What is the ideal lifespan for a circulation design series?

[quaziright]

Doesn't the Japanese series look the same since the end of WW2? maybe I"m mistaken?

[Pabitra]

Apart from Japan, coins of Israel, Kuwait, Kenya etc. may also need a fresh look.

[Alan71]

I would say there doesn't need to be a time limit, it should depend on how good the series is and whether the designs have dated.  Canada's designs date from 1937, I think, and they still look good. Most series that predominantly depict wildlife seem to last, such as Australia's or (some of) New Zealand's.  <k>, I think New Zealand's original 10c design is still in use, but on a different colour coin.

Jersey's landmarks also look good.  As with wildlife, it's depicting something that isn't going to change. 

The UK series don't date as well as they're depicting something that isn't really "real".  Be it heraldry or Britannia, a new artist can come along with a different interpretation and a more modern design. I know you could say that about wildlife (for instance New Zealand's kiwi when it moved from 20c to $1), but by and large there's less of a need to change something that's "real".

New denominations coming along with designs that aren't too sympathetic to what's already there are also a factor.  For instance, the UK 20p in 1982.  Still the denomination going round the top in words and the numeral at the bottom, but it otherwise looked quite different to the Ironside designs with their spaced-out lettering.

Isle of Man had very restricted themes for each series, and presumably intended to have a limited lifespan.  Gibraltar went off the rails in the mid-2000s by introducing and then moving designs around the denominations.

The proliferation of circulating commemoratives is also a factor.  With so many designs appearing year-on-year, the long-standing permanent designs can act as a common reference point. 

I'm hoping the lifespan of the Dent designs on UK coins is as short as possible.  We're 11 years in so only another 29 until they reach Ironside's...

[Pabitra]

Many countries have almost given up on coins. Their last known circulation. Series may hardly be of any guidance. Some of them are Vietnam, Lao, Cambodia, Bhuran, Myanmar, Liberia, Iraq, Nigeria, Mongolia etc.

Pakistan has changed all designs in last few years.

Sri Lanka is due for a new stainless series this year.

Nigeria had a 3 coin series in 2006 but now abandoned. Similarly, Myanmar, Iraq and Afghanistan had a new series not very long ago and they were quite a change from earlier series.

Sierra Leone, Cuba and Liberia announced some series but there does not seem to be any progress, as also with Iceland.

Each country is a specific case and needs to be studied in detail.
Pakistan will never change its obverse but reverse has been changed significantly.
UAE may follow Saudi Arabia which recently revised its series .
Bangladesh too revised its series with effigy of Sheikh Mujibur Rehman, not very long ago.
Swaziland has changed its obverse with change of King as well as ageing effigy.

Oman revised its Coat of Arms few years back, very minor changes, like Russia two years back and Romania this year.

[<k>]

I would say there doesn't need to be a time limit, it should depend on how good the series is and whether the designs have dated.  Canada's designs date from 1937, I think, and they still look good.

I'd be in favour of modernising them now, but not in the style of their recent commemorative and special issues, which is very poor:

Most series that predominantly depict wildlife seem to last, such as Australia's or (some of) New Zealand's.

Most do, it's true, and I'd probably miss them if they were changed.

<k>, I think New Zealand's original 10c design is still in use, but on a different colour coin.

You're right. It's the Maori tiki (?) head.

Jersey's landmarks also look good.  As with wildlife, it's depicting something that isn't going to change. 

A superb set, agreed.

I'm hoping the lifespan of the Dent designs on UK coins is as short as possible.  We're 11 years in so only another 29 until they reach Ironside's...

Let's hope they die before I do. 

[<k>]

Pakistan has changed all designs in last few years.

Thanks for the info. I've deleted Pakistan (and Bangladesh) from my list.

Sri Lanka is due for a new stainless series this year.

Will the designs change too?

Swaziland has changed its obverse with change of King as well as ageing effigy.

True, but the reverse designs, though nice, largely stem from the 1970s.

Oman revised its Coat of Arms few years back, very minor changes, like Russia two years back and Romania this year.

Quite a few Arab countries could do with adopting modern thematic sets. I loved the Romanian historical personalities of their 1990s set and am quite sad that they were replaced by such a boring series.