[sdhotwn]

Originally Posted by stevehecht

Just curious: What are the options other than the ZIIs that you would mention? Nothing against the Dunlop, I just like learning about tires. After perusing TR for a bit the BS RE-11a seems attractive to me. I'd like something a bit more civilized on the road even if it's not the total cat's meow in autoX. I really need to figure out how serious a commitment I will be making to taking my car to autoX and then decide which tire to go with based on that. The RE-11a seems a good compromise between the S-04/PSS and more edgy race tires, I'm just not sure I want/need to go that far into race mode for my car.

The top tires are in roughly this order:
Dunlop Direzza ZII
Hankook RS-3
Toyo Proxes R1R
Federal 595RS-R
Bridgestone RE-11A
Continental Extreme Contact DW (dominant wet tire, not as good dry)
BFG g-Force Rival
Kumho XS

The Toyo's are getting a new compound for next year with a treadwear rating of 200, so it is unknown what their performance will be next year. The Federal tire was a big surprise the last two years, but next year it also sufferes from the treadwear rule (have to be 200 an above I believe) and will not be legal for stock classes.

I believe Bridgestone is planning to bring back the RE01R since the RE-11A has not been a good performer - it's a distinct second tier tire right now. There are certain cars though that the RE-11 and the Kumho XS are the only size options for though, so they have hung in there in a few spots.

Hope that helps!

[stevehecht]

Originally Posted by sdhotwn

The top tires are in roughly this order:
Dunlop Direzza ZII
Hankook RS-3
Toyo Proxes R1R
Federal 595RS-R
Bridgestone RE-11A
Continental Extreme Contact DW (dominant wet tire, not as good dry)
BFG g-Force Rival
Kumho XS

The Toyo's are getting a new compound for next year with a treadwear rating of 200, so it is unknown what their performance will be next year. The Federal tire was a big surprise the last two years, but next year it also sufferes from the treadwear rule (have to be 200 an above I believe) and will not be legal for stock classes.

I believe Bridgestone is planning to bring back the RE01R since the RE-11A has not been a good performer - it's a distinct second tier tire right now. There are certain cars though that the RE-11 and the Kumho XS are the only size options for though, so they have hung in there in a few spots.

Hope that helps!

Yes, thanks. I presume that by "top tires" you are referring only to the performance capability on track or autoX, not talking into account road characteristics like noise, impact/rough road comfort, durability, etc.

[sdhotwn]

Originally Posted by stevehecht

Yes, thanks. I presume that by "top tires" you are referring only to the performance capability on track or autoX, not talking into account road characteristics like noise, impact/rough road comfort, durability, etc.

Correct. That said, comfort and durability are pretty good on most of the newer generation tires. Road noise is pretty bad on most, but frankly isn't that much worse I don't think than run-flats create to begin with.

[DVC]

Originally Posted by sdhotwn

The top tires are in roughly this order:
Dunlop Direzza ZII
Hankook RS-3
Toyo Proxes R1R
Federal 595RS-R
Bridgestone RE-11A
Continental Extreme Contact DW (dominant wet tire, not as good dry)
BFG g-Force Rival
Kumho XS

The Toyo's are getting a new compound for next year with a treadwear rating of 200, so it is unknown what their performance will be next year.

Interesting list. Personal experience, or something more empirical?
the Hankook RS-3 version 2 with the revised tread compound came out at the beginning of this year.

[sdhotwn]

Direct knowledge based on SCCA Nationals this year and various very competitive racers in quite a few classes.

The new RS-3 definitely performed very well. The softer sidewall (although better than previous gen) pushed it down a touch in preference against the Direzza's for some of the guys. The Toyo's have a few "magic" sizes that they are hard to beat, and they have the best lateral grip, just not as good longitudinally. Federals performed VERY well and was a big surprise to a lot of people. So the top 4 are really very close and driver skill can easily mask the variance between them.

Additionally, car weight/drive/suspension filter that order as well. Surface type (concrete versus asphalt) and general temperature also mess with it. Some overheat more than others, some respond better to spraying etc. Lots of factors. That's why there really is never a specific "ONE" tire.

[DVC]

Originally Posted by sdhotwn

You have to remember that whatever end you put the sway bar on picks up more weight transfer, which ... also stiffens the roll rate on that end as well.

As I understand it, sway bars stiffen roll rate to actually REDUCE weight transfer (to the outside tire while cornering)... or is this what you're saying too?

Originally Posted by sdhotwn

Adding a front bar ... the increased stiffness at the front prevents over loading of the rear outside tire, and the reduced (relative) rear sway bar stiffness allows the inside rear tire to maintain more contact during acceleration and stabilizes corner exit power delivery.

A stiffer front sway bar works to mitigate over-loading the outside FRONT tire than more so than the rear; the rear sway bar is more effective at keeping the inside rear tire down to optimize applying power on corner exit.
Not sure I understand why you say that a relatively weaker rear sway bar would be MORE effective at fighting weight transfer in the rear to keep the rear inside tire down (?)

[DVC]

Originally Posted by sdhotwn

Direct knowledge based on SCCA Nationals this year and various very competitive racers in quite a few classes.

The new RS-3 definitely performed very well. The softer sidewall (although better than previous gen) pushed it down a touch in preference against the Direzza's for some of the guys. The Toyo's have a few "magic" sizes that they are hard to beat, and they have the best lateral grip, just not as good longitudinally. Federals performed VERY well and was a big surprise to a lot of people. So the top 4 are really very close and driver skill can easily mask the variance between them.

Additionally, car weight/drive/suspension filter that order as well. Surface type (concrete versus asphalt) and general temperature also mess with it. Some overheat more than others, some respond better to spraying etc. Lots of factors. That's why there really is never a specific "ONE" tire.

Cool, thanks for sharing. I have been researching a new set of tires, so this helps.
My interests are for the track rather than autoX, so that may change things a little though. For example, I've read that the Direzzas get very greasy after about 15 hard minutes. For that reason, I was leaning toward the Hankooks.
Of course I'm also considering going with a streetable track tire like the ContiForceContacts as an alternative as well...

[sdhotwn]

Originally Posted by DVC

Cool, thanks for sharing. I have been researching a new set of tires, so this helps.
My interests are for the track rather than autoX, so that may change things a little though. For example, I've read that the Direzzas get very greasy after about 15 hard minutes. For that reason, I was leaning toward the Hankooks.
Of course I'm also considering going with a streetable track tire like the ContiForceContacts as an alternative as well...

I need to work back through the math and physics in detail on the previous post to respond to make sure that I'm not incorrect in how I'm stating things. That'll take until later when I have some time.

For the tires - there is a brand new ZII compound (star spec) that JUST came out about a month ago. So that is also being looked at and I believe the main difference is temperature profile. The old RS-3 was nearly impossible to overheat, the newer one does overheat occasionally. The Kumho XS is very heat tolerant though, but it's ultimate grip isn't keeping up anymore.

Track DEFINITELY changes a few things though and I don't have strong exposure there.

[sdhotwn]

Originally Posted by DVC

As I understand it, sway bars stiffen roll rate to actually REDUCE weight transfer (to the outside tire while cornering)... or is this what you're saying too?

Here's a quick source that explains it relatively well (and matched what I was thinking - but doesn't mean it's 100% correct! I need the math check to be certain):

http://www.turnfast.com/tech_handling/handling_antiroll

Put another way. A roll bar is like putting a stiffer spring on JUST that axle's outside corner. More load goes there, but with less deflection, hence less roll. Less roll then also changes the weight transfer distribution to the whole car. This works up until you exceed the limit of traction developed mechanically and geometrically at that corner. THEN the reverse kicks in - you get more and more traction issues as you put more and more load in to that corner.

Again, I'll try to provide some math to show it and again make sure I'm not miss stating things.

In general if your rear is already loose - you put on a front bar to stabilize it, if you understeer too much, you usually put a rear bar on. However, braking traction versus acceleration traction versus mid-corner all end up requiring other variations/considerations due to how weight is re-distributed.

[Forgiven]

Oh yeah, i forgot about the kumho xs, they are great for heavy cars like ours.

[DVC]

Originally Posted by sdhotwn

Here's a quick source that explains it relatively well (and matched what I was thinking - but doesn't mean it's 100% correct! I need the math check to be certain):

http://www.turnfast.com/tech_handling/handling_antiroll

Put another way. A roll bar is like putting a stiffer spring on JUST that axle's outside corner. More load goes there, but with less deflection, hence less roll. Less roll then also changes the weight transfer distribution to the whole car. This works up until you exceed the limit of traction developed mechanically and geometrically at that corner. THEN the reverse kicks in - you get more and more traction issues as you put more and more load in to that corner.

Again, I'll try to provide some math to show it and again make sure I'm not miss stating things.

In general if your rear is already loose - you put on a front bar to stabilize it, if you understeer too much, you usually put a rear bar on. However, braking traction versus acceleration traction versus mid-corner all end up requiring other variations/considerations due to how weight is re-distributed.

I agree completely. If the rear is loose, a front bar will stabilize it (by increasing understeer). And if you're understeering already, then a rear bar will tilt the grip balance toward the rear, and effectively reduce understeer.

[sdhotwn]

Originally Posted by DVC

I agree completely. If the rear is loose, a front bar will stabilize it (by increasing understeer). And if you're understeering already, then a rear bar will tilt the grip balance toward the rear, and effectively reduce understeer.

Correct. There are a few caveats though... one of which is sometimes the understeer or oversteer is a factor of suspension geometry change rather than just weight transfer etc. Again, the reason the front bar counter-intuitively can reduce understeer on the front of our cars - it reduces suspension travel and helps optimize tire contact which increases total available grip - at a rate greater than the load transfer overcomes it.

Additionally, on our cars you can get bad inside wheel spin (although an LSD or the eDIF may eliminate this to some extent) it can be from too much rear stiffness allowing the rear inside wheel to get pulled up. This then kills your acceleration.

Those two items are why I recommend a front bar on our cars with our geonmetry.

[DVC]

Originally Posted by sdhotwn

For the tires - there is a brand new ZII compound (star spec) that JUST came out about a month ago. So that is also being looked at and I believe the main difference is temperature profile. The old RS-3 was nearly impossible to overheat, the newer one does overheat occasionally. The Kumho XS is very heat tolerant though, but it's ultimate grip isn't keeping up anymore.

Track DEFINITELY changes a few things though and I don't have strong exposure there.

Regarding the Direzza, do you mean there's a new version of the ZII, or that the ZII is the new version (replacing the ZI)?

[sdhotwn]

Originally Posted by DVC

Regarding the Direzza, do you mean there's a new version of the ZII, or that the ZII is the new version (replacing the ZI)?

There is a new version of the ZII... the history was:

Z1 - Japan only
Z1* - the first Direzza to the States
ZII - the "new Direzza most ran this year
ZII* - the new, new direzza that came out in the last month or so.

[DVC]

Originally Posted by sdhotwn

There is a new version of the ZII... the history was:

Z1 - Japan only
Z1* - the first Direzza to the States
ZII - the "new Direzza most ran this year
ZII* - the new, new direzza that came out in the last month or so.

I just ordered the Direzza ZII Star Specs... Thanks for the heads up!

[sdhotwn]

I did also verify that the mechanisms/logic behind the sway bar info I was posting is correct. One of the guys I work with is an SAE certified suspension engineer from his previous job.

[sdhotwn]

Originally Posted by DVC

I just ordered the Direzza ZII Star Specs... Thanks for the heads up!

Cool! When you going to get to try them out?

[DVC]

Originally Posted by sdhotwn

Cool! When you going to get to try them out?

Weekend after next I will be at NJ Lightning for a couple days

[sdhotwn]

So I got to autocross the car for the first time this past weekend. Was rather interesting and generally surprising to me.

I ran it completely stock - SP001 runflats, no alignment changes, nothing. I ended up winning the class for the day (not a lot of people though), but more specifically beat a guy with a prepped E46 330i ZHP that I had struggled to match previously in our prepped E90 325i.

Overall, yes it understeers, but it was surprising how close to neutral you could get with some added throttle during sweepers. I fought most of the understeer off with harder braking on entry and avoiding trail braking almost entirely.

I did have rear wheel spin pretty regularly as expected, but the car recovers very nicely when you pull out a little throttle.

Overall I was shocked at how well the car ran in stock form on the crap stock tires. Surprising amount of potential there! I wish the guy that runs an E90 M3 had been there to compare against as he usually sets the class time, and I believe is about 1.5 seconds ahead of the guy I beat to take the win. I could easily imagine proper tires, sway, and alignment closing down that gap quickly.

[DVC]

Originally Posted by sdhotwn

So I got to autocross the car for the first time this past weekend. Was rather interesting and generally surprising to me.

I ran it completely stock - SP001 runflats, no alignment changes, nothing. I ended up winning the class for the day (not a lot of people though), but more specifically beat a guy with a prepped E46 330i ZHP that I had struggled to match previously in our prepped E90 325i.

Overall, yes it understeers, but it was surprising how close to neutral you could get with some added throttle during sweepers. I fought most of the understeer off with harder braking on entry and avoiding trail braking almost entirely.

I did have rear wheel spin pretty regularly as expected, but the car recovers very nicely when you pull out a little throttle.

Overall I was shocked at how well the car ran in stock form on the crap stock tires. Surprising amount of potential there! I wish the guy that runs an E90 M3 had been there to compare against as he usually sets the class time, and I believe is about 1.5 seconds ahead of the guy I beat to take the win. I could easily imagine proper tires, sway, and alignment closing down that gap quickly.

Awesome - thanks for sharing!