UKC

I’m about to pick up a second hand Defy 3 as my first carbon bike and would like to upgrade the wheels. Cassette is Shimano Tiagra 12-30 and brakes are rim brakes. Current Wheelset is Giant P-Elite C and tyres Giant PR3. Usage mostly weekend rides and sportives. 
 

Budget for new wheels is £500……any advice greatly appreciated from more experienced bikers on potential upgrade models? 
 

Thanks in advance 

Depends on what you mean by 'upgrade'. What problem are you trying to solve? Do you want lighter? Stronger? Stiffer? You won't get all (if any) for £500.

What's wrong with the current wheels?

Personally, I'd strip and re-build the hubs (or get LBS to do it for you) and, if there's no pitting on the cups, I'd stick with them. A quick search suggests they are DT Swiss hubs, so should be solid.

By all means upgrade the tyres if the current ones are worn - use latex tubes and you may be happy enough not to need to replace the wheels.

Are you going for 2 wheels up front, or two in the rear? Or will it be some form of inline 3-wheeler? Confused.

If they are the stock wheels then they will probably weigh 1800-2000g, may be worth removing the cassette, tyres, and QR's and checking with some baggage scales. Losing a few hundred grams off the wheel weight improves the feel considerably. I run a pair of Hunt Race Aero Wide wheels on my Trek Boone CX bike and use this as my summer bike, these come in as 1496g for £399, are well built and come with an excellent warranty.  I would recommend setting them up tubeless, if you want a really quick racy Moto GP feel then the Continental GP5000 S TR in 28mm or 30mm widths are awesome, currently being ridden by Ineos and a few other teams in the Tour de France, watch Tom Pidcock's race-winning descents on the Alpe d'Huez stage for mind-blowing reference. Alternatives are Schwalbe Pro One Tubeless which are a bit easier to get on/off. They aren't cheap at ~£75 each but bang for buck make a huge difference to the feel and handling. A top tip to prolong the life of your new wheels is to use your existing wheels with a heavy hard-wearing tyre for winter / crap weather riding.

Ideally I was looking at lighter stronger wheels with wider rims to let me run wider tyres. More comfort and faster speed in theory. 

Thanks that’s the kind of advice I was looking for - have heard good things about Hunt Aero and Campagnolo Zonda 

In that case I'd recommend the Hunt wheels (I have the gravel version and they've been bomb-proof). Zondas (I think) are good, but still narrow and very stiff, so not ideal for comfort.

Check what width tyres the frame will take before you get carried away

One thing also to consider is maintenance. Break a (proprietary) spoke on many off the shelf rims and they are bin jobs. 

Would recommend checking out one of the many UK based wheel-builders (I have used DCR before), generally wheels built up light, to your spec and with standard parts. I managed to shift the chain off the top of the cassette into the spokes on one wheel, result was snapped spoke and 5 more damaged, wheel returned and fixed at a cost of under £20. Another wheel the actual rim started to fail (pretty much reached end of life), yet I was able to re-use the hub to build up a new wheel much cheaper than a whole new one would have cost (hub is the most expensive part generally). Its a more sustainable approach as well