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Roll Bar Question

Posted: Tue Nov 12, 2013 3:57 pm
by Jason
If the rules require a minimum of 1.750 x .120 DOM roll bar what would the equivalent wall thickness be for a Chrome Moly (4130) roll bar?

Re: Roll Bar Question

Posted: Tue Nov 12, 2013 6:42 pm
by jerdeitzel
It looks to be the same for alloy 4130 (which i assume is Chromoly but i am not positive?) according to the rules! Also, it says 1.5 x .120 or 1.75x .095 is required not 1.75x .120.

From some quick research it looks like you would not gain any weight saving by using CM over DOM. But, you will gain some extra strength by using the same dia tubing. But, At the expense of cost and harder to weld. Again, i am no metal expert and i do know we have a few people on this forum that might be able to shed some more light on the matter.

Re: Roll Bar Question

Posted: Tue Nov 12, 2013 8:56 pm
by Jason
Yes, 4130 is chromoly. Usually 4130 is allowed to be thinner wall for a given diameter. That's where the weight savings comes in. If you look at section 10.4.2 E, of the 2013 tt rules on page 38, it gives the breakdown. My Camaro weighs 3750 and thats where the 1.750 x .120 in DOM came from. it lists "alloy" as the same wall thickness. Assuming "alloy" means 4130, then you are correct, there is no weight savings. past experience with other orgs. allowed 4130 to be thinner wall or the next diametr down for a given wall thichness. Just wondrring if it were the same with SCCA. The car is brutally heavy and I like to save weight where I can.

Re: Roll Bar Question

Posted: Tue Nov 12, 2013 10:07 pm
by jerdeitzel
These are the new rules. On page three you get the diameter of the tubing you need. It also clearly marks out alloy as 4130 being the same wall thickness. http://scca.cdn.racersites.com/prod/ass ... 20Docs.pdf

Now, is it possible that the PHA could change that rule to something different in the supps in regards to how to construct a roll bar. I Guess you will need to wait and see for the new supps to come out.

Re: Roll Bar Question

Posted: Tue Nov 12, 2013 10:45 pm
by Mark Aubele
I really wouldn't recommend trying to save weight in the rollbar, would just go with DOM, the difference in a four point is going to be a few pounds.

Hopefully someone that actually knows the mystery rules chimes in, the PHA doesn't follow the SCCA's rules, they have chosen to ignore the new TT rules completely.

Re: Roll Bar Question

Posted: Wed Nov 13, 2013 12:51 am
by TKnorr
Welcome Jason. Thanks to all providing info.
Please do not draw conclusions as to how PHA will address the new Time Trial Rules. PHA has not and will not ignore the new TT rules. A PHA committee is currently analyzing the new rules. The objective of the committee is edit our supplementary rules to maintain high standards for our events, a Hallmark of PHA. No one has more experience in running SCCA sanctioned Hillclimbs than PHA. PHA has always supported the highest safety standards. This tradition will continue to best assure the safety of drivers, officials and spectators. Be patient, these changes will be available soon. We do not do business on the forum; our business is conducted at PHA meetings.
Tom Knorr, PHA President

Re: Roll Bar Question

Posted: Wed Nov 13, 2013 8:24 am
by Jason
Thanks for the welcome Tom, and to all who offered their advice. I have some time until I need to get a bar in and can wait to see what comes out of the committe.

Re: Roll Bar Question

Posted: Fri Nov 15, 2013 1:57 pm
by dspgti
Just as a side note, Carroll Smith wrote in one of his books, (Engineer to Win, or Race Car Hardware maybe?) using Chrome Moly was a waste and unless several other skills and heat treating were availavble, could be less strong than mild steel.

Not that I want to stir up controversy here? Just something I read one time.

Dave Y.

Re: Roll Bar Question

Posted: Mon Nov 18, 2013 2:36 am
by TKnorr
Good to hear from Dave Yeager. There is nothing controversial about info and ideas. Thanks to all who provide assistance to new drivers.
Tom Knorr, PHA president.