Possible to convince wife (wood ramp + jack stand) is safe?

Yeah, done my share of roadside flat tire changes using just the scissor jack provided with various cars. Agreed that they're not the greatest, but as you never need to get under the car to change a tire I've never really had any great concerns about doing this. Interestingly I've always done exactly the same procedure as "cnschult" suggests.

1. Crack loose the wheel nuts before you jack it.

2. Jack it up and remove the wheel then immediately slide it underneath the car (adjacent to the jack). Then in the worst case scenario, that it does fall, then it doesn't go all the way or damage anything.

3. Put on the spare and spin on (lightly tighten) all the wheels nuts.

4. Slide the old wheel out from under the car, lower the jack and finally tension all the wheel nuts.

 

I would add a step to the beginning of that procedure:

0. Depress the parking brake pedal as hard as you can, to reduce the likelihood that the car will move as you are jacking it up. (If you are jacking up a rear wheel, then the car is being held in place primarily by the other rear wheel, which is somewhat precarious. The front tires are held by the transaxle parking pawl (assuming the transaxle is in P) but the pawl allows some play which may be sufficient for the jack to slip.)

 

I never get underneath a car to change a flat, you are absolutely free to carry around a cool, heavy expensive aluminum racing jack, but every hydraulic jack I've ever seen at Harbor Freight, Menards, Autozone, Walmart or wherever also advises you to use jack stands after the car is lifted because a Hydraulic jack is meant for high strength lifting, not long term lifting, that's what the stands are for.

plastic $2 chock weights 4 ounces, it can also be used to throw at someone who won't shut up, your parking brake can't do that.

 

Stumbled upon this ancient discussion and got me curious. To give the OP question a scientific answer and close the wood ramp safety discussion once for all: if there is stack of solid wood under the contact of the tire all the way to the ground, you have much greater margin than the tire gives you.

As an example, the worst doug-fir gives 250psi tensile-strength-perpendicular-to-grain property and tires are typically inflated to 36psi. This means the wood can support 250/36 = 6.9 times the car's weight before the split can happen. If it is a 60psi spare, you will get 4x of the margin.

In fact, you can do a 50% slotted design and it still gives you half the margin (3.4x). Or single 2x4 will do but I would stick with 2x10 to prevent putting stress onto the tires.

So the bottom line is the weight of the car does not matter but the pressure of the tires do.



Source from https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch04.pdf

 

Your wife is right. I would never trust getting under the car with it up on just wood. And you never even chocked the wheels.

I use a floor jack I jack it up real quick and slide a metal ramp under the wheel and then go around and do the other side.Its too low of a car to drive it up on this ramp.