Timeline for Impossible/wrong frame length calculation?
Current License: CC BY-SA 4.0
14 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Sep 6, 2021 at 6:41 | comment | added | ojs | The actual and virtual TT lengths have relation of cos(TT angle). So, for 10 degree angle that is quite a lot, the difference is roughly 1.5%. | |
| Sep 5, 2021 at 14:27 | comment | added | Weiwen Ng | General comment: we don't generally size most frames by the actual top tube (TT) length unless they're old-style road frames with a horizontal TT. Bikes these days have sloped TTs, and you don't know the slope angle, which influences how long the TT is. It would be better to use the effective/virtual TT (what the TT length would be if it were horizontal) or the reach (search the site for "stack reach" if interested; there are answers referencing these concepts). I second all those who say that 90deg arm angle is maybe not correct and should be treated as an approximation | |
| Sep 3, 2021 at 22:54 | answer | added | Nathan Knutson | timeline score: 3 | |
| Sep 3, 2021 at 22:45 | comment | added | Jahaziel | Please do not stress too much about exact angles. For general riding use, these angles may be starting positions bur they are not absolutes. Every rider has their own preferences and may adjust the bike as it better fits the use that the person makes of the bike. Your body proportions may also change how much you deviate from and ideal geometry chart, like the one you shared. In my experience, for commuting and non competitive/non training rides on MTB bikes, a more upright position feels more relaxed and is better for longer rides or slow to mid speed paced ones. | |
| Sep 3, 2021 at 19:35 | comment | added | Noise | What type of hat is the illustrated model wearing? | |
| Sep 3, 2021 at 17:22 | comment | added | Adam Rice | @rumtscho The other thing to take into account is that your elbows will be bent on a bike. You don't ride with your elbows locked. So that will change your calculations, even if you are trying to get that 90° angle. | |
| Sep 3, 2021 at 16:19 | comment | added | rumtscho | @AdamRice yes, I saw this picture. I don't expect to get that position with the new bicycle, since it is not Dutch-style. So it appears I will have to ride in a different position - and I want to set up the bicycle such that new position doesn't damage my back. And the second article I linked states that angles in between the 90° and the Dutch-style 20° cause problems. I frankly have no idea what angle I would have with the current bicycle, but it would be very far from 90, not just a few degrees off. | |
| Sep 3, 2021 at 16:08 | comment | added | Adam Rice | A Dutch-bike position is something like this. There's no way to get that with a 90° arm-torso angle. In any case, numbers like these give you a starting point for positioning, they're not absolutes. | |
| Sep 3, 2021 at 16:06 | comment | added | rumtscho | @NathanKnutson the current handlebar is rather straight, with a slight curve towards me. Since I won't be getting a new Holland bike right now, I guess I will have to learn to ride in a posture that is ergonomic for the style of my next bike. In the links I added, the 90° are being recommended for all bikes except Holland, independently of the angle of the torso to the road (which is probably the main factor of whether the position is aggressive). I got a city bike and intend to continue sitting quite upright. | |
| Sep 3, 2021 at 16:03 | history | edited | rumtscho | CC BY-SA 4.0 |
added more links about the 90° recommendation
|
| Sep 3, 2021 at 15:55 | comment | added | Nathan Knutson | What style handlebar does this bike have? The 90° idea is a much more aggressive posture than the bike you've been on. Is that what you want? | |
| Sep 3, 2021 at 15:49 | comment | added | rumtscho | That's why I asked here :) I'm 1.73 tall, but I have quite long arms, at 63 cm from the shoulder joint pivot point to the inside of the knuckles. My torso measurement is also 63 cm (groin to sternum notch). Calculating a simple right triangle with these lengths gives the highest estimate (89 cm length) while drawing more realistic models give the lower estimates. But even with the "shortest" model, if I want to keep the 90 degrees angle, a 60 cm tube means the handlebar would have to go 21 cm below saddle height, which on my new bicycle is the lower edge of the front tube. | |
| Sep 3, 2021 at 15:33 | comment | added | ojs | It would help if you told your measurements. A normal-shaped person who needs 77-89 cm top tube would be 2.5 to 2.9 m tall :) I have never heard of the 90 degree rules except from those who think it's elbows that should be at that angle. | |
| Sep 3, 2021 at 15:15 | history | asked | rumtscho | CC BY-SA 4.0 |
