Tyre size

[colin-java]

Hi...

I have a new Hardtail Mountain Bike, 29" wheels, 700C (whatever that means).
The bike is a Cannondale trail 6 (Large).

I want to use some slimmer puncture resistant tyres, like these..
http://www.tweekscycles.com/Product...n Bike Tyres&gclid=CLvE1NjSisQCFayWtAodfUIA3g

But I'm not sure if they are the correct fit, it says 29 x 1.75, but I'm not really clear exactly what all the sizes refer to precisely on the wheel.

I like these schwalbe tyres, I have some for my road bike, and the've stopped lots of thorns going thru, so I know they work.

Thanks for any help.

 

[mjr]

Use the ISO sizes- a two figure width and a bead diameter in millimetres with a dash between. Ideally the tyre width is about 1.8 times the rim width.

The trouble with inches is that British inch sizes are bigger than American inch sizes! And French mm sizes like 650a are not obvious.

I can't tell what size those tyres are. Www.schwalbe.co.uk didn't list Marathon in 29*1.75 but they're very common in 622mm aka 700c aka 28*decimals in a choice of widths, but that's not what I thought 29er was.

 

[Yellow Saddle]

The trouble with inches is that British inch sizes are bigger than American inch sizes! And French mm sizes like 650a are not obvious.

Perhaps you're thinking of US gallons and Imperial gallons? An inch is an inch.

 

[mjr]

Perhaps you're thinking of US gallons and Imperial gallons? An inch is an inch.

Not in bike tyres! I think we measure to the bead and they measure to the tread, or something like that. For example, UK 27*1 1/4" is 630mm diameter yet USA 28*1.25" is 622mm diameter.

 

[Yellow Saddle]

Tyre sizes are now regulated by ETRTO, European Tyre and Rim Technical Organisation. This regulates all tyres, including bicycles. This is good news for us and makes sizing such as 700C and 650b statutory obsolete, even though it is still used for clarity.

ETRTO now uses the bead seat diameter (BSD) to indicate tyre sizes. The old 700c size is actually a 622mm BSD. Unfortunately us oldies in the game find 622 difficult to convert to and the tyre companies then stamp 700C on there as well. To help the confused get confused a bit more, they also throw in another obsolete size - 29".

If you convert 29 inches to mm, you get 736mm, a figure nowhere near 622. But they are all the same! It is bizarre. However, in MTB terms 29" = 700C = 622BSD.

it gets worse. The BSD is measured in mm but the tyre width is measured in inches.

To cut a long story short, any 622/700C/29" tyre with a reasonable width will work for you. Typical knobbly MTB tyres are about 2.1 inches wide. However, you can go down to 1.5 inches if you want to fit slicks.

I hope that helps.

 

[colin-java]

Okay thanks for replies....

I measured the the diameter of the rim, and its 25", I thought the 29" meant the rim diameter, but apparently not.

I checked on my other road bike - (Merida Glide), which has a wheel size a bit bigger than the standard 26" bike wheel size, and its rim diameter is also 25"
The road bike uses Schwalbe Marathon plus 28 x1 5/8 tyres.

So I guess those tyres would fit on the mountain bike, so I have an idea what I need, but something inbetween, as the MTB
has large nobbly tyres, the road bike has slim smoothish tyres.

 

[vickster]

Why not go to your local bike shop and get them to sell you the correct tyres?

 

[Yellow Saddle]

Okay thanks for replies....

I measured the the diameter of the rim, and its 25", I thought the 29" meant the rim diameter, but apparently not.

I checked on my other road bike - (Merida Glide), which has a wheel size a bit bigger than the standard 26" bike wheel size, and its rim diameter is also 25"
The road bike uses Schwalbe Marathon plus 28 x1 5/8 tyres.

So I guess those tyres would fit on the mountain bike, so I have an idea what I need, but something inbetween, as the MTB
has large nobbly tyres, the road bike has slim smoothish tyres.

29" is the nominal rim diameter based on some arbitrary measurement that is not the BSD method outlined above.

There is no such tyre as a 25" tyre. Your is a 622 x 2.X (I don't know how much X is but I'm pretty certain of the 2.) You asked whether a 622 x 1.75 will fit. Answer is yes.

 

[colin-java]

Why not go to your local bike shop and get them to sell you the correct tyres?

I could do, I like to buy online though, I got my other tyres on amazon, and the rims appear to be the same size on new bike,

 

[colin-java]

29" is the nominal rim diameter based on some arbitrary measurement that is not the BSD method outlined above.

There is no such tyre as a 25" tyre. Your is a 622 x 2.X (I don't know how much X is but I'm pretty certain of the 2.) You asked whether a 622 x 1.75 will fit. Answer is yes.

Yes, but I'm just saying the rims are both 25" diameter on the 2 bikes, so I just need something similar to what I have on the road bike, but with more width and tread.

 

[mjr]

Oh gosh. Millimetres by inches, really?

 

[Yellow Saddle]

Yes, but I'm just saying the rims are both 25" diameter on the 2 bikes, so I just need something similar to what I have on the road bike, but with more width and tread.

I repeat. There is no such thing as a 25 inch rim. 25 inches is 635mm and nominally 29" wheels have a 622mm BSD. Have a look at the sketch I posted above and tell me from where to where you measured.

 

[Yellow Saddle]

Oh gosh. Millimetres by inches, really?

Sad but true.

 

[colin-java]

I repeat. There is no such thing as a 25 inch rim. 25 inches is 635mm and nominally 29" wheels have a 622mm BSD. Have a look at the sketch I posted above and tell me from where to where you measured.

You don't need to repeat, I know there isn't a 25" inch rim, I'm just saying I measured the wheel as 25", so not just the bead set diameter, but going further out to the very edge of the wheel.