Altus 9-speed shifters&derailleur paired with a 10-speed road bike cassette

Question

My family has a road bike, set with Altus 9-speed shifters and a rear derailleur, paired with a Shimano HG200-9 cassette.

Recently, I replaced the cassette with a 10-speed road bike cassette, As a result, it can shift gears, and all 10 gears on the rear derailleur can be accessed. Some shifts are quite accurate, but some require two clicks to engage. So, I have a few questions:

If I switch to a 10-speed chain, will the shifting become more precise? Read in some forums that the cable pull ratio for 10-speed and above systems on mountain bikes and road bikes is different. Can I keep the Altus left shifter and replace the right shifter with a Tiagra sh-4700, while retaining the original Altus derailleur?

Answer 1

There is no compatibility of any kind between the shifter you have and any 10-speed cassette. Being able to kinda sorta get into all the gears doesn't make it work.

SL-4700 and ST-4700 are incompatible with your RD. They use the Shimano "new 10" pull ratio.

If you wanted to 10-speed the bike, from where you're at now you could try replacing the right shifter with a pre-4700 10-speed road shifter, such as an SL-4600 or ST-4600 (it's unclear whether this if a flatbar bike). Your RD will have the right pull ratio for that, though it's low end and may lack the precision needed to do it well.

9-speed front derailleurs don't work great with 10-speed chains, especially if it's a triple. It can typically be made to work, but if you want it to perform as intended you'd need to address that as well.

If the cassette was relaced due to wear, typically the chain should be replaced with it.

Putting a 9-speed cassette on makes the most sense unless you want to do a major reworking of the bike. If that were the goal, it may be worth identifying what problem you're trying to solve, because doing this just to get a little finer increment between gears is a lot of effort for little gain.