Originally Posted by
DaveSSS
[FONT=Tahoma]Anyone who would suggest fitting a bike based only on a rider's height isn't too sharp. As an example, I have the same 83cm cycling inseam that Cyccocommute has posted, but he's 5-6 inches taller, IIRC. I'm only 5'-6.5" or 169cm tall. My bikes would fit his legs, but not his much longer torso.
The three key dimensions of TTL, STA and HTL (with the headset) or better yet - the frame reach and stack - define the frame's possible range of bar height and saddle to bar reach and permit the comparison of the fit among any number of other frames. They do NOT magically fit the frame to a particular rider. If a rider has a fit that he can define, then I can match it with another brand and model.
When someone posts that they ride a particular size and model of bike and wants to buy a different brand that fits the same is when those dimensions are applied. If a person has never ridden a bike and knows nothing about what type of fit they want, I always recommend a fitting by a professional - not some guy whose main job in a bike shop is selling bikes and may have only a rudimentary understanding of bike fitting.
If a person posts only his height and cycling inseam, I always ask if he has some cycling experience and some idea of his preferred saddle height. Two riders can have the same inseam but if one pedals with a horizontal foot, his saddle height may be 2-3cm lower than a rider who naturally raises his heel. Neither is right or wrong, but it needs to be considered when selecting the best fitting frame. All you can do for a person with no expereince is steer them away from a frame choice that is likely to be much too large or small.
All hat. No cattle.
I'll remind everyone, again, what you said.
Originally Posted by
DaveSSS
There are only three dimensions needed to determine the fit of a frame - the TT length, the seat tube angle and the headtube length, with the headset.
Bike fit is based on body size. Height usually determines factors like reach and inseam. If your three dimensions...up from one...head tube
... or is it 5 now, it's so hard to keep track as you move the target... are indeed all that is needed to determine fit, then you should easily be able to tell me what size body fits on each of those 10 bikes. I made it easy for you because all I asked for was height with a 4" range.
Maybe you need it harder. Since you can't tell me a height, tell me the torso size, the reach and the inseam of a rider for each one. Let's make it even harder and only give you a 1/2" range on each of those measurements. If you have the torso size and the inseam, you can tell me how tall the rider is.
I can just as easily tell someone who has a bike and wants a different model which one they should start with based on size. As previously demonstrated to you with 7 different brands at the same level of components and the same price range, the geometries don't vary that much between brands. A 58 cm bike from one brand is going to compare very similarly to a 58 cm bike in another brand...at the same price and for the same usage.
Will the fit be perfect when the person rides it for the first time? Maybe, maybe not. The ride has to be dialed in but that's why we have different stems and adjustable saddles and seatposts.
If someone is new to riding, I look at their height and inseam and suggest a size based on that measure. Will the fit be perfect? Again, maybe or maybe not. But that's why we have different stems and adjustable saddles and seatposts. Do I need a professional fit to get a newbie out on a bike? No. A professional fit might help as they progress in ability but if the rider is just looking to get started, they probably don't need...or want... to spend an extra $90 to $150 for a bike fitting session.