Offset vs. Spacers - Scrub radius affected?

[superclarkey]

It's a complicated subject though, that's why people spend years of thier lives understanding and calculating it.

Only took me 10mins to understand it.. but I am amazing :P






(hahaha)

[kevinLee]

superclarkey, munkul and ade b are talking facts

Honestly, peeps need to go grab a couple books, this is fairly simple stuff too grasp. This forum is making it complex. Google and youtube have some usefull info

BTW if you have low offset wheels or big spacers, you get increased tramlining, less stability during braking ect ect. Cars with diagonal split braking systems utilise negative scrub incase of brake failure and some cars like mk1 and mk2 fiestas have negative scrub and can brake in a straight line safely with a blown out front tyre.

zero offset wheels are really not optimum. maybe mitto means zero scrub, aka centre point steering

[superclarkey]

To most people this stuff isn't relevant... does my wheels turn.. yes, mint lets do a skid

[kevinLee]

[mitto]

Sorry, i was under the impression this was a drift forum... and no, thats not what i mean. I'll make some diagrams
Tomorrow, right now I feel like shit with some kind of flu.

[FireStorm999]

Sorry, i was under the impression this was a drift forum... and no, thats not what i mean. I'll make some diagrams
Tomorrow, right now I feel like shit with some kind of flu.

The fail flu

[mitto]

You can have it if you like... It feels like my nose is about to cave in.

[superclarkey]

Have you got a version in Japanese Anime for mitto to watch, unless it has Japanese roots he will not except it to be fact :P haha

(only playing mitto)

[Munkul]

everyone say "AWWWWW" for mitto!

It's a complicated subject though, that's why people spend years of thier lives understanding and calculating it.

I have 2 or three books on race car suspension and chassis on the shelf next to me, it didnt help me much on this topic cos I am shit at explaining stuff

[CIH]

Don't mistake contact patch and scrub radius; they're not the same thing. The rear wheels have a contact patch but no scrub radius.
Scrub Radius is established by SAI and Camber but what it does and how it behaves is also related to Castor, Ackermann and Wheel offset (either spacer'd or just a different wheel).

Scrub radius can be measured, though TBH I'm never really sure what the number tells us as there's never any OEM info to compaire against.

[Stavros]

It's a complicated subject though, that's why people spend years of thier lives understanding and calculating it.

No its not?! It seemed like the easiest answer ever when I first read it. Thats why I was SO incredibly confused when you and Bizzle was claiming it was different. But it turned out it was the easiest answer ever.

Wierdest thread ever.

Glad its resolved though as I was doubting myself bigtime then.

[alex_200sx]

Its also worth remembering that changing wheel and or tyre size will also alter the scrub radius

[mitto]

OK so to make the point...

Your examples are all "static" and do not take into account the dynamic factors involved.



So without moving the centerline of the wheel and only adjusting the postition of the wheel hub closer or futher away from the cars hub, you are adjusting the load axis point of the hub / wheel and also adjusting the amount of wieght involved.

by using a higher offset wheel you are moving the wieght, or "lever" further away from the axis point. Like trying to use a jack handle from the top or the bottom, the bottom is super difficult, but the top of the handle is easy. The same occours when you move the mass of the wheel further away from the hub / axis point.



Because the axis of load has been moved away from the hub, the effect on the suspension and the force put into the tyre changes, because the movements are dynamic. You've created a longer levering system and will cause geometry changes, the most obvious from this example being camber.

Camber change = scrub radius change.

Thats how I see it anyway.

edit - I'm assuming you can see the images...

[kam]

Your examples are all "static" and do not take into account the dynamic factors involved.
So without moving the centerline of the wheel

ET is static.
You are moving the centreline of the wheel.

What the actual fuck is going on in this thread lol.

[mitto]

ET is static.
You are moving the centreline of the wheel.

How is ET static if you CHANGE the ET and add a spacer to a different wheel?

I haven't moved the centreline in that diagram and you've washed straight over the points i just made.

[kam]

How is ET static if you CHANGE the ET and add a spacer to a different wheel?

I haven't moved the centreline in that diagram and you've washed straight over the points i just made.

An offset change is a static geometry change.
It never changes throughout suspension stroke.

You haven't moved the centreline because you drawing is wrong.
You add a spacer, the centreline moves.
The centreline doesn't care where the spokes are mounted.

*Nice drawing btw

[mitto]

physics care where the spokes are mounted! So what you are saying is that if you shift a point of leverage it has no effect in the slightest? Or that if you shift wieght around relative to an axis it does nothing?

For the principal of this explination the centreline is constant, however, the centerline and balance point of a wheel are different things.

This is my point about it being complicated... It's not a case of "fits the same, must be the same" - you are fucking with a huge number of dynamic factors.

[kam]

Post title:

"offset vs spacers - scrub radius effected?"

Answer:

"no"

Just adding spacers messes with srub radius

You're wrong lol.

[mitto]

You're wrong lol.

How?

Because we are ignoring every other factor involved and the huge variation in wheel fitments? This is besides what happens when you start turning the wheel on lock or actually moving.

[kam]

Lol. I give up.

And RE the rest of your argument (spoke position change), the physical load placement on the wheel would be effected, but after a 10sec ponder I don't even think it would effect any other geometry changes.

That would make your complete argument invalid, not just its foundations.