Size problem, geometry problem or both?
 

I bought a 2014 Cannondale supersix some years back for a great price. I am 5'8 with a 31 inch inseam, the bike is a 54 cm. 54 cm in other bikes fit me fine, but the Supersix never felt quite right and caused lower back pain. I had a bike fit, and the mechanic put a 60mm stem on there with like a 15% pitch. But the handling has been effected.

So I am going to sell the bike and buy something new. If I go for a supersix 52 cm will I be alright? Or is it likely that the geometry doesn't work for me too?

Before parting with the 54, I suggest that you should make a small picture with your preferred seat height current from the saddle nose to the handlebar center and the height difference between the seat and handlebar height. If I were to make an educated guess , I think that If you go through the sell/ buy the next size down (2 cm- 1 thumb width smaller, that it is not going to make much of an an appreciable difference.) If possible to go a store who has a 52 that you can use your dimensions and set it up to try it out?

I do not know what is going on with your back. I am not a doctor. For a long time I had to ride really upright, because it felt uncomfortable to have my handlebars in a low position. I have been on a back/ hip strengthening regiment. It has made a huge impact on my cycling. I have now lowered my handlebars three inches, and my hips/ back are fine. I am short - 5'-6" with a 31" ground to saddle contact point underneath. I used to ride 52 cm road bikes. now I will not consider anything bigger than 44cm. (much nicer) It is possible that you could go significantly smaller. (if necessary)

The effective difference in top tube length is 1cm, which means that you could go to a 70mm stem. Not really an improvement considering the 52 size frame is going to place the bars 1.5cm lower.


This is not the bike for you, IF your current fit is correct for you. If so, your fit is like that of someone with a short torso. The best bike for you would be a small bike with a tall headtube. Like a 50 or 51cm with a headtube that is taller than your current 54's. That will give you a short reach without bending further. Something like a Cervelo.


That said, did you get a real fit, or did a mechanic swap some stuff until you thought it was okay? Sometimes sitting upright isn't the right way of dealing with discomfort on the bike.

With a visual, we are pretty clueless here. So photos of you on bike, from the side:
Hands on hoods in your usual riding position, crankarms in line with seat tube
Hands on hoods, forearms horizontal, crankarms horizontal
Hands on bar tops, usual riding position

That would be a good start.

Someone your size probably will most often be riding a 56 if not a 54. The smaller the bike the more aggressive the body position.

Why would an even longer top tube be "less aggressive" when he's already having a problem with reach?


Smaller sizes aren't automatically "aggressive" - especially if they have a lot of stack. They are used to get in aggressive positions because they can be built with lower bars, but they don't have to be.

Here's the size 54 and size 56 compared (link below). Press "Shadow Bike" to enable a dashed shadow, and "Swap Bikes" to swap between the 54 and 56, and edit saddle height, spacers and stem length as you like.

The 56 can be made a little bit less aggressive. Between 54 and 56 you often get a bit more stack than reach. The seat tube angle is laid back though which should push the saddle further back and add more reach, assuming you have a higher saddle on the larger bike. But as we fit the same person the saddle height is the same and the saddle isn't moved as far back. We still need to push it a little bit forward and there's still a few mm longer reach left on the 56.

Anyway, sizing up is sometimes better than sizing down when you want a more relaxed fit. It depends a bit on how many spacers you can fit under the stem.

https://www.bikegeocalc.com/#22Canno...5F172.5G30H30Z

You can't directly compare the Reach on two bikes with different Stack. Add a spacer to the smaller bike to equalize Stack and you'll find the Reach is greater than the numbers say it is. That's because the head tube makes the Reach 3mm shorter for every 10mm in increased Stack.

The real difference in reach from a given saddle set back to a particular stem height is 11mm.


Seat tube angles don't dictate your saddle set back.

True, that's why I prefer to actually make a drawing of the frames and put my saddle height etc there to see which components and spacers that are needed. Due to the different head/seat tube angles it's a bit hard to predict without making an actual drawing, and I think one should try both a size up as well as a size down and see what spacers/stem and saddle setback that is needed to get the position you need.

About the seat tube angle, what I tried to say is that if it's more laid back it moves further backward in relation to the BB when increasing saddle height a certain amount, and larger frames often have a more laid back seat tube angle to move the saddle further back for a certain saddle height. So if you adjust saddle position of the larger frame to have the same relative position to the BB as your smaller frame (which is a good idea if the saddle/bb fit of the smaller frame is good) you need to move the saddle forward a bit. In other words, if you retain the saddle/bb fit from the smaller frame the handlebar will still be a little bit further away, but considerably higher.

To complement the 54 vs 56 geometry comparison, here's 52 vs 54:

https://www.bikegeocalc.com/#22Canno...5F172.5G30H30Z

You are spot on about the torso. I have the legs to fit the supersix 54, but the torso is the problem.

Yes, it was a proper bike fit, from a place that is known locally for doing good fitting.

Sounds like the supersix is just not for me...

I will take some photos later today.

...looks like supersix in size 54 cm comes with a setback seatpost. On a larger frame you can have a straight post if reach is an issue but still get the knees behind the pedal spindle as a result of a more relaxed seat tube angle.

That's true on larger bikes that have actual relaxed seat tube angles, but even the 56 Supersix still has a seat tube angle that is steeper than the 73° median. With "normal" set back, you aren't going to be able to go to a zero post until the seat tube angle is less than 72°.

Cannondale frames are not suitable for you, apart from maybe a Synapse.

As someone suggested higher up, something like a Cervelo R3/R5 would be suitable for a racier frame.

I'm in the same boat as you, though my arms are a little on the shorter side, so that makes things even more difficult to find a suitable frame/brand. I had to built up a small list of production-only frames for different riding styles when searching.

Was the trek Emonda on your list? As that is one I’m currently looking at.

Here's a comparison between Trek Emonda size 54 and Cannondale SuperSix size 54. I don't know your saddle height, guessed 700mm. What I don't know is how much spacers you get at delivery, probably more than shown on the product photos.

* Press the "Swap Bikes" button to swap between the two bikes
* Press "Shadow Bike" to show a dashed representation of the other bike simultaneously
* Press "Fit Delta" to see how the position of the contact points differ
* Click the numbers and edit directly in the drawing if you want to change spacers, stem etc.

https://www.bikegeocalc.com/#14Trek+...5F172.5G30H30Z

As you can see there is despite shorter reach and higher stack on the Emonda quite small difference in fit overall, about 6mm shorter and 4mm higher if you use the same stem. The best solution is probably to size down to get significantly shorter reach, and then make sure you get a good amount of spacers under the stem, and use a riser stem, and perhaps also a riser bar like the Specialized Hover bar to compensate for the lower stack of the smaller frame. A friend has the hover bar on a bike and it's a sneaky way to get higher stack, in terms of looks I think it looks nicer than having even more spacers or rise on the stem.

Here's another example. I don't have your exact fit details, but I've guessed saddle height 700mm and saw in the initial post that you run 15 degree rise and 60mm stem on the SuperSix. I'm not sure what the reach of the handlebar is so I'm using that of a typical short reach compact bar in the drawing.

Then I've here compared to a Cervelo R3 sized down to a 51, and changed out the 25mm(?) setback seatpost to a 0mm setback, added some spacers under the stem, a 6 degree rise 90mm stem (I think 90mm is the shortest one should go on a road bike, it depends a bit on trail and handlebar reach though), and then it looks like the handlebar has a crazy rise but that's just to represent the effect of a Specialized hover bar which yields 15mm extra rise of the hoods. There's not a huge difference between the Cervelo and the Trek Emonda so you could do a similar solution with that.

The thing here is that even with a typical sportive/endurance geometry you will need to make quite significant adjustments to the stem etc to get the fit you need, but that's ok. Being comfortable on the bike is the most important.

https://www.bikegeocalc.com/#13Cerve...5F172.5G30H30Z

While you're smaller than me, unless for some reason you have extremely small arms it really should not be an issue. I'm led to believe that its you, not the bike and what you really need is to do some more stretching. Riding on a road bike is not meant to be particularly comfortable. You will get better and feel more comfortable on your bike the more you ride it. On downsizing to a 52... The actual difference will be about 1cm in your top tube and 10mm in your handlebars. This is not a significant number that will lead you to having a better fitting bike. I suspect quite seriously you just need to get used to riding the bike.

Not necessarily... I have a tall elf length legs and a long torso I'm 5"10. I can't stand over a 56 comfortably. The human body is very rarely proportionate like that. Actually in my case the difference is having a seat post that would be at the maximum insertion point vs. having a comfortable bike to ride that I do have with this frame which is why I keep spending money on it.

https://farm1.staticflickr.com/801/4...12c51d39_b.jpg

The downward-sloping top tubes may not have the look you want but they do have a purpose--e.g.,


https://bicycles.stackexchange.com/q...google_rich_qa

Given the trade-offs, I'd go for the larger over the smaller frame, taking advantages provided by the endurance/comfort (compact) frame design. For example, a 56 VR (Felt) has essentially the same reach as a 54 SuperSix but not the downside of a higher standover (but then, maybe it's a bit heavier but a little extra alloy isn't that much weight)...

Example of how to get the advantages of a 56 and the standover of a 54...

That's a bit yeah and no, it depends on the rest of the geometry of the bike. If it has a standard length top tube then you will be out in terms of reach. If its a compact bike like a TCR then you might be good. Quite personally I prefer a lower saddle height to begin with. I'm not a fan of compact geometry. That's why I've ridden bikes like CAADs and my Trek which prior to that I had a CAAD5. I believe in classic geometry. What I mean to say is that aggressive geometry that started out with the TCR doesn't really suit me. I much prefer the classic style of a rider like Marco Pantani. That's what I grew up watching in the 1990s in the grand tours and that's what I believe in. Even Lance rode a 5900 once upon a time also.

http://n8leon.com/biking/lance.jpg

I preach what I believe in.

Traditional, "compact" and sloping frames all have the same nominal horizontal top tube lengths for a given frame size. A compact is traditional geometry but with a short seat tube. A sloping frame can be everything from a compact to a bike with an taller than traditional head tube. But other than the location of the top of the head tube and the top of the seat tube, the rest of the fit geometry is the same.


The OP must have a back problem which made his professional fitter unable to get a "normal" reach out of his upper body. In the old days he would have gotten a custom frame with a short top tube compared to the height of the head tube. Today many sloping bikes have such tall head tubes that they are effectively like a tall bike with a short top tube when you size down.

A downsloping top tube isn't something I dislike but for anyone with standover issues it's something I think they'd be better off learning to like the look of, rather than sacrificing an ideal cockpit size for their body type, that only a larger bike can provide. You easily could find a downsloping top tube bike like this Madone in the TdF. A larger bike usually has a bit long wheelbase too which is something I prefer.