TobFromme

Hello everyone,

I recently upgraded my bike to a 2020 Trek Domane SL6, which has the Shimano Ultegra R8000 crankset. The bike was great for the first 50 miles, but then I noticed some rubbing when in the higher gears on the cassette and on the large chainring.

After inspection, I noticed the chain was rubbing the outside resin pad of the front derailleur. Utilizing the Shimano dealer installation guide, I was able to adjust the front derailleur and the chain no longer rubs. The clearance between the outside pad and the chain is approximately 1 mm when on the largest chainring and smallest cog.

However, it also brought on a concern. After adjusting everything to fit, there's only a 1mm gap between the front derailleur and the crank arm. I've never seen a gap this small before. I'm going to have my LBS check it as well, but wanted to check with others who may own or have more experience with this bike.

Is this normal?

Thanks!

blamester

If it doesn't hit it it's fine. The crank will never deflect a mm nor will the seatube. You could probably adjust the FD back towards the chain. I leave them so they just clear the chain
Ride it and bring a small screwdriver to adjust it perfectly. They don't always work the same on the road as the stand.

TobFromme

Thanks for the reply. I wasn't sure how much clearance was enough. My son's Domane AL2 has approximately 7-10mm of clearance from crank to front derailleur, but it's a Sora set.

I'm new to the bike mechanic scene, but have been wrenching on various mechanical things all my life.

blamester

So long as you are sure it stops on the limit screw and not from cable tension you are good.

TobFromme

Before I removed the cable and started from scratch, I noticed a few things:

1. The cable tension screw was all the way in. Odd for a new bike
2. The low limit screw was almost all the way out. Any clockwise turns would cause the chain to rub on the inner pad when on small chainring and large cog.

After my re-install, the low limit screw is in approximately the same state as originally found. The cable tension screw is almost all the way out (i.e. it's placing any additional tension on the cable). Any way I can tell if I don't have it adjusted properly? From a video by Le Mechanic , it's adjusted similar to his.

TobFromme

I should also add that my R8000 FD does not have the metal backing plate on the seat tube. One mechanic explained this was a backup system to support the FD and, to be honest, doesn't mesh with the Shimano instructions. It seems this would put a lot of unnecessary pressure solely on the FD mount.

I'm asking for that plate to be installed and they are going to go through this again. I want to be certain I come away with a clean install.

blamester

I don't know what the backing plate is but Shimano have a lot of experience designing derailleurs and they build them strong enough.
Don't over think this, it's a lever and a cable. With a little practice they are a doddle to adjust.
​​​​​​Ride it and bring simple tools and tweak it as you go. Once it is close use tiny adjustments to perfect it.
What do you mean by the cable tension screw? Is that the barrel adjuster?
When it is set up right you don't really need that.
And tbh your sons bike sounds like it is wrong.

​​​​​

TobFromme

My son's bike is fine. It rides and shifts fine.

For the R8000, there is a tension adjustment screw, similar to a barrel adjuster. Le Mechanic has a great video on the R8000.

I wasn't referring to the strength of the FD. Rather, I referred to the strength of the mount. On the R8000, Shimano states a backing plate should be adhered to the seat post. Then a stabilization screw, if your will, is then tightened into the plate to support the entire FD during shifting. So, instead of only supporting the FD by the front mounting plate, it is supported in two places.

I dropped off my bike at the LBS yesterday and one mechanic says it looks perfect. We agreed to have the owner check it out as well, as he has more experience in the higher end bikes. From what the mechanic has seen, a 1-2 mm clearance is more than enough.