[quote=Andrew_Squirrel]Welp, looks like the Hope RX4 experiment was a complete failure.
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Hope RX4 Front:
Can’t use on the fork because 160mm IS to Postmount adapter hits one of the 4 pistons that hang low (fits fine with 2-piston BR-RS785 caliper).
I could possibly upgrade to 180mm rotor because caliper clears the 180mm adapter but I also discovered that IS mount is too far inboard to allow the caliper to center on any size rotor. DOH! Should have checked that before putting the bike under torch and powdercoat.
Hope RX4 Rear:
Had it sort of working on Saturday for our quick overnight camp but was getting some weird rotor rub that got louder as time progressed. You could reset the noise by flicking the lever.
Got it home, checked the centering and discovered that the new orange powdercoat was thick enough to make the already hairline acceptable tolerance even worse. As I mentioned last month the rear IS disc tab is also too far inboard similar to the front but was barely acceptable with the brown powdercoat. New orange powdercoat thickness has pushed it over the acceptable limit and I can’t center the caliper which was already at the end of the slot.
Also discovered that 4 pistons have their own set of issues, one of the smaller pistons didn’t want to cooperate even after pushing them out, cleaning them with alcohol and cotton swab then reapplying mineral oil to the sides of the pistons. While setting them up I also noticed its a pain in the ass to remove the pads out of the caliper because the right angle banjo & hydro line get in the way with my weird hose routing orientation (caliper on chainstay, hydro tube along seatstay).
For a second I thought I could pull off BR-RS785 on the front and Hope RX4 on the rear but needing to carry two different replacement pads on extended tours and dealing with bleeding two different styles of brakes left me thinking I should just get an XT caliper (for the banjo) to have the front and rear mostly match for ease of everything.
Also, Shimano calipers are amazeballs and easy to bleed compared to the Hopes. Not being able to turn off the bleed hole on the RX4 seems like a stupid design.
Overall it was an interesting learning experience for my first hydro bike. It also changed my feelings about chainstay mounted disc calipers. Going forward I would only recommend chainstay mounting if the frame builder has figured out an easy way to get a allen key to the mounting bolt (closest to the dropout) that secures the caliper to the adapter. Even my extra long Park Tools T-handle driver had a hard time getting into that tight spot. Imagine trying to recenter your caliper in the field only to discover you can’t get your multi-tool close enough to the bolt.
Its crazy that all this trouble is my fault because I really wanted to run the hydro line along the seatstay and toptube instead of the chainstay and downtube.
In conclusion:
The only person I can blame is myself
Chainstay mounted calipers are kinda dumb if you need to adjust them in the field because the seatstay gets in the way.
If you are a frame designer make sure your IS tabs are further outboard because its easy to shim them inboard with washers if needed but the opposite is impossible.
4-piston brakes seem like more trouble than they are worth for road/gravel centric use, doubles the likelyhood of piston issues.
Shimano is awesome (except for the BR-RS785 which doesn’t accept right angle banjo connectors)
Dented an A23 somehow (jumping, probably) on my grando. Didn’t pop the tire though. Probably gonna just yolo it until it cracks, might try to bend it back into shape with pliers.
^is it bent in or out? I heard out is usually the end of the rim.
Opened the garage today to check shifting on jekyll as it was getting funky at Mountain Creek.
After cleaning it and tuning the shifting, I notice the Evil Following and the rear tire off the rim.
Second Maxxis tire in as many weeks just going fuck all, though this happened off the bike and in the garage (not at Snowshoe like last one). But same story of bead/casing just getting fuxxed and tire blowing off rim at 15psi. First was a DH casing that has 2 rides on. This was double down casing, with many more rides, but tread is great.
Andrew that is some grade-A first hand experience thanks so much for the explanations.
Is there room in there for a typical hex-head screw, to be used with an open end wrench?
You’ve probably already explored this, but a search for “stubby short arm 5mm allen” brings up some options too. Or just cut down one you already own.
Somewhere out there is a bicycle multi-tool that has L-shaped allen wrenches, but damned if I can remember what brand it was.[/quote]
Thanks for the tips, I will take a look
I forgot to mention earlier that I really exacerbated the issue by deciding to have the rear light barrel braze-on located halfway down the seatstay where the allen T-handle needs to rotate.
Starting to realize I’m building an obsolete disc bike with IS mounts and QR skewers.
If I had half a brain and better knowledge of disc brake tech I may have changed course earlier.
Also heard back from Hope, must have missed that tidbit on their website (maybe they added it after my first reading?). I incorrectly assumed all postmount calipers were backwards compatible with all IS mount frames.
[quote]Hi Andrew,
Thanks for your email – unfortunately as mentioned on the Hope RX4 product page the RX4 is not designed for IS mounts, partly due to the fitment issues you have experienced. The only way the RX4 will work with IS is using our MOUNT F which is a 180mm front minimum, before using this mount however you should check with your fork manufacturer that this isn’t too large, for both fitment and safety.
As for alignment issues until a correct mount is fitted I cannot comment, but as stated the caliper is POST mount only.
Sorry I can’t be of any more help at this time.[/quote]
He was saying I could upgrade to that spacer and get a larger rotor but would need to contact the framebuilder to verify if 4 pistons and a 180mm would be too powerful.
I suspect he saw the high rake of the fork and was like WTF are these PNW nerds smoking.
[quote=Andrew_Squirrel]He was saying I could upgrade to that spacer and get a larger rotor but would need to contact the framebuilder to verify if 4 pistons and a 180mm would be too powerful.
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Generally, bigger rotors equals lower fork loads, though heavily cantilever adaptors could complicate the analysis.
RE 180mm rotor:
I am definitely not trying to make the RX4 calipers work at this point. Accumulation of too many small problems to make the issue worth overcoming.
I just wanted to share my experience for others that were considering.
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WTF are these PNW nerds smoking.