24 inch Vs. 26 inch

[pdc]

I've got a lightly used 26" Profile Yuni I'm considering selling.

[johnfoss]

Originally Posted by johnhimsworth

I'm always curious about this idea that a 24x3 is the same diameter as a 26, and a 26x3 is the same as a 29. Maybe if the tyres are hugely different in size, but for something like this they won't be.

Maybe, maybe not. The problem here is, people toss around tire sizes as if they are exact. They're not. My 26" MUni has almost the exact same tire diameter as my 24" MUni. It very much depends on the tire. So if one doesn't include the tire width in one's description or question, it's hard to answer.

All things otherwise being equal? Bigger is faster, but also heavier. And also a little weaker/prone to tacoing. I like faster, but the rim on my 29" is a little too skinny for the tires I've been running on it, so I've run into a couple of very inconvenient tire failures far from the car. By contrast, my 24" (with 3" Gazz) is nearly indestructable, and I never have to worry about the same problem. But it's slower.

A 26" Gazz on a strong rim is really heavy, but probably very strong. Rotational weight is always the least desirable kind, but if speed is more important, go bigger.

[rob.northcott]

Originally Posted by johnfoss

A 26" Gazz on a strong rim is really heavy, but probably very strong.

People keep coming up with that one. Surely a 26" wheel and tyre is only 8% heavier than a 24" with the same type of tyre. And that's ignoring the weight of the hub and cranks, which is constant whatever size rim you use - which gives an entire 26" wheelset actually a slightly better weight/speed ratio than a 24" (I know this is over-simplifying things for real-world performance, but I'm just making a point).

You can't have it both ways:
"It's only slightly quicker"
but "It's really heavy"

Unless the 26x3" downhill tyres are a thicker heavier construction than the 24" ones - I suppose that could be true.

Rob

[U-Turn]

The 26x2.6 and 24x3 Gazz tires are the same weight (manufacturer's numbers). Presumably this implies that the tires are also close to the same volume. I don't have the diameter measurements handy at the moment.

[joemarshall]

Originally Posted by johnhimsworth

I'm always curious about this idea that a 24x3 is the same diameter as a 26, and a 26x3 is the same as a 29. Maybe if the tyres are hugely different in size, but for something like this they won't be. a skinny tyre on a 26 might be the same as a 24x3, but that isn't really relevant - the question here is a big fat 24" tyre or a big fat 26" tyre. Even where the 26" tyre is smaller, there is a difference. The 24x2.6 wheel on my muni is noticeably smaller than the 26x2.1 wheels on my bike, so I'm always curious about everyone saying they're the same.

Like John says, my 26x2.6" is just under 2" wider in diameter than John's 24"x3". My 29x2.1" is over 2" wider in diameter than the 26x2.6". Even the 26"x3" is nowhere near as large a diameter as the 29er tyres people are running. All this talk of them being the same is weirdy stuff.

Joe

[U-Turn]

Tire volume and outer diameter are different things. I have to take some measurements to do the math for the volume of an approximately torical space for the two setups.

[Mikefule]

Originally Posted by rob.northcott

You can't have it both ways:
"It's only slightly quicker"
but "It's really heavy"

Various applications of the words "quicker" and "heavier".

Quicker as in higher speed, or quicker as in more responsive - responding faster to rider input.

Heavier as in more dead weight, or heavier in the sense of more rotational inertia.

The 26 tyre will be around 8% heavier in dead weight terms (all other things being equal). The rim will also be about 8% heavier.

But the weight of the tyre is about 8% further from the centre of the hub. Put crudely, that makes the rotatinal inertia about 1.08 x 1.08 = 1.16 as much which is alomost a sixth as much again.

So the bigger wheel accelerates more sluggishly, and brakes less eagerly. That's why Cokeurs (and Cokeuses) find that a lighter inner tube alone is enough to make a significant difference: the weight and the radius are both factors.

On the flat at constant speed, the effect of the bigger wheel (26 rather than 24) will be to make the speed only 8% higher at a given rpm. On a ride where there is a lot of acceleration and deceleration (including climbing and descending under control) the effect will be more noticeable.

[rob.northcott]

That all makes sense Mike. Fair enough. I said I was over-simplifying things

But more rotational inertia should make the ride smoother and therefore easier to maintain high rpm...

OK, I'll give up now. I like my 26 anyway

Rob

[Mikefule]

Originally Posted by rob.northcott

But more rotational inertia should make the ride smoother and therefore easier to maintain high rpm...

That is perfectly true at a steady speed on flat or only slightly uneven ground. That's why the bog standard Coker is so easy to ride, but the Road Razor requires concentration.

(Road Razor: the skinny 700c)