UKC

I currently have a Pinnacle Arkose R2 which is my road bike that ive had for years.  I'm going to convert it to a gravel bike and then buy a new road bike.

First question - what would you do to convert it to a gravel bike?  Which tyres should I go for?  Which diameter?  I'm thinking 38mm?  Do I need a new cassette and bars or will the new tyres suffice to start with?

Second question - which new road bike?  Up to £5k budget.  Mainly for long sportive type riding rather than mad aero racing.  I'm looking at  Trek Domane SL but totally open to other ideas.

Thanks!

Depends on what you expect of your gravel bike. It could be anything from a road-bike-with-slightly-wider-tyres or an MTB-with-drop-bars. Depends on the 'gravel'. I live on the edge of the Peak District and I wouldn't consider anything less than 40mm tubeless tyres, preferably 45mm. Cassette? Depends on what you currently have. I tend to think 1:1 gearing is fine (e.g., a compact chainset with 11-34 cassette), but others prefer lower ratios. Never felt the need for wide, flared bars, so I'd stick with the ones you've got to start.

Depends on what you want from your bike. Go and get some test rides (if you can) and see what you like. Don't just look at specs. I tried a Domane a few years back and found it a bit boring. Ended up with a CAAD12: perhaps not as comfortable, but far more fun. If I want long distance comfort I use my gravel bike (with perhaps slick tyres). the CAAD12 didn't survive an encounter with a car, so I've now got a Fairlight Strael. Lovely bike - worth a look.

Yes, new tyres should suffice. Everything else you can decide later. 

38mm should be fine for actual gravel, but if your "gravel" includes 5-15cm stones rough forest tracks and mud/gloop something bigger would be good.

It's mucky. Ass saver (not tried them) or some short mudguards if there's clearance.

I'm an extremist with 20/32 chainrings & 11-34 cassette, but I still walk more than my mates

My gravel bike came with flared bars but it just makes them catch more obstructions.

Anyway, any bike/tyres/gearing can go over any terrain, provided you are prepared to slow down or walk.

I have a Domane for a few years and love it.  I’d buy the same again but then comfort is high up the list for me.

I’ve also been looking at how I’d use my bike for easier gravel stuff and have a set of tyres coming tomorrow.  I did a lot of research and a big factor is tyre clearance, relative the capacity of your frame, fork and rim profile.  And it seems not all tyres measure as stated.  My Domane is given a clearance of 38mm, so I’ve gone for some 35mm tyres.  That’ll allow a bit for wiggle room in mud, or if I were to buckle a rim.

I suspect gearing will hold me back on steeper terrain.  I have 34:34 on the Domane but have 34:50 on the MTB and use it regularly on steep, techy climbs.

Valid points.  I have a proper mtb so the gravel bike will be for relatively tame, longer distances.  Dirt tracks, fire roads, etc.  We were up in Bellingham at the weekend and saw lots of people on a big race all around Kielder.  That sort of stuff.

The road bike will be for a bit of everything.  100 mile sportives, all training rides, general road riding, etc.  I live in the Peak so lots of hills if that changes anything?!

1:1 gearing is nice to have when it gets hilly or muddy. I was riding with my brother the other day, me on my 1x11 with 42T/11-42 gearing and him with 12sp 2x without that low a gear. Every time we had to plod through a muddy stretch I could keep riding while he had to dismount. And given that we are having a very wet spring so far there were quite a few of them. He was faster on tarmac stretches so YMMV.

Re tires, I would go as wide as the frame will fit, especially when you expect chunky stuff. For smooth gravel (strade bianchi or shell paths) anything from 35-40 is probably enough and preferable if you want to gain some speed. I use my Specialized Crux, currently set up with tubeless 37mm WTB Riddlers for pretty much anything except chunky stuff because then it gets uncomfortable. You could always get a second wheel set with narrower slicks somewhere down the line, or use your road bike. Bigger tires are nice when you are going bikepacking in rough terrain as well. Down south in Belgium it's quite rocky with some slightly technical single track and that's pretty much why I stil have my 26'er monster cross chunky boy. 

Flared bars: it's personal, I think they're nice but more than 16deg is probably overkill for most stuff. I run a 12deg flare on my Crux and a 16deg on my 26'er. Also, they complete the look for me. I know that's not a good reason but wide tire drop bar without flare just looks a bit off to me. 

The Domane SL is a near 10kg bike, I cant personally see any benefits that you will get out of a frameset like the Domane that a good Ti adventure frameset couldn't provide on a long sportive. Something like the Mason Bokeh Ti with a 2x GRX set up and a set of 650b gravel wheels for the off road and a lightweight carbon set of 700's would give you a very similar road bike performance and a far better gravel set up (650bx2.1 tyre clearance!) 

If you are a mountain biker as well, you'll soon be trying to ride everything on the gravel bike that you do on your MTB.   

It can escalate pretty quickly, lol.  There's great raw fun to be had. 

(I'm also in the Peak)

I run 1x11 on a 38T/9-46

If yours looks like the one in this https://off.road.cc/content/news/pinnacle-launch-a-new-arkose-gravel-bike-a... I would have thought all you need to do is try and get as fat tyres on it as possible and nothing else really. On my gravel bike I have a 50 mm at the front - still lots of clearance space and I think 40 mm on the back. For my usage I don't think it's really any slower on the road than when I had I think 38 mm back and front and a lot more comfy. 

My commute goes on a canal towpath some of the way, it's been horribly muddy in sections since the big October rains, so for me mudguards are a must through the winter. SKS Speedrockers and easy to fit - easily fit over the 50 mm front tyre - and whilst not as good a really long mudguard on a narrower tyre, are still massively better than something like an ass-saver and a little MTB style one under the front fork.

Is that 50mm 650b though?

I tried to squeeze on a 50mm 700C Hutchinson Tundra on the front: just no way, and my forks have pretty accommodating clearance.  Settled on 700C 45mm front and 40mm back 

@maybe-si - things is how things escalate, lol

Yes that's exactly what I have currently, the R2 version.

Thanks!

Indeed! I've pretty much abandoned my hardtail MTB (although the full-sus still has a place) in favour of my gravel bike. The one thing to watch out for: Up hill I can pretty much getting up anything that I could on my hardtail, but loose downhills can be absolutely terrifying!

Nope, on 700c. This on my 2019 Boardman ADV, and I think generally many bike manufacturers have become more accommodating on tyre clearance - although perhaps Boardman were just a bit ahead of the curve. IIRC the bike came supplied with 40 mm tyres? Maybe 38s, but anyway not skinny. Various manufacturers seem to do versions of their gravel bikes that come with 650bs from the start, so I guess forks need plenty of width clearance to allow that.

Looking at stock photos of the 2019 fork, I doubt you'd get a 50mm 700C Tundra to work; they come up tall and wide, with aggressive side knobbles. 

I've got one if you want to try it when you're over this way again

I have nothing to offer about gravel. 
 

as far as a road bike is concerned- if you’re not into flat-out speed and want to enjoy road riding, then with that budget I’d start with a pair of hand built wheels on Chris King hubs. The latter will last for years and years and they will be comfortable to ride. 
then decide what sort of frame you want. Carbon, Ti, steel, stainless or alloy. I have one carbon aero, one carbon round tubes, and one stainless. They’re all lovely to ride, but all different.  All are quick. The round tube bikes are both head turners. The aero one just looks like a plastic coat hanger, like all of its ilk. The stainless one will last forever. It’s already been resurrected with two new seat stays after a major fight with a car. They all weigh 8kg or less.

They’re all good for sub-5 hour 100 mile sportives. The steel one has more heft for the hills, but it’s still only 8kg. 
the things, imho, that make the biggest differences are wheels, riding position and brakes.  Wheels don’t have to be the lightest - lightness helps if you spend a lot of time on hills though.  A pair of wheels with Chris king hubs will cost around £1200 now I think. I personally prefer rim brakes to discs, but I know I’m unusual in that, but that’s comparing 105 disc with dura-ace rim.   If you’re trying to crack on, an upright posture will annoy you, but will be fine if you’re just getting some miles in. 
have a look and see what you can find. You can get a lot for your money if you stay away from fancier materials.  I ride on alloy rims most of the time.  A cannondale caad whatever will do you well, for  example.  Finally, have a look at the hills around you as and  decide if a wise man would choose a compact headset. Probably wise if you’re not after all-out speed

Nothing really to add to the good suggestions others have made but the one thing I would say is that before getting any new bike (especially an expensive one), make sure you get a bike fit before you buy. The manufacturer height charts really can't be relied on and a lot of people end up being on a bike that's too big for them, resulting in excessive reach which causes no end of problems. 

For a bike fitter in the north-west I've got nothing but good things to say about Crimson Performance (Alderley Edge).