Front strut travel

[phunt]

I have yellow RSR Bilstein front struts. Spindle raised 19mm. Would someone post a picture of the tops of their struts. Like the one I posted. I want to know how much shock there is out of the top of the strut. How much travel the shock has.

[phunt]

Those pictures are after I raised the car 36mm. That’s at the torsion tube to wheel center measurement. It was 25” at the render now it is 26”
Looks stupid high now to me

[nickelplated5s]

Pheasant Hunt, without looking what is your car and exactly what are you trying to do with it? I'm running 195/50/16's with 22" to lip in the front. BillV says to measure a different way but that is what I have with no raised spindles. I understand the roll center argument but I have custom Koni's for the front.

[phunt]

No it talking about use. I want to understand why the strut has less then 2” of travel. Hit a bump strut goes up. top of strut to top of shock, where it mounts, is less then 2”

[phunt]

Here is the strut fully extended. That is an 8” spring. So there is about 7” of damper (shock) sticking out of the strut. When installed and set at a ride height of 25” measured at the fender lip the is about 1 1/2” of that damper sticking out of the strut. So less the. 2” of travel on that damper? Ride height measured by the height of the torsion bar center line to the height of the center of the wheel method. Was 148mm so 40mm lower than standard. I raised the height of the torsion bar. Now it has a fender lip height of 26. And a torsion to wheel center height of 127mm. Still 20mm lower the standard. And the damper now protrudes about 2 1/4”. So I guess what I don’t get is. Out of the 7” or so of static travel you only get 2” when installed??

[Bill Verburg]

I've been trying to get this info for years

what you measured is about right w/ what I've seen for a 911 front
~7"+/- total travel

midpoint would be ~3.5" bump & ~3.5: droop

here is a rear

[phunt]

If it was mid point and I had 3” protruding I would be stoked. But I don’t even have 2” when it is stupid high. It just doesn’t look right. I guess when I am driving and it breaks I’ll know that wasn’t enough

[PeteKz]

Bill V: I am accustomed to setting up motorcycle suspensions with 1/3 "sag." Sag is the amount of suspension compression, compared to the full travel, at the ride height. Thus, at the ride height, the suspension is only 1/3 compressed. That gives 2/3 travel for compression over bumps.

Is there something about the 911 suspensions that we should set ride height at 1/2 instead of 1/3 travel?

[Bill Verburg]

Originally Posted by PeteKz

Bill V: I am accustomed to setting up motorcycle suspensions with 1/3 "sag." Sag is the amount of suspension compression, compared to the full travel, at the ride height. Thus, at the ride height, the suspension is only 1/3 compressed. That gives 2/3 travel for compression over bumps.

Is there something about the 911 suspensions that we should set ride height at 1/2 instead of 1/3 travel?

I really don't know, which is why I've been requesting any one w/ new or old unmounted shocks and struts to make a few measurements
No joy so far

I'm in the market for new fronts so when I get them I'll do it.

off the top of my head every motorcycle I've owned, admittedly a small sample
1 Honda SL350
1 1970 Triumph Bonneville
1 Honda/Yoshimura 836, which had Koni rear shocks

all had quite a bit of compression travel and none were lowered so not really an apples to apples comparison

another factor w/ the OPs shocks is they are likely based on a B8 so already shorter than the usual B6 used in 911 front

[Nditiz1]

I dont under stand having double springs on the front OR has the OP remove the spring rate from the torsion bars. The height of the front is mainly based on torsion spring.

[Bill Verburg]

Originally Posted by Nditiz1

I dont under stand having double springs on the front OR has the OP remove the spring rate from the torsion bars. The height of the front is mainly based on torsion spring.

The second spring seen above is a tender spring, it's not very strong and doesn't contribute to the wheel rate, it's primary purpose to keep the spring stack in contact w/ both perchs

The tender isn't at all necessary. many dedicated track cars will not have them as they add a second and unnecessary and sometimes irritating set point in maneuver.

I don't use them on my 993

as to the t-bars the OP will need to respond,

Porsche started adding coil springs to their t-bar race cars back in the late '70s when they found that they couldn't fit big enough bars to get the wheel rates that they were after, the added coils would be stronger than a tender but less than a single main spring.

[phunt]

The spring shown is not a tender. It is a 200lb spring used for dual rate purposes. The main spring is a 250lb spring. That is the 8” one. Clint Smith is the one who suggested it and sold it to me. I do have a tender as well but it is not installed.
Bill if you need measurements I will be happy to take them.
I do not know if they are B8 or B6 and frankly I don’t know what that means. The shocks are Bilstein lrevalved by Clint. they were not done correctly. I had to send them and the rears out to get fixed. But non of that matters. Again it just does not seam right when there is that little available travel

[phunt]

Oh and no T-bars just coil overs

[Jonny042]

You aren't going crazy, and your car is completely normal.

I've been on about this for years. The 911 is severely lacking in front suspension travel, especially at the low ride heights our eyes have all become accustomed to. The thread linked below has a lot of facts and information. It ended up going of the rails a bit in the later pages.

You've already done what you can by installing raised spindles, but IMO you should consider cutting the front bumpstops by 1/3 if you haven't already.

The thread also goes into bump steer correction and why it's so important, especially with raised spindles:

https://forums.pelicanparts.com/porsche-911-technical-forum/1116494-front-suspension-travel.html

[Jonny042]

Herein lies the problem:

Originally Posted by Jonny042

The factory also designed around a 14" wheel! We've come a long way from this:



to this... some adjustments are going to be needed!

[Jonny042]

Originally Posted by Bill Verburg

another factor w/ the OPs shocks is they are likely based on a B8 so already shorter than the usual B6 used in 911 front

It is true, that some applications of B8s have shorter strut/shock bodies, not only for 964 and up 911s, but many other cars from different brands.

However, it is not the case for 911s up to 1989 that originally came with torsion bars. I wish it was!

The reason for the above is simple. Consider what would happen if you could actually purchase a B8 strut insert with a shorter body that allowed greater bump travel. The strut housing (which is not changed when you change "shocks") would smack right into the top mount before the insert ran out of travel.

The only length difference in any of the Bilstein offerings for the pre-964 911 is the REAR sport shocks (the yellow ones) have a shock shaft that is slightly shorter. The only thing this does is slightly reduce the overall travel of the shock and limits DROOP travel to some extent.

[Bill Verburg]

Originally Posted by Jonny042

It is true, that some applications of B8s have shorter strut/shock bodies, not only for 964 and up 911s, but many other cars from different brands.

However, it is not the case for 911s up to 1989 that originally came with torsion bars. I wish it was!

The reason for the above is simple. Consider what would happen if you could actually purchase a B8 strut insert with a shorter body that allowed greater bump travel. The strut housing (which is not changed when you change "shocks") would smack right into the top mount before the insert ran out of travel.

The only length difference in any of the Bilstein offerings for the pre-964 911 is the REAR sport shocks (the yellow ones) have a shock shaft that is slightly shorter. The only thing this does is slightly reduce the overall travel of the shock and limits DROOP travel to some extent.

and Bilstein lists b8 for motorsports


the non motorsport s versions are clearly labeled b6

[PeteKz]

On second look at the setup in post #5, it looks like it has 3 springs--a main spring (red), a lower rate spring (black), and a tender (also black).

Bill, as you know, I have Koni Sports on my car, 21mm T bars, and the ride height is not much below stock (1/2" or so). What measurements are you looking for? I may have it up in the air this weekend.

[Bill Verburg]

Originally Posted by phunt

The spring shown is not a tender. It is a 200lb spring used for dual rate purposes. The main spring is a 250lb spring. That is the 8” one. Clint Smith is the one who suggested it and sold it to me. I do have a tender as well but it is not installed.
Bill if you need measurements I will be happy to take them.
I do not know if they are B8 or B6 and frankly I don’t know what that means. The shocks are Bilstein lrevalved by Clint. they were not done correctly. I had to send them and the rears out to get fixed. But non of that matters. Again it just does not seam right when there is that little available travel

Not sure what the advantage of that is unless the actual spring desired isn't available

That's a dual spring setup, as opposed to a dual rate spring setup. They are not the same thing

Your spring setup acts a single rate spring which is less than either of the component springs, What you say???, That doesn't make sense! But it does because each spring

is in a say 1" compression only moves part of that 1" the 200 moves a bit further than the 250, But the important thing is neither moves the full 1"

the formula is
effective rate = (TS * BS)/(TS +BS)

the result is 111.1 lb/in for your 200 lb/in + 250 lb/in

just as a comparison a stock 18.8mm fron t-bar wheel rate is 137 lb/in, the actual t-bar rate is 170 lb/in

[PeteKz]

The way dual springs like that are "supposed" to work:

The two springs together have a lower total spring rate than either spring alone, as Bill described. BUT, if properly designed, the shorter spring with lower rate spring should "coil bind" before the suspension hits its bump stops, at which point the remaining spring rate takes over. In practice, this is difficult to achieve, because the travel and ride height must be precisely known (which also means no more fiddling with the ride height afterwards).

Thus, springs can be selected to give a certain amount of travel with both springs working, before the weaker spring hits coil bind, and then the stiffer spring rate prevails, until the shock/strut hits the bump stop rubber, which increases the spring rate even further.

If your supplier doesn't specify these parameters, then you can be pretty sure they are just guessing. I have yet to see the usual suspension vendors provide these details. (edit) Therefore, I suspect most of them are selling appearance over function.