I've been trying to find out what year the M858 was released, @sillyoldman, so thanks for the nudge - I remember that model well. It seems to have been quietly deleted from Shimano's SPD timeline in the interim. I seem to remember they were pretty stiff to use, but they did allow a 'straight down' engagement... I'll quiz Shimano on your/our behalf 🙂
Strangely, there's no mention of the 858 in Shimano's SPD history - http://www.shimano.com/en/100th/history/products/result.php?id=52 but I'd agree that they appeared in 2000 or so.
I'll add a postscript...
I think we might have at least one pair of 858s in the garage. I don’t really remember them being that bad.
I have a set of M959s, will I die if I use them on my new gravel bike? Anyone know if I need the SH-52 cleats of if I can use the new cleats?
I don't care about UDH, wireless gear changes, carbon rims or upside down Enduro forks; a new Shimano cleat is the most exciting mtb development for a long while. I expect to be using a set until they wear paper thin sometime in 2040.
I just retired my Dura Ace 7410 pedals after 25yrs of solid service, they took an sh-70 cleat.
I loved those pedals,very roadie minimalist ,and I could use mtb shoes ,so avoided the 'penguin' walk at cafe stops.
I believe they have essentially taken away a bit of material from the front and possibly back of the new cleat. As a result they might wear out quicker than the existing cleats, but I guess that it a small price to pay for the benefits.
The Nukeproof SPD cleats have a chamfered front. They are way easier to engage than the SH-51 cleats, so I can imagine these new Shimano ones will be as well (hope so, as the NP ones are few and far between these days).