[R3ctivision]

Hi all, as promised after I bought a set of four SM-10 18x10 et25 wheels from a forum member (https://www.camaro6.com/forums/showthread.php?t=547657 and https://www.camaro6.com/forums/showthread.php?t=547610) for more info), I thought I'd post an update.

I test fitted one wheel on the front. For reference, here is my current setup.

Bone stock EXCEPT for Moreno Motorsports camber plates.
Currently no strut grinding.
-3.4deg front camber
-1.7deg rear camber
I forgot the toe and caster settings I am running, but nothing fancy.

Without any spacer or grinding at these settings, as others have said, the wheel definitely contacts the strut. When I put the 5mm spacer on, no contact.. but it's very close (a few mm). I think if there were any wheel weights, there could be contact..?

I just ordered a set of 285/35/18 Hankook RS4s to get mounted a week from today. I'm going to see if pulling the front camber back out of the knuckle does the trick to get these mounted without the spacer/studs, or grinding. Aiming for -3.0 deg, with the camber plates maxed (they can get around -2.2deg I think), and the rest coming from the knuckles. If that doesn't work, I'll try either the grinding or just suck it up and do the stud install to run the spacer. I've never done any grinding before, nor do I own tools.. anyone have some tips for a total newbie?

Here's a pic of the current fitment with the spacer.

[FNxR3DNECK]

How much camber at the knuckle? I have about -2.5 and had to grind the strut +spacer to get the 19x10.5 et22 to work. Also where did you order the tires?!?! Everyone keeps telling me they still aren't available haha

[carguy55]

grinding etc

https://www.camaro6.com/forums/showthread.php?t=486305

https://www.camaro6.com/forums/showthread.php?t=526353

[5senna5]

Looking good! Those Adaptec spacers I had custom made are 6mm thick rather than 5mm.

[pbsinternet1le]

3/24/19 per tire rack..

[MatthewAMEL]

Originally Posted by FNxR3DNECK

How much camber at the knuckle? I have about -2.5 and had to grind the strut +spacer to get the 19x10.5 et22 to work. Also where did you order the tires?!?! Everyone keeps telling me they still aren't available haha

Why 22 offset?


Is that all Apex was offering?


I have -2.6 with knuckle on 305/30-19 using a 16 offset.

[Vtor_ZL1]

Is that 370 or 390mm front rotor ?

[FNxR3DNECK]

Originally Posted by MatthewAMEL

Why 22 offset?


Is that all Apex was offering?


I have -2.6 with knuckle on 305/30-19 using a 16 offset.

Yea that's just what the specs are on their 19x10.5s, keep in mind these are BMW spec wheels. But it was the best option for a square setup with 305 RS4s.

[R3ctivision]

Originally Posted by FNxR3DNECK

How much camber at the knuckle? I have about -2.5 and had to grind the strut +spacer to get the 19x10.5 et22 to work. Also where did you order the tires?!?! Everyone keeps telling me they still aren't available haha

I'm not sure. Probably 2 degrees or so at the knuckle with the rest in the plates. Got the tires off of tire rack!

[R3ctivision]

Update! Since my last post, I've mounted tires and tested the car on both the street and the track, so I'm ready to share my impressions.

I was originally considering going with a set of Pirelli DH scrubs (about $600 a set for 285/645/18 on usedracingtires.com), but I ended up going with a set of Hankook RS4 285/35/18 square. They are $1088 a set on TireRack: https://www.tirerack.com/tires/tires...m=835WR8Z232XL

I decided against the slicks because I wanted to be able to test the setup on the street before taking it to the track, and because I'm worried about unbalancing the car with too-grippy tires (oil starvation, inadequate brake cooling/brake pads, too-soft springs/shocks/bushings, etc.). My goal is to have a long-lasting track setup that is more practical, fun, and affordable than running stock. TL;DR: I'd say this setup with RS4 tires achieves exactly that.

This setup has a tricky fitment in the front. To summarize, you need to do the following:
- 6mm hub-centric spacer on the fronts (custom made by the forum member who sold me the wheels and mounting hardware)
- 1/2" longer studs in the front (I had a shop quickly knock this one out for me)
- Open-ended lug nuts (to allow mounting OE wheels without spacer -- the stock closed lugs won't work on the longer studs)
- Either grind the strut or avoid maxing the camber angle at the knuckle (I did the latter, and used my Moreno camber plates to settle at -3.0deg camber in the front)

With this setup I got about 3-4mm clearance from the inside lip of the wheel to the strut. Tire clearance is fine, even at full steering lock. I didn't get rub anywhere on the street or the track.

I did run into one snag with this setup. Stick-on wheel weights mounted on the inside of the barrel on the inboard side can rub on the front brake ducts at full steering lock and possibly on the MRC sensor cables. The cable rub issue was easy to solve -- I just took some slack out and secured them with zip ties. As long as no cables protrude further out than the calipers you should be fine.

I haven't resolved the wheel weight rub issue. At low parking lot speeds with full lock, every time the wheel rotates I get a fairly loud rubbing sound as the wheel weight hits the plastic brake duct. I chalked the ducts to see exactly where they hit. The overlap is less than 1mm. For now, I'm just avoiding using full steering lock with these wheels. Alternatively, one could either take the wheel weights off the insides of the front wheels or trim the brake duct a bit. I wasn't inclined to do either -- I want balanced wheels and I don't want to mod the ducts.

Now, driving impressions. On the street, the 18" setup and RS4 tires are much more compliant than the stock setup. Bumps, road imperfections, and potholes are a LOT softer and vibration/harshness is reduced. It's very dramatic. On the other hand, the RS4s make a loud humming noise when rolling at higher speeds, so they are probably noisier overall than SC3.

This wheel/tire setup has an outer diameter that is approximately 7% less than stock. This means you get a VERY noticeable gearing improvement, but the speedometer (and therefore odometer) are now inaccurate. The gearing difference is IMMEDIATELY obvious. Acceleration feels quite a bit peppier -- of course, that's not just the gearing, the wheel/tire setup is probably 10 lbs lighter per corner than stock on average (I haven't weighed anything though). I think this reduction in unsprung weight also explains the better compliance of the car on rough roads compared to stock.

I took some camber out of the car in the front (-3.0deg instead of -3.4deg) at the same time I did this wheel/tire swap. The square setup does lower the ride height by probably 0.75" (due to OD reduction), and it also reduces the rake by a fraction of an inch (because the rear OE tires are taller than the front OE tires, and now I'm running square). The spacers increase the front track, but I think this is compensated by the higher offset compared to stock, so I'll call the front track difference a wash. And of course the rear tire width is reduced by 20mm.

Heading to the track, with all of the above changes, I expected the car to overall be more neutral (less understeer) than stock, but with overall less peak grip. That hypothesis turned out to be true, at least for my driving style. I took the car on the Thunderhill 4.8 mile course and ran for about 3 hours -- easy at first to shake down the new setup and listen for rubs, and harder towards the end.

The car wants to rotate a bit more mid-corner than before, but it doesn't seem to grip quite as much, especially under braking. In areas where I used to carry the brakes deep into the turn, with the new setup I couldn't go quite as aggressively because the car started to understeer. This surprised me a little, but didn't bother me much because if I took it a bit easier on the brakes, the car was quite a bit more playful throughout the corner than stock. The car felt pretty good overall on the new setup. I was confident enough with the handling to run with all nannies off (never did that before in this car, I was always in PTM Race). I think that over the 4.8mi course, the RS4 setup is probably 2-3 seconds slower than the OE SC3s, but it's hard to say since I didn't run back-to-back. This judgment is totally seat-of-the-pants impression of the grip levels. FWIW, my best 4.8 mile lap was about 3:15.01. I think once I get more confidence in the new setup and without traffic I could do a 3:13 or 3:12 on these tires.

The RS4s really REALLY seem to shine in the longevity department. After 3 hours of running (though only about 1 hour of hard running), the tire wear was barely noticeable. Usually, SC3s last me 4 track days at most, with the inside fronts wearing out first from running lots of camber and braking late and hard. I can usually see a difference in SC3 wear after every session or two. I think these tires will easily last me 8 days, perhaps more (since I can rotate them now), but only time will tell. I'm hoping to get through the entire year before running into the cords.

One weird thing about these tires is that they build up a LOT of pressure. On SC3s, I usually start around 26-27 psi cold and carefully warm them to about 30 psi before pushing harder. By the end of a 30 minute session SC3s usually end around 33-34 psi for me. With the RS4s, I started around 28 psi and after just 20 minutes of lapping, the front right was at 44 psi!! I had to keep micro-managing the tire pressures throughout the day. The best I could do was make the tires stabilize at 38 psi. But once the tires cooled in the paddock, they were sitting at 23psi, which scared me. I think the conclusion here is that RS4s seem to build and lose temperature much faster than the GY SC3s. The peak temperature I saw coming in off the track (with a cooldown lap) was 130F on the RF tire on the inside tread block. More testing is needed.

Now for pics! The setup does look small on this car

[TheRealJA105]

I bet your tire temps/pressures are going way up from the increased brake heat going to the wheels. With the 18s being so close to the brakes, there isn't as much air gap to get the heat out of the wheel barrel.

[kropscamaro16]

i loved the rs3 on my old car wish they made em in 20s but o well lol

[FNxR3DNECK]

Originally Posted by TheRealJA105

I bet your tire temps/pressures are going way up from the increased brake heat going to the wheels. With the 18s being so close to the brakes, there isn't as much air gap to get the heat out of the wheel barrel.

This is a possibility, I thought that was very strange when reading his post.

I'm now running my SM-10 + RS4 track setup but in 19x10.5 with 305s, at VIR a few weeks back I was starting them at 26-27psi and they were showing 34psi at the end of each session very consistently. That is no where near the jump he was getting with the 18s/285s so it makes me wonder what the cause is.

[R3ctivision]

Thanks guys for the feedback. I hadn't considered the impact of 18s on airflow. I'll have to take brake temperature measurements next time and see what I learn. Maybe try both setups back to back as well.

Hopefully I don't need brake ducting upgrades, and it's just a matter of starting pressure and warm-up procedures.