Competition -- Strength
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How strong does it need to be? What determines the strength rating?, etc.
We have auto rotisseries that are rated from 1500 lbs. capacity to 4000 lbs capacity. The Automotive Lift Institute which certifies garage type 2 post and 4 post lifts generally requires a 3x strength requirement for safety factor in the design with low carbon steel that we use. When I decided to market a lift in 1988, that I had designed for our own project, I decided that 2x was sufficient for the application. Rotisseries are designed to keep people from working under them, so didn't need the 3x limits of 2 post garage lifts. This would also keep the price within a range the typical hobbyist could afford.
So when we say 1500 lbs, we have designed the unit to hold 3000 at the end of the 4 arms that attach to the car body, without the steel being stressed beyond it's yield limit, such that it was permanently deformed. This weight is freely sitting on those arms, not double bolted to the car frame, so your car is part of the structure holding the end of the rotisserie up!
You see all kinds of claims out there for 3000 lbs. rating, etc. We have not yet found a competitor's rotisserie that we we would rate at 3000 lbs. We have found units that we would rate at 750 lbs. to 2000 lbs. They can talk about all their years of restoring cars, but that doesn't change the laws of physics nor strength of materials.
As a direct result of some previous postings on our web site, one manufacturer shows a 5000 lbs. vehicle on his rotisserie. Well, it's a good illusionist trick worthy of pulling a rabbit out of the hat, but doesn't change the real strength of his unit. I'm not saying they doctored the photo. However, they hope you won't notice that the car is supported way back close to the base of the attachment arms, not at the ends like your body will be mounted. Even a small 1.90" O. D. pivot pipe that we have seen on one unit, would take over 30,000 lbs. in pure sheer stress, but it's the bending stress that is in play here. Kind of like holding a pencil between your thumbs and fingers touching each other, and trying to break it. Then move your hands to the end of the pencil where you have some leverage, and it's easy. It's force times distance. If I wanted to immediately make my 1500 lbs. unit honestly a 3000 lbs. unit, all I have to do is reduce the attachment arm length from 15" to 7.5". (assumes the other components like casters, etc, would take it). One manufacturer who claims 3000 lbs capacity has a big warning on the instruction sheets saying you can put a car body or a frame but not both at the same time on his rotisserie. Hey, a typical frame is 300-500 lbs. A body shell is 600-1000. So why can't I put 1500 lbs on the 3000 lbs. unit I just bought?
I have attached here a photo we took the other day to demonstrate that we mean what we say. We have here a 1974 Roadrunner, less seats, engine and transmission. I haven't had it weighed, but would guess it's about 3000 lbs. We put it on our 1500 lbs. Bottoms Up Lift. We used the hard caster version, as the 12" pneumatic casters are only rated for 500 lbs. each. You will notice no center tongue sag here also.
It's mounted at the end of the 15" attachment arms, like your car will be mounted.
Our 2000, 3000 and 4000 lbs. lift are that much stronger. 1500 lbs. is plenty if you have the car stripped. If you want to keep the glass, doors, trunk on, you probably need 2000. If you want to keep the suspension, you probably need 3000 lbs. Our 4000 lbs. unit is designed (originally) for Chrysler people so you can remove and attach the K frame while on the rotisserie. Pick which one fits your needs.
