THSCC Forums

Double sway bars.

I was wondering if my favorite stock category allowance would survive the transition to street category.

In fact, it's been liberalized quite a bit.

proposed Street Category 13.8.F.2:
Camber bolts may be installed and one bolt’s mounting point(s) on the strut’s lower integral mounting bracket
may be slotted. Caster changes as a result are permitted.

Existing Stock class rule 13.8.E:
If offered by the manufacturer for a particular model and year, the
use of shims, special bolts, removal of material to enlarge mounting
holes, and similar methods are allowed and the resulting alignment
settings are permitted even if outside the normal specification or
range of specifications recommended by the manufacturer. If enlarging
mounting holes is specifically authorized but no material removal
limits are specified, material removal is restricted to the amount necessary
to achieve the maximum factory alignment specification.

Refresh mine too. Why is that so bad?

Chuck, I think we talked about this before but it's just that with 2 bars you can get not only a car that has minimal roll rate, but also one that is balanced. However, I think it will make it difficult and expensive to be competitive because, naturally, running monster bars only works on some cars due to geometric constrains and needing to by insanely large sway bars with custom mounts and endlinks that will destroy your subframe and possibly suspension arms is just going to be a hassle and large expense which I think is going in the opposite direction of what the Street Category intends. I think the front or rear bar change a few years back was quite nice though.

From Hollis blog:

We had the chance to run the 225/45/15 Rival on Buttonwillow 13CW last Sunday. Car was our 95R street project car. Xida 700/400, 15x9's, 140whp, 2550# (with passengers all day). Ambient was 75~85° with track surface temps of 93~106°. We have run this car with RS3's on several different tracks and weather conditions. Very familiar with min corner speeds, braking points and overall feel of the RS3 on 13CW in particular. No A/B testing done against the RS3's Sunday but some impressions stood out.

Lateral grip
SOTP, the Rival seems to generate about the same peak lateral grip as the RS3. The difference was that the Rival would still generate useful grip when well past optimum slip angle. More like a race tire than the RS3 which prefers small slip angle and loses grip more rapidly with large slip angles. This made the Rival easier to drive and allowed a few "toss and catch" entries into double apex turns that were a touch faster than the slight lift the RS3 required in the same spot. This ability to generate useful grip at large slip angles made them feel more like race tires than any other feature.

Steering
Response and feedback were, like the RS3, very good when the tire was lightly loaded as it would be entering a turn at full throttle. The noticeable difference was under straight line or heavy trail braking where the Rival communicated available grip and slip angle much better than the RS3. The RS3's can get a little numb under heavy trail braking. So unloaded they steered about the same. Transfer weight onto the nose and the Rivals talked more. Overall I would rate the steering response and feedback as very good.

Braking
This is where the Rival is significantly different than the RS3. The RS3 has earned a reputation as a tire with braking that does not quite match is stellar lateral grip. The Rival had noticeable better braking grip and feedback compared to the RS3. Of note is the RS3's characteristic of requiring the driver to transfer weight onto the nose more carefully while the same car/driver on Rivals could reach peak line pressure much sooner without locking.

Temp range
Since we were not conducting A/B testing that day, data collected was minimal. Peak temps were only in the low 170's even after a full session. We did see that the Rivals lap times stayed consistent even after several laps at full speed. This is rare for a street tire. Most street tires have slightly heavier casings and more tread mass than a race tire so they tend to not shed heat as well as a race tire. This typically manifests as the street tire being fastest on it's first hot lap. While there was some drop off late in the session it was less than .6s on a 2:05 course. This is excellent for a full tread tire. The indication here is that the tire sheds excess heat very well, possibly better than most other tires in this category. My guess is that autocrossers with a co-driver will fare better than solo drivers on this tire. We did not run the tire in the morning while it was still cold so I can't comment on cold performance. We ended up with about 35psi hot which compares to 29~34 psi we usually run with R compound tires.

Overall, the RS3 feels like a really fast street tire, having a narrower range of optimum slip angle and weaker braking than a true R compound. The Rival in contrast, felt quite a bit like an NT01 (R compound) with about 5 heat cycles on them. An educated guess is that the 225/45 Rival would be less than 1s slower than a 225/45 NT01 on a ~2:00 road course, everything else being qual. That is just astonishing to this driver. A 200 treadwear (grain of salt) that can nearly keep up with medium compound race tires for a full track session.

I could dig a double sway bar with a fixed degree of increase in size (fixed percent? fixed diameter change delta?). This means the market for hollow bars would close up though .

I would say that the rule would have to be percentage based to make sense. Something like "maximum bar diameter may not be greater than 20% larger than stock". Something like a 24mm bar would then be allowed to increase to 28.8mm. Given that stiffness for a solid bar varies with the 4th power of the diameter, this example results in a bit over 100% increase in roll stiffness, so maybe even make that diameter percentage change allowed a bit smaller than that.

Emilio from 949racing (Miata shop) posted some info about his experience with the Rivals at the track last night. Mind you, this is track and not autocross, but there is still a bunch of good info to take from it.

The Rival in contrast, felt quite a bit like an NT01 (R compound) with about 5 heat cycles on them. An educated guess is that the 225/45 Rival would be less than 1s slower than a 225/45 NT01 on a ~2:00 road course, everything else being qual. That is just astonishing to this driver. A 200 treadwear (grain of salt) that can nearly keep up with medium compound race tires for a full track session.

Thanks for posting that Andrew. I can relate to just about everything this guy has said -- pretty amazing correlation with my thoughts on the tires.

I just got back from an "autocross" at the BMW Performance Center where Jackie and I co-drove the M3 on the Rivals, so I have a lot more internal data now. The track is super fast with almost no cones hence the reason I put autocross in quotes. Top speeds in the M3 reached close to 100mph at a couple of places, so this was more like a time trial especially since the course was about 1:30 long.

First takeaway is that I do really need the stagger fitment in tire size or at the very least larger tires all around. I had no choice though to date since the Rivals in the larger size I need won't be available until June. The power on oversteer was ready and waiting anyplace on course, and with a more appropriate rear tire size, I could have been putting down power better no doubt (I'm on 245s all around instead of having 275s in the rear).

I've done this event four times in the past 6 years, each time with the M5 on NT-01s. Hence my thoughts comparing the tires were strong during the event, but since the M3 is so different than the M5, it isn't a direct comparison of course. I felt that maximum braking was really close to the NT-01 perhaps just a tad weaker if anything. Turn-in response seems much more direct on the Rival (remember there is a car issue at work here too though), and I feel like I can tell what the tire is doing much better than the NT-01. Accelerating traction seemed as good or better. The Rival feels "cleaner" than the NT-01 all over the track which I guess simply means it is communicating to me all the time in a better fashion.

I identified with his comment about being able to throw the Rivals into an element and use high slip angles as I overcooked one very slow section a couple of times, knew it at the time, and just cranked in steering angle. They stuck better than I expected, bled off speed, and then I was on the throttle rotating the tail on corner exit. Not the fastest way in this case, but I had in the my mind being off the course with NT-01s under me right then...

We did 21 runs on that ~1:30 course Sunday, so I have some wear on them now. They are still holding up very well though even though I only can get -1.5 camber up front on this car (stock class). I'm looking forward to the larger sizes in the future, but I'm going to have a decision point of what to use then (245/275, 275/275).

Oh, I was doing some instructing and giving rides to people, and Jackie overheard me telling a guy all about the Rival after a run when he asked about the tires on the car -- she said I should be on BFG payroll or something. I'd be happy to just accept free tires though, so I told her to work on that for me.

I need all the help I can get, so having a forgiving tire that grips super well fits me. If we got 10 runs at each autocross, it might be different, but having to create an optimal outcome in just a few runs on some course you've never driven before...well, for me, I need all the help I can get, and it doesn't get easier with age.