Helmet Clearance

[mandalman]

I will apologise in advance because I know this question has been asked previously but II just cannot find anything on a search.

A couple of months ago,  in readiness for my first season of track days I got a roll cage fitted to my superlight R. Because work has gone mental it has sat in my garage ever since and only today have I managed to get it out and take it for a spin. I thought it wise to check how much clearance I have with my Arai helmet on and it is millimeters away from the crossbar above me even though I have a lowered floor (it's an old Safety Devices cage). I've checked the club track day advice and all I can find is this:

Where a safety cage is fitted: positive helmet clearance must exist below the uppermost near-horizontal plane formed by the upper elements of the safety structure.

What is 'positive' clearance? I seem to recall seeing diagrams before where there had to be at least an inch clearance - I haven't got that.

I  think it may have been a mistake fitting it and I'd be better off going back to my track day roll bar. I'd hate to turn up to my first event and be disqualified from taking part.

Out of interest are other roll cages higher than the old safety devices cages?

[BrettJ]

Depending on what type of seat you have, can you not tilt the seat backwards which would lower you in the car? I did this in my MX5 Supercup car to give me the clearance.

[Shortshift]

Replying to #1

"What is 'positive' clearance?"

Anything greater than 0mm clearance between the top of the helmet and the defined plane.

James