Wheel-Engaging Adaptors for Car Lift

[utahrock]

I recently installed a car lift in my garage and, besides the conventional way a lifting a car, I wanted to come up with an easy method to lift a car by the tires. I thought this would make many maintenance tasks easier and also give the ability to store the car like it was a four post lift. I like all kinds of tools and in addition to a CAD/CAM system and lots of design experience I happen to have a horizontal machining center.

Now there are one or two lift manufacturers that offer wheel-engaging adaptors as an option. But they are not very elegant, being heavy and ugly steel weldments and they don’t fit the tires on my sports cars very well. So I made these out of aluminum, 6061-T6 and anodized them. Everything is CNC machined and there is no welding. They were designed to have maximum tire contact to minimize the possibility of flat spots from prolonged storage. Each tire is supported by the two forks of the adaptors and so the tires have about twice the support area that they would have sitting on the ground.

Not wanting to drop an expensive car I did a finite element analysis which verified my initial calculations that they were very strong. The use of them results in somewhat more stress on the lift arms (because there is a twisting component) so the lift should be de-rated to about 50-60% of the normal capacity. My lift is 10,000 lbs., so that means I can use these to lift at least 5,000 lbs., which, while I won’t be lifting dump trucks, is more than enough for the sports cars they were designed for.

I like them so much that they have become the normal way I lift a car if I don’t have to take the wheels off. They have two big advantages:
1) The whole underside is accessible which makes removing undertrays and side panels fast and easy.
2) I can store a car with the weight on its tires just like a four post lift, but the two post takes up much less room.

I almost bought an in-ground lift, but for my garage I’m really glad I got a two-post. I have two cars in this garage, but also a motorcycle and I do some woodworking, too. The ability to leave a car in the air and park the other under it gives me a lot of room for the other things I want to do.

[64dragnwagon]

Nice work! I never really thought about it but would it be bad to lift a car the conventional 2 post way with the tires suspended for a long period of time? What kind of problems could it cause?

[jhelrey]

I like it! Granted, most of the work I do requires the tires to be hanging free.

[rburke65]

Utharock....very nice. Is that a Mohawk lift I smell? I bought a used one but don't have it installed yet....do you like yours? What would a set of these cost if one were able to have a set made? Thanks much!

[billybek]

That is pretty cool!

[Steevo]

Slicker 'n owl shit.

Very cool mod to your lift.

Nicely done.

[utahrock]

Originally Posted by 64dragnwagon

Nice work! I never really thought about it but would it be bad to lift a car the conventional 2 post way with the tires suspended for a long period of time? What kind of problems could it cause?

Some people say that suspension components can be damaged by hanging for a long time since they weren't designed for that. I think it probably depends on the car.

Originally Posted by jhelrey

I like it! Granted, most of the work I do requires the tires to be hanging free.

I like the adaptors so much that I usually use them. If I need to take off only certain wheels, for example on my 911 the right rear needs to come off for an oil change, then I just use a conventional lift pad in that position.

Originally Posted by rburke65

Utharock....very nice. Is that a Mohawk lift I smell? I bought a used one but don't have it installed yet....do you like yours?

Yes, it's a Mohawk System 1. I like it but they are expensive, of course. I found a nice demo unit at a discount. It fits better in my garage than other, taller lifts that have a top plate for a cable. The Mohawk just has the hydraulic lines and they can be mounted so they don't interfere with the garage door opener. One point: Mohawk lifts are supposed to be self-bleeding, but mine didn't get rid of all the air on its own. I had to crack open a fitting to get the air out.

[balddave]

Well executed plan!

I'm concerned with the aluminum tho, did you give any consideration to fatigue? Even if you're below a stress limit of aluminum its only a matter of time before it fatigues and gives out, it might not be for 100's of years in which case you're well past the usable life of the rest of the system, but if the stresses are relatively high then it might be much sooner... Worth investigating if you haven't yet.

Good catch on de-rating the lift, lots could over look that aspect.

[nehog]

Originally Posted by 64dragnwagon

Nice work! I never really thought about it but would it be bad to lift a car the conventional 2 post way with the tires suspended for a long period of time? What kind of problems could it cause?

AFAIK, no vehicle can be damaged that way. I lift vehicles for long periods of time (I use my 2 post for storage in the winter.)

Vehicles are made to handle full droop, with force, which can happen in many driving situations. To think that gentle dropping to the stops would damage something is not very logical.

[carhunter]

great work!

[abstamaria]

Originally Posted by nehog

AFAIK, no vehicle can be damaged that way. I lift vehicles for long periods of time (I use my 2 post for storage in the winter.)

Vehicles are made to handle full droop, with force, which can happen in many driving situations. To think that gentle dropping to the stops would damage something is not very logical.

One torques the metalastic or bonded rubber suspension bushes on some cars at ride height. At ride height, therefore, there is no twisting of the rubber in the bushes. At full droop, the bushes are twisted and strained. Accordingly, the common wisdom is never to store a car in full droop position. Most car museums, high-end storage facilities follow that rule. I suppose a car with rod-ends, as in racing cars, can be kept on full droop.

[utahrock]

Originally Posted by balddave

Well executed plan!

I'm concerned with the aluminum tho, did you give any consideration to fatigue? Even if you're below a stress limit of aluminum its only a matter of time before it fatigues and gives out, it might not be for 100's of years in which case you're well past the usable life of the rest of the system, but if the stresses are relatively high then it might be much sooner... Worth investigating if you haven't yet.

Good catch on de-rating the lift, lots could over look that aspect.

Good question on aluminum fatigue. I've been designing rock climbing and technical rescue equipment for a long time (see my homepage if you're interested) and most of it is aluminum because weight is important. The right alloy in the right use doesn't suffer from worries about fatigue. In fact, we also make some steel equipment and they can suffer their own problems.

For example, carabiners are made from 7075 aluminum which is much more brittle than the 6061 I used on the adaptors. But even so, we can load a carabiner to half its breaking strength 100 times, which generates an impressive amount of stretch and warpage, and then when we test it to destruction there is no reduction in ultimate strength. The adaptors use a much more forgiving alloy, but they are also quite stiff so there is very little flex, far below any critical amount. There are no sharp corners that can act as stress risers; the forks are one piece and the junction between the angled part and the square section sandwiched between the top and bottom plate has a nice, big radius cut with a 3/4 ball end mill.

Because of the alloy and the lack of stress risers, if the adaptors were overloaded they would tend to bend rather than suddenly break. If this happens, the mechanics of this would result in the load moving inward, which would reduce the force causing it to bend.

When I test new climbing gear I'm naturally apprehensive when I'm hanging on it over a big cliff for the first time. I felt the same way when I lifted my expensive car for the first time. But I approached it the same way, calculate it first, then test it. I had a cheap car I could have tested it with, but I was confident enough that I just put the Porsche on.

The picture below shows how much the adaptors incline when loaded. But this is not all due to flex in the aluminum. Over half is caused by the inner lift arm rocking in the outer lift arm, because there is some clearance between them. Some flex is caused by the inner arm twisting along its length. The farther out it is extended the more it twists. Some more flex is due to the adaptor rocking a little on the end of the lift arm. I tested it without tightening the bolt at all, but in normal use I snug them up. Very little flex originates in the aluminum itself. In the picture, that's the heavy end of the 911 and the load on that wheel is about 1050 lbs. and the angle is reading 2.5 degrees.

[admranger]

Originally Posted by abstamaria

One torques the metalastic or bonded rubber suspension bushes on some cars at ride height. At ride height, therefore, there is no twisting of the rubber in the bushes. At full droop, the bushes are twisted and strained. Accordingly, the common wisdom is never to store a car in full droop position. Most car museums, high-end storage facilities follow that rule. I suppose a car with rod-ends, as in racing cars, can be kept on full droop.

Exactly. This is why you set bushing with the wheels under full vehicle load (or you get to do it all over again in very short order).

It doesn't hurt for short periods of time, but you don't want to hang a car off a lift for months on end...

Oh, and UtahRock, the mod is very slick. However, 1050 lbs per corner? Time to put your p-car on a diet! My X5 makes those kind of scale loads.

[utahrock]

Originally Posted by admranger

Oh, and UtahRock, the mod is very slick. However, 1050 lbs per corner? Time to put your p-car on a diet! My X5 makes those kind of scale loads.

That's only on the rear. The front wheels are a little over 600 lbs. each. Still, you're right, a 993 turbo is not a light car...

[fordcragar]

Very nice!

[akdiesel]

That is a great idea and very nice craftsmanship.
As for the twisting effect and the de-rating of the lift due to it, dont the two post lifts have the twisting element already in place at the base of the arms? I am sure the companies have calculated the safety factor in for this, but a 50% de-rating for your improvement?

[tonycastec]

"The picture below shows how much the adaptors incline when loaded. But this is not all due to flex in the aluminum. Over half is caused by the inner lift arm rocking in the outer lift arm, because there is some clearance between them. Some flex is caused by the inner arm twisting along its length. The farther out it is extended the more it twists. Some more flex is due to the adaptor rocking a little on the end of the lift arm. I tested it without tightening the bolt at all, but in normal use I snug them up. Very little flex originates in the aluminum itself. In the picture, that's the heavy end of the 911 and the load on that wheel is about 1050 lbs. and the angle is reading 2.5 degrees."

Here's a suggestion to fix this on the next set you make !
Design the forks to angle upward by 15 degrees ?Would this help?

There are some great ideas for whee/tire engagement among the tools the "Repo" tow truck drivers use.

[240sxguy]

Nice car and very cool idea for your lift. Another big advantage that nobody has mentioned is at full lift height the car sits a little higher. At 6'2" often times I have to duck under a lift and this could solve that problem.

[utahrock]

Originally Posted by akdiesel

That is a great idea and very nice craftsmanship.
As for the twisting effect and the de-rating of the lift due to it, dont the two post lifts have the twisting element already in place at the base of the arms? I am sure the companies have calculated the safety factor in for this, but a 50% de-rating for your improvement?

Yes, it is very conservative and I am sure it would go higher safely. I guess I was so conservative because I can't find any vehicles I want to lift with the adaptors that weigh more than 5,000 lbs. anyway. I sized them to fit perfectly on car tires (specifically sports car tires) and consequently they don't fit very well on truck tires (although if you jack up a truck tire a little to get the adaptors under the wheel it will work). For testing purposes I lifted my Avalanche using two of the adaptors on one axle and two regular pads on the frame on the other axle (the wheelbase is 130" and the arms don't extend far enough to use the adaptors on both axles).

Originally Posted by tonycastec

"The picture below shows how much the adaptors incline when loaded. But this is not all due to flex in the aluminum. Over half is caused by the inner lift arm rocking in the outer lift arm, because there is some clearance between them. Some flex is caused by the inner arm twisting along its length. The farther out it is extended the more it twists. Some more flex is due to the adaptor rocking a little on the end of the lift arm. I tested it without tightening the bolt at all, but in normal use I snug them up. Very little flex originates in the aluminum itself. In the picture, that's the heavy end of the 911 and the load on that wheel is about 1050 lbs. and the angle is reading 2.5 degrees."

Here's a suggestion to fix this on the next set you make !
Design the forks to angle upward by 15 degrees ?Would this help?

15 degrees would be too much. You could go 2 or 3 degrees and then they would end up about level when loaded. But the slight downward inclination is not a problem at all. It actually increases capacity because it moves the load inward. I did my calculations at a worse case senario so the downward slope makes the load rating even more conservative.

Originally Posted by 240sxguy

Nice car and very cool idea for your lift. Another big advantage that nobody has mentioned is at full lift height the car sits a little higher. At 6'2" often times I have to duck under a lift and this could solve that problem.

Yes, that's a good point. I'm 6'2" also and the extra working height is very nice.

[Britwrench]

Neat, the only thing that concerns me is the sideways force of the tires against the forks as the vehicle is lifted.
Could you have a "fork within a fork' so that any sideways movement was taken care of?