Priority when choosing a new frame?

johngti
johngti Posts: 2,508
So, currently own a trek domane in size 54 and a medium giant contend sl2 disc in medium. The contend is more comfortable in terms of riding position but the isospeed system on the domane is lush however, on mine it’s only on the back so I’ve been looking out for a newer frame with front isospeed too. I’ve had a look at a geometry chart (seen a nice domane sl5 frame on eBay in size 56) to see what the difference is. The 56cm domane has exactly the same reach as the giant, while the 54cm is 2cm shorter. Question is should this be the priority over stack? The 56cm domane is certainly taller but that can be changed with stem spacers can’t it? Fewer spacers would bring the actual riding position into a similar place as on the giant, wouldn’t it? Advice would be welcomed! The geometry comparison is in the image.

Thanks!


Comments

  • johngti
    johngti Posts: 2,508
    edited May 2020
    Sorry, nowhere near 2cm shorter! I’d be getting a similar reach and bigger stack but gaining front isospeed. Oh and the potential to fit 28mm tyres which is nice.

    Good thing I’m not a maths teacher or anything... ahem. Think I’m persuading myself to pull the trigger.
  • Ben6899
    Ben6899 Posts: 9,686
    I guess the taller stack is accommodating the Isospeed?

    Anyway, do you know your fit numbers? I know they're not the be all and end all, but I had my custom frame built around being able to run the frame with no spacers under a 100mm stem.

    I would look at what stem and spacer setup each results in and see if you're happy. There's a good website I found which calculates all this for you: http://www.bikegeo.net/
    Ben

    Bikes: Donhou DSS4 Custom | Condor Italia RC | Gios Megalite | Dolan Preffisio | Giant Bowery '76
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  • johngti
    johngti Posts: 2,508
    I had a fit ages ago so they’re probably not relevant now. I did try a 56cm domane for size when I was looking around for one initially and it felt fine but I went for the 54 when I saw a good deal on eBay. I had to get the longer seat mast sleeve to make it fit so probably should’ve hung on for a 56 then. I’ve stuck an offer in anyway, let’s see what comes of it.

    Going to have a look at that link now
  • First.Aspect
    First.Aspect Posts: 14,858
    Classic example of why reach and stack are next to useless on their own.

    54 cm and 56 cm treks have almost exactly the same reach (as does the Giant) - you aren't going to notice 3 mm - there is more variation between different brands of bar tape. So if you go by stack and reach, the only difference should be that you are more upright on the 56 cm, right? You can fix that with fewer spacers, you'd think.

    But reach doesn't take into account what's going on behind the vertical line with the BB. With the Treks, the 56 cm has slacker frame angles, so your bum will end up quite a bit further back, and the distance from the top of the seat post to the bars will be somewhere around 1.5-2 cm range longer, which is quite a bit.

    So, assuming your two bikes fit nicely, I'm going to say the 56 is too big for you. You will be forever trying to push the saddle further forward and lower the bars - by about 1-2 cm each.

    And if you think you are between sizes, the smaller one is the size to go for.

    The seat mast thing might be a red herring, btw - the previous owner may have cut it to size.

    Years ago I got a couple of second hand bikes. I needed a traditional 56 (normally comes up as a 55 on more modern charts). Convinced myself a 58 would do. Felt fine in the shop and round the car park I thought. Different matter 30 miles into a hilly ride. I used that bike all through uni with an 8 cm stem and the saddle rammed forward, because I needed a 56. So, I'd question the wisdom of being like me!!
  • DeVlaeminck
    DeVlaeminck Posts: 8,761
    In an ideal world wouldn't you set saddle fore /aft with reference to the bottom bracket so a slacker seat tube angle shouldn't put you any further back?

    However adding spacers to the 54 would shorten the reach for an equivalent stack to the 56.
    [Castle Donington Ladies FC - going up in '22]
  • First.Aspect
    First.Aspect Posts: 14,858

    In an ideal world wouldn't you set saddle fore /aft with reference to the bottom bracket so a slacker seat tube angle shouldn't put you any further back?

    However adding spacers to the 54 would shorten the reach for an equivalent stack to the 56.

    Very marginally the reach would be shorter I agree. But do the trig for a 3mm spacer.

    In practice you end up adjusting saddle to the bars, that's my point.

    Re to the part of the bike behind the BB was merely to point out that reach does not take it into account at all. Which is fine unless you are one of those cyclists who sit down.

    And the line between the BB and the seat is a hell of a lot longer than a couple of spacers. So there's a bit fat unknown in terms of fit if you only look at stack and reach.

    Personally, I'm not very sensitive to differences in reach, as between two bike that fit. Perhaps some people are, I don't know.

    Stack seems to make a bit more sense for comparisons though, I'll admit. And that 56 looks a lot more upright to me.
  • johngti
    johngti Posts: 2,508
    To be fair the 54 requires me to push the saddle back a lot further than I’m comfortable with and even then it feels like I’m squashed a bit. I could have gone with a longer stem but it’s more about my knee angle being wrong. No knee pain on the giant, some discomfort on the trek. I have the full spacer stack on the giant now so in theory I’d hope that the bigger size would allow some flexibility with spacers. Worth a go and if it works then happy days!
  • johngti
    johngti Posts: 2,508
    And bang in the middle for a size 56 too
  • johngti
    johngti Posts: 2,508
    It arrived, it’s been set up and size 56 is perfect (just because I know you’ll all be wondering!). The setup is pretty much bang on. Picture shows the Domane and Contend superimposed and they’re a good match. I’m pleased! Thanks all for the input.