BayAreaUser

Hello guys,

I got a 7800 dura ace groupo (levers, derailers, chain, cassette) laying ready to be installed and wondered if i could use these items with a new 7900 crank.
I plan on using a 7800 chain, but would a 7800 cassette and 7900 crank work with a 7900 chain?
I searched and did not find and answer.

I figured since a substantial weight difference of the 7800 and 7900 gruppos is on the crank, i figure i would just chance that for now.
I plan on eventually making the transition to 7900 components as i find deals out there and complete the set up.

Thank you very much

keisatsu

You'll be fine.

mechBgon

Chainring spacing's a little different, so you may need to be fairly precise on your FD cable adjustment. That'll come out in the wash once you get the 7900 FD and shifters.

BayAreaUser

But, will i be able to use them for now without problems even though the chainring is different?
It may be a long while before I can actually fully upgrade components.

keisatsu

Really, I had no idea. I've upgraded several 7800 BB/Cranksets to 7900 and can't recall any issues w/ the FD adjustment.

Rippin

Check out the Shimano chart:



Shimano says the 7900 crank should be used with the 7900 chain and 7900 front derailleur, but can be used with a 7800 cassette. I run this exact configuration on one of my bikes without a problem (actually full 7900 with 7800 cassette). This is what Shimano recommends, BUT I'm sure you can get away with the 7900 crank with the rest of the grouppo being 7800.

Trucker Dan

I ran a 7900 crank with everything else 7800 for over a year. No problems and shifted great. You can't use a 7900 front derailer with 7800 shifters. The cable pull is different.

Homebrew01

I use 2009 Campy 10 speed shifters with a 1985 "5 speed" crankset and a 1980 front derailleur ..... works fine ..... I would hope that Shimano 10 is cross compatible.

v70cat

I have a 7800 bike and upgraded the front crank, chain and rear cassette to 7900 with good results. The 7800 shifters work fine and this upgrade conforms to Shimano recommendations.

BayAreaUser

Excellent! Thanks a lot! =)

mechBgon

Shimano considers it a B-level setup, but it works well enough to go on with.

3373jones

no it won't work... ;-) BUT I have a 7800 crankset I'll gladly trade you for your 7900 crankset.

2ndGen

Or 7900 brakes with 7800 shifters either.

idcruiserman

I'm running a 6700 crank with 7800 group and 6700 chain. It's working great.

BayAreaUser

Thanks guys.
Right now I'm looking for a 7900 crank. I can't find anything under 400, but see plenty of 7800 new units going for 200.
Hope the cost is worth it!.

MegaTom

Screw the weight.... the 7800 looks so much better !

keisatsu

incorrect.

2ndGen

If it has to be a 7900, here is a set for $339.

https://www.bikewagon.com/Shimano-Dur...-p8947551.html

BayAreaUser

i just got offered a brand new, still in box 7800 crank for $220. I may jump on it.
What's the total weight difference of the two units? I read somewhere a bit over 1/4 lbs.
Wonder how much of that is the crank alone. I don't foresee a lot of weight saved on the other pieces.

edited. I just looked it up. 15 gram difference. Although the 330 price is tempting. 15 grams are not worth $120+ to me =(
Not right now, or am i missing something?

scirocco

Not, not much, except that 7900 front shifting is even slicker than 7800, if such a thing were possible. Due to the chainrings alone? Probably the redesigned shift levers and FD cage make a contribution.

keisatsu

the rings are stiffer on the 7900

Jharrington

Front derailleur compatibility-

Can I use a Shimano FD-7900 front derailleur with a Shimano FC-7800 Crank Set?

shelbyfv

Yes Also the post you quoted by trucker dan is incorrect.

Jharrington

Thanks!

Jharrington

Thanks! I’m having trouble adjusting the front derailleur.