Stability, durability of 2-wall tents

I'll wade into this discussion as a former Carbon Reflex 2 owner and discuss some of the key differences. I suggest you sign up to be a BPL member, because BPL has really good reviews of both of these tents that alone are worth the price of a membership ($25).

The 'trail weights' (inner tent, fly, poles and minimum number of stakes needed) for these two tents as measured by BPL are:

Scarp 2: 3lbs 4oz
Carbon Reflex 2: 2lbs, 15.8oz

Floor
I personally prefer the PU coated MSR floor which uses thicker nylon. The silnylon fabric used in the Scarp 2 is very slippery and in my opinion it's not waterproof or durable enough to be used without a groundsheet. Others will disagree. For me the MSR floor winds up lighter because I wouldn't take a groundsheet like I would with the Scarp 2. Even if you do take a groundsheet with the Scarp 2 you'll still have a slippery floor that you'll either have to live with, or address by adding silicone (weight) to the floor.

Floor Area
Floor area is one of the biggest weaknesses of the CR2. The floor is not 50" wide like MSR claims. In reality is more like 40-42" wide, so it's just wide enough for two pads. The Scarp 2 is a lot wider, with an honest floor width of 50-52". This means you'll have extra floor width for stowing stuff beside you, or for using a sleeping pad wider than the 20" standard size. I've used the CR2 and the floor area is fine, but if you like your personal space or like to have a lot of gear in the tent with you then it's not so great.

Interior Space
Despite having a small floor, the CR2 has really good interior volume. The tent feels big inside and you can sit up pretty much anywhere in the tent. This is because the walls of the tent are pretty much vertical, rather than sloping inwards. Also the main pole runs from head to foot to keep the the roof high the whole way. The Scarp 2 is also roomy as you would expect, but the roof is a bit lower near the ends of the tent because the main pole runs across the waist of the tent instead of head to foot. Both tents have enough interior volume to make them a livable tent for two, unlike some other really light two person tents (ie. Big Agnes Fly Creek 2) where the walls slope in so much that only one person can sit up at a time.

Other Considerations
It's not a huge deal, but access to the back vestibule of the CR2 is difficult because there is just a vertical zip rather than an L shaped zipper. You can't really pass stuff bigger than a pair of shoes through the slit opening. Anything small enough to pass through the opening is probably small enough just to leave in the tent with you. If you want to put big stuff in there you need to do it externally by lifting up the fly.

Summary
The narrow floor width, single door and difficult rear vestibule access are the main downsides to the CR2. The main downsides to the Scarp 2 is the silnylon floor, heavier weight and lack of pockets inside.

Competitors:
There are a few other tents you might want to consider:

1) The MSR Hubba Hubba HP is about .7 lbs heavier than the CR2 but it's cheaper, freestanding, the floor is an honest 50" wide so it's a really spacious tent and it gets you two doors and a fabric inner tent (warmer).

2) REI Quarterdome T2. It's 0.75lbs heavier than the CR2 and half a pound heavier than the Scarp 2 but it's freestanding which is nice when you camp on sand, snow or rock. That also makes it easier to shake out the dirt from inside. It's also cheap ($275 retail). I just bought a new one on eBay for $152. It's really spacious like the Hubba Hubba HP.

3) Big Agnes Copper Spur UL2. It's around 3.5lbs so it's a little lighter than the two tents above, but the floor is a bit smaller.

4) Mountain Hardware Skyledge 2.1. Nothing really stands out about this tent but if you can find a good deal it would be a nice way to go. The walls do slope in a lot which reduces interior volume but the floor is nicely sized, it's freestanding and about 3.6lbs.

5) Six Moon Designs Haven. This tent uses trekking poles so it's really light (2.25 lbs plus stakes). There is likely to be an even lighter open in the future if you opt for the more expensive cuben fly which will probably save 1/2 lbs. This is a very nice shelter, but since it uses trekking poles the roof is really only high in one place and then the rest of the tent slopes pretty low, so interior volume doesn't seem that generous judging from the pictures. This is your lightest double wall tent option and you're going to need to go all the way to 3 lbs to get a more roomy shelter. The only other double wall near this weight is the Big Anges Fly Creek 2 which as previously mentioned is really only good for one person since the interior volume is so low that two people can't sit up at once.

"One problem is that I don't understand how to compare the floor durability."

Poly coated ripstop is usually more durable than the silnylon you see in ultralight shelters.

I personally go for the lighter silnylon and just be more careful. I don't want the extra weight in my backpack.
Floors are easy to repair and if you are careful about how you pitch you shouldn't get holes. If you do, it doesn't matter if you pitched correctly.

Those replies were really helpful!

Dan, thanks especially for giving the CR2 a fair shake!

Just wanted to note that your other suggestions seem to be heavier than you list..

For eg, the Hubba Hubba has a packed weight of 4 lbs 11 oz and a min weight of 4 lbs 3 oz.. both those figures exceed the CR2 by more than 1 lb 3 ozs!! The other tents are heavy as well.. the REI Quarter dome is 3 lbs. 15 oz (min weight).

Anyway, I guess I have to decide if the extra space is worth it.. or maybe just carry them all :)

I suggested the Hubba Hubba HP, not the regular Hubba Hubba which indeed is over 4 lbs. The HP version is significantly lighter than the regular Hubba Hubba due to lighter fabrics.

The REI Quarterdome is spec'd at 3lbs 12oz. BPL verified this weight in a recent test. I'm not sure where you read 3lbs 15oz.

My ground cloth is a gossamer 1.5 mil piece of very light plastic that extends only 2/3 of the way in from the door, where the most "traffic" is. It protects the floor of my Moment enough to 1.keep it clean & 2.avoid most abrasion.

As for the slipperier silnylon floor I merely put small dots of Ge Silicon II in full width X patterns accross the bottom of my Thermarest pad from top to bottom. Works fine.

Yeah GE Silicone II is good stuff. I used it when I did Jim Woods silnylon floor treatment on my Refuge X. I like your idea to treat the thermarest rather than the floor, because silicone on the floor makes it hard to clean dirt out of the tent since it's so grippy.

There are some good options out there to deal with the slipperyness, durability and borderline waterproof traits of 30D silnylon. The thing is, if you decide to deal with these then you haven't saved weight over 70D PU coated nylon.

For example, a two person tent floor (ie. 84" x 50") is roughly 4 square yards in area and PU coated 70D nylon is about 0.8-1oz/yd heavier than 30D silnylon. So if you went with 30D silnylon you would save about 3.2 to 4oz initially. However, the lightest possible groundsheets for a floor of this size is 2-3oz and then if you add another 0.5 – 1 oz of silicone you wind up pretty much even and you also still have a floor that is slippery on the bottom side so it tends to slip around on the groundsheet a bit.

So if you are going to use a groundsheet, the total weight winds up about the same and it depends whether you'd prefer the simplicity and nice grip of a PU coated 70D floor, or the ability to let your groundsheet take the wear with the 30D floor and you have the option to leave it at home on nicer trips where you expect non-harsh camping surfaces.

There are trade-offs either way though, so it does depend on your intended conditions as to which floor is better. You could use a 30D silnylon floor without a footprint in nice conditions if you are careful with your site preparation. You also have the advantage when using a groundsheet that you can replace the groundsheet easily and cheaply.