Changed my carrying possibilities yesterday and thought I'ld share my first impressions.

Old Setup: performance transit bag
https://www.performancebike.com/shop/...tegory_ID=2312
transit epic dx
11.5x6.5x10==750ci

Advantages:
3 outside and one top compartment
decent carrying room

Disadvantages:
have to either use 4 velco straps or bungee net to fasten to rack
after 5 years, zippers start failing


New Setup: topeak bag
https://topeak.com/products/Bags/MTXTrunkBagDXP
dxp 14.1x9.8x8.5==1175ci

Advantages:
Monster main compartment
Even with winter gear, haven't had to use pannier function yet
very nice reflective strip
shoulder strap if loaded heavy
different size zipper knobs, so you know if you are opening or expanding the bag
nice carry on handle
outside dimensions are about the same as the performance bag, but better utilization of space

Unexpected advantage,
since bag slids into rack, you can open it and throw stuff inside, or rearrange without having the bag fall on the ground

Possible advantage,
again just one ride, but using seat post beam rack, 5 mile ride time dropped by 60 seconds. I think this will be constant, but will provide more information after I had had time and weather to complete a cycle of 15 commutes.

Only disadvantage was initial cost, but thanks to an REI $20 special, I decided to go ahead.

For those who saw other posts, yes I was considering a trek bag and rack. But local trek store is mtb store. "aero doesn't matter, you have to be going more than 20mph for it to matter." Goodbye trek. Hey I learned math. 10mph rider and 10mph headwind means aero does indeed have a significant effect.

Some have asked why I need so much capacity for a bike bag. It's because of the commute conditions here, especially in the spring and fall.

Mornings: cold, often windy.
Afternoon: warm, balmy, often dark

Morning bag load:
bike light
light battery
lunch
regular bike gloves

Evening load:
goretex pants
fleece/base layer
heavy winter gloves with gauntlet
windbreaker, about 1/2 of the time

The combo of pants,fleece and winter gloves eats a log of volume. With the previous bag I had to bungee something on the outside with the common, opps a sleeve is flapping or rubbing.

Anyway thanks for listening.

Very cool - I've been thinking about getting a bag like that. One questions for ya - when you have the panniers down do they attach to the bottom of the rack somehow or do they just flop freely in the wind?

What rack do you have it on? I have a pretty narrow rack but I'm not against getting something else.

Quick question.
Why not just spend 20-30$ more and get a pair of ortlieb (or other) bomb/water proof panniers? Storage capacity would be more than double. (if you needed it.....grocery run, laundry, etc...)

They have a adjustable elastic loop that hooks over the support leg extensions on the Topeak racks. The mounting is via the Topeak rack slide in channel so the bag is only truly compatible with Topeak racks unless some modifications are done to the bag to allow Velcro attachment.

A pair of backrollers is what, $100? I have the same Topeak bag and it was $30 and weighs MUCH less. Yeah I don't have the capacity for two fifty pound bags of dog food, but I don't have the weight and drag associated with that capacity either. I'd feel like a fool using a backroller to bring a change of clothes to work.

Firstly, thank you all for responding. I was beginning to think, why even bother if noone bothers to make a comment.

Another day's ride and another discovery: pants and base layer means need to unzip the expandable top section to avoid stress on zippers. Wasn't warm enough at 55 and 20 mph winds to drop the windbreaker yet. But I've heard warmer weather is coming in a month or so.

Crawdaddio
I didn't really want panniers because of their increased wind resistance. This is a fairly high wind area and every benefit helps. I did review the entire ortlieb line, but wasn't ready to take that step.

Kidpurple
Don't know, I haven't used the drop yet. I just picked up the bags with the drop just in case I needed more storage. There a group ride coming up the end of the summer, I wanted a little extra storage.

The side panels are semi rigid and when opened they drop down 90 degrees. Topeak does not recommend using the drop down on the beam seat post rack without side supports. I picked up the supports, they are very light and easy to install. I'll probably install this weekend just to see what that's like. I can't test as we have about 3 inches of snow coming tomorrow. I'll give a test on a clearer day sometime this next week and let you know.

I had an old rack that I replaced with the Topeak seat post beam rack. I really like it better. it comes with straps to hold down the flapping of the sides if desired. I'll have a review of the rack itself later on when I can find the time and clear weather to run some weight tests.


Lambot_vt
Topeak makes many similar bags. Look on amazon and you'll see this is a $75 to $80 bag. Rei has it priced at $100. I think the primary differences are: semi-rigid side, and big plastic clip to hook into the rack. The REI guy said this is the new model and it has improvements over the previous models.

HiYo, yeah that MTX / DXP is pretty sweet... my only drawback with it is that the panniers are too small (or my laptop is too large) to carry it in them. Otherwise, it's a sleek piece of kit.

Understood; but I've got the exact same bag. I forget where I got it but I paid $65 or so for the bag and matching Topeak rack. So ok, $30 was an exaggeration, but I still don't think this bag is in the same class as a pair of Ortliebs. I do like it though for what it is.

Here's an older pic of it mounted on my Buzz (which just got Big Apples and 1 out of 2 fenders today!):

Just to pass on what an REI reviewer mentioned. Inside the fold down there is an small bungle type cord that is adjustable. The sides of the rack have an inverted V that I could never figure out why this strange look. Duh, it's to bungee the open side to the rack so it doesn't flap around. Just an FYI.

lambo, ok it's the same bag. I heard there was some price creep on the topeak line. Looks very nice on your bike.

I also have the Topeak and love it. It is easy to access things or just slide off and take it with you. Another thing to consider is this type of rack that clamps to the seat post should not be used with carbon posts.

Steve

I've got this rack/bag combo too, and I am happy with it. I carry my work clothes, shoes, towel, small shower kit and some spare clothes (extra socks, gloves and whatnot) without filling the bag/panniers to capacity.

I'll also mention that Topeak sells a rain cover for a little over $10 that slips over the bag (and panniers too if you have them extended). Very handy for winter commuting here in the Pacific Northwet.

I prefer rack and pannier to rack and trunk bag. As others have noted, panniers offer much more capacity, and allow for shopping/errands. Some panniers (e.g., the Trek grocery models) even fold up when they're not filled so they're more aero.

But the main reason I don't use trunk bags is because they would block my DiNotte 140L tail light. I run both the tail light, and my DiNotte 600L head light, from a single battery that rides in a half water bottle on the seat tube. The 140L is always on (day or night), and mounting it further aft would be a hassle.

I use a rack trunk with my dinotte 140L taillight. It takes a bit of creativity but it works nicely. Plus, since I use the AA version I can stick the battery pack in my performance pannier. My other options are my panniers or a messenger bag. I pick and choose what one to use depending upon what I have to haul and the distance.
The topeak rack trunk looks nice but I do not like seatpost mounted racks. Is there any option for normal racks? I do not see anything.

I just found out that my new Ortlieb panniers (just received them today) won't fit on the back rack with the Topeak MTX trunk bag attached. Unfortunately when I slide the Topeak into the track the bag covers up the outside rails where the panniers attach.

I guess I'll only be using the Topeak for short trips with the family (drinks, and snacks for the wife and kid) and I'll use the panniers for commuting to work. This is actually fine with me; I can use the top of the rack with cargo netting and tie items down that way. This will actually give me more carry room than the MTX bag would. I like the MTX bag so I'm going to keep it.

Topeak makes a standard rack also.





Nice hook up lambo, my Hardrock just go a new set of Schwalbe Supremes last night. I need to take photos with the new tires and new Ortlieb bags (I also purchased a Ortlieb handlebar bag with the camera insert, nice bag).

It's no big deal; I was mistaken on the price anyway. I think it's a pretty decent bag and it serves my purposes well for riding to work. I've got a Wald front basket coming for grocery store trips.

Yeah, Topeak makes a standard rack. In the above photo of my Buzz it's wearing the disc-compatible version, and I have a standard one sitting around here somewhere just waiting for a bike to be installed on...

Thanks man. I just put on some Big Apples and I'm really loving them. I thought about handlebar bags but I ended up going this way instead. Just waiting for it to show up at the local REI store...

I'd like to hear how you like the Topeak bag after you've had it for a while. I've been using the Nashbar version of the Performance bag for about 2 years, and have been really happy with it. But there's always something better out there.....

Funny discovery on the ride home. I put my cateye td-1000 on the rack and turned it on today bacause of pending rain. I thought, well this was so nice it fit exactly right. Except, it's upside down. Hummm.

You'll have to IM me in 2 years as I won't remember, but still expect to have the bag.

I only had 2 peeves about the perf bag: zippers gave out, but for price and 5 years, that's acceptable. Bigger problems were having to bungee it on all the time and now that was riding in colder winter morning, I had to carry more stuff off me on the ride home.

As I found myself needing more storage, I soon realized I would use a small set of panniers all the time, instead of only on odd ocassion. Thus, the stowbale panniers weren't needed.

I simply kept my original Trans-It bag like yours, and added one of these small pannier add-ons that are sold by Nashbar.

For only $16.00, they proved to be a very cost effective upgrade.

It's cool man.
I did a quick google and it seemed to be around $80-100. You can get all kinds of cargo bags/equipment in this price range.
I kinda figured OP's reason was aero.
Seems like a nice bag, just not expandable/versatile enough for me in that $$ range.
I don't like proprietary items, no matter what they are. It appears that you HAVE to use a topeak rack/seatpost rack to use this thing.

Just not my style. I like adaptability. I don't even use the panniers for commuting (usually). But it's nice to know I have the capacity if I need it. I like racks that I can strap any sort of bag/cargo onto that I want.

Use what works for you. Glad you guys like 'em.

I use an old Blackburn rack... would this Topeak fit on that?

The Blackburn rack is just a series of round aluminum bars welded together to form a very strong rack. My current panniers simply hook to the top and bottom of the rack, easy on and easy off. But the panniers are old and need replacing... I'd love to get a good trunk.

The Topeak bags have a plastic outer bottom piece which is intended to slide into the plate that runs the length of the center of the rack. The plate has inward angled edges on the sides which mate with the bag bottom. The whole bag slides on the rack from the rear and locks into place via a quick release locking mechanism so the Topeak bags are only intended for ue with a Topeak rack unfortunately.

Topeak makes several racks with dropped pannier mounting bars on the side for use with the bag + panniers. Take a look at their Super Tourist DX series. The disc brake compatible version seems easiest to find but is compatible with standard brake bikes too as long as they have rack mounts.