Bike fit

Unsure. But wanted to say very good luck to you at your upcoming IM!!

Chad

Was the road bike a perfect fit before???? 

When it comes to fit its never a bad idea to have a pro look at your position.  Obviously with a IM coming you'll be on the bike a while to say the least, and will want comfort and performance.

Disclaimer... I'm not a pro, just like to wrench on my bike.  Also, I'm short so the distances I have to adjust my bike, tri or roadie are very small; in fact its only a 14mm diffence in seat position, so I have not spent the extra money to purchased a tri bike, but my fit on the road bike is very areo/tri dispite the bikes geo. because of my size and the tweaks I've made.  Also, I learned most of my positions from slowtwich.com's bike fit section, so its hardly science.

Generally speaking road fit and tri fit aren't that much different in terms of your body positioning relative to your hip angle, but the seat position in relationship to the crank or bottom bracket changes what would be ideal hip angle a bunch if you go aero on a road bike.   This is gonna be a rough discription but hopefully its clear enough to follow. 

Hip angle is normally about 100 to 110 degrees give or take.  For arguement sake lets call it a right angle (heel to hip to shoullder) even though 100 degrees is slightly obtuse.  On a road bike the seat is typically behind the bottom bracket or center of crank and it varies depending on seat height. (the higher the seat the further back the seat goes)  So on a road bike a right angle bottom bracket to seat leaves your spine pointing up about 30-40 degrees.  To get areo and try and get your spine angle to 10-20 degrees you would have to take that right angle (or slightly obtuse angle) and compress it.  Leaving your hip angle well below 90 (now acute) and in a tight position on the bike.  The rule of thumb is to not go acute or below 90, how much it affects performance I don't know, but for me acute hip angle eqauls uncomfortable.  On a tri bike the front of the seat or narrow part is designed to be over the bottom bracket and when you lay that right angle on it your already in a nice aero position with the spine relatively flat 10-20 degrees, and the hip angle is obtuse or greater than 90.  Minor adjustments need to be made to seat height and cockpit length for comfort.  But the biggest issue in aero (IMO) is that hip angle  staying obtuse which is controlled by the seat position in relationship to the bottom bracket.

So, if the road bike is a proper fit now your behind the bottom bracket with a nice slightly obtuse  hip angle; in addition to just adding the areo bars you may also want to move the seat forward up by adding a forward seat post and slide the seat forward on its rails so the narrow part of the seat over the bottom bracket; or at least that's what I was able to do.  People often talk about just using  their road bike and clip-on areo bars, which I don't think is a bad idea;  I think it's a good idea its exactly what I've done, there's just more to it than just adding the bars.  The tri-bike is designed to keep your hip angle greater than 90 or 100 while in that aero position where your spine in around 10-20 degrees.  They accomplish that with frame design... you accomplish that with seat position relative to the bottom bracket.  So, when I hear someone say I'll just put bars on my road bike and go aero I think to myself I hope they're not sitting behind the bottom bracket with an acute hip angle.

Also, a bike ( tri, or road or mountain) is designed with a specific center of gravity, based on where the manufacturer perceives the rider to be.  If you start changing  things like seat position, seat height, aero bars, stem length, handle bar height/width; you change your center of gravity and the bike may handle differently.  Which may be good or bad or indifferent depending on the severity of the changes.  In my case the handling was not affected, but my adjustments were very small.

what Drew said looks rock solid to me.... adding a little from personal experience below...

Profile Designs makes a forward-set seatpost, but you can usually go from typical road bike seatpost angle of 73 degrees to typical tri bike geometry of 76-78 degrees by sliding your seat forward on the rails, or using a zero-offset (ie straight up and down) seatpost, or by using a tri specific seat.... or some combination of the three. And I highly recommend a new tri-specific seat. It'll have more cushion up front (more than a normal road seat), and will have longer seat rails, to allow you to slide the seat forward about 10-20mm (also more than a normal road seat). I know from personal experience that Fiziks and Profile Designs have long rails ... you can get a Fizik Nisene with Ti rails on chainreactioncycles.com on sale right now for less than sixty bucks.

Then check your fit ... if you need to, post a pic of yourself on a trainer spinning on your new rig, and some pretty experienced guys/gals will check you out. Don't try to get to aggressive with your geomtry.... the issues about frame weight and balance and center of gravity are true. Pushing the weight forward can twitch out your steering. And don't slide your seat further forward than tip-of-seat-nose about 5-6cm BEHIND the centerline of your bottom bracket .... 7 or 8 cm is ideal... if you need to shorten the cockpit any more than that, you should use a shorter stem. Seat angle too steep (>80 degrees?) will definately screw up your balance on the bike and maybe could also screw up your knees.

Put that pic up ... I'd be interested in seeing how it works out.

Edited by jsselle 2009-12-28 5:57 PM

WOW!! I'm great at math and I got an idea of what was going on there, but wow! is there a web site that can walk you through. I looked at the one mentioned slowtwich.com but nothing?

Thanks,
Chad

http://www.slowtwitch.com/Bike_Fit/F.I.S.T._Tri_bike_fit_system/Hip_angle_24.html

Hopefully this link and picture will help.

I'm 5-5 and ride a 50 cm road frame, and like I said my adjustments are very small and I'm in  great "tri/areo" riding position even though my bike frame was built with conventional road geometry.  At 5-7 I would think you could make minor adjustments to get into the same positiion as well but it will depend on your body shape.

I also wanna add that I think tri-bikes are great and I often thinking about getting a tri-specific frame but haven't because at 50cm frame size MY ideal numbers are very close..  I also PREFER brakelever shifting because most of my riding is training in traffic and not on a closed course and most of my shifting is done when approaching intersections.

If you wanna post a picture of your bike alone, and one with you on it in aero; I'm sure the better cyclist here will give you some great feedback.

Are the aerobars you purchased "full size" or the shorter ones like PD Jammers? I have the latter, and feel like you could probably do that by yourself, but if you've got the longer ones, I think the changes will be more substantive and would consequently be a bit more hesitant to DIY in that case.

They are the short aerobars so I may be able to adjust them myself.  The link is very helpful.

Thanks again!