650B...ollocks?

Northwind

Thelonegroover wrote:

Testers in magazines are riding bikes to the limit

Har. Some are quite fast. Some are not. Some reviews are based on in-depth longterm riding on varied terrain. Some are not.

supersonic wrote:

650b is not midway though - it is 25mm larger than the rim of a 26er (559 vs 584) - so not even an inch! 29er is 622mm. '27.5' is very misleading - mind you, so is 29er and 26 in reality! If we take 26er as granted, then the sizes with the same depth of tyre are 27 and 28.5.

Aye... This one rings the skeptic bells, as soon as they started saying "27.5" I thought "the marketing men want to hide the fact that the change from 26 to 650 is very small" Exaggeration's not often innocent when you're selling things.

What's nice about 650B is that it's very easy and cheap to test the difference that change in rolling circumference makes- just fit a bigger tyre to your 26 inch wheels and discover the difference is 1.7 metric bawhairs. Course, you can also fit big tyres to a 650b rim but it helps focus the mind to find what the basic difference is, and then think about the cost of changing.

The Rookie

So say you ride with 2.1" tyres on your XC bike, to replicate a 650B would require 2.6" tyres, but I do think that extra width would have other effects that may just influence a straight decision as to which to buy?

bennett_346

I was thinking that, surely bigger tyres have many more effects on ride handling and rolling resistance that a simple larger rim wouldn't experience.

ddraver

I think you re both agreeing with each other....

I agree also that one shouldnt sell a bike to buy one with a different wheel size (maybe unless you re a very keen racer) but when one comes around to new bike time, then these things are worth really considering!

bennett_346

I'm disagreeing with Northwind but agreeing with Beginner..

ddraver

yes....I think

Northwind

You're actually not disagreeing with me either- I was talking about the rolling circumference, which is what the marketing people want us to think makes the biggest difference due to changed angle of collision, lengthened contact patch etc. Goes without saying there are other differences, not all of which will be good, but you can test this "important" difference and discover how little difference it is.

I heard a chap talking about how he was going to fit 650b wheels to his old bike and get "most of the benefit of a 29er" but was going to avoid the ill effects by using skinny tyres. Congratulations sir, you've invented the 26 inch wheel.

bennett_346

But part of the marketers reasons to change to 650b is the better rolling capability generated from the larger diameter, but on a lot of surfaces a bigger tyre will increase the rolling resistance, so how could you tell?

As i do mostly smooth surfaced trails and super long distance rides these days, fat tyres absolutely kill your energy after a few hours so i have 2.1s fitted. Fitting 2.6 inch tyres would kill any benefit of the increased diameter straight away surely.

Northwind

It's not just rolling resistance, it's how the tyre meets obstacles. A bigger wheel isn't automatically faster on a reasonably smooth surface, nor is a fat tyre automatically slower - a fast, fat tyre can be faster rolling than a thin, slower tyre (partly because narrower tyres tend to need to be stickier or knobblier to generate the same amount of grip from less contact patch).

My real world example is going from a 1.8 mud tyre to a 2.4 Nobby Nic- the Nic's a faster tyre anyway so I'm not losing a big-tyre advantage to extra drag.

bennett_346

I still don't really understand what you mean, a different tyre is a different tyre and there's many more variables it changes that you wouldn't experience with a larger rim and same size tyre which would "pollute" the test. It just wouldn't be controlled enough to understand the change in feel imo.

eg. bigger volume tyres feel significantly different in corners not just because of their increased height but also the grip, the squashy feel, the elastic rebound etc and how would you know that it was the larger diameter that changed the cornering handling, not the other variables?

Northwind

The big difference that people keep banging on about is how the rolling circumference effects rollover, and that's what I'm talking about here. Very easy to compare- yes the 2 tyres will act differently, but that's no different to any 2 tyres regardless of wheel size, and so isnt an argument for or against a wheel size. But that feeling of how it reacts when hitting a square edge or a wheeltrap, which is supposed to be where 650b is better, that's down to size.

And frankly if that change is so small that you can lose it in the background of a tyre change, why is it interesting at all?

bennett_346

Once again i'm sorry but i disagree. Like for like a larger volume tyre will still react differently hitting a square edged bump than a larger wheel and same volume tyre would, so how would you tell if it was the tyre or circumference that gave the desired (or undesired) feel?

If you're testing one variable, the rest must be the same on both tests, this is basic science.

What if someone new to riding with a 26 inch wheeled bike decided to do this test so fitted a larger volume tyre and did the square edge test, found that it was more "absorbent" of the impact and held its speed better and decided it was entirely down to the increase in circumference without taking into account the effects of larger volume on square edges?

To me that is like saying you can test a slacker head angle by fitting longer travel forks - yes, you can and the head angle would be slacker, but you also have the effects of increased travel which would dissolve the difference between two different head angles.

Northwind

bennett_346 wrote:

What if someone new to riding with a 26 inch wheeled bike decided to do this test so fitted a larger volume tyre and did the square edge test, found that it was more "absorbent" of the impact and held its speed better and decided it was entirely down to the increase in circumference without taking into account the effects of larger volume on square edges?

If you can't distinguish the two, it's because the difference is too small to be interesting. Any perceptive rider knows the difference tyre pressure/squish makes, and can draw conclusions accordingly. Anyone who can't distinguish between a hard or soft tyre probably doesn't need to worry much about wheel size either!

If you like, you could fanny around with tyre pressures til the bump resistance is comparable, simple enough. But if you're going to discount any opinion or test that isn't done with only 1 variable changing, it becomes impossible to compare anything between the two, there will always be other differences- so no matter what there's a compromise there.

bennett_346

I still disagree that it's a worthwhile test in any way. And i would disagree with anyone that suggested there was any accurate way of testing the two against each other because as you say the difference is too small to really be noticed.

29ers are a big enough step up that you could tell which characteristics came from the bigger wheel but 650b? Nope. I don't think there's such a test that you could get any meaningful comparison from.

Northwind

Ah, I getcha. Yeah, looking back, I didn't explain that well in the original post- I don't think you can tell exactly what the difference is- but I think you can tell that it's not big enough to be fussed about. More about bracketing than exact measurement, if you like.

bennett_346

Yeah i thought you were saying it was a way of seeing if a 650b bike would be for you, but since you mean it shows that the characteristics are so indifferent it would show how little you'd notice, yes, i agree with that.

thelonegroover

The actual rim diameters:
26er - 22"
650b - 23"
700c/29er - 24.5"

So, there is a significant difference and the 650b is only within 0.25" of mid point.

Northwind

This is a nice illustration- 2.1 tyres on each

http://brimages.bikeboardmedia.netdna-cdn.com/wp-content/uploads/2012/06/650B-wheel-size-comparison-with-tires05-600x376.jpg

bails87

Northwind wrote:

This is a nice illustration- 2.1 tyres on each

The Rookie

So how come I can see a second rim behind the 26er almost dpwn to the tyre if the tyres are the same size? Doesn't quite make sense!

Chunkers1980

You don't. The rim you seem is behind the 650

thelonegroover

The Beginner wrote:

So how come I can see a second rim behind the 26er almost dpwn to the tyre if the tyres are the same size? Doesn't quite make sense!

Not quite sure what you're referring to here.
The tyres may have the same width (2.1) but the rims and tyre diameter aren't the same size. A 26er rim is 22", a 650b rim is 23".

chez_m356

Chunkers1980 wrote:

You don't. The rim you seem is behind the 650

no it's the 650b, unless the 29er has two presta valves, full size pic here http://www.eqip.co/img/blog/22.jpg

the 650b tyre must have a mahoosive tyre wall on it if that pics right

ddraver

Is nt it far easier to look at the left hand picture? Why are you all so focussed on the right?!?!? Could it maybe be a bit of confirmation bias?

Chunkers1980

I see now. I was looking at the top. Does look odd. Should all be about the same at the bottom.

thelonegroover

bails87 wrote:

Northwind wrote:

This is a nice illustration- 2.1 tyres on each

I think this picture just confuses things. A 2.1 tyre should be the same width on a 26er, 650b or 29er. The bottom of the wheels should all be the same. The axle of the 650b should be 1/2" higher than the 26er. The axle of the 29er should be 1.25" higher than the 26er. Unless the tyres are different.

chez_m356

ddraver wrote:

Is nt it far easier to look at the left hand picture? Why are you all so focussed on the right?!?!? Could it maybe be a bit of confirmation bias?

because if the right hand pic is correct and both those pics are of the same wheels, then it suggests to me at least that the size of your tyre wall makes more difference than the rim size

i am of course talking complete b*ll*cks about something that i have no knowledge of

The Rookie

Thelonegroover wrote:

Not quite sure what you're referring to here.
The tyres may have the same width (2.1) but the rims and tyre diameter aren't the same size. A 26er rim is 22", a 650b rim is 23".

If the tyres are the same width and height, the bottom edge of the rims should all be in the same place, not one about 1/2" higher - obvious innit!

thelonegroover

Yes, completely agree, thats why this picture is confusing. Unless he's taken it from level with the top, in effect looking down at the bottom of the wheel, that would have the same effect.

supersonic

There are distance effects in the picture, and the tyres don't look to be the same model.