3.2 Carrera and SC handling

[911st]

Way cool point of reference!

Only reason I maxed my caster was to get a little more neg camber when the front wheels are turned on our camber challenged front end.

[stlrj]

Originally Posted by stlrj

Ride height can make a difference too. Quite possible the Carrera was lower than the SC causing more negative camber that also results in heavier steering.

Originally Posted by jwakil

... But if I lower the front to make look similar, it will be way below spec and too much steering effort. Already tried that, don't want to go there...

http://forums.pelicanparts.com/porsche-911-technical-forum/571092-why-does-my-ride-height-look-so-high-even-though-its-lower-than-spec-3.html

[911st]

Most lower there cars to a genneraly accepted height termed Euro Height.

With proper tires this puts the front fender bottom lip at 25.5" and the rear at 25".

This is somthing like 3.5" lower than stock 85 front height and somthing like 2.5" lower than the pre bumper 73 911's front before head light and bumper laws became an issue with US laws.

Some where along the line somone discoverd that by lowering the front more relitive to the back it eather just looked better of actually improved stick. This puts our Euro Look ride height much lower in the front that stock and mildly lower in the back.

You do not have to be overly worried about the A arm angle. When it changs, the tie rods go along for the ride and change to. Adding the cheap aftermarket spacers under the steering rack is all that is typically needed to keep toe steer in an acceptable range.

There are a couple reasions to get the front lower. For most it is the look. For those that track their cars it also lowers the front's center of gravety but more importantly, I belilve it gives you a little more neg camber up front. We just can not get enougth neg camber up front without modifictions. The more caster and the more we lower the front the more effective neg camber we can achive up front.

I lowered my front to 25.2" up front with 25" tires. With the front rack spacers I had not issues I could detect with bump steer.

I think you know about the front spacer washers that often came on the US front shock tops. In the back one should also cut down the bump stop's under that are under the shock hats to prevent bottoming out and the crazy handling that can come with it.

I am not sure I buy a 911 should be significantly more difficult to steer when lowered if the alignment is reset.

Tire width / compound, the friction cofecent of the ground, and air pressure might have some effect. As can gas level or trunk contents.

If you can leave the spare, jack, and tools at home that is about 50 lbs up front where the wheels that will typically carry about 600 lbs each. Change out the battery from the stock 60lb to a 25 lb and that is about 85 lbs or about 7% of the fronts weight you can take off the front tires. A stock sized steering wheel is a good idea to.

[Wil Ferch]

Quote... " Most lower there cars to a genneraly accepted height termed Euro Height. With proper tires this puts the front fender bottom lip at 25.5" and the rear at 25". This is somthing like 3.5" lower than stock 85 front height and somthing like 2.5" lower than the pre bumper 73 911's front before head light and bumper laws became an issue with US laws.......


No way !.....by 1983 all 911's had essentially the same ride height, and there were no ride height differences anymore.... certainly not to the tune of 2.5 or 3.5 INCHES !!! No way......

Further info--> this post, search out a,b,c dimensions from Porsche Tech/Spec books, and reconcile that data with my post #30 within....
http://forums.pelicanparts.com/porsche-911-technical-forum/571092-why-does-my-ride-height-look-so-high-even-though-its-lower-than-spec.html

...I think you mean US/Japan/Canada cars were maybe 5-9 mm higher at some point...NOT 2.5-3.5" higher !

[911st]

Wil,

Thanks for the challenge. I may be mistaken.

I am not a great techinical wrighter but I went back and tried to look up some of the info to see if I was way off in my memorie and will try to forward my points of referance.

Per the limited info in Bruce Anderson's book:

Just looking at the rear, stock 73 torsion bar center to wheel center was +12mm, in 75 the rear was raised 21 to 25mm so now we are at say + 45mm. Euro Height is with the TB center about 1.25" or -30mm below the wheel center. Thus, the difference is 75mm so this puts the rear as much as 3" lower in the rear.

Factory spec 911's in the 80's were so high they could not get any neg camber in the rear.

The front was only raised about 9-15mm in 75 so we are lowering it about 60mm plus about an additional 20mm to get our 1 deg of rake. So about 80mm or about 3" in the front.

Again, this suggests 3" front and rear.


I also have an old height recommendation sheet from the 1972 Porsche racing program. They give lowering recomendations based on weight and if a Rally, Minor Competition, Hill climb, or Circuit racing.

It shows lowering the front and rear equally up to 50mm each. That is up to say 2" of lowering front and rear. They lower the front and rear the same amounts with no mention of adding rake.

Remember in 1975 the rear had been raised about 1" and the front about .5" so that would put us where we would have to lower an 85 as much as 3" in the rear and 2.5" in the front to achieve a square setting.

However we now like to lower the front more to achieve 1deg of rake. I think that puts the front about .75" lower than the rear.

Thus now up to about 3" lowering for the rear and the front 3.25".



My gut tells me it can not be that extreme but I just took two different sources and both come up with up to about 3" lowering front and rear from out high water mark.

I agree this is not the best reference info and there is a good chance I mucked it up. However, I have since looked at old pictures of the long hoods and there is a lot of tire to fender clearance.

Again, I could be as much as way off on this.

[Wil Ferch]

I don't follow your math at all....but I can say with a great deal of assurance.....the Euro/USA differences were NEVER as large as 2"-3". The rear may have been higher by 1"....the front maybe also 1"...as mid/late 70's SC's even had the big fat washer on top of the shock.

But please....think about this and look at a ruler and envision the air space above the top of a typical tire....an extra 2-3" . No way. I will gladly stand down once a viable reference is produced. I recently ate crow on a recent other thread...but I don't think I will this time.


EDIT--> you also say this--" You do not have to be overly worried about the A arm angle."...My response?...Ahhh...you CERTANLY DO !. Your answer is only partially correct. The factory setting has a the lower A-arm angled downward toward the ball-joint. This still gives you an aceptable camber "curve" as the suspension moves up and down, compared to static ride height. If you lower to get the A-arms level and parallel to ground....you alter the camber curve but it's still acceptable. Now...if you go EVEN lower....you will get a really screwed up camber curve and the suggestion that lowering is OK is not a good one without this nuance stated.

Lastly....getting the lower A-arms level and assuming the steering arms go along for a "similar" ride....to minimize bump-steer, is also wrong. The lower A-arms length between its end-point pivots is DIFFERENT than the steering arm lengths...so their reactions to ride height change IS DIFFERENT ( notwithstanding the tie-rods sit above the lower A-arms and have a completely different swing geometry...this affects a change too).

Getting the steering arms "level" at static ride height will change the "effective" length the least amount when bumps are encountered. My point?---> getting the lower A-arms "level" and getting the tie-rods "level" won't necessarily happen at the same time, they have to be tuned to this point of goodness independently. Hard to do without using spendy bump steer kits ( the "full" kits that allow fine tuning of the tie rods...not just using the rack spacers). Rack spacers work to "get close" as they can't be more than (say) 12-15 mm thick, as the rack can't move vertically more than that amount. Works "reasonably" well to re-establish the small amount of bump steer you had with the factory setting, if you then lower the same amount as the thickness of the rack spacers....pretty limited in effectiveness.

[burgermeister]

I vaguely remember, based on some previous thread about rear suspension height measurement, that the spec in the rear for some time period was wheel center to bottom of torsion tube ( number was wheel center 15mm or so above bottom of torsion bar cover tube), and then changed to center of torsion tube (wheel center 16mm or so below torsion bar center). Though both work out to be roughly the same thing.

But 911st is right IMO - the fender measured 25.5/25 "euro height" results in something 40 or 50mm below the factory ride height.

[Wil Ferch]

3" = 76 mm..... don't buy it.

1.5" = approx 40mm.....hmmm....maybe.

I'm ready to stand corrected ( again!)...but let's go over some stuff.

The Tech'Spec books info I showed in the posted link.... shows a 9-15mm variation in the "factory specs" for the different ride heights for cars delivered to different countries. Am I to believe Porsche would then change the front height by 9-15 mm ( 0.35" - 0.6") ....but would change the rear close to 3" ??. Then "our" cars would not only have off-road ride height....but have SEVERE rake. I never saw original USA cars with rakes like this.

Then there's this---> shock travel. Don't you think with a suspension that has about 7" of suspension travel.....that if one setting is 3" higher than another...that there would be 2 different shock replacement part numbers?. One of these would either be at risk of bottoming out or tearing apart at extension, if the static setting changed 3".

I know 944's had their rear-ends raised for US bumper laws some incredible amount...maybe even 2"....but I still can't see maybe more than 1-1.5" total variation for 911.

As to the 25.5" / 25" setting...this is clearly Bruce Anderson's statement from the early days before the internet...and it has been repeated ad nauseum so everyone takes it to be "Euro". If you study Anderson's writings, he himeslf will admit 25.5/25 is lower than true Euro factory spec.

So maybe we need to clarify the question.....are we debating whether 25.5/25 is 2-3" lower than Euro spec?....OR...are we debating whether factory USA settings were 2-3" higher than factory Euro settings?. I thought we were debating the latter. That might be my misunderstanding.

[Flieger]

1 inch = 25.4 mm

[Wil Ferch]

More---> the Tech/Spec books show this...as it relates to the front suspension settings, disregard the turbo numbers as turbo is different in anti-dive characteristics and spacers used.

for 1975....the Tech Spec books show---> 108 mm for the 911 and 911S, 113 mm for the Carrera, 93 mm for USA, and 93.5 mm for Turbo.

for 1976/77... it shows---> 108 mm ( Carrera)...93mm ( USA Carrera)...93.5mm (Turbo)

for 78/79/80/81...the same book shows---> 108mm (911SC)....99 mm ( 911SC for USA/Canada/Japan).....94mm(Turbo)..... and 85mm( Turbo for USA/Japan/Canada).

for 82/83....108mm ( 911SC)....99mm ( 911SC- USA/Canada/Japan) with footnote " 108mm for 83 onwards".....94mm ( Turbo)....85mm ( turbo for USA/Canada/Japan) with footnote "94mm for model year 83 onwards.

for 84/85/86/87...... 108mm(Carrera, all markets).....94mm( all markets)

All measurements are (+/-) 5mm.

--------------------------------

Look at the differences. 83+ became a world-standard.

[Wil Ferch]

continued from my previous posting....use this image for the numbers listed in the tech/spec books...and insert in the place-holder where "124mm" number is shown on the image--->




I don't see anything approaching 2-3" as variation...and certainly not "from '85" settings as originally stated by 911st ...as by 83+ all world market cars were set the same.

[Wil Ferch]

OK fleiger.... I *am* an engineer and do know 1" = 25.4 mm.... and if you insist.... 3"= 76.2mm.

I changed my posting to read 3" ~ 76 mm. Are we all happy now?

We needn't debate 0.2mm...when there are full inches under deabte here ! ....LOL !

[Flieger]

I wasn't actually doing any mental calculation. I did not have my metric kinesthesic senses working so I did not know if the numbers you listed were close. I just wanted to make sure you knew the conversion because it almost sounded like you were wondering.

[gwiggill]

or maybe the SC is just lighter, faster, stronger, better

[prebordao]

Back to the original caster issue..

What would be the factory caster range for a 74' S...?
I also feel my steering is heavier than it should on tight bends, but having never driven another 911, I can't really compare...

[stlrj]

It is not so much a caster issue when it comes to heavy steering feel as I have found on my 74 as it is about too much negative camber as a result of excessive lowering. If you bring your suspension back to stock height as it was designed, you will notice a significant reduction in steering effort.

Cheers,

Joe

[prebordao]

It migh still be camber related, but not due to lowering.
For some time it's been back to stock height as the PO really did lower it before.
Tires are 195, so not an issue too.

[stlrj]

Originally Posted by prebordao

It migh still be camber related, but not due to lowering.
For some time it's been back to stock height as the PO really did lower it before.
Tires are 195, so not an issue too.

Camber is mostly a height issue. What measurement are you using for your wheel center to front torsion bar center ( a-b=?). Stock height spec calls for 99 to 108 mm.

My guess is that your number might be significantly higher which would result in a much lower than stock height.

[prebordao]

I don't have the numbers here, but looking at it, height appears reasonably stock.
My concern is caster, as it, among other things, really influences steering effort when cornering.

[911st]

Originally Posted by Wil Ferch

...
I don't see anything approaching 2-3" as variation...and certainly not "from '85" settings as originally stated by 911st ...as by 83+ all world market cars were set the same.

I agree. Dose not seem right to me either.

It might be the numbers I used would achieve the lowest race setting one might run at.

However, for euro look we do lower the front more than the rear to achieve the 1 deg of rake that has been adopted as part of the look.

I had 25" tires on my 85 and with the front fender at 25.25" my a arms were significantly slanted.


When the cars were set at the same height, did they raise the ROW or did the US soften there requirements?