Energy gels

[Deleted User]

I did the Milford 21 on Sunday and was knackered! It occurred to me that I propably could have done better if I had taken an energy gel or isotonic drink as I began to feel really tired around the 15 mile mark.
How soon into a race should I take them and how soon before the end? Presumably I'm OK for the first 5 miles and there isn't much point in the last 5 miles. Any opinions more scientific than that out there? I'm doing the Stafford 20 this Sunday and I'm planning to experiment then.

[Deleted User]

I use Lucozade Carbo Gels. I tend to take the first one after about 45 minutes and then one every 30 minutes after that. Work well for me.