Wheel weight and/or tire pressure vs. acceleration??

Discussion in 'Cycling Equipment' started by CyclinYooper, Jan 9, 2011.

  1. CyclinYooper

    CyclinYooper New Member

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    Hello all,

    This is my first post, and I have a question regarding my tire/tube setup and how it impacts my bike.

    My bike's stock tires were Vittoria Zaffiro (700x23) which I rode at 120 psi with Forte standard tubes. The Zaffiro tires weight 340g and the Forte tubes weigh 90g.

    I ride in the southwest, and due to constant thorn flats (I'm sure you've heard of our goatheads), I recently upgraded to a set of Continental Gatorskin (foldable) 700x23 tires and True Goo tubes. The gatorskins weigh 230g and the goo tubes weight 180g (verified). However, these tires I've been running at 110 psi, per Continentals recommendations (although the Max is 120 psi).

    Since I made this change my bike is noticeably "slower." Slower to accelerate, slower/harder going uphill, and my perception is that it takes longer on flat surfaces to reach top speed.

    But, the tire & tube weight is similar for both setups? Vittoria (340g) and Forte tubes (90g) total 430g; the Continentals (230g) and Goo tubes (180g) total 410g.

    So, is my bike dogging because of the lower pressure? Or am I missing something else?

    Thanks for the assistance! No other changes have been made to the bike during this time-frame.

    Scott
     
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  2. oldbobcat

    oldbobcat Well-Known Member

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    Rolling resistance is directly related to friction of the tire on the road surface. Friction is affected by tread pattern, tread compound, and the ability of the tire's contact patch to conform to the surface with the least amount of pressure. With a heavy tube and a tire with a stiffer sidewall, your contact patch is less pliable so it generates more friction as it comes in contact with the ground.

    Unless you had been getting a lot of sidewall punctures and failures with the Zaffiros, you probably don't need the extra sidewall protection of the Gatorskins. The Continental GP4000 has a thinner, more pliable tread that is still durable for a performance tire, plus the most effective puncture-resistant belt in the business, in my experience.

    Reducing tire pressure, as you've done, is one way to reduce rolling resistance. You can also reduce rolling resistance by increasing the area of the contact patch using a slightly fatter tire.
     
  3. CyclinYooper

    CyclinYooper New Member

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    Thank you for the new perspective. This was exactly what I needed, as I was focused on weight/moment-of-inertia.

    Scott
     
  4. dhk2

    dhk2 Active Member

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    To add to the good info from OBC, some tires are built for low rolling resistance while others are primarily made for durability. When you switched from a Vittoria race tire to the Gatorskins, you made a big move from a "fast" tire to a durable one. This is the reason Conti, Michelin and others offer a range of tires. Michelin website has diagrams for each of their tires to illustrate the design priorities.

    The GP4000 is my personal favorite, as it has proven to be puncture-resistant for my riding while still offering fairly low RR. The "fastest" tires I've used have been the VIttoria Open Corsa EVO, but I gave up on them due to punctures, cuts and quick wear. No point in saving two minutes on a century event if you get a puncture and have to spend 10 minutes fixing it.

    Here's a link with some more info and tire test data: http://www.rouesartisanales.com/article-1503651.html
     
  5. CyclinYooper

    CyclinYooper New Member

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    Thanks again for the feedback. That's two votes for the Continental GP4000 ... perhaps I should give 'em a try. /img/vbsmilies/smilies/biggrin.gif

    I purchased the Gatorskin tires at Performance; so I can return them per there guarantee (phew).

    Do you guys use slime/goo tubes in the GP4000s? Or just standard tubes?

    Due to the thorns/goatheads here, may guys with whom I've spoken recently use slime/goo tubes and fast tires. Some also use a liner. So, I'm debating whether I should just try the Vittorias with a goo tube. True goo makes an X-lite tube (145g) that I debated trying also.

    Scott
     
  6. maddogbubba

    maddogbubba New Member

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    had no luck with slime tubes - still got flats . went to a tube that has a removable valve stem , add a small amount of stans no tubes and have been better off for it . I like the continental GP 4000 , currently running the hutchinson kevlar fusion 3 - love them just like the continentals .
     
  7. dhk2

    dhk2 Active Member

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    I've never heard anything good about slime/goo tubes. Only use standard tubes here since flats aren't a problem (with GP4000s). The problem with using a goo tube or liner in a "fast" tire is that you've just defeated the "fast". And, you're still left with cuts in the tire which can open up with more miles. To me, the right tire for your riding conditions paired with a standard tube is a much better solution.

    For the puncture-resistance you need, Gatorskins in fact may be a great choice. I know several riders who use Gatorskins here because they like the long life and high puncture-resistance. If you have to sacrifice 3 or 4 watts of rolling resistance for durability, that's really not the end of the world unless you're racing. Doubt Performance will give you a refund or credit on perfectly good used tires just because you've decided you don't like them. But at least you've got some good reliable tires now. What if you bought Vittoria EVO or other "race" tires and had them cut-through on your first ride? I had that happen once with the old ProRace tires and haven't gone back to Michelins since then, despite their claims (and experience of friends) that the new ProRace 3's have a lot better puncture resistance.

    The other thing important in puncture resistance is pressures. Conti website used to give puncture resistance test values @ 95 psi. If you're a lighter rider who can use 95 psi on 23mm tires, my experience is that you'll get noticeably fewer punctures and cuts vs running them at max-rated pressure. If you're heavier, a good strategy would be to use 25mm tires @ 95 psi.
     
  8. oldbobcat

    oldbobcat Well-Known Member

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    Most riders don't need to run at the maximum rated pressure, anyway. I'm no lightweight, and 105/front with 110/rear is plenty for me, on 23mm tires.
     
  9. dhk2

    dhk2 Active Member

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    Hey, that's what I run on the 4000s too. Even at my porky "winter weight" ( 190 lbs ) that seems to be plenty. But a lot of riders still go up to the max rating, thinking they are going to reduce rolling resistance in any measureable way. I was one of the "max or over" crowd for a long time too; wasn't until I started using Michelin's with the "6-8 bar" recommendations that I started trying to find the correct tire pressures.
     
  10. zoomod

    zoomod New Member

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    even tho its an old friend, had to point this out for the folks who see it.

    the first answer is cracked out. lowering pressure *increases* rolling resistance. duh. of course you knew that (bike does NOT feel fast when your tires are low now does it?)

    higher pressure in your tires will definitely make you faster, with the consequence that your ride will be increasingly harsh and abrasive on your body (part of the reason for using air in tires at all is to absorb shock -- at high psi this quality diminishes even though you shall gain speed)

    references: http://www.rouesartisanales.com/article-1503651.html
     
  11. zoomod

    zoomod New Member

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    also want to point out that running tires below their max pressure does not help prevent flats:

    low psi is useful in either sketchy weather conditions (increasing grip) or long distance riding (increasing comfort) but it does not help reduce flats -- in fact it can increase your risk. running at maximum pressure makes the tire harder and more immune to pinch flats. if the pressure is too low, you risk bottoming out when you slam into something like a pot hole, which can blow a hole in your tube or damage your rim (especially on narrow tires you need to stay above the minimum psi!). for things like glass and staples you're fubar either way unless you have tough casing

    references: http://www.sheldonbrown.com/gloss_p.html
     
  12. danfoz

    danfoz Well-Known Member

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    My 2 cents... your subjectively slower ride has little or nothing to do with the air pressure. That does indeed factor into rolling resistance, but you went from a "normal" inner tube to an absolute slow rolling beast, and the Gatorskins are no picnic for a supple fast rolling tire either. If you are talking Contis the 4000's roll quick, and even the 4-seasons I am currently running feel faster than the Gator. They use different materials for puncture resistance at the diff price points. Vectran (which is more supple and rolls faster) for the more expensive tires vs the Poly X breaker for the less expensive.

    Consider going back to your normal inner tube for a faster feeling ride.
     
  13. danfoz

    danfoz Well-Known Member

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    Your reference makes note of rolling resistance tests performed on smooth rollers or drums. It is indeed correct under those circumstances but one must consider that tire rolling resistance on the road is caused by: (1) internal friction and hysteresis within the tire’s materials, and (2) on rough roads, small bumps lifting the bike and rider slightly on each little impact. On roads that include irregularities, which in my experience is most roads, pressures appropriate to a riders weight and road condition will likely roll faster than the max pressure.

    Edit: I should probably include a reference - http://velonews.competitor.com/2012/03/bikes-and-tech/technical-faq/tech-faq-seriously-wider-tires-have-lower-rolling-resistance-than-their-narrower-brethren_209268
     
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  14. CyclinYooper

    CyclinYooper New Member

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    Interesting that this post has been dragged up after so long! I've long since remedied this issue:

    1. For puncture resistance with tiny thorns ("goatheads" are what they are called here in NM), I discovered that 2oz of Stan's NoTubes sealant is the ticket. It adds minimal weight (~40g / tube if I remember correctly) and it's so effective, that when I yank out a thorn ... I see a brief spurt of the white sealant ... and that's it. Ready to ride. I've gotten into the habit of spinning the tire once, just to re-distribute the sealant, before I pull the thorn. I have not had a flat due to a thorn in over a year now (and I was getting 1-2 flats per ride, for months when I started riding again).

    2. Now, to get the feel of "fast" tires again, I was using Stan's NoTubes sealant and Vittoria Zaffiro folding tires for a bit. A fast outfit for sure; however, I had a couple flats due to road debris (rocks, roadside sh%t, etc.). In both cases, the Vittoria tire ripped a pretty sizable gap and the tube was shredded. So.... I started using GP4000S tires.

    So, my current rig is GP4000S 700x23 tires (110 psi on both), Conti Tubes (need a removable valve stem for Stan's), and 2oz Stan's in each tube. This has been a very easily rolling and flat resistant system for me.

    Scott

    P.S. The only reason I tried Gatorskins was for flat resistance. I found that for thorns, Stan's was much better, and that I was very disappointed with the rolling resistance on the Gators.
     
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