a mtb debate - could it cross over?

jimbonorth

Theres a big hoo-har at the moment about the "29er" ... putting it simply mtbs built to ride with 29" wheels.

Search google and you will find an absolute ton of forums and debates and magazine articles about them, comparisons and ride tests, racing them against 26" wheeled mtbs - the only downside Ive ever heard is some drawbacks when riding technically offroad

So why then have I never seen mentioned of road bikes with 29" wheels? Surely if the only thing stopping mtbs is the technical inefficiencies which road bikes won't need to contend with and if they are proving as efficient as people in the mtb say world surely theres scope there for roadies? Am I missing something?

redddraggon

29" wheels on MTBs are the same size as 700c you get on road bikes , the rims are probably a bit wider on the 29" though. The hubs will probably be a different size, but otherwise I think they are largely very similar.

jimbonorth

Do many racers use 700c wheels? Seems like a logical choice if its going to give that much advantage?
I wonder, is there any rules against using 700c in a road race or TT?

redddraggon

700c is the standard road wheel, and the only one I believe that is UCI legal for road racing and TTs.

As far as I know as all adult sized road bikes come with 700c, smaller bikes with 650c.

I know that in the past for TTs people used to sometimes use a 700c on the rear and 650c on the front, but you don't see that much these days.

http://en.wikipedia.org/wiki/Mountain_b ... ire_design

Bicycle wheel sizes are not precise measurements, a 29 inch mountain bike wheel actually has a 622 mm (24.48 inch) bead seat diameter (the term, bead seat diameter (BSD), is used in the ETRTO tire and rim sizing system). 622 mm wheels are standard on road bikes and are commonly known as 700c.

jimbonorth

Thats really useful info - Ive been riding a fair while under the false impression that 27" wheels were different to 700c! and therefore 29 ers were different too. Thanks RedDragon!

Steven Martin

27" are different from 700C, but they are a similar but not identical size.
To extrapolate your thought on bigger is better, I suspect that any bigger than 700C wheels would mean that toe overlap would become a real issue.

redddraggon

Steven Martin wrote:

27" are different from 700C, but they are a similar but not identical size.
To extrapolate your thought on bigger is better, I suspect that any bigger than 700C wheels would mean that toe overlap would become a real issue.

27" are old size wheels aren't they?

and 28" and 29" are just the same as 700c aren't they?

aracer

redddraggon wrote:

and 28" and 29" are just the same as 700c aren't they?

Not necessarily (though more than likely)
http://sheldonbrown.com/tire-sizing.html#isoetrto

maddog 2

as said, 29ers are just 700c

one reason why roadies don't go bigger than 700c is, as SM says, toe overlap.

Road bike have for a long time been stuck on a single wheel size (700c). Recently we've seen this change with 650c starting to be specced on the smaller frames such as WSD frames, which is clearly a good idea. My sister-in-law has a small roadie with 700c wheels and quite frankly it's a design mess. Toe overlap is a real problem and it's a dog to ride.

Perhaps we should also have a bigger wheel for the bigger frames, say "750c"...?

Steve I

The 2 road bikes and the cross bike I have now both have quite a bit of toe overlap. I sold a couple of Ribble frames in the past year, both had toe overlap, one of them was too big for me. I generally ride a 52 or 54cm frame and have size 10 feet. To be honest, I had always thought that toe overlap was an accepted fact with road bikes.

nicklouse

just to note there are moves for the 650 b (iirc) rim size to be also used in MTB due to there being less geo changes needed than for the 29"ers