Top Tube question

So I've been browsing around LBS's the past few weekends as I am seriously contemplating a new bike. As like many of you, I'm currently on a 51cm Cannondale Synapse (Carbon Fem 3 Ultegra). I'm thinking about switching over to SRAM (tested one and immediately liked the feel of it)...but the switch also involves getting a bike that fits me better, due to ongoing fit issues that I've had since day 1 with the Synapse. And yes, I've had 3 pro fittings, including 1 Retul fit and I still can't get dialed in correctly with regards to my hands (pain, numbness, tingly).

While at a TREK dealer, the guy there told me that Cannondales are known for having very long top tubes, which is probably why I'm having issues. I went online to get the measurement of my top tube - it's 52.5cm. I then went to the Trek site to get the measurement of a 52cm Madone - it's 52.9cm! Why in the world would this guy tell me that my Cannondale has a long top tube, when in fact, the Madone has an even longer one?!? Was this guy just trying to push a Madone on me? Did he actually think I wouldn't go and check the measurements myself?

Also stopped at a Specialized dealer the same day. My DH bought his bike from this dealer, so the owner sort of knows us. Personally, I think he is a tool (to put it nicely) and we tend to not do much business there. But I wanted to take an up-close look at a Ruby. He too, told me that my Synapse has a longer top tube, which is going to stretch me out more. Naturally, I checked the TT measurement on the 51cm Ruby, and it's 51.5...so he actually was right about the Ruby being shorter.

I'm also a bit confused as to why some the C'dale race geometry bikes (Supersix & CAAD) both have a SHORTER TT (52cm) than the more relaxed Synapse in the same frame size? Is the longer TT common with all plush geometry bikes? Or am I missing some other key element here?

Linda

Could they be measuring them differently? Just a thought...

What are their respective seat tube angles? Top tube measurements can't be directly compared unless the STA measurements are the same between the two frames.

Quote:

---

Originally Posted by Becky

What are their respective seat tube angles? Top tube measurements can't be directly compared unless the STA measurements are the same between the two frames.

---

Ahhh...I did not know this. Thank you for pointing this out. I will go check those measurements out.

Quote:

---

Originally Posted by Catrin

Could they be measuring them differently? Just a thought...

---

Well, it appears they all use the "horizontal" or effective TT length...so I would assume that they are all measuring the same way. But I suppose it's always a possibility that they aren't.

Eh, I've talked to any number of LBS sales people over the years to know that some of them don't know their product lines very well. A few weeks ago, someone tried to convince me that a particular company's WSD FS bikes had short top tubes/standover than their unisex counterparts. No, actually they don't but thanks for the helpful salespitch.

Now, don't get me wrong; it's hard to commit that stuff to memory year and year. I get it to some degree, but I think they should be careful in making geometry generalizations.

Quote:

---

Originally Posted by indysteel

Eh, I've talked to any number of LBS sales people over the years to know that some of them don't know their product lines very well. A few weeks ago, someone tried to convince me that a particular company's WSD FS bikes had short top tubes/standover than their unisex counterparts. No, actually they don't but thanks for the helpful salespitch.

---

Indy, so true! My only "WSD" bike has identical geometry to the company's unisex "comfort carbon" geometry....and a girly paint job ;)

Maybe they measure differently? Giant's bikes seem to have freakishly long top-tubes, so by comparison, Trek and Cannondale aren't too bad.

I have the same question about the CAAD/SuperSix. They're on the long side, but they might actually work for me. Shorter top tube, less steep seat tube angle. What gives?

Quote:

---

Originally Posted by Becky

What are their respective seat tube angles? Top tube measurements can't be directly compared unless the STA measurements are the same between the two frames.

---

Yeah, I would try to measure something else that takes into account angle differences, like seat post to stem.

Quote:

---

Originally Posted by nscrbug

Well, it appears they all use the "horizontal" or effective TT length...so I would assume that they are all measuring the same way. But I suppose it's always a possibility that they aren't.

---

They may all be "measuring the same way", but that doesn't mean they are measuring equivalent lengths.

Imagine a bike with a very vertical seat tube. To set up a proper saddle to crank relation, this bike would use a seat post with a large setback. Now imagine a bike with a very tilted back seat tube. This bike might have a seat post with no setback. With identical saddle to handlebar length, the second bike will have a much longer (effective) top tube.

The weird thing is that my 50 cm '07 Synapse Feminine has a 50.5 ETT. It does have a pretty steep STA though. Unfortunately they took the archived specs down and I didn't save a copy, but I want to say mine is 75° vs. your 74°. Wasn't somebody just talking about trigonometry - will 1° of difference over say 70 cm of seat tube, seatpost and saddle make a 1.5 cm difference in the reach??

A little bit of reading on the subject:

http://www.billbostoncycles.com/seat_tube_angle.htm

http://www.velofitter.com/storage/Ro...lines.4.10.pdf (page 4)

The rule of thumb is that, for every degree that the STA increases, the effective top tube increases 1 cm.