Axle Hardness...how can I tell???

Sonny Lowe · Posted: Sun Sep 28, 2003 3:41 pm Post subject: Axle Hardness...how can I tell???

I have a friend with a CRG chassis that bent his rear axle yesterday. We think it is a medium, but we are not sure!?!? The problem we are having is determining the hardness (stiffness) of the axle we have. How can I check the axle I have? Are they actually harder (Rockwell)!?!? Or are the harder ones thicker walled!?!? Any way I can tell what I had right now?

Thanks,
Sonny

Rob Daniel · Posted: Sun Sep 28, 2003 5:26 pm Post subject:

Usually CRG marks the axle in the keyway. Look for two or three letters scribed in the bottom of the keyways(one or both) for the wheel hubs. Any CRG dealer will be able to tell you what the letters mean.
The wall thickness of the axle determines the stiffness, i.e., hardness. Hardness is a misnomer as the modulus of all steel axles is essentially the same and heat treating it to a higher hardness will not change the deflection with load.
The best way to compare axles is wall thickness. If you have a tubing micrometer just measure the wall thickness.
Rob Daniel

Jean Salvati · Joined: 03 Jan 2003 Posts: 139

Doug Welch · Posted: Sun Sep 28, 2003 7:31 pm Post subject:

I have cut up dozens of axles and have completed chemical and physical tests on the material. I have found that when the axles are of the same wall thickness, they do in fact vary the material. in general, the Italians us a low carbon steel for soft axles, a medium carbon steel for medium axles and a high carbon steel for hard axles.

However, as Rob pointed out, regardless of the steel's alloy, almost all steel deflects the same amount under a given load when the wall thickness is the same. What does change dramatically is the amount of energy the axle can absorb with out being permenantly deformed, ie, bent. A high carbon steel can often absorb twice the energy before it is premenantly deformed. If you change the wall thickness, you do change the flex of the axle. That is why on the 50mm stuff you do see the axles rated by wall thickness.
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Doug

Larry Andrews · Posted: Sun Sep 28, 2003 8:43 pm Post subject:

Here's a question for the axle guru...

Do the various steels used for kart axles have the capacity for varying levels of dampening, springiness or whatever? Or is it simply a matter of "soft axles bend easier and that's that"?

I'm curious if a chassis tuner is balancing the effects of spring rate and dampening when using various axles. If so, would it make sense to make a 2.75mm axle with the material used for the hard axle, just to help box in the square of variables?

tks, la

Doug Welch · Posted: Mon Sep 29, 2003 5:21 am Post subject:

This year I have taken a bit different approach to axles and grades in my personal karts. I have been using the softest axles I can. My thinking is that I am trying to keep the bearings from binding and robbing power with chassis bind. I have then been stiffening from the bearing out as needed to attain grip. I have been changing ride height, hubs and stiffeners to change the grip levels. I can always add/remove the torsion bar across the back if I need to stiffen the area between the bearings.

I talked with a chassis designer and he claimed that chrome moly axle was too "springy"(if that's a word) and I have found that my thin wall 50 does exhibit a bit of "springyness" However, I then made some from low carbon steel and found them to be just as "springy". So it appears that claim is not valid. All I did was increase air presures and the bounce disappeared and the kart was much better on turn in than with a stiffer axle.

I think that some of the bounce we atribute to axles is actually the tires. After all, we tend to run fairly low air presures at times. Very soft axles seem to need a bit more air in the tires to control bounce.
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Doug

Darren Elliott · Posted: Mon Sep 29, 2003 9:01 pm Post subject:

The axle thickness isn't the tell all. There are stiffer 2mm than some of the 2.5mm stuff. It's probably best to buy the axle that your looking for base on the markings on the axle. They have done all the homework for you. I doesn't seem worth it to guess on an axle. I don't know which CRG you have but and M-20 should get you around most of the tracks.

S-25 Soft (S-25...2.5mm)
M-20 Medium (M-20...2.0mm)

If you can't find a CRG dealer, call SSC Racing @ 760-864-1320

Mike Goebel · Posted: Mon Sep 29, 2003 9:15 pm Post subject:

Tom Jensen · Posted: Mon Sep 29, 2003 9:22 pm Post subject:

Darren Elliott · Posted: Mon Sep 29, 2003 9:45 pm Post subject:

I have read these kind of threads before. Which axle does this and which axle does that. I'm not sure if I should have jumped in. Very Happy

I dig when you find out how smart the karting world is. For real. I also enjoy reading some of the things on these thread when it gets real technical.
There is probably a lot of ways to achieve stiffness. Maybe Sonny Lowe wasn't able to figure out the basic way to get the proper axle in his kart? So now he has both ways.

Tom Jensen · Posted: Mon Sep 29, 2003 10:01 pm Post subject:

Larry Andrews · Posted: Tue Sep 30, 2003 8:37 am Post subject:

Hmmm. Thickwall 3/2.5 Ti axle. Nice dampening due to the vibration absorptive properties of the titanium alloy, a little extra resistance to bending too possibly. Of course, it'd cost about a thousand bucks...

Whatcha think Mr. Welch? I've read that you've put tool to Ti before.

Sonny Lowe · Posted: Tue Sep 30, 2003 5:31 pm Post subject:

Thanks for all the info guys.

I'm sure different manufacturer achieve stiffness different ways IE wall thickness, hardness (Rockwell) and maybe even material compound. I was hoping for a standard LOL, but it doesn't look like there is one. It also doesn’t look like there is an easy was to determine the stiffness of an exciting shaft without a lot of known info. It would be easy to deflect it, but without a standard to go by the data is of no use. We’ll try a medium shaft to see how that works for now.

Thanks again for all the replies…

Sonny

Doug Welch · Posted: Tue Sep 30, 2003 6:48 pm Post subject:

Mike Goebel · Posted: Tue Sep 30, 2003 7:01 pm Post subject: