Frame size buying advice!!!!!

what brakes

I shall be getting a new frame soon but im torn on the size!

my current bike has a Horizontal TT of 557mm, with 73.5 seat tube and 73 Head Tube with a 110mm stem and feels good.

new frame is either a 545mm horizontal top tube or 565 horizontal top tube with a 73 seat and head tube.

Now do i go for the smaller frame and use a 120-130mm stem or the larger frame with a 100mm stem?????

Help please

i know most people say get the smaller frame if your torn between 2 sizes but the smaller frame is quite abit smaller!

maddog 2

punctuation alert!!!!

bigger, IMO 8)

Berk Bonebonce

If you currently ride with a few centimetres worth of headset spacers, go for the larger. However, if you ride with no spacers, go for the smaller.

what brakes

I do have about a 1-1.5cm of spacers!

cookiemonster

The change from 73.5 to 73 degree seat post will (assuming you keep your saddle in the same position relative to the bottom bracket) shorten the reach - basically move you closer to the bars and give an effect similar to having a shorter top tube. So 565 effect tob tube with a 73 ST will likely give much the same reach as a 557 and 73.5

Have a look at the "Geometry and Fit" presentation here: http://www.cervelo.com/en_us/engineering/tech-presentations/

As BB says, the other thing to check is stack height

Jon

kfinlay

cookiemonster wrote:

The change from 73.5 to 73 degree seat post will (assuming you keep your saddle in the same position relative to the bottom bracket) shorten the reach - basically move you closer to the bars and give an effect similar to having a shorter top tube. So 565 effect tob tube with a 73 ST will likely give much the same reach as a 557 and 73.5

Have a look at the "Geometry and Fit" presentation here: http://www.cervelo.com/en_us/engineering/tech-presentations/

As BB says, the other thing to check is stack height

Jon

I thought it was the larger the seat tube angle the closer you are to the bars so for the OP going from 73.5 to 73 degrees would effectively make the reach a few mm longer?

Agree about the spacers though

cookiemonster

Hi

A larger seatpost angle (say going from 73 to 73.5) moves the seatpost more upright. This means that you have to slide the saddle back on the seatpost to achieve the same position relative to the bottom bracket, giving you a longer distance from the tip of the saddle to the handlebars. So, for example, a frame with a 74 degree ST and 555 mm TT is effectively the same length as one with a 73 degree ST and a 565 mm TT.

Its easier to visualise (at least for me) if you take an extreme - compare a frame with a 73 degree seat tube to one with a 90 degree, vertical seat tube. If they both have 550mm tob tubes, then you can see that you'll need to push the saddle way way back on the "vertical" 90 degree post to get the same position over the bottom bracket. Then you'll end up with a massive reach to the handlebars.

jon

maddog 2

cookie has it right but I'm not sure the explanation is 100% clear, as you throw seat adjustment into the mix.

The new frame has a slacker SA than the old one.

So you'll need a longer ETT to compensate for this.

So, approximately, the new frame with a 565mm TT with be very close (in terms of reach) to the current frame with a 557mm TT.

So you should buy the bigger frame, as it'll be very similar to ride.

(unless something else is different, like head tube length etc.)

what brakes

kool cheers guys. i shall aim for the bigger frame unless someone show that we are all wrong! lol

kfinlay

Think we were all on the same page just looking at it slightly differently as I agree the saddle would need to be moved back to keep the same relative position to the BB. Not the easiest thing to explain in words

Wheelie Bin

Go larger. I think if you need a 120/130mm stem on a 55/56cm bike, it's an indication that the bike's too small.