In the question Sirius Black and his motorbike it is revealed why Sirius gave Hagrid his motorbike, but as I was re-reading this paragraph in the book:

" -and a huge motorbike fell out of the air and landed on the road in front of them. If the motorbike was huge, it was nothing to do with the man sitting astride in it."

The motorbike is clearly big enough for Hagrid to sit comfortably in it, and is described as being "huge"- however, if the motorbike belonged to Sirius, why did he have such a large one?

  • 43
    Clearly, he was compensating for something.
    – phantom42
    Commented Sep 14, 2015 at 14:54
  • 8
    Huge motorbikes contribute to the cool factor though! Sirius seems like the type of guy who'd use that.
    – Saturn
    Commented Sep 14, 2015 at 14:54
  • 11
    Hagrid might have also cast an enlargement charm using his umbrella (something which he may have had a lot of practice with given his size). Or, alternately, Rowling might not have settled on that being Sirius's motorbike when she started writing it.
    – FuzzyBoots
    Commented Sep 14, 2015 at 15:04
  • 6
    @SeanDuggan or sirius enlarged it for hagrid, shouldnt be to hard to do at sirius level of skill, vs hagrids level of might blow this bike the F up lol.
    – Himarm
    Commented Sep 14, 2015 at 15:27

2 Answers 2


What do we know for a fact:

  1. Sirius owns a motorcycle that can fly

  2. Sirius gives motorcycle to Hagrid

  3. The motorcycle is described as big, big enough to fit a half giant Hagrid.

What we can safely assume:

  1. Motorcycle was muggle-manufactured.

  2. Sirius enchanted the motorcycle himself.

What assumptions are less safe, but still very reasonable:

  1. The motorcycle was manufactured at a normal size.

  2. Sirius being a normal sized human would ride uncomfortably in an over-large bike.

What conclusions these could lead us to.

  1. Sirius upon handing the bike over to Hagrid the night of Lily and James' deaths, enlarges it for Hagrid.

  2. Hagrid himself enlarges the bike after being given it.

  3. The bike itself was enchanted to fit the rider (similar to both the Weasleys' car and the Ministry's cars).

Canon info to further our ideas:

  1. Cars are shown to be magically enhanced

    a. motorcycle can fly

    b. Weasleys' car can fly, become invisible, and has some enchantment to enlarge the cabin to fit more people/luggage.

    c. the Ministry owns cars that are magically enchanted to also have more room than physically possible.

  2. Sirius is an accomplished wizard, probably similar in skill or better than M. Weasley.

  3. Hagrid has been shown to be able to enlarge things magically, like his pumpkins.

My belief.

The bike itself was enchanted to fit the rider.

This fits best with other enchantments we have seen on other cars, where the car would magically enlarge to fit the riders and luggage.

  • 5
    "Engorgio!!" + umbrella = oversized bike
    – Valorum
    Commented Sep 14, 2015 at 17:34
  • 8
    This is reinforced by the description of Sirius' bike in the "Harry Potter: The Prequel". Since the police don't note that the bike is outsized ( something they would surely have spotted), we can assume that it's normal sized.
    – Valorum
    Commented Sep 14, 2015 at 19:40
  • I might be missing something, but if the bike adjusted itself to fit the rider, wouldn't it re-adjust to fit Sirius here?
    – kettlecrab
    Commented Sep 15, 2015 at 0:53
  • @Richard - true, but remember that muggles tend to not notice a lot of magic... Knight Buses, invisible houses etc. Harry: But the Muggles! Can't they see us? Stan Shunpike: Muggles? They don't see nothing, do they?
    – Jon Story
    Commented Sep 15, 2015 at 15:51
  • 1
    Alternately, it could just be a bike that's normally huge. Being made in England probably eliminates the chances of that, but they do come in large sizes
    – user40790
    Commented May 16, 2017 at 18:16

An excerpt from the HP wiki:

Magic made it much larger than when it was manufactured, emitting a very loud roar. When Hagrid rides it, it is large enough to fit him, a half-giant, and still can carry an ordinary-size person in its sidecar,. Another spell made it able to fly, fast enough to compete with a broomstick.

I think Sean had the right idea; the bike was enlarged after Sirius lent it to Hagrid.

  • 8
    What is the basis for this assertion in the wiki though?
    – Valorum
    Commented Sep 14, 2015 at 15:23
  • 2
    @milk way better than any of my first answers ever were, welcome to Stack Exchange Scifi/fantasty :D
    – Mikasa
    Commented Sep 14, 2015 at 16:07
  • 1
    Wikia isn't canon, it's just something random people typed on the internet. Sorry, -1 Commented Sep 17, 2015 at 16:13

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