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Geometry is confusing! Please help!

Hi all (again!)

About to pull the trigger on a FS MTB.

It’s a choice between 2 and one is on serious offer! (It would save me £1000!)

Obviously there is slight spec changes like GX gear’s v NX, revelation fork’s v a pike but on a beginners scale it’s saving me some serious money as both bikes are far better and will continue to be far better than my ability!

The 2 bikes are from the same manufacturer albeit different models,
one is a XL (last size they have and also the cheaper of the 2) and one is a L.

I’ve rang and spoke to the maker and I’ve told them that I’m 5’10, currently ride a 19 inch Large Hardtail (a decathlon rock rider 520) And not the smallest built of blokes.

They have told me I need the Large bike (that’s also a 29ner)

On the geometry when comparing both, there really appears to be not a lot in it, but were adamant I needed a L and the XL would be too big

Of course in an ideal world I’d love to try and see them pre parting with cash, but current situation and the lack of stock everywhere dictates otherwise.

So.... What’s people’s opinions?

Things to note, the XL comes with a 150mm dropper, the L comes with either a 150

Posts

  • reaperactualreaperactual Posts: 828
    Do you trust 'they' are giving you good advise on sizing or trying to sell the bike that is £1000 more expensive?
  • Do you trust 'they' are giving you good advise on sizing or trying to sell the bike that is £1000 more expensive?

    I’m always the skeptic myself.

    They do the large model in a spec that’s the same price as the XL but that lacks things like dropper post, cane creek dB air shock etc. If I fit on the xl I’d have it in a heartbeat but at the same time I don’t want to be left with a bike that’s too big and causing me issues.

    The geometry they are recommending is L- 5’10”-6’2”. XL 6’2”+

  • steve_sordysteve_sordy Posts: 2,141
    Is the L a 29er and the XL a 650b?

    The chain stay on the XL is 17mm less than on the L.
    Strangely the XL has a shorter wheelbase than the L.
    The BB drop on the XL is 15 vs the 40 of the L

    All suggesting to me that the XL has the smaller wheels. What sort of bikes are they? A link to them would have helped.

    In my opinion, reach and stack are the two most important dimensions. If you have a bike you are comfortable with, either look up those dimensions on the makers website or measure them yourself (You may need some assistance).

    Compare the two dimensions and try to visualise whether you can live with them.
  • liamjayjacksonliamjayjackson Posts: 15
    edited May 2020

    Is the L a 29er and the XL a 650b?

    The chain stay on the XL is 17mm less than on the L.
    Strangely the XL has a shorter wheelbase than the L.
    The BB drop on the XL is 15 vs the 40 of the L

    All suggesting to me that the XL has the smaller wheels. What sort of bikes are they? A link to them would have helped.

    In my opinion, reach and stack are the two most important dimensions. If you have a bike you are comfortable with, either look up those dimensions on the makers website or measure them yourself (You may need some assistance).

    Compare the two dimensions and try to visualise whether you can live with them.

    The XL is a 650b and the L a 29ner.

    They are a Sonder Cortex and a Sonder Evol

    https://alpkit.com/collections/sonder-mountain-bikes

    I didn’t name them on purpose for neutrality lol!

    My bike dimensions are here now too.

    Also worth knowing is the stem length of my current bike is 80mm
    Stem length of the XL is 35mm
    Stem length of the L is 45mm

    Do I add that to the reach of the frame?







  • steve_sordysteve_sordy Posts: 2,141

    .........................

    Also worth knowing is the stem length of my current bike is 80mm
    Stem length of the XL is 35mm
    Stem length of the L is 45mm

    Do I add that to the reach of the frame?
    ............

    No, the stem length is a different part of the geo. But obviously it affects how far you stretch out to reach the bars, but then so does the width and sweep of the bars. You need to take it into account.

    You will notice a shorter stem length immediately as it quickens the steering response. It will move your hands (and body) towards you unless the reach is longer. Wider bars will move your body forwards and downwards, countering the movement of the shorter stem. The wider bars gives you more leverage to resist the turning forces on the front wheel. The head angle may be slacker than your current bike. This will make the bike less twitchy and more stable when descending but increase the climbing problems. There is loads of stuff to consider and you can get yourself into a right tiz thinking about it all and end up not doing anything! (Paralysis by analysis?)

    There is no easy answer with geometry and I'm still learning. Don't forget that the seat angle affects where your bum is. A high seat angle moves you forward on an otherwise identical bike. Most of these individual geometry differences only make a small difference by themselves, but boy do they add up!

    Years ago, I just used to buy a bike because I liked the look of it, could afford it and it had good reviews. Actually fitting it was the least of my problems!
  • But would you look at the geometry of the 2 bikes and say that the differences are big to be noticed and I will be left with a bike that don’t fit?
  • steve_sordysteve_sordy Posts: 2,141
    I know nothing about you or what you ride now, I cannot advise which bike would fit you better. I do't even know if either bike will suit the kind of riding that you want to do.
    The obvious advice is to ride them or at least sit on them. But I realise that as you are buying off the internet that this will not be possible. Maybe you will see one about, in which case ask the owner very nicely if you may sit on it for a brief period. Failing all that, the only thing you can do is to compare geometry with a bike that you know fits you.

    Do not ignore what the maker has recommended, they said they were adamant you needed a Large. If in doubt, go for that.
  • reaperactualreaperactual Posts: 828
    edited May 2020
    In my opinion, reach and stack are the two most important dimensions. If you have a bike you are comfortable with, either look up those dimensions on the makers website or measure them yourself (You may need some assistance).

    Compare the two dimensions and try to visualise whether you can live with them.

    I am also 5'10" an my medium sized hardtail reach (j) is 450mm and stack (k) is 621mm with a 50mm stem.

    My medium frame bike's recommended rider height is between 5'6"-5'10" and either the medium or large frame would be fine for me according to the bike shop I bought it from.



    The large frame version of my bikes reach (j) is 473mm and stack (k) is 622mm also with a 50mm stem. Recommended rider height for this large frame size is between 5'9"-6'1".

    Both the Sonder and my bike have the same seat tube angle (b) of 74°.

    To put these measurements into perspective, the reach difference of (23mm) between the medium and large versions of my bike could be lost by just moving the saddle position forward and replacing for a shorter 40mm stem.

  • JBAJBA Posts: 2,721
    An XL at 5’ 10”?
    I’d say no.
    I am 6’ and ride a M full sus and a L hard tail.
    “Life has been unfaithful
    And it all promised so so much”

    Giant Trance 2 27.5 2016 ¦ Sonder Broken Road 2021¦ Giant Revolt Advanced 2 2019 ¦ Giant Anthem 3 2015 ¦ Specialized Myka Comp FSR 2009
  • reaperactualreaperactual Posts: 828
    edited May 2020
    They do the large model in a spec that’s the same price as the XL but that lacks things like dropper post, cane creek dB air shock etc. If I fit on the xl I’d have it in a heartbeat but at the same time I don’t want to be left with a bike that’s too big and causing me issues.

    The geometry they are recommending is L- 5’10”-6’2”. XL 6’2”+

    Nothing wrong with the most common brands of suspension, Rockshox, Fox, etc. Dropper posts are £100ish.

    My bike has RS Revelations, great forks and NX/Shimano mix drivetrain and has been faultless so far and I've been very impressed with their performance.

    Most other differences in frame measurements are not so important or more to do with 29" vs 27.5" wheels rather than sizing so don't get too hung up on comparing those numbers.
  • steve_sordysteve_sordy Posts: 2,141
    The manufacturer has made it clear that size L is the one to go for. But it looks like the OP clearly wants to buy the XL and is looking for any reason to do so.
  • liamjayjacksonliamjayjackson Posts: 15
    edited May 2020

    The manufacturer has made it clear that size L is the one to go for. But it looks like the OP clearly wants to buy the XL and is looking for any reason to do so.

    Incorrect.

    I was asking at the differences and supplying the geometric numbers, as the differences between a L of one model and a XL of another are small, and not as dramatic an increase of a L and a XL of the same model.

    Further to my confusion my current L hardtail is bigger than the XL in some measurements, hence why I’m here asking these questions.


  • reaperactualreaperactual Posts: 828
    edited May 2020
    Most other differences in frame measurements are not so important and more to do with 29" vs 27.5" wheels rather than sizing so don't get too hung up on comparing those numbers.

  • steve_sordysteve_sordy Posts: 2,141

    The manufacturer has made it clear that size L is the one to go for. But it looks like the OP clearly wants to buy the XL and is looking for any reason to do so.

    Incorrect.

    I was asking at the differences and supplying the geometric numbers, as the differences between a L of one model and a XL of another are small, and not as dramatic an increase of a L and a XL of the same model.

    Further to my confusion my current L hardtail is bigger than the XL in some measurements, hence why I’m here asking these questions.


    My apologies! :'(
  • reaperactualreaperactual Posts: 828

    The manufacturer has made it clear that size L is the one to go for. But it looks like the OP clearly wants to buy the XL and is looking for any reason to do so.

    Incorrect.

    I was asking at the differences and supplying the geometric numbers, as the differences between a L of one model and a XL of another are small, and not as dramatic an increase of a L and a XL of the same model.

    Further to my confusion my current L hardtail is bigger than the XL in some measurements, hence why I’m here asking these questions.


    My apologies! :'(
    No one is an 'expert' on making other people's decisions and a definitive answer on what to buy. It's just another forum and another place to gather information to help make the right choice based on others knowledge, experience and opinions.

  • In the end I didn’t get either! Haha!

    I got a good deal on a 2019 Rocky Mountain Element A50 from Paul’s Cycles. (Didn’t want the carbon as I was too scared of breaking it!)

    And it’s a large!

    Thank you everyone anyway :-) hope I’ve made the right choice!

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