hureemusaizu to norigokoti wo kakuninsita sueni, oritatamizitensya ha erabanakatta.

Because フレームサイズと乗り心地 is one combined noun phrase: "frame size and ride comfort."
The particle と links the two nouns, and then を marks the whole list as the object of 確認した.

So this part works like:

• フレームサイズと乗り心地を確認した
• checked the frame size and the ride comfort

This is very natural in Japanese. You do not need to say フレームサイズを乗り心地を.

末に means something like:

• after ...
• as a result of ...
• in the end, after going through ...

In this sentence, 確認した末に does not just mean a simple sequence like "after checking."
It adds the nuance that the speaker went through some process of checking or consideration, and then reached a final conclusion.

So:

• 確認した末に = after checking and considering things, in the end
• not just a neutral "checked, then..."

Good question. The difference is mainly nuance.

• 確認して、折りたたみ自転車は選ばなかった。
  = I checked, and then I didn't choose a folding bicycle.
  This is more neutral and simple.

• 確認した末に、折りたたみ自転車は選ばなかった。
  = After checking things carefully / after going through that process, I ended up not choosing a folding bicycle.
  This sounds more like a considered final decision.

So 〜た末に often suggests:

• time/effort went into the process
• there was some deliberation
• the result came at the end of that process

Here, は gives 折りたたみ自転車 a topic or contrastive feeling.

So 折りたたみ自転車は選ばなかった means something like:

• As for folding bicycles, I didn't choose one
• I didn't choose a folding bicycle
• A folding bicycle was not what I chose

Using は often implies contrast, even if only slightly. It can suggest:

• other options were considered
• maybe something else was chosen instead
• folding bicycles, specifically, were ruled out

If you used 折りたたみ自転車を選ばなかった, that would be more like directly marking it as the object of choose.
With は, the sentence sounds a bit more like "as for folding bikes, no."

Yes. Japanese often omits the subject when it is clear from context.

This sentence does not explicitly say I, we, or they, but in English we usually supply one:

• I didn't choose a folding bicycle
• We didn't choose a folding bicycle

The most natural assumption is often I, unless the broader context says otherwise.

乗り心地 means the feeling or comfort of riding something.

In this sentence, it refers to how the bicycle feels when ridden:

• how smooth it is
• how comfortable it is
• how stable or pleasant the ride feels

It is often translated as:

• ride comfort
• ride quality
• how it feels to ride

The word is made up of:

• 乗り = riding
• 心地 = feeling, sensation, comfort

So it literally has the sense of "ride-feeling."

The dictionary form is 選ぶ (えらぶ) = to choose.

Here is the breakdown:

• 選ぶ = choose
• 選ばない = do not choose
• 選ばなかった = did not choose

So 選ばなかった is the plain past negative form.

Usually it simply means didn't choose.

Depending on context, English might translate it as:

• didn't choose
• decided not to choose
• ended up not choosing

Because this sentence includes 確認した末に, the overall meaning strongly suggests a deliberate decision after consideration. So in natural English, decided not to choose may fit well, even though the Japanese verb itself is just 選ばなかった.

The comma helps separate the introductory clause from the main clause.

So the sentence is divided like this:

• フレームサイズと乗り心地を確認した末に、
• 折りたたみ自転車は選ばなかった。

In English, this is similar to:

• After checking the frame size and ride comfort, ...

The comma makes the sentence easier to read and shows that the first part sets up the reason/background for the final decision.

Yes.

It breaks down as:

• 折りたたみ = folding / foldable
• 自転車 = bicycle

So 折りたたみ自転車 means:

• folding bicycle
• folding bike

In natural English, folding bike is often the smoother translation.

Yes, very possibly.

折りたたみ自転車は選ばなかった can carry a nuance like:

• I didn't choose a folding bike (though I may have chosen something else).
• Folding bikes were not the option I went with.

This contrast does not have to be stated explicitly, but は often gives that feeling.
So the sentence may imply that after checking frame size and ride comfort, another type of bicycle was chosen instead.

Yes. A simple structure is:

• [フレームサイズ と 乗り心地] を 確認した末に、
• [折りたたみ自転車] は 選ばなかった。

In gloss-like English:

• frame size and ride comfort
  • object marker
• after checking / after considering
• as for folding bicycle(s)
  • topic marker
• did not choose

So the flow is:

1. check the important points
2. reach a conclusion
3. that conclusion is: not choosing a folding bicycle

Because フレームサイズ is a loanword expression based on English: frame size.

Japanese often writes modern borrowed terms in katakana, especially for:

• technology
• product features
• brand-related vocabulary
• measurements or specifications

So フレームサイズ sounds like a practical product-spec term, which fits the context of comparing bicycles.