75 Deg' seat tube.

[cycleruk]

Looking at perhaps N+1 with a Dolan Preffisio 2019 model.
States that it will take 28 size tyre with mudguards.
What, I wonder, is the effect of the 75 Deg' seat tube angle on the frame.
https://www.dolan-bikes.com/road/road-f ... -6721.html

Would probably go for the 52 size frame with 54 toptube.
Any thoughts positive or negative appreciated.

[amediasatex]

Far too steep for me, I wouldn’t be able to get my saddle far enough back. Whether or not that’s an issue for you is only something yonly you can answer, possibly with the assistance of a tape measure and your existing bike...

Steep seat angles on smaller sizes are often used to artificially shorten the on-paper top tube measurement which implies a shorter reach (not necessarily true). It’s an annoying trend IMO, slacker seat angles have few drawbacks as you can always slide a saddle forwards and/or use an inline post if necessary but layback posts only get you so far back.

Look at measurement G on that chart, the 45/50/52cm frames actually have longer reach than the 54! the TT measurement isn’t a result of the frames being shorter, just a result of the seat tube being steeper, which is only good if you want to run your saddle forward in relation to B.B: ie: they’re making the bike short by moving the rider forward instead of bringing the bars backwards.

[Brucey]

a) will you be able to get the seat back far enough? and

b) would you be happy with a ~56cm top tube and a ~72 degree seat angle? (which gives about the same forward reach with the saddle in the same place)

cheers

[cycleruk]

Thank's guys.
Will look into your observations. The 75 deg' did seem a bit steep compared with my other frames but I couldn't see the effect it has.
Reach is the main criteria for me these days.
Cheers.

[Brucey]

just in case I wasn't clear; regardless of the seat angle you should set your saddle in the right place WRT the BB. This has the effect of increasing the reach (for any given TT length) on frames with steep seat angles. [the handlebars are set w.r.t. the saddle of course]

75 degree seat angles suit a small fraction of people and those are mostly racers who favour/can tolerate a forwards saddle position.

cheers

[531colin]

….Look at measurement G on that chart, the 45/50/52cm frames actually have longer reach than the 54! .....

Yes, thats what the geo. chart says, isn't it?
But I don't entirely believe it. 45, 50 & 52 all have slacker head angles than 54......so if they all had the same front centre, then the smaller bikes would have shorter "reach" (G) which is what you expect. So the smaller bikes have longer front centre than the 54?
Theres insufficient information to make any sense of it all, but I suspect its a case of "typos 'r' us".

Setting the saddle forward throws weight onto your hands. I work on the basis that one degree steeper seat tube sets the saddle roughly 10mm further forward for a rider of average height. In my case with a 72 deg. seat tube angle and a Brooks or Gilles Berthoud saddle I'm seeking out long layback seatposts. 74 degrees doesn't work for me.

[amediasatex]

….Look at measurement G on that chart, the 45/50/52cm frames actually have longer reach than the 54! .....

Yes, thats what the geo. chart says, isn't it?
But I don't entirely believe it. 45, 50 & 52 all have slacker head angles than 54......so if they all had the same front centre, then the smaller bikes would have shorter "reach" (G) which is what you expect. So the smaller bikes have longer front centre than the 54?
Theres insufficient information to make any sense of it all, but I suspect its a case of "typos 'r' us".

yes, it's a shame they don't list the wheelbase or FC measurements, they do on some of their other frames.

[reohn2]

.......Any thoughts positive or negative appreciated.

A 75degree seatube angle is bonkers!
And a 74degree seatpost angle on the largest frame size is even more bonkers!

[MikeF]

Using Colin's approximation of 10mm per degree, the difference between 72 and 75 degree SA is 30mm in relation of seat post to BB (if I've understood correctly). That's a lot.

[cycleruk]

Thankyou all for your input.
Questions to sort out before committing.

Cheers.

[peetee]

Setting the saddle forward throws weight onto your hands.

Is that the case? If it is just the saddle that moves the rider will be more upright and more of the weight of their torso will be taken through the hips.
Although I would agree that the front wheel would be taking more weight.

[hamster]

It's one of those counterintiuitive things I discovered from 531Colin's detailed fit piece that to lighten weight on the hands you may have to move the saddle BACK. This then balances the trunk of your body over the saddle and so lightens the hand weight. This is entirely different to reach and how upright you sit, which is related to bar position.

I had a bike that felt to heavy on my hands - I moved the saddle back one cm, hand weight lightened up as I was no longer falling off the front of the saddle.

[531colin]

Setting the saddle forward throws weight onto your hands.

Is that the case? If it is just the saddle that moves the rider will be more upright and more of the weight of their torso will be taken through the hips.
Although I would agree that the front wheel would be taking more weight.

Quick and easy to try!
Go out on your bike. Ride along with just one digit (each hand) on the bars where your hands "normally" are, eg the brake hoods.
Slide back in the saddle and see what happens to the weight distribution.....slide forwards too.