So -- - I'm not entirely blaming it on my tires, but it is a big coincidence.

After I put on BF Goodrich KDW2 285/40ZR18 in the rear I noticed how I can no longer really burn out, it takes a lot to burn out - - I just grab and go..

However, having testing my car on the 1/4 mile, I am nowhere near 12.67, my best so far has been 13.75 - - and it averages around 14.00 at 101...

I noticed, my gear to mph has changed drastically.. I would hit hit 3rd after 70mph and hit 4th around 111.. However, I noticed that I still hit 3rd around 70mph, but it only lasts til 100 - 101... Can thicker tires in the back really cause a 10mph difference?? Are they that much heavier vs a regular 275/30/r18??

So now I have to switch to 4th, but by 4th comes in 1/4 mile is over..

WTF?!?! My camaro is losing its muscle...

 

Tires can offer 3 things -

1. Rolling resistance (more width = more resistance, thus a slower time and/or mph)
2. Gear ratio (take a car with 3.73 gears and go from a 26" diameter to a 28" diameter tire, and your effective ratio drops a little. Cruising and trap rpm will change).
3. Traction (self-explanatory here. What used to spin slightly could have kept your rpm up in the powerband for a better time, but a dead hook and bog will hurt).

IMHO, 12.67 at 113 mph is damn good for your mods (if that is all you have done), almost unbelievable. Don't forget summer air will slow down a car 2-5 tenths depending on what conditions your best pass was made under.

Derek

 

When I bought the car stock, I would run constant 13.5 around 105 or so. So after $1,500 engine upgrades, and $600 in tire upgrades, I am now slower than stock

I also had the cutout on - - but I was under the impression that the more back pressure the better..

 

Huh? If that were the case we'd all be running stock cat-backs and dragsters wouldn't be loud.

 

WOW, are those tire sizes you have in the first post correct? if so you were running some really low profile tires since the 275/30 18's are a little less then 24.5" tall and the new tires are just under 27" tall, that is a huge difference and changes everything about your gearing setup. You have probably have the same amount of power as before but lost a lot of mechanical advantage from the shorter tire you had on there before. I ran the numbers and your change was exacltly like changing from 3.73 gears down to 3.23 and keeping the same tire size. not to mention the other things from above...

 

285 wide? damn thats a wide tire!

 

+1 on this.. you just went to a wider, heavier, and most importantly taller tire so you effectively just change the overall gear ratio of the car.