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Discussion Starter · #1 ·
I'm looking to invest in a new crankset and since I need a new bb as well I'm thinking of going with the Dura-Ace. I've got a full Ultegra set-up and want to make sure it's compatible with the 7800 cranks. I'm thinking that it should work out ok because I run 9-speed XTR cranks with 8-speed everything else on my Fuel 100. Anyone else running a similar set-up?

Also, my current Ultegra cranks are 175mm and I'm thinking of going with 180mm. I'm 6'3" with a 34" inseam and have read (from Zinn) that at this height I should be going with 180mm. Any thoughts on this would be appreciated.
 

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should work...

Chainrings aren't near as critical with regard to chain width as cassette cogs. I haven't seen any Shimano information published on what changes they may or may not have made to the chainring spacing for the narrower 10-speed chain, but it's unlikely that there would be a problem.

If your cycling inseam is 34 inches or 86.4cm, that's really not very long. That leg length would be typical for someone riding a 57-58cm frame. Long legged riders using 180mm cranks would typically be riding 62-64cm frames. Height has nothing to do with suitability of longer cranks, it's based on leg length.

Is your posted inseam a "cycling inseam", measured from the floor to firm crotch contact in bare feet, or a pants inseam, that is typically a couples of inches less?
 

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Discussion Starter · #3 ·
After further measurement...

...it looks like my 'cycling inseam' is actually 35" or 88.9cm. If you go by the rule for crank length (20% of inseam) it comes to 177.8 so it seems that 177.5 might work well. I know that this rule is by no means the end all so any other ideas would be very helpful.

Does anyone have the info that was up on Tech Talk with Zinn on velonews.com in early November regarding proper crank length? Any crank length calculations that anyone might know of would also be much appreciated.
 

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I work at a LBS that has multiple stores and while I havn't seen it attempted personally, I heard one of our mechanics at another store tried to do it on his bike and it didn't work. Shimano says that you can use the cranks, you just have to swap to 9 speed chainrings, evidently our mechanic found the same thing.
 

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Discussion Starter · #5 ·
^^^up for more insight nm^^^

nmnmnm
 

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bburgbiker said:
I'm looking to invest in a new crankset and since I need a new bb as well I'm thinking of going with the Dura-Ace. I've got a full Ultegra set-up and want to make sure it's compatible with the 7800 cranks. I'm thinking that it should work out ok because I run 9-speed XTR cranks with 8-speed everything else on my Fuel 100. Anyone else running a similar set-up?

Also, my current Ultegra cranks are 175mm and I'm thinking of going with 180mm. I'm 6'3" with a 34" inseam and have read (from Zinn) that at this height I should be going with 180mm. Any thoughts on this would be appreciated.
I've recently built up a new 5500 with a DA9 kit from last years bike, the only exception being the new 7800 crank and BB. In MN we still have 20+ inches of snow on the ground so the only saddle time I've got on it is an hour on the rollers. Everything seemed to work fine but I wasn't really going through the gears. I'll mount it up on the fluid trainer tonight and play around with it and report back if shifting isn't great.

I was under the impression that the rollers on the 9 & 10 speed chains are the same width and that the outer links are the only sizing difference. I was also told that the 10 speed chain would work fine on a 9 speed setup which leads me to believe that at most, I'll need to change out my chain if the 9 speed chain doesn't shift well.
 

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DA10speed with 9speed

I have recently gone to the 7800 crank with DA 9 speed. You also need to go to the DA7800 font derailleur and chain. If your rear 9 speed cassette is worn, you may need to put on a new 9 speed cassette. This combo shifts better than the all DA 9 speed combo. On going to the 177.5 vs 175, I also used this as an experiment when I went to 7800 crank. I saw more power with 177.5 with only a slight drop in cadence. I did at first feel more strain after a hard ride on my patellar tendon in right knee. As per one poster, this may have been because I did not move seat forward enough. I have been riding this combo now and am getting more used to it. For those considering going longer, do so no more than 2.5mm and be sure to move saddle forward by about 2mm and also, do not drop your saddle height by 2.5mm as some suggest. Keep the saddle height the same as with 175 as your stroke at top will be compressed by longer crank. You will need to play with adjustment before deciding if 177.5 is right for you. Either way DA7800 crank set-up improves the current 9 speed set-up and will allow you to upgrade the rest of the way to 10 speed as budget allows.
 

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Follow-up

Shifting on the front was fine, even better than the previous 7701 crankset & rings, with the 9 speed chain and derailleur. The only problem I see is that the shifting ramps on the large chainring touch/catch the chain when in the 13 & 12 tooth cogs on my 12/25 cassette (not a huge issue as cross chaining isn't my thing) and cause some noise. I can't tell you the last time on the road that I used either the 12 or 13 when in the 39 on the front so I don't really see it as a problem and won't replace the chain until it's wore out.

Over all, it works great with no additional new parts.

Cheers
Pete
 

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Question

texracer said:
I have recently gone to the 7800 crank with DA 9 speed. You also need to go to the DA7800 font derailleur and chain. .
Did you use the 7800 FD bcause you had to or becuse Shimano says to? 'Shimano says' isn't always true in actual practice.
 
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