How much will adding 16 lb to my car affect ET/mph(rotating weight)

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Actually, 32 lbs would theoretically be .032 seconds. But regardless of the formula between static weight and rotating weight, there are variables that can't be predicted. As noted, the "regular" DOT street tires will likely spin more. Then the shorter diameter may help accelerate the car, but it can also aggravate the potential to spin because it increases the gear multiplication off the line. There is also the slight variable that the added gear ratio may reduce converter flash just a little bit, which may or may not be a good thing and, last, but not least, there is a "margin of error" whether it be in how consistent your staging and shift points are as well as the weather from day to day (temperatures, humidity, barometer & strength/direction of breezes.

Ideally, you can see what the shorter tire is revving the engine to at the finish. That may help in determining the diameter of softer compound DOT/street legal drag radials you should consider. Then to help consistency, you can add weight (ballast - securely & legally) to the back of the car while you tinker with suspension tuning. (i.e.: spring clamps, shocks, pinion snubber, launch rpm's, etc.)

Track prep has been known to vary as well.
 
Cudafever said:
Our track has divided all the races in half. Half d.o.t tire, half slick only races.
So i dug up my old street tires and rims as the first race is d.o.t only race.

The street tire/rim combo weight 8 lb more per tire. so 16 lb total
The plus side is that the tires are two inch shorter. So i should be closer to the rev limit,at the finish line, with these tires.

The bad news is that i don't think i can get them to hook off the line. Even if i leave at a idle.
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Well you’ve done it this time Cudafever. LOL
You’ve asked a question that can’t be answered here. However you CAN find the answer at the track. Good Luck!
 
Locomotion said:
Actually, 32 lbs would theoretically be .032 seconds. But regardless of the formula between static weight and rotating weight, there are variables that can't be predicted. As noted, the "regular" DOT street tires will likely spin more. Then the shorter diameter may help accelerate the car, but it can also aggravate the potential to spin because it increases the gear multiplication off the line. There is also the slight variable that the added gear ratio may reduce converter flash just a little bit, which may or may not be a good thing and, last, but not least, there is a "margin of error" whether it be in how consistent your staging and shift points are as well as the weather from day to day (temperatures, humidity, barometer & strength/direction of breezes.

Ideally, you can see what the shorter tire is revving the engine to at the finish. That may help in determining the diameter of softer compound DOT/street legal drag radials you should consider. Then to help consistency, you can add weight (ballast - securely & legally) to the back of the car while you tinker with suspension tuning. (i.e.: spring clamps, shocks, pinion snubber, launch rpm's, etc.)

Track prep has been known to vary as well.
Click to expand...
Locomotion thanks for all of that,
adding weight is something i'm considering. What is the least expensive way to add weight.(safely) with the price of lead. A lead bumper is out of the question.:D
Each tire/wheel combo weights 8 lp so it 16 total. the 32 was double weight to get translate it to car weight to us the 100 per a tenth .100 rule
 
Cudafever said:
Locomotion thanks for all of that,
adding weight is something i'm considering. What is the least expensive way to add weight.(safely) with the price of lead a lead bumper is out of the question.:D
Each tire/wheel combo weights 8 lp so it 16 total. the 32 was double weight to get translate it to car weight to us the 100 per a tenth 1.00 rule
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Well, a tenth is .10!

If I remember correctly, NHRA has rules where every 100 lbs should be bolted down with at least 2 grade 8, 1/2" bolts to the frame or solid crossmember. You can bolt ballast boxes above & into the frame rails to make it easier to add/subtract weight, bolt steel bars or plates to the frame rails or weld in crossmembers between roll bars or frame rails to bolt weight to also.
Depending on the car & bumper configuration, you may be able to add some weight around there. '74+ A-body bumpers using shock absorber brackets, for example, have some contoured braces/reinforcements inside the bumper that make a good place to bolt some weight into. People have also been known to have lead shot poured into the rear portions of roll bars and/or in added bars.

You don't have to get carried away. Adding 80 lbs to a bracket Challenger I had years ago made a big difference in consistency, especially at marginally prepared tracks.
 
yes i have already corrected that.:BangHead::D

If i had the money i would just add dual battery in the truck, that would help a lot.........Someday
Was thinking about bar bell weights. Simple/easy to get a hold of. but will have to think about how to secure them.

Maybe i will just throw in a couple of 3d member and forget to take them out at the track. Just kidding. just something i did as a youngster because i was Sooooooooooo afraid that i was going to brake a rear end on my 318/276 gear car that i all way cared a spare axle and a third member:wtf::D
 
Cudafever said:
So i found a sight that said that 1 gram of rotating weight was equal to 2 grams of chassis weight.
this was a dirt bike forum so if that theory holds true on a car. That means that my addition of 16 pound X 2 is 32 lbs
a tenth (.010) take 100 pounds..........So 32 pound would equal ruffly .003 of et..........Fishmens67 you, and most every on else may be right and it just don't matter.

I thought that it would have had a bigger impact.

Come on all you Mathematicians show us a formula :)
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Well you're gonna lose that from burning out + 1.5 Seconds probably so the weight won't be the concern. If anything it's going to help plant the street tire sooner
 
Just make changes when time and budget allows. Hope you have a driveshaft loop and perhaps consider upgrading u-joints & yokes also when you start hooking better. (Peace of mind.) Traction has a habit of eventually finding the weak link in the driveline "chain". Good luck!
 
Agree.
have a built drive shaft, can't remember the u joint sides but had to get a new Pinion yok because of it.
Have a drive shaft loop, and run slicks most of the time. 28 10.5 15. Which is why it's going to be a challenge to make a 215 70 15 hook.
 
Rotating weight has more more effect on acceleration than static weight. The further the rotating weight is from the 'centre', the greater the impact it will have.
David Vizard's research has some examples.
In his A series engine book, taking 1lb off the f/wheel was equivalent to taking 17 lb off the weight of the car. A formula is given to calculate the numbers.
Using a Mustang as a test vehicle, the moment of inertia was reduced using lighter wheels. The static weight that was removed as a result of the lighter wheels was added to the car, so that static wt did not change. Result was a 1/3 of a tenth in the quarter mile. Full article is in Feb 06 issue of PHR.
 
If the tires hook the same I doubt there would be much ET difference. I've ran tires with and without tubes (less than 16lbs but still weight) without affecting ET. I broke my Sportsman/Street car and had 1 race left in the season so I took my Pro car and swapped all 4 tires around to make it legal for the class. I've ran a 31x14 (12" rim) to a 30x12 (10" rim) and car ran the same. I've tried racing front tires vs M/T sportsman DOT tires, not difference in ET.
 
Cudafever said:
Locomotion thanks for all of that,
adding weight is something i'm considering. What is the least expensive way to add weight.(safely) with the price of lead. A lead bumper is out of the question.:D
Each tire/wheel combo weights 8 lp so it 16 total. the 32 was double weight to get translate it to car weight to us the 100 per a tenth .100 rule
Click to expand...
Fill the spare tire with water.
 
That is a thought :lol:

The first time out i will be just feathering out of the hole and see how that works.
The full truth of this matter is that i need to test and prove my repairs to the LM-2, 02 sensor and data logger is fix.

Got what i think is fix but the last race was cancel last fall due to rain. Been hibernating all winter.

Memorial weekend is coming fast. Need to get out there and make sure it still starts and runs.
 
All I can think about in this scenario was wayyyy back when I was towing my old 24ft enclosed with my 95 1500 (wrong tool for the job). Now I was using some LT tires and figured I’d better step up to some E rated rubber. Dropped the pickup off at the tire store and when I picked it up with my new shoes I literally checked to see if the e-brake was on....

i was amazed at the anchor I was pulling with just heavier rubber.
 
Were they taller tires.
I know when you lift your truck and add bigger tires is sure kills HP.
 
fishmens67 said:
not enough to notice. maybe a 100th. lol
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toolmanmike said:
Lord Jesus, just bolt the other wheels on and make a few test and tune passes to see where you are.
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:lol:

OK.
Here is the results.
My Average mph is 86 MPH and ET around 7.90s in the 1/8 mile 60' in the 1.7 1.8 range.
So i bolted on my heavy skinny cheater slicks. when from a 28/10.5/15 to a 26/7/15

Was never able to get them to hook.....Even leaving from a idle and feathering the power in.
So ET was a total waste.......started out with a 9.65 @ 79.2 MPH. Having to lift several time to keep the paint on car.:eek:
After several attempts using my right foot better. I ran 9.20 9.30 @82 esh MPH

After doing some tricks to keep the car from washing out to the right every time it spun and i could keep my foot in it.
My ET improved to a 8.65@84 MPH

That's 2 mph slower.......was it because of them heavy aarss tires or was it do to lack of traction..... or both. You decide.........

And as Paul Harvey would say " and here is the rest of the story"......................
 
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I have been wanting to experiment with chassis mods with my SS Spring...... More accurately Torsion bar tuning.

When i do my burn out the rear kicks out to the right, when i loose traction down the track it wants to go right also.
with these skinny cheater slicks, it was painfully more of a problem.
So after i had done all i could to make it go down the track with my right foot..........I got my big long 1/2 inch beaker bar out and 3/4 socket. Slide under my car and loosen the torsion bar 1 full turn. (right side only)
Burn out and launch seem to be just a little less of a sideways spin. So i turned it one more full turn looser. I know for sure, now, i'm going in the right direction!!!!!
After a couple more passes i climb back under and give it one more full turn looser. Burn out is straight and the launch is under control, enough, that i can even note who and what car was in the other lane.

So now its time to do a full throttle, out of the hole, and see what happens........It spun hard, as i suspected it would do.
It spun all the way through 1st gear and half way through 2nt............. The surprise was that i didn't have to lift!!!!!!!

I still had to steer it, but the fact that i could control it, and NOT lift, was AWESOME!!! I wanted to make a 2nd run and verify what i had felt and done on the last pass.................But good old Mother Nature said that's enough!!! Thunder Cloud Ended the day.
 
I understand your elusive search for the tenth of a second. My buddy was a class racer for years. I came over to his place one day and he had the car in the air using a small torch and a scraper to remove the undercoat. I laughed until he said that so far he had scraped 30 lbs off. !!!
 
agree that we are all ways looking to improve on our ET.
But i would spend the time to remove my interior before i started scraping undercoating.....which i'm not willing to do.

I didn't loose weight, i gained weight. Why? Because i needed a DOT tire to go racing and theses tires, i had kicking around and cost me zero Dollars. And in the end(although wasn't my original intention) allowed me to do some tuning to my suspension.
 
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Red arrow 26/7/15 cheater slick.
Blue arrow is the slick i took off.

cheater slicks.JPG


Torsion bar bolt i loosens

t-BAR BOLT.PNG
 
Cudafever said:
I have been wanting to experiment with chassis mods with my SS Spring...... More accurately Torsion bar tuning.

When i do my burn out the rear kicks out to the right, when i loose traction down the track it wants to go right also.
with these skinny cheater slicks, it was painfully more of a problem.
So after i had done all i could to make it go down the track with my right foot..........I got my big long 1/2 inch beaker bar out and 3/4 socket. Slide under my car and loosen the torsion bar 1 full turn. (right side only)
Burn out and launch seem to be just a little less of a sideways spin. So i turned it one more full turn looser. I know for sure, now, i'm going in the right direction!!!!!
After a couple more passes i climb back under and give it one more full turn looser. Burn out is straight and the launch is under control, enough, that i can even note who and what car was in the other lane.

So now its time to do a full throttle, out of the hole, and see what happens........It spun hard, as i suspected it would do.
It spun all the way through 1st gear and half way through 2nt............. The surprise was that i didn't have to lift!!!!!!!

I still had to steer it, but the fact that i could control it, and NOT lift, was AWESOME!!! I wanted to make a 2nd run and verify what i had felt and done on the last pass.................But good old Mother Nature said that's enough!!! Thunder Cloud Ended the day.
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If the car is going the same direction every time, you need to roll the tires out. Do not just measure the diameter. You have to roll them out at race weight with a driver in the drivers seat. All you need is some tape, a sharpie and a square. And you need the tire pressure set where it is when you make a pass.

Get the car ready with someone in the drivers seat who is your weight or close to it. Take a piece of tape and stick it on the sidewall of the tire and another piece on the floor, then take the square and make a straight line from the tape on the tire to the tape on the floor.

The roll the car forward until the tire makes one full Revolution and use the square to make sure you are one full turn. Put down another piece of tape and use the square to make a mark on the tape on the floor in line with the mark on the tire.

Grab your tape measure and measure between the marks on the floor. Write it down, and then go do the other side.

The roll out SHOULD a be within a half inch of each other. If they are not (lots of tires aren’t the same size) then you need to add air or remove air to make the tires roll out the same.

This is the only way I know of to accurately measure the actual diameter of a tire that wrinkles. Never played with a radial, but I suspect it needs to be done the same way.

Just measuring the diameter doesn’t take into account the side wall wrinkling.
 
Hmmm, that is something to think about. considering that these tires are a Recap. vary good chance that they don't have the same role out.
will have to check that out soon.

I added a lot for load on the L front torsion bar when i installed my new SS Spring. taking 3 turn out and it goes straighter. was a mistake on my part when i re did my front suspension last year.

But the role out i haven't check on these cheater slick as well as my regular slick. How ever both tires swing the *** end to the right, when doing a burn out. So i still thing the t bar adj was a good idea.
We will see on Memorial Day when i go back to my slicks.......
 
If you chop off your head, you can loose 20 lbs of ugly fat to offset the 16 lb increase for the tires....
 
Cudafever said:
Hmmm, that is something to think about. considering that these tires are a Recap. vary good chance that they don't have the same role out.
will have to check that out soon.

I added a lot for load on the L front torsion bar when i installed my new SS Spring. taking 3 turn out and it goes straighter. was a mistake on my part when i re did my front suspension last year.

But the role out i haven't check on these cheater slick as well as my regular slick. How ever both tires swing the *** end to the right, when doing a burn out. So i still thing the t bar adj was a good idea.
We will see on Memorial Day when i go back to my slicks.......
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If that’s the case, you need to make a perpendicular line about 50 inches forward of the axle centerline and measure the wheel base to that line.

If you try and measure the wheel base up to the front spindle you can be off enough to skew the results.

You need a couple of plumb bobs and that square. Just drop the plumb bobs of the center of each axle and then make a mark on the floor (thats why I use tape...Id end up with a hundred marks on the floor, plus it looked like crap) and then get your perpendicular line and measure each side to that.

It’s possible the axle isn’t square in the car.
 
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