Pot stiring question

So if 29er wheels roll so well, how come motocross motorcycles use 21 front and 18 or 19 rear wheel sizes???

smaller wheel= better acceleration/decceleration.

Just because bigger wheels roll better, doesn't mean it's better, you need a compromise,

The rear tire has a much taller sidewall, which makes its rolling radius similar to the wheel in front.

Also, motos have engines so rolling resistance isn't as important as it is on a pedal bike.

You're comparing apples and oranges, a valid comparison and ensuing discussion cannot be had.

oops .. I though the title was "pot smoking question " … better take my spliff advice somewhere else.

PS … moto bike wheels are sized to allow for proper sidewall height and overall centre of gravity (bike height) .. the geometry would be too funky if they were much larger. IMO

well, color my pot stirred. Damn oldfart, you really shake things up around here.

So if 29er wheels roll so well, how come motocross motorcycles use 21 front and 18 or 19 rear wheel sizes???

They have huge suspension, huge air-volume, huge rolling-weight, and huge power to help them roll over things. Think about it, the force of rolling over a 3" bump is negligible on a motocross bike, because you just suck it up and grab the gas.

You're comparing apples and oranges, a valid comparison and ensuing discussion cannot be had.

I think it's more like Granny Smith to Gala apples. Both two wheeled off road vehicles. The physics that govern balancing and riding, handling and suspension are the same but the scope and magnitude are different.

I think it's more like Granny Smith to Gala apples. Both two wheeled off road vehicles. The physics that govern balancing and riding, handling and suspension are the same but the scope and magnitude are different.

you forgot one major difference tho,

moto bikes have one rotating axis on the human body, compared to a bike which essentially has 3….

also, another good explanation of the smaller wheels could have something to do with torque… but hey, i dont get gass powered vehicles at all..

Oh I forgot, MX bikes also have really fucking slack head-angles, that helps.

smaller wheel= better acceleration/decceleration.

Just because bigger wheels roll better, doesn't mean it's better, you need a compromise,

I believe Trek offers the compromise you are thinking of, the 69er.

http://www.trekbikes.com/us/en/bikes/mountain_hardtail/69er/69er3x9/

So if 29er wheels roll so well, how come motocross motorcycles use 21 front and 18 or 19 rear wheel sizes???

I'd suspect Wayne P and Sideshow can answer that the best.

Though my suspicion about it has to to with leverage and torque. Especially sideways, meaning the larger the rim and the longer the spokes. Well that would create a longer lever that side force could exert with. And then adding the fact that MX bikes put out way more toque then a 29er powered by a human could.

Well, one would go through way more wheels.

Just imagine how huge a moto would be with 29" wheels. Now ask yourself if it looks rideable.

They would also break every 10 minutes. With the weight of a motorbike and the forces from ramming into stuff and casing big jumps, theres just too much flex..

So i guess 29" wheels arent used in moto becuase

-they are weaker
-heavier
-huge
-dont accelerate as well
-take longer to spin the front back up upon landing
-and 29" wheels still pretty much suck for mtb aswell.

A few years ago, the guy from BCD was praticing for a race at Mammoth, or bear…I forget which one. When the split times were compared, it was found that his 29" wheeled bike was making better times through the rock gardens and rougher sections than the rest of the pros.

Remember…..racing used to be done on 24" wheels and people chose them for the qualities that were improved on over 26" wheels: acceleration and strength.

29" wheels are here to stay. They offer a larger contact patch and smaller entry angle which are huge advantages over 26" wheels, and still remain in the realm of acceptable weight and strength.

I predict that the 29" trend will evolve to be used by riders who porportionally fit bigger wheels, not entirely replace 26". 26" is a great size for the average user, but one size doesn't fit everyone. Look at 650B wheel sizes. That trend is as weird as 29" wheels were about 8 years ago.

Hell…suspension was considered weird and sucky for biking.