fatbillybob

It is pretty easy to mount aluminum seats to cages vs the floor. Manufacturers are pretty liberal in where you can drill a metal seat and mount it to a cage.

Fiberglass and composite seats that are FIA legal are only designed to be mounted at their factory base mounting points. Backbraces are typically contact with the seat back but not attached to it.

How can you attach plastic seats at the shoulder to the rollcage? Drilling plastic seats and bolting them may create some unknown structural problems for a plastic seat. Any ideas?

chrisp

look at Racetech's site. Last time I was there I recall seeing their recommendation for mounting their seats to the cross bar.

fatbillybob

That's because racetech was one of the first plastic seats to get on the bandwagon with halo seats for the viper's. They had molded in mounting points about shoulderblade level that were just like the base mountings. They also claimed at the time that their seat was good to 60g's IIRC where the FIA was using 20g as a standard IIRC. No other plastic seat to my knowledge has anchors in the back like racetech. I wonder if that will be part of the new CS218.08 homologation of new rally seats which may help them attain the supposed 100G crash survivablity.

I am just looking at mounting FIA seats that have gone past the 5 year point and looking at more secure ways of mounting them besides from the factory base and a "passive" back brace.

chrisp

At one point I thought about making a cradle to wrap around the seat at about shoulder level rather than just have a flat back support. If your seat has high enough bolsters at shoulder height you could build get a really nice cradle hugging the seat that will minimize side-to-side movement of the seat. Keep in mind that most plastic seats are designed to absob energy by flexing. To keep room for flex you could put 1"-2" of high density foam (roll bar padding) between the seat and the cradle to compress and absorb energy.

fatbillybob

I agree that your idea sounds good. But unless it is attached to the seat vs passive mount you suggest (like a really nice back brace) it may negate the advantages of having your seat mounted to the cage vs seat mounting to floor. There is a risk in making things too solid but it is pretty accepted practice in the metal seat world to mount is 6-8 places. Plastic seat makers are totally silent on this issue. Maybe the backs of plastic seats just are not able to take the potential loads and should not be called upon to take them. Maybe giant washers and many attachment points could distribute loads well enough with ruining the integrity of the seat. I think this is more of an issue when someone wants to use a seat longer than the FIA 5 year period.

RedlineMan

Simple;

Treat your plastic seat just the same as an alloy one. The important points are indentical.

- Brace at shoulder height.
- Give some thought to supporting the headrest portion of the seat.
- Make sure you have sufficient surface area included for both the backing of the brace, and for the bolt holes, so they will both spread load over a wide area. If you are nervous about drilling, use bonding adhesive.

Remember, regardless of what the FIA says, the idea of flex is not necessarilly a good thing. Prolonging the event, whip effect, occupant dumping, etc, etc....

kurt M

I can’t find any info that points to plastic seat flex as planed by the seat makers. There might be pleny to the contrary as I don’t have real inside info or training. What I have found so far and in simplistic form is body movement during a wreck is not “energy absorption” and movement is not good. I remember watching a Porsche supercup car video and being surprised to see how much the seats and drivers wobbled around during normal driving much less a wreck.

The composite seat makers all seem to prohibit any drilling of the seats or mounting in locations other than original. My guess is that added fastener points would be considered unplanned stress risers. I bet you could make a large surface area conforming plate that has its own threaded bolt points and then bond the two together. You could also scuff up the surface of the seat back to promote adhesion and lay up more of the same material as was used to make the seat. Lay in threaded sockets or studs that have large washers or better a perforated plate or framework that spreads the load out. This would add mounting points without drilling or reducing the original strength. You could also lay in a boxed frame like structure with bolt points to give more stiffness and strength if that is wanted as well. I bet the composite seat makers would all prohibit any of this regardless of it truly improving the seat or not.

fatbillybob

Thanks REDLINEMAN. That's what I was looking for. Me fear was as Kurt posted above which was drilling and creating stress risers. I have thought about bonding or glassing in additional anchors but feared that if you did not get an anchor integrated into the seat at its base layers that the glass would just fail at the new to old interface.

RedlineMan

I agree;

Most people do not have the expertise to lay up glass properly. I imagine the seats are bagged or pressure molded anyway. I would not be confident that anything added on would integrate. If you created some sort of bracket that encompassed a wide surface area, used four fasteners across the shoulder wing plane, and then bonded with panel bonding adhesive besides, I would not worry. It would be bullet proof.