Originally Posted by
EdIsMe
I've noticed a trend in road bikes in the last year or so, perhaps longer, that tends towards super steep seat tubes and super slack head tubes, especially in smaller frames (I lean towards the smaller end of the spectrum).
Once upon a time, the generally accepted standard road geometry was 73/73; 73 degree seat tube, 73 degree head tube.
Lately, especially the smaller sizes, look closer to 70-71 degree head tubes and 74-75 degree seat tubes.
The obvious effect of this is the bikes ride great in a straight line, but feel like steering a cadillac into a sharp corner. I noticed this specifically when comparing the 3 bikes I've owned. My Neuvation FC100 (while arguably not a perfect 'race' bike) has the typical 73/73. The bike fits me well and handles great. It's a bit flexy in certain key areas which hold it back a bit, but the bike handles great otherwise. My favorite bike of the bunch is a Mercier Kilo TT (also the cheapest of the bunch, go figure). Sure, it's fixed and a 'track' bike. The reality is it's a steel road bike with relatively classic road geometry with track dropouts. ST/HA is 74/73. On this bike I ride a ~20mm setback post with the saddle almost all the way back, so effective angle is likely close to 73.
Now enter the outlier... for reasons I can bring up in a separate discussion, I purchased a 44cm (way small for me) Specialized Dolce and fitted with a 400mm seatpost and 110mm stem (to stretch it out to fit; I normally ride a 47-49). Anyway, this silly bike has a seat tube angle of 75.75 and a head angle of 70.25. I noticed the bike tended to "lag" a bit on the front end in corners and was very noticeable in a particular criterium where I noticed myself entering turns much earlier than most of the other riders, and tracking much wider. So I went researching.
What I found was there are almost no bikes left on the market (in size 50 or smaller and sometimes in larger frames also) that are anywhere close to the 73/73 geometry!
What gives?
As a rider that had 50-52 cm frames for close to 30 years I've had my experience with slacker head tube angles and steeper seat tube ones. Remember to keep them separate though - head tube angle has to do with handling, seat tube angle with fit. (If you want to get technical seat tube angle can be part of the frame and since weight distribution, chainstays, BB height, fit, etc all come into play then technically ST angle has to do with handling but it's really about fit, within a certain normal range).
Virtually all my 50 cm frames had a 71-72 HTA. They had 74-75 STA.
When I went to a compact (Size M Giant) the frame was really meant to be a bit more versatile and it was meant to be closer to a 54-56 cm frame. They went with a 73 deg HTA. I forget the STA but it was in the 73-74 deg range. The 73 HTA was spectacular. I went to a size S Giant and it was still good, I think 73 HTA.
I then went to a Cannondale 52, 73/75 or so. This was the best handling bike I'd ever ridden, 73 HTA with 43mm rake, a front end that didn't mush around in the corners, and I had noticeably faster cornering speeds on fast curves. I think the laterally rigid set up really helped because I felt like there was no deflection to the side. At the same time it was comfy enough for 7+ hour rides.
If I could ask for any combo of angles on a bike it'd have a 73 HTA and a 75.5 STA (to fit my short quads). This is what I got when I got my first custom frame.
As a note on STA with fit etc I found that my particular set up, with a longer TT (56.5), longer front end (14 cm stem with compact bars or 12 cm with regular), I need to have shorter chainstays to keep enough weight on the rear wheel. Instead of the very neutral 40.5 cm stays on the Cannondale I found that a 39 cm chainstay works much better.