tire offsets, whats the deal

so this is my second year racing and I dont understand how people know that running a 3" on this tire and 4" on this one will tighten or loosen up the car. last year I just listened to what I was told but this year with a different track and car I need to figure it out mostly on my own. this previous weekend I was asked what I had on for tire offsets and the minute I told the guy he said my car was going to push and it did. I'm just wondering if anyone could fill me in on how the tire offsets work in tightening or loosening the car

leverage against spring , move wheel in will raise spring rate , move wheel out will lower spring rate. most of the time its you see you do . most springs are cheaper than wheels. nascar runs same offset wheel all the way around. another track = spring rate change

are you allowed to use spacers instead??

wheel offsets will also change balance point of car. move lr out, corner gets heavier,
to tighten our car for dry slick, I move lr out, if real bad move rr in also

Changing offset in the front changes wheel rate, scrub radius, camber curves, track width, the turn radius that your tires are travelling when steered, it can exaggerate or reduce Ackerman effect, and the position of your brakes in relation to the tire center (this one is actually more important than some think). When you move the mounting point of a rim closer to the inside of the tire (inside meaning the part closest to the chassis), the tire as a whole will move more because now it’s arc of travel during wheel movement has changed. This causes the wheel rate to decrease, and simulates a softening of the spring. This also means that the tire is going to change camber more. The spindle and arm lengths aren’t changed, so that arc remains the same but because the mount on the rim is moved inwards, the wheel itself moves out in relation to the chassis, because the suspension travels the same amount but the wheel is further out, the changes are amplified at the wheel. This would also slightly exaggerate Ackerman because the wheel again moves more being further out on the arc the suspension is moving. Talking about scrub radius, your upper ball joint and lower ball joint create an axis which your tire turns about, the closer your KPI is to the center or the wheel, the more that wheel will turn more “true” to that axis and have zero scrub. The further away from the KPI axis the tire center is, the larger scrub radius you have meaning the tire actually moves around the radius, this changes your wheel base front to rear slightly but allows the tire to “scrub off” some of the forces generated on it through the steering input along a radius, instead of just twisting on the spot with zero scrub. Too much scrub obviously is a bad thing, just like zero scrub is a bad thing. Regardless, changing wheel offset with change your scrub radius and that will change how the car handles. It will increase scrub if you move the wheel away from the car, and decrease it when you move it in. Moving the wheel out, also, causes the turn radius to change of the normal steering inputs. If you move the wheel out, a steering input will cause the car want to turn more than before. Because in this case the wheel is moved away from the chassis the track width increases and this reduces weight transfer onto that tire. Another thing like I mentioned about wheel offsets is that it can move the tires closer to or further away from the brakes which can be a source of a lot of heat that can be used to keep heat in the tire allowing it to fire quickly. Changing offset in the rear changes track width, and drive angle. Moving the RR in would cause the car to develop a slight “yaw” in the drive angle acting to tighten the car up under acceleration. Also, moving the RR tire in also narrows the track width of the tires, and puts more load on the RR which depending on your wheel loadings, can either tighten or loosen the car. Typically if you move the RF out you will tighten entry handling. If you move the LF out you will loosen entry handling. If you move the RR inboard you will tighten entry, and change drive angle that will also tighten the car. If you move the LR outboard, you will tighten entry and exit. But here’s the other thing. Moving both outside tires in and left side tires out will tighten the car tremendously on entry and loosen it on exit by changing right side weight. Moving the center of gravity way over. Moving both outside tires out and left side tires in you will loosen it up on entry and tighten up exit. adjusting offset in the front changes way more than in the rear so you need to be careful about that.