Flexible gravel/road bike - 38c to 25c - Will I really notice the difference?

You can obviously ride sportives on any bike, but if you are planning on doing more of that type of event in the future, I'd be thinking seriously about buying a more road-focused bike.

I've no interest in doing sportives but I've ridden a 200km audax on my cross bike with either 28mm or 32mm tyres on it. Can't remember what it had on at the time. I'm usually running 32mm Vittoria Voyager Pro Hyper and find they roll plenty fast enough for me and are comfortable with plenty of grip. The bike will be fine with something like that on.

aarondown wrote:

Thanks @Veronese68. I think we're departing from the question somewhat. Simply switching my 38 tyres for 32 isn't gonna do much, I'm pretty confident on that.

It's not the weight or size of the tyres but the type of tyre that will make the biggest difference, and switching tubeless tyres is a pain in the aris so get a spare set of wheels. I just changed from a pair of CX tyres at 30psi to the road tyres mentioned above at 80psi, both at 32mm and the difference is marked. Tyre pressure accounts for some of that I grant you, but tread pattern and tyre construction also makes a difference. No need to go as thin as a 25mm, that's not the biggest difference. Go for something a bit bigger enjoy the comfort and you won't have to worry about every little bump.
With regards to the 500g difference, weigh a full water bottle. It'll help a bit, but in the great scheme of things...

aarondown wrote:

I have a gravel/tourer bike that was built for me last year as a new commuter (having used my old hardtail for the preceeding 20 years!).

The spec is:
Light Blue Darwin frame -https://www.thelightblue.co.uk/Sport/FMLBDD1K/Darwin-Frame-Set (link is external)
Wheels - 29" Halo Vapours - https://www.ison-distribution.com/engli ... t=WHHAV9SK (link is external) - with a dynamo on the front to power lights
Tubeless Schwalbe 38c G-One tyres
Shimano S106 hydro disc brakes
Compact 11 cassette with twin chainrings

I love the bike as I can pretty much take it anywhere without worrying about it. However, I've started to do some sportives, the longest of which was 80 miles and I'm considering whether I could improve my setup with a second set of more road-specific wheels which I'd switch out for sportives or other long road rides.

Within my budget this tubeless setup is available:

Wheels - https://www.ison-distribution.com/engli ... =WHHAWDF7K (link is external)
Tyres - Probably Schwalbe Pro-One 25 Discs and cassette to match the existing

The question is - am I going to see much difference by switching the wheels, tyres and the loss of dynamo etc? It's not an insignificant amount of money and I want to be sure I'll be glad to have spent it.

Can’t really say about Dynamos drag though I thought it was quite low now?

I have a Norco Search Gravel bike, with GravelKing SK 32/35mm tyres which are reasonably similar to the G-ones. I’ve found that that bike with those tyres is at worse equal to the road bikes I had with full on road tyres. In terms of speed, measured.

Quite different feel really, I personally like that the wider gravel tyres ride out potholes and what not, and cope with rougher roads much better, equally more rubber on road makes them feel much more sure footed. But road bike tyres do have that zing, and different feel.

your bike looks to be very similar to my commuting/do everthing bike, which is a Norco Indie Drop steel frame which I have fitted with halo vapour 29er wheels. My advice would be to firstly try fitting a set of good folding 28mm tyres to the wheels you have to see if that gives you at least some of the benefit you are looking for. Should you wish to get another set of wheels after that then you can still use the tyres so there is minimal risk. I have been riding with more gravel oriented tyres for a while - 32mm MSO Xplor on the front and a 35mm Gravel King on the rear at the moment - but this is just to cope with mud, leaves and grass shortcuts as well as allowing me to try some bridal paths if I get the urge. In the past i have used 28mm tyres on the same wheels and they do definitely feel faster but I have never tried to test this.Incidentally, the vapours are not really very heavy and are available as single wheels rather than as a set so why not just buy a single wheel to replace the one with the dynamo hub so you can swap it out for the sportives as required?

aarondown wrote:

kingdav wrote:

I've kind of gone the other way round.
So - even though the cx tyres are rated narrower at 31 mm they are slower than 32 road tyres.

Surely that's due to the massive difference in rolling resistance of knobblies vs slicks no?

Yes, type of tyre and pressure makes the biggest difference. I'd go with at least a 28 though as speed difference is debatable and a bit of extra comfort after a long day in the saddle is something you will really appreciate.