I started riding 4 years ago, then had our last baby, moved across the country, etc... then started riding again after settling here in Missouri. I upgraded from a Walmart bike to a Trek Skye and broke my leg the first 5 minutes due to my ignorance on psi. I am eyeing the nice, smooth highway 54 with the wide shoulder to ride on instead of our country roads. Though I've never done that either. So, two questions, bear with me... I am wondering if I need to change the psi if I go from one type of road (gravel/dirt) to the other (pavement) during a ride? Also, what psi is recommended for a mountain bike on pavement at 200 lbs? Is there a psi chart or something out there on the internet? I was never nervous about riding a bike before, I just did it but my ignorance cost me. Thanks a lot for your help.

I have never had an issue with psi . did you crash or skid out becuase your tire was at a bad psi for the terrain. Different tires have psi ratings printed on the side . different terrain with your tire psi can effect ride but its mostly personal preference. More psi will make a tire more firm and can increase istability on ruffer terrain , but can increase speed and effeciency on smoother terrain. Lower psi can soften a tire allowing it more grip on ruff terrain or soft terrain like snow mud sand . but decreases effeciency which can effect speed mostly on smooth pavement . best exaple is lowering psi in muddy terrain will make you faster but once you hit smooth tarmac you will be saggy and loss speed . its kind if simple kind of complicated if your off road to pavement 60psi to 80 psi should be fine id say .

Should have recommended PSI range on side of your tires. Sometimes hard to see but you'll find it. Every brand and model have different recommendations. Or maybe you can look up your tires online but by the time you find Make/model and size on your tires you'll probably find the pressure range. You can find the right pressure charts and graphs online for you weight + bike to tell you their suggestions. But I just run highest tire range for hard roads and toward lowest for gravel. But I'm just that way.

General rule of thumb; rougher the terrain, lower the psi. It allows more surface area of the tire to make contact, thus improving traction while also allowing it to better absorb/cushion over stones and other road imperfections. I don't think you need a chart, just trying riding at various settings among different terrain types and see what you like; you'll be able to feel the difference immediately.

Thank you all for your replies. Yes, it was bad psi for the terrain. We found the psi range on the side of the tires, thank you very much. I have a lot to learn. : ) Sounds like I need to give it a try and see how it feels at different settings. Thanks again...

Tire manufacturers often have something like this: https://www.vittoria.com/us/tirepressure

The psi range on the side of the tires is good to bracket your tire pressure (pressure is what you are setting, psi is the units*). You should know that the thinking has changed over the years on tire pressure. This article gives some guidelines:
https://www.cyclingweekly.com/news/p...ressure-270668
One thing to keep in mind: the optimal tire pressure depends on tire size. If your tires are 32mm wide, you can use a lower pressure than if they're 25mm. As a guideline, I just bought new tires for my wife's bike. You go by rider weight plus bike weight. For about 170lbs, I inflated new 32 mm tires (Bontrager R3) to 55psi in front, 65 in the rear. She loved it - much better than the 70-80 psi we had used before. But the article cited is for road bikes: search around for similar articles suited to the type of riding you intend to do.

The tire guidelines should get you to a safe pressure that is within 10psi or so of the pressure that will have you most comfortable and confident. I would especially emphasize that whatever recommendations you find for tire pressure, DO NOT exceed the max pressure recommendations on the tire.

*psi is pounds per square inch*, which is a pressure, not a weight. The "bar" is the pressure unit used elsewhere in the world. It's about 14.5psi. Atmospheric absolute pressure is about 14.7psi. So one bar is about one atmosphere. There's a discussion on gauge pressure vs absolute pressure (your gauge reads the difference between the tire and the atmosphere - the absolute pressure is the gauge pressure plus atmospheric). But that's not necessary: just remember that when properly inflated, the pressure your tire gauge indicates should be within the range specified on the tire. And all the tire pressure recommendations are for gauge pressure.

The second calculator down on this page is a good guide to start with:
Bicycle tire pressure calculator

My wife has a Trek Skye with 27.5 x 2" tires at 40psi. We ride on paved roads and rail trails with gravel and dirt. 40psi works well for pavement and off-road.

Not really. Tires at very low pressure can be squirmier on pavement, but that's only noticeable if you're really cornering hard. Excessive squishiness can also reduce your rolling efficiency somewhat on smooth surfaces.

For the most part, it's cumbersome to change PSI during a ride, and usually not worth it. Most of the time on a mixed-surface ride I'll configure my tires to something that makes sense for the rougher stuff, and then just not worry about it.

For a paved-only ride, given the stock tire sizes on your bike, I might start at around 40r/30f and work from there.

Mostly you just need to learn to feel your connection to the surface beneath the bike. Charts are a good starting point, but tires and riders vary, and they're no substitute for experience.

Some tires can be safely ridden at much lower pressure than recommended by the manufacturer. Michelin recommends 75 psi for my Protek tires at my weight (160 lbs). The tires felt harsh and jittery at that pressure. I experimented and mostly prefer them at 50 psi now. No problems. It's a reasonable compromise for pavement and gravel, etc., so I don't need to fuss with adjusting pressure.