Technical Wheel Offset For Dummies Like Me (Up Date)

I'm not following the train of thought of this attached to that. A longer lever arm with the same applied force means a higher applied force.

We're not talking about ride quality. We're talking about resulting load on bearings and shocks. If your suspension only moves directly up and down, then only sprung/unsprung weight matters. However that's not reality, and therefore a greater distance from your tire center to your shock or bearing will increase load. However, in all but extreme cases the difference is negligible. What does impact shock operation more is the installed angle of the shock.

 

All I need to know is where the center line of the tire from axle flange is. No more, no less.

 

I should be. I'm that guy. I can pull in the pits after a hot lap and say "Give the fribit a turn and a half anticlockwise".
But the ol' "I'm a legend in my own mind" factor more thickly overlays my perception of reality the older I get.
I think I recall Paul Newman still racing at 82 (a half-year older than I am now).
I might not be as sharp as he was on the track....... but I am way better looking.

 

It's intuitive and often useful to think about suspension in terms of a fixed sprung mass with a moving road acting upward on it. For many purposes it makes no difference, and it's easier to consider the movement of various components relative to the sprung mass than to get your head around those components and the sprung mass as moving simultaneously, but not in exactly the same way, relative to the road. There are instances, however, when it is wise to remember that the sprung mass isn't really fixed in space, but only more or less held in position by its inertia.

The heavier the sprung mass, the softer the springs, and the more rapid the suspension movements you're considering, the safer it is to treat the sprung mass as actually fixed in space. Hence my prior reference to single wheel bumps.

Your point is entirely valid as regards wheel bearings, because they are part of a structure which is entirely part of the unsprung mass. It can be reduced to two downward forces — the outer and inner wheel bearings — resisted by a single upward force acting at or near the middle of the tyre contact patch. Stock hub designs will tend to carry a bit more load on the inner wheel bearing than on the outer, but I'd expect the sizing of the bearings to have more to do with the practicalities of actually being able to assemble the hub onto the spindle and devise a working brake around it than with the ratio of anticipated loads on the respective bearings.

If we move the wheel outboard we reach the situation where all the corner weight is carried on the outer wheel bearing, and the inner wheel bearing is just along for the ride — when the car is at rest. It changes as soon as we introduce lateral loads. If we move the wheel even further outboard we get a situation where there there is a downward force on the outer bearing and an upward force on the inner bearing.

But as you also say, it's largely splitting hairs. Wheel bearings seem to be one of those things which underdesigning would make too small to be practical. So typical wheel bearings tend to be well up to the task, and then some: enough to take a fair amount of abuse in their stride. There have been enough applications which have repurposed car hubs in wildly cantilever configurations (like the lazy Susan I built for my wife on the basis of a New Mini bolt-on spindle and hub. The thing will practically last forever. But I think also of stuff like homebuilt windmills etc.)

The same is not true in the case of elements between the sprung and unsprung masses, however, like springs and dampers — except, as I have said, in the case of sudden momentary inputs like single wheel bumps, where the sprung mass is effectively held stationary by its inertia. In all other movements, like roll in corners, reaction forces at the tyre contact patches cannot be regarded as modified by a lever arm, because they are themselves determined by forces acting through the springs and dampers modified by the same lever arm. The load on the springs and dampers will be as before: determined by spring base, installed vs. effective angle, roll centre, and CG height. The actual track width doesn't enter into it.

This was hugely counterintuitive to me for a hell of a long time, until I found myself doing a design exercise which required thinking it through. That's when it occurred to me that, if we have an unsprung mass moving relative to an axle, gluing that axle to the ground wouldn't change anything for a whole lot of important purposes. My intuition was telling me that widening the track would reduce roll stiffness because the spring base would be narrower relative to the track width, but if you think about it it should be obvious that the roll stiffness wouldn't change at all. It is determined by the spring base absolute, and not the spring base as a proportion of the track width.

 

then you don't need a thread, you need a straight edge and a tape measure...but always nice to get the GOB's going...lol

 

I ran neg off set wheels for 300,000 miles.... went through 3 sets of axel bearings on my olds.... I ran zero off set on my 65 mustang for 300,000 miles and never once had bearing failure.... could be because the mustang was lighter????

 

Offset makes it easy to place the Wheel where you want it.
Just measure from the center of where you want the wheel to the wheel mounting surface and that's your offset.

Offset by Hutkikz posted Oct 6, 2024 at 12:37 AM

 

Since I work on things that go around corners way faster than nay HAMB-era vehicle, I find offset highly useful in maintaining suspension geometry equivalence when fitting wider rubber.

It's not about simply getting the rubber between the metal.

Do only that and you can toss proper steering function and handling out the window, especially on any vehicle with multilink suspension, which includes every HAMB-era vehicle with independent front suspension.

People are far too comfortable with the notion that "old cars handle poorly", when they are often the ones that made them do exactly that.

 

Except that what you illustrated is not offset.

You illustrated something akin to backspacing by referencing the wheel mounting surface, and called it offset.

Offset refers to the distance that the wheel mounting face is away from the wheel centerline, and references nothing else.

 

Im sure if smaller bearings worked car companies would use them

 

A bit of understeer can be desirable. Too much can be a painful and expensive experiment.

What we see WAY too much of in the hot rodding world is dangerously excessive increases in positive scrub radius, often exacerbated by inverted Ackerman, and by impossibly narrow front tires.

The only saving grace might simply be that the vehicle is so difficult to drive, at any speed, that the prospect of carrying too much speed into a corner is minimized.

 

Yes, it’s been a while. Father in-law had a brain bleed so things came to a holt. Moving forward now.

Mounted wheel/tire from red 56 15 7 wheel and 255/60/15 tire.

15 8’s it is!