UKC

I'm quite new to climbing and am looking for advice on how to improve my rudimentary understanding of solo top rope—   

1) Is anchoring to a tree with a figure 8 knot OK? If not, then why not?

2) What's the difference between a GriGri and a microtraxion?

3) I was thinking of getting a microtraxion, will this alone be adequete to ensure my safety if I fall? Have they ever been known to fail?

4) Do microtraxions do a good job of feeding the rope through as I climb or will I have to use other methods to do that?

That's all for now thanks.

Can I be the first to say, don't!

Get confident at climbing with a partner before you even consider rope solo. There are so many things that you won't even have thought of, and you do not want to be finding out the hard way.

Firstly, if you're new to climbing, roped solo probably isn't the best way to start. It's an option and I'm sure other people have done it, but you'd really be better off looking to meet up with some other climbers who can help you get started. Climbing Facebook groups for your local area could be useful, or the lifts and partners section on here. Not everyone will want to go out with a beginner but there are a lot of helpful people in climbing who enjoy sharing skills.

I realise that starting an answer by telling you that you're asking the wrong question is a bit of a cliché but I think it's warranted. Your questions give the impression that you're lacking quite a lot of foundational knowledge that would be necessary to rope solo safely. You might get some useful info here, and there are other resources online that go into detail on setups and options, but without some basic knowledge and experience of your own on anchor building, you're not going to realise if you're making mistakes that could have serious consequences.

Depends on the tree! But also, you'll be lucky to find very many climbs that have a good solid tree directly above them, so you'll need to know how to be flexible and use other options. On top of which, a single-point anchor is never going to be particularly stable, which increases the amount of back and forth movement of your rope on the edge, which isn't good.

Any device can fail in some circumstances. The textbook way to top-rope solo would be to have two different devices on two independent ropes. Plenty of people don't bother doubling up, but it is a compromise on safety.

Depends how big the tree is and how well it’s attached to the ground!

Most people would put along sling around the tree and fix to that being sure crabs weren’t three way loaded and knots weren’t being pulled apart.

The micro traction will self feed, the grigri needs a bit of string added to hold it in a position it’ll self feed.

I think most microtraxion users use them in pairs. One at belay loop level and one extended from the belay loop up to chest level with a sling around the shoulders to position it.

I’d not tried a microtraxion but they are pretty popular so I guess they feed well.

I use a DMM Buddy and Shunt on a separate rope.  The Buddy works well and doesn’t have teeth on the cam which I’m sure saves your rope. I recently started using a bit of shock cord and plastic crab to pull the crab the Buddy is on, up towards my chest. This takes some “slack” out of the system and gives a softer catch.

You've already received some good advice, so I will only answer these specific questions

No, a single microtraxion will not ensure your safety.

Yes, microtraxions have been known to "fail" in top rope solo applications (where the teeth are accidentally locked open, meaning they do not engage the rope).

Gosh, I didn’t catch that bit about being new to climbing!

I agree, the OP could well be caught out by stuff that’s second nature to experienced climbers.

First, plant the tree on the top of the Old Man of Hoy....

Troll.