Gear ratio dragster

March 24, 2019, 11:14 AM

David Covey

I would think it would depend on power level, also if you are in the sweet spot with a shorter tire then more gear with a taller tire would keep you there..

I've went from 4.30-4.11-3.90 with the bubba's. Still with the 3.90 and now big Bubba. Last weekend it went .981 60' with some additional power to get rid of a little tire shake.

Dave

March 24, 2019, 05:44 PM

TORQIN

All 3 of my dragsters have 4.30 gears...

March 24, 2019, 07:59 PM

diceman1530

quote:
Originally posted by TORQIN:
All 3 of my dragsters have 4.30 gears...

What rpm do you run in 1/4 ?

March 24, 2019, 08:49 PM

racerdude2054

4.30 gear on both cars with 3190W tires. One running 4.50s and other running 4.80s

March 24, 2019, 08:56 PM

Alaskaracer

4.10's here. 3196 mickeys.

March 24, 2019, 10:19 PM

Mike Rietow

162 mph and down (lower) will cross @ 7000 or down (lower) with 9% converter slip and 10% tire growth 34-35 diameter tire 1/8 mile, these are conservative percentages at 162mph.

I'd be thinking 1.64 low with a 4.56 if I ran 1/8 mile exclusively at around 165-170mph. That would make it hustle when put it in high gear. 6% slip and 10% growth crossing 7300 @170mph. 35

1.64 x 4.56 = 7.47
1.80 x 4.30 = 7.74
1.80 x 4.10 = 7.38

This message has been edited. Last edited by: Mike Rietow,

March 25, 2019, 07:33 AM

NC3x58

quote:
Originally posted by Mike Rietow:
162 mph and down (lower) will cross @ 7000 or down (lower) with 9% converter slip and 10% tire growth 34-35 diameter tire 1/8 mile, these are conservative percentages at 162mph.

I'd be thinking 1.64 low with a 4.56 if I ran 1/8 mile exclusively at around 165-170mph. That would make it hustle when put it in high gear. 6% slip and 10% growth crossing 7300 @170mph. 35

1.64 x 4.56 = 7.47
1.80 x 4.30 = 7.74
1.80 x 4.10 = 7.38

Was just talking about this with a group of buddies.. If you took a car that has a 1.80 first gear PG, 4.30 gear and little bubba tires and switched it to a 1.69 first gear, 4.56 and left the tire the same, using the Wallace calulator for starting line ratio, first gear would essentially be the same (I got 7.74 vs 7.71) and then you would gain more mph in high gear, would make a good 1/8 mile setup for typical bracket dragsters IMO

March 25, 2019, 07:36 AM

NC3x58

To the OP, I went from a 33.5/16/15 (M/T 3084S) with non-beadlocks and a 4.10 gear to the Little bubba with beadlocks and 4.30 gear and for the most part lost zero ET. Most of the guys around N.E. Ohio run 4.30 gear in their bracket dragsters, mostly 1/8 anymore.

March 25, 2019, 08:07 AM

Mike Rietow

You can also go 200 mph 1/4 mile crossing 7500 rpm with a 4.30 gear, converter slipping five percent,35" M/T tire growing fifteen percent. I'd have a 1.64 low gear in that instance as well.

This message has been edited. Last edited by: Mike Rietow,

March 25, 2019, 10:33 AM

Mike Rietow

quote:
Originally posted by NC3x58:
quote:
Originally posted by Mike Rietow:
162 mph and down (lower) will cross @ 7000 or down (lower) with 9% converter slip and 10% tire growth 34-35 diameter tire 1/8 mile, these are conservative percentages at 162mph.

I'd be thinking 1.64 low with a 4.56 if I ran 1/8 mile exclusively at around 165-170mph. That would make it hustle when put it in high gear. 6% slip and 10% growth crossing 7300 @170mph. 35

1.64 x 4.56 = 7.47
1.80 x 4.30 = 7.74
1.80 x 4.10 = 7.38

Was just talking about this with a group of buddies.. If you took a car that has a 1.80 first gear PG, 4.30 gear and little bubba tires and switched it to a 1.69 first gear, 4.56 and left the tire the same, using the Wallace calulator for starting line ratio, first gear would essentially be the same (I got 7.74 vs 7.71) and then you would gain more mph in high gear, would make a good 1/8 mile setup for typical bracket dragsters IMO

("774") Ratio's get even better if you have the power. Sonnax manufactures a 1.58, TSI a 1.64 low rated at the least, to 2000hp. Less efficient converter early for boost if you have a super charger, in low. More efficient converter less rpm (boost) drop back when you put it in high, it'll hustle. Decelerate better too, more efficient converter closer to one with engine rpm at the stripe, to kill. That's what id be think'n 1/8 or 1/4 super charger, N/A or nitrous. Hitting the brakes at 200 plus mph ain't gonna be a long lasting option, for long at least, I wouldn't imagine. I could be wrong on that though, I suppose.

March 25, 2019, 10:36 AM

Lenny5160

I've been having this debate for the upcoming season. My car has always had a 4.10 gear and always a 33.5 tire.

I really want to go to a 34.5 or 35 tire, and I want to replace the gear set in the car due to age. I can either stick with the 4.10 and lose about 4% gear ratio, or change to a 4.30 and gain about 1%. This is using 106 and 110 as the respective circumferences, right off the Hoosier spec chart. I'm not sure how real-world measurements and growth will affect it.

I'm really happy with how the car works, but it needs tires and I like the idea of a little more ground clearance and like how the tall tires look.

The car is mostly used for Super Comp on the quarter mile, with just a couple 1/8 mile bracket races per year.

March 25, 2019, 10:40 AM

sc4087

I've always run 4.30's in my bracket cars. Only car doesn't have 4.30 in it is my T/D car

March 25, 2019, 10:55 AM

Mike Rietow

quote:
Originally posted by Lenny5160:
I've been having this debate for the upcoming season. My car has always had a 4.10 gear and always a 33.5 tire.

I really want to go to a 34.5 or 35 tire, and I want to replace the gear set in the car due to age. I can either stick with the 4.10 and lose about 4% gear ratio, or change to a 4.30 and gain about 1%. This is using 106 and 110 as the respective circumferences, right off the Hoosier spec chart. I'm not sure how real-world measurements and growth will affect it.

I'm really happy with how the car works, but it needs tires and I like the idea of a little more ground clearance and like how the tall tires look.

The car is mostly used for Super Comp on the quarter mile, with just a couple 1/8 mile bracket races per year.

"Real world growth" There's an equation. Gear,rpm, Mph, converter slip at the stripe and Tire part #, is the input. They grow more than you might think, 10% to 20% depending on the MPH.

March 25, 2019, 11:39 AM

Lenny5160

quote:
Originally posted by Mike Rietow:
quote:
Originally posted by Lenny5160:
I've been having this debate for the upcoming season. My car has always had a 4.10 gear and always a 33.5 tire.

I really want to go to a 34.5 or 35 tire, and I want to replace the gear set in the car due to age. I can either stick with the 4.10 and lose about 4% gear ratio, or change to a 4.30 and gain about 1%. This is using 106 and 110 as the respective circumferences, right off the Hoosier spec chart. I'm not sure how real-world measurements and growth will affect it.

I'm really happy with how the car works, but it needs tires and I like the idea of a little more ground clearance and like how the tall tires look.

The car is mostly used for Super Comp on the quarter mile, with just a couple 1/8 mile bracket races per year.

"Real world growth" There's an equation. Gear,rpm, Mph, converter slip at the stripe and Tire part #, is the input. They grow more than you might think, 10% to 20% depending on the MPH.

The growth doesn't really matter unless there is a significant difference in growth between the two different size tires. The bigger concern is probably the actual measured circumference of the 33.5 and 34.5 tires.

March 25, 2019, 12:10 PM

Mike Rietow

105.19 vs 108.33

The equation to figure roll out at the stripe, is the more pertinent observed number to know,for performance. No matter the roll out (33.5, 34, 35) sitting on the starting line. A trend more accurately forecasts any given adjustment.

This message has been edited. Last edited by: Mike Rietow,

March 25, 2019, 12:30 PM

Lenny5160

quote:
Originally posted by Mike Rietow:
105.19 vs 108.33

The equation to figure roll out at the stripe, is the more pertinent observed number to know,for performance. No matter the roll out (33.5, 34, 35) sitting on the starting line. A trend more accurately forecasts.

Well thanks for doing 3.14 x 33.5 and 34.5, Mr Wizard! Not quite the same as putting a tape around a mounted and pressurized tire.

March 25, 2019, 01:14 PM

Mike Rietow

quote:
Originally posted by Lenny5160:
quote:
Originally posted by Mike Rietow:
105.19 vs 108.33

The equation to figure roll out at the stripe, is the more pertinent observed number to know,for performance. No matter the roll out (33.5, 34, 35) sitting on the starting line. A trend more accurately forecasts.

Well thanks for doing 3.14 x 33.5 and 34.5, Mr Wizard! Not quite the same as putting a tape around a mounted and pressurized tire.

You can put a tape around the 33.5's at the stripe with the input. For the purpose of a trend that'll forecast any given adjustment. Or remain "not sure". It don't matter to me either way. If I were you I'd leave it the way it is, If I'm a "wizard" in your eye's for lending a hand, and you're "not sure".

It's not a subjective matter.

This message has been edited. Last edited by: Mike Rietow,

March 25, 2019, 02:49 PM

TOP38

Here's the magic formula

MPH = (RPM x TD)/GR x 336 Or TD = (MPH x GR x 336)/RPM

where:
MPH = Car's speed at finish line - See time slip! LOL
RPM = driveshaft speed at finish line
TD = Tire Diameter (inches)@ finish line
GR - Gear Ratio
336 = constant to converter units

So you need a data logger to get DS RPM or if you don't have one then you would have to guess at converter slip at the finish line and use engine RPM instead.
So 7000 RPM (engine speed at stripe w/8% slip)
7000/1.08 = 6481.5 DS RPM's