Gear ratio selections

[ALLDIRT]

Question is . depending on the track , as the night goes on , would you go up in gear , or down .

[MasterSbilt_Racer]

Question is . depending on the track , as the night goes on , would you go up in gear , or down .

Depends on what your engine and driver needs. Seen both ways win.

[7uptruckracer]

To expand on that I'll use my own motor as an example. 427ci. Makes peak Torque at 4500. We come out the corner at 5,500rpm. If I am getting wheelspin if its motor overpowering the track. I don't drop gear. That will get my closer to my peak torque and just causes more wheel spin. I go up in my gear number. It gets me on the back side of my torque and I can modulate better. It is something you have to look at your engine package. I also knock timing out. Some of these guys run the box where they can retard it at a certain RPM with the crank trigger stuff. Or run dual boxes on the crank trigger setup where box two they switch to and it has less timing dialed into it or different parameters.


Depends on what your engine and driver needs. Seen both ways win.

[hipower17]

so if you where using a 628 and overpowering the track you would go to 630's or more?

[billetbirdcage]

This is an old post of mine, but it still applies.

I really depends on several things, but the big 2 are:

1. The engine itself
2. The driver

Personally, more gear (IE higher number) too me made it easier to control wheel spin. If the engine is a large engine with large stroke, you may find it's better to take out gear and with a smaller short stroke engine its better to add gear.

The idea behind the add gear deal is basically this: It takes a certain amount of time for the driver to sense the wheel spin and then react and move his foot, lets say this is an average of .5 seconds. Lets also say your engine, when it goes into wheel spin and the driver can sense that it gains RPM at a 1000 RPM per second.

Just throwing out those random numbers to show something here:

Less gear: 26" tall tire and 5.0 gear and wheel spin occurs at 6000 RPM off corner. MPH of the tire is 92.86 MPH. The MPH of the tire .5 secs later when the driver can react is 6500 RPM = 100.60 MPH. You gained 7.74 MPH at the tire before you can react.

More gear: 26" tall tire and 6.0 gear and wheel spin occurs at 6000 RPM off corner. MPH of the tire is 77.38 MPH. The MPH of the tire .5 secs later when the driver can react is 6500 RPM = 83.83 MPH. You gained 6.45 MPH at the tire before you can react.

While that 1.5 MPH may not seem like much, when you trying to back pedal and rehook the tires it actually makes a fair difference, IMO.

Next thing is the engine and it's torque curve. More gear allows you to run on the back side of the torque curve, meaning your likely already past torque peak and any increase in RPM the torque is going down not increasing. If your running below torque peak, you can hold the throttle steady and it incur wheel spin from the increase in torque from the engine. Even if you're not on the back side of the torque curve, you are at least closer to torque peak where the engine isn't making large gains in torque like if your way below the torque peak.

Example: Engine torque peak at 6000 RPM and gains 10 FT pounds for every 100 RPM above or below that RPM (again fake number, just using something easy). Say you are running a 6.00 Gear and torque peak is 600 foot pounds.

So at 5000 RPM the engine has 500# and is on the verge of wheel spin so you are holding the throttle steady and waiting. Then engine is slowing gaining RPM as it comes off the corner, so once it gains to 5200 RPM it's now at 520# of torque (520# X 6.0 gear = 3120# at wheels vs 500 X 6.0 = 3000#). This gain of 120# at the wheels is enough to induce wheel spin even though you didn't push on the gas any harder.

If your already past the torque peak by adding gear then the # at the tires isn't going to increase cause the torque of the engine is actually going down and thus reducing the # at the tires.

I over simplified this and took some liberties to get the basic idea across, but you should get the point.

[billetbirdcage]

I should also add this above is more about open engine racing and not so much about limited stuff as that adds a ton of other variables like: Restarts, starting up front or in back, one lane or racey track, MPH vs power off the corner, ETC.

[billetbirdcage]

Just for laughs I pulled up some data:

Car induced wheel spin off the corner:

1. RPM before wheel spin incurred 4071 and rear wheel speed of 56.2
2. wheel spin occurs
3. in 2 tenths of a second the RPM was 5058 and rear speed was 69.2
4. The throttle moved 0% over that time, after the 2 tenths is when the driver reacted

[Jim11h]

That's very interesting info/data

[TheJet-09]

Back in '96 or so, my hero the zero (technically the 18 car then) said you gear a car for corner entrance, not exit. Was he able to say that because he had a better engine (or right foot) than everyone else, or is there something else to it?

Curious what others think...

Come feature time (slicked off), I get killed into the corner yet have to wait to get back in the throttle to not run into whoever just lapped me. So I'm seeing that being better in must lead to better lap times, but I'm not sure on how to "reverse" my issue (better in but sacrifice coming off). I should also point out that whenever I talk gear ratio with someone, I'm always a good 20 points higher than them. I always equated that to a difference in horsepower, but with what I see come feature time, I'm not sure that's the case.

[billetbirdcage]

Back in '96 or so, my hero the zero (technically the 18 car then) said you gear a car for corner entrance, not exit. Was he able to say that because he had a better engine (or right foot) than everyone else, or is there something else to it?

Not sure I'd agree with that or at least as the way you repeated it. (Again going off what was said and only dealing with entry here)

For starters how much gear you have is obviously going to effect how much engine braking happens on corner entry but so does a lot of things like:

1. How heavy the rotating assembly is. The heavier that is the less engine braking the rear tires see when the throttle is closed.

2. Trail braking. How much I close the throttle will have a HUGE effect on it and I can vary that at any part of the corner and deceleration.

3. My point is someone using a ton of gear to help induce engine braking thus more slowing of the car with the rear tires may not be the same as someone using less gear and a very light rotating assembly that stops easily may induce more engine braking then the guy with more gear.

4. Now granted if dealing with just your package and not various other engines or combo's, sure you can adjust gear to help corner entry not arguing that fact but I'm not sure its the most important let alone even with the other aspects of gearing, but for sure possible as everyone has ways that work best for them. I look at several things as far as gearing and sometimes there is a situation the trumps area's that would likely be more important in typical situations.
Example: one lane race track on bottom and he who gets into corner first gets the preferred line, then I might on limited engine stuff add gear for the start and give up straight speed and entry just to get to the bottom first then hold them off the rest of the race because you can't pass.


Curious what others think...

Come feature time (slicked off), I get killed into the corner yet have to wait to get back in the throttle to not run into whoever just lapped me. So I'm seeing that being better in must lead to better lap times, but I'm not sure on how to "reverse" my issue (better in but sacrifice coming off). I should also point out that whenever I talk gear ratio with someone, I'm always a good 20 points higher than them. I always equated that to a difference in horsepower, but with what I see come feature time, I'm not sure that's the case.

Always go for corner speed every time, faster entry and middle over drive off corner unless it's one lane where your speed into corner is dictated by the car in front. To me, gearing is way more important on limited engine stuff then open stuff by far.

Also sometimes you will see a trend assuming engines aren't that much different, guys that run more gear likely use less rear brake and guys that run less gear probably use more rear brake.

[TheJet-09]

^^^ Thank you for the response. And the last part about the gear is spot on for me, without even having ever thought about it.

[hpontap]

I know it is not a late model but racing modifieds on American Racer KK-704 tires taught me a lot about gearing as the track got slicker.
Tackier the track, the less gear I ran.
Slicker the track, the more gear I ran. Seemed to help entry and exit.

[let-r-eat]

All depends on how much wheel spin you're set up for. For example: The other night we were at 81mph. 7800 rpm x 5.83 gear. Zero wheel spin we should have been running 109.46mph. 81/109.46 = 73.99% effective gear mph. Different track conditions/configurations/etc will determine what effective gear mph to run.

This can also tell you a ton about the car/driver.