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Roll out time

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BK:
If a car 60 foots say 1.25 seconds with a 25" diameter tire. Any thoughts on how long it takes to drive the tire out of the beams.

THE FRENCHTOWN FLYER:
That is a good question. I don't have a precise answer, but I have played with adjusting rollout when I occasionally run Nostalgia Comp which is a .400 Pro Tree at our track. When I shallow stage my lights are in the .100 range. When I roll in and deep stage I can get my lights down in the .030 range. So by rolling in an extra six inches I've cut about .070 second off the reaction time. By extension, I'm thinking it would now take about .070 seconds to roll the half foot to trigger the timers.

My (orange) "Last Logghe" altered sixty-foots in about 1.25 seconds.

JrFuel Hayden:
BK that's an interesting question , So why are you asking, what do you really want to know ?
Because the time it takes to drive out of the beams, depends on the car, track slicks , etc, a 1.25 sixty ' time will be different with a 1.00 sixty, right ?
I assume your question is a theory , 1.25 with 25" tall tire. Your photo is a FED, and more than likely you have a 21.5" to 22.25" tall wheel/tire, if you ran a 25" tire that would be about a 3.00x18 tire  [ big and kinda heavy] A 2.50x18 tire is 23 3/4", and a 2.75x18 tire is 24 1/4" , so yes a taller tire will have more roll out.
If that is your question, I have something for you; about 4 years ago I built a 21" wheel with a 27 1/2" tall tire, for more roll out for a FED to race on a Full tree in Comp Elim, not a .40 pro tree like we run in JrFuel. I measured the roll out difference on two cars one with a 21 1/2 tire and the other 27 1/2" tire, the 27 tire had  5" more roll out. before the start line beam would make contact.
Keep in mind a full tree means you can leave before the last yellow light, not so on a pro tree. BTW the 27" front wheel racer has sub 1.0 sixty's like .956, one reason is he is getting a 5" head start on the lights.
Our JF car I run 18" wheel with a 2.00x18 rib tire, which is 22 1/2" tall, the same as front runner tires , but less rotating weight and less friction., on a .40 Pro tree.
I don't know how you could figure the time to roll out of the beams with your 25" tire, because each car combo is different. Like compare a Big Show NHRA Top Fuel car with 23" tires but sixty's in the .8"s
I hope this doesn't make things more confusing !
Jon   

BK:
Jon it couldn't get much more confusing and both replies are helpful.
I have an Altered now and I'm trying to race it without a delay box on a full .500 tree. I have a Transbreak button with a bit of throw but just not enough to not redlight.
I also have an MSD Grid in the car and I'm going to try pulling some timing out at the release of the brake to slow the reaction time without killing a lot of ET.
I'm thinking I will start with -5deg for .100 sec and see if it even shows up in the reaction time.

JrFuel Hayden:
We race a full tree when we race Sonoma Div 7 race, because we get 3-4 qualifying runs, so that's 5 things I can try outside of our NHRA Heritage JrFuel points races.
But the transition between the .40 Pro to .50 full tree is not easy.
 We use a Boido 3" long trans-brake switch, but we also change the transbrake valve and spring [ weaker] in our PowerGlide. because it's better to change the car than to expect the driver to slow-up a tenth.
The other thing for you to check is to maker sure you are not lifting your front wheels UP before it moves forawrd. I have had customers call to order a light shield only to find out they are hitting the slicks so hard and quick that it pulls the wheels up out of the lights.  Also try running a looser converter, it will not hit the tires as hard.

Jon

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