Better to go wider or lighter?

[OrbitalEllipses]

Originally Posted by hankster

I'm in the same boat. I have my FRS which is my DD but I'm interested to try some auto-x and hpde. I've been pondering the exact same wheels.

One question I have on the Kosei 17x8: the offset is 36mm, is that not enough? Any problems with that? Extra stress on bearings? Stick out too far, past fenders?

Eh, there's old wives tales about low offset wheels destroying bearings on Subarus...but you'll be fine methinks. The problem with low offset is (forgive me, I've forgotten the technical terms) moving the wheel center outwards so that rotational mass is further from the car, impacting handling. Ask RCE about that.

[Black Tire]

Look at the tires that you are planning to buy, and look at their measure rim width and the recommended rim width range. For example this tire on the Tire Rack:

Example Tire

has a measure rim width of 7.5". This means that all of the other measurements for the design of this tire were done using a rim of 7.5". The rim width range lists as 7-8.5", so this tire will work on either of the rims you were looking at. Also, since the measure rim width is only 0.5" either way, you should get good results from either one.

[xwd]

How serious are you about autocross and what other mods are you going to do to the car? 17x7 allows you to stay in stock class if you want, anything wider and you'll go to a higher prep class.

If you don't care that much, go with the wider wheels, put some 225/235 tires on it. The weight isn't that much difference and you'll probably never notice it.

[coyote]

Originally Posted by OrbitalEllipses

Eh, there's old wives tales about low offset wheels destroying bearings on Subarus...but you'll be fine methinks. The problem with low offset is (forgive me, I've forgotten the technical terms) moving the wheel center outwards so that rotational mass is further from the car, impacting handling. Ask RCE about that.

It effects the scrub radius and is not an old wive's tale. Perhaps ask RCE to calculate the offset that results in a perfect scrub radius for the car.

[Vracer111]

I can tell you that the 17x8, +36mm offset Kosei K4R's work really well on track with 215/45-17 Kumho XS tires (which are wider than the stock Michelins, having a 7.9" actual tread width). They also measured in at 15.6lbs without the valve stems...

A lighter weight stock sized tire on 17x8, +36mm offset wheels for this car is an improvement in feel...

[BRAWL]

Originally Posted by Vracer111

I can tell you that the 17x8, +36mm offset Kosei K4R's work really well on track with 215/45-17 Kumho XS tires (which are wider than the stock Michelins, having a 7.9" actual tread width). They also measured in at 15.6lbs without the valve stems...

A lighter weight stock sized tire 17x8, +36mm offset wheels for this car is an improvement in feel...

How about street use? Pretty well behaved? Not much noise? I know this mostly down to the tyre choice, but at least it is something.

It was your setup that made me look at the Kosei wheels in the first place

If I bought Motegi's or Konig's, it would be because I think they look slighty better.

[Vracer111]

Better than stock in all regards other than tire noise - smoother, more precise ride quality with a grip level so ridiculously high it becomes almost boring to drive on the street. More akin to driving an AWD Subaru on sticky tires kind of grip as it takes some of the perceived handling 'edge' away of the less grip stock tires while allowing much higher cornering limits.

[BRAWL]

Only other thing I have to consider is the Australian nanny state nonsense we have to put up with. Officially ADR42 is the biggest potential problem as it states that it has to be inside the guard/fender perpendicular (ie no massive camber yo ).

That could be a problem with the fitment of the 17x8 wheels, so may be better to play it safe with either the light weight 17x7 or get slightly more tread on the 17x7.5.

ADR23 might also stop me importing tyres from tire rack (got to meet ADR standards), but will send a message their way and see what they can do for me as I am pretty sure if a tyre model is sold locally then they stamp it internationally.

So much to think about!!!