dvdslw

Just got back from my first ride after swapping my FSA SLK-Light 53/39-175mm out for the new Ultegra R8000 52/36-172.5mm crank and I'm not sure I made the right choice? The quality and look of the Ultegra is quite nice plus the Wheels mfg bottom bracket conversion kit installed nicely and noise free but I don't know if its the change in gearing or shorter crank arms but the bike feels totally different and not in a good way. I plan to give it a few rides just in case I was just not feeling it today.

It's hard to explain but it felt like the bike didn't thrust forward while pedaling at a lower cadence. I'm thinking 99% of my ride was using the 52T which is only 1 tooth different than my previous 53T crank so that should be hardly noticeable but the 2.5mm shorter crank arms may be the culprit? I may be overthinking this but I am an auto mechanic so looking at this like building an engine and selecting the length of your crankshaft stroke, rule of thumb is long stroke for low rpm and more torque and shorter stroke for high rpm and high horsepower builds. It seems I favor a slower cadence and/or longer crank arm.

Any input on my experience would be appreciated but it seems I'll be selling off this new crank to get the 53/39-175mm version.

Campag4life

The psychological element to cycling is undeniable and therefore real even if unsupported by physics.
Maybe introduce a bit of science. Too bad you don't invest in a Stages powermeter with your new R8000 crank to quantify any 'perceived' difference.

Btw, I ride 175mm cranks but don't believe I would be much slower if any on 172 mm...perhaps the opposite.

What is your cycling inseam?

Many years ago before the great Sheldon Brown died unexpectedly I emailed him several questions about cycling. He was very gracious to respond. I asked him about crank length affecting power and speed on the bike and his response was crank length makes no different at all when it comes to how fast a rider is. We were about the same height with similar inseam and he owned bikes with cranks from 175 to well into the 160's. Of course it may for example affect the balance of the rider on the bike. KOPS is different for example with the same saddle position and we do control balance on a bicycle by our feet which is our platform and why saddle setback matters.


Probably most of perception is your head but don't believe many would argue that there maybe a discernible 'feel' difference...but not likely a great deal of difference in actual speed on the bike.

Elvo

Your body has gotten used to the extra tooth in the front. Just keep riding and you'll probably get used to the new crank in no time

RNAV

Did you raise your saddle 2.5mm to compensate for the shorter crank arms?

anotherbrian

Most of my bikes have 175mm cranks, though a few are different (180mm on a 29er singlespeed MTB and 170mm on another geared MTB). I do have one road bike with 170mm cranks. I rode the Davis Double century on the back of a tandem that had 170mm cranks that I'd only done a few rides on before.

All the crank lengths have felt perceptively different, especially if I've spent a lot of time on a different crank length, but all those sensations disappear and are forgotten within a couple miles.

PepeM

If saddle height wasn't changed, it might be that. Otherwise, maybe you were just having a bad day.

tagaproject6

As written earlier, adjust your saddle. Then, keep riding and your body will make its own adjustment.

dvdslw

Good question and no it didn't cross my mind.

RNAV

I'd be willing to bet that predominately accounts for how the bike felt on your ride: you were in a much less efficient position and didn't even know it. Try raising your saddle 2.5mm and see how it feels. The shorter cranks will open up your hip angle compared to the longer cranks, which means you should be able to lower your handlebars 2.5mm as well (or thereabouts).

sanmi

I find I can tell the difference between different crank lengths and prefer 165 (I'm short). I would guess you are feeling the length difference more than any difference in materials/design of the models. You might have luck adjusting your saddle but you might want cranks of a certain length.

dvdslw

Definitely going to try that on my next ride this Wednesday and hope for the best, thanks.

dvdslw

Another thing to note is I believe my chainline is further out away from the frame, haven't measured anything yet because my old crank is at my work but looking at the bike when its in the 52 up front and 28 in the rear, it looks like the chain is at much more of an angle than I ever remember seeing with the FSA. According to the spec's, the FSA has a 44mm chainline and the Shimano has a 43.5 so would the Wheels bottom bracket conversion come into play here? Don't think so but today I noticed when I was pushing hard I could feel the chain rolling, kind of a rough feeling throughout the bike that wasn't there before.

I have cross chained my previous setup without issues for three years and the chain is brand new.

DrIsotope

Are you for any reason opposed to using the 36? Sure would have a straighter chainline in 36-19.

dvdslw

Not really but for my local terrain and my style of riding I spent 99% of my time in the 53. Not sure why but it just always felt right. I'd shift down to the 39 for the few rolling hills here in Central Florida.

DrIsotope

Then wouldn't it make more sense to go to a super-tight cassette, like an 11-23? What's that 28 doing on there?

dvdslw

Maybe so and I had an 11-25 on there for quite some time before I found the hills to climb, then swapped it out for the 12-28 thinking that would be enough to stay in the 53 for my whole ride. I really don't have a good explanation for why I'm treating my bike like a 1x? Plus, front shifting is easy with di2.

dvdslw

I have a theory about what I posted above about my drivetrain being noisy while riding in the 53T and in the taller section of the cassette with the new crank. Is it possible that the new Shimano crank is just that much more rigid (ie no flex) compared to the FSA and more sensitive to cross chaining?

WhyFi

Did you adjust your FD? Do you use the Trim position?

rpenmanparker 

Usually the word "taller" is used to mean a higher gear, not a bigger cog. Jus' sayin'.

Campag4life

Probably not. Chainline in 53 maybe fractionally different due to BB and crank combo...which may affect front derailleur tuning and potential rub against FD cage if not trimmed.

dvdslw

Had my friend at the bike shop do the BB conversion and adjust the FD, doesn't mean its not adjusted incorrectly. Going to have him take another look just in case he missed something.