It's definitely not as simple as any 110mm FSA chainrings fitting exactly the same as the 'custom' ones supplied with the Giant Road E+. The rings
@soundwave linked to for instance I think have a different bolthole thickness and the outer a different teethline dishing, meaning a straight swap will result in a slightly different chainline and chainring gap, and potentially problems with the chainring bolts bottoming out before tightening fully against the thinner chainring arms.
Fortunately Giant stores can supply exact replacement chainrings for their Road E+ bikes - I already got an extra set thrown in when I was bartering over the price of my Road E+1 (although they weren't in stock and had to be ordered in and posted to me). The bad news is the RRP would have been £80 for the 50/34 pair. In any case, they should last much longer than 3,600km.
As an aside, as a fairly strong/fit rider I find the 50t chainring too small, particularly during non-winter months when I ride quite a bit faster on both e-bikes and non-e-bikes. I therefore decided to investigate the options for fitting a larger chainring to my 2016 Road E+1.
On close examination of the space available between the 50t ring and the chainstay, I could see it was going to be touch and go whether a larger ring would even fit, due to the way the chainstay flares outwards immediately past the outer ring's teeth. I nevertheless thought there was a fighting chance a 52t ring would fit IF I also fitted some chainring spacers to offset the 52t ring outwards to help ensure that the teeth cleared the flaring chainstay.
It was a very close-run thing, but when I did the first phase of my proof-of-concept testing, I found the 52t ring JUST cleared the chainstay when 1.2mm chainring spacers are used.
I went for the
FSA Unisex Pro Road N10/11 110BCD Chainring ('Unisex' - how ridiculous!). However, as mentioned, this has a different (thinner) bolthole thickness and teeth-offset (i.e. dishing) compared with the fitted 50t ring, meaning the use of chainring spacers of some kind becomes essential anyway.
For this experiment, I established that 1.2mm was the minimum spacer thickness needed to clear the chainstay. I haven't actually ridden the 52t ring yet, as I only tested clearance in the workstand before removing the 52t again for the winter, so don't know how shifting between rings may be affected by changing the ring separation. I'm not too bothered if shifting is compromised, as I only use the 34t ring for 10 metres at the start and 10 metres at the finish of my commute, spending the whole of the ride in the big ring, even the steep hills.
I may of course find, when I eventually test-ride the 52t set-up, that whilst the teeth cleared the chainstay during static testing in the workstand the forces going through the chainset during riding may flex it enough to mean the teeth do make contact with the chainstay, in which case switching to thicker (e.g. 2.0mm) chainring spacers may provide enough clearance. I've got various sets of spacers from SJS Cycles to play with:
chainring spacers.
Lastly,
@Gubbins, how did you get the chainring assembly off the bottom bracket shaft? Was it just a case of using the left crank for leverage against the locknut spanner? One Giant shop said they use a special tool to grip the large chainring when undoing the locknut - they couldn't confirm whether it was possible to buy this tool as consumer rather than retailer, though. So far I've just undone the chainring bolts in situ, but it is a royal pain in the backside trying to refit the chainring nuts and holding them in place while tightening the bolts back up - this is due to the motor housing severely obstructing access.
