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  1. #1
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    What are the advantages of wider rims, if any?

    In my simplistic way of thinking, wider rims only decrease the amount that the sidewall of a tire must deflect as it's surface area increases (ie running lower pressure or landing a jump). If this is true, then what is the advantage of using a wider rim with a tubeless system where there is no risk of pinch flatting?

    And for snow riding, if a tubeless system lets you run pressure at extremely low pressures anyway, are there any other advantages to be gained by using a wider rim? Very interested in everyone's thoughts on the matter.

  2. #2
    aka Willy Vanilly
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    I'm certainly no tire expert but I am pretty sure that running a wider rim will allow a tire to have a larger contact patch with the ground (as opposed to mounting the same tire on a narrower rim).
    Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius -- and a lot of courage -- to move in the opposite direction.
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  3. #3
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    About that contact patch...

    Quote Originally Posted by will8250
    I'm certainly no tire expert but I am pretty sure that running a wider rim will allow a tire to have a larger contact patch with the ground (as opposed to mounting the same tire on a narrower rim).
    I'm pretty sure that the tires' PSI determines the total area of the contact patch; for example a combined bike/rider weight of 200 lbs. on tires run at 25 psi would dictate a contact patch of four square inches per tire. This is the argument that everyone uses against the idea of 29" wheels providing an increased contact patch- bigger wheels in and of themselves do not increase the contact patch, but only alter its dimenions (in this case elongating it instead of widening it).

    Assuming the above to be true, the advantage of both 29" wheels and wider rims (in regards to contact patch) is that they allow substantially lower pressures, which will increase contact patch. However, a tubeless system will also allow substantially lower tire pressure, so the questions is what are the other benefits of 29" wheels/wide rims? For 29" wheels it is lower rolling resistance, better angle of attack, and I believe a preferable contact patch shape (run a 26" tire vs. a 29" tire at the same 35 psi and the 29" tire will have much better grip in low traction situations, not to mention what happens when you lower the 29" tire psi appropriately).

    Which brings me back to my original question about wide rims. If you are going to run a wider tire (say 2.6"), will a wide rim (say 36mm vs. 24mm) offer any advantages? If contact patch area and shape is determined by tire pressure and wheel diameter, then it cannot do much to alter that. If a tubeless system lets you run the pressure as low as you want (say 20 psi), then that is no longer an advantage either. So other than being stronger (and proportionately heavier) what are wide rims good for?

  4. #4
    Code Burr
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    .

    Quote Originally Posted by miles e
    Which brings me back to my original question about wide rims. If you are going to run a wider tire (say 2.6"), will a wide rim (say 36mm vs. 24mm) offer any advantages? If contact patch area and shape is determined by tire pressure and wheel diameter, then it cannot do much to alter that. If a tubeless system lets you run the pressure as low as you want (say 20 psi), then that is no longer an advantage either. So other than being stronger (and proportionately heavier) what are wide rims good for?
    I think a wider rim should allow the tire to expand horizontally as well as vertically if
    if the tire is capable. I dont know about the 'contact patch', but it makes
    sense that a wider rim and tire will make more contact with the ground.
    Which creates more friction and resistance but increases stability and grip.

  5. #5
    Baliw
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    Quote Originally Posted by miles e
    So other than being stronger (and proportionately heavier) what are wide rims good for?
    I think wider rims enable you to have better stability for the tires you use, useful when cornering. Narrow rims make the tire sides bulge out, the beads being spaced narrower than the sidewall width. Consequently any lateral loading on the tire, such as when cornering, may deform the tire cross-section a lot more, with effects on traction and steering.

  6. #6
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    Quote Originally Posted by Juramentado
    I think wider rims enable you to have better stability for the tires you use, useful when cornering. Narrow rims make the tire sides bulge out, the beads being spaced narrower than the sidewall width. Consequently any lateral loading on the tire, such as when cornering, may deform the tire cross-section a lot more, with effects on traction and steering.
    My experience with a 2.2, 26" tire is that on a narrow, XC rim (Shimano), you have to be more diligent about keeping the psi up in the tire as it tended to roll over the bead easier on a narrow rim. With a wider rim, (RhynoLite), I didn't notice that as much when the psi dropped.

  7. #7
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    Hope better workout

    Oh man, you get such a better workout on those climbs with the extra weight, Its awesome!
    No really, though. I have a 35 pound FS bike that I normally ride, but when I switch it up and ride my hartail thats at least 10 lbs lighter, I can fly! I think it is a valid training technique! Sorry, maybe I should have posted this somewhere else .. .-t

  8. #8
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    CONTINUED - additional details

    I am running 2.5’s on rims which at 17mm inside to inside so approx 21 mm outside to outside. These Weirwolfs are pretty light weight perhaps 600g, and have thin sidewalls which undoubtedly increase the squirm tremendously, but allow for a fattie that does not weigh as much as a DH tire.

    I like to rum lower than average PSI for increased traction perhaps 25 to 28 front and rear. I notice that the tire currently is pretty squirmy at speed on babyheads and rough rocky terrain. Were one to grab the tire and wiggle it on the rim one could see how it wiggles on the rim.

    When airing up to around 30 and 35 PSI (front and back) one cannot wiggle it nearly as much while it is on the same rim. The tire does ride noticeably stiffer , is less squirmy ( tracks better), give up traction in climbing rough stuffs well as in loose turns which can get a bit scarier.

    Although I do not recall the physics involved with pressurized round systems, I was hoping that someone had already lived through this conundrum and switched a single variable – namely internal rim width – and could provide a technical and well reasoned personal experience.

    The 519’s should have a 19mm inside width since that is how MAVIC names their rims this diff in width would be immaterial. One would have to switch up to about a 21mm inside width to evaluate the rim width variable and use the same tire and PSI’s for comparison.

    Many posters are not aware of the inside width. A 17mm inside width would have about a 22mm outside width. A 21 mm ( for example 521’s,721’swidth would likelty have a 25 or 26mm outside. Rynolites have approx 22mm inside with approx 27 outside widths. The Sun singletracks ( I have my notes at home) are about 23mm inside with 30mm outsides. The key figure is inside widths NOT outside widths.

    Weights per manufacturer advertisements ( are these realistic?):
    Most 17mm insiders, claim weights of about 400 – 450g
    Most 21mm insiders, claim weights of about 550 - 600gs

    I wonder if the sensitive, in tune rider, could notice acceleration and overall weight differences if the only variable changed was the weight of the rim from 425 to 600gs?

    Perhaps I will eventually be the expert here. Nevertheless I am riding at the higher PSI’s stated earlier and will drop 2 more PSI and will see…but I still haven’t decided what to do about the new possible wider rims.

    Cheers and keep the technical posts coming…J

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