I'm new to road bikes and like the compact frames Giant puts out because it reminds me of my mountain bike.Would one size a frame like picking out a mountain bike?Compact frame sizes seem much more general then regular road bike frames.I'm I missing something here is there something more than just picking out a stem size and saddle height within your size range.Giant says I would be a small size because I fit in the 5ft 2in to 5ft 6in range.Has anyone had any problems using Giant's sizeing chart? I will go down and fit the bike in person but what do Iook for and better yet feel for on a road bike?

I used to have a Giant OCR-1 that was a medium (I'm 5' 6 1/2") that fit me fine. It's more compact, meaning a shorter top tube, but not smaller height-wise, and meant to have you sit more like it's a mountain bike.

The only difference is the top tube slopes.

You should end up with the same saddle to pedal and saddle to bar dimensions as you would on a regular frame. The only difference is the slope on the top tube and the smaller rear triangle.

Go in and get fitted if you're interested in one of these bikes. If they do a proper fit they'll be able to tell you if you are a good match for a compact frame. It may be that you are between the sizes. (Since there are fewer sizes) If that is the case they should steer you away from the Giant and recommend another frame that is available in more specific sizes.

I turn out to be a perfect fit for the large giant frame. But once the stem and saddle are attached, all the dimensions are exactly the same as my Trek which is not a compact frame. (Pedal -> Saddle distance, Bar -> Saddle distance, Saddle -> Bar drop, etc..)

You just can't compare the lengths of the tubes since the frames are quite different. How you fit on the bike should be the same if you are comparing two frames with the same goals. (I.e. you are not comparing a TCR to a classic style touring frame)

Ben

A proper geometry chart for a sloping top tube or "compact" geometry frame is not much different than a chart for a conventional frame.

A compact geometry chart will often list an "effective" top tube length, which is really a misnomer. The proper term is HORIZONTAL top tube length, measured in exactly the same manner as a conventional frame, as a horizontal line through the center of the top tube.

Seat tube angle (STA) is measured the same. When comparing frames with different seat tube angles, add 1.2cm per degree to the TT length of the frame with the numerically larger STA.

The seat tube length is far less critical, although it may be safe to always purchase a 350mm length seat post just to be safe.

The other critical dimension is the head tube length. Since compact frames are generally made in fewer sizes, pay close attention to the head tube length. If the frame has an integrated head tube, add 5mm or 15mm (for an extended top headset) to the HT length to get the total length with headset. If the frame has a conventional headset, add 25-35mm. This will help determine the stem angle and amount of steering tube spacers required to get the desired handlebar height. It's quire common for the head tube on a compact frame to be shorter and require more stem angle and/or spacers to get the proper bar height. The exception is if you select the larger of two possible sizes in which case you can have the opposite problem, using no spacers and a short length 73 or 80 degree stem to get the bars low enough and close enough.