slowing down?

[brianW]

The last few rides I have noticed I have slowed down a bit. These rides have been on colder days (below 50) Just wondering if this is common or am I just getting old. Never noticed it before but than again never had a computer 'til a few months ago.

[ted]

Maybe your new computer is slowing you down? If you don't have anything to compare your current ride speed to then you'll not feel like you're going slower.

My advice, judge your ride by your "perceived" speed and not your "actual" speed.

It's like catching air. You always catch more air when you are the height judge as opposed to someone measuring for you.

Maybe the combination of cold air (harder to breathe), foliage and debris on the ground, and the ground itself being softer (more rolling resistance) contribute to the slower rides?

[brianW]

I am basing my observations on times/speeds I was having back in September to early November and comparing them to mt last 3 rides on the same trails.

[Mark Y]

Are you enjoying yourself any less? I'm the slowest dude out there and could not care less. I guess it is all about WHY you ride.

[imnav8r]

Well Brian I can say that as the temps drop, the air mass gets more dense. So there's more air resistance against you moving through it. At least that's what I learned in flight school. Airplanes love it because it provides more lift to the wing; golfers hate it because the ball doesn't fly as far. Now it probably has very little effect on a mountain bike rider since we aren't travelling anywhere near the speeds of an airplane or a golfball, but it is the excuse I've been using for years this time of year!

Keep in mind too, that you are wearing additional clothes, hence more weight although only a pound or so difference but you have to work harder to move your muscles in the extra clothing. Now this extra weight thing has been my new excuse ever since I started wearing that 20 pound Bike Patrol backpack.

Getting older....maybe. One of these days, maybe you'll slow down enough to where you'll be at my pace. Relax, have fun, enjoy!

Be safe and Merry Christmas!

[dgaddis1]

I'd attribute it to the ground conditions. Can't go as fast when there's less grip and more rolling resistance.

[lefty29er]

1. The trail is softer, more sand and mud.
2. You are up a couple of LB's
3. In cold air 02 shrinks in your tire, making them softer, bet you rode over 50 psi this summer.

I rode skinny today and it took me 48 min, just could nt get going, but i felt great when I got home!

[brianW]

I am suprized I did not think of the trail conditions. Trails have been either wet or covered with leaves.

As for O2 in the tires. since air is composed of 78% nitrogen I would be more concerned about that know i would of been more impressed if explained to the lower tire pressure to one of the gas laws.

[lefty29er]

Well I think the rule goes something like this.

For every 10 degree drop temp. You lose 2 psi in your tire.
Now thats for your car, not sure what it would be for a bike tire, but it would be softer.

[OopsFellDown]

A little scientific background: Pure Nitrogen is inert and contains virtually no moisture. Therefore, it's density remains pretty much constant as temperatures change. This is why most race cars run nitrogen in their tires as they can set the pressure in a cold tire in the pits, and it will pretty much stay the same as the tire heats up as the car runs on the track (it does still take time for the rubber compound to heat up and reach optimum adhesion, however). Most serious racers (cars, motorcycles, etc) use nitrogen in their gas-charged suspension components as well for the same reason. Good old air, on the other hand, contains oxygen and typically water (gaseous, otherwise known as humidity), both of which expand and contract significantly with temperature changes. As far as MTB tire pressure on cold days, if you set your pressure just before you ride, it should be no different than setting it just before you ride on a hot day. The only way you will have less pressure is if the temperature drops (alot) while you are riding. 50 psi is 50 psi, regardless of temperature.

[brianW]

I would have to disagree. Nitrogen will expand/constrict at low pessures like an ideal gas, just like oxygen and water vapor. However it used like an inert gas to prevent possible formation of iron oxide on the wheel (car) or other oxidation reactions.

[OopsFellDown]

Here's something I copied from an Internet site (so it must be true, right?...). According to this, we may both be correct:

As for moisture, changes in humidity affect tire performance two ways. First, the density of humid air fluctuates more with temperature than that of dry air, so removing humidity can keep your tire pressure more consistent, especially when the temperature climbs over 100 degrees Fahrenheit. That may be a legitimate concern in Formula One racing, but it's not much of an issue if you're just tooling around town.

Humidity can also be a factor in wheel maintenance - since pure nitrogen doesn't have moisture in it, supposedly your wheels won't rust as quickly, which could lead to improved wheel performance and air sealing. The question is, how big a problem is wheel rust these days? According to a few tire and wheel shops we contacted, not very. Seriously rusted wheels are uncommon in typical steel-wheeled cars, and many high-performance cars have alloy wheels that don't rust at all. One exception is work vehicles such as dump trucks, which are exposed to a much harsher environment.

[Timothyjames]

mumble mumble something about the porous nature of rubber and gas diffusion relative to gas molecule size and typical butyl rubber tubes. Moisture wouldn't seem to make a difference, that would throw fluid dynamics out the window and render hydraulics useless if while under pressure and temperature change the volume change significantly to allow your brake pressure to change.

blame it on your body in my opinion. colder air is harder to condition in your nasopharynx and you end up breathing through your mouth because your body can't condition it (warm it, moisturize it) to not be so harsh on your lungs. Mouth breathers tend to huff more and hyperventilate a lot so that plus soggy trails and cold muscles sound about right

[brianW]

Is this the reason for cold weather induced asthma in colder areas?