Information/knowledge about Toyota Vitz 2014

Open the driving door and check the sticker on the door-jam. The actual/recommended size would be mentioned there.
To get the best output from vehicle, ideally you should go for as per OEM recommendation.
But generally people opt 10mm plus size for better looks.
For example, if OEM recommended size is 165/70/R14 then using 175/70/R14 will be fine. But never go for 185

Reason of the knocking noise from engine compartment can be for Engine or Gear Mountings. You can visit workshop and ask them to check if all mounts are good.
Usually they jack up or go beneath the vehicle and give wiggle to engine & gear. But sometimes the worn out mounts tells itself with physical inspection.

Recommended engine oil is 0w-20 or 5w-20 for 1KR.

1. You’re using the correct tire size.
2. Vibrations are also normal in 1krfe. Just get its throttle body cleaned to reduce them a bit. Make sure engine mounts are all good.
3. Use 0w20 fully synthetic oil. Any reputed brand available locally in official capacity, like Havoline, Shell, Toyota. Change after 8000km.

Liqui Moly is unnecessarily expensive - you’ll just be wasting money. Better than LM is Mobil fully synthetic if you really want to spend money for no reason.

I own the same model vitz and what i m sharing with you is my personal experience.
Regarding the tyre size for this model, the oem recommedations are 165/70/14 but due to the ground clearance issue, people mostly go for bigger sizes. I am personally using 185/70/14, although compromising a little on fuel avg. As i am getting 11.5 to 12km/l in city with ac and 14 on long routes with ac. with this tyre size but still having a great experience with drive nd grip. Have been using yoko blueearth es32 series for the past 2years.
If you have no budget issue, go for yokohama, bridgestone or dunlop. Would do the job perfectly for you.

Regarding engine oil, 5w30 is the recommended grade as per oem. Any reputed brand would do the job like caltex havoline, total quartz etc. but make sure it is meeting the Api Sn/ Sn plus or ilsac criteria. Leave liqui molli, too expensive and no need as it ain't any racing car or some mercedes/audi.
1krfe is notorious for noise. You have to live with it. But make sure you are pouring the right engine oil, as i mentioned above as it has alot to do with the engine noise.
Check the cat converter, whether is is present in your car or not. Nowadays cat converters are being removed instead of changing them when choked and you wont notice it until you check it. If absent, it increases the exhaust noise.

There’s a reason why you’re getting such poor average (11 in city or 14 on long). Should easily get 13 minimum in city and 17 on highways.

0w20 is the right engine oil and Toyota recommended, please read any Vitz manual. They even ask to switch back to 0w20 if temporarily you pour in a thicker grade if 0w20 is not available.

Been using 0w20 with amazing performance.

Also, the tire size compromise can be made for ground clearance correct, but it’s again not the OEM tire size and will again affect fuel average.

I am using 185/70/14 size and guess what, still cannot get enough of clearance when my car is fully loaded nd have to be careful with some speedbrakers at times. You have to compromise on something for something as i mentioned in my statement (compromising on fuel avg. ) earlier.
And bhai jee, both are recommended grades.
Please find attached the owners manual.
I am personally using 5w30 nd totally satisfied

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If you want good ground clearance then aftermarket shocks is your best bet.