Can I just buy a bicycle online or is it something you have to get fitted or a feel for? Are there size guides somewhere I can use to measure myself to get the right size for me?
And second side question: i've seen the bicycles they sell periodically at aldi have 'must be assembled by bicycle mechanic' all over the advertising and boxes. Is that true? And does it wipe out the saving?
You should probably get one you can try in store.
In terms of putting together they are mostly straight forward, but aligning the gears can be a royal pain.
The gears on a decent bike should be good to go or of the box.
Sounds like you're only getting into biking recently.
My advice would be to get something cheap so you can use/abuse it until you're more proficient. At which point you'll know better what to look out for, so buying online would be less risky (you'll know what to look for etc) and by that point your savings would've gone up to get a pricier bike.
The Aldi bike is fairly affordable, it punches above its weight, great for starters. It comes half assembled in the box, so no issues for a regular folk to do.However, those tubings are pretty darn cheap (mine came punctured). Also the tyres aren't great. Before upgrading bikes, it makes sense to just do a quick service and replace the tubing and tyres…. sometimes you feel the difference. I only go riding on weekends/holidays, so can't justify spending more for the gear I want ($2k MTB) unless there's great friends and great tracks.
I should say, around the holiday period, check facebook/gumtree.
You might be able to buy a, basically a new bike, which someone doesn't want anymore. And it'll come preassembled, you might get a modest upgrade, whilst saving lots of money. One man's trash, is another man's bargain.
"'must be assembled by bicycle mechanic' all over the advertising and boxes. Is that true? And does it wipe out the saving?"
If you are handy and know what to do - but if you did, you probably wouldn't buy the aldi bike.
If it's just a casual bike $200-300 then whatever but if you're going to use it more invest a bit more like $600-900 so that you don't need to buy it twice and at that price you can just get it from a store.
Potentially the Aldi bike could be the really good value mountain bike. Think it was around $350, but you’d pay $6-700 for a bike brand equivalent.
There are cheap and nasty Aldi bikes too though, so you need to get the premium model ones.
Depending on your budget, gumtree or marketplace my be a goer if you're only just starting out. Would not suggest buying online if you haven't ridden/don't know the bike as all geometry is differenty, sizes vary greatly from one brand to another etc.
IMHO if you're buying from stores, anything under $400 will likely be junk (think 40-50% markup + shipping costs) doesn't leave much for parts.
If buying new your budget should be around $500 at least.
Unless you are really confident in knowing the fame size that suits you, buying online could be a headache. A decent local bike store will charge a premium, but can be very helpful in correctly sizing the bike for you and making a range of adjustments to make your ride comfortable.
Try gummy/FB marketplace. You might not know your exact size but there are guides online to give you a rough idea. A second hand road bike for $500 will be much better than something for the same price new. If you're looking at people's bikes ask to take it for a spin and see how it feels.
As a point of reference I.am 180cm and ride a 56cm frame road bike, although I think I need a 58cm.
Online is ok if you know your size. No good if you have no clue. Most bikes with the correct size frame can be adjusted to suit your body proportions, but it may require a different stem or handle bars.
It’s nice to be able to throw a leg over and check if it feels right as there are subtle differences in geometry that make some bikes feel a bit wrong even though they might be the right size. You want to be comfortable first and foremost on a bike.
Anyone who is reasonably handy can assemble a bike out of a box. It usually only takes an Allen key and a pedal wrench.
Would I biy a bike online? Yep, and have done, but I already knew what size and geometry I wanted and I’ve ridden for a long time and built several bikes. Would t recommend for a newbie.
Yes you can buy them online. Some companies like LeonCycle have their bikes pretty much pre-assembled with minor fixing needed that anyone can do.
Example video: https://www.youtube.com/watch?v=vqt1QE1cG-Y
You can pop into a Decathlon or 99Bikes etc shop to have a look at sizes. They're generally pretty standard and most likely will need a 26" one.
You'll probably want to order from Decathlon anyway to pickup a gel seat cover, side stand, bottle holder and gloves anyway. Cheap addons but well worth it.