Axle 40 mm vs. 50mm

[joseph hollinger]

[patrick slattery]

Some karts are designed and tested with 40mm and some with 50mm. You would need to figure that into your testing.

pat

[Bill Angel]

Kevin, you're getting close. I weighed three 40mm axles of different brands. The heaviest was 6#3.1 oz, the other two were 6#2.0 oz, all were medium axles. I weighed a fourth axle also marked as medium that only weighed 5#12 oz. The first 3 had almost identical wall thickness and the lightest was .010 thinner. This brings up the question of how much difference in wall thickness does it take to notice a difference in performance. Would the thinner axle be 8 percent more flexible or 16 percent (accounting for both walls). Would a .002 or .004 difference in wall thickness have a noticable effect?

[Will Anderson]

http://lsrmotorsports.com/CRGAxleChart05.pdf

If you look at the Chart the CRG boys have made up the 50mm S20 is softer then any 40mm they offer. According to most of what I have read this is impossible. And if Axle thickness is the major difference between a hard and soft axle how can they offer a S20 that is very soft in 2.0mm and a t-5 that is very hard in the same thickness? What the points on the chart stand for I dont have a clue. I can tell you being a GP 6 owner and having almost all of the 50mm axles. There is a huge difference between the T-5 and S20. I also know that you can get the T-4 in a 2.0mm or 2.5 mm. I can assure you a 2.5 mm T-4 is softer then a 2.0mm t-5. Track test have proven this. I can also say that a 2.0mm T-3 axle bends alot easier then a 2.0 mm t-5 or t-2 . (From normal track wear, not in a crash) But thats impossible because its just a tube of steel and the only difference between hard and soft is thickness.

All track test were done on a GP 6 with a 125cc ICC, with YJB tires at New Castle Motorsports Complex and a 6 ft 2 in driver.

[joseph hollinger]

[Tommy Griffith]

In talking about the importance of which axle is "lighter", you need to define what "Type" weight you are looking to reduce. The kart sees "weight" in many different ways when it comes to performance.

Overall weight, sprung or unsprung weight (in cars with suspension), or rotating weight and Inertia. Even if the particular 50mm axle that you install is lighter than the 40mm axle you took out, it still could be detrimental to the karts performance.

Let's say that the 50mm axle is 5% lighter than the 40mm axle you took out, BUT the 50mm axle is 25% greater in diameter than the 40mm axle, so the "Moment Arm" that the kart sees is GREATER. The 50mm axle will be more difficult to accelerate and decelerate than the slightly heavier 40mm axle, thereby HURTING the karts performance by robbing horsepower. The detriments of the 25% increase in diameter far outweighs the benefits of the slightly lower overall weight, performance wise.

The farther away the rotating weight is from the absolute centerline, the more horsepower is used up in trying to accelerate it and the more braking power is used up trying to decelerate that particular part.

The acceleration and deceleration has to do with Newton's Laws of Physics and Inertia.

So, you can reduce the weight of certain objects, but still go slower by changing their physical characteristics and demensions of that object.

The only place to creat horsepower is inside the motor, but you can waste and consume horsepower in many, many other ways.

The most important Horsepower numbers are the horsepower that gets to the ground to accelerate the vehicle. That's why all of the major race teams now use chassis dynos in addition to engine dynos.

The horsepower at the rear wheels is far more important than the horsepower that's under the hood.

[Kevin Willmorth]

I'm not necessarily looking for any new axles. I was simply making comment to the affect that if I were looking at axles, the 50mm is not as far off as I initially thought.

Now, for total opinion and conjecture: Personally, unless the weight means something, I don't beleive the differences between the two tubes is anything more than the chassis makers playing games in the interests of planned obscelesence. Nothing says old more than a 40mm axle amongst a grid of 50mm equipped machines. Those new axles just LOOK so big and beefy! Must be better, right?

I am beginning to beleive that the stuff we buy from the chassis makers is not as well thought out and tuned as we are led to believe. In fact, it appears that the "universal" initial setup of most new chassis requires more tuning to suit individual needs than ever.

In my own experience, which is just that, mine alone - without implying any universal law or truth in it, is: Chassis tuning trims more from lap times than any other single factor outside driver skill (which is still the #1 factor.) Engine tuning is also important, but meaningless until the chassis is doing what the driver feels right with. The axle is but one of at least 20 other factors involved in finding that chassis sweet spot. Two seasons ago, we found one other important item - seat flex. The difference between a soft Tillet Kevlar/carbon seat, and a hard fiberglass seat is very noticable. I'm amazed how many people select seats based on price, or some other feature, when it is so much an integral component of the karts structure and flex characteristic. Add seat struts to the formula and things get more interesting. Move that seat around a little, up and down/fore and aft, etc.. THEN play with the axle flex, hub length, rim meaterial, tire pressure, and on and on.... one thing here, another there, each subtle, and next thing ya know, the kart is either flying, or getting whipped by the kids karts!

Are we having fun yet?

[Mike Goebel]

[Mike Goebel]

[joseph hollinger]

[Kevin Willmorth]

[Will Anderson]

Mike I'll let you be home doing the test on your workbench while i test and learn how it works under the strain that an axle goes through in its environment. I dont understand how if it acts softer feels softer and make the chassis softer and unbound how it isn't softer. If it looks like a duck, talks like a duck, its really a horse???

I'll let you guys simulate and find the ideal numbers on the axles.. i'll find the real way it works in its environment.

I'm 16 years old and don't claim to know everything, I understand what Kevin is trying to say.. but this numbers are Ideal numbers... and numbers that are assuming alot of things.. its assuming that all axles are made of 100% steel. Its just a test on a stationary axle when in reality a sationary axle wont do you any good. I really dont give a crap about the numbers.. I'll figure out how to go fast by testing everything.. I'll let you guys do the numbers.

I would much rather be young and stupid then old and ignorant.
To answer the original question.. for auto X i would buy a stiffer axle, i'm assuming its a 125 shifter and everything i have tested on the tracks points to a 50mm being faster and easier to drive. Sprint tracks since it has more rubber on the track i would get a softer axle. really you just need to test.
Later on guys, i'll see you at the track

[Rick Begeman]

Then I'd have to understand all this math.

[Mike Goebel]

[Ray Foster]