JackJohn

Yes sure thing, the Shimano br-r451 calipers mentioned above are among those recommended and apparently the only available for purchase. Curiously, they’re also labeled “New” super slr, like those incompatible I have, but have longer reach, maybe this makes them eligible. Anyway, think I’ll have no choice and they respect manufacturer recommendations, so I’ll go for those. Having said that, clearly Shimano is not making things simpler on this issue...

Iride01 

Are you squared away with your knowledge as to what long and short reach means for brakes? Bikes typically need one or the other. Seldom will both work well for a particular frame and rim diameter.

JackJohn

Thanks for raising the point, currently used calipers have a max. reach of 51mm, they’re set at maximum extension and correctly fit on the rim, so I conclude that 51mm is the needed reach for my frame. The br-r451 calipers I should buy have a 57mm max. reach, but the lower end of the range is not specified on the Shimano page:
https://bike.shimano.com/en-EU/produ...o/BR-R451.html
The vendor I’m looking at specifies a 47-57mm range, so the needed 51mm should be within. Unfortunately I can’t find more details, I’ll try to contact Shimano again.
Should the 47-57mm be confirmed, do you think such calipers could properly fit and provide adequate braking?

smashndash

The proof is in the pudding at this point. We've done as much due diligence as one could possibly hope to have a consumer do. Unfortunately, there are no guarantees in this industry. There are claims, and there are results. The only way to verify those claims is to buy and test. Shimano tends to live up to their claims pretty often, though.

JackJohn

thanks, I agree. Only my last comment and question referred more to the reach issue (i.e. the remark that bikes need long or short reach, whereas min reach for the new calliper is not specified) rather than compatibility issues, on which as you rightly said there’s been enough talk and now it’s time to buy and try.

JackJohn

There we are, the new compatible r451 calipers arrived. They’re labelled NEW SUPER SLR, just like the non-compatible r4700, which seems weird.
First I have to say that while waiting I fine-tuned the 4700 by getting the pads closer and more parallel to the rims, then tried again but on dry conditions only. Rear braking felt ok, with the wheel slowing and then quickly skidding. On the front it was better than before. Using both, the bike could stop in a reasonable distance, although my 26’’ v-brake mtb still did better.

Then I installed the new compatible calipers and gave them a try always on dry conditions. Rear braking was the same and if anything, not better. Front braking seemed marginally better, but cannot tell with certitude, the difference not being significant. So here are my conclusions:
- difference between non-compatible and compatible calipers is not tangible, at least on dry conditions, still needs to be checked on wet
- the extra 45$ spent on the new calipers are not worth if related to braking power only, but they at least bought some peace of mind when looking at Shimano compatibility recommendations
- Shimano compatibilities remain opaque to me, ok one has to stick to official guidelines, got it and will check them in the future before buying new components, but after having mixed levers/cranksets/derailleurs in the past which worked fine, and after this calipers experiment, I keep wondering if marketing weighs somehow on such guidelines...

Thank you all and hope this feedback might be useful...