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Thread: Tire Presure

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    Tire Presure

    Found the link below and was wondering what your thoughts are. My bike and I weigh 195 lbs (on 25c) and based on using the Race Bike ratio, my front tire should be around 67 psi (seems really low). What do you think?

    http://www.bikequarterly.com/images/TireDrop.pdf

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    I personally wouldn't go lower than 80 on 25mm tires.

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    Try 95 to 105 psi, depends on the tire.

    Above 90 degree you can go a little higher psi.

    U want some tire deflection or it will be like sitting on a bench grinder ...

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    I am lighter (175lbs) but regularly run 70 psi in my front tire (25mm) and even lower in a 28mm. I don't see much deflection in the tire and have yet to run into any issues.

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    What is interesting in this report is the front vs. rear suggestion. Use the road bike sample (40/60 load front/back), you would end up running tire pressures in the back around 50% higher than in the front. I doubt that many folks do that.

    dave

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    I run about 10psi higher on the front than this chart shows just so it's not too squishy when sprinting and climbing. My rear pressure is pretty much what the chart recommends.

    http://www.crw.org/safety/12safetyPg...v-pressure.php


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    These charts are a guide. Tweak for your purposes.

    That said, I suggest 80-85F and 90-95R for you.
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    At 170 lb I am running 85/100 in 23s. Pretty even tire deflection, reasonably comfy, and no pinch flats or rim dings so far.
    Robert

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    Yeah, personally I would probably defer to keeping the inflation within the specifications of the tire manufacturers even if the deflection guides suggest lower PSIs are 'optimal' -- simply because there's no way a pinch-flatted tire resulting from underinflation would exhibit better performance than using a 'sub-optimal' pressure that increases likelihood of preventing a pinch flat. Eg. Michelin doesn't recommend below 87psi or over 116psi on its road tires, no matter the weight.. Of course there's likely some margin of safety on both ends of the scale, but I wouldn't probably extend more than another 10psi either way. Tire Pressures - How to fit (Video) | Welcome to MICHELIN Bicycle - North America

    (BTW, the below link has a couple options that do similar calculations) to your linked article
    Bicycle tire pressure calculator

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    Quote Originally Posted by PeteDman View Post
    Found the link below and was wondering what your thoughts are. My bike and I weigh 195 lbs (on 25c) and based on using the Race Bike ratio, my front tire should be around 67 psi (seems really low). What do you think?

    http://www.bikequarterly.com/images/TireDrop.pdf
    Personally, I think there's a lot of merit to the thinking behind that article, and have certainly shared it a bunch myself -- BUT -- I'm not on board with the more unbalanced tire pressure ratios, like 40%/60% or even 35%/65%. The reason being that if you climb or descend steep hills, the weight distribution shifts away from that static measurement a lot.

    I think it's better to stick to 45%/55% for road bikes. That's enough to get you more hand comfort and pinch flat protection in the rear. After maybe 5 years doing it, I've had no pinch flats whatsoever with the calculated tire pressures. Concerns about increased rolling resistance went away when I noticed that I actually felt fresher after long rides, rather than being "beat up".

    Here's what I use for a total weight of 190-200 lbs, listed as front/rear:
    28mm: 65/80psi
    30mm: 60/70psi
    37mm: 40/50psi
    42mm: 32.5/40psi
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    Sounds about right.

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    You're supposed to weigh yourself fully dressed to ride, and the bike fully equipped to ride. I weigh 145 lb. and my bike weighs 20.5 lb, but when dressed to ride with water bottle etc. on the bike and using a 40%/60% split between front and rear wheels, the chart says I should use 110 psi in back and 75 in front for 700cx23 tires.

    Ideally you're supposed to actually find out what you and your bike weigh on a scale by putting the scale under each wheel (and a support under the other to keep everything level) and then look up the pressure on the chart.

    If I remember correctly, the article mentions that if the recommended pressure is too low, use a narrower tire; if too high, use a wider tire.

    I converted the chart into a calculator that you plug numbers into and it tells you the matching psi values from the chart. It also offers the numbers from Michelin Bicycle Tires weight-based chart for 700c tires as an alternative.

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    I weigh 150lbs and have I been using the charts recommendations for the last three years on my 25 and 28 mm Conti GP4000 tires. The ride is more comfortable, I have stopped looking for better saddles, the wear on the tires is more even, not a narrow center strip that wears through first and I get about one flat per year. No change in performance, on the contrary on rough tarmac I think the lower inflation rolls much better. I would however recommend actually weighing your weight on the front and rear tire, since I am closer to 45/55 as well. I have 3 different wheel sets and never had any problem with the lower pressures, even on high speed descents in the Alps with lots of hair pin turns.

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    These charts are primarily for touring. Note most say "gear" with riders weight. A touring bike, especially loaded, handles a lot differently than a racing style.
    You're just trying to start an argument to show how smart you are.

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    Today I used the recommended psi and I was just as fast but with the added benefit of extra smoothness. This is something I'm always seeking because I ride an aluminum frame. I thought the 70psi on the front was going to be too low but it actually feels right. I've found my new tire pressures (R-105 & F-70), for now.

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    Quote Originally Posted by PeteDman View Post
    Today I used the recommended psi and I was just as fast but with the added benefit of extra smoothness. This is something I'm always seeking because I ride an aluminum frame. I thought the 70psi on the front was going to be too low but it actually feels right. I've found my new tire pressures (R-105 & F-70), for now.
    105 rear sounds about right, but you will probably want higher in front (~80). The low front works fine for normal riding, but under hard braking, the weight shifts to something like 70/30, and the front tire will wallow and squirm. So its a trade-off between normal comfort, and handling under braking.

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    Scale under front tire, scale under rear tire, balance in a doorway with one hand on door frame other on bars and a good weight/wheel is the result.

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    110 front / 110 rear.

    Low pressure is for kids bikes and child size adults on small rims. Higher is faster.

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    I ride Continental GP4000SII 25mm with 100/110.

    I've ridden with lower pressure and find the bike sluggish and squishy.

    I'm 200# and the bike is 14#

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    Quote Originally Posted by BigJeff View Post
    110 front / 110 rear.
    Useless statement unless you add how big you are and how big your tires are.

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    Quote Originally Posted by Athens80 View Post
    Useless statement unless you add how big you are and how big your tires are.
    23mm
    remember 25mm and larger tires are oy faster when at equal preassures running lower pressure increases the deflection/contact patch further.

    Only comfort bikes and beach cruisers run low pressure

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    I run 110 - 115 front and rear on 25mm and weigh about 145. I prefer a firm ride and anything under 100 would feel way too soft.

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    Many studies have show that slightly lower tire pressures produce a faster ride ... less deflection and rebound.
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    Quote Originally Posted by OldTryGuy View Post
    Scale under front tire, scale under rear tire, balance in a doorway with one hand on door frame other on bars and a good weight/wheel is the result.
    Yes but during braking the effective mass shifts forward so it is wise to over fill the front slightly relative to the result you get from your measurement.
    Robert

    My hero: "Tar-Baby ain't sayin' nuthin'..." (Joel Chandler Harris, Uncle Remus")

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