4 lug spacers, Yea, or nay Options

[Blake]

Okay, here is an extensive quote on the subject, stright from Fred Puhn, a respected expert in the field and author of How to Make your ar Handle. My comments are in brackets.

"Adding positive offset to wheels can make a car corner faster because the resulting wider track reduces weight transfer. However, there are some side effects. On the front of the car, increased positive offset increases the distance between the steering pivots and the center of the tire [BQ: Scrub radius]. This makes the car steer harder. It also increases the loads on the steering system which increases the steering-linkage deflection, and this may require extra toe-in to compensate. These are all undesirable, so if possible keep the front offset near stock.

At the rear, increased positive offset is not as bad. There ususally is more tire clearance problem in the rear, requiring positive offset. If the car has independent rear suspension, increased track may cause more toe change during acceleration and braking which may require a change in rear toe setting. This is usually not important enough to notice in street driving, but could cause problems on a racing car. [BQ: How strong are those 914 trailing arms?]

Changing offset affects wheel-bearing load. On some cars the wheel bearings are so marginal in strength that an increase in positive offset causes them to fail prematurely.

A road car is designed with wheel offset to minimize loads on the bearings in straight-line driving, but in a corner the wheel bearings get higher loads. In most cases, a positive-offset wheel will increase the loads in straight-line driving, but reduce loads in a corner. This is shown in Figure 35. The best bet for street driving is to keep the offset as close to stock as possible. If necessary, go ahead and with small changes in offset and don't worry about bearings. It only becomes an intolerable problem with a large change in wheel offset, say more than 2 inches [BQ: that is quite a lot, in my experience, but he is the expert]."

So that's the quote, taken from page 128 of Puhn's book. Smaller is better, but his idea of small and mine are quite different. I suspect this is highly dependant on the cars in question.

Another quote, this time from Herb Adams' (Chassis Engineering, is thus:

"Track Width – Because the lateral spring base is proportional to the track width, a wider track dimension will reduce the roll angle. As was the case with center of gravity height however, most cars already have as wide a track as practical. This means that for any given car, we cannot expect to cause much of a reduction in the roll angle by increasing the track dimension."

Not too much there, but I thought I'd throw that in for consideration. Carrol Smith (the GOD of race car engineering) talks a lot about track, but his is all in the context of literally moving the suspension outward; not "faking it" with wheel offset. This was actually the approach I was considering for my project car, should we go to such extremes.

[ArtechnikA]

Okay, here is an extensive quote on the subject...

yeah, well, many of us have read all those books too ...

we also have 30 years of empirical experience with the car in question, not generalities.

a bearing capable of supporting an IMSA GTU 914/6 (10 inch or so wheels with racing slicks) on Daytona banking for 24 hrs will take anything we can dish out.

[Blake]

having had my share of physics, i challange that definition ...

Sounds like just enough physics to be dangerous... Sorry, but you are 100% mistaken. Track is measured from the center of the wheel and offset is the distance from the hub face to the track, positive or negative. If you match the hub and wheel offset, the track remains the same irrespective of wheel width. Think of proper offset like a lever with the fulcrum at the center and equal forces applied to either end. If you make the lever longer, but equally so on both sides of the fulcrum the forces cancel out and everything is balanced. If you then move the lever to one side (i.e. offset), the equal forces on either end will torque the lever one way or the other. Wider wheels and tires with proper offset transmit their loads through the bearing to the suspension. Widening the track will apply torque forces directly to the bearing unless the suspension itself is reengineered.

[SirAndy]

Track is measured from the center of the wheel and offset is the distance from the hub face to the track, positive or negative. If you match the hub and wheel offset, the track remains the same irrespective of wheel width. Think of proper offset like a lever with the fulcrum at the center and equal forces applied to either end.

yes, and here is where you are mistaken (IMG:style_emoticons/default/wink.gif)

you are extending the lever with a wider wheel, even if the centerline of that wheel falls into the same position as that of a smaller wheel.

your explanation ONLY works if you drive in a straight line.
as soon as you add any kind of corner load, you're off the track (pun intended) ...

granted, a larger outside lip might flex under load, absorbing some of the force, but you DO have a longer lever (if you look at it as force-vectors) ...
and yes, it's actually even more complicated than that. i know. (IMG:style_emoticons/default/wink.gif)

gosh, where's alfred when you need him?

Sounds like just enough physics to be dangerous

more than you can handle, i can assure you ...

Andy

[TheCabinetmaker]

Quote"on the street where driving at anything over 7/10th of the limit is really dumb. "

If I wanted to drive a car at 70 % of it capabilities, I would sell my 914 and buy a buick. I too, have 30 years and over a half a million miles in a teen. I have always driven my car to both mine and it's limit, and sometimes over the limit. With regular wheel bearing clean, grease, and adjust, I've replaced only two bearings in that 30 years. They were both on the back.

I work with engineers on a daily basis, and believe me, they do make mistakes. Sometimes they are huge and costly mistakes.

[Blake]

yeah, well, many of us have read all those books too ...

we also have 30 years of empirical experience with the car in question, not generalities.

a bearing capable of supporting an IMSA GTU 914/6 (10 inch or so wheels with racing slicks) on Daytona banking for 24 hrs will take anything we can dish out.  

At no point have I said what will or won't work; only that it requires reflection and a true understanding of both the risks and rewards. The whole crapstorm started because I preached erring on the conservative side. What is wrong with that hard-earned wisdom? People seem to have an exaggerated idea of the rewards and a under-appreciation of the risks of bearing failure on the street (y'know, that place where innocent people walk around and there are trees to hit).

Your "30 years of empirical experience" is crap if it's based on racing alone, as I previously noted. Even the quoted text indicates that the increased bearing loads are experienced in straight-line driving, where street cars spend most of their time. Cornering force reduces those loads. Last I checked, most racing involves a high proportion of cornering loads; not cruising straight. Also consider that those cars get new bearings several times a season, if not every race.

I stand by everything I have said and would ask that people please not get too worked up about my opinions, which are merely based on (1) actual catastrophic bearing failure while traveling at ~80mph, (2) a lifetime of too many short-odds bets that eventually caught up to me more than once, and (3) some real research into the subject of suspension tuning. I might not have direct 914 experience, but that is why EVERYTHING I have said has not defined "less" or "more"; simply that less is more. Just be conservative if you are guessing! Are you (or anyone besides SirAndy) really arguing this point?!?

If the factory used spacers to increase offset (track), then I will submit that is acceptably conclusive evidence. If people have gotten away with doing it themselves, then that bodes well but doesn't prove anything conclusively. The larger the sample, however, the more reliable the information. Given what has been said, I would agree that a one inch spacer might be a reasonable mod. I never said otherwise! Thanks to those who actually provided some data points. Everyone else needs to seriously evaluate their caffeine intake. (IMG:style_emoticons/default/boldblue.gif)

[Blake]

yes, and here is where you are mistaken  

Bzzzz. READ THE BOOKS. That's all I have to say. You are arguing with Smith, Puhn, Adams, and every other expert in the field. Do so at your peril. I'm not making this stuff up.

QUOTE (Blake @ Nov 3 2003, 12:44 PM)

Sounds like just enough physics to be dangerous

more than you can handle, i can assure you ...

Great, this is just a pissing match, then?! Try not pissing in the wind next time.

[Jeroen]

Ok, here's some "real world" numbers for ya...

The 5-lug fuchs come with these ET-values (offset) and I've calculated the backspace for your convenience...

5.5J - ET 41.0 - 110.8mm backspacing
6.0J - ET 36.0 - 112.2mm backspacing
7.0J - ET 23.3 - 112.2mm backspacing
8.0J - ET 10.6 - 112.2mm backspacing
9.0J - ET 15.0 - 129.3mm backspacing

As you can see, the 6 through 8J wheels have the EXACT same backspacing, thus increasing track
And guess what... Porsche mixed and matched these wheels with and without spacers on cars with the very same suspension components from the late 60's throughout 1989

cheers,

Jeroen

[onrails]

oh no!! (IMG:style_emoticons/default/sad.gif) it appears that a prior owner had put
a electric windshield washer on my car!
am i in any danger Blake?
(IMG:style_emoticons/default/bootyshake.gif)

[Jeroen]

Oh, another thing... the strenght of the rear trailing arm...
It's strong enough to break the mounting eye off a koni shock absorber
Is that stong enough for you?

cheers,

Jeroen

[SirAndy]

the attached picture shows the 3 most important triangles in your front suspension in yellow. note, this is NOT a 914 suspension, but close enought to illustrate my point. also note, this is still a somewhat simplified model and not intended to accurately explain the forces at work.

the last triangle to the right is the one in question.
if we replace the wheel with a wider one that has the same centerline, this triangle will change, the section marked in green will increase and we add additional load to the point where the triangle meets the axle under cornering. in my humble opinion, this is in fact a increase in track as the forces at work change.

Andy

[SirAndy]

Try not pissing in the wind next time.

i've learned that one before i was 5. haven't done it since. (IMG:style_emoticons/default/laugh.gif)

Andy

[SirAndy]

Bzzzz. READ THE BOOKS. That's all I have to say. You are arguing with Smith, Puhn, Adams, and every other expert in the field. Do so at your peril. I'm not making this stuff up.

i have not read any of those books. but if they say "exactly" what you said, i challange their knowledge in physics.
maybe you are misquoting some of their statements?
do you actually understand the physics involved or are you merely digesting someone elses opinion?

Andy

[Blake]

oh no!!  it appears that a prior owner had put
a electric windshield washer on my car!
am i in any danger Blake?

Man, when I found this board I was impressed with the maturity level, but I guess first impressions are very deceiving. Certainly, some have come forth with actual experience and data points to contribute meaningfully to the knowledge base, and the majority are wisely just keeping quiet, but surprisingly many can't seem to overcome their ADD and do anything but argue points I never made. And then there are idiots like this one quoted above! Jesus, Mary and Joseph, dude, are you really that stupid?! I give up. Actually, I have no choice. I've got work to do (writing tech articles on suspension tuning!) before catching my plane to SEMA in the morning, where I can at least have grown up conversations.

Peace, love, dope.

[SirAndy]

[I've got work to do (writing tech articles on suspension tuning!) before catching my plane to SEMA in the morning, where I can at least have grown up conversations.

dude, you need to chill out. (IMG:style_emoticons/default/cool.gif)

in case you haven't noticed, you're not the only one on this planet who knows "something".
i know, i know, you think you're the top of the cream and all and that's OK.
everybody needs a dream.


so, if i read your posts right, you don't actually have a 914, do you?
Andy <== who's glad that he can have "non" grownups conversations here ...

[Jeroen]

Yeah, well, unlike you, most people who hang out here don't have a life (IMG:style_emoticons/default/biggrin.gif)
And don't forget... we put the BS in BBS

cheers,

Jeroen

[onrails]

sorry to offend you"wise one"
but this "idiot" thinks that your stand on
wheel spacers is just as insane as thinking
you were in danger by the electric washer pump.
obviously you don't think i have the I.Q. to argue a point w/ you{even if i went about it wrong}
go purchace a sence of humor!
if you can be an opinionated bung,
than i can make fun of you! (IMG:style_emoticons/default/pissoff.gif)

[Blake]

have not read any of those books. but if they say "exactly" what you said, i challange their knowledge in physics.

Fine, two of the three you are challenging are among the greatest race car engineers of all time! Mr. Puhn is no slouch himself. Not a smart move.

maybe you are misquoting some of their statements?

Not a chance. Your line of questioning is a desperate attempt at discrediting proof positive of your reckless disregard of the subject in which you claim mastery. At least, mastery exceeding those who earn their living at it.

do you actually understand the physics involved or are you merely digesting someone elses opinion?

I do not have a physics degree, if that is what you are asking. I was a Combat Engineer in the Army, if that means anything to you. I did take a few physics classes in college but my real experience is practical and, indeed, learned at the alter of those who made careers of race car engineering. Are you suggesting they are all wrong. I was misled?!? Damn, your talents must be in high demand in professional racing circles! Should I inquire on your behalf with Chip Ganassi when I next see him?

Just be a man and admit you don't know what the hell you are talking about! Too much physics can blind you to reality, which is a dangerous thing. Engineers are also not immune to reality blindness, as they often hold too many variables constant to keep the calculations reasonable. In Economics (in which I hold one of my degrees), we call that practice Ceteris Paribus, or all other things remain the same. It is a pleasant but impractical fiction of presuming changing one variable doesn't change everything else. Race car engineers, however live in a world where their work is immediately and incontrovertibly proven or disproved on the spot by actual lap times. They produce results and are paid well for it. Tell them they don't have a grip on physics and they will laugh their asses off.

BTW, can you tell me whether race cars need more or less Ackerman than a street car and why? Just a test of race car dynamics 101. First day stuff.

[Blake]

Sorry to offend you"wise one"
but this "idiot"  thinks that your stand on
wheel spacers is just as insane as thinking
you were in danger by the electric washer pump.
obviously you don't think i have the I.Q. to argue a point w/ you{even if i went about it wrong}
go purchace a sence of humor!
if you can be an opinionated bung,
than i can make fun of you!

I'll give you ten bucks if you can tell me what my "stand" is on wheel spacers. For, against, or NO OPINION other than due diligence. Take your time...

[SirAndy]

Race car engineers, however live in a world where their work is immediately and incontrovertibly proven or disproved on the spot by actual lap times.

so, YOU are a race car engineer?

... in which you claim mastery

i do not claim mastery, but i do claim that your argument has significant flaws ...

this is fun (IMG:style_emoticons/default/rolleyes.gif)
Andy