If I am 5' 10.5 " tall with an inseam of 33". What size 2006 Cannondale Prophet do I need? Can not test ride

Question

Local bike shop said that I needed a Medium frame, just by looking at me.

Answer 1

I have two cannondales, I'm 6'3 34" inseam and ride XL. Fits just right. Based on this limited info...I'd have to say you're going to need a Large.

Enjoy!

Answer 2

To determine your proper frame size, you’ll first need to get an accurate inseam measurement . Stand with your back against a wall, your bare feet 6" apart on a hard floor,
looking straight ahead.
Place a book or carpenter’s square between your legs with one edge against the wall, and pull it up firmly into your crotch, simulating the pressure of your saddle while riding. Have a helper measure from the top edge of the book to the floor, in centimeters. (You can convert inches to centimeters by multiplying inches by 2.54.) Repeat two or three times, for consistency, and average the results to get your inseam length.


Frame size refers to the length of the frame’s seat tube. Pro frames are measured along the seat tube in one of two ways, center-to-top (C-T) or center-to-center (C-C). C-T measures the distance from the center of the bottom bracket to the top of the top tube or seat lug (See image bellow). C-C measures from the center of the bottom bracket to the center of the top tube. Since C-T measures to a point higher on the frame, a frame measuring 55cm C-T would also measure roughly 53.5–54cm C-C, a difference of 1–1.5cm.

To size your C-T road frame, we use a guideline of .67 x inseam length. For example, if you have an 85cm inseam, your C-T frame size would be .67 x 85cm, or 57cm.

LeMond’s formula, from his former coach, Cyrille Guimard, establishes C-C size by the formula .65 x inseam length, which yields virtually the same frame size when you add the 1–1.5cm difference between C-C and C-T.

Larger riders (6'0" and up) may find that this formula puts them on a too small, and uncomfortable, road frame. A taller cyclist who wants a more comfortable frame may be better off selecting a frame 27–28cm less than inseam length, C-T.

For a mountain bike, we start by recommending a frame in the range of 10–12cm smaller than you take in a road frame. For example, if you ride a 55cm C-T road frame, look for a 43–45cm (17–18") C-T mountain frame.



Frame Dimensions
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A1 Seat Tube Length (C—T)
A2 Seat Tube Length (C—C)
B Top Tube length (C—C)
C Stem Length (C—C)

Answer 3

Wait, you are planning on buying a bike without seeing it first or test riding it? That would be like buying a car or a house site-unseen.

Find a local bike shop and test some out to see exactly which one would be best for you.

Answer 4

Large