Your posts are always interesting.

But remember, while the overall roll stiffness increased by 40%, it is all in the rear. So that changes the front to rear stiffness ratio. I wonder how the car would have reacted to a 20-20% increase evenly split front and rear. It is just a curiosity question. Also, your observation about your JCW is very interesting to me as that is basically the suspension that I have. But I am going a different direction. I wonder what the Bilstein sports will do for my car? The rears seem much more stiff, proportionally, than than the fronts, which, if my figuring is right, should take out some of the oversteer.

 

wouldn't a stiffer rear increase oversteer?

 

Well, I have to admit that it a bit of a guess on my part. But here is how I figure it...a stiffer sway bar and/or stiffer springs in the rear increases the roll stiffness of the back of the car, which reduces oversteer. To some extent a stiffer shock in the back should act like a stiffer set of springs or sway bar, at least during the transient part of a turn thus reducing oversteer. I could be wrong, but I can't imagine that these shocks, which were "part of a killer autocross" setup, would have added any oversteer. I am very open to being corrected on this, though, as I haven't been able to find a good post about how to set up adjustable shocks for autocross or the track. I know Btwyx is working on it, maybe he has a suggestion.

 

Just to be contrary, I ordered my first set of R-comps today. I've never used them before, for track days I don't think they'd suit Cathy, though I've been interested in trying some. For autocross I've only ever thought I wanted to run on street tires. The SCCA handily changed the rules just as it would make a difference for me.

But for a few track days this year, we're running in different cars. I'm running Bertie, and Cathy running in Algy. So I started wondering about maybe getting some R-comps for me to use on the track.

Then I was surprised by the result of our tire test and the ZII tires on 16x7 worked better than the Rivals on 15x6.5. I'd expected that to be the other way around. The plan was to run the good tires at SCCA and the also rans at BMW club events to use them up. I've never been particularly serious about BMW events, I use them for practice for the SCCA events. Except for the TDS at the end of the season, I take that seriously.

The BMW club assigns points to the car for various modifications, and basically assigns an extra two points for every half inch of wheel width you have. (1 for the front and 1 for the back.) Last year Bertie or Tristan were assigned 34 points on the 16x6.5 wheels, or 36 on the 17x7. So there was not much effective difference, they're both C class, which goes up to 39 points.

The mods we've made to Bertie are worth an extra 4 points (2 for the shocks and 2 for the rear bar). So he'd be 38 points on 6.5" wheels or 40 points on 7" wheels. The 40 points would put him into the B class. As I wanted the freedom to run either wheels, I was going to enter Bertie in class B no matter which wheels he had on. I was expecting that to be the ZIIs on 7" wheels. As a bonus I beat all the usual suspects in B class at the TDS last year, so I was thinking i had a chance of winning the class if I could get to enough events. Even if I'd have the fewest points of any entrant in class B.

But with the result of the tire test, I'll be running the 6.5" wheels at the BMW club. So he'll have 38 points, and basically have a spare 11 points I could spend and not change his class. That was when I remembered that "cross-tread R-Comps" are worth +10 points. Basically I could run R-Comps at BMW club for "free". (ie without changing the class I'd be entered in.) That sounds like a substantial advantage. Rules are meant to be exploited to your advantage right?

So I decided to get some Toyo R888, I'll use them on the track and we'll use them for events which aren't the SCCA championship or national events. I'm even considering running them at the Pro event we're going to at Crow's Landing, to save the ZII so they can last long enough to get to Nationals. We'll probably be the only HSR entry. It'd be interesting to do a tire test of the ZII vs the R888 to see how much faster they are. Then I could work out if it'd be better to run the ZII or the R888 at the BMW club's TDS at the end of the season. The TDS is worked on index, so dropping 10 points would give a substantial advantage to the ZII (if they've lasted that long.)

As another ulterior motive, I was comparing my runs at the last event to Cathy's. She lost 1 second by being slower around the first corner (and thus slower down the straight), and another second around the next 180 (and thus being slower down the following straight). She needs to be a little more aggressive around corners like that. She knows this, but can't manage to be quite that agressive. If we have a car which has higher limits (thanks to R-Comps) for some events, I'm hoping she'll learn to use higher limits when we don't have them.

 

Ooooo...
You are going to love the R888s.
I bought a used set just to "try them out". They are far better than the Z1s I also had at the time. A lot more grip and much more responsive. On my first drive with them I found that I was over turning each turn; they were that much better. On the track, I can brake deeper into the corners was well as go faster around the corners. I am hooked. (More "track crack"...)

Also, unlike Hoosers, they wear longer and you can run them in the rain and on the street. Not sure I would run them on the street for 100 miles or more, but I would go 10 miles to an autox event on them and have.

Just a word of caution. As for Cathy using the R888s to get used to higher limits, this can be a problem as their limits are much high than the ZIIs. If she goes back to the ZIIs and doesn't back off a little, she could over drive the ZIIs and that might not be pretty. This happened to me going back to the Z1s. I went too deep with my braking and was beyond the there limits when I got off the brakes and had the back end step out on me. Everything was OK (I drive on the track with the DSC on and that helped), but it did teach me a lesson. If she does back off with the ZIIs, she may over compensate and could be even be slower.

One other suggestion - with these tires they say that you should run them with at least -1.5 deg camber in the front. You might want to think about putting in a set of IE fixed camber plates.

 

After damaging a wheel and killing a tire yesterday, I managed to buy Tirerack's last ZII in 225/45-16, which was in Indiana.

Given the shortage of ZII tires around, I bought some backups in 215/40-17 which Algy can use on the track or Bertie can use to save his 16"s.

 

What did I miss? Damaged wheel and destroyed tire? What happened? Hope all is ok otherwise.

And what is with the "last ZII"? I bought a set of ZIIs as track rain tires...noticed that they were on closeout on Tire Rack. Any idea of what gives with that? They just came out with them.

 

I'm not going into detail about the problem with the wheel. We're fine.

The ZII is discontinued in favour of the ZII Star Spec, which will be available in the autumn. I started a thread about that: https://www.northamericanmotoring.co...continued.html

 

Understood.

Thanks for the link about the ZIIs.