27.5" & 650B – are they the same? – Singletrack World Magazine

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This topic has 12 replies, 11 voices, and was last updated 10 years ago by tom200.

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27.5" & 650B – are they the same?
gavmoir
Free Member

a quick google didn’t answer my question so the STW forum is the next best thing!

Posted 10 years ago

wiggles
Free Member

Yes… Well no.

They are not but manufacturers have decided to call 650b products 27.5

Posted 10 years ago

momo
Full Member

Yes, they are one and the same

Posted 10 years ago

Northwind
Full Member

Yep, same thing but manufacturers switched to calling it 27.5 to trick people into thinking that it’s in the middle of the 2 existing sizes.

Posted 10 years ago

darrenspink
Free Member

Copy and paste job..

“The term 650b comes from French tyre sizing nomenclature – the number indicating the approximate diameter of the wheel, including tyre, and the letter corresponding to an approximate width.

A 650b wheel is one that’s about 27.5 inches in diameter, when measured from tyre edge to tyre edge. This compares to 26in for a standard mountain bike wheel and 29in for so-called “29er” wheels.

Bear in mind that because tyre sizes vary, this is only a rough measurement. A high-profile tyre fitted to a 26in wheel will usually be 27in or more in diameter.”

I actually think the public decided on ‘27.5’ didn’t they?

(Sorry kittens)

Posted 10 years ago

wrecker
Free Member

A 650b wheel is one that’s about 27.5 inches in diameter

About? yeah, about 27″. If we’re being that rough, I’m calling my bike a 26.5.

Posted 10 years ago

bartimaeus
Free Member

The BSD (Bead Seat Diameter) of a 26er is 559mm. A 650b wheel is 25mm bigger with a BSD of 584mm.

As there are 25.4mm in an inch that means a “27.5 inch” wheel is slightly less than an inch bigger than a “26 inch” wheel with the same profile tyres.

A 29er has a BSD of 622mm which is just under 2.5 inches bigger than a 26er.

Posted 10 years ago

brant
Free Member

A decent 27.5/650b tyre is circa 355mm radius. 710mm diameter. Which is 27.9in.

Posted 10 years ago

wrecker
Free Member

A decent 26 tyre has a diameter of 690mm. 20mm difference; less than an inch.

Posted 10 years ago

howsyourdad1
Free Member

Kitten time

Posted 10 years ago

chiefgrooveguru
Full Member

26 tyre = 559mm rim = 22″
then 25mm = 1″ bigger:
27.5 tyre = 584mm rim = 23″
then 38mm = 1.5″ bigger:
29 tyre = 622mm rim = 24.5″

You can call a 27.5 a 650b but it really isn’t, just as a 29 isn’t a 700c.

Posted 10 years ago

eshershore
Free Member

29’er is a 700c rim with a 2.1″ + tire which generally gives a 29″ measurement from tire edge to tire edge across the wheel axle centre

I measured my first 29’er which had a Specialized Ground Control tire and it came up 29.2″

obviously the exact measurement depends on the brand and model of tire, the 29’er Specialized Fast Trak currently on the rear of my bike actually comes up just smaller than 29″

rim width also has a big influence on tire shape and height, as I found when I mounted a pair of Fast Trak tires on my hybrid’s Mavic A319 rims

Posted 10 years ago

tom200
Full Member

Same as 26″?………………..yes, but you will need to buy a new bike 😆

Posted 10 years ago