lost 4 mph in 1/4 mile after new rims?! Help

[91stang50GT]

Im a little frustrated, First off, i have an 87 gt with just headers-back exhaust and 3:55s. During the summer i made three passes, the best of the three being 14.37 at 96 mph with a 2.09 60 foot (all three passes were 96 mph though). Since then, i have added tubular lower control arms and swapped out the stock ponies for a set of 17x9 03 cobra replica rims and 255 tires. i just went to the track last weekend and was able to make one pass, this time i ran a 14.65 at 92 mph with a 2.08 60 foot I know my sixty foot wasn't great on either of the passes but could the new (possibly heavier or taller) rims be the cause for a 4 mph loss? I didn't miss any shifts and the mph was consistantly lost down the track, 2 mph in the first 8th mile and another 2 mph in the second 8th.

Any input is appreciated

 

[91stang50GT]

the 14.37 pass that was made during the summer was also in more heat and more humidity than last weekends 14.65 pass. And both were made at the same track.

 

[U2SLO450]

bigger rims=slower turning wheels, try putting on a 15in wheel and i bet your times drop

 

[91stang50GT]

i figured it would slow me up slightly but i didn't think it could kill 4 mph. And you use a smaller rim, wouldn't the tire just be taller to make up for the difference in the size of the rim?

 

[Boss 351]

The weight of the wheels make a HUGE difference too. I know the 16" pony wheel with 245/50R16 (50 or 55?) weighs 37 pounds! And of course like stated if you end up with a taller combo, it has a direct effect on your final drive ratio...

 

[notch22]

i figured it would slow me up slightly but i didn't think it could kill 4 mph. And you use a smaller rim, wouldn't the tire just be taller to make up for the difference in the size of the rim?

This doesnt have to be true if you dont want it to. Just get a 15" wheel with some small tires on the back. Less weight, quicker car. The only thing I might be worried about is blowing off the tires on the launch.

 

[8950HO]

Smaller wheel,faster car,yet all I seem to read about are guy`s wanting and running 18" and larger wheels these day`s.

 

[notch22]

Heck its gonna be 17s for me and nothing more. I never get to go to the strip, so its gonna be set up to handle, not to pull the wheels up.

 

[MikeC]

It really hard to tell much from one run. May have just been a bad run. You need to go to the track for a few more runs before you start worring.

 

[vristang]

The problem has more to do with where the weight of the wheel is, as opposed to what the weight of the wheel is.

Since the diameter of the wheel is larger, there is more mass farther from the center of the axle.
It takes more force to accelerate the same mass at a larger diameter.

The same principle is involved in using a breaker bar, rather than a stubby 2" end wrench.

Hope that makes sense
jason

 

[Threeo2]

do you know at what RPM you crossed the finish line with the new & old wheels? I know puttin on heavier wheels is never a good thing, but I thought the rotational weight only made a difference at the starting of the run? Once you get all of that mass rolling the difference becomes minimal. true or false? Im asking cuz im getting ready for some bigger wheels my self
also, does anyone know of anybody making 16"x8" pony's?

 

[Snikt89GT]

Hard to fit big brakes under 15in wheels. Those 03 cobra wheels are pretty heavy though. I'm going with the 98 cobra wheel which I believe is the lighest of all FMS 17in wheels

 

[stangman8825]

put the stockers back on it and see if you trap the same... that's a quick way to find out whether it's the wheels or something else

Kris

 

[91stang50GT]

thanks for the input and what vristang said made sense. I didn't really pay attention to what rpm i went through the traps at, i guess i should of. I guess my best bet would to just go back down with both sets of wheels and make runs with each.

 

[Flavadave4]

the outside air was 96* your first runs which also made for a good warm track temp, maybe the colder air was enough to hinder your traction enough to lose some time........but it doesnt really explain the lower MPH?

 

[Darkwriter77]

I wonder if going with, say, 15" 10-holes would be significantly lighter than 16" ponies...? We should all just yank a wheel off our cars and go weigh them on the ol' bathroom scale to get some official numbers to compare.

If it turns out ponies are heavier than 10-holes, I'd be more than happy to swap wheels/tires with anyone who wants a nice set of custom-painted 15" phone-dials in exchange for those fat, nasty, horribly heavy and ugly 16" pony rims...

 

[CRASH7772]

What size did you start with? What size are you running now?

If you had a 225/60/15 the tire height should be 25.62 or 225/55/16 25.74...assuming your running a 255/45/17 the height would be 26.03. This is like dropping your gearing (3.55 to 3.4XX) and between that and using a much wider street tire (about 2" wider) this could cause some ET and MPH loss with more rolling resistance. If the weight of the wheels and tires is 10lbs or more per wheel over the previous ones that's not going to help either.

 

[91stang50GT]

i started with i believe a 225/50/16 on ponies and went to a 255/45/17 on 03 cobra R replicas. And as far as spinning goes, i didn't spin at all on the 14.65 run because i wasn't exactly ready for the tree and i only launched at 2k but considering i still had a 2.08 sixty foot, that shouldn't have anything to do with mph loss

 

[86bluecobra]

larger tires will not always make you lose hp or mph in 1/4 mile. But if they are heavier then the previuos combo this will happen. Infact if you run larger brakes on a car and do a dyno pull the car will make less hp then when it had factory brakes on it. Rotating mass is the enemy here. Why do you think aluminum driveshafts actually do work to improve drivetrain lose. less rotating mass. i don't know how true it is but i was told that every 25 lbs of rotating mass is worth 1 tenth in the 1/4 mile, the same as 100lbs of total wieght or 16 hp does for you. So if you added 25lbs of rotating mass you could be killing 16 hp of your engine which will effect you mph in the 1/4 mile. Atleast that is my take on what i have been told. take it with a grain of salt i'm not an expert.

 

[millhouse]

I could see the rotating mass effecting the et and mph as well…but not to that extent. I don’t think the et is that far off…but the mph loss is a bit goofy. Id look elsewhere to find where it went. It's quite possible you slightly altered your shift points which could effect your mph. Considering you made only one run…I would not worry about it to much. You cant go off of one drag strip pass to make any conclusions about what has/has not been effected IMHO.