Wheel spacers and handling-hypothetical

[rootmatt]

This forum often has talk of spacers and the main concern appears to be the "look" of having the guards filled better. None of these threads seem to indicate what this may do to the handling.
I have a relatively stock SC on 16x6 and 16x7 Fuchs with stock rubber. I probably won't do this but, if I were to put 6mm or so spacers all around to fill the guards, what is it likely to do to the handling and the steering feel?

Matt

[Josephphp]

hello everybody....I like this website.

[gamin]

I have the same stock wheel/tire setup as you on 88 3.2. I put 21mm H&R spacers on the rear. I didn't put spacers on the front. Looks better for sure. I have not noted any negative handling effects. There may be some positives due to increased track but I don't know since the car is not tracked.

[911-32]

Originally Posted by rootmatt

This forum often has talk of spacers and the main concern appears to be the "look" of having the guards filled better. None of these threads seem to indicate what this may do to the handling.
I have a relatively stock SC on 16x6 and 16x7 Fuchs with stock rubber. I probably won't do this but, if I were to put 6mm or so spacers all around to fill the guards, what is it likely to do to the handling and the steering feel?

Matt

I doubt you will even feel the difference with 6mm spacers/shims. I moved from narrow body to wide body specs last summer and increased track widths by apprx equivalent of adding 45mm and 75mm spacers front/rear per corner. Now that increase is obvious.

[tobluforu]

On my 72 before I had adjustable sways I put spacers in the front to help combat push and they helped some.

[Bob Kontak]

I have the 6mm spacers on my rear (81) I can tell no difference.

[914efi]

If you widen track with no other changes, you reduce the wheel (spring) rate. If you do unevenly that would change the balance.

You change the weight transfer characteristics to some extent, that is why the usual push for wider track.

In front, you change the scrub radius on steering. Did Porsche make kingpin angle changes when they added spacers to the 930?

[Quicksilver]

In addition to the reduction in wheel rate that 914efi mentioned you also increase the track of the car which when taken by itself is a positive thing for handling but there is so much more to it then that. There is no single attribute in a car's suspension that doesn't change a multitude of other attributes. It gets really complex in a hurry.

As mentioned before, taken as a single attribute an increase in track width will increase grip. If you do it at one end of a vehicle it will reduce weight transfer which has the same general effect as softening the swaybar on that end of the car or stiffening it on the other end. Another comparable example is it would be like lowering the center of gravity. One example of why this isn't always the best thing is a slalom course. The car now has to go farther back and forth to negotiate the course. Other possible issues are increased scrub radius, loading of suspension components, etc...

The interactions between everything can be mind numbing or rivetingly interesting depending on how it interests you...
Either way a 6mm increase won't be noticeable. It just isn't a large enough percentage of change to be felt by mortals.

[Bill Verburg]

Originally Posted by rootmatt

This forum often has talk of spacers and the main concern appears to be the "look" of having the guards filled better. None of these threads seem to indicate what this may do to the handling.
I have a relatively stock SC on 16x6 and 16x7 Fuchs with stock rubber. I probably won't do this but, if I were to put 6mm or so spacers all around to fill the guards, what is it likely to do to the handling and the steering feel?

Matt

The primary issue is going to be from any change in the scrub radius, this affects the feed back at the steering wheel and steering effort

all cars are designed w/ a specific amount of scrub radius on 911 thru '89 Carrera it is a small positive value from '89 964 w/ ABS it is a small negative value, you do not want to change this # by much or there will be adverse results.

The ET if the wheel will tell you by how much the scrub radius changes,
6" Fuchs all have an ET of 36, 911 7" wheels have an ET of 23.3, both are oem 911 front fitments, the 7 increases the scrub radius by 12.7mm this will be acceptable. So since a 6mm spacer increases the scrub radius by only 6mm you will be fine wrt scrub radius.

A second issue is the length if the lug nut studs, a 6mm spacer will reduce the lugnut threaded depth by 6mm, is there sufficient thread engagement? probably. But it's certainly something to look into.

In back the only issue is the stud length

[Flieger]

Adding spacers does not decrease the spring rate on a strut suspension. The critical distance here is from torsion bar to ball joint. Swing axle, yes. In the rear (semi-trailing arm), yes, but not in a 1:1 ratio.

On Porsche 911 strut suspensions the kingpin axis is the strut, so there were no changes to that with the widebody.

Adding spacers increases wheel scrub and so steering effort.

Adding spacers widens the track and so reduces total lateral weight transfer during cornering, evening out the loads on the tires and so increasing the grip on the axle that has the spacers all else being equal (assuming you have corrected for any spring rate changes).

[KTL]

Here's a good discussion on scrub radius and how adjusting the front track affects it dimensionally

Question about scrub radius

I can say from recent experience with my "new" racecar that the difference in scrub is noticeable in terms of steering effort at speed. With longer A-arms, different wheel offsets and spacers, my car requires some effort to steer. It handles quite a bit better than my '87 did when set up for track use, and it requires noticeably more physical effort to wheel it around the track.

My a-arms are only slightly lengthened by maybe 3/4 to 1 inch?

How much camber...

Wheel offsets are a bit less than usual up front at +18mm with a 1/4 in spacer. So effectively let's say they're +12mm which is around a 1/2 inch less than a regular 16x7 Fuchs wheel or a 951 16x8 Fuchs wheel. Basically those two seemingly minor changes in A-arm length and wheel offset make a sizeable difference in steering the car. Thankfurlly they also make the car handle quite a bit better. Front grip is pretty darn strong.

[Quicksilver]

Originally Posted by Flieger

Adding spacers does not decrease the spring rate on a strut suspension. The critical distance here is from torsion bar to ball joint. Swing axle, yes. In the rear (semi-trailing arm), yes, but not in a 1:1 ratio.

. . .

If the suspension has rising negative camber in compression and the increase in track didn't come from a change in suspension pivot points then it will will decrease the wheel rate.

[Flieger]

I am a little unclear on the first part of your statement but if you want to get down to the nitty-gritty the spacer will slightly reduce the wheel rate until the point that the A-arm is level. At that point it will start to add wheel rate. It is trying to get the wheel as far away from the car as possible in response to upward force. That means maximum track width. Lateral force will force the wheel down when the A-arm is downsloping to the ball joint and left the wheel when the A-arm is upsloping. This is the jacking force. The jacking force will be increased slightly because with negative camber and spacers the wheel moves up just like raising spindles.

All these effects have less than a 1:1 correlation on the lever arm like the swing axle. You won't notice it at all. I do not know if you could even feel 6mm added to a swing axle style torsion bar suspension.