[Closed] Hung up on reach and stack numbers

I have a Genesis Datum, size M. Im almost 5’9″ with a 30″ inseam. Im definatwly longer body and arms, than legs. On the Datum i have a 120mm stem and its -6°. Its a bit too high but v comfortable. The saddle is on an inline seatpost and is as far forwards as it will go. I have 18cm from top of seat tube to top of saddle.

I'm all for riding whatever's comfortable if it works, but that just sounds wrong. Do you really need the saddle ~2" further forward than average and a 1" longer stem?

Sometimes the frame you want simply isn't available in the size you need.

Can you find a way to adjust the fit of your Genesis to approximate the Mason and then try it out?

Test ride each bike with the correct sized frame for you. Figures etc are meaningless and tbh should only ever be used as a rough guide only.

@TINAS the sizing for the datum is up to 5'8" for the small, and the medium is for riders 5'6" to 6".
I seem to be very comfortable on the datum, so im going to have to measure my road bike and my rigid mtb.
Now ive written it down, it does sound a bit odd. I have put tribars on it and i do seem to be comfortable. Ive ridden it for long days without problems. im mow worried ive adopted some oddball position that affects what i can chose next.
I guess if i get a shorter stem and move the saddle back by a corresponding amount, i may be able to replicate a more normal position?

Edit: I see you've pre-empted me while I was typing 🙂 hey ho…

Looking at the sheets, the 56cm Bokeh looks very close to the medium Datum, so I don't think you're missing anything; there must simply be more slope in the Datum's top tube (or more head tube above the top tube junction).

Your setup does sound unusual, though. If you went for a smaller Bokeh then you'd still be able to get the same fit in terms of upper body; what would change would be your leg fit: you'd be sitting further back relative to the BB (or your pedals would move forward, if you prefer).

So I guess the question is whether you feel your current position is right in terms of your hips and knees. If it is then you'd be looking at the 56 Bokeh; if you'd actually be more comfortable sliding further back then you might be better with a smaller one. (IME the more I ride, the more comfortable I am further back.)

You can do a test by swapping your current stem for one that's, say, 20mm shorter and sliding your saddle back by the same amount: your upper body position will be unchanged but your pedals effectively move forward.

(Caveat lector: I know maths but not biomechanics. And I'm a completely different size and shape to you.)

@Bez, thanks. I understand that, i will give it a try.

Im fairly sure i have the bottom of my kneecap over the pedal spindle when the crank is at the 3 o'clock position....however now ive been measuring and writing it down it does seem like i have done something odd.

The 56 seems to be ridden by 6′ riders,

FWIW I'm an average proportion 6' and that spec would feel too small/short.

Im definatwly longer body and arms, than legs. On the Datum i have a 120mm stem and its -6°. Its a bit too high but v comfortable. The saddle is on an inline seatpost and is as far forwards as it will go.

As has been said above, for general road / distance use it seems odd to me for someone with a long torso to pitch themselves that forward over the BB - your c of g is less likely to be in balance. That steep eff. ST angle may well work for aerobar use, not something I've used though.

Im excited to get home and try this new position...and see where my knees end up.

I'm 178cm with ~82.5cm cycling inseam (book wedge method), my road bike has 388mm reach and 610mm stack.

~73cm BB to saddle top, ~54cm BB to top of seat tube clamp, 172mm cranks.

Saddle tip to near side of bar tops ~52.5cm.

110mm stem with -6 degree, currently 10mm spacer above and 20mm below (excluding conical spacer) to make turbo sessions a little more comfy, I'll drop the stem 5/10mm once spring outdoor season properly arrives.

I'd pick the 56cm Brokeh, for a slightly more upright position off-road, but I suspect I'd have to flip the stem to raise the bars a bit more to keep my lower back happy.

I have put tribars on it and i do seem to be comfortable. Ive ridden it for long days without problems. im mow worried ive adopted some oddball position that affects what i can chose next.

Makes sense as a Tri/TT position, just an odd bike to try that out on! If it were me I would ditch the Tri bars (are they Tri, or TT bars?) and go back to a normal road bike position (layback post, 100mm stem and adjust the saddle to relieve any knee pains). IMO for a gravel bike you want the bars higher than a road bike (more like a CX bike) to make the drops as comfortable as possible unless it's for doing ITT's in which case keep the Tri bars but maybe compromise the rest of the position less.

FWIW I ride a 56cm cannondale, in an ideal world it would be a 57cm. I'm 6ft. It varies from brand to brand, cannondale's 56cm sized up bigger as the angles were steeper (and it was measured center to center). Other 56cm bikes are sized for people ~5ft10.

A very aggressive position is fine on tri bars as they take your weight through the elbows, trying to ride that position with normal bars means your quadriceps are overworked and your hamstring/glutes/core will be trying hard to keep your body upright rather than pedaling. Generally with a long torso you'd want to balance it out with the saddle backwards to help your glutes keep you stable and a slightly longer stem to get the fit right.

I'd shuffle the seat back 5mm (and fit an normal stem), then go back 5mm each week until you're back to a normal position and see how your body adapts to that.