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Help me understand bike fit numbers
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I was hoping someone could help educate me on bike fit numbers. I just had a fit done last week and have attached the numbers. I'm a little lost on how to use these numbers to determine either how to setup my current bikes, or how to choose a new frame. Is there some sort of calculator to plug these numbers into that will show me what size stem and spacers to use? I know that frames all have different stack and reach numbers, but how do those equate to these numbers from my fit?

Any and all help is appreciated.


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Re: Help me understand bike fit numbers [summers_jm] [ In reply to ]
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If you want to know how to set up your current bikes - let us know what those are (model and size)
If you want a new bike - yes there is a calculator (advanced bike finder at velogicfit.com, there is a fee for use)
Or you can read through Dans material on the site to learn how to do the calculations manually

Note: I created the velogicfit bike finder, but I don't think I'm biased in saying it is the best one available for tri bikes - mainly because it is the only calculator that can handle aerobars.
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Re: Help me understand bike fit numbers [summers_jm] [ In reply to ]
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did your fitter not tell you how to set up your current bike? I would have done that for you....

Eric Reid AeroFit | Instagram Portfolio
Aerodynamic Retul Bike Fitting

“You are experiencing the managed opposition coverup of a foreign backed cryptofascist hostile takeover of a mafia shakedown of an authoritarian religious slow motion coup. Persuade people to vote for Democracy.”
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Re: Help me understand bike fit numbers [ericMPro] [ In reply to ]
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What Eric said.... most fitters should give you more than just the numbers. There is a lot of nuance that goes into picking out a bike based on a set of bike fit numbers and you can easily go down the wrong path and make a poor decision. I would go back to the fitter you employed and ask for assistance with this.

Jonathan Blyer,
ACME Bicycle Co., Brooklyn, NY
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Re: Help me understand bike fit numbers [summers_jm] [ In reply to ]
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like clockwork, every end-jan, beginning-feb, we get these threads. and, in response, i rewrite my bike fit reasonable expectations article. so, there you go. if you want to know what you should expect from a fit session, read that article. if you want to throw yourself and the mercy of the fitter, then avoid that article.

Dan Empfield
aka Slowman
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Re: Help me understand bike fit numbers [summers_jm] [ In reply to ]
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To determine what bikes work, take your arm pad stack of 662 and arm pad reach of 432, and compare them to charts like THIS, published by most forward thinking triathlon bike producers in some form. Be careful whether the chart lists back of pad or center of pad as you numbers are for the back, so you should add roughly 3-4cm to get a center of pad measurement. So for this chart by Felt, you would use 662 and 472 and find you fit on a 51, 54, 56 and 58. The 51 is out as you are probably close to or over 6 feet tall, and close to both limits on that bike anyway. You are nearly dead center on reach on the 54 but really stacked up close to the limit, which is not pretty on the IA's, so the question is how set are you in this position, how many extra lbs are you carrying, etc? You are in the aesthetic sweet spot of the 56, and that would be my top choice on this bike, certainly when we look at that 795 saddle height, it makes a lot of sense. You only have 1.5cm to go down on the 58, and at your size, maybe after you shed those 20 extra lbs, you would want to drop down 2-4 more cm, so the 58 is out.

And if you fit on a 56 IA, you fit on quite a bit of other 56s, from Cervelo, Trek, QR, etc.

To set up your current bike, read this:

You need only a tape measure in cm, a level and a set of allen wrenches. Additionally, you may want a plumb line, torque wrench and digital level, but these are generally not required. Sometimes your bike may need new parts installed or it might need to be re-cabled or have some other specialized task completed. Below are the measuring conventions I use, and these are fairly standard across the bike industry. There are different ways to measure some of these, and I try to include the simplest solutions.

· Saddle Height – measure from center of the bottom bracket to the top of the middle of the seat. (For Adamo and other non traditional saddles we measure to the top of the front 1/3 of the seat, as that is the usable portion of the Adamo, while the entire top of the seat is the usable portion for most others)

· Setback – Method 1, With the back wheel up against a wall, bike on level ground, measure the level, straight line distance from the wall to the center of the bottom bracket (A) and again from the wall to tip of the saddle (B). A – B = Setback

· Setback, Method 2, Drop a plumb line down from the tip of the saddle and measure the horizontal distance behind (or in front of for some triathlon set ups) the center of the bottom bracket.

· Setback, Method 3, Hold a level vertical, with the back edge passing through the center of the bottom bracket and measure the horizontal distance back or forward to the seat. Back is a negative setback and forward is a positive setback.

· Cockpit – measure the straight line from the tip of the saddle to the pivot of the aerobar shifters, if you have them. If no shifters are present, measure to the end of the extensions.

· Drop – Place the level on the and angle it over one of the armrests without the pad installed. Make sure it is level and then measure the distance down to the center top of the armrest. Alternatively, you can measure this similar to setback. Measure up from the floor to the top of the seat, and again from the floor to the center top of the armrest. The difference is the drop (or rise in some cases)

· Saddle to armrests – With the elbow pads removed, measure the straight line distance to middle point on the back of the armrest.

· Armrest Width – measure the center to center distance on the armrest pads. Or outer to outer if you prefer.

· Aerobar width – measure the distance between the aerobars at the ends, but before the shifters. Any canting to the bars should be noted as well.

· Aerobar tilt – The simplest method to set your tilt correctly (if you run any) is to make sure everything else is correct and then measure the distance the tips of the bars are off the floor directly beneath them. No angle measure is required for this.

Be aware that moving one thing on your bike almost always affects something else. For instance, when your seat goes up, it also goes back, affecting your setback. So put the setback close to desired, set the seat height, and depending on how much the height changes, you may need to make a small change to setback.
Same principle applies to the handlebars. Moving them up or down also moves them back and forth slightly, so always double check everything and be prepared to make small adjustments.
Last edited by: FindinFreestyle: Feb 8, 18 16:29
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Re: Help me understand bike fit numbers [summers_jm] [ In reply to ]
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I'm going to answer with your bike specifics here as I can't attach images in PM and we're not talking about anything delicate.

Your fitter was, how can I put this nicely... wrong about being able to set your bike up
Your target position can be achieved on the BMC, within 1mm on XY and 3mm on Z. This is based on the Profile Design T4 bars that were probably stock on your bike.
However, it requires a 110mm stem with the pads in their most forward position, so you will have quite a lot of weight over the front wheel.

I'd suggest that you get the current bike set up to match the stated position, then, if that works well for you - consider a new bike. The M-L would be a better fit. Or an L if you want stability.

Or a 56 in the standard geo (shared by Cervelo, Trek, QR etc) would fit really nicely.
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