Track Tac

Gear selection

M

mtpcage

New member
New to karting so deal with me easily. Understand how to read the gear charts. I know the gear will affect the rpm. How do you determine what the gear would do. If your try to hit max 6400 rpm. What do you use for that math. Or can you convert the gear your running over some how?

thank you in advance
 
Most do it from experience, knowing what gear from a similar track, or asking questions.
Theres no math to determine the proper gear, experience, and asking questions is the way to go.
 
There are a lot variables that can affect your reaching that target rpm, so it's best to find out what gear the other guys are running and use that as a reference point. You could be on the same 17/64 as your neighbor, but you're only at 6100 and he is at 6400? You could be a little tight.

Track size can also play into gear selection. Is it a momentum track with long sweeping corners or are the corners a little tighter and you need to pull up off of them a little more. Final ratio could be the same for both applications, but driver/rear gear selection would be different.

In our experiences, we always tried to run as large of a driver as the track conditions would allow. Remember, the gear that you qualify on may not be the one you want to race on. We have sat on the pole at a new track and finished third because we raced on the same gear. The track always changed after sundown, but we didn't know that.

It will take some trial and error to learn the tricks. We ran Jasper a few years back when they had that $20,000 clone race down there. We sucked on Friday night, but changed our thinking and qualified 17th out of 140 karts on Saturday. We had the right gearing, we simply missed the track surface at first. My best advice on that is to walk out on the track and feel the surface for yourself, don't just rely on what others say. But that's a whole other ball of wax there.
 
mtpcage said:
New to karting so deal with me easily. Understand how to read the gear charts. I know the gear will affect the rpm. How do you determine what the gear would do. If your try to hit max 6400 rpm. What do you use for that math. Or can you convert the gear your running over some how?

thank you in advance
Click to expand...
with years of experience, lots of experience, and going to a track you've never been to before, you might get close, but that's a big might
a few fundamentals can help. For instance; with gear ratios in the 4.0 range, plus or minus, if you add one tooth to the axle you will need to pick up right about 100 RPM to be going the same speed at the end of the straight. The reverse is also true. For instance; if you subtract one tooth from the axle and lose 100 RPM, again you will be going the same speed. If you know what a rule of thumb is, this is one.
Now that 100 RPM number will change a little depending on how high, or low, the final gear ratio is. I have an Excel spreadsheet that tells me exactly.
One really dependable method; ask someone who races at the track you're going to. And don't wait till race day to ask.
Be aware that after the sun goes down, the "air density" will more than likely increase, and this means more power. More power means less gear. Depending on how much the air density goes up, you may be able to take one, maybe two, teeth off. Air density can also change your jetting needs, but I would suggest leaving that to after you get more experience.
"It's called tuning, and tuning is tough." (Al Nunley)

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.
 
Do not take any teeth off for Jasper when it turns night!! You may even be adding a tooth. What Al dont understand is a dirt track will change, and by the end of the night this track will slow up just a bit.
Now if you start at night, like a local show, then its the opposite.
 
mtpcage said:
So at jasper 17/64 maxville 16/62.
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Which tires? When we won the Goldspeed Friday Night Shootout a couple years ago, we were on an 18 front, pinks and blues. That was when they raced all day Friday, this last year, when they started at night, i believe they were on 17, pinks and blues. Els are different and dont bite nearly as well.
 
SoCo Tire Treatments said:
Do not take any teeth off for Jasper when it turns night!! You may even be adding a tooth. What Al dont understand is a dirt track will change, and by the end of the night this track will slow up just a bit.
Now if you start at night, like a local show, then its the opposite.
Click to expand...
it would be interesting to see your notes on temperature changes, mixture changes, and track changes, gear changes and the difference in lap times these changes made. And if you could include air density changes that would be interesting too.
 
mtpcage said:
New to karting so deal with me easily. Understand how to read the gear charts. I know the gear will affect the rpm. How do you determine what the gear would do. If your try to hit max 6400 rpm. What do you use for that math. Or can you convert the gear your running over some how?

thank you in advance
Click to expand...

Here's my canned answer for those new at it. There is no real math to do, other then to know an additional tooth on the axle should be worth an additional couple of hundred rpm or so. It doesn't even matter how much a tooth is worth starting out, all you need to know, which you already do, is more teeth should mean more rpm.

The next thing which comes into play is to know what rpm you need to hit with your engine at the end of the straight. And you already have that answer, which in your case for a particular situation happens to be 6400 rpm.

The rest is simple. The first thing most new karters will experience is with the gearing everyone else uses, they just can't get up to the rpm they know and have been told they need. You may not of experienced it, but I think most do. The answer is if you can't hit the rpm you want with the gearing everyone else uses, forget about what everyone else uses and throw gear to it getting as close to the top rpm as you can.

If you find even after throwing gear to it you still can't get to the rpm you want, then forget about gearing and concentrate on getting through the corners better and getting as much seat time as you can. What you will find as most everyone on here has found starting off is as you start to get through the corners better and as your driving improves, you'll just start hitting the rpm you want all the time.

The next thing which will come is now your hitting your rpm and can even now get more rpm out of it if you want. At that point it will hit you like a light bulb going off, "hey, I can do the rpm now... what do I do to go faster?". The answer you'll tell yourself is to try taking gear off and getting to the same rpm and you'll be going faster. At that point your experience will be up to a point where you'll start taking gear off faster and more and more then you ever realized was possible. You'll then quickly get to the point where if your not running the same gear everyone else is, your real close too doing it and your actually in a fine tuning process.

You don't want to hear the rest of this. Also at that time you'll find the fine tuning process is never ending and getting everything fine tuned so you can kick butt and win is addictive ... and your hooked on karting and racing. ... :)
 
paulkish said:
Here's my canned answer for those new at it. There is no real math to do, other then to know an additional tooth on the axle should be worth an additional couple of hundred rpm or so.
Click to expand...
still, if you had done the math, the amount of rpm you would need to pick up or lose depends on the gear ratio your running. In the area of 4.0 – 1 ratio, one tooth on the axle equals about 100 RPM to be going the same speed. As a ratio goes up and down the number of rpm's you'll need to pick up or lose, to be going the same speed, changes. For instance; at 6000 RPM, 15/60 gear ratio, you'll be going, with 34 inch tires, 48.30 miles per hour. If you add one tooth to the axle, you'll need to pick up 105 rpm to be going the exact same speed. The higher the gear ratio the less RPM with a one tooth change, the lower the ratio, the more RPM to be going the same speed. You have my Excel spreadsheet, easy enough to check my math.
Comments compliments criticisms and questions always welcome.
 
All of what you say is true Al and you'll get no argument from me on it. Very nice post Al.

The point of my post was and is that until you have the skills needed operating and setting up the kart, to be able to obtain the needed rpm, gearing is pretty much meaningless. You just put enough on and go. And if mtpcage is at that point, he should not worry about it because every new karter experienced it starting out. I also saw that the word 'cage' was in his name and figured starting out being able to hit the needed rpm right out of the shoot, is even harder then on a flat kart. I'm very likely wrong on my call, but I made my best call and tried to help, the same as you are trying to help.

We have no reason to debate method, were simply viewing the situation from different perspectives and offering help differently.


paul
 
cage was a nick name i am running a flat dirt track kart. thanks for the info it surly is a learning process.
 
I was reading your last post it said the speed would not change but rpm would go up. I probably misunderstood. Thank you
 
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