It doesn't make much sense to spend a lot of money on tires for what you say is a cheap bike, but you can find slick tires with a width of about 1.5" that are great for urban riding. As long as they have a bead-seat diameter of 559 mm, they will fit.
Solid innertubes have notoriously high rolling resistance. I would only choose them for a bike where ...
There is no need to have the same dimensions. To make it short, the width of a bike tire is mostly dependent on your rim inside width (that you can measure when the tire & tube are removed) and frame clearance. Given you'd like something smaller, it's only the rim inside width that is relevant. It's quite easy to find tables (search for: tire rim chart).
Hm. Let’s think about this for a second. Info is specific to Shimano:
Flat mount MTB calipers are just relabeled road calipers. Therefore, MTB levers can properly actuate road calipers.
Accordingly, since road levers and MTB levers can both actuate a 2-piston caliper, one can then deduce that road levers can properly actuate MTB 2-piston calipers.
The problem with your proposal is the spacing of 9 and 10 speed cassettes is different. The 9 speed shifter will pull the 9 speed amount of cable and the derailleur will move the 9 speed space between cassette cogs. If the cassette is a ten speed with 10 speed spacing, the cable pull and derailleur movement (being 9 speed) will be off and shifting will be ...
No, the number of gears you get is defined by the shifter. Even if the cable pull was compatible, which I don't think it is, between Tiagra 9 speed and 105 10 speed, you wouldn't be able access all 10 gears.
The answer is no, you cannot use any of your older shifters, unless they're one of these time trial shifters:
or the satellite shifter:
Shimano has not given any of the other older components the firmware updates required to work with the 12-speed components.
While you can connect those components using the ...
No, Shimano 11 mountain and road cable pull are different. If you want bigger than the 42t that GRX rear derailleurs can do, you're going to either be dropping down a road derailleur with one of the hanger extensions, or using an adapter to a mountain derailleur.