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

[L99CAMA2011]

Guys. How many here went from 20" stock wheels to 19" wheels setups with shorter overall diameter wheels and noticed your top end speed dropped on the long straights. This is an issue I noticed and was thinking of going to the L99 rear end on my SS to get back that long leg stretch so I can be at 75mph in second gear like I was with stock 20s. Or option 2 is to go back to 20"s in light forgeline wheel setup.

[jamestown]

You are running out of gear (redline limited) on a straight? I was of the impression that the camaro would benefit from lower gearing and therefor benefit from a shorter 19" wheel and tire setup.

At mosport I dont get anywhere near redline limited (on my stock wheels). Mustang gearing for example on the track pack is much much shorter, and a friend of mine literally runs out of rpm at 220kph with shorter wheels and tires.

Gearing issues would be track specific however.

[Destructo09]

I never get out of 4th at the front straight at VIR. Actually at VIR North course this year I was only shifting once around the track and that was for the front straight, everywhere else I stayed in 3rd lol.

I do think it might have required a shift on the bridge straight though if I had shorter tires. I was just topping out 3rd before the braking zone.

[So Cal Camaro]

I have had both, and prefer the 20's to the 19's...it does mess with the gearing and you end up shifting more from my experience.

[L99CAMA2011]

Originally Posted by So Cal Camaro

I have had both, and prefer the 20's to the 19's...it does mess with the gearing and you end up shifting more from my experience.

As well as working and heating up the transmission more. Revving the engine more than needed. Look at it this way. Slower cars are now keeping up with me. Also my car was faster with even stock SS 20s. Let's say on a certain stretch where I would see 147 mph with 20s I now see 133 with 19s.

[Synner]

19 has better tire selection, 20 is better for big tracks. I went 20 but have 3.91 gears, if I had to do it over I'd go 19" wheel and stick with 3.45 gear for the happy medium and extra tire selection.

[jamestown]

There are some gear speeds vs rpm calculations from this thread:

http://www.camaro5.com/forums/showpo...1&postcount=15

And 305/30R19 are about 6% smaller than the stock 285/35R20, so topping out in 4th gear afterwords would be around 129.49 compaired to the 137.76mph stock. Are you getting no acceleration at all in 5th?

Aside from what causes you to shift more, I wonder what actually gives the better lap time.

[X25]

My lap times were not effected significantly when I switched to same width 19" wheels, and times with 19" wheels were a bit better. I have to shift to fifth in one of the tracks, which is a slow shift, but you more than make up for it by being able to maintain a higher average RPM. LS3 makes its most power at 6000 RPM, so whenever you're away from that, you're not using the most of your engine. Riding the torqur wave feels good, just like drifting the back of the car around the corner, but neither are the fastest ways to do the job

[L99CAMA2011]

Originally Posted by jamestown

There are some gear speeds vs rpm calculations from this thread:

http://www.camaro5.com/forums/showpo...1&postcount=15

And 305/30R19 are about 6% smaller than the stock 285/35R20, so topping out in 4th gear afterwords would be around 129.49 compaired to the 137.76mph stock. Are you getting no acceleration at all in 5th?

Aside from what causes you to shift more, I wonder what actually gives the better lap time.

be careful with the 19s gives better laps thing. Many of us are going from heavy 20"wheels to super light 19s. On tighter courses where agility is more required 19s win, autocross for example but on more open courses like Watkins Glen I assume 20s would be better especially light ones. My car actually pulls in 5th very well even with 20s but honestly it seems like the computer holds back a tad bit when the parameters met with 20s original size aren't met. My car accelerates harder with stock heavier 20s than 19s. I guess we need a really capable tuner who knows how to adjust the settings to give me the full brut force upon acceleration.

[jamestown]

hmm, how would the car know the difference if both setups are square? were you spinning out of corners with the 19's?

[X25]

Originally Posted by L99CAMA2011

be careful with the 19s gives better laps thing. Many of us are going from heavy 20"wheels to super light 19s. On tighter courses where agility is more required 19s win, autocross for example but on more open courses like Watkins Glen I assume 20s would be better especially light ones. My car actually pulls in 5th very well even with 20s but honestly it seems like the computer holds back a tad bit when the parameters met with 20s original size aren't met. My car accelerates harder with stock heavier 20s than 19s. I guess we need a really capable tuner who knows how to adjust the settings to give me the full brut force upon acceleration.

Does your stock (staggered) setup have different front and rear tire diameters? Perhaps you're activating stability control (engine drag) for some reason?

I did not have any issues with 19s on my 1LE. I actually hit similar trap speeds, if not better.

[jamestown]

Originally Posted by X25

I did not have any issues with 19s on my 1LE. I actually hit similar trap speeds, if not better.

This would be my expectation.

If the op's oem setup is staggered he would need to maintain the diameter ratio from front to rear as to not upset the car computer. This would be independant of the 19 vs 20 debate though, he would have to do that regardless of rim diameter.

[L99CAMA2011]

Originally Posted by X25

Does your stock (staggered) setup have different front and rear tire diameters? Perhaps you're activating stability control (engine drag) for some reason?

I did not have any issues with 19s on my 1LE. I actually hit similar trap speeds, if not better.

My front and rear tires/ wheels are exactly the same height. I actually measured them inflated and mounted. And how did you get the same trap. My car hits the same spot at approx 139 mph with 19s where it did that at 147 with 20s. I assume it has something to do with the system monitoring the 20s rotation per second or so vs the 19s. Also yes we do have to be careful with wheel heights not being the same as stock. I did this in the past and my car was slow as hell. The front tire was actually .5" taller than the rear.This is also my 3rd set of 19s and I think my last unless the L99 rear end plan works. I saw in a magazine the Z28 hits 75mph in second just like my stock setup did with 20s. My car pulls hard is hell with stock wheels and even spins the rear at 80mph cammed of course no heads .

[X25]

Originally Posted by L99CAMA2011

My front and rear tires/ wheels are exactly the same height. I actually measured them inflated and mounted. And how did you get the same trap. My car hits the same spot at approx 139 mph with 19s where it did that at 147 with 20s. I assume it has something to do with the system monitoring the 20s rotation per second or so vs the 19s. Also yes we do have to be careful with wheel heights not being the same as stock. I did this in the past and my car was slow as hell. The front tire was actually .5" taller than the rear.This is also my 3rd set of 19s and I think my last unless the L99 rear end plan works. I saw in a magazine the Z28 hits 75mph in second just like my stock setup did with 20s. My car pulls hard is hell with stock wheels and even spins the rear at 80mph cammed of course no heads .

Just to make sure, when you switch to 19s, do you update your speedometer? Well even if you didn't, 19s would (falsely) read higher than what you really hit, not the other way around. hitting 147 vs. 139 is a huge difference. You need a whopping 12% more power(!) to hit 147MPH vs. 139MPH within the same time, which cannot be explained by wheel weights, etc.