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  1. #1
    Senior Member mtalinm's Avatar
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    should I worry about "tire bulge"?

    as a Clyde I'm always sensitive to being too heavy for the frame, wheels, tires, etc I'm riding.

    last week I switched from 32s on my commuter to 28s. the new tires, while at full inflation (85psi), seem to "bulge" more than my 32s did...and also more than the 25s on my road bike (though at higher pressure - 125).

    by "bulge" I of course mean that the part of the tire that touches the ground flattens out a bit.

    should I worry about the bulge? obviously if the rim were touching the road that would be bad, but short of that I'd love to put it out of my mind.
    Trek Domane 4.5 (commute/distance), Specialized Roubaix (climber), Xootr Swift (winter/travel), Trek Soho (around town)

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    im ridding on 23's 120 psi conti gatorskins. we weigh about the same. your tryng to get to 166 how tall are you?

  3. #3
    Senior Member mtalinm's Avatar
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    5' 8.5"

    and my 12 year old is 5' 7", yikes!!!
    Trek Domane 4.5 (commute/distance), Specialized Roubaix (climber), Xootr Swift (winter/travel), Trek Soho (around town)

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    Quote Originally Posted by sancle1 View Post
    im ridding on 23's 120 psi conti gatorskins. we weigh about the same. your tryng to get to 166 how tall are you?
    yes you should 100% be worried 700x28 tires that list a max of 85psi are generally cheapo piece of crap tires. I know, they came stock on my Giant Rapid and I had all sorts of problems and I'm 230lbs. If you simply try to inflate above and beyond the max psi, you may find yourself blowing the tires off the rims. Get a decent quality 28c tire and you'll be fine.

    I also had this problem with some 700x 25's that were only rated for 100psi. I got pinch flats at 100psi and it would blow of the rim sometimes at 120. I ended up getting gatorskins that have a max of 120 and I run the rear at 120 and the front at 110 with no issues.

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    Single-serving poster electrik's Avatar
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    32 will bulge out more, extra cushion... as long as you're not flatting or the tire threads aren't showing or something you'll be ok...

  6. #6
    Senior Member mtalinm's Avatar
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    well they're the Vittoria Randonneur tires, which are not supposed to be crap... I'm not planning to exceed the recommended PSI, so sounds like I am probably OK.

    I have Contin GP 4-seasons on my road bike and they are wonderful
    Trek Domane 4.5 (commute/distance), Specialized Roubaix (climber), Xootr Swift (winter/travel), Trek Soho (around town)

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    Unless you get pinch flats don't worry if they bulge out.

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    Uber Goober StephenH's Avatar
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    I've got Vittoria Randonneur tires on my Sojourn, but they're 35's. On the tires that came on the bike, they have the reflective strip, and I can't see anywhere on them where it says a pressure. When I bought the bike, the guy said, "I aired the tires up to 80 psi", so that's what I kept them at and they worked fine. I finally replaced the rear tire due to wear, and the replacement was the same tire without the reflective strip, but it also says 75 psi max. I just run it at 80 anyway.

    On the "bulge", if you're not getting pinch flats and don't feel like you're riding through peanut butter, don't worry about it.

    If I remember right, years ago, when radial tires became popular for cars, one issue was that they bulge more than bias-ply tires- but in fact they were better tires.
    "be careful this rando stuff is addictive and dan's the 'pusher'."

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    I run 28's on two of my bikes, I've tried some 85psi tires when I was about your weight (I'm now down to 240) and found them to be too slow and poor handling, though I never had a pinch flat issues (even when I was experimenting with psi when I was still over 275, I never pinch-flatted with anything over 75psi in 28s)
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    go with gp gatorskins got 1k miles on my first set and no flats so far

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    I don't know how at 265 lbs you could not get pinch flats. 85psi might be fine on a 32mm tire because it is larger but your pushing your luck on 28's. btw, you can safely go above the max recommendation. When tires are tested they are tested up until the point they sort of get destoyed and then they cut that number in half and give that as the max psi rating so you realistically you can always go somewhat over the max. I probably wouldn't push it past 95-100 though.

    This is a good article about proper tire pressures for weight, it's been linked on here a million times
    http://www.vintagebicyclepress.com/images/TireDrop.pdf

    According to this if you weigh 260 lbs and 60% of that weight is on your rear wheel for a 28c tire you should be running at 112 psi to get the appropriate amount of "bulge" which gives the ideal mix of comfort and control. With the remaining 40% on the front wheel you need about 80psi up there.

    FWIW, the gatorskins in 28C are rated a max of 116psi so they would allow you to feel confident in getting the pressures up to where they are recommended to be. I would ride the tires now as is but if you start having problems, i'd look to make a switch

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    Quote Originally Posted by sancle1 View Post
    im ridding on 23's 120 psi conti gatorskins. we weigh about the same. your tryng to get to 166 how tall are you?

    So you're 265 lb, riding 23's at 120 PSI, and you DON'T have problems?

    I just moved to 23's myself but at even at 195 lb, everything I've read has suggested that I should be using 120 PSI in the back. (Before, when riding 25's, I was running 105-110 in back and 100-105 in front.)

  13. #13
    Senior Member mtalinm's Avatar
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    Quote Originally Posted by cappuccino911 View Post
    I don't know how at 265 lbs you could not get pinch flats. 85psi might be fine on a 32mm tire because it is larger but your pushing your luck on 28's. btw, you can safely go above the max recommendation. When tires are tested they are tested up until the point they sort of get destoyed and then they cut that number in half and give that as the max psi rating so you realistically you can always go somewhat over the max. I probably wouldn't push it past 95-100 though.

    This is a good article about proper tire pressures for weight, it's been linked on here a million times
    http://www.vintagebicyclepress.com/images/TireDrop.pdf

    According to this if you weigh 260 lbs and 60% of that weight is on your rear wheel for a 28c tire you should be running at 112 psi to get the appropriate amount of "bulge" which gives the ideal mix of comfort and control. With the remaining 40% on the front wheel you need about 80psi up there.

    FWIW, the gatorskins in 28C are rated a max of 116psi so they would allow you to feel confident in getting the pressures up to where they are recommended to be. I would ride the tires now as is but if you start having problems, i'd look to make a switch
    thanks...this matches my gut feel. the stock Bontrager tires were 90psi and I always wanted to push them higher due to the tire drop. probably should have gotten Gatorskins; the Conti GPs on my road bike have been fabulous at 125psi.

    well maybe I'll push these up to 95-100 and see if it makes a difference. they feel a bit squishy, moreso than the 32s.

    thanks for the article as well - looks like the technical term is "tire drop" not "tire bulge" :-)
    Trek Domane 4.5 (commute/distance), Specialized Roubaix (climber), Xootr Swift (winter/travel), Trek Soho (around town)

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    lol, yes we have used the word "bulge" more than a group of junior high kids!

    If your tires are new, try to sell them to someone and replace them with gatorskins. also, shop on line for the gatorskins, you can prob find them at a more reasonable price.

    They really ride great, i had armadillos on my bike before which truly were a durable tire but they are SOOOOO heavy and slow. The gatorskins feel so darn soft that I keep looking down because I think they may be soft bu tthey aren't, they just have a really nice soft feel to them.

  15. #15
    Senior Member mtalinm's Avatar
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    good idea. I got them at REI, so maybe I can take them back and plead obesity
    Trek Domane 4.5 (commute/distance), Specialized Roubaix (climber), Xootr Swift (winter/travel), Trek Soho (around town)

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    Well i'm 259 now but no i've had no problems with the gators. Rode on gp4000 before. They roled nice but i only got 1000 miles off them . Gators are cheaper too

  17. #17
    Senior Member Wogster's Avatar
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    Quote Originally Posted by cappuccino911 View Post
    I don't know how at 265 lbs you could not get pinch flats. 85psi might be fine on a 32mm tire because it is larger but your pushing your luck on 28's. btw, you can safely go above the max recommendation. When tires are tested they are tested up until the point they sort of get destoyed and then they cut that number in half and give that as the max psi rating so you realistically you can always go somewhat over the max. I probably wouldn't push it past 95-100 though.

    This is a good article about proper tire pressures for weight, it's been linked on here a million times
    http://www.vintagebicyclepress.com/images/TireDrop.pdf

    According to this if you weigh 260 lbs and 60% of that weight is on your rear wheel for a 28c tire you should be running at 112 psi to get the appropriate amount of "bulge" which gives the ideal mix of comfort and control. With the remaining 40% on the front wheel you need about 80psi up there.

    FWIW, the gatorskins in 28C are rated a max of 116psi so they would allow you to feel confident in getting the pressures up to where they are recommended to be. I would ride the tires now as is but if you start having problems, i'd look to make a switch
    Your not quite on the mark with tire pressures. Tire companies employ engineers who design tires, a tire is designed for a certain pressure, the only thing you can be sure of is that the wider the tire, the lower the design pressure. The tire will test to at least this pressure without failing, if it doesn't then the engineer who designed it should be encouraged to seek employment elsewhere. Then it gets interesting, legal because lawyers are lazy and like getting paid big bucks for nothing, ask for a low pressure, to ensure that the company does not get sued for a tire failure, marketing because a higher pressure makes it look like a better tire wants a high number. They fight over it, come to an agreement and that agreement is the number moulded into the side wall. What is unknown is how close that agreed to number is to the design pressure.

    There are 3 factors with tire pressure and weight, first is the weight itself, second is the pressure and third is the size of the tire contact patch. Tire bulge is the tire making the proper size contact patch for that rider on that bike at that pressure. The physical width of the tire only determines the amount of that bulge.

    Let me explain, take a 170lb rider on a 30lb bicycle, the total weight is 200lbs, 60% of that, on average is over the back wheel, cruisers and upright hybrids will be a little more, racers in the drops a little less. With the rear tire at 120PSI the rear tires contact patch will be 1 square inch, whether the tire is 25mm wide or 5mm wide, does not matter, more bulge will make for a more comfortable ride, but require more input energy and at an increased risk of pinch flats. Some experts say for the best balance between comfort and efficiency 15% drop, other experts say the first group is full of it.... Determining drop is easy, take the bike, inflate the tires to the maximum rating, measure from the edge of the rim to the ground, get on the bike and measure it again, the difference should be no more then 15%. If the before measurement is 20mm the after would be 17mm. If the after is more then 17mm, you can reduce the pressure slightly, if it's more then you need either a wider tire with the same maximum or the same width tire with a higher maximum pressure.

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