Why is this?

[c-m]

Can anyone tell me why sports bikes tend to have the front axle go through the fork legs, but bikes that have spoked wheels, particularly dual sport type machines, tend to have an extra bit welded on to the forks for the axle?

I can't imagine it's to do with rake or trail as that is usually set by the angle of the forks.

[bacon]

[pits]

weight, upside down forks, not being a cheap shitty commuter to name a few
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[Pete.]

Having the axle through the forks makes for quicker and more neutral steering. Having the axle through a block in front of the forks introduces a fork offset which causes the steering to want to centre more readily as the fork bottoms are essentially 'hanging' off the axle.
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132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Teflon-Mike]

It IS usually to reduce trail.

Common on dirt bikes due to 21" front wheel, and greater rake than a road bike.

If you draw line through axis of the head-stock, to where it interects the floor, that's the steering center. Now measure back from there to the center of the contact patch of the tyre. That distance is the trail.

More trail you have, the more the steering will try and self-center through castor effect.

Now, bigger the wheel, the further behind the steering center the contact patch is going to be. Think about it, all else equal, you have a 19" wheel, radius is 1" smaller than a 17" wheel, so the axle is going to be 1" further back, further from the steering center, ergo 1" more trail.

Now, rake the forks more, from the steep angles run on sports-bikes, steering center moves even further ahead of the contact patch, so more trail still.

Dirt bikes have big front wheels, and more rake, hence they use 'Leading Axle' forks to reduce trail and keep castor effects in check, without having to have such huge off-set in the fork yokes.

If you look at some scooters; they have 'trailing axle' forks, the wheel spindle on a boss behind the fork slider, for the exact same reason, the other way. Steep fork rake, coupled with diddy wheel, its needed to actually give the thing some trail and castor effect.

Adventure sports? Related to dirt bikes; tend to have larger front wheels. Use leading axle forks for same reason as dirt bikes.
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[Ste]

Mike, what about sports bike front axles; modern ones that you've got experience of riding?

[sickpup]

[MattJ]

[sickpup]

[Raffles]

[sickpup]

[kestrel]

[bacon]