whats wrong with riding a bike with a too short of a top tube and a 130mm stem?

will the rider feel a loss of frame stiffness?

handling?

my caad9 50cm doesnt feel stiff/responsive after riding a supersix 52cm.

what is wrong here

how are you defining "too short of a top tube"?

You're comparing two different frame materials and geometries.

Also, generally smaller frames are stiffer.

LBS owner told me that have a stem around 120mm helps with more stable handling. I currently have a 110 on my roadie. Lastly, there shouldn't be anything "wrong" with riding with a long stem; why else would there be a market for them?

A lot of pro riders use long stems, 110 - 120 - 130 - 140mm are all fairly common. it is uncommon to find anything shorter. The main reason for using a small frame and long stem is to get a low front end. I ride a c59 with a 140mm stem purely to get a low front end. I dont find the handling is adversely affected in any way.

I also ride comfort fit bikes with larger frames and shorter stems, again handling is fine.

Now if you ride with a stack of spacers and a long 130-140 stem, your frame is too small. Similarly if you chose a comfort bike to get a long head tube to get the front end high, then ride a really long stem, you would be better getting a larger frame with an even taller head tube and riding with a shorter stem. so it depends what you want to do but basically no stem is wrong so long as the bike fits how you want it to

It depends.

The geometries of the bike change as the size of the frame change. Someone with short stubby legs but a longer torso may require a smaller frame to accommodate their legs and a long stem to accommodate their torso.

My main fit criteria on a bike is balance. if you can support your weight with your legs on the pedals -- kind of half-standing -- and comfortably reach the bars and your butt hovers right over the seat, then everything is good.

You've got it backwards. Someone with a proportionally longer torso would actually lean towards a larger frame size. Fit the cockpit size, then adjust saddle height appropriately.

Put it on and see what happens? Only way to find out for YOUR PARTICULAR SITUATION. Everyone is different. Every bike is different. No way anyone can know what YOU will feel with a change in equipment but there are generalities, yes.
My Tarmac is more responsive than my equal-geometry Allez was and my Tarmac has a longer stem. Was it the stem that made the difference? No. It is the carbon frame that doesn't flex as much.

Indeed. Time for more coffee.

It's all in your head. You rode a supersix and now you want one so your current bike feels inadequate. Truth is your caad is probably the stiffer bike.

Of course, it's possible that you are noticing the effects of flex in your bars/stem compared to what's on the supersix.

OP, my guess is that you were able to put out more power on the 52 frame due to the taller head tube.

Too often people go for smaller bikes and longer stems to get low and aero and look like the pros. The problem is that in doing so, they sacrifice power. Not many people are flexible enough to ride bike set ups like the pros. Decreasing your hip angle with the taller head tube probably gave you more power.

+1. That's been my experience. I'm 6' with long legs and ride a 57cm. The limiting factor is my case is seat post extension on a small frame (check) and seat to handlebar drop (3", check), but I did need a 16deg stem to avoid what would be too much drop for a senior citizen. A 60cm frame had me too stretched out.

The length of stem has very little effect on bicycle stability or handling and in fact, longer may make it feel less stable because of the tiller effect. Stems of 100mm or less are actually quite common, just not among racers.

You don't necessarily have that backwards. Depending on how extreme the short legs are, it makes sense to have the frame fit the legs and use stem length to provide the proper reach. Most frames have much smaller changes in reach between sizes, than head tube length. Going up a size may gain you 10mm in reach, but the bike will probably be 20mm taller and less suitable for the short-legged rider. It might take a 4cm larger frame with no standover clearance to get a meaningful increase in reach.

I have the opposite issue - long legs and short torso. When I started riding, most stores wanted to sell me a frame the was much too large, to fit my legs, and ignored the too-long reach.

One well-respected authority in the cycling industry told me directly that, given the choice between a too-long toptube + a short stem, versus a too-short tobtube + a long stem, you want to go with the latter, because the bike handling will be more sure, less squirrely.

But many well-respected authories in the cycling industry have told me indirectly, via their writings on website & industry fora etc that it's better to have a correctly fitting frame in the first place, rather than try to bandaid a poorly fitting frame via compensating components.

+1. A longer stem setup means more movement is required per degree of turn, so when you pull the bars an inch to go left, you are not actually turning the front wheel by as much as if you had a shorter stem.

It is not all about Top Tube length. One must also consider the head tube when considering proper fit.

The head tube length will impact saddle-to-bar drop, and too much saddle-to-bar drop can actually reduce your power output.

what about head angles and length? i rode an allez with a 14cm head tube(54cm) vs an 11.5cm headtube on the (50cm). because im more upright and stretched out, does that mean my legs are hitting the right angles for the down strokes on a larger bike?

Bikes are not turned with large movements like you mention, at any speed above single digits. At normal riding speeds, a very small movement of the bars, in a direction opposite the turn (countersteering) is used to lean the bike, so it can turn. A whole lot of pros use stems in the 120-140mm range. It's merely a matter of what you get used to.

Agree about steering. But that's not the significant thing a stem can do.

A longer or shorter stem can significantly affect weight distribution, both front vs rear and also how high your center of gravity is. More weight on the front wheel and a lower center of gravity generally makes a bike handle better. Generally.

Usually the difference in eTT length between 2 frames of the same model is 2-2.5 cm, 20-25 mm. That may not be enough to make a difference especially if you setup the two frames with identical stack and reach.

It's fine as long as you fit the bike right with that setup.