First off all, I am not in any way trying to instigate any debate over which kind of descenders are the best.
I own a Petzl rack, have done for about a decade and am very happy with it.

I do however have a couple of question for other rack users:

* How often do people find they end up changing their rack bars? (I guess this culd be measured in time, trips, or metres!)
* When swapping, how do you decide the time is up?
* Are the bottom two bars indestructable? (In 10 years I've changed the top 3 bars 4-5 times, but don't recall ever changing the bottom 2)
* Are there any pro-tips for getting the bottom screw back in? (I always find that a horrible fiddly job and result to pliers and hammers!)

You'll also find rope diameter and rope muddiness affect how quick they wear out.

I tend to just do them when I start to get scared, or when they start to create a sharp edge. Not sure what Petzl recommend, but I haven?t died yet!

The top bars do most of the work, so wear much faster, so you can get a bit more life by swapping them around to even out the wear, or you can do what I did and make steel bars, which last a lot longer, but are heavier and the heat dissipation might not be so good?

Kev,

From the report I read, it sounded like it was way past the time V should have replaced her bars 

I've replaced my top 3 bars twice now. (in 8 years, but with two not very active years).
so I guess from your and my stats that's about 2-2.5 years for changing your bars (but I guess you may have changed yours more regularly when you were averaging 100 trips in 2010 ish- get number crunching your log book!).

I decided the last time that my time was up when I was sometimes having trouble descending the rope because the rope wasn't running smooth enough over the rack and I was stopping. but other times having a rather fast descent!

I changed out the 4th Bar this time, I think it might have become my 5th bar?

I hate putting the bottom screw back in, and like you resort to similar techniques and getting the screw in however it will go.

I remember being told the bars are fail-safe: they (apparently) bend and pinch the rope once they're thin enough, thereby slowing your descent and telling you it's time to change them I suspect I didn't read that in a Petzl manual.

You can trash a set of bars on a single trip if the rope is mucky. I managed to cut  3mm deep grooves in a set of aluminium bars on a very mucky  rope on a 45 foot pitch .  Nowadays I use bars made out of 316 stainless which are much more wear resistant albeit somewhat faster than aluminium.

Years ago when using fig-8 descenders, I seem to recall someone asking the manufacturers how much wear they'd take.
The answer was that they were ok until worn down to one-third the original diameter!

I assume racks would be similar - I've had a Caving Supplies rack I bought on eBay for around 7 years.  I've never replaced any bars (you can't get them) but just swapped them round from time to time.  It's still got a few trips in it yet, I reckon.

Tamarole - that must have been a very mucky rope, or you had some very soft bars!

JasonC said:

Years ago when using fig-8 descenders, I seem to recall someone asking the manufacturers how much wear they'd take.
The answer was that they were ok until worn down to one-third the original diameter!

I assume racks would be similar - I've had a Caving Supplies rack I bought on eBay for around 7 years.  I've never replaced any bars (you can't get them) but just swapped them round from time to time.  It's still got a few trips in it yet, I reckon.

Tamarole - that must have been a very mucky rope, or you had some very soft bars!

Click to expand...

It was a particularly grotty in situ rope contaminated with quartz fragments (we are talking mines here).

I change rack bars when they are half way or at worst two thirds worn through. Descents get pretty fast by the time the bars are this worn. All my caving and mining friends are aghast at how long I keep using them but I've never had a failure, nor experienced the rope pinching described up-thread. However I'm pretty light so my experience may not be the ideal guide.

If you can sight along the length of the rack and see an oval of daylight through the alternating / overlapping grooves worn in the bars, then it's time to change the bars.

Gritty ochreous mine ropes can easily put visible wear on bars in a single trip.