Wednesday, September 24, 2014

How Low Can You Go?

Along with the "wider rim/bigger tire volume" craze you also have to add in the lowered air pressures. If you have a fat bike, for example, or have gone to wider mtb rims and big tires, are on the 29+ bandwagon, or even if you've got wider road rims and 28mm tires, you aren't getting the full benefits of the idea here unless you go lower on the air pressures.

Now, this isn't a post to tell you what you should be running for air pressures. No- you should do your own reasearch. However; I can tell you what is working for me, and you know what? I know other cyclists doing similar things. This just isn't me spouting off. In fact, research has been done to prove this out, if you worship at the church of all things science. So, there is that as well.

Anyway.......I was reminded of this air pressure deal with my 29+ set up on the MukTruk. The set up is Velocity Duallys with Surly Knard 120TPI tires set up tubeless with the home brew sealant I use. The MukTruk has been my main commuter rig for the last month and a half.

The air pressures I set the tires to at first was 20psi rear, about 18psi front. Then I just kept riding the MukTruk day after day without really keeping on top of the air pressures. There towards the end I may have huffed them up a bit. Maybe a couple of times. Then there were a few kind of bouncy rides last week, but honestly, I was not working all that hard to keep going. A recently bulldozed field was a piece of cake on this bike at the (assumed) lower pressures.

The MukTruk, for reference.
Then the other day I thought the rear tire was too soft. Time to add air! I put in 20psi into the rear tire, according to my Topeak Joe Blow floor pump, which is about seven years old now. I left the front tire alone. Then yesterday I thought the front was also too soft. Aired that up to 18 or so on the Topeak pump.

Now, I've been using the Topeak pump as a reference for a long time, but I figured it was time to get a more accurate read. So I purchased the "Accugauge" as seen above, and found out what I thought was 20 was actually 15! The front was at 14 psi, so at least the differences were similar. (Assuming the "Accugauge" is as accurate as its name suggests.) what? Well, obviously the last few days I used the MukTruk before resetting the pressures I was likely into the single digits for riding pressure. All I can say is that the Topeak gauge didn't register a pressure when I pumped up the tires recently!

At the 15/14 set up, I can tell you that I was only maybe marginally faster. Maybe. I find that usually tires have a sweet spot for air pressure which balances comfort, control, and speed. I almost always ride tubeless, so pinch flatting is not an issue. Only in regard to fat bike tires and skinnier gravel road set ups do I still often use tubes, and even then, I am dumping air pressures. I have ridden much of my gravel road stuff at around 40 psi or less. (And I weigh about 230lbs, for reference.)

I will be using the MukTruk as my "less severe weather" commuter this Winter, and I know I'll be dumping the pressures into the single digits at times for ultimate traction. On my fat bikes, there have been times when the air pressures were so low the side walls were wrinkling. (Ultimate traction scenarios only) So, play with your air pressures no matter where you ride. You might find speed and comfort are not mutually exclusive when it comes to air pressures, and you may discover another higher level of performance at the same time.

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