56cm or 58cm frame

Chefshaw

hi guys, im currently riding a trek 4.5 with full dura ace, and mavic kysrium sl wheels its a size 56cm and fits great.
but i have just been given a trek 5.5 frame but in a 58cm size.
i have built it up with all the stuff off the 4.5 bike and taken it out for a ride. all seemed ok.
my dilemma is should i stick with the 4.5 in a 56cm or keep the 5.5 in a 58.
my only real reason for keeping the 5.5 is because its a better and lighter bike?

the 2 real questions are?
how much weight am i saving between the 2 frames?
what are the disadvantages of riding a slighltly oversized bike

Pretre

Chefshaw wrote:

the 2 real questions are?
how much weight am i saving between the 2 frames?
what are the disadvantages of riding a slighltly oversized bike

2. Depends - I'm not an expert but there only seems to be 2 areas of concern -
a) Saddle height - this can be adjusted by lowering the seatpost, if it has one, but if it is an ISP then you could end up straining your knees & hips really badly as you'll be rocking from side to side at the bottom of each stroke, even if you don't realise you're doing it.
b) Handlebar reach - this can be adjusted by changing the stem length.

There may well be other differences but a 2cm frame size change isn't that much

rjh299

It doesn't matter how much better the 5.5 is if it doesn't fit properly.
If the 5.5 fits aswell as your 4.5, keep it. If it doesn't, than stick to your 4.5.
Try the 5.5 a few more times and see if you develop any aches you normally don't on your 4.5.
Oversized bike can cause back, knee, neck, hip pain

Chefshaw

Seat height is definitely not a problem. Think I will try a couple more 3 hour rides

John.T

1.5cm longer TT (virtual) and 2cm (assuming a 'Performance Fit' 5.5) longer head tube. Providing you are comfortable use the one you like best.
By changing seat masts and stems it is possible to get a good fit on 3 different sizes and a fair fit on 5. The govening factor is how long or short a stem you want and how high your bars relative to saddle.

Pross

As John says, it should be fairly easy to set up both bikes so the key measurements are the same. As long as the 56cm isn't at the limit for you it shouldn't be a problem - lots of people fall between sizes (I'm one who could easily use a 56 or 58, got a 58 as it was the right length without changing the stem).