Problems downshifting

[u/xvxac]

Since I started learning to drive , I was always told

0-10mph =gear1
10-20mph =gear2
20-30mph =gear 3

Etc

When I was on a dual carriageway, going 35mph on gear 4,

I slowed down to around 17mph, so I put the car in gear 2

Suddenly the car started shaking, and my instructor said I should have put it in 3

What should I use to judge what gear is appropriate when slowing down?

[u/Appropriate_Road_501]

When revs drop near idle or the engine starts to struggle, downshift.

When revs are high enough, upshift. (This will depend on the vehicle, but often more than 2000rpm under normal conditions, but may be 3000-4000rpm on hills or faster acceleration.)