Compatibility between Shimano 4-piston hydraulic calipers and levers (possible connection to German DIN cargo bike standard)

There are not too many 4-piston calipers by Shimano.

M640 Zee and M820 Saint are identical (calipers), and upon release Shimano claimed to have a ‘slight difference in leverage’ (i.e. a different brake lever) due to ‘much bigger caliper’

It’s my understanding that Shimano pistons are 2 x 22mm in 2-piston calipers, and 2x15mm + 2x17mm in 4-piston calipers.

That’s a difference of around 6%, which doesn’t seem too significant in displacement terms. However they said that things would not work well without the matching lever.

However, in 2017 Shimano released the M8020 caliper, which appears to be another paint job for the Zee/Saint caliper.

And they said it would work just fine with their existing M8000 brake levers (2015).

Then they decided more people would like 4-piston brakes and:

• in 2018 they released XTR M9100, which had a new 4-piston caliper design (M9120) and matching lever
• they updated (or renamed?) their MT500 brake lever (which was itself just a non-series version of the Deore M6000) and called it MT501, and supplied it either with their existing MT500 2-pot caliper, or the new MT520 caliper, which was a lower end 4-pot caliper with straight rather than banjo hose joint. It’s possible that the new part name reflects new combinations of caliper, hose + lever and there is no change to the lever itself, but that I don’t know.
• the next year they released another 4-pot caliper, the MT420, which is lower-end than the MT520 in that it has resin pistons rather than ceramic. And again, they updated the paired levers, so that MT400 (old lever) was only for 2-pot MT400, while there was a new MT401 lever for both MT400 and MT420 calipers.
• they have also released two other versions of M9120, that is M8120 and M7120, and another name for MT520, that is M6120
• this year they have released a new version of their T8000 lever, the T8100. This appears almost identical to the old one, BUT they say that you can use the T8100 lever with the M8120 4-piston caliper (presumably this is intended for e-bikes)

Shimano specifically say in their compatibility guide that the MT400 lever is NOT for MT420, while the MT401 works with both MT420 & MT400.

However I’m not really ruling out that there is no difference between these levers after all. Because on the one hand they could update the specs of the XT M8000 levers with no change in the product to be ok with a new (to XT) 4-piston caliper, but on the other they have (subsequently) released new (?!) levers to go with the new 4-piston calipers on lower ranges.

There is one section in the Shimano Compatibility guide which has me wondering:

https://productinfo.shimano.com/#/com?cid=C-651&acid=C-672

Compatibility for DIN 79010:2020-02C-672
DIN 79010:2020-02
Fahrräder – Transport- und Lastenfahrrad – Anforderungen und Prüfverfahren für ein- und mehrspurige Fahrräder

This is a new German standard for cargo bikes, and it provides

"Brake lever reach adjustment might be required to follow Minimum braking force value of 5.5.1.3"

and then five groups with a weight multiplication factor:

• Group 1 1.5x
• Group 2 1.4x
• Group 3 1.3x
• Group 4 & 5 1.1x

All five groups use 4-piston brakes, but:

• Group 1 is with the XTR/XT/SLX caliper & the most expensive rotor https://bike.shimano.com/en-EU/product/component/mtb-ebike-e8000/RT-EM910.html
• Group 2 is with the identical rotor except without the ‘Super high heat dissipation by black painted radiator fin’ https://bike.shimano.com/en-EU/product/component/e-bike-e5000-series/RT-EM810.html
• Group 3 is the same but with a slightly less fancy rotor https://bike.shimano.com/en-EU/product/component/deorext-m8000/SM-RT86.html
• Group 4 & 5 are with the Deore/MT520 & MT420 calipers

So it seems possible that:

• the levers were updated in some way, and some levers do not work well with 4-piston calipers (though I don’t really see why)

or

• the levers weren’t really updated but Shimano want to get their products certificated and would prefer to re-issue a ‘certified’ combination such as BL-MT401 + BR-MT420, rather than saying ‘you can use this old lever with this new 4-piston caliper’, even if nothing has changed.

Any thoughts?