Curvy or Pointy

[northwind]

Originally Posted by SmudgeK3

why would they call it a rigid alloy frame if it wasnt rigid? and why would you want flex in a frame? shurely the point of the frame is to keep everything alined and held in place

Any modern bike frame's going to be rigid... (see also: Get the one you like the look of).

As for "why"... There's 3 reasons.

One is that a totally rigid frame transmits every bump. The SP-1's a great example of this- Honda spent a fortune making it the stiffest bike frame ever produced. Then when they started racing it, they ended up removing one of the engine bolts to restore some flex. The SP-2 swingarm was totally redesigned for the same reason.

Second, suspension effects- sometimes called tuned flex. Bounce a bike over a 5cm bump while vertical, and the forks (ideally) compress by 5cm then return. Lean the bike to 45 degrees and the forks now have to compress by 7cm to achieve the same vertical compression- but the force applied on the direction of travel is actually less. End result, forks have to move more but get pushed less, suspension doesn't move enough, bike moves instead.

So, add a third variable, lateral flex. Instead of having travel in only one direction, allowing the suspension to deflect horizontally introduces an additional suspension action, much like a leaf-spring.Like I mentioned, road racers are where you see this most- they place more demands on the suspension than any form of tarmac motorcycling, so this is where you see it most clearly- £2000 Harris swingarms built to have minimal vertical flex but huge lateral flex (by road bike standards), Guy Martin and his hacksaw...

Thirdly, think on impact resistance... A totally rigid structure doesn't dissipate impacts or changes in pressure well at all. It can be very strong, but it bears the full brunt of each impact or flex. A slightly flexible structure can spread any impact far more effectively. What's stronger, a cardboard box or a steel box? But which survives a drop from 100 metres better? What's stronger, concrete or rubber? But which survives a hammer blow unscathed?

Of course, it's all a matter of degrees. I suppose the easiest comparison is regular suspension. What's better, hard or soft? If you hit a speedbump at 100mph, soft. If you're braking from 100mph to avoid hitting that speedbump, hard. This is the same- sometimes totally stiff is what you want, sometimes a lot of flex is what you want, the hard part is hitting the balance.

Anyway. I get distracted Buy the one you like the look of.

is this the reason Ducati never use rigid frames then, i didnt think any frame would flex unless the suspention bottomed out, so the frame on the curvey has more flex i wonder why they took it out. thanks for all the info