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I'm new to road bicycles, sorry if this question is beat to death. What I'm wondering is what to measure as far as frame clearance, rim width, etc. to put the 'widest tires that will fit' on my road bike for durability purposes?

The bike is more or less a glorified BSO, and because of this I can't find any real specifications other than the amazon.com page: http://www.amazon.com/Victory-Vision-Mens-Road-Bike/dp/B002D126EW

Victory Vision Road Bike

The ones that came on it are unmarked, but appear to be 27mm or 28mm, the rim width is 25mm. How do I know whether 32mm or larger will fit before buying them, without rubbing and such?

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You're in for a treat. Many manufacturers label tires a bit narrower, others a bit wider. I have a pair of Panaracer Paselas that are labeled 700cx35, but really measure ~37mm wide on my Velocity Synergy rims. They might run true to size on narrower rims, but you never know until you can fit them. Go to a bike shop and have them fit a pair. If they don't fit, don't buy them. –  WTHarper Jul 11 '13 at 2:07
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There are three things that limit the size of the tire: The rim width, the clearance between tire and frame/fork, and brake clearance. Generally you can go about 50% wider than the rim, but it's going to vary a bit with tire and rim. Sheldon may have some details. Frame and brake clearance you have to assess yourself. –  Daniel R Hicks Jul 11 '13 at 22:24
    
@DanielRHicks Is there a single place where the 'bulge' is the greatest? My frame and forks are curving upward, so where should I measure for the tire width clearance? 5mm above the rim? 10mm? Some set distance? –  Ehryk Jul 12 '13 at 4:32
    
A standard inflated tire (ignoring any heavy lugs on the tread) will adopt a roughly circular cross-section when inflated. So if you're thinking of installing a 35mm tire, the tire would extend a bit less than 35mm up from the outer rim edge, and the widest spot would be about half that distance up. But of course no tire size is exact, and the actual width will also vary depending on the size or the rim used, so you need to allow a bit of extra clearance. (A bike shop might do you the favor of fitting various wheels/tires into the frame to see what "reality" looks like, if you ask nice.) –  Daniel R Hicks Jul 12 '13 at 11:10

1 Answer 1

What tire width can be safely used it mostly determined by the width between the bead seats in the rim. This can be measured and is often listed in the specifications for your rims.

Then I use Sheldon's Tire sizing chart to figure out which tires will work. That link is to a long article on tire sizes, the rim vs tire width chart is red & green and is near the bottom of the article

Edit

Near the top of the linked article is a nice picture showing where to measure inner rim width. This determines if the tire will stay put on the rim. Both too wide a tire on too narrow of a rim and too narrow of a tire on too wide of a rime will not seat correctly.

As freiheit points out you also need to check for clearance issues around chainstays, seatstays brakes etc.

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Yeah, but these are generic cheapie rims and I can't find that. I do have a caliper, so is it measured from the inside of the bead seat groove or just where the caliper will sit nturally? –  Ehryk Jul 11 '13 at 22:10
    
@Ehryk - Rim width is measured on the inside. –  Daniel R Hicks Jul 11 '13 at 22:25
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Road bikes also have brake and frame/fork clearance issues with fitting larger tires. –  freiheit Jul 11 '13 at 23:51

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