19" vs 20s" on road course better or not so?

[X25]

Originally Posted by JusticePete

My 305/30/19 testing was done in the fall of 2009 with 530+ RWHP. It followed the square 275/35/19 setup we ran on the G8. There was no such thing as a ZL1, 1LE or Z/28. Funny how things change. GM was working with a 275/30/20 315/30/20 SC mule in 2009. I was told by almost everyone that a square wheel and tire setup was not going to be the fastest. Fast forward to the Z/28 with 305/30/19s. The more things change, the more they stay the same.

Yeah, I remember you mentioning this. Funny, I would have never ever thought I'd buy a Camaro back in 2009, or anything else that weighs more than 3800 lbs, including then-recently-introduced GT-R.

Back to subject, I'm honestly pretty happy with my 1LE with all the Z/28 improvements. The car is very entertaining to say the least.

[L99CAMA2011]

Originally Posted by JusticePete

Entry, mid corner and exit speeds will be higher on the 19s. They lower the CG by an inch without compromising the geometry of the suspension. They weigh less than a similar tire in a 20. The wheel is lighter.

I've seen some 20 options that are actually lighter than the 19 options. That's one thing that really ticked me off. I was like why does the smaller diameter tire weigh more? Bridgestone RE-11 305s for example weigh 32 lbs new. 20" options I considered were in the 28lb to 30 lb range. Also like Dropspeed said earlier I am considering 18" as well for track only. That in my eyes would be real cart handling material. The I would get L99 rear end gears.

[X25]

Originally Posted by L99CAMA2011

I've seen some 20 options that are actually lighter than the 19 options. That's one thing that really ticked me off. I was like why does the smaller diameter tire weigh more? Bridgestone RE-11 305s for example weigh 32 lbs new. 20" options I considered were in the 28lb to 30 lb range. Also like Dropspeed said earlier I am considering 18" as well for track only. That in my eyes would be real cart handling material. The I would get L99 rear end gears.

Are they also 305-wide? What tires are they? If a tire is lighter than tires of other comparable sizes, it's usually at a lower load rating, or a different class (like competition).

[Norm Peterson]

Originally Posted by JusticePete

Norm,

The test driver I used is an outstanding driver. He has moved up the food chain at GM so I can no longer hire him. His laps are incredibly consistent. Where we tested we ran three hot a cool down and three hot. The difference between his fastest and slowest hot laps all day was all of 1/10th of a second. That is the result of countless laps, countless hours of seat time at Gingerman. 2.2 seconds with the 305/30/19 Bridgestone RE-11s over the OE staggered setup.

Kind of my point, actually. (caught by the daily 8AM forum AWOL-ness)

I'd fully expect half of that 2.2 seconds to have resulted from the difference between a top-rated extreme performance tire and a mid-pack-ish max performance tire.

Your erstwhile driver whose lap times fall within a tenth or so lap after lap would have found that second from lowering even if the tires were simply different sizes of the same make and model tire. People whose unimpeded track day lap times scatter over a full second or more wouldn't be able to separate out the improvement due to lowering from the difference between a hero lap and just a decently driven one.


The main reason I pick up these lowering vs performance discussions is to get people to think unemotionally about lowering. A 1" lowering represents something like a 20% reduction in ground clearance, which is what you notice right away. The way people chase lowering options and the heavy mention given to "CG lowering" sounds like they're expecting a matching 20% performance improvement (or at least half that much). T'ain't so.


Norm