kenshireen

I am looking at a bike that is 7800 Dura Ace 53/39.
I like the bike but I want to change out the chainrings to a 34/50 without having to replace the whole crankset.

Can this be done and what Dura Ace chain rings would be compatible to switch out.

alcjphil

Dura Ace 7800 53/39 cranksets have a 130mm BCD. Compact 50/34 chainrings use a smaller 110mm BCD, they will not fit your crank

Wilfred Laurier

alcjphill is correct. 39 is generally the smallest chainring that you will find for a 130mm BCD crank. Any smaller than that and the chainring bolts well be occupying space where the chainring's teeth should be.

fietsbob

You can change out a Chainring but not have it smaller than the circle of bolts that hold it on the crank arm .

as Above, You change out the whole crankset to get any smaller inside chainring than 38t, just 1 less than the 39.

alcjphil

The good news here is that you have a huge selection of compatible compact cranksets you could buy, without even having to change your bottom bracket. Any 105, Ultegra, or Dura Ace 10 or 11 speed crank will fit. If you shop around you can probably find a complete crank for very little more than the cost of the chainrings, and probably less if you look at 105 or Ultegra cranks

kenshireen

the whole bike is dura ace so I really would like to keep it that way... I'm a roadie snob... if I can't ride good I may as well look good

alcjphil

I see your point, but Dura Ace 7800 is 2 generations out of date. One could argue that newer versions of lower end components have shared upgrades from later generation Dura Ace, and a true aficionado would appreciate your choice of having chosen a later version of a lower end component over an earlier Dura Ace crank. I would go with what works best for the price.I would add a few bucks for the bling, but not many

dtrain

There was no 7800 compact. r700 was aimed at 7800 & 6600 compatibility. r600 or 6750 actually match better than 7900.

FastJake

I'll admit that I am sometimes vain about this stuff too. If you want to keep the matching crank for the looks, then make sure you have the legs to get up whatever hills you're going to climb. Since it would be really pathetic to have to get off and walk your fancy matching DA bike.

Put on a cassette with a 28T large cog and you'll be fine. If not, you've wasted your money on too much bike and should keep training.

kenshireen

I never understood why shimano came out with R series.... How does the R700 compare with Ultegra

dtrain

Shimano had a little heartburn deciding if/when they were going to jump on the compact crankset 'wave'. They were just testing the waters with the r700 as an option to going with 7800 and 6600 groups. I think they made some 6650G's in the 50/34 (that ice grey colored Ultegra SL) as well. By 7900/6700, the compact was a more widely-available option.

The r700 is pretty darn nice (but kinda rare). Lightweight with hollow arms. Worthy of an Ultegra group for sure (nearly identical to a 6600) - and looks fine with 7800. The r600 is quite a bit heavier with forged crankarms, much more of a 105/Tiagra level piece. Here's an r700:

New Still in Box Shimano FC R700 Double Compact Crankset 50 34T 172 5mm | eBay

kenshireen

I took a look at this item... it has an intergrated BB which the seller switched out to a 105..... Could I replace the BB if I wanted and what kind would I use.
What does integrated refer to... Usually BB are separate from Cranksets

dsaul

It uses a Hollowtech II bottom bracket, which is the same as the current gen. external bottom brackets. Any current Shimano 24mm external road bottom bracket will work, but there is really no reason not to use the 105.

T Stew

Do the rings themselves need to be DA? You can swap out the big ring for lower, but the small ring is kind of stuck at 39. Add a cassette with your lower gears in the back instead. I'm working on a project right now using 7800 crank, derailleurs, and a 11-36 cassette with help from a Wolf Tooth Roadlink to get the 7800RD to clear 36t. Haven't got it put together yet though.