On mountain bike tire pressure for heavy riders

Posted by SuperClydesdale on January 31, 2011 under Commentary | 2 Comments to Read

Note:  From my tire survey (which you should participate in if you have a strong recommendation):   This link is to the PDF summary of the Full Tire Survey with Comments from fellow heavy riders.

When you’re a big guy, tire pressure (and beer) is always on your mind.    Being a heavy rider, my immense weight will lay waste to an improperly inflated tire (as well as most other bike parts).

Too low, and you are going to pinch flat, rip the sidewall of the tire, or damage your rim.    You may burp out on a rock or around a tight corner and end up, as the tire manufacturers might say, “experiencing a loss of control.”  Well, in my experience, a loss of control on a mountain bike ends up with me bleeding.   I know enough people — and have received emails from readers of this site — that have ended up injured (some in the hospital) after a tire failure, usually related to running too aggressive a tire pressure.  Once your front tire is gone, you’re technique degrades… fast.

Most of these tire failures were an attempt to run too low of a tire pressure for the rider’s weight, or the condition of the trail.  What might work for hard pack is not going to be ideal for climbing up over sharp rocks, or a rapid, rocky, technical descent.  You might end up with a rapid descent, but not too technical.

If you ride with too much pressure, the tire is so hard that it makes for a jarring ride, and can also lead to diminished control, particularly over irregular surfaces where the tire will chatter across.  More tire pressure means less tire touching the ground, which makes for less grippy tires, which also limits the amount of control the rider has.   If you ride a hardtail like me, a high-pressure rear tire will transfer all of the bumps straight to your butt and back.  It’s like you’re riding a crappy deathtrap rollercoaster at the county fair.  You get back, and you feel pretty beat up, even if you stayed on the bike (or on the rollercoaster) for the entire ride.

What everyone strives for is the perfect pressure, which for cross-country trail riding almost always means “what’s the lowest pressure I can safely ride with?”  Unfortunately, there is no simple answer.   There are many variables that impact the correct tire pressure:

  • The rider’s weight (as well as the weight of the bike and other gear being carried)
  • The tire volume (2.1, 2.2, 2.3, etc)
  • The terrain
  • Bicycle type (hard tail, full suspension, etc.)

While it seems like it would be easy enough for a properly motivated tire manufacturer to create a chart or some sort of guidance, nothing seems to exist (if you know of such a thing, please let me know!).  For the most part, it’s left to the trial-and-error of the cyclist.   I’m all for trial, but with mountain bike tire pressure, the “error” part can be painful.

“How did you break your clavicle?”

“I had an error.”

I’m sure that at some point, some well-meaning engineering type at a tire manufacturer created such a document.  That poor fool but was quickly rooted out and fired by the company’s lawyer.  Once someone makes a formal recommendation, they are responsible for the consequences.  The corporate lawyer wants to avoid creating guidance that could be used against them by another lawyer — the lawyer of the guy that made the “error.”   As a consequence of our litigious nature, we are left to our own devices.

Each tire also has a recommended pressure range on the sidewall of the tire.   There’s not a manufacturer on the planet that will go on record telling you that you can go less than that.    While I have read many a story of feather-light whippet runts using significantly lower pressures, big guys like us are almost certainly going to be within the recommended ranges, and possibly at least several PSI above the minimum recommended.

Stan’s NoTubes is the only company I can find that provides anything close to useful information.   As a result, I’m sure the poor sod that published it is not longer with the company.  The recommendation is based on size 2.0-2.2 tires:

Rich O’Neil of Stan’s NoTubes sent me:

To determine a starting tire pressure when running NoTubes tires with our ZTR rims use this simple formula:

Front tire pressure in PSI:   (Rider weight / 7 ) – 1
Rear tire pressure in PSI :  (Rider weight / 7 )  + 2

For those of you who went to a California public school, this is called a formula.  I know it’s not really fair to expect that a bunch of public-school-educated mouth-breathing knuckle-dragging mountain bikers can solve a formula.

While Stan’s NoTubes says that this is just for those people using their system, it seems pretty darn accurate for just about any tubeless set-up, based on all information I can collect from conversations with people who have used tubeless tires for years, and from many hours of culling information from the Internet.

I am going to try the following, based on Stan’s NoTubes recommendations, and a 15% increase in PSI for trails with a lot of sharp rocks/roots:

Tire pressure chart for rider weight. Uses Stan's NoTubes recommendations, with a 15% kicker for rocks/roots.

Some of the Kenda guys came back with the following, with regard to tires with tubes:

“For tire pressure there is not necessary a rule, it is best to check the suggested tire pressure that is print on the sidewall of the tire, and normally I would have them start somewhat in the middle probably about 40~45psi. Test the bike with this set up, and decrees or increase “in case of pinch flats” the pressure by 3~5psi, the secret is to have a tire that deforms enough to the terrain which it allows good traction, but not to the point where you are having problems like pinch flats and such.”

-  Stafano Lumbaca, Kenda

” Pressure recommendations, cannot be based solely on rider weight. To do so, is only looking at one part of the equation. There are many other factors that need to be considered, such as bike type (rigid, front suspension, full suspension), your wheel selection, the terrain where you are riding, they type of riding you are doing, and what particular tires the riders are using to name a few.

Tire manufacturers set the recommended tire pressure ratings based on standardized testing as per country of sales. Those pressures aren’t necessarily what racers or even enthusiasts use when riding, but they are the base line.

The recommendation that I have always given riders is to solicit feedback from friends who are similar body type and who ride in the same area as you. In your case, your website would serve as a fantastic touch point for this type of user generated content. Then you can start with either the recommended pressure as a base line, or if you cannot find a suitable comparison point, just start with your tire pressure in the middle of the range and adjust as necessary. If a tire feels too sluggish, slow to respond, and you keep bottoming out on the rim; you need to put more air in. If the bike is skittery, you keep sliding out, or the ride is overly harsh; let some air out.”

-  Ben Anderson, Kenda

To me, these are “manufacturer cop-out” recommendations.   They basically say, “trial and error,” and expect you to pinch flat or crash your way to a higher level of understanding.   Great.  One thing I hope is that I will get more recommendations from the mountain bike tire survey.  It’s had thousands of people looking at it, but relatively few recommendations.

From my tire survey (which you should participate in if you have a strong recommendation):   This link is to the PDF summary of the Full Tire Survey with Comments from fellow heavy riders.

From other sites (one of which is the bikeforums.net site below), I’ve distilled some of the relevant ones:

  • Weight:  235 pounds plus gear.  Front & Rear Tires:  Panaracer Fire CX 2.1 front and rear @ 48 PSI.   Bike: hardtail
  • Weight:  275 pounds with gear.   Front Tire:  Tubeless WTB WW LT 29” x2.55 @ 35PSI.    Back Tire:  WTB Stout 29″x2.3″ rear @ 40 PSI.    Terrain:  big bad pointy rocks of the Rockies.
  • Weight:  250 pounds.   I run mine at about 40-45 when out on the same KS single track that Ed was talking about. When I go bomb around campus they are at 65.
  • Weight:  240 pounds.  Tire:  mfr misc.  Size ranges from 2.1-2.5  psi: ranges from 28 (sloppy steeps on dual ply sticky rubber) to 36 (railing smooth hardpack on semi-slick)
  • Weight: 210 pounds.  Front & Rear Tires:   26×2.14 WTB Mutano Raptors @ 40PSI.  Terrain:   hardpack and a fast trail.   Same rider, terrain:   lots of climbing/rock gardens, roots 35-37psi, depending on the conditions.
  • Same rider – Weight: 210 pounds.  Front & Rear Tires:   26×2.14 WTB Mutano Raptors @ 35-37 PSI.  Terrain:   climbing/rock gardens, roots.
  • Weight:  215 pounds.   Front tire:  Maxxis Crossmark 2.1 @ 40 OSI.  Rear tire:   Maxxis Crossmark 2.1  @45 psi (5 psi less based on conditions).  Bike:  Full suspension.

Additional information:

http://mountainbike.about.com/od/tipsandtechniques/f/tire_pressure.htm

http://www.bikeforums.net/archive/index.php/t-552024.html

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