OK guys let's straighten this thread out. A hollow tube of the same diameter is not as stiff as a solid bar of the same diameter.
For example let's think about a 1.25" diameter tube with a .250" thick wall vs a 1.25" solid bar axle. The simple way to think about this is that the stiffness of the tube axle is what would happen if you took a .75" piece of bar stock out of the center of the 1.25" solid axle. You loose exactly the stiffness of the .75" bar. In other words the stiffness of the 1.25" bar stock is the same as the stiffness of the 1.25" x .25" tube + the stiffness of a solid .75" diameter bar. I hope this does not confuse the issue of actual stiffness. Now the resistance to ultimate yield is a different matter. If the 1.25" bar axle was mild steel with an ultimate yield of 70K PSI & the tube axle was made out of heat treated 4140 CMoly steel, or other similar material, with an ultimate yield of 125K PSI then the tube axle would have to bend farther to ultimate yield. However the modulus of elasticity of the 2 steels is almost exactly the same so the tube axle would bend more but fail later. I hope I have not confused this issue, but this is physics. Thanks ... Jay Novak -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Chris Reinhardt Sent: Wednesday, January 31, 2007 7:07 PM To: [email protected] Subject: RE: [F500] Bent Axle Wow, that must have got your attention!!! Phil, like I said, I don't know why it works, it just does. Is a 1x8 weaker than a 2x4? Depends on how you lay it. I think if they are both on the vertical plane, the 1x8 is stronger. I think it works on that principal, you have essentially a 1/4" by almost 4" wide piece of flat, versus the 1 1/4 round. The cost difference along with the weight savings, would make me change even if it wasn't any stronger.. CR Phil Green <[EMAIL PROTECTED]> wrote: Don't see how a tube could be stronger than a solid if the materials are the same. I would suspect if you have seen a difference, it was also due to a material difference. It will be lighter, of course. But, a larger diameter tube will be stronger than a thicker wall. Imagine trying to bend a 2" fencepost tube or conduit compared to a 3/8" solid. On the subject of bent / breaking axles.... Had an axle break on me at Grattan in May during a test day. It was something that we were trying with Don Handley, using a larger axle with the ends turned down to the normal 1.25". There wasn't a good radius on the transition which created a huge stress riser. This decided to snap at the apex of the last turn going on to the straight at Grattan. Somehow I didn't hit the wall. However, the flailing axle broke both carbs, of which pieces went completely through the engine. So, the bill included: axle (of course), carb bodies, bearings, complete engine tear down, Gates drive belt ($$$), and an assload of work. Now have a continuous diameter axle. It may bend, but it shouldn't snap. In fact, the drive belt tension causes a little bit of a bow in the axle. Look down the hollow tube and see for yourself, I bet I'm not the only one with a little bit of rear toe-out! Phil -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Chris Reinhardt Sent: Wednesday, January 31, 2007 5:28 PM To: [email protected] Subject: Re: [F500] Bent Axle Ain't no engineer here, but a hollow axle will resist bending better than a solid one. I believe it has to do with #1 the flexibility, #2 the surface area both inside and out... Plus the missing 3/4" bar, assuming you're using .25 wall axles, is equal to about 5.5lbs. CR Dave Phaneuf wrote: John The axle ( 1.125 dia. solid ) that came with my car was slightly bent so following a recommendation from Don at Red Devil I made one up out of a steel he suggested, ETD150, it's 150ksi tensile and yield is about 125 ksi. It bent, no crash just bumps, at that point I redid the whole rear suspension and used a piece of 4340M also called 300M ....it's has held up fine. I seem to remember the certs that came with it showed a tensile of about 280ksi and a rockwell of about 52-53 on the c scale. Maybe overkill but I haven't had to mess with it since. Dave Phaneuf --------------------------------- 8:00? 8:25? 8:40? Find a flick in no time with theYahoo! Search movie showtime shortcut. --------------------------------- No need to miss a message. Get email on-the-go with Yahoo! Mail for Mobile. Get started. -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.17.17/661 - Release Date: 1/30/2007 11:30 PM -- No virus found in this outgoing message. Checked by AVG Free Edition. 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