In English there are set ways that you can say things in pairs, that usually wouldn't necassarily come in twos. For example: two Jeans is wrong, yet a pair of Jeans is correct. Two glasses is wrong, but a pair of glasses is correct. Two shoes is ok, but a pair of shoes is better. The list could go on; headphones, shoelaces, scissors, shorts, gloves... etc.
In Mandarin I got very confused because the classifier for veichles is very similiar to the word for a pair. So when I learnt bicycle I had assumed I was hearing a pair of wheels or similiar because of our sometimes odd rules about pairs.
What I was really hearing is the above sentence telling me it is a bike that you can travel on, maybe an excercise bike would have a different classifier?? (Can anyone confirm that?)
Anyway, so When I was learning the numbers in Mandarin I learnt that 2 is 二 èr.
The Chinese tend to use 两 liǎng in a sentence instead of 二 èr (unless counting or reciting a number). Thanks for everyones helpful replies on twitter when I got confused earlier on. But this was put best by my new friend @megoizzy who lives in China.
"We use 二 èr in numeric counting sequence, use 两 liǎng with measure words. We would never say 'èr ge'. but we would use 'èr' in telling our phone number to someone."
两 liǎng is used before classifers (measuring words) such as 天，个，辆. Otherwise 二 èr would be used.
So I think I am right in saying then a pair of bicycles in Mandarin would actually be said:
liǎng liàng zì xíng chē.
However if you are spelling out a number, like a telephone number, you would say 二 èr not 两 liǎng (Although I wonder if you might use 两 liǎng for double numbers...)
edit: To spell out numbers, you can say 两个二=two 2s
And maybe when replying to "how many sweets have you got left?"
You might reply "Two" 二 èr, so long as you weren't going on to say "I have two sweets left..."
edit: 2 (sweets) = 两颗糖
I wonder if in Chinese then a pair of scissors would mean one or two pairs of scissors when translated back into English as they don't seem to have the same problems with a pair of trousers, shorts etc.
edit: a pair of scissors=一把剪刀，it's the measure unit that changes!
So what I have learnt from this is that the Chinese doesn't have a silly pair rule about bicycles at all. In fact it is the English which makes this harder to grasp. Mandarin speakers just use 两 liǎng as their word for a couple, a pair or both items.
This was an interesting point as I was learning this morning and got a little stuck, but think now in general I am a bit clearer on the matter. Though there are some points I have highlighted that if you can clarify would be most useful.