Just gonna vomit some notes here in case someone finds them useful...
Focusing on understanding what I can expect from increasing scrub radius by x, I found the following, which is the most confident statement on scrub radius increase as a concept that I've found, made by Andrew of Racecomp Engineering- who appears to be, at the very least, involved in BRZ rallycross.
The key statement for me is:
"
a very large [scrub radius] value can feel pretty awful in terms of steering kickback, effort, and also do some funky things with toe change.
I don't have any set numbers for you guys, but -10mm in offset from stock is certainly fine IMO.
"
(statement made in a BRZ forum, where it appears -10mm offset translates to +10mm scrub radius via 215/45-17x7ET48- same increase for a VA WRX)
Scion FR-S / Subaru BRZ / Toyota GT-86 Forum and Blog | ft86club
www.ft86club.com
As an aside on spacers, I also stumbled upon this statement which surprised me a bit:
"The TMG CS-V3 cup cars have optional 10mm spacers front and back to increase track width with et48 ultraleggeras. In case you didn't know, TMG are Toyota's offical motorsport team in Europe that build the le mans cars and won all those rally championships in the Celicas.... if they say its okay to run those spacers. ... "
Scion FR-S / Subaru BRZ / Toyota GT-86 Forum and Blog | ft86club
www.ft86club.com
Here is some subjective input from random people on the internet...
[scrub radius increase (mm) where OE scrub radius is assumed to be 0; is calculated based on VA WRX specs unless specified] :: [statement context] :: [provided feedback on steering feel change]
- 54 (from 235/45-17x8ET53 to 285/35-18x10.5ET22 with additional 25mm spacer) :: WRX/STI forum ::
I can’t really relate it to stock because I’ve done a lot of suspension mods too. It’s not too bad, I went with a lighter wheel setup so it’s good.
- 11 (from 245/35-19x8.5ET55 to 215/60-17x8ET38) :: WRX/STI forum ::
As far as this specific setup, so far my review is overall positive. The tires obviously have less grip than my summer wheels (duh), so my car tends to understeer more than I'm used to. I don't know if it's imagined or not, but I think I can feel the larger radius tires - my car feels slightly less powerful and I feel like I need to hit the brake 5% harder than I'm used to.
I had no idea scrub radius was a thing, but totally makes sense. I'm a little more squeaky doing tight turns in parking garages, and the steering feels a little heavier, so if I had to guess I increased my scrub radius a tiny bit. It feels safe and stable enough on the road at both high and low speed, though I'm curious to test out what they talk about where driving through water will yank your steering one way or the other. I did have it out in the desert messing around in all sorts of terrain (sand, dirt, rocks), and didn't notice anything funky. And of course the fact I was able to easily play around on that stuff is a huge plus to this!
You hear about people doing lifts/wheels on their car and taking it out for the first drive and being like "Oh my god I turned it into a death trap". I had the opposite reaction, I was like "omg I hope I didn't break it", then took it out for the first drive and my reaction was "Oh, this is fine." Any feelings I talk about above are at max, like a 5% difference from stock.
- 36 front, 74 rear (38mm spacer front, 76mm spacer rear) :: rallycross group ::
Less body roll around corners. Steering response nearly the same though the back seems to want to let go more easily now. Overall worth the time and money.
- 38 (OE scrub radius of -19, from +53 to +15) :: rallycross group ::
That changed my scrub radius from negative to positive by about the same amount. [....] Positive SR causes the wheels to want to toe in under acceleration and toe out under braking. I have not really noticed this, but I don't drive hard on tarmac and on loose surfaces, the grip in low enough that I think the tires break loose before there is significant toe change. Also, usually if I am braking at the limit it is in preparation for a corner and my steering inputs overpower any effect I would feel from the toe out.
- 23 (from 245/35-19x8.5ET55 to 255/35-18x9.5ET35) ::
Not much difference in steering feel. Traction definitely increased, corners well at high speed, and seems to brake more quickly.
- 20 (from 245/40-18x8.5ET55 to 255/35-18x9.5ET38) :: WRX/STI group ::
I've had a whiteline track suspension set up for a while and while the car already drives good, made a world of difference. Drives better but hair more noise.
- 20 (from 245/40-18x8.5ET55 or 235/40-17x8ET55 to same minus 20 offset) :: WRX/STI group ::
It made a huge difference in cornering stability feel. My new rims are much lighter also, that would contribute
- 19 (from 245/40-18x8.5ET55 to 265/35(?)-18x9.5ET38) :: WRX/STI group ::
The car itself, not the steering wheel, feels a lot more planted. 245 stock to 265 on each tire is a huge improvement for grip. I miss is. I am on 245 now and the car feels floaty at times. This could be due to my driving as well, as I do spirit drive a lot. The 2015 felt planted majority of the time.
- -24 (from 185/65-15x6ET25 to 215/45-17x7ET48) :: rallycross group ::
Not much change noticed from the wheels and tires from a feel perspective. The alignment does make a difference in feel.
Intent was a slightly track width, but narrower footprint so the tires would dig into loose surfaces better.
- <~22-29 (from 245/45-18x8.5ET55? to 215(?)/60(?)-16x7ET45 or from 225(?)/65(?)-17x7ET55 to 215(?)/75(?)-16x7ET45 with additional 25mm spacer) :: rally racing company employee ::
The driver of the Outback loves the car, I would have to explain to him why it might be an issue for him to even realise what I was referring to because it really isn't noticeable at all.
- ~22-29 (from ? to 255/70-16x8+20) :: rally racing company employee ::
We also have a 2017 Outback (shop car, same brake setup) with 16x8 +20 fuel vector wheels they are very heavy, almost 30 lbs with 255-70-16 BFG K02 each tire/wheel is almost 70lbs and the scrub radius is worse but is still barely noticeable when you drive it. We've used it for Road Rallies, pre-running the course for stage rallies, we've loaned it to organizers for the course opening and everybody absolutely loves driving it and these extremely experienced people.
- 12 (from 245/40-18x8.5ET55 to 265/35-18x9.5ET45) :: WRX/STI group ::
hard for me to isolate the changes (wider tyres/rims, slight offset change, grippier compound) but steering feel is slightly heavier and it just grips like shit on a rag
I will call out that this wheel/tyre size is absolutely ideal for the VA platform - at least according to the japs. If you look through any JDM hyper rev magazine focused on the VA chassis, every feature car runs the exact same 18x9.5 +45 265/35R18 setup.
Gotta love that mad lad with SEVENTY SIX MILLIMETRE spacers- I even clarified to make sure we were talking about the same "offset". The man bolted a 1.5in spacer to his hub...
and then bolted another 1.5in spacer on top of it. The man doesn't play by the rules!