Offset vs. Spacers - Scrub radius affected?

[Andy_F]

I'm a bit 'tarded with scrub radius, so forgive me if this is a dumb question. Also tried a search but couldn't come up with what I'm looking for.

Basically, if I had a 9j et10 wheel fitted with no spacers, or a 9j et30 with 20mm spacers (effectively making it into a 9j et10 wheel with spacing), would the scrub radius in both these cases be the same? Logic tells me yes, but I just want to check.

EDIT: to save peoples sanity who may come accross this post from a search, the answer is yes, the scrub radius will be the same.

[Joe-sef]

haha, andy. i just brought some 20 mm spacers - excatly the same thing crossed my mind.i concluded yes. and just went for it. purchased this morning!

[JameS15]

I dont think it is the same... Mitto explained this to me ages ago. From what i remember, if you add a big spacer to the front it causes the wheel to 'swoop'. I cant recall anything more than that haha. Mitto is the man to ask

[kevinLee]

Yep both the same dudes. Logic is all good this time

[kevinLee]

If you removed the spacer but ran a ~20mm longer lower arm. then you would have same fitment BUT smaller scrub radius

[mitto]

Basically, if I had a 9j et10 wheel fitted with no spacers, or a 9j et30 with 20mm spacers (effectively making it into a 9j et10 wheel with spacing), would the scrub radius in both these cases be the same? Logic tells me yes, but I just want to check.

Wheel centre is in a different position, fitting spacers doesn't change a wheel's offset, only it's fitment.

[Munkul]

That doesnt really clarify things though. Fitting spacers doesnt change the wheel's offset, but it does change the "effective offset" if you want to call it that.

[Robbs]

Wheel centre is in a different position, fitting spacers doesn't change a wheel's offset, only it's fitment.

I can't get my head around this, im sure the wheel centre on a et30 with 20mm spacer would be in exactly the same place as the same wheel in et10

[Mikko]

It´s just the same is offset made by wheel or by spacer, no difference.

[Stavros]

Just for mopre backup, yes, its the same, fuck knows what all that swoop wierdness is about.

[Cheshire190e]

Its pretty basic really. If you add spacers you move the wheel outwards away from the lower ball joint. Meaning when you turn your wheels will move in more of an arc than before. This is the same for lower offset wheels tho. Its when you start putting like 50mm spacers on it becomes really noticable. Best bet is to extend the lower arms to move the pivot out not just the wheel, then the wheel wont move in an arc, giving more clearance inside arches etc

[magicmat]

confused.com

[Dotun]

if you read a bit on king pin inclination (kpi) or steering axis inclination (sai). it took me a little bit of time to get my head around ways to reduce the scrub radius.

[MrLuke]

I can see that a spacer affects it, but not how it is any different to fitting a lower offset wheel. The inside edge of the tyre will be the same distance from the lower balljoint.

Correct me If im wrong but we are talking about the arc the wheel moves through within the arch as it cant just rotate.

[mitto]

Postive offset plus a spacer does not move the centreline of the alloy. Offset is not just determined by making a bigger hub face, it's relative to the centerline of the wheel.

I didn't say "swoop" I said "swing" - because you are moving the inner hub face of the wheel further away from the hub. So the wheel sits further away from the axis, meaning it travels in an arc rather than pivoting on one axis point. Hence the comments about extending the lower arms...

Just adding spacers messes with srub radius, akerman, etc...

hub]--l

hub]------------------l

make sense?

[kevinLee]

Lol do what I did and read a book.

Adding spacers really does alter the EFFECTIVE offset.

It's pretty basic.

If you add a 20mm spacers you increase the scrub radius by 20mm

And the offset will be altered. FACT.

Google or YouTube search scrub radius.

I can feel the difference that a 5mm spacer makes, instantly on my mx5

[kam]

Offset is the centreline of the wheel, to the hub face.
Adding a spacer changes that.

Spacers alter "effective ET" if you want to get really pedantic.

Where's Chapman?!

[Jason]

dont get chapman started on this FFS!

i see what you mean mitto, having massive offset on the front pushes the wheel further away from the pivot point, and is probably bad for steering. thats as technical as i care to get with it

[mitto]

That's pretty much it Jason. Spacers don't change the offset of the wheel, just the position of the wheel. Effectively :/

[Mr Bizzle]

You're all saying the same thing.