The STX thread!
01-26-2010, 08:10 PM
#752
I wonder when they will be out, and how much of a benefit they would provide. The wheel would be lighter, but the OD would still be 25.3" which is the same as the 265/35/19. a 3.7 inch sidewall vs a 4.2 inch sidewall...
So other then the fact that they will be cheaper, and you will be able to find lighter wheels, think they will be faster with a taller sidewall?
So other then the fact that they will be cheaper, and you will be able to find lighter wheels, think they will be faster with a taller sidewall?
01-26-2010, 08:33 PM
#753
Ouch. Just bought the 18s. That hurts.
Sidewall is an interesting question. Perhaps the 18s could get away with a lower pressure? Or transition faster at a given pressure? Or just keep more of the tread on the pavement? Don't know my tire tech well enough to know one way or another. I suspect a test will be needed...
[edit] I suspect the 265/40-17s will be about 1 lb heavier than the 265/35-18s (taller sidewall), which would about cancel the difference between a light 17 & 18 inch wheel. So the weights will probably be a wash. So would the OD, so yeah, it really is down to sidewall, unless the 18s have a wider actual tread (can happen).
Sidewall is an interesting question. Perhaps the 18s could get away with a lower pressure? Or transition faster at a given pressure? Or just keep more of the tread on the pavement? Don't know my tire tech well enough to know one way or another. I suspect a test will be needed...
[edit] I suspect the 265/40-17s will be about 1 lb heavier than the 265/35-18s (taller sidewall), which would about cancel the difference between a light 17 & 18 inch wheel. So the weights will probably be a wash. So would the OD, so yeah, it really is down to sidewall, unless the 18s have a wider actual tread (can happen).
Last edited by GeorgeH; 01-26-2010 at 08:43 PM.
01-26-2010, 11:30 PM
#756
Row faster, I hear banjos
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No...taller as in will a 265/40-17 be faster than a 255/40-17??? You lose the gearing advantage that the 255/40-17 has over the 265/35-18, and the tire most likely weighs more due to the taller sidewall.
01-26-2010, 11:39 PM
#757
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+1 I also thought it related to '09+ cars AND the '08 40th anniversary edition that came with bilsteins. Apparently the stock perch height was changed on those models from the earlier cars. Bilstein has had HD shocks available for the RX-8 as a direct OE replacement since late 2004 iirc...
AFAIK, back in 04-05 Fastmike measured the RX-8 Bilstein HD shocks for stock purposes and he said the perch height was not correct for stock. Being that he is the biggest proponent of Bilstein shocks on stock class cars I would think that if it was legal he would know.
As far as the 40th Anniversary and Shinka OE Bilsteins, they are similar to what comes on the Solstice and are a far cry from the HD's. First, the gauge of metal used on the shock bodies is thinner than the HD's. Also, they are not "easily" revalveable due to them being a sealed shock that requires you to cut off the top of the shock to get to the guts. Once open the internal parts are the same as the HD's however, sealing the shock back up is difficult. Fastmike has done this conversion, he scavenged shock bodies from an old set of HD's or Sports (don't know which) and welded them to the upper part of his original shocks reusing the OE shock rod and upper mount in order ot make his Solstice shocks rebuildable and stock legal.
01-26-2010, 11:56 PM
#759
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I wouldn't be surprised if 265/35-19 was the way to go.
All things being equal I think the shorter the sidewall the better. However being cheap the 17s are sooo much more economical.
All things being equal I think the shorter the sidewall the better. However being cheap the 17s are sooo much more economical.
01-27-2010, 12:01 AM
#761
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Nope.
http://www.tirerack.com/tires/Sizes....=Potenza+RE-11
Look four up from the bottom.
or
265/30-19
http://www.tirerack.com/tires/Sizes....VAN+Neova+AD08
third from the bottom
http://www.tirerack.com/tires/Sizes....=Potenza+RE-11
Look four up from the bottom.
or
265/30-19
http://www.tirerack.com/tires/Sizes....VAN+Neova+AD08
third from the bottom
Last edited by StrokerAce; 01-27-2010 at 12:07 AM.
01-27-2010, 12:07 AM
#762
Well thar ya be. Yet another choice to consider.
Although I've narrowed down my prefered tire to either the Dunlop or Hankook, based on Jason's testing.
How light are reasonably priced (<$400) 19" wheels?
[edit] scratch that question - 265/35-19 have an OD of 26.3 inches. That would be a fail.
Although I've narrowed down my prefered tire to either the Dunlop or Hankook, based on Jason's testing.
How light are reasonably priced (<$400) 19" wheels?
[edit] scratch that question - 265/35-19 have an OD of 26.3 inches. That would be a fail.
Last edited by GeorgeH; 01-27-2010 at 12:09 AM.
01-27-2010, 12:15 AM
#763
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Well thar ya be. Yet another choice to consider.
Although I've narrowed down my prefered tire to either the Dunlop or Hankook, based on Jason's testing.
How light are reasonably priced (<$400) 19" wheels?
[edit] scratch that question - 265/35-19 have an OD of 26.3 inches. That would be a fail.
Although I've narrowed down my prefered tire to either the Dunlop or Hankook, based on Jason's testing.
How light are reasonably priced (<$400) 19" wheels?
[edit] scratch that question - 265/35-19 have an OD of 26.3 inches. That would be a fail.
Also the 265/30-19 25.4 only .1 more than the other 265's
01-27-2010, 12:18 AM
#765
OK, the 30 perhaps. But, raising the car up 1/2" increasing the gearing, increasing the rotating weight, and increasing the MOI (due to to larger diameter) all add up to the 265/35-19 being a poor choice when there is a 265/35-18.
Again, the 30 series 19", well, perhaps that would be faster. But that's not a bet I'd take.
Again, the 30 series 19", well, perhaps that would be faster. But that's not a bet I'd take.
01-27-2010, 08:50 AM
#767
If I ran 17s, I'd get the 265. The height difference will only be 4 mm (nominal). My guess is that the added corner exit speed will overcome any acceleration deficiency.
It would take a very good (consistent) driver to come up with reliable data that shows the true performance difference. In the absence if that data, I'd say that in this case, wider is (probably) better.
01-27-2010, 09:39 AM
#768
Row faster, I hear banjos
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While it's 4mm more, it's still 4mm in the wrong direction. By my calcs, estimated sidewall lengths are as follows:
255/40-17 = 102mm
265/40-17 = 106mm
265/35-18 = 92.75mm
While I'm not going to be on the national stage this season (just local/regional events, a divisional and maybe a NT), I'll probably run the 255-17 Hankooks this season and hopefully have more than one choice for a 265-17 next season...
255/40-17 = 102mm
265/40-17 = 106mm
265/35-18 = 92.75mm
While I'm not going to be on the national stage this season (just local/regional events, a divisional and maybe a NT), I'll probably run the 255-17 Hankooks this season and hopefully have more than one choice for a 265-17 next season...
01-27-2010, 07:56 PM
#769
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It obviously has to be taller in both overall diameter and sidewall height than the 255/40-17, right. How much so remains to be seen since nobody offers that size and we're all guessing at what that may end up being.
The irony is the 17" argument has always been lighter weight, shorter, less expensive, and the width difference doesn't matter, but now we'll be hearing "Wait, we can get a taller, heavier, wider, more expensive tire? Where do I sign up?"
Now if it was a 265/35-17 I'd be ordering a $2200 set of 17 x 9 SSR Type C-RS wheels from Tirerack tomorrow ....
The irony is the 17" argument has always been lighter weight, shorter, less expensive, and the width difference doesn't matter, but now we'll be hearing "Wait, we can get a taller, heavier, wider, more expensive tire? Where do I sign up?"
Now if it was a 265/35-17 I'd be ordering a $2200 set of 17 x 9 SSR Type C-RS wheels from Tirerack tomorrow ....
In all honesty, I think the difference between a 255/40-17, 265/40-17, and 265/35-18 (all other things being equal) is well within the realm of driver noise anyway.
Now a 265/35-17 would have completely changed the game, imho.
It's not just the diameter. You're also adding a pound or two of additional weight at the outermost radius, which is the worst place you could add it.
01-27-2010, 09:19 PM
#770
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I'm not sure that a pound per tire, even though it is in the worst place, is as significant as many have come to believe.
The extra rotational inertia of a heavier wheel or tire contributes to the effective linear inertia of the car, no doubt. But, the theoretical absolute upper limit is 1 pound more at the surface of the tire tread contributes to inertia as if it were 2 pounds in the cabin, contrary to the old racer's myth and the fine tuned "buttometers" of many autocrossers. If you're talking about the wheel itself, the farthest out the weight can be added is the rim. So, for an 18" rim with a 25" tire, the "bonus" weight drops from a maximum of 1 pound per pound to about 1/2 pound per pound. The bonus weight is less than that if it's not all concentrated at the lip, but in the instance of simply an increase in tire weight, you revert to the 1:2 ratio...reduced for the fact that not all of the additional tire weight is actually at the tread.
So if you want a realistic estimate of how much weight savings (as it effects acceleration) you're going to realize with a lighter tire, or be penalized for a heavier tire, multiply the weight change by about 1.7. Using this multiplier and given tires that weigh fully 2lbs more, you're talking about an overall "increase" in cabin weight of less than 14lbs. Do you think that is going to translate to significant negative change in accelerative capability?
btw, the only other really credible estimate I've ever seen regarding reduction in rotational mass vs. "cabin weight" is in Herb Adams' book, where he gives a 1:3 ratio, at the axle...which needs to be corrected for rim diameter and distance of total mass from axis, I believe. Even so, if we used Adams' larger multiplier value, that still results in only a 24lb gain in the example considered.
I would really like to see someone prove, through objective data, that small variance in rim or tire weight equates to measureable change in acceleration rate.
The extra rotational inertia of a heavier wheel or tire contributes to the effective linear inertia of the car, no doubt. But, the theoretical absolute upper limit is 1 pound more at the surface of the tire tread contributes to inertia as if it were 2 pounds in the cabin, contrary to the old racer's myth and the fine tuned "buttometers" of many autocrossers. If you're talking about the wheel itself, the farthest out the weight can be added is the rim. So, for an 18" rim with a 25" tire, the "bonus" weight drops from a maximum of 1 pound per pound to about 1/2 pound per pound. The bonus weight is less than that if it's not all concentrated at the lip, but in the instance of simply an increase in tire weight, you revert to the 1:2 ratio...reduced for the fact that not all of the additional tire weight is actually at the tread.
So if you want a realistic estimate of how much weight savings (as it effects acceleration) you're going to realize with a lighter tire, or be penalized for a heavier tire, multiply the weight change by about 1.7. Using this multiplier and given tires that weigh fully 2lbs more, you're talking about an overall "increase" in cabin weight of less than 14lbs. Do you think that is going to translate to significant negative change in accelerative capability?
btw, the only other really credible estimate I've ever seen regarding reduction in rotational mass vs. "cabin weight" is in Herb Adams' book, where he gives a 1:3 ratio, at the axle...which needs to be corrected for rim diameter and distance of total mass from axis, I believe. Even so, if we used Adams' larger multiplier value, that still results in only a 24lb gain in the example considered.
I would really like to see someone prove, through objective data, that small variance in rim or tire weight equates to measureable change in acceleration rate.
Last edited by mwood; 01-27-2010 at 09:23 PM.
01-28-2010, 09:33 AM
#771
^Agree with Mike & Mark, which is why I'm going 18". But, if I was just running local & not making a run for nats, I'd be on 17s for sure.
Tires are the absolute last place you should try to save weight in an autocross setup, where corner exit speed is king. The straights are just too short to be of primary importance. Of course, all other things being equal, lighter is better, but that's not what we are (apparently)talking about here.
As Mark points out, the important question is: will a 265 allow you to carry more speed through corners and transitions? If so they will be the faster setup. If not, then the 17" setup would be preferred, IMO.
Tires are the absolute last place you should try to save weight in an autocross setup, where corner exit speed is king. The straights are just too short to be of primary importance. Of course, all other things being equal, lighter is better, but that's not what we are (apparently)talking about here.
As Mark points out, the important question is: will a 265 allow you to carry more speed through corners and transitions? If so they will be the faster setup. If not, then the 17" setup would be preferred, IMO.
01-30-2010, 04:43 AM
#774
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First slush series event is next weekend, with the first BSCC practice day the weekend after. Unlikely I'll have my cat/midpipe ready by then though and there's a high likelihood I'll be on last season's tires. Still, I'm happy to have events on the calendar now, I'm going into this season a lot better (in both driver skill and car prep) prepared than last season.
Should we fork this thread for 2010?
Should we fork this thread for 2010?
