Is there a "rule of thumb" for how fast new technology "trickles down" from higher-end to lower-end bike models? Can you for example say that a mid-end bicycle frame or suspension fork is as good as the previous high-end, or does it usually take more than one generation for the technology to spread?
They say that this year's Tiagra is generally last year's 105, which is true to an extent. You'll see things like 10 speed cassettes move down the product line at a rate of one series per year or so.
It's not entirely true though. Features creep down, but quality stays about the same. The different series will maintain their relative build qualities year after year. I.e. a higher priced series will have better materials used throughout.
Having said that, I don't believe that build quality is really a deciding factor in most groups. I've put 20000km into a Sora group that is still running just fine. You just need to keep up the proper maintenance.
My knowledge is mainly about downhill mountain bikes. Firstly I don't think the technology has really gone very far at all. Secondly you need to buy the top, or middle model bike for the good components, that's always been the case.
Most downhill mountain bikes still do not have a gearbox inside the frame. The price for this bike of gear box bike has not gone down one bit.
There are still plenty of single pivot frame designs around.
A lot of bikes come with DT swiss cheese wheels, which are notorious for bending.
Forks like Fox and Rockshox still require a lot of maintenance (oil seals). The suspension will have fewer adjustments. If you buy the bottom model the suspension will probably be rubbish. Marzochi still have ridiculously bad dampers on their low end forks.
Can you for example say that a mid-end bicycle frame or suspension fork is as good as the previous high-end
No, it doesn't work this way at all. There is no moore's law like computer hardware. Just like cars, the bikes will sometimes improve when a company ditches their old frame design and releases a new model of bikes. The suspension companies are always going to reserve their best technology for their premium model products. That technology hasn't really improved much so there is not much trickling down going on. Usually they just fix flaws in their previous products.
Avid now make brakes that have problems with air bubbles. Their old brakes were perfectly fine. Still, at least we have moved on from Hayes, that is definitely an example of technology trickling down.
Shimano now make disk brakes with a crappy sline attachment. Hope ditched their spline design years ago.
If anything the technology is going backwards in some ways.
The new price has come down slightly. But the second hand market is a lot better now since there are plenty of bikes around. This wasn't always the case when these downhill bikes were a new technology. I always get a top end bike, but I never buy it brand new. It has to be a few years used or