I've new to ripping down the strip always been around with friends but this season is the first I have actually taken a car down the strip.

I have a 2013 GT /w 3.55 (Mods listed in Sig)

I can't seem to keep the stock 245/45/19 P-Zeros connected
best I've muster with these tires is a 12.86@112 ET, 8.427@87 and a 2.107 60'
Given on a average day our DA Correction is between 3500-3700ft

Obviously my first place to look and browse is AmericanMuscle.com and am looking at a set of 15" Darkstar Race Star Wheels (15x8).

I am looking at the two different tires well same tire two different sizes
Mickey Thompson ET Street Radial - 275/50-15
Mickey Thompson ET Street Radial - 275/60-15

From what I can understand with searching is the 50-15 would be a 26" tire and adjust my gear ratio to 3.78 and the 60-15 is a 28" and would adjust my gear ratio to 3.50.. I can't seem to find out how these tire sizes would affect RPMs.

My understanding is its best to cross in 4th (could be wrong and would appreciate any knowledge on that topic aswell)

So my main question is which tire would most of you prefer I use and how would it affect my RPM/MPH range to keep me from shifting into 5th (assuming 4th is the optimal gear to cross in)

Any and All help would be appreciated

 

I can't answer the tire question, but i can tell you...if you're shifting into 5th on a 1/4mi, you're definitely not winding that car out. Unless you're running 4:10 gears, you should be passing the line in 4th.
Where are you shifting at?
Just keep an eye on the dash, it will light red when you hit the red zone on the tach.

Improving your 60' time is the obvious key and the drag radials should help that...which was my problem as well. I've made 6 passes in my '12 with a best of 13.03 and 2.+ 60' times on street radials

The other thing to do with street tires is stay out of the burnout box. Heating those tires up doesn't help much and since the groves are obviously deeper than a drag radial, you're carrying water with you off the line, thus improving the chance for slip and no hook...other than the fact that those stock Pirelli's just plain suck.

 

With a 3.55 rear gear go with a 26" tall tire.


if you trap less than 115 your fine, 115 w/ that set up will = 7000-7100 RPM, you can run to 7500 then you have to 122 in 4th

 

Steel:I have been shifting at the 6000-6200 mark cause from I've been reading is after 6200 on the '13 and I would assume the 11-12 are the same is that our powerband basically flat lines at around 6200 that we aren't really producing more power but not losing any so ive been trying to shift just as I enter the flat spot so that I keep pushing the car rather than riding a flat spot.

again like I said I am new to the drag scene when it comes to actually racing on it so I have obviously got a lot to learn so if this logic i am using is completely wrong I would definitely appreciate a little touchup on what the right logic would be.

Yea I gotta improve my 60' cant seem to crack anything faster than the 2.107 I got on my 12.86 run some have managed to crack into the 1.9s but I would love to know how they managed it with the pirelli tires.

Stkjock: thanks that is kinda what I figured from what I could gather on how it would affect my RPM and MPH so looks like I will have to buy a set of 26" and see how I run..

to be honest until after all my runs I didnt bother looking at the RPM I crossed at from what most peoples formulas or calculators have been pretty accurate as far as ET and MPH and they all seem to point between 4800-5000 I am crossing the line at.

 

that seems low for the 5.0 motor, I shifted my old 3V at 6500-6700 (I did have a centri blower)

from what I've seen 5.0s should be shifted more in the 6800-7100 range, 7500 w/ Boss manifold.

crossing the line at 4800-5000 leaves a lot on the table IMO

 

To your points, yes the stock intake manifold starts to fall flat on its face at about 6000rpm, but it will hold pretty steady from 6-7000...so wind it out to 7000.
Don't get caught up in the "numbers game" since you don't have much seat time, get used to the car and focus on one thing until you have it down. The biggest mistake of any newer drag racing person is getting caught up in what the car "should" be doing...if you don't know the car well enough or the track well enough, then that 12.86 is a pretty damned good number and you can use that as your benchmark.

Based on the calculations of the RPM @ the line...IF...if you are shifting into 5th, then that explains alot...thats a pretty long throw, especially for a stock shifter and chances are you're dropping right out of your "sweet spot" a fet feet from the line and the trap...

Go get some seat time, have fun and don't get caught up in everything...learn the car and it will come with time

 

275/50-15 is a good size for your combo. But don't underestimate the value of suspension upgrades. Tires are only part of the equation.

 

My best 60' with the stock Pirelli's was 1.9x. My tire pressure was 30psi. I launched at 3k rpms and slipped the clutch for minimum tire spin while maintaining the 3k rpms. Once my foot was off the clutch I roll the throttle to the floor. My 60' time range between 2.0x to 1.9x.
Normally I try to shift around 6500 - 6800 rpms. I got my best times shifting at about 6800rpms. I was locked out of second gear when I tried to shift at 7k rpms.
IMO you are okay with either size tire, but I would go with the 50-15s. With the 50-15s you will still cross the line in 4th. I have 3.73 gears and I cross the line in 4th. Shifting into 5th gear will waste too much time.

 

BairdGT,

I would stick with the shorter 275/50/15 tire for better results, as these guys already said. You'll have plenty of room to finish in 4th gear and cut a much better 60'.

Also, I would shift each gear at 6500-6600 RPM. Then wind 4th out as long as your need to finish. This always got us the best time with the factory intake manifold at the track.

Hope this helps!

Shane