Now the weight doesn't exceed 6.3kg(13.9lbs).
I know that the green of cables parhaps don't suit too well but i didn't want black ones. The light green gives some "life" and stands out from the blackness of whole bike. I know all black bikes without decals have some charm but they are just too simple for me and a little boring.
How it rides, you ask. It rides as its rider does
But let's get down to the nitty-gritty, it's super comofortable - Simplon Vibrex design really works. I met with this technology in their hardatail MTB frame 2 years ago - Razorblade, during a first ride in terrain i checked all the time if i didn't get the puncture and if the pressure in rear was right casue i got feeling as i was sitting on a full suspension bike until after 30min i realised that it must have been their Vibrex. Of course i doesn't work like full suspenison but riding on gravel , rubble was much smoother than on other carbon high end frames. Slim seatstay slightly bent arcuate do their job very well but in Serum vibration absorption goes even futher, it goes exactly into integrated seat tube which is also slightly curved and quite skinny (26.8mm) what causes yielding. When you push from above on the back of saddle it moves about 1-1.5cm. In my second Simplon - Pavo which also has Vibrex but only in rear seatstay and standard seatpost(31.6mm diameter) ride feeling is harsher but still smoother than Specialized SL3 and SL4 for example i had chance riding at the begining of this year.
If comes to stiffnes i can't complain about that. I have no idea how stiff it's acording to test in Tour etc, but anyone who takes a ride first what says is: "wow, how it accelerates and how responsive it is!" The frame handles really well with my weight of 74kg and with many pulls on short climbs at races. Perhaps it's due to quite wide(BB86) and massive bottom bracket. If we are at BB, here's one thing i'd like to mention. I use Rotor 3D+ crank that has 30mm spindle, the frame has BB86 standard so i had to use THM pressfit cups. Somewhere on this forum is topic about them and many says that they can't be durable it's not true, they hold surprisingly well and spin very smooth after 2500km and washing with Karcher. Other thing improving stiffnes may be also Double chamber technology - carbon rib inside tubes(maintube and seat tube) it also makes tubes stronger and it works too, i think. After many kms and three years of riding on Stomp(Simplon too) in mountains where there is lots of loose stones downtube still holds without any crack despite many hits with this terrifing sound that makes you think you have a big hole in your frame. By the way i saw two Pavo's broken but both of them were hit by cars so i doesn't count.
Geometry - slightly different form Pavo, Serum has top tube 5mm shorter than Pavo and base wheel too, the same tube in Serum has more sloping too. I know it's not a lot but in tight turns i feel this little difference, Serum doesn't require so leaning as Pavo does that's why i usually take Pavo into mountains. It's simply more "handy" on long descents. Other things about geomtery don't stand out everything seems to be carefully thought out. I didn't have to think over spacers, stem length. I just put my favorite handlebar and stem 120mm and that's perfect for me nothing hurts, i'm low in drops on straights and upright on top of handlebar on climbs. Bike's handling is as it should be - predictible and reliable, not too lazy and not too "nervous".
Sorry, but i just can't find the weak point of this frame set(what comes me easy with products of other brands), i don't work for Simplon, i live in country where i don't even have a dealer of this brand. I could have many frames high end frames for 1/2 or 2/3 of the price but paid retail for Serum. I saw, rode and repaired many top bikes, in my opinion simplon's frames(not only Serum) offer many ideas and technologies that are thought out and created to make riding a bike nicer and more effective but what i like the most is the finish of their frame i don't mean the painting but the way they are made and details they focus on.
If you have more questions please ask. I'll be happy to reply.