Can I use it on my mountain bike wheels and chain?

You COULD in a pinch but shouldn't, you'll want to find an appropriate lubricant that isn't also a penetrant. Basically, this isn't lubey enough for your needs.

Can I use it on door hinges that are squeeky?

You can, and it will get into the hinge quite well and should stop the squeak. But it will evaporate over time, so I tend to use oil, such as 3 in 1 or even motor oil. Let it drip from the top and wipe off any residue. I have also raised the pin a bit and let the oil drip into the hinge.

Does it cause harm to car paint?

Yes. Paint is oil based and so is wd 40.

Is it suitable for garage doors that get hung up

Yes, however you are better off using WD-40's Specialist Gel Lubricant for a garage door. The gel lubricant will stay in the general area where you spray it, regular WD-40 will run down the track provide less friction control where you need it.

ASIN	B01ECA63ZE
Item model number	490058
Manufacturer	WD-40 Company

WD-40 Multi-Use Product with SMART STRAWÃ‚ SPRAYS 2 WAYS, 12 OZ [6-Pack]

Details

Description

Specifications

Reviews

Common Questions