Top Tube question

[nscrbug]

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

[Catrin]

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

[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.

[nscrbug]

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.

[nscrbug]

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.

[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.

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.

[Becky]

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

[Owlie]

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?

[ny biker]

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.

[laura*]

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.

[OakLeaf]

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??

[Becky]

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.