Rotor 3D+ on a PF86 frame with Rotor BB cups

Discuss light weight issues concerning road bikes & parts.
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Omiar
Posts: 218
Joined: Wed Dec 14, 2011 8:20 pm

by Omiar

So I have a Scott Foil, which is a frame with PF86 BB standart. I wanted to have a power meter in near future and got my hands on a Rotor 3D+ crank for a reasonable price. I could now install Power2Max power meter, but I ran to an issue with the plain crank first.
Rotor 3D+ is a crank with 30mm spindle, PF86 standart accepts cranks with 24mm spindle. That's a mismatch, but Rotor has made available BB cups which go into a 41mm diameter PF86 frame and accept a 30mm spindle (http://www.bike24.com/1.php?content=8;n ... duct=34356). So looks like problem solved.

I installed the Rotor 4130 cups and then the crank. The spindle was pre-attached to the NDS crankarm. I put on the DS arm and tightened the center bolt to 30Nm. I used the compression ring to adjust the preload.
Now, when I'm on the small chainring, I can't use three smaller sprockets. The lower I go, the more chain starts to rub against the big chainring and on 38-11 the chain wants to switch itself to the big chainring without actually changing the gear. It helped a little when I put a 2mm washer behind the DS crank and removed the plastic washer from the NDS so it would sit more outward.
I wouldn't mind if the problem was with just the smallest sprocket, but three are just too much for a solution that should work.
Also, when on the big chainring, the chainline looks different when compared to my old Shimano crank. Currently, the chainline is straight on one or two sprockets higher. I'll go to my LBS today and compare to a stock Foil, but it seems to me that somebody has forgot something when this solution was developed.
Scott Foil Ultegra Di2
Scott Scale 35 26"
Scott Spark LTD 29" M8000

thisisatest
Shop Owner
Posts: 1980
Joined: Sat Jun 13, 2009 4:02 am
Location: NoVA/DC

by thisisatest

What cranks were you coming from? Shimano?

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by Weenie


Omiar
Posts: 218
Joined: Wed Dec 14, 2011 8:20 pm

by Omiar

Yes, DA7900
Scott Foil Ultegra Di2
Scott Scale 35 26"
Scott Spark LTD 29" M8000

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Tinea Pedis
Posts: 8416
Joined: Sat Mar 14, 2009 6:08 am
Location: Geelong
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by Tinea Pedis

Found this exact issue on bikes I have tested with Shimano and Rotor chainrings.

The problem seems to lie with the cranks, as it happened on a Fuji and a Cervelo.

thisisatest
Shop Owner
Posts: 1980
Joined: Sat Jun 13, 2009 4:02 am
Location: NoVA/DC

by thisisatest

It's the rings. but it's technically not a "problem", more of a "characteristic".
I described the issue earlier here:
viewtopic.php?t=116422
HELP! problems with Praxis rings on SISL chainset

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Omiar
Posts: 218
Joined: Wed Dec 14, 2011 8:20 pm

by Omiar

The gap difference between DA7900 crankset chainrings and Rotor crankset chainrings is very small, maybe a 1mm max (hard to measure exactly). However, the big ring on DA7900 crank does lean outward, which allows for more cross chaining.
I already had a 1,3mm spacer but I added an extra 3,6mm spacer between the DS crank and BB. I can now use all but the smallest sprocket and the second smallest sprocket is slightly rubbing against the big chainring on the bottom where there is less tension on the chain. It totals up to 4,9mm of spacer. That can't be a problem of chainring only. That is more of a design problem or a very product information.
Scott Foil Ultegra Di2
Scott Scale 35 26"
Scott Spark LTD 29" M8000

by Weenie


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