lyrrad wrote:
Youngtano wrote:
SummitAK wrote:
Youngtano wrote:
lyrrad wrote:
The real problem here is manufacturers substituting cranks and running out of spec chainstays.
I am the local mechanic.
You are a mechanic? Like to your neighbors or friends, or one who works in a shop? Please show me the chapter in the unwritten rule book of frame design where it states what makes a chainstay in or out of spec. Also, please tell me how you'd appreciate a customer (or your neighbor) coming to you and saying "fix your F up".
The specs actually come from the component manufacturers based on such things as the front derailleur to be utilized, chainring diameters, rear hub width, etc. Go short on the chainstays and there will be shifting performance trade-offs due to the chainline. Experienced mechanics understand these issues.
Just out of curiosity:
What kind of shifting issues would I have if my bike has standard 135mm hub spacing, a chainstay length of 40.5, 53/39 chainrings, Di2 group, a chain length of 108 links, with a B tension gap of 3.8mm on a 25T cassette. Let's say for simplicity, I'm running a Shimano crank with Shimano chainrings, just incase you want to bring shifting ramps or chainring flex into this.
If you could provide your complex experienced mechanic math formula to calculate this, it would be greatly appreciated.
Asking for a friend.
You also need to consider the BB and the associated chainline.
Also where the front derailleur is mounted in relation to the chainring, as in it rotation around it as well as it's setback.
But 40.5 is right on the minimum limit for chainstay length for a complete Shimano road setup.
Let me know when you both can answer my original question, on your own. Lyrrad, congratulations on knowing how to do a basic front derailleur setup.
Also, the chainstay length mentioned, is from an S3 disc.