15 Fuchs.

I was running Yoko A008 205/55 and 245/45. I’m now running Avon 215/60 and 225/60. Believe tire OD is roughly same in front and 1” more in rear.

Doing a baseline measure of ride height before tweaking and #s surprise me. Would appreciate a sense check.

Front - Floor to arch = 25 5/8”. Measured WC to TC it’s a whopping 160mm. Less 16mm raised spindles yields a WC-TC of ~149mm and 142mm respectively.

Am I right in thinking that larger wheel OD is making the arch to floor measurement “ball park” Euro with the car actually running very low using factory measurements?

The rears are +10 and +5 respectively. If I don’t change fronts, I’d have to lower by 22 and 27mm respectively to be on the factory chart for setup.

Have I done my math wrong?

lets stick to the front
Yok 205/55 x16 has a of 12.0" (306mm) and od of 24.8"
avon 215/60 x15 has an a of 12.5" (317mm) and od of 25.0"

b measures the actual chassis height and is the single most important metric

the bigger a is the bigger a -b can be for the same chassis height

raising the spindle has no affect on a, it only affects shock compression travel.

[PeteKz]

Having messed with these settings many times, both measuring the Porsche spec and fender heights on my car and others, I can say that at the Porsche spec, even for ROW cars (Euro), the car sits pretty high. We have become used to seeing cars that have been slammed down 1-2", but that ain't how they were engineered. Given your tires, and not accounting for a raised spindle, your fender would be about 26" or slightly more at the front, and 25.5-ish at the rear. Accounting for the 16mm raised spindle, your front number might be slightly high, but not by much.

As they were delivered from the factory in the 70's and 80's, these cars sat much higher than most people think.

[Glenfield]

Thanks all for the check.

Somewhere along the way, I cocked up the front measurement. I was so off that it's a little unclear how I got there but will leave that to the post mortem.

I'm about ~115mm at the front and ~ -15mm at the rear. That does correspond to ~25 5/8" in the front and a little under 26" at the rear. Probably do need to bring front up a little which will get me close to your numbers PeteKz.

[Bill Verburg]

Originally Posted by 76FJ55

the overall strut length has nothing to do with it. it will only determine how much droop you get when the car is lifted off the ground. at any given ride height, the strut sits somewhere within the compressible range.

The overall strut length changes b

all the bottom/sliding pieces are the same the inserts are different lengths

MCS insert length can be specified when ordered and looks to be ~2 3/4" shorter than the b6 that came off the car

[Bill Verburg]

Originally Posted by LJ851

The wheel hub position won't change, 76FJ55 is correct.

The only ride height effect a strut insert can make is from gas pressure.

Static internal gas pressure of MCS is considerably higher than for Bilstein, the gas pressure and piston area determine the extensive force of the shock
Bilstein ~42#
MCS ~86#

[Glenfield]

Thanks Bill. Intuitively I was sure that the MCS would change ride height, all else equal. That said, I still buggered the measurement.

Am I right in thinking that all said and done, I can still reference factory measurement as instructive of ride height.

Ie. Once all buttoned up, WC - TC and TC - WC is what it is.

One other observation - adjusting rear suspension 9 clicks softer ostensibly reduced rear ride height by 5/8”. That struck me as odd … I just got car of stands from bleeding breaks and admittedly hadn’t rolled car back and forth to make sure all fully settled.

[Bill Verburg]

Way back ,when Porsche wrote the specs a CN36185/70 x15 tire was a common fitment.
for this tie a is 12.2"(310mm) which means that the spec height of the t-bar center is 7.9"(199mm)

coincidentally a 206/55 x16 has a = ~12.1" which puts the t-bar center 7.7"(195mm)

anecdotally a euro ride height car measured decades ago w/ 185/70 x15 tires and a-b of 112mm measured a fender heigh of ~27"

my own car when I had a -b of 150mm measured 25 1/2" at the fender
and w/ a-b of 177mm measures 24" at the fender

note that the above a - bs are from 112 to 177 mm (4.4 - 7")

fender height is notoriously unreliable