Hey folks, just wanted some of your opinions about the dimensions of a bike I am going to relay to a builder. The bike is intended for century races with mountain ascents. I weigh about 180 and I am pretty flexible. The specs are:
Seat Tube (center to center): 54 cm
Actual seat tube angle: 72.5 degrees
Top tube (center to center): 56.5 cm
Exposed seat post: 10.8 cm
Saddle to handlebar drop: handlebar is 5.8cm below the saddle.
Stem length: 120mm
Chainstay length: 410mm
My questions are: 1) How high should the head tube be? 2) what bottom bracket height would you recommend? 3) would you recommend a top tube of 57.5 cm with a 110 mm stem instead? 4) the current head tube angle we are going to use is 73.3 degrees, would you suggest another angle, and why?
I did get fitted, but I wanted to see others’ opinions before finalizing everything.
Thanks,
Wei (and also thanks to the folks recommending places to ride around San Antonio/Austin, it was definitely hilly and steep! Not to mention, blazing hot over the summer.)
Depending on the rake of the fork you are going to use I would use between 72.5-73 head tube angle, probably more toward 72.5. 73.3 will be on the twitchy side particularly for the way you are describing the intended use.
I greatly prefer 8.0cm BB drop over the 7.0 on most road bikes. Much better for descending and stability in general.
Head tube height really depends on the angle of the stem you want to use. But probably 13-14cm would be in the ballpark.
Stay with the longer stem. I would go with a 13cm stem. It gives you more steering leverage and seems to act as a counterbalance and mute steering inputs not initiated by you - like rocks or holes in the road.
But that’s my ideal and not knowing more about your preferences you might hate it.
Quite possibly the least answerable question I’ve seen.
If your builder isn’t able to help answer these questions, he should not be building bikes.
If you are just confirming his suggestions, no one here can help other than offer general guidelines based on what they may have seen in spec sheets on other bikes. Not exactly a great way to find a custom bike.
If you can’t determine this for yourself, you should not be ‘designing’ a frame. Why bother with custom at all, the numbers you provided don’t seem terribly unusual, except for a somewhat shallow seat tube angle and longish TT?
You have some curious numbers. Exactly 10.8 cm of seatpost? How do you know?
A 56.5 cm TT combined with a 72.5 seat tube angle and a 120 stem makes for a long reach to the bar. Is this what you were after?
Thanks folks, I know these questions are vague (and depends on personal preference) in nature, but I wanted to see how other people thought about the subjects (not just mine and the builders). Yes, the builder knows what he is doing too! After looking at the questions, they probably are unanswerable.
By the way, I opted for the custom option not because I have abnormal body proportions, but rather the bike is a piece of artwork and is the same price or less than some boutique bikes. Once the bike gets finished, I’ll post a picture, and thank you Mises for the suggestions and reasoning behind it.
After looking at the questions, they probably are unanswerable.