DRLski

Would I really notice a difference between a TT length of 53.7cm and 54.9cm?

badkarma

You might notice it - if so, just change your stem.

botto 

almost a centimeter, and if you use the same length stem? you bet.

cslone

I personally noticed a difference in a 110 to 120 stem, so I would think yes. But whatever you change in top tube, you can negate in stem length and seat rail adjustment.

xthugmurderx

never touch your seat to move the reach. get a new stem. moving the saddle forward or back will mess up your alignment over the pedals. not a good idea.

Al1943

Yes, and I would avoid a stem length of less than 100mm if possible.

jimbud

The other question for you to consider is how stretched out you feel on the 53.7 TT bike?

DRLski

enough, but mostly because I'm not very flexible just yet...although I'm getting there. I'm also only using a 100mm stem so not sure if I'd actually consider going to a 90mm. Another thing I'm looking at is the seat angles, isn't it something like the steeper the angle the shorter you want for a TT or something like that? For instance if my bike with a TT of 53.7cm has a 74degree seat angle would I not notice as much of a difference on the 54.9TT if it had a 73 or 73.5degree seat angle?

jimbud

I don't think the half degree seat post angle will make a big difference on a road bike set up. If it were a multi-sport set up with aero bars I think it would. It does change the amount of body weight put on your hands or bars. You can counter act that by saddle angle. Find a 110mm stem and put it on your 53.7 TT bike and see if it works for you. It will be similar to the longer TT bike's set up.

OCRider2000

first question I would have is where are you most comfortable relative to KOPS (KOPS or rear of the spindles?). Where do you find you make the most power relative to KOPS (position relative to spindles). Once you have identified that location I would not change your the fore\aft position of your seat. So in order to get the overall reach you want you need to get the right combination of top tube length\seat tube angle and stem. Then you need to consider how different stem lengths will effect handling. 1.2CM is a pretty significant difference in top tube length assuming the same seat tube angle and to a lesser degree head tube angle. My personal preference is to go with a seat tube angle plus top tube length that lets me ride with a 12cm stem. Of course everyone's riding style, body dimensions and flexibility are not the same. Do your own research on proper road bike fitting and all of this will make a lot more sense to you and you will understand the relationship between frame size\geometry and how it effects your position on the bike.

SpongeDad

also - do the bikes have the same seat tube angle? by the time you get your saddle to the same setback relative to the BB, the actual TT length may be different than the nominal TT length.

curiouskid55

Thats the shortest time trial I have ever heard of.

jimbud

OCRider2000 has a great post. I have two bikes that I ride regularly. Bike one is set up with a more relaxed set up. (55.6 top tube, 100mm stem) Flipped up stem with a saddle to bar drop of 5 cm. This bike I can ride all day, handles great and goes fast. Bike two is set up according to wrench science's fit system. (55.5cm top tube, 120mm stem) It's much more stretched out then my other bike and has a 9 cm saddle to bar drop. This bike fits me perfectly to make tons of power. Power transfer from the bars through my arms down in to my legs is instant and I can cruse much faster on this bike then on bike one but the bad thing is I can only ride this bike for about a hour and a half before getting a sore back. So in the long run which bike is better. I guess I could go to the gym and find some exercises to strengthen my back but I'm not going bike racing any time soon. So there's a argument as to which bike fits me better.

terry b

Using your standard 53.7/74 bike and assuming your position relative to the pedals is ideal and that you don't want to change it, a 54.9/73 bike will fit like a 54/74 bike, and a 54.9/73.5 bike will fit like a 54.5/74 bike due to the required forward movement of the saddle to retain proper setback. At this size frame it's about .45cm per 1/2 degree of seat tube angle.

DRLski

I think I understand what you're saying but what exactly does this tell me?

DRLski

Yes, Thanks for the clarification jimbud

terry b

It tells you that you're adding the equivalent of .3cm if you go with a 54.9TT/73STA frame or .8cm with a 54.9TT/73.5STA bike compared to your standard.

Because the bikes with the longer TT have a shallower seat tube angle, you must move your saddle forward by a specified amount to achieve your current position on the smaller bike. This means some of the increased TT lenght is reduced by the forward movement of the saddle.

Only you can tell if .3 or .8 CM makes a difference to you.

OCRider2000

Of course if you really want to get your numbers closer to dead on then the two frames you are comparing would need to have identical seat tube lengths as a frame with a shorter seat tube will add more overall reach once you've adjusted the seat height verses the frame with a longer seat tube....

terry b

Yes, about 3mm per 1cm of seat tube length.

cslone

What I mean is if the bike is bigger and depending on geometry, he may have to sdjust his seat rails to get the right saddle to bar reach.

ed073

+1.

terry b

You never adjust the saddle position to achieve reach associated with changing frame size. You change stems. Once the saddle height is set and the fore/aft is correct for position over the pedals, you leave it alone.

The only adjustment you make to the saddle when going up in size is lowering it and adjusting fore/aft to get it back to where it would be on a smaller frame.