Originally Posted by
WalksOn2Wheels
The short answer: a quick search tells me that a Shimano 105 front hub is about 200 grams and an Alfine dynamo is nearly 700 grams. So, roughly 500 grams, or about 1.1 pounds.
However, you might be able to minimize the weight penalty if your current wheel is pretty chunky. Building from scratch, you can go with a decently light rim and spoke combo, making the overall difference a little less.
It's not the overall weight of the wheel that matters. It's how far it is from the centre. A 500g weight penalty in the middle (hub) is much different than 500g around the outer edge (rim).
I'd wager that 500g in the middle is similar to 100g on the rim.