a 15% drop …

Screen Shot 2016-04-30 at 3.07.05 PM

How hard do you inflate your tires?

Many cyclists simply inflate both the front and rear tires to the maximum recommended on the sidewall of the tire. That’s what I did for years. I never considered that too much (or too little) pressure may affect my comfort on the bike, not to mention speed or safety.

It turns out there is an optimum tire pressure given your weight, the bike’s weight, road conditions, and tire width. It turns out that under a full load, the tire performs best when there is a tire drop of ~ 15% as illustrated above. This drop puts more tire on the road improving traction (particularly when cornering and in wet weather), and comfort.

So, how do you determine the optimum tire pressure for your bike. Fortunately, there are several on-line calculators that make it easy. This is the one I use regularly. I have 3 sets of 700c wheels each equipped with different tire widths – 23 mm, 25 mm, and 28 mm – and subsequently optimum tire pressures.

Screen Shot 2016-05-01 at 10.10.59 AM

Credit Jan Heine commentary and science on this topic. Click here to load the calculator.

The first thing to understand is that both the front and rear wear must have a 15% tire drop, and yet there is not an equal amount of weight on them. The rear wheel generally carries more weight depending on the type of cycling you do and the bike fit. Generally, road bikes have 60% on the rear wheel and 40% on the front. This is the weight distribution I use.

The above example is the calculation I use for the Garneau carbon bike with 25 mm training tires. Given my weight, I do not inflate anywhere near the maximum allowable – 90 psi in the rear and 72 psi in the front.

And one other thing. Don’t forget to check your tire pressure before every ride. The high pressure and low volume of air in these tires makes them deflate more quickly than that in higher volume, lower pressure car tires. Too little tire pressure not only roll more slowly, but are more susceptible to flats, and possibly rim damage.

Let me know if you notice a difference 😎

Advertisements

22 thoughts on “a 15% drop …

    • Same. I discovered this several years ago and have been experimenting since. I don’t always follow the calculator’s recommendations exactly but always inflate the front less than the rear tire. This winter I trained on 28 mm tires, and because of the wet conditions, inflated both tires less than the recommended psi. This made a huge difference on both comfort and grip.

  1. Good post. I have been running lower and different pressures in my tires for a while now wit the front usually 5psi or so lower than the rear (85f/90r). I have seen that chart before but it recommends 62psi for the front which just seems like a pinch flat waiting to happen.

  2. Interesting. I’ve been whacking 100 psi front and rear in my 23mm tyres for years now and hitting the roads! According to that calculator I should be around 92 / 74 psi for my pressures. I’ll have to give that a go and see. My bike is pretty harsh so any extra cushioning would be a bonus.

    • I did the same for years. Now I dial it back. Also, I ride with 25 and 28 mm tires on my training wheels which makes a huge difference on rougher or wet roads. Let me know what you think.

  3. I knew not to inflate them to 120 psi, but I had no idea there was supposed to be a difference between the front and rear tires. I am gonna try out the recommended pressures tomorrow and see what happens!

    • Thanks Gail. The calculator I reference only supports tire widths up to 25 mm. If your tires are wider than that there are other calculators. But the principal is the same. If you are carrying loaded panniers, then the 40/60 distribution will not be accurate. More weight will be over the rear wheel. You can actually measure this yourself with a set of scales. Good luck and let me know how you make out.

      • Thanks Gary. That’s helpful. I thought the same about the weight being greater for the rear wheel. So with a little adapting, it shouldn’t be too hard to work out what’s right for my tyres. When we’ve driven a 4wd vehicle on the beaches, we’ve always reduced the tyre pressure for better rolling. After I read your post I thought, it makes sense to do the same for a bicycle 🙂

      • Yes. It’s the same principle. I would always inflate my road bike tires to the maximum until one day I was mountain biking and realized I needed less not more pressure to grip the gravelly trails. That’s the point I began doing some research.

  4. Pingback: Tire pressure – Cranky's Corner

  5. Pingback: What tire size? | PedalWORKS

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s