Commencal measure their frames ct of top tube to centre of seat post horizontally…..guessing here but this measurement is always going to be longer than the actual seat tube length?

Possibly a daft question content.

Yup, many frames state an effective top-tube length – more useful than actual top-tube length.

So it is longer. Eurika. The medium is too small 🙁

IMHO as a rough guide I’d say effective TT is generally about 0.75 of an inch longer than actual TT.

hora – Member

So it is longer. Eurika. The medium is too small [:(]

Medium Commencal? Yes, they are quite short. Though from your previous threads about the Giant Trance, a Medium Trance would be the order of the day rather than a large.

nukeproof – Member

IMHO as a rough guide I’d say effective TT is generally about 0.75 of an inch longer than actual TT.

TOTAL CRAP. Completely depends on the size of bike you’re buying. If you’re buying a diddy little 13″ frame, the actual TT length will be longer than the effecive TT length! If you’re buying a rather large frame, so the TT is totally horizontal, both measurements will be the same. It’s only in the more average sized bikes, say where the TT leaves the head tube at an angle close-ish to 90 degrees from the head tube, that the actual TT length is significantly shorter.

ALSO. TT length is not a totally reliable way of measuring a suitable bike. If you’re looking at 2 bikes, both with a 23″ effective TT, but both with significantly different seat angles, both will feel totally different reach wise!

TOTAL CRAP. Completely depends on the size of bike you’re buying.

Wwwwooooah there, steady now. Did I not put enough caveats in my comment…’IMHO’,’as a rough guide’. Given not all manu give both actual and effective, its works quite well for me although generally I get 16″ to 18″ and for those sizes its worked okay…and I should have said this: thank you for pointing out my glaring omissions 🙂

Wwwwooooah there, steady now. Did I not put enough caveats in my comment…’IMHO’,’as a rough guide’. Given not all manu give both actual and effective, its works quite well for me although generally I get 16″ to 18″ and for those sizes its worked okay.

Yeah sorry, reading it back does sound a touch harsh! Ooops

Anyway, yeah for say a 16 to 18 inch frame, roughly the sizes I’ve owned and ridden, you’re about right. But actual TT length does vary drastically compared to effective based upon the size of the bike. Hence why effective TT length is the only TT measurement to go by really, and even then you have to look at seat angle, wheelbase, chainstay length etc. in addition to be able to work out whether a bike should suit or not. Best way as always is to try a bike out for fit!