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32mm hollow bars = what in solid bars?
Just bought a 1977 that was a divorce sale project. Guy told me had done alot of stuff but the car was still a project. Some of the work I questioned some, so I'm tearing it back down to make sure it's right. Did the rear suspension today. Well surprise he didn't lie about the parts. I'm building the car to autocross, run the canyons, and take Honey to dinner in. Are these 32mm hollow bars going to be to stiff? What would they equate to in a solid bar? It also had Neatrix bushings, any thoughts on those? Thanks, Mike.
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Mike Trashed Turbolook Cab per Milt, 1965 Pontiac Tempest 1953 Lincoln Capri La Carrera copy(finished soon I hope) 2008 HD Orange Roadglide (The Flying Carrot) 1961 Chevy C10 V-8 shortwide, big back window(project) |
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Max Sluiter
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I am still waiting on some 32mm hollow bars from Sway-A-Way ordered through Pelican. They are an effective rate of 31mm. Should be good with anything up to 22mm fronts. If you don't have sway bars I would suggest 21 or 22.
That said, they do make hollow bars with an effective 32mm rate. So unless you measure the OD and ID you can't tell for sure what the rate is.
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1971 911S, 2.7RS spec MFI engine, suspension mods, lightened Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance |
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bars
Max, I measured the outside and came up with 32.5mm, did not measure the inside. These bars are brand new/installed but never driven. I think they are going to be to stiff for my purpose. Got any 27/28mm to trade?
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Mike Trashed Turbolook Cab per Milt, 1965 Pontiac Tempest 1953 Lincoln Capri La Carrera copy(finished soon I hope) 2008 HD Orange Roadglide (The Flying Carrot) 1961 Chevy C10 V-8 shortwide, big back window(project) |
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If I am not mistaken, whether or not the bars are hollow or not makes no difference as to their torsional spring rate. Only the material used and the outer diameter make a difference.
[remembering materials science from the '80s] |
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Max Sluiter
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Quote:
In fact, Sway-A-Way says their 32mm actual OD hollow bar is an effective 31mm solid rate.
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1971 911S, 2.7RS spec MFI engine, suspension mods, lightened Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance |
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The torsional spring rate has the relationship of (OD^4-ID^4) so you can compare easily; ID of a solid bar is zero. All other components of the equation are constant to the comparison.
So a 32mm bar would have a "rate" of 32^4 or 1,048,576 A 32mm x 19mm ID bar would have a "rate" of 1,048,576 minus 19^4 or 1,048,576 - 130,321 or 918,255 which is 88% that of a solid 32mm bar. If you take the 918,255 and square root it twice you get the equivalent rate for a solid bar or 30.96mm. Also, within very small differences of metallurgy all steel exhibits the same modulus of elasticity so a heat treated 4340 rod and junk steel will behave similarly for elasticity/spring rate...the difference being the junk steel will yield/fatigue much more quickly than the heat treated 4340.
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Paul Abbott Weber service specialist www.PerformanceOriented.com Last edited by 1QuickS; 06-02-2014 at 09:22 PM.. |
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Caveman Hammer Mechanic
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Quote:
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1984 Carrera El Chupacabra 1974 Toyota FJ40 Turbo Diesel "Easy, easy, this car is just the right amount of chitty" "America is all about speed. Hot,nasty, bad ass speed." Eleanor Roosevelt, 1936 |
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Eric... Reminded me of this...
Dr Venkman: Ray, pretend for a moment that I know nothing about metallurgy, engineering, or physics, and just tell me what the hell is going on. Dr Ray Stanz: You never studied. |
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No need to bust out the calculator.
Hollow bars are marked and sold with the solid equivalent rate, not actual diameter. Hence a hollow bar marked 32mm has the same rate as a solid 32mm bar. But if you actually measure the 32mm hollow OD it will be larger than 32mm.
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Chuck Moreland - elephantracing.com - vonnen.com |
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