Bike sizing and 29 ers

[Sandra6]

Working where I do I should probably know this - and I think I do, but humour me.
Is there any difference in bike sizing when it comes to 29ers?
I know mine is a 17, and next one up a 19 -rather than the 16,18,20. But is a 16 in effect an 18 because of the wheel size?

 

[Spiderweb]

No, wheel size doesn't change the size of the frame main triangle.

 

[HarryTheDog]

I think manufacturers should stop using this way of describing a bike frame size as its not consistent anyway, and start using the effective horizontal top tube length. I always just jump to the geometry chart and find that value. I'm a shorty so its usually the smallest frame anyway so around 56cm effective top tube length is for me in a MTB.

 

[Sixmile]

I bet you the new manager in the bike section knows the answer

(wee jokes!)

 

[Sandra6]

I overheard a colleague, not that one , saying to a customer that the 16 was in effect an 18 because of the wheel size and I very nearly said "what the flip?!" but I didn't. I wish I had.

 

[Crackle]

I overheard a colleague, not that one , saying to a customer that the 16 was in effect an 18 because of the wheel size and I very nearly said "what the flip?!" but I didn't. I wish I had.

In some ways that's right as the BB and the Headtube will all be taller, so standover clearance will differ. The top tube of a 29er goes up steeply to meet the headtube on smaller frames. In terms of reach, it won't be true and in terms of how the frame is described it isn't true. Here's a picture of my FF29 with my old 26" Marin in the background.

 

[Kajjal]

For the same brand the actual sizing should be the same, just the frame design varies to make space for the larger wheel.

The contact points will be in the same position, saddle, bars, pedals. The reach and stack measurements are useful for comparing similar styles of bikes from different brands.

 

[Sandra6]

In some ways that's right as the BB and the Headtube will all be taller, so standover clearance will differ. The top tube of a 29er goes up steeply to meet the headtube on smaller frames. In terms of reach, it won't be true and in terms of how the frame is described it isn't true. Here's a picture of my FF29 with my old 26" Marin in the background.

View attachment 344504

But see how your saddle heights are the same - so you still need the same size bike?
If I normally ride an 18, I wouldn't buy a 16 29er.
I get that sizes differ between brands, that makes sense, it's like wearing a size 14 in next and an 18 in H&M. I just thought his advice to the customer was a bit dodgy. I always encourage people to sit on a bike anyway, especially if they tell me they want a 20 and they're 5 foot 2.