Micro-Rack Vs. Full size. U-Frame Vs. J-frame

[bronzzhorse]

We are planning some large drops (Maybe Neversink, Stevens Gap, and some others in OUR area) for the winter season, and I would like some of You folk's opinions on racks.
First off.... I only weigh about 140 soaking wet, and even with a Micro Rack, its still all I can do to counter the rope drag (weight of the rope below me) on a mere 20 foot drop. If i engage just ONE hyperbar, I litterally CAN NOT move on the rope.... even if I just Flip the rope OVER the Hyper-bar,,, I dont even have to fully engage it and apply pressure.
Considering my weight, and my personal experience with a Hyper-bared Micro Rack, I feel like I would be plenty safe using it on something in the size range of neversink.
What would YOU say is the MAXIMUM safe height for a Micro Rack for someone of my size??? Is there one???? The higher you are, the more rope drag you get, so it seems logical that the HIGHER you get the safer your rack is (theoreticaly, of course).

What about someone Heavier than me? Does weight of the person really matter when it comes to choosing the right rack for the drop???
Now as for U-frame Vs J-frame...
Through reading regulations for Bridge day, it came to my attention that there is an obvious safety concern around U-frames. Is this because of the CHANCE that the Nuts may come loose or strip, resulting in a catastrophic release of ALL the bars? I understand if THAT is the concern, but is there another reason?
Is there any difference in them ASSIDE from the Shape direction?
I havent got a rack yet (yes im still in the dark ages, using a CMI rescue rack), but plan on getting one VERY soon. I have Used one SEVERAL times, but t was borrowed. I was using a Micro Rack, U-frame, with 2 hyperbars (though i never could use but one of them), and i positively LOVED it. I would LIKE to just buy one like I was using and feel confidednt that it will meet all my needs, but I want to get some opinions (from some people who's opinions I value) before I make the investment.
CHEERS!!!
Josh

[NZcaver]

Josh, were you using the short frame or long frame micro rack?

It does make a difference. The longer frame would definitely be better for you because it allows you to spread the bars, thereby decreasing friction and increasing your descent speed. I would think a micro would be just fine for doing the drops you mentioned.

[Chads93GT]

I have friends i cave with every weekend who weigh what you do and they use 4-5 bars with a long rack. If you can't move its becuase you haven't learned to spread the bars. They have no problems moving as fast as they want.

[cavedoc]

The higher you are, the more rope drag you get, so it seems logical that the HIGHER you get the safer your rack is (theoreticaly, of course).

While this sounds good I don't think it's so. The more drag you have, the more you may need to feed rope into your micro-rack. This can be dangerous. I haven't figured out how to post a link to the previous discusson of this but I encourage you to search for it. The lighter you are the more likely that this will become an issue. As has been noted, you want to be able to spread bars to decrease friction when starting a long drop then put them closer and add bars as you get closer to the bottom where friction/rope weight will be less. This is a lot easier on a standard rack. Don't get me wrong, I love my micro-rack, but I have 70 pounds on you so mine slides a little easier. If I were going to do more than about 150' (rare in these parts) I would probably haul out my long rack.

[bronzzhorse]

I know how to spread the bars and it does help, but only a little....I know for sure it was the Long rack, i had to spread the bars as far apart as they would go, and still was having to "feed" the rack. of course, that was with some SUPER stiff 11mm PMI Pit rope
I was talkin to a friend today that said you have to "tune" the rack out of the box... the one i was using was BONE stock.. straight out of the box.... could that have something to do with it?
After some of these comments, i believe i am going to go ahead and get the long micro-rack, and possibly only get ONE hyperbar instead of 2.
Cheers and thanks!!
Josh

[chh]

Yep, I would think a micro rack would serve you well on any of the pits you mentioned or any around that depth.
I may be in the minority here, but I don't really think a person's weight has all that much to do with the type of device used, though I think lighter folks have it worse than heavier folks. It's more about comfortably dealing with rope weight that changes my mind as to what device I personally reach for. But it has to get around 400 feet or so to change. Sometimes less if it's just an entrance drop or if it's really sandy or muddy.
I think most of the time it's just what people find user friendly.

Have you ever tried a rack with spacers? Perhaps this is what your friend was referring to when he said "tuning". I think bobbins can be good devices for smaller/lighter people as well. That's what I use, as does my girlfriend who weighs in at a whopping 98 pounds.

[Chads93GT]

Tuning the rack has more to do with getting the bars to fit the rack and slide freely. Involves filing metal, if your rack works, it needs no tuning.

[Scott McCrea]

The main benefit of the 2nd hyperbar on a micro rack is for ease of tying off. You might need to use it if you are rappelling on 8mm or some thing very flexible.

The ideal descender depends on many, many factors. Length of drop, diameter of rope, stiffness of rope, cleanliness of rope, access to the drop, type of trip, goals of the group, etc, etc. You should really have one of each.

U-frames are not allowed at Bridge Day because you can't drop and add bars. Well, you can but only two at a time. That's too much friction to lose in one step.

Nuts coming off is possible but highly unlikely, especially if you check your gear. The chances of both nuts coming off is silly. Actually, threaded rod and a nut is very strong. Probably stronger than the weld on a J rack. Check the breaking strength of the two.

A standard length SMC J rack with stainless U-shaped bars can do any rappel in the world and beyond. It might be overkill for some drops, but it will work. Determine your need for a straight eye or a 90 degree twist eye by the harness that you use and how you attach your rack. If you have a common caving harness with a main attachment point of a half-round screw link that is flat against your belly and you attach the rack with a biner, you should get a twisted-eye rack.

Micro racks are great but they are an advanced device, for cavers that have fully learned the ways of the rack. There is less margin for error with a micro. Here's the discussion about feeding micro racks. Another informative thread about micro racks.

[bronzzhorse]

Thanks for the info scott..... VERY informative reply.... i just got some "learnin"...lol!!!!!!!

[Cody JW]

I weigh 220 and have a transitional rack ( 4 bar with hyper bar and opens like a regular rack) from On Rope 1 that they no longer sell and it will drop me like a rock if I do not use the hyper bar.Sometimes if you are not careful going over a lip and the rope is stiff the rope can slip off the hyper bar so I only use it with easy lips that are not undercut.

[Cavernuke]

In addition to my big CMI 6-bar J-Rack, I use a long-frame, dual hyper BMS Micro-Rack. Because Wisconsin lacks really deep pits, most of my vertical work is done with the micro. The longest drop I've done with the micro is only 80 feet (since I have the Big Rack, I use it on longer drops) but I think with care it should be good for 200 feet. I have rappelled on very stiff ropes where I have had to feed the Micro (dangerous); in such conditions, a 6-bar J-Rack allows you to remove bars and spread them to allow descent.

If someone is buying a Micro-Rack, I would suggest the BMS long dual-hyper model because:
1. Stainless bars don't mark ropes and have long wear life;
2. The long frame allows bars to be spread further, giving better control for different conditions;
3. having two hypers and two slotted bars allows you to swap bar positions when the top bars wear, like rotating your tires... much cheaper than buying a new rack!

Nuke

[Dwight Livingston]

...I know for sure it was the Long rack, i had to spread the bars as far apart as they would go, and still was having to "feed" the rack. of course, that was with some SUPER stiff 11mm PMI Pit rope.
I was talkin to a friend today that said you have to "tune" the rack out of the box... the one i was using was BONE stock.. straight out of the box.... could that have something to do with it?
After some of these comments, i believe i am going to go ahead and get the long micro-rack, and possibly only get ONE hyperbar instead of 2.
Cheers and thanks!!
Josh

I have a long microrack. I used a short at first, and found it took too much feeding. The long has worked well.

I attach my rack via a quicklink, and you might try this to reduce friction. Mounted on a quicklink, instead of directly to the D ring, the tail of the rope can feed directly onto the bottom bar, without contacting the rack frame. To do this, you let the rope hang between your legs instead of around your hip. I find this drops a lot of friction. It also makes it easier to adjust the bars. When you need more drag, you can move the rope over to your hip. Give this a try and see what you think.

Dwight

[NZcaver]

I attach my rack via a quicklink, and you might try this to reduce friction. Mounted on a quicklink, instead of directly to the D ring, the tail of the rope can feed directly onto the bottom bar, without contacting the rack frame. To do this, you let the rope hang between your legs instead of around your hip. I find this drops a lot of friction. It also makes it easier to adjust the bars. When you need more drag, you can move the rope over to your hip. Give this a try and see what you think.

I also have a longer micro rack, and find it nicer to use than the short frame. I use an oval maillon rapide screw link to attach to my central D ring too. I found the default setup for micro racks is 'backwards' from the traditional U-frame racks I started using 20 years ago. Those rack always had bars which swing upwards (towards your face/chest) to open, not downwards. Luckily it's a simple matter to take the micro apart and reassemble it the other way. This seems to keep the rope path more linear, avoids the rope curling over the rack frame as it enters at the bottom, and allows the user to adjust friction more effectively.

[Cody JW]

I am going to get the slightly longer rack frame for my standard rack because I feel if you use all six bars on a standard rack you do not really have enough room to move the lower bars so it will adjust the friction much without having to drop a bar.I think for a long drop like Ellisons, Bridge day or Golondrinas it would make a big difference.Any body have one and if so what do you think?

[Dangerjudy]

I use a long micro-rack for shorter drops in cave and I love it. BUT for anything taller than Neversink I would use my 18" 6 bar rack. In fact for Neversink I would use it too. I get so much more control from the long rack... and I think if you are lighter you want more area to spread the bars not less...

anyway I have an SMC 18" rack with a BMS hyperbar, a BMS grooved bar on top, and BMS Tubular slant bars below. It rocks.

One more thing - Tiny and Nikky have trained me on the use of the French Wrap and I don't get on rope without it now - no reason not to!