Monday, December 28, 2009

Feeling Slow? A Simple Explanation

It's funny that no matter how much cycling experience we gain, we remain susceptible to those silly mistakes and those "duh!" moments. I am sure I have many, but the most recent one really had me smacking my forehead.

For the past month I had been favouring my vintage Raleigh and not riding the Pashley as much. When I finally did take out the Pashley last week, I noticed that it felt more sluggish than I remembered. I thought this was strange, but chalked it up to my having gotten out of shape and the vintage Raleigh being easier to ride. But the sluggish feeling kept growing worse, and neither of us could figure it out. Until finally, cycling behind me, the Co-Habitant realised what was wrong: My tires were nearly flat! There were no punctures; they were just low on pressure and neither of us had noticed.

I know it's absurd to overlook such an obvious thing as tire pressure; it is the equivalent of wondering why your computer is not working only to realise that it is not plugged into the wall. We do usually top up the air in our tires at reasonable intervals, but my Pashley slipped through the cracks. I wonder whether the cold temperatures played a role in it as well? Now that my tires are re-inflated, the Pashley flies again (really, the difference in speed and handling is amazing). However, I do think that I will replace its native Marathon Plus tires with Delta Cruisers come springtime; the latter just feel livelier and more enjoyable to me. In the meantime: If your bike is feeling slow, do check your tire pressure before looking for more complicated or sinister explanations!

28 comments:

  1. Then there's me. I often wonder why I feel slow. I check my tires frequently but they are usually fine. This forces me to realize that it's just me, being wimpy. Or maybe I'll blame it on the headwind...

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  2. Low air pressure will creep up on you like that- I have to remember to check it every once in a while, and when I'm newly pressurized, it's amazing the difference it makes!
    Some days however, I just don't have any mojo, and I just have to creep along in lowest gear until I get there- I try to take advantage and enjoy the scenery those days.

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  3. Do y'all have a floor pump? I put 4-6 strokes into the tires of my commuter bike each Monday. Floor pumps (with a gage) are the most useful tool a cyclist can own. If not, get one that'll put out 160psi. Those will get to the much lower pressures a Pashley will be needing without even noticing it.

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  4. You might consider replacing your stock tubes with premium tubes from Schwalbe. I've found they hold air much better than their generic counterparts.

    http://www.ecovelo.info/2009/07/20/whats-in-a-tube/

    http://www.schwalbetires.com/bike_tires/tubes

    Alan@EcoVelo

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  5. I tend to check my tyres every week now using a floor pump with a pressure gauge. The Schwalbes on my Pashley and Mixte aren't like normal tyres where you can squeeze with your hand and think, "Oh, that doesn't feel like it's got enough pressure in it." Because they are puncture-resistant the tyre walls are thicker so not as sensitive to touch. I've had 'slow' days on my Pashley and checked the tyre pressure when I've got home and guess what, it's been down even though the tyres felt hard to touch.

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  6. Steve - Yup, we have a floor pump with a gage that we normally use. This time we used the frame pump during the ride, then did a proper job with a floor pump when we got home. You top up your air every Monday? Wow, that seems frequent.

    Alan - Thanks, perhaps I need to try those.

    Carinthia - That is an interesting point. It would certainly explain why I did not notice that the tire pressure was low when taking the bike out.

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  7. Alan-- Pashley uses Schwalbe inner tubes on Roadster/Princess Sovereign. Didn't you notice that on your bikes?

    Steve-- Yes, we have a bright racing orange Pedro's 160 psi floor pump. It was in my other jacket, so I had to resort to the wimpy old frame number.

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  8. During the summer, it seemed I had to top off the tires before every ride. Now in winter, it's almost disconcerting to me that the tires of each of my bikes seem to be holding the air like misers. I keep wondering if it's just because the tires are a bit stiffer in the colder temps?

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  9. Maybe rubber is a little less porous in colder temps. Or the micro-punctures are more so, uh--micro--in the winter.

    In any case, inflating with a frequency of more than once a month per bicycle is plainly absurd. Who has that kind of time? I looked at the calendar and Filigree's Pashley was last inflated in August. So that's 3-4 months. Something's wrong if the pressure drops more than a few PSI per week. I don't have to mess with car tyres for many months at a time.

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  10. Good tip. I'm always forgetting about my tire pressure.

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  11. MDI, didn't we have a debate once about tire pressure and the readily noticeable effects on rolling resistance??? (wink, wink, nudge, nudge)

    riding the same exact route five days a week, i've become attuned to the effects of tire pressure on my commute. i feel a noticeable difference in rolling resistance between 40 lbs and 70 lbs, even though 40 lbs is enough to make the tire appear "fully" inflated, even with a full load.

    rubber is in fact slightly porous to air, and since bicycle tubes are so thin, they lose air pressure more quickly than car tires.

    and now for a velo-physics fun-fact: even with quality tubes from schwalbe, which tout superior air retention, it's normal for the tube's pressure to decrease with decreasing temperature (and conversely, increase with increasing temps). this is caused by the moisture content in the air that was pumped into the tube. while the gases in air (oxygen, nitrogen, etc) are "perfect" gases whose pressures do not fluctuate with temperature, vapor pressure does vary with temperature. if you ever fill your bike tubes with air from those noisy gas station pumps, you can sometimes see water spitting out of the nozzle along with the air!!! that water is floating around inside your tube as water vapor. if you were to fill your tire with "dry" air lacking any appreciable moisture content, you wouldn't see any change in pressure with changing temps.

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  12. somervillain - I'll let MDI answer, but just want to say that the Marathon Plus tires call for different pressure than the Delta Cruisers. I think we were discussing specifically the Cruisers : )

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  13. That's always one of the first things I check. I tend to be very sensitive to low pressure.

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  14. unfortunately... my issue seems to be actually remembering to top off the tires. Often I'll know while I am riding that my tires are low, but it's retaining that memory after I get home that is the issue. Often I only remember the next day as I am riding along and realize "damn, didn't I want to put air in my tires?!"

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  15. true, the marathons call for a minimum of 45 or 50psi, depending on the size, and the delta cruisers call for a minimum of 30 or 35 psi. but that doesn't mean there won't be a high rolling resistance associated with that low pressure. the delta cruisers are rated to 65psi max... marathons can go higher (80?), but i never go above 70 on my marathons-- 70 is the "sweet" spot for my marathons. anything higher and the ride begins to feel harsh. the stock raleigh roadster tires and other older roadster tires are typically rated to 50psi max.

    anyway, there *is* going to be a noticeable difference in rolling resistance between any tire's minimum and maximum recommended pressures... just sayin'...

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  16. The stiffer the casing the more sensitive tires are to inflation pressure. Stiff casings don't support the tire, only the air does that, but they take more energy to flex and that energy has to come from somewhere. That would be you.

    That's why racing tires use "skinwalls." They're actually relatively insensitive to inflation pressure, except that if you inflate over the optimum you start going the wrong way because of LACK of compliance.

    People who ride road bikes on skinny tires pumped rock hard don't even know what skinny tires are for and think it's to reduce rolling resistance. In fact, the DIFFERENCE in the rolling resistance between any two decent performance tires is so small its noise. For that matter so is total rolling resistance in most cases, because by far the most significant source of resistance to the forward motion of the bicycle is the air.

    And THAT is why ultra skinny tires got introduced into road racing. As a specialty tire for time trials, to reduce the section of the tire to that of the rim. The high pressures are a negative side effect of being skinny, not the purpose.

    Now most people ride them all the time and get nothing for it other than beating up their bikes, themselves and going SLOWER in most cases.

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  17. haha. that happened to me once, kind of. i figured i was just having a really tough time of it going up the hill, but turns out my brake was sort of on and rubbing against the wheel. no wonder it was extra hard to ride :)

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  18. Very funny! I've noticed though that I kind of prefer a lower tire pressure on my workcycle. When I pumped them up to the recommended pressure, I felt like I was going shake apart. But the is certainly a too low.

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  19. the very first ride I had over a year ago with the kids in the trailer no less my mountain bike tires were flat. I rode it a mile to the school and back and struggled so hard. Yeah- a good pumping fixed it really well.

    Now whenever I feel sluggish I feel the tires and actually feel sad when they feel nice and full. No easy fix avail then.

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  20. Another note- some people actually recommend letting out some pressure and riding on slightly low tires for snowy icy conditions- when you're going to be slower anyway, the thought is that the contact patch gets a bit bigger and therefore you have more traction. Haven't ever tested it- am curious if anyone has?

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  21. That's standard procedure for dune driving. On the other hand, letting air out and thus getting a wider tyre may keep you from sinking all the way down to the road surface, something a skinnier tyre can do better. It's really a mix where at certain times you want to float and other times sink through the slush. Ultimately it depends both on conditions and on individual preferences. Do what feels right. Perhaps that's what makes it so hard (and causes all the debates).

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  22. "That's standard procedure for dune driving."

    And rain.

    "a wider tyre may keep you from sinking all the way down"

    A tire squished only a couple of millimeters wider will give you a significantly larger contact patch. It's a cube law thang. Like why an elephant needs thicker legs proportional to its body size than does a sparrow.

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  23. From my observation , tire pressure tends to decrease more quickly with less frequent use of the bike.

    I quick check of my bike tires (pressure, etc) before my first ride each day ('safety-first' habit :D)... it takes just a few seconds. In normal conditon I need to increase the pressure once in about 10 days.

    Lemony

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  24. Anonymous said...

    From my observation, tire pressure tends to decrease more quickly with less frequent use of the bike.


    You know, I noticed that too but cannot really substantiate that mechanistically. But it's true, isn't it?

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  25. Re: "But it's true, isn't it' ...
    MDI,
    My friend,c-m, has a 'scientific hypothesis' on this and he tried to explain this to me ... but alas I do not have scientifically orientated white-matter in my skull/cerebrum to grasp even a modicum of what he said. :p

    However, many other 'veteran' cyclists have observed this 'phenomenon' (At least to me it shall remain a 'phenomenon' :D heehee).

    Nota bene: To 'novice' cyclists:
    Prolong use of tires with 'low'/'lower' pressures especially over surfaces with 'indentations', such as cobbled paths , road with badly maintained surface or stoney areas, could damage not only the tires but also the rims/wheels (quickly).
    There is also the danger such 'lower-pressured' tires would not respond well/effectively to 'emergency'/evasive 'manoeuvring' which you may have to execute to avoid an 'accident'.

    Lemony

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  26. i think the phenomenon of tires losing pressure more quickly when unridden is a psychological one :-)

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  27. Nay, it can be easily explained by fringe science. :)

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  28. My fiancé and I noticed that I was having a lot of difficulty going up hills; more than could be attributed to his wheels being slightly larger than mine, and certainly when we consider the fact that I have been cycling more than he has. We had no idea why this could possibly be.

    We eventually realised that it was because my panniers and my handbag were adding about 10% to my weight, and that's not including the mass of the bike itself! No wonder I was struggling!

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