# How does tire/rim sizing work?



## z3phrn

I upgraded (I think) my wheelset a while back, and now I'm looking for new tires to replace my existing ones. My question is: what size tires (and tubes for that matter) are going to going to fit for the rims I've got now? I read Sheldon's article on tire sizes but I still couldn't figure it out. Specs below: 


Weight: 715g (front), 935g (rear)
Tire Size: 700c 
Tire Type: Clincher
Hub: Forté™
Spacing: 100mm (front), 130mm (rear)
Spokes: Stainless Steel 
Spoke Count: 20 (front), 24 (rear)
Lacing Pattern: 2-Cross
Skewers Included: Yes
Rim Height: 30mm
Rim Width: 18.4mm (I'm unsure of what this 18.4mm rim width infers)
Compatibility: Shimano® 8/9/10
Accessories Included: None
http://www.performancebike.com/bikes/Product_10052_10551_1089993_-1___

Thank you!


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## erj549

Assuming you are doing road riding (as opposed to commuting or something), you probably want 700x23 or 700x25 tires for those wheels. The 700 is the wheel diameter in millimeters, and the second number is the tire width in millimeters. The larger the tire width, the more plush the ride, but many road bikes wont' fit anything much larger than a 700x25 tire.


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## cfoster

*Tire Chart*

Here's a great resource from Sheldon Brown,

http://www.sheldonbrown.com/tire-sizing.html

You need a 700c size tire, for your 700c wheels. The main question you'll need to answer is what width tire do you want. Given your internal rim width as 18.4mm, you could safely use a narrow 700 x 20 tire (usually for racing) all the way to a wider 700 x 28 or maybe a 700 x 32 tire. "Rules" regarding tire width have loosened up a bit over time, due to improvements in tire fit quality, but it's still never a good idea to put too narrow of a tire on a wide rim, or too wide a tire on a narrow rim. Given your rim width, you'll most likely going to want to go for a 700x23, 25, or maybe 28 tire width.

Have fun.


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## z3phrn

Ahh, now I understand the width chart. But according to the graph, wouldn't 18.4mm wide rims only support a range of ~25mm to ~40mm? I've got 23mms on right now, and I was mostly just wondering how far I could go in either direction. 

Also, I've noticed that I have to pull really hard to get a tire onto these rims (compared to other wheels); is this due to a wider total rim width?


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## T0mi

23mm is the standard for the road (21.5/22 for tubular). Narrower ones are mostly used for for specific applications (time trial, hillclimb) and wider for comfort. You can't go wrong with 23. 25mm and 28mm are mostly used by people riding on rough roads and cobbles or for commuters.


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## wim

z3phrn said:


> But according to the graph, wouldn't 18.4mm wide rims only support a range of ~25mm to ~40mm?


The rim width numbers in Sheldon's chart were correctly established and listed. They are inside rim widths exactly as shown by "a."

Often, rim width designations are established and listed _incorrectly_ as outside widths shown by "b." (Rarely and also incorrectly, they are established and listed as as inside widths shown by "c.") Chances are high that your so-called 18.4 mm rim is actually a nominal 13 mm rim. The 6 mm subtraction is approximate. It helps you to convert incorrect listings into correct ones.

The difficulty of getting tires on has more to do with rim- and tire circumference than rim width. Because of manufacturing tolerances, some tires are difficult to put on some rims, some tires go on some rims with almost no effort, and some tires are almost impossible to mount on some rims. Which tire has difficulty with which rim can change with date of manufacture, so past experience is not a reliable guide.
.


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## Kerry Irons

*Width limits*



z3phrn said:


> Ahh, now I understand the width chart. But according to the graph, wouldn't 18.4mm wide rims only support a range of ~25mm to ~40mm? I've got 23mms on right now, and I was mostly just wondering how far I could go in either direction.
> 
> Also, I've noticed that I have to pull really hard to get a tire onto these rims (compared to other wheels); is this due to a wider total rim width?


No, you could fit very narrow to quite wide tires on that rim. Your frame and fork would probably limit the maximum tire size you could fit. 

There are techniques that ease the installation of tires, primarily being that you get the bead of the tire right in the center of the rim as you install the tire. But there are tire/rim combinations where the spoke bed diameter is too large and it is very hard to get the tire on.


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## z3phrn

Thanks for the advice! I guess those rims are just slightly larger than normal, since it usually involves two tire levers and blood spewing all over the place rather than the normal yank and tug.

As a followup question, I've always wondered why tubes come in a range of widths (such as "700*23-26" and "700*23-28"); what is the difference between those 2 tubes?


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## cxwrench

erj549 said:


> Assuming you are doing road riding (as opposed to commuting or something), you probably want 700x23 or 700x25 tires for those wheels. The 700 is the wheel diameter in millimeters, and the second number is the tire width in millimeters. The larger the tire width, the more plush the ride, but many road bikes wont' fit anything much larger than a 700x25 tire.


a 700c rim is definitely NOT 700mm in diameter. it's 622mm, which is what is printed or molded on every 700c tire made.


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## erj549

cxwrench said:


> a 700c rim is definitely NOT 700mm in diameter. it's 622mm, which is what is printed or molded on every 700c tire made.


Excuse me for my EGREGIOUS mistake. I will now perform 500 hail Marys in an attempt to atone for the hurt I have caused. It's interesting to note here that you didn't actually add anything to the discussion other than telling me how obviously wrong I was. 

To the OP, after a little research, the 700 is the outer tire diameter.


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## wim

cxwrench said:


> a 700c rim is definitely NOT 700mm in diameter. it's 622mm, which is what is printed or molded on every 700c tire made.


Not really. The "622" refers to the bead seat diameter (BSD) in millimeter, which is always smaller than the rim diameter.


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## Kerry Irons

*Tube size*



z3phrn said:


> As a followup question, I've always wondered why tubes come in a range of widths (such as "700*23-26" and "700*23-28"); what is the difference between those 2 tubes?


The odds are good that if you measured those two tubes, they would be the same size or perhaps different by 1 mm.


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## AndrwSwitch

Too big a tube is a pain in the butt to get inside a tire before inflating the rest of the way. Way too big a tube may have folds and stuff, after inflation. But that would be something ridiculous, like putting a tube intended for a 29" MTB wheel in a 23-25mm road tire, or using a tube with the wrong diameter. Too small a tube is the budget-conscious racer's secret weapon.  But you might notice a little more air loss over time.


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