Wednesday, July 2, 2014

The Frugal Mountain Biker: Part 7 - Lower Tire Pressures

What is the most important part of equipment on your mountain bike?

Suspension forks and shocks? Nope! Rigid bikes don’t need those. 30 speed derailleur drive trains? Nope! Single speeders only need one set of sprockets. Carbon fiber frame? Nope! Steel, aluminum, and titanium frames are still very popular and work perfectly well. Hydraulic disk brakes? Nope! Mountain bikes had cantilever brakes for many years and they were still very usable.

It is true that almost all of those components are very important for most modern mountain bikes. However, back in the 70’s when BMX & mountain biking started, the one thing that made it all possible was the development of off-road knobby bike tires. Without them, it was nearly impossible to get off the pavement without any kind of measurable control. Since then, MTB tires have made huge improvements over decades of development.


To me the computer designed WTB Bronson tread pattern really is a thing of beauty.


Because your MTB tires are so important and there is so much material to cover on this subject, I will be breaking it up into several articles. In this article I will be covering how important tire pressure settings really are.

Using the correct tire pressures on your mountain bike is possibly one of the most effective ways to dramatically improve your riding. One of the most common problems that I see in beginner MTB forums is that many riders use tire pressures that are way too high. This is from one of the forums:
MTB beginner: “I am having trouble staying on my bike. I am not sure what I am doing wrong. I really want to improve and it is very frustrating.”
Me: “What kind of bike do you ride?”
MTB beginner: “I bought a Kona Explosif for $200 at a garage sale. The previous owner said that it sat in his garage for many years. I had it checked out by a local bike shop mechanic. He tuned it up and said that everything is in good shape and working well. Here is a pic of it. Is it a good bike?”
Me: “Major congrats! You landed yourself the bargain of the century. That is one nice ride that should give you many years of enjoyment out on the trails. Where do you ride? Dirt path walking trails? Fire access roads? Limestone trails? Single-tracks? Ski parks? Pump tracks?”
MTB beginner: “All of those except ski and pump tracks. There are some really nice trails very close to where I live. I want to try them all.”
Me: “Those look like Kenda Nevegal tires with plenty of meat still on them. What tire pressures are you running?
MTB beginner: “I run 45-55 psi. I like a firm ride (for both my bike and my car).”
Me: “There is your problem… 45 – 55 is good for pavement, but those air pressures are way too high for off-road dirt riding. That will make your bike bounce and jolt you over every little pebble and twig on the trail. When it gets bumpier, you will have even more problems keeping the bike under you and in control. I weigh around 210 Lbs and run around 25 - 30 psi. If you weigh less than me, then you can probably run slightly lower psi to smooth out your ride even more.”
MTB beginner: “Wow, OK, I will try that. Thanks!”
He later on thanked me because it made such a huge difference… I am always willing to help a fellow mountain biker! Even for us riders that have been at it for a while, maintaining proper tire pressures is very important. Make sure your tire pressures are always properly set.

Last month, I noticed that my bike was slow and I was pedaling with more effort than normal. I then noticed that my rear tire was a bit noisy. I stopped and checked my tire pressures (I always ride with a small pump and gauge). It read 15 psi front and 12 psi back. I pumped them both up to 28 psi and off I went. It made a huge difference in the amount of effort that it took to get up to and maintain speed. I probably also had just avoided a flat tire. Now-a-days I check my tire pressures much more often; usually right before I get ready to take my bike out for a ride.

So what are the best pressures to run? Is it the same pressure for every kind of surface?

  • Like I previously mentioned, 45 – 55 psi is a good pressure if you are riding pavement or packed limestone trails. For off-road use, you will lose a lot of grip at these kinds of pressure. High tire pressures like this do tend to lead to tire slides on dirt trails. It also makes the bike much too bouncy, jittery, and more difficult to control.
  • For fairly smooth hard pack dirt trails and fire access roads, running between 32 – 42 psi works great.
  • The best pressures to run at for regular dirt trails are between 25 – 35 psi. This gives the tires the ability to flex, deform, and wrap itself over the smaller debris on the trail. This absorbs most of the small trail chatter and also offers superior grip. 
Lower pressures can offer even bigger benefits but there is a limit. Too low and you start to get pinch flats. What is a pinch flat?
Pinch Flat Definition:
A pinch flat is when you run over something with your bike tire that pinches your inner tube against your rim, causing a flat tire. A pinch flat is distinctive because it usually results in double punctures about an inch apart in your tube. This is commonly known as a snake bite. It happens because the contact usually occurs on both sides of your rim at the same time. A pinch flat usually happens on a fairly hard hit when your tires are under-inflated.



To optimize tire pressure settings, I like to find the sweet spot between traction, rolling resistance, and pinch flats.  It can take a little time, but once I get it right the benefits are huge. I mostly ride fire access roads, hard pack dirt, and single track trails. For my weight, I will usually start at around 30 psi. I then adjust up or down by around 3- 5 psi increments.
  1. Pavement and hard packed limestone fire roads, Raise tire pressure.
  2. Single track trails and softer soil, Lower tire pressure.
  3. Getting pinch flats, Raise tire pressure.
  4. Too much sliding on dirt trails, Lower tire pressure.
  5. If you are a heavier person, Raise tire pressure.
  6. If you have high volume tires (2.3" up to 2.5" or higher), Lower tire pressure.
  7. If you have tubeless tires, Lower tire pressure.
OK, so as you can see on the numbered items listed above; bigger volume tires running tubeless give you additional benefits of being able to run lower tire pressures than normal with a lower risk of pinch flats.


Going tubeless makes tire assemblies even lighter still, and lets you go with even lower tire pressures. I personally decided not to go tubeless just to keep maintenance super simple and down to almost nothing. Most mountain bike riders will agree that going tubeless is the only way to go. If you find yourself patching flats fairly often because of where you ride,the additional tire flat protection also adds to all of the benefits I just mentioned.


So, keep those tires properly inflated to the correct pressure, and check it often. Stay tuned for the next write-up in this series of “The Frugal Mountain Biker”.

2 comments:

  1. Nice article! I intend to pass this along to a couple friends who are new to mtb. I've tried to explain this, but you did a much better job!

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  2. Thanks! I am always glad to help any fellow mountain biker...

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