Any question answered...

Asking for a friend: is it possible to use a 1.2mm shifter cable with a brake cable housing for 1.5mm cables on an 11speed shimano 5800 derailleur? Is it likely to have an impact on shifting performance?

.

Brake housing is (usually) wound so that it doesn't burst under use and make your brakes not work, this also means it compresses slightly in use, that compression means it won't work for gears as they need the cable to move the same amount at the mech as it does at the shifter to index properly.

Much appreciated, I'll pass on the info :)
p.s. the brake canle housing he wants to use is the jagwire elite aluminium 'pearls' one, which is compressionless, would that make a difference?

Inner tubes. On my cross bike I use 28mm tyres to commute and 32mm cross ones for riding around in dirt. Inner tubes generally say 18-25, 23- 28 or 28-42. Which are the best ones both my tyres? Will the 18-25's just stretch up to 32 without issue?

I'd go with the 28-42 as you're gonna be riding cross. Thinner tube is only gonna lead to more pinches right?

The reason I've not just gone straight for the 28-42's is they can feel like fitting a mtb tube into a road tyre and I'm constantly worries about pinching them.

Will the 18-25's just stretch up to 32 without issue?

I've always found the answer to this to be yes, but YMMV.

Yeah same.

What you need of course is Challenge CX latex for the CX tyres and 23-28 for the commuting tyres.

It'll be less shit but just use gear housing for gears, because it's made for gears.

Not me but yes, I'll let him know, cheers!

Challenge CX latex

RRP is £17.50. lol.

What's the proper name for the kind of bolt head that stem bolts tend to have, and where online can I find one that is M6 x 15/16mm and preferably black, which will arrive quickly?

In my experience, you'll want different set of tubes for each pair of tyres, as the tube will stretch when using the larger tyres and be a massive pain to into a smaller tyre.

I've never had an issue using 23/25mm tubes in cross tyres before, so the same size tube will be fine for both, as long as you have a separate set for each tyre pair.

It's a domed head, but search engines seem to bring up button heads, which are a lot shallower...

Not me but yes, I'll let him know, cheers!

These are less than £3 and decent in my experience:
http://www.wiggle.co.uk/lifeline-essential-gear-cable-set-shimanosram/

Thanks for the suggestion but he already has decent shifter & brake cables on his bike. He just wanted to upgrade to the jagwire elite ones cause he likes the look of them and was wondering whether he could use the leftover brake cable housing for the shifter cables to get a uniform finish.

Any recommendations for nice but not too pricey hollowtech 175mm alternative to shimano fc5603 (10sp triple)?

Ultegra or DA off eBay.

^ Ta. Options for new also? 2nd hand likely to have additional cost / faff of replacing worn rings.

Sounds like the reasoning of someone who likes wasting money

Eh?

It'll be much cheaper 2nd hand, if you don't want to replace worn rings, don't buy worn ones on ebay. Buying new is a waste of money

Buying new is a waste of money

What utter shite.

2nd hand also not known if crashed, cross threaded etc, what's in photo might not be what shows up (swap old rings on before post). No warranty either.

Would consider 2nd hand if found some at a jumble and could check out on the spot, but otherwise reluctant.

Still looking for options for possible new, ta.

Ok mate. Soldier on, I'll continue to save money.
If you buy something on ebay that arrives not as described, guess what? You get your money back.