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Bar style change relative TT length

Hi Brent, I hope you're doing great. I just love using BikeCAD, it's a ton of fun.

So I was wondering lets say I have a road frame geometry and I switch from road drop bars to flat bars.
Assuming that the hand position on the drop bars is on the hoods, and the hand position on the flat bars is a given.
Shouldn't the TT length automatically increase to adjust for the shorter rider compartment?
If I design a road bike and then swap to flat bars, will it be too short?

One more question:
When measuring a customer, should they be barefoot or in their riding shoes?


Bar style change relative to top tube length

I can understand how when you switch from drop bars to flat bars, you might like for the top tube length to change. However, changing the top tube length is not the only way to control the distance from the saddle to the brake hoods, or the distance from the saddle to the handlebars. You could just as well change the stem length. Furthermore, while it might at times be desirable for the top tube to change as you describe, I don't think I would want that to happen automatically. After having modeled a frame, it is sometimes nice to see how that same frame would look with either drop bars or flat bars.

Let's assume that we do have a well fitting road bike with drop bars. Would that same bike feel too short if we swap in a flat bar? I'd say it depends.

Your position when riding the flat bar is actually going to be similar to your position when riding on the tops of the drop bar. If that's the kind of position you're going for, then you'd be fine with the same top tube length. If you are trying to replicate the position you have when riding on the hoods, then you will need either a longer stem or a longer top tube.

As for your question about taking measurements barefoot or in riding shoes, the key is to be consistent. The Fit advisor has been designed to be customized to suit any fitting philosophy. The Fit advisor takes body measurements and through customizable formulas calculates values for frame geometry such as saddle height, effective top tube length, rider compartment etc.

If you take an inseam length with shoes on, the resulting measurement will be larger than one taken without shoes. However, you can compensate for that by using a smaller coefficient in any formula that multiplies inseam length by a coefficient to obtain some dimension of frame geometry.

BikeCAD Pro does come with a set of default formulas for various types of riding, and the assumption is that those measurements are taken barefoot. However, these default formula should not be taken as gospel. They cannot possibly agree with every fitting philosophy. It is entirely possible that some fitters will coincidentally find that the default formulas work well for them when a rider is measured with shoes on.

At the end of the day, I encourage fitters to examine the formulas in the Fit advisor and tweak the numbers until the results suit their own fitting philosophies.

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