Classic Road - Measuring Rim Size
 

'88 Schwinn World Sport. 6-speed rear freewheel/sprocket assembly with QR skewer. Front skewer also.

Original wheels aren't great; rusty, noticeable lip at seam. I want to replace with similar size, but new. Tires are marked "27 x 1 1/4." Actual outside rim diameter is app. 25 1/4". Do I want a 26" or 27" rim? Can I buy a complete front and rear wheel/spoke assembly? Thanks.

You need and can buy new 27" fully built wheels. Buy ones for the width tires you plan to ride.

rims are sized by he tires. 27" tires take a 27" rim.

If you want the same size wheels, you can find 27" wheels easily. Note that the diameter of the wheel has nothing to do with the marked size--it's dumb, I know.

Or, if you want a larger selection of tires, you might be able to use 700c wheels, which are slightly smaller in diameter. If you have enough room to adjust the brake pads down 4mm+, you can most likely use 700c.

Here is more info: http://velo-orange.blogspot.com/2011...ake-reach.html

I don't know that it's unusually dumb. 27" or 700c or any other nominal sizes are just that -- Nominal sizes -- or what we call them. Nominal sizes are often (usually?) different than actual sizes, just approximations for reference.

2x4s aren't 2 x 4, a 1/4" power drill isn't 1/4", a 10# sack doesn't weigh 10#s, and size 10 shoes aren't 10 of anything.

So the bike world isn't any stranger than the rest of the world in how it approaches nominal sizing.

As above, you have 27" wheels. It's just a name, not a measurement of anything. Read this, especially if you're looking to cure your insomnia: http://www.sheldonbrown.com/tire-sizing.html

No, it's dumber than all those, IMO. Nominal sizes are one thing, but at least they're consistent. For instance, the 5/16" drill bit may not be actually 5/16", but at least it's bigger than than 1/4" bit. Here we have 27" (630mm) rims, which are bigger than 29" (622mm) rims which are the same as 700c rims, then you have 26x1.25" decimal rims (599mm), which although they're thankfully smaller than 27" and 29" rims, they're different (bigger!) than 26"x1-3/8" fractional rims (590mm).

It all makes sense if you use the mm sizes--but nobody does.

want to be international about it?

the bead seat diameter is what the many companies use.. its an agreement ..
so tires and rims fit each other

the Number for 27" tires its 630mm

700c just a bit smaller , but incompatible then the number is 622mm

you should see these numbers engraved in the mold, so a raised number on the tire sidewall



2nd number is the width such as 622 - 32

It makes sense if you consider that nominal tire sizes are based on the approximate overall diameter. Then the nominal rim size is based on the tires that fit.

As for 29r it's a new creation, and they had to call them that because 26, 27, and 28" were all already taken.

As for the millimeter sizes, they don't make any more sense, if you talk about the nominal tire sizes such as 700c, 650b, etc.

The ERTRO sizes such as 25-622, were intended to clarify the rim/tire fit, but aren't super useful if you're interested in knowing the overall diameter of the tire.

No system of nominal sizing sis ever perfect at describing the actual size, but it's a decent shorthand for reference.

i logged in and came to this thread
for the sole purpose
of making this exact suggestion

the only reason i can think of to not use
the far more common 700c wheel size
is if you were trying to restore the bike into a museum peice
and so wanted everything to be original

also
on brakes where the pivot is above the wheel
like road bike style caliper or centre pull brakes
reducing wheel diameter decreases braking power

but on almost every 27" wheel bike i have owned
i converted to 700c for added tire selection
and for extra clearance for fatter tires

LOL, I just realized that you are the poet "Laurier" of BF.

Actually found 2 new 27" aluminum rims - a front AND a rear - at the LBS this afternoon. A lucky find, I thought. The front wheel is a bolt-on type, like the one that was already on the Nishiki. That's okay - I get the feeling that this new tire and tube will last for a long time. This will be my first time adjusting cup-and-cone tension with a bolt-on wheel, but it looks easy enough. Thanks all, for the input here.

Just a bit of symantics: a "rim" is only the outer hoop of the wheel, without spokes or hub. In general, "rims" are not specific to front or rear. It sounds like you got a nice pair of wheels. :)

Noted - thanks!

Only after I got the wheel back on the bike did I notice that I'd installed a 700-size tube (with its Presta valve), rather than the Schroeder-valved tube it's meant for. But apart from the larger stem hole (which is covered by the stem nut), it installed perfectly and is still holding air this morning. I guess I'll run it. :-)

the only issue
that might happen to the valve
is too much movement

if youre not careful when you are pumping you might tear surrounding tube

Tubes stretch- they're only there to hold the air in. It's the tire that needs to be precisely sized. You might think that "27-inch" and "700C" tires are interchangeable, but they aren't. Trying to put a 27" tire on a 700C wheel will usually result in a blowout.

You can get adapters to properly fit a Presta valve in a Schraeder valve hole: http://www.biketiresdirect.com/produ...ta-stem-savers . These will keep the lip of the valve hole from cutting the tube.

Thanks, Jeff. With the retainer nut tightened onto the threaded Presta valve, all SEEMS secure, and I rode the bike 30 miles this morning without issue. I would think that that retaining nut would keep the tube from trying to pooch through the over-sized hole. Hoping, anyway.

This Nishiki has been a hoot. Because of its long, 56 cm top tube, I've been able to make this 50 cm frame fit me quite well, simply by raising the seat post a bit. (I'm 5' 10".) I may spring for a quill stem with a slightly longer extension . . . but it's quite nice as set up currently. I loaned my 56 cm carbon Tarmac to a friend for this morning's ride. I rode the Nishiki. We finished at the base of the 1200 VF hill to my house. I put the Nishiki in the Jeep and rode the Tarmac up that hill. Because it's 16 lbs. it was probably less effort to get it up that hill than it would have been on the 25 lb. Nishiki. But the Tarmac is definitely less comfortable. . . and I'm beginning to understand why the Nishiki gets so much use, and why these old steel bikes are so enjoyable. Thanks. DB

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