Possibly going to look at a new (to me) bike. It’s a 2018 Cannondale Synapse aluminum 105 SE. The only thing that doesn’t make it “perfect” to me is the mechanical discs, but mechanical vs hydraulic is a whole different topic. My question is sizing. I know I can’t tell if it fits until I ride it, I’m just looking for personal experience with this frame (I’ve read they run big). It’s hard to make this trip with a new born and mine and my wife’s work schedule, so I’m just looking for advice before I even commit to go looking at it. I’m not looking to get told to sit on it first.

I’m 5’11” with a 33”-34” inseam. I thought I’d be a 56, but after reading some other posts I wonder if I should be looking at a 54 because of how these frames are sized? If it seems a little big, would I be ok shortening the stem a little or will that throw off the geometry too much? I’m by no means a great rider, I just want to make sure I get the right bike for me. Funds don’t allow for a new bike, especially with how they’re priced these days, so im working with what I got, which will be used. Any help regarding this frame size is appreciated!

6'2" with similar inseam, my 2015 Synapse is a 58 and fits me well.

Are you talking about Cannondale's listed size or did you actually measure it using a virtual TT length? My Cannondale CAAD 12 is labeled a 52 but if you measure it the frame size is really a 54. I have a 32.5" inseam and can ride anything from 54-56 frame perfectly. FWIW I spoke to my Cannondale dealer about the sizing and he said smiled and said, "Yeah, it's actually a big 52." I thought that was pretty laughable.

just the listed size. I haven’t been able to physically get on the bike yet. Just trying to figure out if the trip will be worth it

Maybe ask them to measure the virtual TT and frame from the virtual TT point where it meets the seat tube and then from there to BB for frame size? also re: disc brakes......I have mechanical discs on my Colnago cross bike and they have been flawless for the 6 yrs I've owned the bike. I should also mention that generally we can usually ride a range of frames.

The Synapse SE was a one year only model and I regret not purchasing one. Wider tires (700Cx35) and 11/34 cassette along with some other things set it apart from the regular alloy disc 105.

As to size - I’m 5’6” with a 29.5” inseam. I tried a 54 but standover was really uncomfortable and reach was too much. I have it since tried several 51cm Synapses and ended up purchasing a 2016 105 Alloy frame and built it as I wanted. I think a 54 would be too small for you…

I can also speak to the CAADX - it feels much larger than the marked size and I passed on a friend’s CAADX for that reason.

Thanks for the info! I am on the longer side when it comes to arms and legs, so I’m still debating on this 56. I wish I could go and try it out but it’s just not that easy for me at the moment. I really do love this SE model so it makes me want to gamble on it 😂.

The most significant thing to me is the frame stack difference between a 54 and a 56cm model will change by 21mm, if I found the correct model/year Synapse. So if you want to get a lower bar position then you'll be able to go 21mm lower with the 54cm. However if you prefer more upright, the 56 will let you get the bars 21mm higher than the 54. Frame reach only changes by 8mm. So not a big difference and easily handled by a different length stem. Other changes are minor IMO, however the seat tube has a 30mm difference in length. So make certain the seat post of the 54cm has enough remaining in the seat tube when the saddle is set to your correct height. Which will essentially be virtually the same from the BB center on any size road bike you look at.

For some reason the C-Dale sizing guide for a carbon Synapse suggests a 54 which is for 5’-7” to 5’-11”, where the 56 is for 5’-9” to 6’-1”, so I’m not understanding their logic. I’m 5’9” with a 83cm inseam, but long torso and am perfect on my Topstone with a 56 ETT. I can’t see you in a 54.

As well, I would not get mechanical disc, I would pay more for hydraulic. Worth the money and really very little maintanence other than disc pads. My 2019 has only been bled once, has never needed fluid changes.

great info, thank you!

That green

I am 5'8" with a 31" inseam. I had an '18 Synapse 105 that was 54cm, and it fit me perfectly. My opinion is a 54 will be too small for you and a 56 or 58 would be a better option.

I would recommend ignoring the size 'label'. Rather determine what it is that you wish to have - and since you've been on BF for a while, I would assume having a bike for that time.
Determine what the objectives are with the additional/'new'/replacement bike and what changes you wish to have with the new bike. Position wise or ride expectations wise.
Then compare your current/old bike with bikes you are considering - to determine if the considered bike may provide for those desires.
you'll likely find your current bike and the new one on geometrygeeks.com Then compare the important geometry numbers. It's not a final decision point, but a strong influence on how the bike.
might ride.
Geometrygeeks does have the geometry info for a 2019 SYnapse SE 105, so prolly similar to the one you are considering...
relative 'sizing' labels for it seem very in-line to what other companies, like Specialized, are using for 'sizing'...
Things like cosmetic and 'appearance' might be strong influencers, but those are independent of how the bike will actually perform.
The Synapse has a quite tall headtube, so if I was looking for a deeper drop and more aero position, and 'endurance' frame/geometry would not be what I'd consider.
At 5' 11" and 33-34 cycling inseam (not pants inseam...) would likely put you in the listed 'L' , which they call a 56...
It happens to be the general sizing/geometry specs which suit me as well. so I have some 'feel' for those sized bikes... A 54 would have me all scrounged up, leading to discomfort on longer rides.
Larger than that would have the bike feeling like a truck/lorry...
The tendency these days is to go 'smaller frame', but that doesn't always work out...
Since you don;t give any info on your current bike, all of the posted comments are really just speculation, based on our own preferences...
Ride On
Yuri

I’m also 5-11 with a 34 inseam and I find my 56cm Synapse fits me well. I could even fit on a 58 but the 56 is a better fit. I think the 56 will be perfect for you. The mechanical disc brakes should be fine as well unless you have some serious elevation changes on your regular route. They are also much easier to maintain in my opinion.

I'm 6'0" with a 32" inseam, and I've been riding a size 58 Synapse since they first came out...and in truth, it really is too big for me. Not so big that I'm injuring myself riding it, but it is conspicuously less comfortable than my other bikes (which were custom made for me, but measure closer to 56 or 57). A shorter stem helped.

But OP, at 5'11" (shorter than me) with a 33”-34” inseam (longer than mine) that makes me think you should definitely be on a 56 ...or maybe even a 54 ...but then make sure your seatpost is long enough to get your saddle height where it needs to be. I'm running 765mm from center of bottom bracket to top of saddle; sounds like you would need alot more.

I’m 5 ft 11 inches tall. I ride a 56

For the mechanical disc, check out the TRP HyRd brakes, they are a excellent option if you don't want to replace the whole system to go hydraulic. I ran a bike with them back when they first came out, it was worth the cost. The bike I had them on I sold to a friend, and he is still using them and I am thinking they are close to 10 years old