small tube or big tube chassis

flattop1

Dawg 89
Chassis design plays in as well .
Stiff transfers faster . Returns faster too . So not loaded as long .
 

flattop1

Dawg 89
It doesn't transfer as easy , when it does it happens fast , then its hard to keep it there ; ie it rolls over to the rt frt but is hard to keep that transfer .
Then it starts back to the rr and finally lft rear all suddenly .
The chassis is a spring , a stiff spring is less compliant then a soft spring .
Therefore less forgiving .
Personally i don't think they make the big tube chassis for the higher weight classes or bigger drivers .
More for the high g force tracks and high bite situations .
 

flattop1

Dawg 89
Flex is involved here also there is very little flex in most big tube chassis .
That goes hand in hand with the stiff spring .
Though design would come into play .
 

XXX#40

TRUMP 2020
What are we calling big tube 1 1/4? thats stand diameter good for any weight, some companies offer an 1 3/8 RS rail and they are fine for any size driver, now some companies offer 1 1/8 chassis, smaller drivers and saturday night tracks, or where bite is lacking
 

Rocket07

Member
Seems like your typical weekly racer would be better off on small tube then. I’m in NY on 33s and our tracks don’t really lock down normally.
 

msquared

Member
Low bite tracks generate less cornering forces meaning less weight will transfer from left to right. So you want a small tube chassis to keep the weight more evenly distributed between all the tires during cornering (higher VCG and less leftside). The chassis will not flex as much either. On high bite tracks more cornering forces will be generated meaning more weight will transfer from left to right (lower VCG and more leftside). A bigger tube chassis is stiffer and will flex much less than a small tube chassis under the cornering forces. Something else is the I.D. of the tubing. Most 1 1/4" chassis RS tubing is .095 I.D. where the left may be .065 I.D and the connecting tubing a mixture of I.D.'s For a driver and kart weighing 425 or more I would want a big tube chassis not only to reduce sag but to reduce flex. A lot of energy is wasted in chassis flex.

Driver weight, the bigger question is driver build. You have two drivers, both are 200 lbs. and they both are 5'10" tall. One, driver A carries most of his weight in his waist and legs, the other, driver B has chicken legs and most of this weight is in his upper body. They require two very different setups. The reason is they will have very different VCG's which is the lever arm for weight transfer. Air pressures and tire prep will also be different. Always run the highest air pressure that you can run. This reduces roll resistance.

Msquared author of Understanding Chassis Theory and Dynamics
 

alvin l nunley

Premium User
Have you ever written anything about the choice of tubing material. I.e. Chrome Molly, seamless 1018 and welded 1018? I believe these are the most common materials used.
 

msquared

Member
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
 

msquared

Member
Sorry Rocket, 1 1/4". He would need more leftside and a more laid back seat. Air pressure would also be different as well as tire prep. Driver A may have a VCG of say 9.5" but driver B may have a VCG of 11". Huge dfference when it comes to dynamic (in motion) weight transfer.

Msquared - Understanding Chassis Theory and Dynamics

Anyone can email me for purchasing the manual at zimacat20@comcast.net
Please no setup questions at that email.
 

alvin l nunley

Premium User
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.
Terry Ives, in California, has a vintage square tubing framed kart that he just loves. He's been taking it to all the vintage events for 10+ years. I have a picture of him driving it at Riverside in 2008 and 2019. In the same corner.
 
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