How will offset affect handling?

I am looking at some SSR Type-C wheels for my 07 Mazdaspeed3 later this week and I am wondering how they will affect the car's handling.

07 MS3 stock wheel/tire size: 18x7", +52.5mm offset, ~24lb., 215/45/18

SSRs: 17x7.5", offset unknown (see below), ~16lb, 235/45/17

The seller is not sure of the offset, but I think it is +41mm or +49mm because he mentioned they would fit an Eclipse. A Mazda3 forum I go to confirmed both offsets will fit. The seller test-fitted them to a 2010 MS3 and said they fit perfectly, though the picture he sent me is small and only shows the car with the front wheel up in the air.

If the wheels are +49 then there will be little change in the wheel track. If the wheels are +41 then they will stick out further from the suspension and will need me to roll the rear fenders. How would going with the +41 offset wheels affect handling? Would they increase the torque steer by a large degree?

Could make the torque steer even worse. Not sure if there's an easy calculator for that one, though.

Think of the wheel as a lever sticking out and it's easy to see that yes more negative offset can affect things like wheel spring rate and torque steer. Then there's scrub radius to consider too.

Unless they actually rub, which doesn't sound likely, I doubt you'd even notice a 10mm decrease in offset. Maybe on a full race car with slicks but probably not on a driver.

I'm with Jay, you won't notice anything but increased grip from the wider tire (assuming the compound is the same), and increased acceleration from the smaller diameter you're moving to.

our jeep XJ-R went wider and more negative offset, and our first trial attempt at autocrossing it had 8" wheels with 3" backspace combined with a 5" smaller diameter tire meant the scrub radius went from stock (slightly positive i believe) to by my extremely rough visual calculations had something like a 4" positive SR. conditions were drizzly all day so grip was inconsistent and it had some wierd steering shakes under braking. ultimately she's sitting on a 10" wheel now with the same outer measurement so weve effectively moved the SR back in closer to where it ought to be and i believe its helped as we havent experienced it since.

but that's a pretty extreme example of a change and on normal vehicles i havent felt much difference when changing offsets. plus thats usually combined with a wider tire so its hard to say. i bet they'd look great at +41mm filling out the wheelwell.

49 I think you would not notice at all. 41 you would notice initially with slightly increased tram lining and slightly more torque steer, but I think you would become inured to the tendency within a week or so.

Not really a significant issue.

m

That tire setup's gonna make that car a lot more fun, that's for sure. I've got 245's on mine, and she's a whole lot deeper into the corners now.

On my ZX2/SR the stock wheels were 6" with 42mm offset. I have run 7" wheels with 35mm offset. I can't say that I noticed any difference .

Autocrossing my Mazda 3 in HS, I ran 47mm on the front and 55mm on the rear of the car. The couple of times I ran the 55mm wheels all around, the handling difference was night and day.

On my Corolla, the street wheels are 14x6 ET10 , and my HPDE wheels are 14x7 -9. AutoX wheels are 13x8 ET4. HUGE difference at slow speeds without power steering. VERY hard to turn with a larger scrub radius. Granted, they get progressively wider, and rubber to match, but after I instaled power steering last month, the issues I was having at slower speeds went away. I can't wait until next spring to see how it actually affects my autoX times.

--sarge