would trap speed be affected from a change in gear ratio due to tire size??

went with a 275 60 15 mickey thompson drag tire 28 inch tall tire and with my rear end gear being a 3:73 would change to a 3:55 from having a taller tire . so how would my trap speed be affected by the change being all other variables are the same ? btw tire is on weld prostar 15x8 if that matters. thanks in advance randy!

If I understand what you typed, you went from a stock height 26" tall tire to a 28" tall tire. Your rear gears are still 3.73. If so then yes it would be like keeping your old tires and putting 3.55 gears in the diff. The advantage of a taller tire is that it also makes a larger footprint on the ground from front to rear. If the width is still the same, you've increased the amount of rubber on the ground just from putting on a taller tires.

If all you did was added tire height, your mph should increase and your ET may slow down. It's all going to depend on how well it ran with 26" tall tires. If properly matched, you should be crossing the finish line at or just before your shift point. If it was already doing that with 26" tall tires, you'll be crossing the finish line before the shift point with the taller tires. Putting on taller tires normally means having to install deeper gears to compensate for the tire height. With 28" tall tires you should look into getting 4.10 gears.

even in an auto 4:10s? i mean either way i will be in third gear going through the traps cause its an auto correct???If I understand what you typed, you went from a stock height 26" tall tire to a 28" tall tire. Your rear gears are still 3.73. If so then yes it would be like keeping your old tires and putting 3.55 gears in the diff. The advantage of a taller tire is that it also makes a larger footprint on the ground from front to rear. If the width is still the same, you've increased the amount of rubber on the ground just from putting on a taller tires.

If all you did was added tire height, your mph should increase and your ET may slow down. It's all going to depend on how well it ran with 26" tall tires. If properly matched, you should be crossing the finish line at or just before your shift point. If it was already doing that with 26" tall tires, you'll be crossing the finish line before the shift point with the taller tires. Putting on taller tires normally means having to install deeper gears to compensate for the tire height. With 28" tall tires you should look into getting 4.10 gears.

The goal is to be at or just past your peak hp rpm in high gear (3rd in an auto)at the finish line, you usually adjust tire sizes and gear ratios to achieve this...what prompted you to go to a taller tire? was it also wider to improve traction (60' looks decent, though)? your trap speed will probably depend on the change in the rpm range the taller tire creates at the finish line. if 1)your rpm with the shorter tires was way past hp peak, you'll probably improve e.t. and mph 2)your rpm was near hp peak, you'll probably have a slightly slower e.t. and slightly higher mph 3)your rpm was well below hp peak, you'll probably hurt e.t. But I'm not an expert, can anyone verify my thinking?

Sounds about right.

If you're shifting at 5500 rpm before and crossing the finish line at 5500 rpm in 1:1 gear then installing 28" tall tires means you're probably going to cross the finish line in the high 4000 rpm range.

If you're shifting at 5500 rpm and ran out of track before reaching peak rpm then the taller tires will help.

If you're shifting at 5500 and cross the finish line at 5000 or so, putting on taller tires is going to lower that even more.

My daily driver truck has a 4L80E with 4.10 gears and 28" tall tires. Sometimes I wish it had 3.73 gears just to bring the rpms down when on the highway even in OD. 60 mph is around 2800 rpm or so. The 4.10 gears do get me off the line in a hurry though.

Years ago my car had 27.3" tall tires and 3.27 gears. I was shifting at 6800 rpm but crossing the finish line at around 5200 rpm. I needed something like 3.90 gears to make the combination better. I jumped up to a full 28" tall tire and installed 4.10 gears and the combination was just about perfect. I'm now at a 30" tall tire and 4.56 gears. The powerglide is only a single shift but I do the 1-2 shift at 6500 and cross the finish line around 7200 rpm. The valves start to float at 7800.

As mentioned above, you need to adjust tire and gear ratio to achieve the best performance. First start with the tires. Stuff the tallest tire possible under the fenders then select the best gear ratio to get you down the 1/4 mile depending on how many gears you have and at what rpm the engine is shifted at. If everything is set up correctly, you should do your last shift at the 1/8 mile mark and the last 1/8 mile is a high gear, brute hp pull to the finish.

the car doesnt shift at 5500 i dont think it has a tune from pcmforless. i think its a little higher. the tires i got real cheap 100 a piece from a friend with a trans am who had clearence issues they only have 5 passes on them brand new almost. the last sixty i cut was on bald bfg drags and i think i can do better! the only changes the car has faced since the last times is no front bumper support ,shocks drag springs eibach, welds fronts and rears and a dyno tune so i guess if the car doesnt pick up wich i think it will then go with a smaller tire cause i dont want to change the 3:73 .. what do u think??

I was only using 5500 as an example since that's just a relatively stock shift point.

Install the 28" tires. Your 60' times will probably slow down. If you're after a personal best ET then you're probably not going to get it. If you're a bracket racer then the car will probably be more cosistant since there's less of a chance of spinning the taller tires off the line without deeper gears.

well my goal is to go faster ! i want 12.00 or 11.99 so if thats the case im going to be pissed! i will not buy these tires !

here's what i would do....find out about what your hp peak rpm is (cam company should be able to tell you this, and a dyno session will tell you exactly). program the trans to shift 100-200 rpm past this rpm. after this adjustment, see what your rpm is at the finish line.
if rpm thru the traps is below peak hp rpm (which it probably is), you actually need shorter tires or lower (numerically higher) gears. keep in mind that this is optimum for the track, but may not be optimum for the street. it's up to you to balance it out.
bottom line, you probably don't need the taller tires and they probably will not help achieve your e.t. goal.

thats crazy had no idea a taller tire would cause so much confusion!!!!!! i just dont want something so crazy as a tire ruin my chance at improving my track goal after the bits and pieces here and there to get it ready for the track in just two weeks. so the question is if i do run the taller tires and my time improves but not enough to reach 12.00 or 11.99 i will wonder if the smaller tire would get me there ??? i mean come on so hard to understand !!!!!!!!!

You don't want to go smaller than a 26" tall tire. Remember, a taller tire gives more of a footprint on the ground from front to rear. Going to a smaller tire means you increase the torque multiplication similar to putting in deeper gears and decrease the contact patch on the ground. It's just too easy to spin off the line and you're right back to where you started from.

Gear ratio means nothing unless the tire size and peak engine rpm are calculated into the equation. Look in magazines at some pro street car. They have 5.13 or deeper gears but also use 33" tall tires. Total effectivness is probably the same as having 3.73 gears and 26" tall tires but they have a huge contact patch on the ground for traction. Driving around they're probably in the same rpm range even with the 5.13 gears because of those tall tires.

Putting on the taller tires without going to a deeper gear probably won't increase your ET very much. You may gain a bit just from the fact that you'll have better traction. Running a taller tire without going to deeper gears will increase your gas mileage on the highway because the engine will be turning at a lower rpm at the same mph.