front derrailler & gear change

anoble66

hey,

Just a quick question from someone who has just got their first road bike (planet-x DA 7900). Apologies if this is a stupid question!

At the moment when I try to change from the 34t cog to the 50t cog on the front it will take 2 gear changes to move from the small to the large. And the same to drop back down.

The question is, is this normal? Is the gear change pre-set for a triple or something? I notice the other halfs does the exact same and we have completely different bikes / group sets....but both shimano

Apologies for such a stupid question but I have already spent the entire day trying to fix this and ended up going back to shimano's recommended settings which brings back the same issue.

thanks

DirkVoodoo

Check the shimano tech docs (which I'm guessing you are using) for details on "trimming". Basically, you can adjust the front derailleur so it moves between each ring, but you can also move it a smaller amount on each ring to stop rubbing. So if you are in 34-25 and move to 34-16, you give the front lever a small push and it will shift more to the right without shifting rings so you can use this gear without rubbing the chain.

Of course this doesn't permit chain crossing, don't run the chain at extreme angles, not good for chain and cassette wear.

anoble66

thanks for the reply dirkvoodoo. I am indeed using the shimano docs for trimming. Everything looks right, chain guide is approx 2mm above largest gear and is parallel. There is 0.5mm of space between chain and chain guide inner plate when I am in the small gear at the front and the large gear on the rear. The problem is, I shift once - no change on the front. Shift again, now it goes into the large front cog. I have tried all day to get it right, and I found if I increase the tension on the front barel adjuster then I can get it to shift up on the first try but it will then not shift back at all....I then tried un-tightening it slightly but that didnt work either....plus once its tightened to the point where it changes on first attempt, the chain is hitting off the chain guide so that cant be right either.

man this is complicated

Any other advice or tips would be welcome!

thanks

anoble66

AHHH wait, the penny has just dropped for me. So basically this is working correctly. So, if I did need to use the extremes of the gears, I could change up once, which doesnt really change it but just bumps the front derailler a litle......makes sense now! Cant believe I have spent about 7hrs on this

DirkVoodoo wrote: »

Check the shimano tech docs (which I'm guessing you are using) for details on "trimming". Basically, you can adjust the front derailleur so it moves between each ring, but you can also move it a smaller amount on each ring to stop rubbing. So if you are in 34-25 and move to 34-16, you give the front lever a small push and it will shift more to the right without shifting rings so you can use this gear without rubbing the chain.

Of course this doesn't permit chain crossing, don't run the chain at extreme angles, not good for chain and cassette wear.

Morgan

anoble66 wrote: »

I shift once - no change on the front. Shift again, now it goes into the large front cog

I haven't used Dura-Ace shifters, but it's very likely you can move from the small to large chainring in a single movement - just keep pushing the shift lever until it clicks twice - same for downshifting (works with SRAM).

Lumen

I'd add that there's nothing really wrong with cross-chaining, in the right situation. That's why the trim function exists.

If you're zipping up a short sharp hill, you don't really want to be going into the small chainring for a few seconds, especially with a compact.

(and no, I don't want to start another discussion about the (dis)merits of compacts)

anoble66

thanks very much everyone for your replies, I am going to enjoy the cycle more tomorrow knowing everything is as it should be

Weighed the bike today 5 times to be sure, a nice 7.1kg - very happy with that

DirkVoodoo

Lumen wrote: »

I'd add that there's nothing really wrong with cross-chaining, in the right situation. That's why the trim function exists.

If you're zipping up a short sharp hill, you don't really want to be going into the small chainring for a few seconds, especially with a compact.

(and no, I don't want to start another discussion about the (dis)merits of compacts)

The trim function exists to increase the usable number of gears, crossing the chain from biggest rear to biggest front, and vice versa, does not come under what the manufacturer would probably classify as a "usable gear". Selectable, yes. Usable no.

If you want to increase the rate of wear of your drivetrain, then by all means cross chain. It's not a good habit to develop.

Lumen

DirkVoodoo wrote: »

If you want to increase the rate of wear of your drivetrain, then by all means cross chain. It's not a good habit to develop.

This is not the only place I've read this:

The RED front derailleur gets a titanium cage and loses 30 grams over FORCE. Although controlled by the front shift lever, the front derailleur’s one trim position has moved from the small ring to the big – based on pro rider feedback who spend the majority of their time on the big ring.

In a race, why would you want to switch chainrings if you can achieve the required gear ratio more quickly using trim?

DirkVoodoo

Lumen wrote: »

This is not the only place I've read this:



In a race, why would you want to switch chainrings if you can achieve the required gear ratio more quickly using trim?

That's fair enough, but for the non racing folk who have time to shift between chain rings is this really an issue? If you want to make your cassette/chain last as long as possible, besides cleaning and lubing regularly, avoiding cross chaining is the obvious solution. Fine for the pros who don't need to worry about cost and performance is the primary concern.

Also, I don't think any amount of trim will allow you ride 39-23 or 25, then angle still has to be the same you are just avoiding any rubbing.

EDIT: When I was riding in Planet-X's grupetto earlier, I shifted down on the front when we hit the first hill on the second lap. Granted we weren't racing at that point but the bunch was still moving quick and I didn't slip out the back (shock!).

Lumen

DirkVoodoo wrote: »

That's fair enough, but for the non racing folk who have time to shift between chain rings is this really an issue? If you want to make your cassette/chain last as long as possible, besides cleaning and lubing regularly, avoiding cross chaining is the obvious solution. Fine for the pros who don't need to worry about cost and performance is the primary concern.

Sure, but this is Dura Ace 7900 we're talking about. You know, for professional racers like us.

DirkVoodoo

Lumen wrote: »

Sure, but this is Dura Ace 7900 we're talking about. You know, for professional racers like us.

Oh yes, I forgot, it's this human growth hormone I'm taking, it makes my brain not work so good.