Bicycle sizing 49 tt 5' 1' or 5'5'

[samsbike]

A friend is selling her bike which has a 49tt.

Convectional wisdom suggests that this is for a small person, say around 4 11 to 5 1.

However an old ad for for a similar sized bike, states that Roberts designed this for someone around 5' 5, would that bike not really be too small?

I am just curious as to sizing.

 

[vickster]

What’s the bike?

 

[si_c]

Some TT bikes are "sized down" as that allows the rider to get into a more aerodynamic position. I'd be very cautious buying one as a larger (6'5") rider so would want a fit. For a regular road bike I'd go on the geometry charts but TT bikes are a bit more "special".

Edit: Realised my skimming of the OP has bitten me in the posterior. Not a TT bike, but some of the point is still valid, Pro cyclists size down on road bikes as well as they tend to use longer stems than the rest of us. It may well be that the bike is designed around racing so would have a lower more aggressive geometry and expect a longer stem as part of the fitting. As @vickster says would be good to know the bike brand and model.

 

[HarryTheDog]

My Daughter was a Junior National TT champ. It took us forever to find a TT bike with a TT of 49cm. She is 5ft 2. She was sized on the bike proffessionally. Later in life she gave up TT ing and I borrowed it and set it up for me at 5ft 5 and it was fine as a TT bike fitted me like a glove.

Normal road bike I use 50 or 52 cm.
Her bike was a Fuji , I believe a C6. She still has it,
( note I was told by the fitter I had fairly long thigh to body measurement, ie my torso)

Edited because I realise the op is not neccasarily talking about a Tt time trial bike, I have 2 x 50cm top tube road bikes and they are ok for me.

 

[samsbike]

Its a chas roberts, touring bike definitely not a TT bike. Effective tt is 50cm while the sloping tt is 49cm. Seat tube is c 2 c is 42.5 and headtube is very short at 10cm.

 

[T4tomo]

Effective tt is 50cm while the sloping tt is 49cm.

Impossible in any Maths I've ever done.

Bike sizing is never exact, due to difference in reach for people of same height and / related leg length to torso ratios.

 

[MichaelW2]

A Roberts would have been custom sized for one particular person who may have had short torso and/or arms for their height. Factory bikes have to cater for the average rider but when it comes to small sizes they dont seem to do a good job.

 

[samsbike]

Why impossible, but I may well have made an error with the measuring tape!

However while I get it maybe sized for an individual person, I was curious what the range of height would typically be able to comfortably ride the bike.

 

[T4tomo]

Why impossible, but I may well have made an error with the measuring tape!

Basic trigonometry. the horizontal virtual distance is always the shortest. cant find a "squared" shortcut on my keyboard to do the formula but the square of the hippopotamus is equal to sum of squares of the other 2 sides.

 

[HarryTheDog]

Remember the seat frame tube is angled as well, not vertical, so the effective TT ie top of steerer tube horizontally to the seat post could be longer than the top of the steerer tube to the top of the seat frame tube.

 

[Spiderweb]

Impossible in any Maths I've ever done.

Bike sizing is never exact, due to difference in reach for people of same height and / related leg length to torso ratios.

The effective top tube will be longer than the actual sloping (compact frame) top tube.
My compact frame Hewitt top tube measures 52.5cm c/c but horizontal (effective) it measures 54cm.
Seat tubes thus seat posts slope back.

 

[HarryTheDog]

here TT horizontal is longet than Tt actual

 

[T4tomo]

The effective top tube will be longer than the actual sloping (compact frame) top tube.
My compact frame Hewitt top tube measures 52.5cm c/c but horizontal (effective) it measures 54cm.
Seat tubes thus seat posts slope back.

ahhhh yes i was assuming a vertical seatpost Fail!

 

[Cycleops]

What’s the bike?

I assume it's the one he's advertised on here:
Thread 'Roberts 49cc tt touring bike with small dent in tt' https://www.cyclechat.net/threads/roberts-49cc-tt-touring-bike-with-small-dent-in-tt.282280/

 

[Ming the Merciless]

Basic trigonometry. the horizontal virtual distance is always the shortest. cant find a "squared" shortcut on my keyboard to do the formula but the square of the hippopotamus is equal to sum of squares of the other 2 sides.