Bicycle Mechanics - What tire pressure should I run?

Hi. It's been a long time since I've posted. I'm just starting to use my bike again after a lapse of a few years. This time I'm going to keep at it, even during the winter. I'm fed up with being fat and unfit. I've already modified my diet, eating more healthy and counting calories, and I've started riding again as part of my fitness program.

I'm 55, 6 feet tall, and unfit. I weigh 232 pounds today. Six weeks ago I was 257 pounds. I'm riding about 50 to 60 miles a week now, and looking to increase that as I get more fit. I know that is not much, but at my current couch potato level of fitness, it seems like a lot to me. And it seems to be helping me to drop the pounds.

I have a riding partner who also has a weight loss objective. He is 40, 5 foot 6, and 148 pounds.

We don't know much about bicycling, and don't know much about our bicycles, but we are looking to learn. Hence the basic question about tire pressure.

I have a 2007 Trek 7.7 FX, Bontrager Hard Case Race Lite B 700x28 tires. He has a 2007 Trek Soho, same type tires, but 700x32 size. Those tires are both rated to max 125 PSI, according to the sidewall legend. We've been running 110 PSI in front and back tires on both bikes, but based on what I've gleaned from recent threads on this forum, I gather that running the same pressure regardless of tire size and total riding weight is not the typical approach.

So I'm wondering what PSI we should use for our weight and tire size? Should front and rear be the same pressure? What would be optimal? We ride only on smooth dry paved roads and paved bike trails, if that makes a difference.

We're not trying for ultimate speed, as neither of us are fit enough to go very fast at the moment anyhow. Neither are we looking for ultimate comfort, and we are trying to push our exertion to useful levels. The objective is daily exercise to burn calories. So we just want to know what pressure is "normal" for our bikes, tires, and our weight.

The rear wheel carries a much higher portion of the weight. I think at your weight and with good quality 28 mm tires it would be better to run the rear tire up to 120 psi.
Your friend with less weight and bigger tire could run significantly less pressure.

Inflate them both up to what they're supposed to be. Take it easier! Do more and more gradually! And id reccomend a bike trainer for the winter. A great brand for trainers is Cyclops.

Here's a chart of recommended tire pressures vs tire size and wheel load to achieve a "tire drop" of 15%, which the author feels is a good compromise between comfort and performance. http://www.bikequarterly.com/images/TireDrop.pdf

So, 120 for my rear tire. Is 110 OK for the front then?

I notice that my tire pressure goes down about 10 pounds between rides. That is, each day before I ride, I've noticed that the pressure on my rear tire will be 100 PSI, and I have to add air daily to get 110. And that's with a brand new rear tube. The front doesn't lose as much in only a day, but it will after two or three days.

I had not heard of a cycle trainer, but I looked it up, and it seems like a neat thing to keep you riding in bad weather. I live in Texas, and the winters here are not especially severe, so I'm not sure I'd use one much. Even so, a spell of bad weather would put a crimp in my exercise program.

Here's a chart of recommended tire pressures vs tire size and wheel load to achieve a "tire drop" of 15%, which the author feels is a good compromise between comfort and performance. http://www.bikequarterly.com/images/TireDrop.pdf

Ah, thank you. That's an interesting article. I need to figure weight distribution, and I need to extend the chart, as my weight is pretty far off to the right of where it ends. I suspect it's going to be more like 40/60 for me, as I have a more upright position than someone with drop bars.

Here's a calculator based on the bike quarterly information.

http://www.dorkypantsr.us/bike-tire-pressure-calculator.html

So, 120 for my rear tire. Is 110 OK for the front then?

I notice that my tire pressure goes down about 10 pounds between rides. That is, each day before I ride, I've noticed that the pressure on my rear tire will be 100 PSI, and I have to add air daily to get 110. And that's with a brand new rear tube. The front doesn't lose as much in only a day, but it will after two or three days.

Yes. You could experiment with 115 in the front and 125 in the rear, but the ride will be relatively harsh.
I weigh about 165 and run 110 in the front and 118 in the back. My tires lose about 5 pounds overnight, and 10 pounds is not unusual.

I'm a beginner as well. I posted a few threads with similar questions that may help you out.

http://www.bikeforums.net/showthread.php/854148-Im-new-so-I-dont-know-if-this-has-been-asked-Tire-pressure-question

http://www.bikeforums.net/showthread.php/854335-Looking-at-Conti-Gatorskin-Hardshells

Good luck and congrats on your weight loss!

Here's a calculator based on the bike quarterly information.


Here's the article itself. It does a decent job explaining the logic, and the graph makes it to know where anybody should be, absed on their tire width and weight (with some adjustment for pavement conditions).

I'm a beginner as well. I posted a few threads with similar questions that may help you out.

http://www.bikeforums.net/showthread.php/854148-Im-new-so-I-dont-know-if-this-has-been-asked-Tire-pressure-question

http://www.bikeforums.net/showthread.php/854335-Looking-at-Conti-Gatorskin-Hardshells

Good luck and congrats on your weight loss!

Thank you, MIke, for the well wishes and for the link to your previous questions. I learned a lot from both threads. It seems there is no single definitive answer, which doesn't really surprise me.

I feel comfortable riding with 110 in the front and 110 in the rear, but I'm going to experiment with other pressures. I'm sure I don't want to drop the pressure in the rear tire, but I might drop the front to 100 and raise the rear to 120 just to see the difference.

Run 90 lbs front and rear with the 28 tires. I'm 200 lbs and I run 90-100.

15% tire drop is important.

Tires need to flex when you sit on the bike, tires need to flex when you go over bumps. If the sidewalls do not flex because you've pumped them up too high, then the spokes will flex and the wheels will take the brunt of the bumps and your weight. The rims will crack at the nipples because nothing is flexing.