frame

Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

Sign In Register

Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

Starting immediately, all new users must be approved by a moderator (due to spam issues). #sworry
You can dismiss this message by clicking the little 'X' in the top right this box.
If you are a pro triathlete, please click here to DM AaronWebstey for access to the 'Pros-only' private forum. Don't forget to include your real name, and a link to pro race result would be great if you're a 1st-year pro.

Tire Pressure – Stop Guessing And Read The Science

edited June 2016 in Articles

imageTire Pressure – Stop Guessing And Read The Science

New discoveries about the relationship between pressure and performance indicate new directions for research and development.

Read the full story here


«1

Comments

  • Options
    Is there a variance for the weight of the rider? I've seen quite a few calculators that show higher pressures needed for heavier riders. Is this really necessary or should we all be riding closer to the 70 psi Poertner is riding?

    Either way I will be trying a (slightly) lower psi on my test ride and see how it works.
  • Options
    FLO recently posted that for their wheels and 23mm GP4k II tires that 95psi was a sweet spot as a system. This appears to fall in line with the impedance data posted above, 100 ish psi or less depending on conditions.

    @jimmymstevenson weight, rim width, and tire width all come into play when adjusting your pressure. You have to be careful not to go so low to fear pinch flats. I'm assuming that Poertner is 170lbs and running 70psi. I'm 205lbs on 25mm tires and usually run 100-110psi however i will also be trying a lower pressure, maybe 90psi?
  • Options
    Great article Jim, like the comment or below, ots of questions remain for the age group crowd were body weight is typically higher than pro cyclists....
  • Options
    Can Poertner model his impedance factor mathematically to allow for people to calculate their own pressures based on weight, in the same way that one can model speeds based on CDa and CRR - it seems like something best bike split indirectly consider (with road surface quality) but could be better quantified to allow us to input rider + bike weight to estimate pressures for conditions!
  • Options
    Thanks @Nazgul350r. I'm right there with you. Hovering just a bit above 200 and running at 110 psi. I definitely don't want to go too low and flat out. I think I am going to try about 95-100 as a start just to expiriment a bit.
  • Options
    Hey Jim, good food for thought. However several things are undefined, such as rider weight correlation and if we are talking clinchers, tubulars or both? Bcs Bradley was on tubulars and tubulars normally carry much higher pressures, right?
    What about latex tubes, any thoughts on that?
    Monosyllabic-AZ
  • Options
    RashRash Member
    New Silca tubes will be available for purchase soon. $900 each and woven from thinly sliced Caviar. You can run down to 5 psi and if you buy ten, you get a free handcrafted titanium sculpture of one of their pumps.
    balsdorfGasBombTad_MBrent_RM_WareKenElPescadoPeladoet5504yournotuniqueellsworth53tMonosyllabic-AZ
  • Options
    NemoNemo Member
    It seems the tests controlled for a 170 pound rider. It would be interesting to see what impact the weight of the rider (and bike combined) has on the results. For example, I'd hypothesize that the results would be directionally similar for a 110 pound rider, but just how much lower would that PSI go?
  • Options
    Nice article. Along with many of the other readers who question how the weight of the rider should influence the selection of tire pressure I wanted to follow up on the comment about pumps being wildly inaccurate. Clearly if your pump is giving you a fictional number then it really doesn't matter what pressure you inflate to as you don't actually know where you are at anyways. I am curious what advice you or Mr. Poertner have to neutralize that issue (I'm guessing it will have something to do with buying a really expensive pump but perhaps there are other solutions?)
    andrewm88
  • Options
    KHilgendorfKHilgendorf Member
    edited June 2016
    @TeamDGBG the pump inaccuracies was not an issue with any individual pump. It's an issue when you take multiple pumps together which are all inaccurate. Multiple pumps of the same type with varying gauges means you may not have things correct when grabbing one in the heat of the moment.

    If you have only one pump, you can determine the error of that (offset or slope bias) and accurately compensate. But if you're lazy like I am, err on the side of less pressure. Most pumps are accurate to +/- 7 psi, so if you want 100 psi, pump it to 95 and you're going to be okay. Sure, you may be at 88 or 102, but missing on the low side is better than missing on the high side.
    AaronWebsteyGasBomb
  • Options
    I have been preaching for years to all the Triathletes, road racers, recreational riders, commuters etc about running appropriate air pressure in their tire. There has never been a need to put 170 psi in your tire (Tufo recommendation on sidewall). I have always said 100psi is all you need regardless of your weight. Now, after reading Mr. Poertners findings, I think that I will scale that back to 90psi
  • Options
    very cool. i weigh 280 lbs 6ft 4inches tall. i ride vittoria 32mm training tires with schwalabe tubes on basic shimano aero wheels. on a cannondale with a carbon fork. i use 60psi in the front and about 65 in the rear. this gives me the best comfort speed and control. id like to try wider rims from hed or something but they have to many rider weight limits. so i just stick with shimano wheels. all the clysdale specicif wheels are way to damn heavy. this combo works really well for me.
    AaronWebsteyTad_M
  • Options
    et5504et5504 Member, TRS/Baucco Team Member
    All this does is make me second guess the tire pressure that I've been riding for 5 years without issues.....
    Tad_M
  • Options
    Is this all based around a 170 lb athlete? What is you're lighter?
  • Options
    Cancellara may have been running 60psi on cobblestones, but with (I assume) tubulars which don't get pinch flats. I would be interested to see how a clincher would perform in an identical situation.
  • Options
    It's like I'm back in the classroom again. Thanks. 6'3" 250 lb Clydesdale scared to lower the pressure since I kill my wheels. I'll try....
    KenElPescadoPelado
  • Options
    Tad_MTad_M Member, TRS/Baucco Team Member, Level 2 Supporter
    My HED Jet plus wheels show a Max pressure of 100 psi, so I've been running 90. 202#
    Tried 80 and feels fine. Looking forward to trials on the rail trail course where I can evaluate changes vs. net speed.

    Great post/article!


    #Sworry 2019 - See you there!
  • Options
    EXCELLENT!

    The various spreadsheets and calculators on the web give both higher and lower pressures for the rear tire, with www.biketinker.com being the closest at 6 psi less. All but the Vittoria app show VERY low pressures for the more lightly loaded front tire, 20 to 40 psi less. From my experience running the front tire at much more than 5 psi less than the rear results in very poor bike handling and also more of a tendency towards high speed shimmy.

    Can you also address front tire pressure in the future.
  • Options
    @cbratina The front vs. rear difference you see are primarily for road bikes where you keep more weight on the back end and support the upper body with your core. On a TT bike, since you're resting on the areobars, you have a lot more weight on the front end and need to increase pressure accordingly. You'll still have more weight on the back since legs are heavier than arms/head, but it comes closer to a 50/50 balance than a 30/70 you may see on the road bike.

    Think of it like a car with a front engine or a mid engine (I'll leave out those idiotic beetles/911's). With a front engine, you'll likely want more pressure in the front tires than the rear for optimal traction and mileage (normally 35psi front / 32 psi rear for an unladen sedan). For a mid engine sports car, the front tires have much less weight, so the rears may be 32, and you'll put 28/9 in the front (my lotus, being under a ton, uses 28 rear and 25 front for cornering, a bit more for highway driving).
  • Options
    Jan Heine did the same experiment in 2009 and published the results in Bicycle Quarterly back then.
    It's nice to read that someone else repeated his experiment with the same results but I believe Jan Heine and the BQ staff must be credited for being the first ones.
  • Options
    MattMatt Member, Administrator


    Think of it like a car with a front engine or a mid engine (I'll leave out those idiotic beetles/911's). With a front engine, you'll likely want more pressure in the front tires than the rear for optimal traction and mileage (normally 35psi front / 32 psi rear for an unladen sedan). For a mid engine sports car, the front tires have much less weight, so the rears may be 32, and you'll put 28/9 in the front (my lotus, being under a ton, uses 28 rear and 25 front for cornering, a bit more for highway driving).

    Mx-5 is 50-50 weight balance with engine up front + rear wheel drive. Tire recommendation?

    Pics of the Lotus, please!!!!!
  • Options
    kjrunninkjrunnin Member, TRS/Baucco Team Member, Level 2 Supporter
    OMG, why is there so much math?? I usually pump to 100-110 psi - and now that seems silly... 70 seems awfully low though. :/
    M_Ware

  • Options
    IanLIanL Member
    Keep dropping the PSI and training on the same piece of road. Stop dropping the pressure when you stop getting faster and getting too comfy. Or stop when you blow a tube and go back up 5 psi.
    kjrunninTad_M
  • Options
    Matt said:



    Mx-5 is 50-50 weight balance with engine up front + rear wheel drive. Tire recommendation?

    Pics of the Lotus, please!!!!!

    Way too many factors go into tire pressures on cars:
    1) Tyre
    2) Intended Use
    3) preferred handling characteristics
    i) major understeer - think stunt drivers might be the only one interested in this - or prius drivers
    ii) minor understeer - how most cars are designed
    iii) minor oversteer - rear-drive road cars
    iv) moderate oversteer - race cars, Jeremy Clarkson
    v) major oversteer - Ken Block

    For better handling in the miata, you'll need to run a few tests or ask a miata forum what they run. I have little experience with those. They're light, and 50/50 is good, so I'd look at 29-29 cold as a start and move up/down a psi from there. For that car, I'd shoot for a little loose in the back end with the tires cold.
    Matt
  • Options
    mbrekk44mbrekk44 Member, TRS/Baucco Team Member
    I run 100 on my peterbilt
    ellsworth53tTad_MKenElPescadoPelado
  • Options
    Last week I tried going 20psi lower (raced at 100psi). The ride felt much smoother and I felt I was keeping a better speed. I weigh 180#, and run Conti grandprix's. This weekend I'll try 95psi and see how that feels.
  • Options
    MartinMartin Member
    I'm running 85 on my tubeless. Maybe the whitewalls, but I've never had better handling.
    AaronWebsteyTad_MKenElPescadoPelado
  • Options
    This 'science' still leaves me guessing by not presenting any of the variables. As an engineer, I'm always appalled by this kind of generalization. I'm not Fabian Cancellara. I weigh 230 dripping wet and my ride weight is around 240lb with shoes, clothes, food and repair kit. I ride a 14 lb Trek Emonda for road racing. This data is for a rider and bike weight that is unspecified, and so the 'breakpoint pressure' is undoubtedly quite different than that for Fabian due to the friction caused by rolling over different surfaces. Although the article shows that a breakpoint exists, which we all assume, it still gives most riders no way to determine it, unless you assume you weigh the same as Fabian. It also doesn't specify important data such as which tire he used, whether he used latex or butyl tubes, etc., and as such the entire article is interesting, but completely useless since I'd be rolling on the rims at 70 psi...
    James Lange
  • Options
    One more thing, no one has mentioned. It's entirely possible that there's also a small relationship between the 'breakpoint pressure' and the stiffness of the wheel itself. And then of course someone mentioned pinch flats. Fabian doesn't get them because he's undoubtedly on tubulars. Tubulars can safely run much lower pressures. And they have no sidewall stiffness. And the Crr for a tub is much higher to start with than a clincher. In fact, it's not clear to me that the curves presented - assuming they're for tubs, would even apply to a clincher with a stiffer sidewall, even for a thin open clincher. Hmmmm....
  • Options
    AaronWebsteyAaronWebstey Administrator, TRS/Baucco Team Member
    @RGRHON boy, if you hadn't said 'as an engineer', I never would have guessed.
    simonsen77M_WareTad_MMattellsworth53tMartinkjrunninJames LangeyournotuniqueKPSwim13

Leave a Comment

Drop image/file

The Roost

@ 2016 The Triathlon Roost, All rights reserved.

Contact us

webstey@triroost.com

Get In Touch