I'm wondering about how often does SRAM or Shimano change their components. For example, is a Shimano Deore XT RD from 2006 the same as one from this year? How often do they usually do significant design changes?
Thanks

Typically, both companies will announce an upgrade within 2 weeks after you buy a new bike.



But that said, being on the absolute cutting edge isn't necessarily all that great. It is a lot easier to source parts for gruppos that are installed on 1000s of bikes that have already been sold by your LBS than it is to find a replacement for the latest and greatest gruppo that came out just last week. I'd think twice about buying two generations back unless I was getting a really good deal, but I'd never worry about waiting for a new release from shimano or sram before buying a bike. Either it shifts and rides nicely or it doesn't. That's all that really matters.

--sam

"How often do they usually do significant design changes?"

Don't worry, there have been no significant design changes since the 1920's. Maybe a few improvements due to new materials.

Seriously, with the exception of internally geared hubs, and maybe tires I really do not see anything that really has improved much since the late 80's. The stuff just weighs a bit less.

Major manufacturer component upgrades are mostly designed to enhance their profits. I ride a Fisher HooKooEKoo mtb and a custom road bike I constructed in the 1970's. I've upgraded saddles to appease my old bony butt and changed things like handle bars to fit my urge to be different, but the major components still work perfect. The only modern item I find interesting are new era V-brakes and disc brakes. Most of them are much more effecient particularly on mountain bikes and can be used with one finger as opposed to my old grab and pray brakes. A new set of brake pads every 15 years or so would probably help there.

I agree with most comments here.

The cosmetics will change nearly every year in some small way. Also, minor technological changes will crop up every couple of years.

The last significant change in technology was integrated shifters. Everything since then has been incremental at best.

However, with that said, a component from a few years ago may, or may not work if mixed into a current component set. At least it may not work as well as a modern component... due for example to things like chain width changes from 9 to 10 speed etc.

I just had a bike built with 105 components. If I had been able to find a new old stock 9 speed 105 group, I wouldn't have hesitated to build with it since 9 cogs is plenty fpr me (in fact, 7 or 8 would be fine).

So, if I were to find older stuff in a parts bin that is in new shape, I wouldn't hesitate to use it.

Here's one more vote for the notion that significant changes are so rare you can count them on your thumbs. I think the last one was the introduction of indexed shifting, and I'm not fully convinced even that was a big step forward. A couple of my bikes are still friction-shift, and I switch back and forth without even thinking about it.
I'll grant that I'm sort of a retro-grouch, but for the kind of riding I do, meaningful progress stopped at seven-speed cassettes. I do like seven more than five, but nine aren't any better than seven, which leads me to question why I need 10.

+1

Not if you're racing.