What rucksack size for commuting

Alpkit gourdon for me too. Don't get a fabric bag that needs a drink bag inside. The outer bag soaks up water and adds to the weight. Alpkit is cheap 100% waterproofing and I've had mine years - very durable.

Used it for a 45 mile walk this summer and it worked for that too. Really impressive.

Alpkit gourdon for me too. Don't get a fabric bag that needs a drink bag inside. The outer bag soaks up water and adds to the weight. Alpkit is cheap 100% waterproofing and I've had mine years - very durable.

Used it for a 45 mile walk this summer and it worked for that too. Really impressive.

I've got one of these Alpkit Gourdon 20 and can really recommend them -

https://www.alpkit.com/products/gourdon-20

Waterproof and good quality, £32

No backpack carradry sqr 17 litres waterproof mounts on seatpost. Can carry lunchbox laptop notebook and clothes.

I love my Syncro 15, have had it for ~5+ years daily commuting, about 30 mile round trip.

Good things:  

• holds lunch box, some fruit,  spare tyre, CO2, multi-tool plus 3 or 4 shirts or similar amount of laundry. just wide enough to hold my work laptop. Can take a pair of shoes if not packed with other stuff
• top pocket holds keys, phone, cash etc for easy access
• excellent side pockets expand to hold whatever extra bits of clothing I might add or remove during the course of a ride home or during the day - changes with season, but today that means gilet, defeet gloves, overshoes and arm warmers
• sweaty back not a problem with the pack being held away from my back, even during a daily fast lap of Richmond Park
• not too heavy
• pretty water resistant, but the foldout waterproof cover works when there's proper rain
• zips are excellent - secure and pretty waterproof, and easy to use with gloves
• chest strap is height adjustable, waist strap is removable

Not so good:

• looking a bit grubby now 
• could maybe do with just a little more capacity, but I reckon that'll always be the case 

I'd get another if I had to replace it, but I'd be tempted by the next size up.

I hope you don't have to fill it to the full 20litres very often. I managed with a 6L backpack from Aldi for 3 years and wouldn't have wanted to go any bigger just because of the weight. Adding a bottle of wine a couple of times made my back ache over 15 miles.  Recently switched to  6l saddle bag which squashed my work shirts, but stops my back sweating. 

I used to have the Osprey Momemtum 26 and it was perfect.  Used it everyday for 5 years in all weathers.  You could even overload it and it was still comfy to wear!  The backing material failed first and then the zips so replaced it a few months ago.

Dissapointed with the Momemtum 32, it's nothing like the old style and could never get it to fit the same as the 26.  After a few weeks I decided that it was also way too big.

I got the Osprey Syncro 15 a few weeks ago and love it.  I'm suprised how much I can fit in; full uniform, large amount of lunch, snacks and fruit, paramo jacket & windblocker jacket, small dry bag with punture repair kit, inner tube, pump, tool kit ect.  It's like that bag out of Marry Poppins!

Still got the 32 for any days I need to carry another set of clothing for trips to the pub/cinema ect.

Deuter Cross Air. 20l with expandable zip to take it up to 22l (or 24l maybe?) if you anything extra to squash in there.

I've found the air mesh back invalubale in reducing the sweaty back on my commute, and it's very comfortable.  Fluoro rain cover too.  Had mine 3+ years and still going strong.

For me it comfortably fits change of clothes for the office (minus shoes which I leave under my desk), lunch, wallet+keys, pump/inner tubes/multi tool etc, plus emergency waterproof jacket/overshoes when weather demands.

Timbuk2 large courier bag.  Bit bigger, but good compression and you can really fill it.

My very similar requirements were fulfilled by a Deuter Race 15 pack up until it suffered terminal rips and tears in an off a few months ago. I replaced it with a Rapha item that was cheap in the sale, because I liked the idea of all the pockets and compartments. I'm on the verge of binning it off for another Deuter. The pockets and compartments are restrictive and take up too much space!

20l waterproof backpack no zips, good price, very waterproof, from overboard. I also have the 30l but find it very big and only use it on the odd occation when I need the extra space, go for the 20l it will be enough.

http://www.over-board.co.uk/classic-waterproof-backpack-20-litres.html

Careful with sizing . I went first for a ebay cheap bag which was stated to be 28L. It lasted about 6 months before the zips broke. I then went for one from a more reputable source which was 20L I thought it might be too small but when I got it, it was way bigger than the supposedly 28L one.

I carry shopping and it is as big a bag as I can carry fully filled. I wouldn't want a bigger one but then it is 20 hilly miles to and from the supermarket for me.

I don't know if they still have them but I found one which is just big enough for my D-Lock and wallet and perhaps two or three small items from a shop. Its not waterproof or anything but it cost a full £2 from Tesco. Pound for Pound it is probably the best buy I have ever made. It might look silly (I think it was intended for 5 year olds) but it is perfect if I don't want to take the big bag you can carry it in a pocket if empty.

My advice is go for YKK zips as they just last longer and several other bags broke there relatively quickly.

I just came from a trip to Paris and bought a Samsonite Paradiver Light L+ laptop backpack. In yellow. 

I'm a sucker for yellow bags, and the thing's usefully weather-resistant, with a tarpaulin-like material and rubber lining along the zippers. It's rated for about 24L; there's a smaller L version that gives up 5L. It's got a rather trim profile for a rucksack its size, and usefully "hugs" its load against your back closer than, say, a 28L Deuter Giga - despite having only a sternum strap.

My only real complaint is the top carry handle. It's set a little too far up the top. When bent over on a road bike it tends to rub on your nape, which can be irritating since it's textured for grip, but can be dealt with in a few creative ways I suppose. Also no reflectives.

Not particularly cycling-specific mind you, and it will serve you better riding on a more upright bike, but pretty damn good considering. Cost me 96 euros.

I'd go for a tailpack if it weren't for the size of the book. No heavier than a backpack but keeps the weight off your back and should be 100% waterproof. Much lighter than a pannier arrangement.

Two things to consider with backpacks - First, I'd recommend using a Hump cover on any backpack - adds waterproofing and visibility to pretty much any backpack and you can take it off so you don't look like too much of a dork at your destination. If you did that, waterproofing on the bag itself shouldn't be so important so that opens more design types to you.

Second, when I've done my 20mi commute with a backpack, it's only been with a Vaude 17l backpack which has a frame that spaces the bag away from my back to retain some airflow - limits the sweatmachine. Worth considering that side of things too.

For that distance of commute, I'd really prefer panniers to a rucksack. Some panniers have straps so they can be carried like a holdall, or even a rucksack too.

I've been using a DHB 25l waterproof rucksack for the last 6 months and it's superb. It's just one of those roll-top jobs but it's light and completely waterproof.

I got this 18L drybag and it has handled my commute for a year (same distance as you'll be doing) without flinching. Looks brand new after a wipe/enough of a downpour. https://huubdesign.com/collections/triathlon-bags/products/huub-triathlo...

£70, but I'm a wally of a triathlete who has to spend a certain % of his income each year on stuff that there are cheaper versions of.

I'm sure that there'll be decent stuff half its price, but I never bothered looking because HUUB make Good Shit, and I'm a wally of a triathlete who...

I have a Deuter and 2 Ospreys - while both have waterproof covers i find the Deuter, despite supposedly being cycling specific sits too high up and interferes with my helmet (if you know what i mean). Whether it's that specific model or not i dont know but i have no such problems with the Ospreys I have.  So my advice is to try first if possible.  

DHB slice 30L (http://www.wiggle.co.uk/dhb-slice-30l-rucksack/)

Best rucksack I've ever bought, has all the pockets you will ever need and a built-in high-vis and waterproof cover.

http://www.wiggle.co.uk/osprey-momentum-32/

This is very good, could have got away with the smaller version, 26L 

Limiting factor for me is being able to get a laptop in.

I used to use a Lowe Alpine Pax 15, but was a very tight fit and I could barely zip it up.

These days, I use a Berghaus Remote 25, which is perfect - only niggle is the base fabric could do with being a bit beefier for being put on the floor. Laptop is in a padded neoprene sleeve and have an Aldi hi-viz cover over the top, which is fine for a light shower. If it looks like proper rain, I put everything inside plastic bags.

My advice is to go for something slightly bigger than you need, but with compression straps to take up the slack.

I use a Deuter Speedlite 15 (15 L), I liked that it was light and had a low profile. It's very comfy but it's not waterproof, in fact it's pretty poor at resisting any moisture so I wouldn't recommend it for commuting. I probably should have gone for the Alpkit that Paul7189 linked to. Thanks for that.

I'd recommend a 20L bag so you have a bit of spare capacity for the days when you need to carry additional items or do some shopping on the way home. My kids both use cheap 20L rucksacks from Millets which do the job well.