alexk_il

I am running used TRP Spyres with unknown almost new pads they arrived with. New Ashima rotors, 180 front, 160 rear. By the look of it, front and rear pads are identical, 3.8-3.9mm thick.

I get a decent but not amazing performance in dry weather, maybe need to put more miles on them to bed in properly. Front performs better than the rear.

Took the bike for my first ride in rain today, noticed a significant drop in performance and squeling on the front. Almost no braking power on the foint. Surprisingly, the rear brakes performed well, were silent and actually stopped me.

Any ideas why my front loses more braking power than the rear? If anything, I did more bedding for the front brakes.

FBinNY 

off the cuff, and assuming that nothing is actually wrong with the parts or your installation.

It's very possible that the rotors still have an oil film left over from the manufacturing process. This is especially problematic when wet because the oil and water together form a super slick emulsion.

If this case it will resolve itself with a few more miles including some hard stops (dry is better). Or you can try to speed the process by using acetone on a paper towel and wiping the rotors.
The easiest way it to fold the towel over the rotor , pinch and spin the wheel. WARNING -- while nail polish contains acetone, it also includes oil which will leave a fresh residue.

Otherwise, look to installation issues like a kinked cable, bad routing, etc. I sometimes us a dollar bill test, placing a dollar bill between brake and rotor. It should only take light finger pressure to trap the bill so I can't pull it out, leaving plenty of lever room to ramp up braking force beyond that.

Andrew R Stewart 

Disk brake pad bedding is generally thought of an initial use requirement, not a many miles result. If not bed in well at their beginning we do see more noise and "power" issues later.

disk pads are like sponges in that they soak in any contaminates. Be they hand/skin or chain oils, cleaning products and road surface splash ups. Sometimes cleaning rotors will help, I suggest a last wipe off after other cleaning products of 90%+ alcohol. Now cleaning the pads is another thing. Sometimes a sanding of their surfaces can refresh them. Sometimes the sponging up was too deep. Often we replace the pads to insure best first results. Andy

pdlamb

INCONCEIVABLE!! Everybody who posts on the internet knows disc brakes are a panacea for wet weather braking! How dare you post about an actual experience, and one that counters what Everybody knows?

Ahem. Had to get that off my chest.

It's almost got to be contamination of the front disc or pads. Have you (or the previous owner) removed the front wheel and perhaps touched the disc, for example to put the bike in a car?

alexk_il

One of my kids is genuinely confused between a pocket fidget spinner and the front wheel of my bike on the stand. Bingo! I think you nailed it. Will try sandpaper and isopropyl alcohol next week, hope it will improve the front.

pdlamb

Ah, yes. You might try a dishrag with Dawn and water to wash away the chocolate and potato chip grease first.

Trainbike

It's also worth checking the alignment of the calipers and the compatibility of rotors and adaptors. (Just make sure the whole pad contacts the rotor) on those brakes I like to slightly loosen the mounting bolts so the caliper has play, pull the lever, then tighten the bolts so it will be centered.
Also
My go to with disk brakes is: Rubbing alcohol or brake cleaner the rotors wipe with a clean paper towel. Pop out the pads and take a look at them, they should be worn symmetricaly, often you can see contamination but not always. put a bit of sandpaper on a level surface and rub the pad ontop of it in circles. Clean the pad with alcohol again and reinstall.

streetsurfer

In defense of noshers around the world….it was aliens.

Or maybe the petrochem contaminants from the street surface thrown up in road spray.

bikebikebike

2 alexk_il
If your kid is young and anywhere as dumb as I was at that age
be careful,
as sharp rotor edges have amputated kid's fingers to the point of CPSC recalls.
https://thehill.com/blogs/blog-brief...lds-fingertip/

alexk_il

Thanks.

Got the sandpaper, finger crossed it will help. Another trick I learned from another thread is to swap rotors/pads from the good wheel to see if the problem is with these or with the brake itself.

alexk_il

OK, found the reason for loosing the power on the front while having a decent power on the back. Turned out the fixing bolt of my right brifter wasn't tightened properly and the brifters sligtly moved down the drops causing slack in the brake cable. Took me a while to figure it out, the braking was so inconsistent during the re-bedding time that I finally started to suspect that it's not the usual contamination or cable tension thing. And then I found the lose position of the brifter.

I also noticed that the rotor "ate" about 1mm of each of the pads on the front from that single ride in the rain. I guess I have to get better pads.

squirtdad

too bad....i liked the idea of blaming the cookie muncher

alexk_il