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#1
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Mavic x221 Tire size help
Hello all,
I had a wheel built for me with a Mavic x221 rim at my lbs. I had specified that it was to run a 559 x 1.9 tire but now I've got it home and had a good look at it, I can't believe that a 17mm rim would be able to keep a 1.9" (48mm) tire on properly. Would someone please reassure me that everything will be fine as I can't get back to the shop until next Saturday and I hate to be bikeless. Thanks Tom |
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#2
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"Tom" wrote in message ... I had a wheel built for me with a Mavic x221 rim at my lbs. I had specified that it was to run a 559 x 1.9 tire but now I've got it home and had a good look at it, I can't believe that a 17mm rim would be able to keep a 1.9" (48mm) tire on properly. Would someone please reassure me that everything will be fine as I can't get back to the shop until next Saturday and I hate to be bikeless. Rest assured, I've used everything from 1.25" Pasela road tyres to 2.1" knobblies on 221's. Pete |
#3
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Peter B wrote:
Rest assured, I've used everything from 1.25" Pasela road tyres to 2.1" knobblies on 221's. Perhaps you'll know the answer to this: why do so many mountain bikes have these ultra-narrow rims with hugely fat tyres? OK, you /can/ run a fat tyre on a narrow rim, but surely a fatter rim would be more appropriate? d. |
#4
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"davek" wrote in message ... Perhaps you'll know the answer to this: why do so many mountain bikes have these ultra-narrow rims with hugely fat tyres? OK, you /can/ run a fat tyre on a narrow rim, but surely a fatter rim would be more appropriate? In a nutshell: weight! The narrowish 32 hole rims I have nearly always used for many moons (about 144 IIRC) have proved up to the job bouncing down boulders, steps, gawd-knows-what etc whilst carrying my 80kg (more with a loaded 3litre Camelbak), what problem would making the rim wider solve? Rgds, Pete |
#5
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Peter B wrote:
In a nutshell: weight! Should have guessed! what problem would making the rim wider solve? I guess I assumed that wider rims would be stronger (assuming comparable quality of build/materials) which might be an issue for mountain bikes. And like the OP I also assumed that a tyre could be too wide for a rim and be at risk of coming off. I don't object to having my illusions on this subject shattered. d. |
#6
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Peter B wrote:
what problem would making the rim wider solve? I'm not sure I agree with it but here is Sheldon Brown's view: "If you use a very wide tire on a narrow rim, you risk sidewall or rim failure. This combination causes very sloppy handling at low speeds. Unfortunately, current mountain-bike fashion pushes the edge of this. In the interest of weight saving, most current mountain bikes have excessively narrow rims. Such narrow rims work very poorly with wide tires, unless the tires are overinflated...but that defeats the purpose of wide tires, and puts undue stress on the rim sidewalls." - www.sheldonbrown.com/tire-sizing.html and from rec.bicycles.tech: -------------------------------------- Imagine two similar tires, one of which is 2 inches wide from bead to bead, the other 4 inches. We'll suppose them to be inflated to the same pressure, lets say 100 psi, though this wouldn't be appropriate in practice. Imagine a 1 inch length of tire/rim. The section of tire fabric in this length is 2 square inches for the narrow tire, 4 square inches for the wide one. Thus, at 100 psi, the narrow tire is withstanding 200 pounds of force, while the wider tire will be withstanding 400 pounds. This represents the difference in "hoop stress" between them. As a practical matter, tire width varies more than rim width, so narrow tires tend to assume more of a "U" profile, while wider tires tend to assume a profile like a capital omega. The narrow tire pulls up nearly straight outward from the bead, since the rim is nearly as wide as the tire. The wider tire, on a similar rim, will bulge out, so, where it contacts the edge of the rim, there's a strong sideways component to the force. This places a high stress on the cords that are in contact with the rim edge (also a high spreading stress on the rim.) Normal working of the tire as you ride can cause the cords to rub against the rim and be abraded by it. This is a common failure mode of wide tires. Using thicker cords helps resist this sort of damage. Sheldon "Does That Help Clarify?" Brown -------------------------------------- ~PB |
#7
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"Peter B" wrote in message ... Rest assured, I've used everything from 1.25" Pasela road tyres to 2.1" knobblies on 221's. Thanks Pete, I've fitted the tyre and had a little test ride and everything seems to be ok. Still looks weird though. Tom |
#8
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"Pete Biggs" wrote in message ... Peter B wrote: what problem would making the rim wider solve? I'm not sure I agree with it but here is Sheldon Brown's view: snipped Well I'm a great admirer of Sheldon but...... In practice I've never heard of, let alone witnessed an mtb rim bursting for any reason other than the sidewalls being worn away by rim brakes, based on Sheldons argument a wider rim may delay this failure mode whearas disc brakes will prevent it. And as it happens without much warning I'd sooner prevent it. Regarding the narrower rim altering the tyre footprint due to the "U"ness of the ty this is something that struck when I first started using narrower rims in the days when Panaracer Smokes were state-of-the-art. Because the Smokes were superior to the tyres I previously used the benefit of them would have masked any detriment caused by the narrower rim. I'd also assume, perhaps incorrectly, that high performance tyres are designed to be used with high performance rims which by default are narrow. Regarding sidewall wear and tear and bead abrasion again IME performance mtb tyres are scrapped because the tread is worn, the sidewall damaged by trail debris or simply because the rider is a fashion victim. Mtbers paying circa 25 quid for a tyre that lasts perhaps a year are no more bothered by this overhead than roadies whose tyres manage 2000 miles (and I fall into both camps). Regards, Pete |
#9
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"Peter B" wrote:
In practice I've never heard of, let alone witnessed an mtb rim bursting for any reason other than the sidewalls being worn away by rim brakes, based on Sheldons argument a wider rim may delay this failure mode whearas disc brakes will prevent it. And as it happens without much warning I'd sooner prevent it. Rim failure isn't always instant: the rim walls may begin to crack or splay long before any separation takes place. Disk brakes certainly solve the problem of rim wear, but to disk-equip a diskless bike might cost several hundred pounds. I'd also assume, perhaps incorrectly, that high performance tyres are designed to be used with high performance rims which by default are narrow. There are a lot of broad, high-performance rims on the market, assuming you're not limiting your definition of performance to XC racing. The Sun Rhyno Lite is one example, and the trend is toward both broader rims and broader tyres. A Nokian Gazzaloddi tyre and a Snowcat rim are both high-performance (if extreme) products in their fields. That many people use fairly broad tyres on narrow XC rims shows that this isn't a big problem, but broader tyres handle much better at lower pressures on broader rims. James Thomson |
#10
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"James Thomson" wrote in message ... There are a lot of broad, high-performance rims on the market, assuming you're not limiting your definition of performance to XC racing. I must admit I was for two reasons: 1) I based my comments on my own experience of long trail rides, often quite rugged (Peaks, Lakes, Welsh purpose built trails, enduros etc) and to a lesser extent XC racing which to me is a refinement of the former. 2) Outside of the above I have little knowledge but assume weight isn't a factor for downhilling and certain types of playbikes designed for getting air-time etc.so yes, I can't see a detriment with wider rims and those bikes generally have even wider tyres than XC racing and trail bikes. Pete |
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