Roll cage main hoop size- Why?

My question is a follows: WHY was the main hoop size changed from 1.5" to 1.75"? Were there a number of main hoop failures in the sport and prompted a change? Was better analysis software available and so better models of failure could be examined? The safety factor was too low? FIA also changed at the same time?

I suppose this question could be asked about door bars, sill bar etc too. I am mainly interested in the Main hoop though.

Why and who cares? It's changed, it's the rule, it's not going back so it's a wasted effort to wonder.

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Grant Hughes

That was possibly the least helpful response you could have given me. At no point did I suggest a rule change, want a rule change, and I care, that's why I asked the question. I am interested in the progression from where we started to now. I am guessing you can't see the value in that, which is fine, but I can, which is why I want to know.

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Frank Gossett
My question is a follows: WHY was the main hoop size changed from 1.5" to 1.75"? Were there a number of main hoop failures in the sport and prompted a change? Was better analysis software available and so better models of failure could be examined? The safety factor was too low? FIA also changed at the same time?

I suppose this question could be asked about door bars, sill bar etc too. I am mainly interested in the Main hoop though.

Strength.. strength in bending vs weight...
The rule in much of the rest of the world began coming into for waaaaaaaaaaaaaaaay back in around 1991-----that's when I suddenly started seeing the main hoops on cage kits I was bringing over from Sweden going to 1.75 x .095 so I asked...

I was told it was new FIA requirement..
Made sense as there had been a) more heavier cars (Group A8 cars...that is "2000cc turbo" which had a min weight of I think it was 1230kg or 2706 lbs and b) they were faster than shit..about 3-5km/hr average faster than the old Group B cars...and because of the rules for minimum numbers of cars for complaince (Group B mandated 200 cars --of which 10% "could be Evolution of of base car' 9those were the bad-ass ones you see in the rallys) versus Group A where (until 1 Jan 1993) was minimum 5000 cars and very restrictive mods---so the were pretty bad ass out of the box)

So more people were going MUCH faster in heavier cars than before

So MAIN hoop diameter was increased.

Denting aside we have other examples of larger OD and slightly less wall has been used to make stronger things to resist bending>
We all saw the OD of motorcycle forks go from 35mm (1965 thru about 1979 when the for travel went from approx 150-160mm travel up to approx 300mm travel) which would bend every heat and the tube OD went to 38mm then 40 then 42 then 44mm and wall thickness went down...and the result being VERY strong and reliable forks where bending is virtually unheard of..

I should point out that the old FIA rule from then gave options for the rest of the tubes
They could be either 1.5" x .125 OR 40mm x .095....

Of course for the majority of people..obedience to any authority is a reflexive thing..so you get the "It's the rule, why wonder? Just obey" And, since those writing the rules here and those defending and enforcing the rule tend to be let us say less accustomed to dialog and analysis, their answer to nearly everything is "its the rules, must obey. Resistance is futile!"

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

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john vanlandingham

Strength.. strength in bending vs weight.... (valuable content).... Resistance is futile!"

Excellent answer, thank you so much. Exactly what I was looking for.

For the record, I prefer to be safe and follow the rules but I question also. Gotten me into trouble with employers........

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NoCoast
Why and who cares? It's changed, it's the rule, it's not going back so it's a wasted effort to wonder.

Stupid shit like this is why so many things are wrong in this world...

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Frank Gossett

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john vanlandingham

Strength.. strength in bending vs weight.... (valuable content).... Resistance is futile!"

Excellent answer, thank you so much. Exactly what I was looking for.

For the record, I prefer to be safe and follow the rules but I question also. Gotten me into trouble with employers........

You're welcome. I try...doesn't always work, especially with authoritarians and conservative, conventionally thinking consumers

And the last bit...Today in Merikuh asking question is almost universally considered to be an attack>

Really any response to anybody other than "That's so marvelous and you're so marvelous, so can I suck your big whanger? I'll let you come in my face" is considered a moral outrage.

It's hard to get reasonable answers when EVERYTHING anybody says is always wonderful.

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

In the USA the rule changed to not allow 1.5" main hoops in the 2005 Rally America rulebook for new builds. While I'm not certain of the exact motivations other than alignment with the FIA ruleset that happened that year, I suspect the lack of scales and increase in vehicle size and power led them to justify the change also. It used to be 1.5" main hoop was allowed on cars weighing less than 2500 pounds, which also happened to be cars that were small so the smaller tube is beneficial for clearances and such.

Now, NASA still allows for 1.5x0.120 main hoops for cars that: Allowed for cars weighing 2650 lbs or less, weighed without cage installed and full fuel but without drivers.
I would imagine many cars that could easily fit this category, probably every Open Light Subaru, many Open class GC cars and nearly every Group2 and most Group 5 cars I would hope.

The Rally America version used to say, "the vehicle weight is determined full of fuel and spares and race ready but without occupants" and the cutoff was 2499 pounds so easier to measure at tech provided there is a scale there

Now there should only be one time that you have to show that your car qualifies to use the smaller tubes in theory.

Software was likely not utilized in the decision. The incidence rate of main hoop failures may be monitored by the FIA and influenced their decision but definitely not enough sample in the USA to draw any valid inference. However, the USA sanctioning bodies, constructors, and competitors do like to make broad sweeping changes after single incident failures.
For example, the popularity of the bent V style door bar comes from an accident where the welded X failed and had the driver not died from massive trauma initially, he would have bled out from the door bar taking out his femoral artery. 120MPH sideways into a tree doesn't go well and the door bar style would not have saved his life, but it has become the preferred and common method after that incident.
Another example, Rally America requires every tube in top of car in front of driver to have roll cage padding after one wreck where the top of the a-pillar deformed all the way in to the driver's space.

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Grant Hughes