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Fit vs Fit(13 posts)

Fit vs FitPhilharmonic
Jul 1, 2002 3:47 AM
I was going to get a professional fitting in order to better choose my next bike (based on geometry and , yes frame material---Litespeed, Trek, Lemond, Colnago). I visited www.wrenchscience.com and did their measurements which seem pretty complete. Will a professional fitting add any more info? (i.e. is it necessary) I know this comes hot on the heels of the fit no fit thread.
Thanks
Tom
re: Fit vs FitMXL02
Jul 1, 2002 4:48 AM
If you have enough experience to sort of know what your frame size is anyway, the wrench science site is a good one. If not, spending $40-$50 to make sure you don't get the wrong sized $2000-$4000 bike is money well spent. If you order the wrong size from WS, they will not take it back on the exchange...especially if you buy a threadless fork and they shorten the steering tube. If you decide to go the WS route, my suggestion is to measure yourself with a friend who understands cycling and measure yourself in CMs to be extra precise. Measure yourself numerous times and take the average. Good Luck.
If you trust the pro, then OK.hayaku
Jul 1, 2002 4:56 AM
They should be able to give you a pretty good fit. You will have to trust them though. I am going to be fitted for a custom steel bike soon, the guy doing it is a legend in Japan but still, I can't help worring a little bit. That's just my nature.

Either way, it will most likely be better than the wrench science fit. That doesn't take enough info to give you a reallly great fit, unless it's by chance.

Fit is not an exact science but it is still extreemly important of racing, training, comfort, and safety. I say spend the money on a good fit.
M.
I'd beware of anybody's "pat formula."Spoke Wrench
Jul 1, 2002 5:38 AM
Imagine a room full of guys, each exactly 5'10" tall, doing toe touches. Some can touch their toes, some can barely touch their knees, and some can flatten their palms against the floor. Trying to fit them all on the same bike makes no more sense to me than telling them all to use the same "optimum gear ratio" to climb a mountain.

To me, the vertical relationship between the seat and the handlebar is key. Flexability and abdominal strength are going to be huge factors in determining what is going to be comfortable and efficient for you.

To me, the ONLY purpose of the formula is to get you close on sizing. It's what you do after that to custom fit your bike to you that makes the difference between OK and wonderful. A fitter who understands and can help you to do that is well worth the cost. A fitter who just crunches the numbers isn't.
I'd beware of anybody's "pat formula."B2
Jul 1, 2002 6:08 AM
Ditto that for me too.

Oddly enough though, WS site does have a flexibility "measurement" that is used to recommend a TT/Stem length.

I don't if I just got lucky, but when I did the WS fit deal just for fun, they came up with exactly what I am riding on now (very comfortabley I might add). Again maybe it's because I have pretty "average" body proportions or just lucky that the recommendation came out that way... you got me!

Bryan
your opinion counts...C-40
Jul 1, 2002 8:03 AM
A pro fitter can't tell from measuring your body, what the most efficient KOP position is for you. Only you can determine that by trial and error over many miles of riding on varying terrains.

If the fitter sets your knee directly over the pedal spindle, but your most efficient position is 2cm further back, then the "custom" fitting is just crap. You'll end up with the wrong seat tube angle and top tube length.
your opinion counts...Philharmonic
Jul 1, 2002 9:32 AM
Where can I read more about seat tube angles?
How does it impact on riding position?
Thanks
Tom
seat tube angle...C-40
Jul 1, 2002 2:10 PM
Seat tube angle (STA) affects the nominal saddle position and the range over which the saddle can be moved to place the knee in the desired relation to the bottom bracket and pedal spindle (KOP). Each degree of additional angle moves the nominal saddle position forward by an average of 1.2cm. To obtain a more accurate calculation of the difference, use the formula: saddle height x (cosA-cosB). As long as you can achieve the desired KOP and still have some fore/aft travel left for experimentation, you have no problem. If you have the saddle all the way back or forward, something's not right. It could be the STA is not optimal, or it could just mean that a change in seatpost is needed.

The range of seat tube angles available in stock frames is really pretty small. For midsizes frames the range is 72.5 to 74 degrees. Large frames fall mostly in the 72-73 degree range. Small frames vary from 72.5 to 75 degrees, but most are in the higher 74-75 range.

To fully evaluate frame geometry you have to consider the combination of STA and "effective" TT length:

On a frame with a 74 degree seat tube angle for example, the saddle must be moved further back than a frame with a 73 degree seat tube angle, to achieve the same position relative to the bottom bracket. This movement of the saddle must be accounted for. Since the TT length is the standard reference value for comparing the reach to the handlebars, the difference in SADDLE POSITION is added or subtracted from the actual TT length to produce an "effective" TT length. The effective TT length will accurately predict the difference in reach to the handlebars between any two frames and allow you to determine the difference in stem length that would be needed to maintain the same reach. When comparing frames with different STA, add TT length to the frame with the steeper (74) angle or subtract length from the frame with the shallower (73) angle, using one of the following formulas: 1.32 x (cosA-cosB) x frame size, or an alternate formula, saddle height x (cosA-cosB). An average amount is 1.2cm per degree for a midsize frame.
seat tube angle...Philharmonic
Jul 1, 2002 6:07 PM
Well I was measured today in LBS and the optimum STA was determined to be 72 degrees. (Measured femur length, KOP, optimal TT and favored riding position). (I'm 5'8" and measured to take a 50cm c-c). Looking through stock bikes I see the Lemond Ti has a STA of 73 1/4--Litespeed 74. Would taking a 73 1/4 with angled (back) seatpost work or would I feel a difference (comfort) going custom as suggested by LBS?
Tom
measured?C-40
Jul 1, 2002 6:48 PM
I hope you were measured on a fit bike and not with a tape measure. A legitimate fitting must be done on a fit bike ( or a real bike). Even then, you must also know what your optimum KOP is, have a seatpost of the same style and the exact type of saddle that you intend to use, to get a valid fitting. Otherwise the STA may be off by 1 degree or the TT length off by 1cm or more.

What TT length and stem length (110mm?)did the LBS suggest? Your limited info describes someone who is a little short on legs and long on torso. The 50cm c-c frame size compares to a 51.5cm c-t. I'd figure on a 52cm c-t.

In Litespeed's you would choose between a 51cm and a 53cm. The 51 would be very small for a 5'-8" rider. The STA is also 73 degrees, not 74.

I'm close to your height (5'-7") but I have longer legs (83cm inseam). I ride a 54 or 55cm c-t. If you read carefully the info that I provided on comparing TT lengths, you will note that different combinations of TT length and STA will fit the same. For example, a 54.3cm TT with a 74 degree STA will fit the same as a 55.5cm TT with a 73 degree STA. I ride either of these combinations with a 110mm stem.

If your inseam is only 79-80cm, you should look into one of the many compact frames, like the Litespeed Siena. This frame design will provide additional standover clearance, allowing you to ride a larger frame (probably a 53) with more TT length.

The last thing that an inexperienced rider should do is purchase a custom, unless there is a lot of evidence backing up the suggestion.
Send them tomorrowPhilharmonic
Jul 1, 2002 7:35 PM
C-40: Thank you very much. Tomorrow I'll have the LBS fax me my measurements so I can answer the calculated TT and stem length question. I was fitted on a fit bike. I would appreciate if I could post or e-mail you these measurements for your opinion. Clearly your knowledge may help me make an informed purchase.
Tom
tkolbmd@bellatlantic.net (if you wish, e-mail me your address)
your opinion counts...kilimanjaro
Jul 1, 2002 10:16 AM
But for the those of us less experienced rec riders, how do we know what is most efficient for us?

I think I know the answer: "Ride lots" and ajust our setup and test it on the same run. However, it does seem daughnting for a beginner.
re: Fit vs Fittarwheel
Jul 1, 2002 10:39 AM
I missed the earlier recent discussion on fit, but I am a proponent for having a professional fitting done. If you already know what size works best for you, then there's little reason to get a fitting. In my case, I was riding a bike that felt too large, then bought a newer frame that felt too small. The fitting helped me nail down the size and -- more importantly -- the correct geometry. I realized I would fit best on a frame with a shorter top tube, and using that information I was able to go out and find a bike that fit just right.

BTW, I also completed the Wrench Science "formula" as well as the Colorado Cyclist one, and both recommended smaller frames than the professional fitter (Serotta). I know from experience that smaller frames just don't fit me. What the computer formulas don't account for very well are flexibility and riding style. I am not flexible enough to ride with low handlebars and it's just not comfortable for me. The computer formulas recommended a 54 c-c frame for me, which would have required a lot of seat post and a large drop from the saddle to handlebar. The Serotta fitting recommended a 56 c-c seat tube and slightly shorter top tube, which feels just right to me.