I have a pair of 16,000 lb Rhino ramps I drive my cars up when I change the oil. Because of stories of ramps and jacks failing, I like to use a stack of boards that I have in my garage, as a backup plan. I put them in between the two tires on each side.

My question is—is there a given height that my stack of boards should go? Do I simply have to put my stacks high enough to allow me to have room, below the level of the boards, if the chassis falls? Or could the innards at the bottom of the car, drop lower than the frame itself, that is resting on the boards—in which case, I’d need to give myself a few extra inches of leeway here.

How high do you want? Each board is about 1.5 inches thick. So for whatever hight you need you can calculate from there. I put in four layers. It got my Versa up 6 inches. Perfect for my oil change on the Versa. Need higher? Add layers but know that wood can be heavy so you are adding weight as you add on height.

I’d recommend the full height to the chassis and tight against the chassis. May I recommend to pick up a set of jack stands on sale. They are are much easier to work with. (But rememeber to pull them out at the end of the job. )

https://www.walmart.com/ip/Torin-Jacks-3-Ton-Jack-Stand-Pair/14560047

Regular price is over 100 bucks. Is this a reputable company? WM has them for $24. 3 ton capacity would cover the Sienna as well.

Alternately, PB has this set: https://www.pepboys.com/product/details/1154551/00773?quantity=1

Harbor Freight: https://www.harborfreight.com/3-Ton-Steel-Jack-Stands-61196.html

Not sure which companies can be trusted here. Rather not use chinesium as my backup plan.

$100 is [censored] wishful thinking, marketing. Those are around $25 anywhere you go.

There, I fixed that for you.

I'll vouch for these (That all pretty much come from china, no matter who sells them)

The ratings are utterly ridiculous - 3 tons (6,000 lbs) is wishful thinking at best.

Used properly in general auto use, they are just fine.

I like to place a 12" x 12" square of 3/4" plywood under each one
when used on any surface other than concrete.

My grandfather built something similar to these about 50 years ago.

They are nearly indestructible & will hold a semi-truck!

If you are worried about the ramps failing make some of the pine-o ramps. That is what we used when servicing semi's.

I see why he has wheels … mine are heavy enough that I put a gate handle on the end

Purchase 2, 2"x 10" x 12' boards. One board will make a ramp. Lowes will cut to lengths shown. Get some nails, or screws and adhesive. Cheap. simple, and heavy. I have used them for 8 years.

One nice thing about these is they will not slide away when bringing a RWD vehicle up on them … the first 1-1/2” rise pins them down tight
Pine-O Ramps have their place …

I use the harbor freight jack stands when I need to use jack stands.

If wood is capable of holding up the car as the primary support, it should also be ok as a backup support, shouldn't it?

If possible, I'd like to get more input on my original question--assuming I'll continue using wood boards, how high do the boards have to get? Snagglefoot said take the boards up to the height of the chassis. Is that what is best or what everyone does, who uses boards?

My ramps are a stack of 2 x 12s. For safety I throw a short log or two under the car and chock a wheel. It's not worth taking short cuts when it comes to safety.