Wheel sizes ?

kary wrote:

Was riding my street bike this afternoon and thought about that. Why do the motocross bikes don't follow the "the bigger your wheels are, the faster...

Was riding my street bike this afternoon and thought about that.

Why do the motocross bikes don't follow the "the bigger your wheels are, the faster you'll be" rule that performs in the MTB world for years now ?
They went from 26" to 27.5" and now to 29" and everybody seems to love these bigger wheels ? (Actually I don't ride or own a MT .
Technically it's not a big deal to run bigger wheels on a MX bike (22" front and 20" rear maybe ?) and it would allow to absorb more bumps.

I don't say that it's a good idea or anything else, was just wondering why it never went this way ? Maybe it was tried back in the day (Maybe HRC ? As they ran 20" front and 18" rear, that's a proof that they tried different things).
To be honest, I only see 2 bad points right now : these big wheels look odd on a MTB and the wheels are weaker due to their size.

Do some of you have inputs ?

Falcon wrote:

They experimented with wheel sizes for a long time in the '70s, I think. Eventually, the rolling diameter became a standard and it is part of...

They experimented with wheel sizes for a long time in the '70s, I think. Eventually, the rolling diameter became a standard and it is part of the AMA rules (and probably FIM, as well.)

When we talk about 19" vs. 18" rear wheels, and 20" vs. 19" fronts from more recently, those are experiments with the tire profile; those changes don't alter the rolling diameter of the tire, only where the sidewall connects with the rim. (A 19" rear has less sidewall than an 18" rear, for instance.)

The current sizes are probably a good middle ground between strength, weight, and rolling ability. For my part, I'd like to see a bigger diameter just to see how it would feel.