headwind_hater

Any Idea what I should expect by going from a 73.5 degree seat tube to a 75.3?

ehidle

A lot more load on the quads and a lot less on the hams, probably more knee problems, lower speed from excluding the hams, lower endurance since you're loading one muscle group more than its fair share, and your posture will look all hokey, resulting in jeers from the non-TT/Tri crowd.

AnthonyG

You should expect to have to use a rear set seatpost in order to move the saddle back to where it should have been in the first place.

Seriously we need more information on the situation to give a better answer. Nominally if you moved your saddle that far forward on a road bike you could expect to have too much weight on your hands/shoulders. Unless its a TT/TRI application you don't want a seat tube angle that steep even though those on small frames are given no choice. If by chance you have a small frame with the said 73.5º seat tube angle then HANG ON TO IT. They don't make them like that anymore.

Regards, Anthony

carpediemracing 

Seat tube angle is related to fit only, not handling. Yes, for a given seat rail position on a seat post it'll be different, but seat tube angle is used for both femur length and riding style. Handling won't feel too different unless something else is changed.

Therefore, for fit, unless your seat is locked in position on your seatpost, there will be no difference in pedaling fit (unless you want there to be one). You should be able to move the seat back to compensate. 2 degrees is somewhat significant so if your seat is far back already you may have to buy a different post.

Having said that, the top tube length may not be the same. Even if the number is the same, the "start point" (i.e. location of seat tube) is different. So on a 75 degree seat tube frame, your top tube will be a bit longer for a given actual measurement. If you have a 55 top tube on a 73 and you get the same top tube length on a 75, it may feel like a 56 because your seat is further back relative to the top tube.

Such a radical seat tube angle difference implies there may be other things different with the bike - head tube angle, fork rake, etc. These make a handling difference and that makes the bike a totally different creature.

cdr

headwind_hater

head tube angle is only 1/2 degree difference. My seat is currently all the way forward on my bike which is a little too big for me. So I'm hoping the seat tube angle plus a smaller bike should work.

carpediemracing 

The 1/2 headtube angle might be related to the smaller size. Sounds like the smaller frame would work better for you.

I have a 52 and it had a 73 head. The 50 has a 72.5, the 48 a 72. The slacker angles will help your foot clear the front tire, sort of. My size 41 hits my tire if I turn the wheel at the right time.

My seat tube is 74, and it gets steeper on the smaller frames. My seat post has zero setback and my seat rails are all the way forward.

cdr

AnthonyG

Why is your seat all the way forward on the seatpost? Does it need to be all the way forward to achieve KOPS (Knee over pedal spindle) or are you moving it forward in an attempt to reduce the reach to the handlbars?

I've done exactly that myself (moved the saddle all the way forward in an attempt to reduce the reach) but it doesn't work. This is counter-intuitive but you need to move the saddle REARWARDS in order to take the weight of your hands/shoulders.

If you are short (I'm very short) then what you need is to maintain the more relaxed seat tube angle while also having a frame with a short top tube. This is HARD to find and you most likely need to look at bikes with 650c wheels. Now unfortunately 650c off the shelf frames have steep seat tube angles as well but at least you can fit a rear set seatpost to relax the seat tube angle while still having a genuine top tube length that isn't too long.

Regards, Anthony

headwind_hater

Yes I do have it for KOPS, and I am 5'7" (and shrinking)

Thanks for the advice.