From: muratlanne@gmail.com   
      
   "Bob La Londe"  wrote in message news:10d0tg9$21llh$1@dont-email.me...   
      
   Don't get to bogged down in the basics. We know most of it. 4130 is   
   easier to weld than 4140, and maybe harder to heat treat. 1020 is easier   
   yet to weld, but lower tensile strength.   
      
   My son's engineering class (club?) is build a 4wd race cart for a big   
   competition. He has done the structural calculations with what he   
   considers a decent safety margin using 4130. Some years back I had a   
   chat with a local marine shop owner (Keith) who was building race carts   
   for his son at the local speedway for their 2wd youth cart racing class.   
   He said they were using 1020 DOM because it flexed more in hard racing.   
      
   Now there are some class differences. The cart my son's group is   
   building is using a specific nominal 14hp motor and using a full 4x4   
   drive train. The Keith's son was racing nominal 6.5hp Subaru Robin   
   clones like the Predator 212.   
      
   I'm not sure what my question is. I'm just trying to wrap my head around   
   it as "not an engineer."   
      
   --   
   Bob La Londe   
   CNC Molds N Stuff   
      
   -----------------------------------------   
   There are some strongly believed misunderstandings about the properties of   
   steel, and physics in general.   
      
   I think the choice depends on how they deform vs break in a crash. Below   
   their yield points their bending resistance (Young's Modulus) and thus   
   chassis stiffness is practically identical, like all steel, but 4130 has a   
   higher yield point.   
      
   https://classicmotorracingclub.nz/chassis-stiffness-and-tuning-h   
   w-much-is-enough/   
      
   https://amesweb.info/Materials/Youngs-Modulus-of-Steel.aspx   
      
   Likewise hardening steel doesn't make it stiffer, hardness lets it bend   
   further before taking a permanent set. You can see this with two long bugle   
   head screws held in a vise by the tips. Annealing one with a torch doesn't   
   change how far it bends with equal moderate pressure on both..   
      
   The suspension geometry's job is to keep the tire tread flat on the track   
   while the body rolls in turns, and chassis flex can interfere. My   
   understanding is that 1020 controls the limited deflection permissible as   
   well as the same size and weight of 4130.   
      
   The goal is to limit crash deceleration to what the driver can handle   
   because race car frames became too strong and stiff, the car survived but   
   the driver didn't. I don't remember the auto numbers, for aircraft Col. John   
   Paul Stapp raised the limit of survival from an estimated 20g to a proven   
   40g with proper restraint.   
   https://en.wikipedia.org/wiki/John_Stapp   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)