small tube or big tube chassis

Hey Al, its been a while. I have not written about the tubing material. It does make a difference. I had a chassis builder make me a chassis out of an oval shaped tubing once. No wonder the rules specify round tubing only. Not sure if this holds true today but all the "Factory" drivers were not on what the public was riding.

The main thing is that on any chassis the numbers that they "suggest" is what works 80% of the time anywhere. Most people are afraid to step outside the box and try different numbers. The main thing is that you have to look at the drivers build and work from there. For the 425 class and above I would prefer a bigger tube chassis. Another thing people do not pay attention to is the seats on karts. If you look at the front runners, they shave the lip off the seat. This causes the seat to flex and acts as a damper. What they are doing is controlling weight transfer. The rear bumper should be torqued. The sidebars should be loose. Again, it is the little differences that make a big difference.

When I look at the karts that I ran back in the early 2000's the rear was somewhat soft, the waist was wide and flexed a lot and the front loop was not the same. Now, the karts are ultra stiff in the rear, the waist is narrow and stiffer and the front acts more like a torson bar in that it is a constant bend. Back in the day 45 nose, 55 left, and 60-65 cross was the norm. Now you see 48 nose, nearly 60 left and cross anywhere from 58 to 75. If you remember Pat Dotson, he built a chassis with 50% nose, 58 left and 65 cross. That thing was a rocket! It was way out of the norm back then. But look where we are today. What is still neat is that a lot of things that I wrote in my chassis manual still hold true. I have several people on newer chassis running old school numbers and are doing very well. My point is all the numbers must complement each other. Then there are the tires and tire prep.

Msquared - Understanding Chassis Theory and Dynamics


Most karts being built today are relying on a lighter nose weight....... I have customers on Ultramax Rivals that are around 44.5-45....


Kart Manufg. are building smaller tube chassis' due to the demand of tire issues..... Especially on Maxxis...... You are not able to wait on a tire to cure out long enough to have a tire to have speed built into it. As for Burris generally you are going to be running on tracks that dont create a lot of bite. The smaller tubing chassis would be a plus with the lack of sidewall stiffness of a Burris tire thus giving more of a broader range of tires to choose from. (by date codes).
 
JRCP:

Yes I have seen lower nose karts. I am also seeing karts with cross from 55 to 65 plus. Here is something very interesting, I have had people on a wide variety of chassis and this setup always seems to be a great starting point.
Nose 45 Left 55 Cross 60

With those numbers all the chassis seem to handle very well and are pretty neutral. It seems that the speed is found by adjusting the front-end (caster and camber) to match the track and getting the tires right (air pressure and prep).

With the Burris tires, I feel that people do not run enough air pressure in them. I hear numbers of 6 psi or lower. They need way more than that. If you think about it, the softer sidewall of the Burris gets stiffer with more air and flexes less. To me any tire operates best at an air pressure that is on the edge of crowning it.

Kurt Burris and I have had a lot of discussions about tires and I remember when I did a tire test for National Karting magazine, Kurt told me to NOT use lower pressures for his tires. When I was hooked up with Intercomp and looked at tire spring rates with different air pressures and was measuring the duro of the sidewalls, it all made sense.

All in all, with the money that has come into karting, on a professional level you need a set of tires to practice on, a set to qualify on, and a set to race on. Those tires are then sold to the "local" racers. Then again, the "local" track that I ran at back then, a guy spent well over $8,000 on just tires to outrun me!

I know for a fact that when people like Rodney Vaughn or Josh Phillpott show up, the average local racers that they help will more than likely win many classes instead of a few classes.

Anyway, it is an interesting chess match.

Mike McCarty - Understanding Chassis Theory and Dynamics
 
Hey Mike (msquared), nice to hear from you again. Been a long while, thought you wouldn't be back. Lately I haven't been coming here very often.
 
JRCP:

Yes I have seen lower nose karts. I am also seeing karts with cross from 55 to 65 plus. Here is something very interesting, I have had people on a wide variety of chassis and this setup always seems to be a great starting point.
Nose 45 Left 55 Cross 60

With those numbers all the chassis seem to handle very well and are pretty neutral. It seems that the speed is found by adjusting the front-end (caster and camber) to match the track and getting the tires right (air pressure and prep).

With the Burris tires, I feel that people do not run enough air pressure in them. I hear numbers of 6 psi or lower. They need way more than that. If you think about it, the softer sidewall of the Burris gets stiffer with more air and flexes less. To me any tire operates best at an air pressure that is on the edge of crowning it.

Kurt Burris and I have had a lot of discussions about tires and I remember when I did a tire test for National Karting magazine, Kurt told me to NOT use lower pressures for his tires. When I was hooked up with Intercomp and looked at tire spring rates with different air pressures and was measuring the duro of the sidewalls, it all made sense.

All in all, with the money that has come into karting, on a professional level you need a set of tires to practice on, a set to qualify on, and a set to race on. Those tires are then sold to the "local" racers. Then again, the "local" track that I ran at back then, a guy spent well over $8,000 on just tires to outrun me!

I know for a fact that when people like Rodney Vaughn or Josh Phillpott show up, the average local racers that they help will more than likely win many classes instead of a few classes.

Anyway, it is an interesting chess match.

Mike McCarty - Understanding Chassis Theory and Dynamics
That starting point apply to Jr cage karts you think? Something with a floating cage. Our cross is greatly lower and I had to put a hard LR tire on to get it to turn center off. I'm not sure that was the correct thinking but it got it rid of our push and we are very balanced now. Went from a 40 duro to a 55
 
That starting point apply to Jr cage karts you think? Something with a floating cage. Our cross is greatly lower and I had to put a hard LR tire on to get it to turn center off. I'm not sure that was the correct thinking but it got it rid of our push and we are very balanced now. Went from a 40 duro to a 55


Typically on any cage kart (bolted/welded) you are going to run a "lower cross" set up..... The VCG and how the kart reacts to the cage has a lot to do with it.

The only time I would run 55 left side on any of the karts that are being built today is if it is a rookie/red plate on a tack that has no bite..... You run 55 left side on a southeastern track you are going no where but backwards....
 
Exactly JR. What I did not mention in the 55 (besides it was only a starting point) left was in order to run lower left you have to soften the RR. I have noticed karts today are extremely stiff on the RR. Collars on both sides of the bearing. This would explain leftside of nearly 60%.

For example, on an adult, free float the RR and run less left. On a Jr. stiffen the RR and raise the VCG, based on the drivers build. My point is it is all the little differences that make a big difference. My point is, is that the manufacturers numbers are only suggestions. Do not be afraid to step outside the box. But to do that you must understand all of the other variables and how they work together.

HEY ARC! Same here. My chassis manual will be 20 years old next year! Can you believe that? I have been working with some drivers at a local track and have them flying! It is sooo funny to see their faces when I suggest something off the wall, explain the setup to them, they go out and run and say "HOLY COW!" The one thing that they tend to do is what everyone else is doing and NOT what they should be doing for themselves. Just because a winning driver is doing XYZ does not mean that they should follow. Different chassis, different numbers, different driver build and so on. To me people tend to go with the "suggested" chassis manufacturers numbers and that is it. You have to work with left and nose to find the sweet spot and use cross to fine tune to your style. They should not be afraid to play with caster and camber and move the front tires in and out. At Providence, when I hear some of the rear stagger numbers, I cringe at how low they are. That track has tight turns and very short straights.

Msquared - Understanding Chassis Theory and Dynamics
 
Exactly JR. What I did not mention in the 55 (besides it was only a starting point) left was in order to run lower left you have to soften the RR. I have noticed karts today are extremely stiff on the RR. Collars on both sides of the bearing. This would explain leftside of nearly 60%.

For example, on an adult, free float the RR and run less left. On a Jr. stiffen the RR and raise the VCG, based on the drivers build. My point is it is all the little differences that make a big difference. My point is, is that the manufacturers numbers are only suggestions. Do not be afraid to step outside the box. But to do that you must understand all of the other variables and how they work together.

HEY ARC! Same here. My chassis manual will be 20 years old next year! Can you believe that? I have been working with some drivers at a local track and have them flying! It is sooo funny to see their faces when I suggest something off the wall, explain the setup to them, they go out and run and say "HOLY COW!" The one thing that they tend to do is what everyone else is doing and NOT what they should be doing for themselves. Just because a winning driver is doing XYZ does not mean that they should follow. Different chassis, different numbers, different driver build and so on. To me people tend to go with the "suggested" chassis manufacturers numbers and that is it. You have to work with left and nose to find the sweet spot and use cross to fine tune to your style. They should not be afraid to play with caster and camber and move the front tires in and out. At Providence, when I hear some of the rear stagger numbers, I cringe at how low they are. That track has tight turns and very short straights.

Msquared - Understanding Chassis Theory and Dynamics
I just looked up this Providence track you say has short straights and tight turns. Our big track here probably fits inside that place lol. But 1-2 is a very tight turn I agree.
 
For the Southeast Providence is a very small track. You are lucky to see speeds above 55 mph. Liberty (Liberty, NC) is a 1/4 mile track with very high speeds. Margrettesville is similar to Liberty but has very long straights and tight turns. There the draft comes into play. Before it was shortened speeds were in excess of averaging 90 mph plus!
 
If kart A has a stiffer tail section than kart B, kart A will always be some what looser thru the apex than kart B. If kart A is stiffer in the front than B ,It will be tighter all things being equal.If kart A is stiffer everywhere(bigger pipe) It will be more responsive to changes,but the sweet spot where the kart is driving good gets narrow.If you can hit that spot it will be faster.
This opens up a whole new topic because on a ever changing dirt track that sweet spot is always moving. This where the theorys of making the karts stiff in some areas and flexable in others come in to play.
 
I haven't seen any mention on class . High horsepower classes like RWYB need a stiffer chassis, most chassis are built for clones . With big hp this chassis will twist out of shape. You need a chassis design for what you're doing
 
Horsepower would be a big consideration, no doubt. Class weight would be another important consideration. I'm sure that a junior driver and a senior heavy driver need different frames with different stiffness ratings.
 
Horsepower would be a big consideration, no doubt. Class weight would be another important consideration. I'm sure that a junior driver and a senior heavy driver need different frames with different stiffness ratings.
Actually kids and adults, theres more on the very same chassis than there are thats on small or big tube.
 
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