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RhynoCZ |
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 RhynoCZ Super Spammer

Joined: 09 Mar 2012 Karma :     
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 Posted: 15:26 - 24 Sep 2020 Post subject: Road bike gearing question... |
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Hi, this might be a simple one, but I've recently got a road bike with 2x9 gearing. Piror to that I was used to ride 3x7 (to 9) gears and knew that you can't cross the chain too much but this lead to griding noise and I just shifted the gears accordingly. Also, the middle front cog was universal for the full range of the cassette.
Now, the 2x9 setup, yesterday I went for a ride, having the small cog front and somewhere in the middle of the casset back, after a climb. Then I wanted to speed up, shifing the casset down to the lowest gear when all of the sudden, when putting more power to the cranks, without prior griding, the chain caught on the big front cog.
Now, do I have an issue or one just should never ride the small cog front with the smallest cog or the one before that in the back, on such bike? When using the big front cog I can use full range of the cassette.
I use the Shimano SORA R3000 Compact groupset. ____________________ '87 Honda XBR 500 - '96 Kawasaki ZX7R P1 (sold) - '90 Honda CB-1 (sold) - '88 Kawasaki GPz550 (sold)
'95 Mercedes-Benz w202 C200 CGI; At my disposal: MZ 150 ETZ, not anymore. |
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weasley |
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 weasley World Chat Champion

Joined: 16 Oct 2010 Karma :    
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Ste |
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 Ste Not Work Safe

Joined: 01 Sep 2002 Karma :   
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 Posted: 17:30 - 24 Sep 2020 Post subject: |
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Sounds like someone needs to adjust the H and L limits on their derailleurs.
As weasley says, cross chaining is something that you shouldn't do but riding with the chain on the small front chainring and the smallest gear on the rear cassette shouldn't cause the chain to try and change to the bigger chainring at the front.
Once you've set H and L limits on the derailleur and indexed your gears properly you'll have silky smooth shifting and it won't try to change gears on its own. A quiet bike is a happy bike.  |
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Easy-X |
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 Easy-X World Chat Champion

Joined: 08 Mar 2019 Karma :   
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 Posted: 20:02 - 24 Sep 2020 Post subject: |
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Read this...
https://www.sheldonbrown.com/chainline.html
...there will be a test later  ____________________ Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter |
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ThunderGuts |
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 ThunderGuts World Chat Champion

Joined: 13 Nov 2018 Karma :   
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Ste |
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 Ste Not Work Safe

Joined: 01 Sep 2002 Karma :   
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 Posted: 12:50 - 16 Oct 2020 Post subject: |
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The bottom bracket for the groupset only comes in one size so it's unlikely that the wrong size has been fitted.
I'd expect that the frame width at the bottom bracket will be 68mm so there will be 2mm of spacers and I can't be arsed to check the manual from Shimano to see whether they all go on the drive side or if it's one 1mm spacer on each side.
Shimano manuals and instructions are good, they're really good.
I'm guessing that Rhyno has fixed it as he hasn't returned to this thread? |
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ThunderGuts |
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 ThunderGuts World Chat Champion

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Ste |
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 Ste Not Work Safe

Joined: 01 Sep 2002 Karma :   
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 Posted: 14:00 - 16 Oct 2020 Post subject: |
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ThunderGuts |
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 ThunderGuts World Chat Champion

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RhynoCZ |
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 RhynoCZ Super Spammer

Joined: 09 Mar 2012 Karma :     
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 Posted: 17:07 - 17 Oct 2020 Post subject: |
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Ste wrote: | I'm guessing that Rhyno has fixed it as he hasn't returned to this thread? |
Well, yes and no. I went through the Sheldon Brown's site, watched some Park tool videos as well, and I did adjust the rear derailleur again. Very nice and quick shifting, no noise, the derailleur stops exactly where it should. Then, I had a look at the front derailleur. Fidling with the cable adjustment and L and H limit screws. I was succesful, the derailleur cage stops where it should, shifting is smooth and quick and there is no apparent rubbing.
Now, that being said and I think the bike well adjusted, I found out what probably caused my ''issue'', appart from forgeting how to used the gears on a bicycle. The frame (or something else) flexes under load, not very much but more than enough for the chain to rub against the derailleur cage when running the front big sprocket (50t) and the rear smallest one (11t) or the one next to it (13t). This doesn't happen when testing the bike in the stand with no actual load, so it's either the frame flexing or something is loose, I guess it's the frame.
So, my wild theory is, one of the magnets around the big front sprocket pulled the chain ''up'' just when I was putting some ''serious'' power down onto the cranks. As said before, there was no prior rubbing/grinding. But hey, I've learned my lesson and ever since then I just don't cross run the chain and I'm also more aware of what gears I use and when. The frame (or something else) flex remains though, so next I'm gonna try to set the 4th index position of the front derailleur shifter so there is enough room for the front big sprocket to ''wobble around'' under ''heavy'' load.
I've never had such gear ratios on a bicycle that would alowe me to flex the frame under load. Or am I just that strong these days? Perhaps the frame isn't the best, considering it's an entry level bike from Decathlon.
EDIT: And yes, Ste, the BB-RS500 bottom bracket is exactly what's on the bike.  ____________________ '87 Honda XBR 500 - '96 Kawasaki ZX7R P1 (sold) - '90 Honda CB-1 (sold) - '88 Kawasaki GPz550 (sold)
'95 Mercedes-Benz w202 C200 CGI; At my disposal: MZ 150 ETZ, not anymore. |
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Dave.... |
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 Dave.... Trackday Trickster

Joined: 13 May 2016 Karma :     
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Ste |
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 Ste Not Work Safe

Joined: 01 Sep 2002 Karma :   
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RhynoCZ |
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 RhynoCZ Super Spammer

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weasley |
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 weasley World Chat Champion

Joined: 16 Oct 2010 Karma :    
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Ste |
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 Ste Not Work Safe

Joined: 01 Sep 2002 Karma :   
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 Posted: 16:12 - 19 Oct 2020 Post subject: |
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Unfortunately derailleur trim functions is all new to me due to not being a road bike person.
Having watched a few youtube videos about front derailleur trim adjustment it does look like it could be the answer to the problem your having. As it's a topic I know nothing about, I'm reluctant to recommend any particular videos therefore all I can say is start at the top of the page and work your way down. https://www.youtube.com/results?search_query=derailleur+trim+adjustment
It's going to be something that's really quite simple to fix as the setup is so nearly perfect, it's just one combination of gears that's unhappy. Personally I'd do some reading up / youtube video watching on trim adjustments and then try playing around with those.
There is flex in your frame (and other components) but there would have to be something seriously wrong for for the flex to be the cause of the problems you're having.  |
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