about offsets... not THE question everyone asks though

[Kreator]

Say we have a wheel with 0 offset. In other words the wheel sits on the hub right in the middle of hte wheel. Now assuming the hub rotates exactly around its vertical axis and has no physical volume (just assume for now) the wheel will also rotate around its center.

Now suppose you throw on a wheel with -30 offset. That means that the actual center of th wheel is 30 mm away from the rotating axis, and the wheel actually rolls around a circle with a 30mm radius, every time you turn the wheel.

Now i know the first example is unrealistic, and it probably impossible to get a setup where the wheel moves does rotate exactly around it own access and not roll in a circle, but my concern is - this additional rolling diameter achieved bu putting on lower offset wheels - is it beneficial or damaging to the overall suspension geometry?

[atom]

It's not doing anything to the suspension geometry, everything else being equal. You're changing the scrub radius which changes the steering geometry, not suspension.

[RBS14]

It's called scrub radius. Having some is good, but too much is bad. It increases the "feel" of the car, in addition to other things. The larger the scrub radius is, the easier it is to feel the back of the car rotating. But you do get to a point where it does affect handling, if you get too much of it. When you get too much, you put extreme forces on the steering rack and system, which can blow stuff out. If you're putting really low offset wheels on the front of your car, I highly recommend a steering cooler. Will help keep temps down and minimize the effects the large wheels have on the system.

[Kreator]

oh cool, never knew that was called scrub radius.


Well hypothetically, the setup i'm planning for a project car i'm working will replace stock 15x5.5 +40 with 15x8.5 or 15x9 around +0 offset paired with a 1" spacer (i know these are bad, but its an adapter to 4x114.3. try and find a 15x8.5 or 16x8.5 rim with a 4x100 bolt pattern).

I would guess this is enough to run a cooler? And by feeling the back coming out - do you mean bigger scrub radius increase oversteer or just better the feel?

[RBS14]

it just creates more feel. And technically if you didn't put rear wheels on that had an offset low enough to match the fronts, it could create oversteer too. I would run a steering cooler with that setup, they're only like $10 on ebay for used ones out of SUV's at stuff. boiling power steering fluid = BAD. Could cause many problems in the steering system not having one, as well as if any of it somehow got onto the manifold (from boiling out of the reservoir) you've got an instant engine fire. Don't risk it.

[Kreator]

sounds fair. i did some research so correct if i'm wrong. car is a FWD w/ mcphersons all around

lower offsets - positive scrub radius.

The bad:
cars with mcpherson struts deal better with negative scrub radius
at high speeds car can possibly be harder to control
torque steer can be a bitch
harder to turn the wheel.

The good:
better steering feel
wider stance
more solid on the road

i'm not really worried about high speeds and torque steer. And i can muscle with the wheel some. So as long as i guess the axles and bearings can stand it should be all good?

[cheez80]

hi, is this a scion?

sounds to me like it is. if you're into old school wheels, work's old school equips come in 4x100. my brother would like to run equip 02's in 15x8.5 -6 on his xb, if he can ever pony up the cash.

[RBS14]

negative scrub radius is then the center of the contact patch of the tire is INSIDE the steering axis (the strut in this case). Positive is where it is OUTSIDE of the steering axis.

Have you ever noticed huge lifted trucks with deeeeep wheels and huge tires have the "steering dampers" that are basically shocks running horizontally across the front axel? This is to help eliminate severe wheel shimmy at high speeds that comes along with extremely positive scrub radius'. Just a little bit of info I found interesting.

About the steering cooler. I didn't realize this isn't a 240 we are talking about until now. Just assumed it was. If these wheels are going on a xB, and it's just a daily driver, you don't need to put a cooler in. My previous comments pertain mainly to track cars.

[Kreator]

it is going on a track car, but it's not an xB :)
thanks for the help guys.

Work wheels are expensive mothers. And chances of finding them used in 4x100 is like miniscule. The idea was to adapt to 240sx pattern since its like impossible to find decnet priced wheels in 15 or 16 diameter wider than 7.5 inches that are 4x100.

[cheez80]

ahh, my apologies. the offset, width, lug pattern sounded like it was going on a wide-bodied or flared xb. in either case, if you're ordering new wheels (unlikely for a track car), some of the works come in 4x100.

[F3600]

I got 0 offset wheels is it bad enough to think about running a cooler? where the "danger zone" ?

[Ian]

i'd presume anything outside of stock is going to have a somewhat negative effect

[RBS14]

I don't really know where the "danger zone" is. If you're doing a lot of drifting, get one. That sounds like a good rule of thumb.

Mainevent: I wouldn't say that. I like the steering feel much more after putting on my wheels. No negative effects that I can feel. If you have a lot of bump steer, more scrub radius would accentuate it, but that's about all.