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Big/Big and Little/little (sprockets)

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Big/Big and Little/little (sprockets)

Old 07-07-19, 03:39 PM
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sirjag
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Big/Big and Little/little (sprockets)

So I have a new Giant Contend SL Disc. It came with the Shimano 105 group set. 50/34 up front and 11-32 in the back (11 speed).

I was told to never drive in the 50 - 32 or 50 - 28, as well as the 34 - 11 or 34 - 12.

When I got the bike the front derailer needed some adjustment so I made it to where I get never touching on the front derailer in either sprocket selection except on the final two gears on each end of the spectrum. Is this normal? Should I have no rubbing anywhere up front? And I am not sure how that is possible...11 gears is a lot!

Thanks yall, new to cycling but I am learning much here.

JAG
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Old 07-07-19, 03:49 PM
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The big-big and little/little combos are called “cross chaining” and although you want to avoid those combos, you can use them briefly if you need them. Ideally shift the front earlier in your sequence but that will come with time. Learn to use the “trim” on FD to minimize chain rub.

The reason to avoid these is because they do cause more wear on your cogs (as chain has too much sideways angle).

But again, you can use them. Try to make it a rare use.
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Old 07-07-19, 03:57 PM
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The Shimano 105 shifter for the front derailleur has 4 different positions: L-trim, Low, T-trim, Top.

The L-trim and T-trim are there so the rider can trim the derailleur and keep it from rubbing when in the "big front-big rear" and the "small front-small rear" combinations, respectively.

The Shimano dealer manual has detailed instructions on how to adjust the front derailleur. If you follow it carefully, you'll have a perfectly adjusted derailleur.

Shimano : Dealer's Manual : Front derailleur
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Old 07-07-19, 03:57 PM
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sirjag
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Originally Posted by datlas View Post
The big-big and little/little combos are called “cross chaining” and although you want to avoid those combos, you can use them briefly if you need them. Ideally shift the front earlier in your sequence but that will come with time. Learn to use the “trim” on FD to minimize chain rub.

The reason to avoid these is because they do cause more wear on your cogs (as chain has too much sideways angle).

But again, you can use them. Try to make it a rare use.
Sir, thank you for this information!

JAG
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Old 07-07-19, 04:03 PM
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WOW! Reading that PDF....the place i purchased from did not install the backup plate as shown on page 7! No wonder i could never get it set correctly...that 1/16 of play was maddening.
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Old 07-07-19, 05:29 PM
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That instruction is a hold-over from the past when chains were wider and less flexible.

Cross- chaining with 10/11 speed equipment there's a bit more friction & maybe a bit more wear, but it's not significant.

I spend a fair amount of time in the big/big combination & my chains go ~7,000 miles & the cassettes are fine as well.

It can be tricky to have no rubbing at the extremes, I favor the big/big end since I hardly ever use the small/small.
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Old 07-07-19, 06:21 PM
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Newer chains like the Shimano ones handle cross chaining much better than they used to. Still good to avoid, but less of an issue than before.
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Old 07-07-19, 11:24 PM
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If you need to compromises your FD make is so it doesn't rub in big big and don't worry about little little. There is really no reason to use little little. You are going to spend most of your time on the big ring and it is nice not having to shift the FD every little rolling hill you hit so big big is nice to have as an option more so with an 11-32 in the back.
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Old 07-08-19, 01:26 AM
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Even with a 7 speed cassette I avoid using the small /small and large/ large cogs as a general rule of thumb. Even the middle chainring I prefer the 5 middle cogs.

That said, I will use any combination in a pinch, which with 7 or 8 speeds may still keep the chain angle reasonable.

With an 11 speed I would avoid the sprocket combinations suggested, But in a pinch, I might use all but the big/big, small/small combo, and the 9 middle cassette cogs with the middle chainring.

There is a chart I stumbled on searching for gear inch calculations that shows a small chain angle using the above recomdations.

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