2 road bike. The rear tire keeps popping. I have replaced the rear rim and tube. Every time I go for a ride I inflate the tire to around 70-80psi. I am on the heavy side (310 lbs). What are my options. A stronger tube if they make one. Or a different bicycle in which case what do you recommend?
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8What width is the tire? Do you know how wide a tire your bicycle can fit? If not, what’s the bike model, if you know it?– Weiwen NgCommented Jul 20, 2020 at 16:22
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7What does your tube look like? - popping to me means that the tire is blowing out the side. Puncture means that the tube is getting a hole in it. If the tube is being punctured the cause of the puncture can be identified. "snakebite" flats bicycles.stackexchange.com/questions/9660/… punctures from road trash etc. can be identified.– David DCommented Jul 20, 2020 at 19:08
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3Do you ride through potholes and over kerbs ?– Criggie ♦Commented Jul 20, 2020 at 22:33
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3Also note that most bicycles (at least here in Germany) are only certified for a "total system weight" (bicycle + rider + luggage) of between 120 and 150 kg - meaning the maximum rider weight is between about 90 and 125 kg. At 310 lb / 140 kg you most likely need a bicycle specifically for "heavy riders" to remain within the usage prescribed by the manufacturer.– sleskeCommented Jul 21, 2020 at 7:09
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1Without tire width it is impossible to make a reasonable pressure recommendation! (Although if in doubt, it wouldn't be unreasonable to assume that you should go to the max pressure written on your tire given your weight as stated in one of the answers).– user2705196Commented Jul 21, 2020 at 13:03
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5 Answers
Increased load (i.e rider weight) on a pneumatic tire does not increase the pressure in the tire. The contact patch on the ground just increases in size until the contact patch area x pressure = load (or the rim contacts the ground).
What might be happening is you are getting pinch flats when hitting bumps or holes. This is when the tire and tube are deformed so much by the impact that the tube gets pinched between the tire and the rim often resulting in two symmetrical holes in the tube.
You can try running higher pressure which will stop the tire from deforming as much. 70-80 psi is on the low side for a road bike 28-23mm wide tires.
If you have clearance in your fork or frame run a wider tire. Also if your wheels will support it consider running tubeless tires, which are of course not susceptible to pinch flats.
Trying to avoid bumps and holes in the road, and standing up slightly to absorb impact through bent arms and knees can also help avoid pinch flats.
answered Jul 20, 2020 at 17:07
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3Just to add: Silca's tire pressure calculator suggests that for a 310 lb rider with a 25 lb bike, a tire measuring 28mm should have 86 PSI front, 88 PSI rear. On current road rims, many tires will measure wider than their claimed width, but we don't have the information to guesstimate that. Anyway, 70-80 PSI is very likely too low, unless the OP clarifies some information. I agree that the OP should run as wide tires as his frame will allow. info.silca.cc/silca-professional-pressure-calculator Commented Jul 20, 2020 at 17:22
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2@WeiwenNg That low? I’m 140 pounds and I run 75/80psi F/R on 28mm tires, are my pressures excessively high? I would expect 310 pounds to be well over 110psi. Commented Jul 20, 2020 at 18:34
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@MaplePanda The linked calculator is a generic recommendation. There's a more detailed version where you have to provide your email (same link). In general, though, you can run lower pressures than you think. It is definitely more comfortable to do so. You do increase your rolling resistance (RR) if your pressure is lower than optimal, but your RR increases much faster for pressures higher than optimal. Also, your 28mm tires may well measure out to 29 or 30mm on your rim, so you are almost certainly running them too high unless you're a track cyclist (but why 28mm tires, then?) Commented Jul 20, 2020 at 18:49
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4@WeiwenNg I'm over 200 lbs right now (and need to be in really good race shape to get under 200...), and that calculator is WAAAAY low for a 310-lb rider. I usually run 100 psi front, 105 rear with 25s and 85/90 or so front and rear for 28s. This site gives 107/134 psi for a 310-lb rider with a 25 lb bicycle, which is more inline with what I would expect. Commented Jul 20, 2020 at 19:39
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1Not that this comments section is intended for extended discussion, but I run a 27C @ 90-100PSI front & back, I weigh ~200lbs. Commented Jul 21, 2020 at 10:30
Other than Argenti Apparatus' great advice, if you get punctures frequently, one of the following might also be the case:
You may have a small sharp object stuck in your tyre.
Your rim tape may be worn out or misaligned, resulting in spoke holes rubbing through your tubes (happened to me personally, resulted in about 4 flats within a month before I realized it). You say that you replaced the rim, so this is relatively unlikely, but still worth a check.
Your tyre may be too narrow for your rim.
As a 310lbs person, you absolutely must inflate your tires to the max rated value. It's printed on the side of your tire. For safety, it is advisable to also check the rating of your rim, as it also needs to withstand the tension of your tire.
If you ride at 80psi, that means that you have a contact area with the road that's 310lbs/80psi = 3.75inch^2. I.e. a patch of 1 inch x 3.75 inch (that's 2.5cm x 9.7cm), or similar. That's a lot, more than your tires are designed to provide, and it means that your tires are squished flat by your weight. There is simply not enough air between your rim and the road to carry you over potholes, roots, and other unevennesses in the road. Instead, the rubber of your tube will be forced to carry you, and it will fail, giving you pairwise punctures where the rim has pressed through to the bottom of the tire.
Bikes are generally built for persons of norm weight (around 70kg). Any person that's significantly more heavy needs to put the max. rated pressure into their tires. Not more because that's the maximum that the tire is built to handle, but lower pressure will increase the likelihood of pinch flats.
answered Jul 21, 2020 at 7:24
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FYI, simply dividing tire load by tire pressure does not give you contact patch area. There are a whole lot of variables at play. The experiment here was done for car tires, but you can see how far off it is: enginebasics.com/Chassis%20Tuning/Tire%20Contact%20Patch.html– TristanCommented Jul 21, 2020 at 20:46
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@Tristan Ok, you need to multiply with the tread portion (the part of the surface area that is not cut away to channel water). And, yes, a tire has some stiffness that reduces the contact area. That direct contact area is important for grip. But not for structural integrity. For the mechanics of carrying a bike+rider, you need to take into account that a stiff tire will be deformed across a larger area than the actual contact area, and that area is what you get by the division, roughly. That's what I meant. Unfortunately I don't know a more precise word for it than "contact area". Commented Jul 21, 2020 at 21:43
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inflate your tires to the max rated value Be careful to check the maximum pressure and tire size that your rim is rated for, too, especially with large tires. The volume of a torus is
(2*pi*r)*(2*pi*R). For a 700x40 tire, that's right around .25 square meters. A mere 3 bar is 300,000 pascal, or 300,000 newtons/square meter. So a mere 3 bar will cause almost 75,000 newtons of force to be pressing outward against the tire. 75,000 newtons is about 17,000 lbs or 7,500 kg. Not all of that is held in by the rim, but a lot of it is. Overpressurizing a tire can be dangerous. Commented Jul 21, 2020 at 22:39 -
@AndrewHenle Right. I've added a sentence about checking the rim's rating now. Btw, the outward force is not really that relevant, as most of it is counteracted by equal force on the other side. What is relevant is the curvature of the tire's material along its cross section: That's what translates the tire pressure into tension, which acts as a force on the flanks of the rim. The thinner the tire, the larger the curvature, and the less tension is generated by the same amount of pressure. That's why you can put thin, high pressure tires on the same rims as thick, low pressure tires. Commented Jul 22, 2020 at 7:46
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1Most OEM rims supplied with bikes do not have any pressure rating available anyway. One has to assume it is able to at least support the maximum pressure of the tyre it was supplied with. Commented Jul 22, 2020 at 9:01
A lot of good advice so far. Pinch flats are very likely, but also check the rim strip/tape which protects the tube from the spoke nipple ends on the rim itself. ( the location of the punctures should offer a clue as to the cause of the punctures )
Assuming you have the common 700x23c tires, I'd ditch those skinny tires and put some 700x28c tires on there instead. I'd specifically recommend Continental Gatorskin tires, based on 1000s of miles of personal experience, if you can get them. A properly inflated, larger tire, will be more comfortable, and have fewer pinch flats, while still offering acceptable rolling resistance.
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Another excellent point. I'd go as far as saying that a 310lbs person should put the widest tires on their road bike that will fit the bike. Those slim tires are simply not made for such loads. - Welcome to this site, btw. Commented Jul 21, 2020 at 21:47
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1I think there's a 32c size available, but the clearance between the tire and the brake calipers may become an issue, which is why I mentioned 28c instead. For safety reasons, I'd also look at downgrading any "high performance"/reduced weight parts, e.g. handlebars and seatposts, to something heavier and sturdier. Commented Jul 23, 2020 at 20:21
Yes, good advice here, esp re: ”pinch flats“ —sometimes called “snakebites“ because you’ll see two parallel holes. I learned this the hard way, too: check tire pressure is near or @ the maximum psi printed on sidewall before every ride, even *daily! Evidently, *all tubes lose air gradually; under-inflation has caused three flats here in as many days. Shop did not even mention inflation psi and assumed it was weight-related on our tandem (now my *former shop). Important tip to use your limbs as shock absorbers on street bikes.
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While it is recommended practice to inflate your tires prior to a ride, you shouldn't just inflate them to the maximum pressure printed on the tire - the pressure should be based on the rider's weight in order to create the optimum contact patch on the road surface. Heavier riders will need more pressure than lighter ones. There can be other factors, such as wet conditions or an extremely bumpy surface (pave) which can alter this a bit, but rider weight should be the primary factor. Commented Jul 22, 2020 at 14:30
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On 28 tires if I inflate anywhere over 90psi my bike is virtually unridable. The rear seems to skip / bounce along the road rather than follow it. Ideal tire pressure for me is around 75 rear / 70 front.– Dan KCommented Jul 22, 2020 at 15:41