Just wondering if the other backpackers here insist on the strap or not.

Two of my last three didn't have one, and the one that did was so poorly designed that I removed it after the first use.

Never used one with a waist strap. The two for my shoulders are plenty for whatever I am carrying around.

When I wear a backpack on a bike, then yes, definitely. It helps to keep the weight at the waist rather than on the shoulders, although it's not a important as when hiking, and keeps the pack in place, prevents side-to-side movement. It's also less beneficial for short commutes than for trail riding.

I actually bought one of those new Camelbaks that puts the water bladder down, horizontally around your waist, for mountain biking. A big difference. I actually started wearing in on long weekend road rides.

I use a standard backpack for commuting, a Targus computer pack.
Holds what I need and stays where I want.
Fitting a rear rack to my hardtail has been a problem, so I just use a pack.
No waist strap, and so far never missed it.

When I use a backpack, I always use the chest and waist straps.

Aside from stabilizing the pack, the straps help to distribute the weight and reduce strain on your shoulders.

Depends. If the pack is very light I only use the shoulder straps and sternum strap. The heavier the load, the more I rely on the hip belt to carry the bulk of the weight.

My current backpack only has the shoulder straps but I think having one with a chest strap and a waist strap would probably be better for riding with it on. It just seems more comfy and would allow less side to side play while riding.

I have a northface pack with a chest strap. I usually just use that one and forgo the waist strap.

I used to be heavily into hiking and backpacking, before I got into biking to save the wear and tear on my knees and ankles. As I recall, the rule of thumb for a backpack is if you are going to be carrying more than about 20 lbs, you want a hip belt. As with bike gear, proper fit is important for a backpack. The hip belt has to sit on your pelvic bones to distribute the load directly to your legs and not to your back. The sternum strap functions to keep the shoulder straps properly positioned and not to slide outward. There are usually a bunch of other straps to compress and support the load to keep it from flopping around while you're climbing over boulders and such.

That said, for biking, I've never worn anything bigger than a Camelbak HAWG which is pretty tiny by backpack standards. I used to use the hip belt with it, but later took it off and I can't say I've noticed much difference (probably because it's crap anyway, compared to a real hip belt like on my Granite Gear Nimbus pack). I did like the sternum strap though, until that broke on me so now I don't use that either. But I would still use the sternum strap if I could. You definitely don't want the pack flopping around while cornering or on rough terrain.

I bike commute with a Dakine Apex backpack, that has just about the best lumbar straps made. They make an enormous difference when cycling with heavy loads. They allow me to loosen up on the shoulder straps, lowering the pack down closer to my waste, thus relieving me of undue upper back strain. I honestly can't imagine not using the lumbar straps with a load greater than maybe 8 or 10 pounds.

For really light loads, the Apex allows me to remove the straps by simply detaching the heavy duty velcro. Very easy to add and remove, and easy to stow away in the hydration slot.

For the record, I also use the sternum straps when cycling. The more straps the better. I don't like the load shifting.

I have a Jansport backpack I use for more or less everything except hiking. It's sold as a outdoors pack, but in reality is a horrible hiking pack. Anyways, I resorted to tying the waist strap in knots because it tends to get caught under the saddle when I start. For example, standing with the bike under me and one leg on the ground, I press one pedal to get the bike going and to lift myself, up, the waist strap catches on the nose of the saddle and traps me in a weird riding position until I can safely stop.

Yes I do use the straps. The backpack I use (Deuter Race Exp Air Daypack) has 2 straps, 1 on the chest and the other on the waist. Very easy to lock and easy to adjust. I prefer using the straps because I find that when I am pedaling out of the saddle my old backpack (with no strap) would flop up and down and sideways. The straps keep the backpack firmly in place.

I would also highly recommend the Deuter Race Exp Air to those who want a sweat free experience (from the backpack). It is designed in such a way that the backpack itself does not rest at your back but is suspended and what touches your back is a screen/mesh that allows for free circulation of air from your back.

The Deuter Race Exp Air also accepts a water bladder if needed.

YES.

My biggest pack is 45L pack that I use when I go on a long tour without my bike. 70% to the hip, 30% to the shoulder weight distribution.

I don't, but the light loads I carry are secured well enough to not need the extra stability or weight transfer.

When the mornings are light and warm enough that I don't have to bundle up like Bib the Michelin Man and carry 10 pounds of batteries for retina searing redundant lighting systems, then I put the pannier and handlebar bag equipped boat anchor commuter bike in the garage and ride a road racing bike to work. I use a 15 liter Rapha backpack with waist and sternum straps. The pack is stuffed to capacity with work clothes, street shoes, books, breakfast and lunch. It remains very stable on my back and doesn't shift from side to side on out of the saddle climbs. Shaves several minutes off each direction of my 29 mile r/t commute.

You do realize that there will be some heat over this statement? But that's alright, as the pendulum has swung back to backpack over panniers again (for now, at least).

On the bike, sternum strap is crucial. Waist straps typically don't work for me because my torso is super short (5'6" with 32.5" cycling inseam).

I usually end up with packs with waist straps. My current Marmot Zephyr has two padded bits extending from the body of the bag where the straps are attached. They have pockets in which to stow the straps and zippered mesh pockets on the front of them in which I typically store my phone (right) and keys (left).

If I had a taller torso or found a pack with a higher waist strap I'd probably use it on bike a lot.

My bag came with a chest and a waist strap. I use them. I find it reduces the bag from shifting side to side.

There are two kinds of lumbar belts on backpacks:
- load bearing belts;
- just a strap (similar to the chest strap), used only to stabilize the backpack.

The first type is essential and should always be used, but those backpacks are intended for hiking/trekking, not for carrying on the back while riding a bicycle.

The use of the second type is optional. This type is usually found only on small backpacks (including backpacks designed for bicycle riders).

How do you get that much stuff in a 15 liter bag? Even if you don't wear size 11 shoes like me, I'd have a hard time getting that much in 15 liters without smashing my food.

i absolutely prefer a waist strap, not just to take some of the weight off the shoulders, but it also helps keep the backpack from moving around too much. i also prefer a sternum strap for the same reason. my daily commuting backpack has both a waist and sternum strap; i wouldn't want to ride with a backpack without them.

I don't use a backpack anymore, I love my bike rack and bags, would'nt go back to backpack but in those days I did'nt use waist strap.

I use the chest and waist straps and I love them.

On the bike I don't use a lumbar strap. I'm typically leaned over far enough that a waist strap isn't going to do much good to transfer any weight bearing of the pack to my hips, but it will interfere with my ability to get into my tuck. I do like having a stabilizer strap or sternum strap to keep the shoulder straps in place.

So far, it appears that the sternum strap is universally as a 'must', while the waist/lumbar strap is more of a personal preference thing.