Road-to-tri saddle heights
1.14.04 by Dan Empfield
(www.slowtwitch.com)
I scratched my head for years over why it is I believe saddles ought to be about 5mm higher on tri bikes than on road bikes. I believe this although it is nonsensical on its face. Since one's pelvis is rotated forward while in the aero position, this ought to put the hamstrings on stretch to a greater degree than when simply road riding. If anything, tri bike saddles ought to be a smidge lower. So why do I believe the way I do?
After spending some time analyzing this, the truth finally became apparent to me, and in a way that is so transparently obvious I feel like an idiot sitting here writing it. But write it I will.
My saddle height is... what? Depends on where you measure. The USAT rule book requires it be measured 14cm behind the nose for purposes of legality, but in general I just measure midway between fore and aft. My road bike's saddle height measures out at 78.9cm, as can be seen at right. This is the height of the saddle when measuring from the center of the bottom bracket axle to the top of the saddle, midway between the saddle's nose and tail.
The saddle on my tri bike, as advertised, is about 5mm higher than my road bike's saddle when measured the same way. As one can see from the image at left, the saddle height on my tri bike is 79.4mm. (the shell of both saddles is roughly level with the ground).
For what it's worth, my road bike's saddle is set at exactly 73 degrees of seat angle (in order to establish some continuity and order to this question, I now measure from the BB through a point 17cm back from the nose of the saddle). My tri bike's seat angle is 81 degrees.
But this is not the whole story. One must also consider where one sits on the saddle. This is going to vary, rider to rider, and it's also going to depend upon what sort of riding we're talking about. It's common for a road rider to be sitting near the rear of the saddle when riding easily and while climbing, and nearer the nose when riding hard on the flats (or in my case right in the middle of the saddle). In general, though, most of a road rider's time will be spent with his trunk roughly two-thirds of the way toward the back of the saddle.
So I measured the seat height at this point—two-thirds of the way toward the back of the saddle—on my road bike, and lo and behold, I'm at 79.4cm of seat height. This is the same as the seat height on my tri bike.
One my tri bike, I'll spend my time riding either dead in the middle of the saddle while climbing (still in the aero position), and closer to the nose when I'm riding hard on the flats.
Were one to investigate the flex in my knee while riding both my tri and road race bikes, I'd have an angle of about 150 degrees with my knee as the apex and with lines running through my maleolus and greater trochanter (see our tri bike fit page for a fuller explanation of this). In other words, the pedaling action is the same for both road and tri.
When I am on the nose of my tri bike, my saddle height will of course shrink a few millimeters. Adjacent is an image of my saddle height about two-thirds of the way toward the nose. The ruler shows a seat height of 78.9cm, the same as on my road bike when I'm sitting in the middle of the saddle.
What all this means is, there really isn't any difference in seat height between the two style of bikes I ride, if you consider where it is I sit in the saddle on each bike. But when I measure the saddle in a way that is common to both bikes, that 5mm difference is evident.
I scratched my head for years over why it is I believe saddles ought to be about 5mm higher on tri bikes than on road bikes. I believe this although it is nonsensical on its face. Since one's pelvis is rotated forward while in the aero position, this ought to put the hamstrings on stretch to a greater degree than when simply road riding. If anything, tri bike saddles ought to be a smidge lower. So why do I believe the way I do?
My saddle height is... what? Depends on where you measure. The USAT rule book requires it be measured 14cm behind the nose for purposes of legality, but in general I just measure midway between fore and aft. My road bike's saddle height measures out at 78.9cm, as can be seen at right. This is the height of the saddle when measuring from the center of the bottom bracket axle to the top of the saddle, midway between the saddle's nose and tail.
The saddle on my tri bike, as advertised, is about 5mm higher than my road bike's saddle when measured the same way. As one can see from the image at left, the saddle height on my tri bike is 79.4mm. (the shell of both saddles is roughly level with the ground).
So I measured the seat height at this point—two-thirds of the way toward the back of the saddle—on my road bike, and lo and behold, I'm at 79.4cm of seat height. This is the same as the seat height on my tri bike.
When I am on the nose of my tri bike, my saddle height will of course shrink a few millimeters. Adjacent is an image of my saddle height about two-thirds of the way toward the nose. The ruler shows a seat height of 78.9cm, the same as on my road bike when I'm sitting in the middle of the saddle.
