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Mixte seat tube design.

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Mixte seat tube design.

Old 02-11-13, 07:14 AM
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mickey85
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Mixte seat tube design.

I was building up a Raleigh Rapide mixte frame last night (flat bars, VO Model 8 saddle, 3X5 gearing, 27" cyclocross tires and fenders), and started wondering something...

On both of the Mixtes that I own (Taiwan made Rapide, French rebranded Peugeot), as well as most of the others I see, why is the seat tube significantly lower than it would be on a diamond frame?

Given the dimensions of the Rapide, it should be a 58cm bike - the head tube is as long as my 58 bikes, and the stretch is about the same (from head tube to seat tube); however, when you draw the top tube, the seat tube barely reaches it, and you have to have a good foot of seatpost sticking out where otherwise it would be 4-6". Why is this the case with this design?
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Old 02-11-13, 07:20 AM
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I think swept back Northroads style handlebars require a longer top tube in proportion to seat tube height. Also, urban bikes generally want the handlebars at or above the saddle height.
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Old 02-11-13, 07:42 AM
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Most mixtes are designed for women who generally are shorter than men. That requires a shorter seat tube. I know men ride mixtes but that is not who the bikes are designed for. Roger
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Old 02-11-13, 07:52 AM
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Originally Posted by rhenning View Post
Most mixtes are designed for women who generally are shorter than men. That requires a shorter seat tube. I know men ride mixtes but that is not who the bikes are designed for. Roger
I understand that, but standard step-through frames are generally "square" as far as the virtual top tube goes. It seems just the Mixte frames that have a "compact" geometry...

Case in point:
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Old 02-11-13, 08:49 AM
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My observations on the subject indicate that most manufacturers offer a mixte frame that it 1-2" smaller than their step-through frames.

Most mixte are designed around a 27" wheels versus 26" for step though. This results in a slightly higher head tube. While the manufacturers could compensate with a shorter head tube, it is more economical to cut and stock a single size of head tube, since mixte frames are not limited by a standard top head lug requiring a horizontal top tube. The longer head tube also increases headset stability and ensures a safe amount of stem insertion, which becomes an issue with very short head tubes, especially those with butted steering columns, which further restrict insertion.

Mixtes also typically have slightly longer crankarms and higher bottom brackets to allow for more sporty ridng. The shorter seat tube compensates for these factors, to allow the same saddle to ground measurements for a given leg extension.
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Old 02-11-13, 08:50 AM
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I believe as pointed out since Mixtes (Mixties? Mixti?) are intended for women the seattubg is cut short since most women want to have their feet flat on the ground while seated when they are stopped.

I believe the reason for the tall Stepthrough is simple economy of scale. If your producing 10,000 bikes a month and you only need 10% to be stepthrough you just keep everything the same and drop the TT. I never thought to measure but I bet the 'top tube' on the step through is close to the correct size to be used as a standard TT.
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