I'm considering leaving a 42lb floor jack in the trunk of my car (I have to do my wrenching off site, so this would save me the hassle of bringing it from my apartment to the car, and back, every time I needed it). Plus, I'd much rather have a floor jack and stand than the scissor jack in a roadside repair situation, but this is a secondary motivation.

As far as extra weight, I'll take the scissor jack out and put in a jack stand, so those will roughly cancel each other out, so figure 40lbs of extra weight. Given that the car is ~3100 lbs with me in it, it's a 1.3% increase in load, so I'm going to assume only trivial gas mileage difference.

As far as handling, I suppose securing it in the center forward portion of the trunk (closer to seat) is optimal, and would keep the jack out of the way for routine loading/unloading of other stuff.

The most important issue is how can I secure the jack so that it's not a flying projectile that damages the rear quarter panels, or worse, comes flying through the back seat in an accident? I'm thinking strong nylon rope, backed up by bungee cords, but not sure where to attach them. It's going in a 6th gen Accord EX coupe.

 

You're seriously worried about 40lbs of extra weight? Just get some bungee cords and strap it down to the webbing in the trunk you don't need a thread for this.

 

That was my initial reaction, then I read this thread: ideas for how to store a floor jack in the trunk.

 

I've carried my jack in my trunk from time to time, and it doesn't really move that much. Mostly the movement is side to side, or it will try to push forward if you have to brake hard. So I just put it against the back of the rear seats. If you really want to keep it steady you can put things on either side of it, but honestly for normal driving you could probably keep it in the center of your trunk and it wouldn't even move by the time you got to where you are going. It's not like a 40 lb jack is just going to bounce around all over the inside of your trunk.

I guess if I was serious about making it permanent and stable for aggressive driving I'd probably screw in some tie-down loops in the back of the trunk and do some rigging.