Modern length bike sizes vs RAD sizing- Mtbr.com
Results 1 to 59 of 59
  1. #1
    mtbr member
    Reputation:
    Join Date
    Jun 2019
    Posts
    19

    Modern length bike sizes vs RAD sizing

    Hello everybody. I would like to hear your opinion about how modern bikes are getting longer in reference to their suggested rider size, specifically in the reach and wheelbase measurements. I am also curious if anyone has heard of the bike fitting measurement called RAD (rider area distance) that Lee Mccormack invented. These two ideologies seem to be at odds, so I think it would be great to hear your personal preference of bike length for your specific body type.


    I know that every rider has a different anatomy, muscular structure, and riding style, which is what interests me. It seems that "modern" geo favors downhill, straight-line, stability, while RAD favors maneuverability and control. Please list your height and bike measurements (reach, wheelbase, size) along with any objective, subjective, anecdotal, scientific, or empirical analyses regarding length and sizing for the community to digest.

  2. #2
    Professional Crastinator
    Reputation: Fleas's Avatar
    Join Date
    Jan 2006
    Posts
    5,607
    It's never easier - you just go faster.

  3. #3
    mtbr member
    Reputation:
    Join Date
    Jun 2019
    Posts
    19
    Hmm yeah, that thread is pretty similar to what I was asking. I guess I was more curious on how much reach is desirable for everyone, given their specific height (and not so interested their actual RAD measurements). But thank you, I will enjoy reading through that!

  4. #4
    since 4/10/2009
    Reputation: Harold's Avatar
    Join Date
    Dec 2003
    Posts
    27,216
    I think if you want to get the information you're after, you're going to have to create a specific survey with the specific questions you want answered. You just won't get anything useful from people who are just free-forming the answers.

    For that matter, I'm not even sure I know how to answer your question completely the way you want. I have two mountain bikes.

    medium Guerrilla Gravity Pedalhead, reach is 451mm but I can't give you the other numbers because they're based on a 120mm fork and mine has a 140mm fork
    medium Salsa Bucksaw, reach is 436.7mm but again none of the other numbers are exact because I'm using a slightly longer fork than stock

    I'm 5'8 with a longish torso and long arms. Both bikes feel good. I look for some level of balance between stability and control and I feel like I am in that ballpark with both of these bikes. I don't dwell on numbers when it comes to fitting a bike. I focus on what feels right. So I haven't calculated RAD for any bikes I own. The whole concept seems rather contrived, anyway.

  5. #5
    mtbr member
    Reputation:
    Join Date
    May 2018
    Posts
    94
    Quote Originally Posted by Harold View Post
    medium Guerrilla Gravity Pedalhead, reach is 451mm but I can't give you the other numbers because they're based on a 120mm fork and mine has a 140mm fork
    medium Salsa Bucksaw, reach is 436.7mm but again none of the other numbers are exact because I'm using a slightly longer fork than stock
    To be honest, RAD measurement doesn't change with different size fork. Same frame, longer fork, shorter reach, higher stack, but RAD is the same.

  6. #6
    since 4/10/2009
    Reputation: Harold's Avatar
    Join Date
    Dec 2003
    Posts
    27,216
    Quote Originally Posted by s-master View Post
    To be honest, RAD measurement doesn't change with different size fork. Same frame, longer fork, shorter reach, higher stack, but RAD is the same.
    No, but that's not what OP asked. He wanted reach, wheelbase, and size.

  7. #7
    mtbr member
    Reputation: vikb's Avatar
    Join Date
    Sep 2008
    Posts
    13,502
    Quote Originally Posted by bikinson View Post
    Please list your height and bike measurements (reach, wheelbase, size) along with any objective, subjective, anecdotal, scientific, or empirical analyses regarding length and sizing for the community to digest.
    Asking for Reach without asking for Stack is pretty meaningless as Reach depends on Stack so two bikes can have the same Reach, but be different sizes due to varying Stack values.
    Safe riding,

    Vik
    www.vikapproved.com

  8. #8
    mtbr member
    Reputation:
    Join Date
    Jun 2019
    Posts
    19
    Stack would be cool to know too. I said reach and wheelbase because these can vary a lot and are not easily changed (whereas seat post related measurements and stack can be adjusted with an Allen wrench). But honestly, I was just interested in what sizes/dimensions people are riding nowadays, and how they feel about these sizes/dimensions. So I welcome any information riders wish to provide!

  9. #9
    mtbr member
    Reputation: vikb's Avatar
    Join Date
    Sep 2008
    Posts
    13,502
    Quote Originally Posted by bikinson View Post
    Stack would be cool to know too. I said reach and wheelbase because these can vary a lot and are not easily changed (whereas seat post related measurements and stack can be adjusted with an Allen wrench).
    Stack is a function of the bike design and never changes once the bike is built. You define Reach by the frame's Stack you can't really understand Reach if you don't have Stack as well.
    Safe riding,

    Vik
    www.vikapproved.com

  10. #10
    Meatbomb
    Reputation: Phillbo's Avatar
    Join Date
    Apr 2004
    Posts
    6,568
    6'4" riding an XL ...

  11. #11
    mtbr member
    Reputation:
    Join Date
    Jan 2016
    Posts
    1,397
    Forget about new, old.
    My legs are way too long.
    My bikes are way too long.
    I reverse seatpost to shorten the frame.
    When that fails, i cut frames then glue back.
    620 mm handlebars.
    Ya i am not average but with a good position i go up, down and turn.
    The idea is 95 % is about the rider, frame BS is if you hope
    your bike will turn u in an expert.

  12. #12
    aka bOb
    Reputation: bdundee's Avatar
    Join Date
    Feb 2008
    Posts
    8,737
    Quote Originally Posted by vikb View Post
    Stack is a function of the bike design and never changes once the bike is built. You define Reach by the frame's Stack you can't really understand Reach if you don't have Stack as well.
    This^^^

  13. #13
    battle stag commander
    Reputation: planetx88's Avatar
    Join Date
    Mar 2012
    Posts
    58
    Reach and stack are important, but I find that some perspective is important in understanding the fit of modern bikes that seem to all be converging on steeper seat tubes, and slacker headtubes.

    I am 5'11" riding a gg megatrail v3 with a stated factory geometry with a 482mm reach for a size "3", basically a large. Below are numbers comparing bikes I have ridden in the past few years, plus a pole stamina 180, just for fun.

    5010 v2 LG- reach-445, stack-605, tt-621, seat angle-73.8
    Evil Calling MD- reach-440, stack-601, tt-603, seat angle-74.8
    Evil Wreck LG- reach-455, stack-611, tt-640, seat angle-72.8
    GG MT size 3- reach-482, stack-627, tt-625, seat angle-77.1
    Pole stamina LG- reach-510, stack-645, tt-630, seat angle-80

    So reach and stack are important, but steep seat tubes can skew reach numbers longer without representing a stretched out riding position. In a lot of ways, thats the whole idea behing this "foreward geometry" trend. top tubes remain nearly unchanged, while they are pushed foreward by steep seat tubes. Another way to look at this is if I shopped for bikes on reach/stack alone, shooting for 440mm/610mm zone at 5'11" (which has fit well on previous bikes), I would concievably be looking at a small Megatrail or Pole, and even a Medium in the new v2 Hightower or Yeti SB150 would be a touch big.

    That is a very long winded way of saying reach/stack can be important, but are not entirely how we should size bikes. My personal belief is pushing a rider forward more closely replicates an "athletic position," putting the rider in a more dynamic and comfortable position, but maybe not for everyone.

  14. #14
    aka bOb
    Reputation: bdundee's Avatar
    Join Date
    Feb 2008
    Posts
    8,737
    That's why when I'm looking at a frame effective top tube is just as important at least for myself and my type of riding. A bike is a sum of all numbers and just can't just summerized by just a couple of measurements.

  15. #15
    mtbr member
    Reputation:
    Join Date
    Jun 2019
    Posts
    19
    What about when you’re not in the seated position and top tube is irrelevant? At what point is the extended reach and wheelbase overkill? At 5’10”, I’m unsure if I should be around 450mm/1200mm or 470mm/1220mm. I’ve done test rides but without a lot of experience it’s difficult to evaluate in that short amount of time.

  16. #16
    aka bOb
    Reputation: bdundee's Avatar
    Join Date
    Feb 2008
    Posts
    8,737
    I'm 5'9.5" on a medium offering and with around a 450mm reach with around a 1200mm wheelbase and a 50mm stem ( I have long legs and arms) and it feels great from the tight singletrack as well as park riding. I also spent the last couple of years on a Kona Wozo with about the same geo but higher stack. Now with let's say an Ibis Ripmo with roughly the same numbers ( lower stack and a tad shorter tt) felt cramped seated. For me Ibis bikes have always felt smaller than their numbers show and I'm thinking some of that has to do with stack height.

  17. #17
    mtbr member
    Reputation: vikb's Avatar
    Join Date
    Sep 2008
    Posts
    13,502
    Quote Originally Posted by bdundee View Post
    That's why when I'm looking at a frame effective top tube is just as important at least for myself and my type of riding.
    I size bikes based of eff TT and Reach/Stack. I need them to fit me well seated and standing. I don't have an exact magic formula, but I use existing bikes to get a feel for what I am comfortable with. Then between stem/bars/steerer spacers I can fine tune the fit once I have the bike at home.

    Quote Originally Posted by bikinson View Post
    What about when you’re not in the seated position and top tube is irrelevant?
    Safe riding,

    Vik
    www.vikapproved.com

  18. #18
    since 4/10/2009
    Reputation: Harold's Avatar
    Join Date
    Dec 2003
    Posts
    27,216
    Quote Originally Posted by bikinson View Post
    What about when you’re not in the seated position and top tube is irrelevant? At what point is the extended reach and wheelbase overkill? At 5’10”, I’m unsure if I should be around 450mm/1200mm or 470mm/1220mm. I’ve done test rides but without a lot of experience it’s difficult to evaluate in that short amount of time.
    Top tube length isn't irrelevant when you're in a standing position. It's not the focus at that time.

    Honestly, there's not enough information presented here to say what you SHOULD be riding. Figuring that out requires more information about your body than just your height. Do you have a longer torso, or longer legs? What is your arm length? How flexible are you? How is your core strength? Those things are all going to affect what feels best to a rider, especially when you're in a standing position.

    Mountain bike fitting has some wiggle room. What matters is that it's comfortable. If you have less experience, dwelling on the numbers is going to add to confusion. And for that matter, if you have more experience, dwelling on the numbers can be exhausting, too. What matters is that it's comfortable. Forget the numbers for a minute. If both bikes feel good, you're comfortable on them, and you like them, then you should just pick one. Buy it, ride it for awhile, and get to understand it deeply. It'll inform you for later. Maybe you'll decide after awhile you don't like it. Maybe you'll decide after awhile you love it. Maybe you'll be somewhere between and want to try something a little different anyway.

    If you can't separate yourself from the numbers and want to buy something that's "perfect" then go pick a custom framebuilder and spend the money.

  19. #19
    mtbr member
    Reputation: vikb's Avatar
    Join Date
    Sep 2008
    Posts
    13,502
    Quote Originally Posted by bdundee View Post
    .... and I'm thinking some of that has to do with stack height.
    Yes. And that's exactly why looking at Reach separate from Stack makes no sense. You can get two bikes with the same Reach, but different Stack measurements that fit quite differently.
    Safe riding,

    Vik
    www.vikapproved.com

  20. #20
    Professional Crastinator
    Reputation: Fleas's Avatar
    Join Date
    Jan 2006
    Posts
    5,607
    Maybe a little OT... but maybe helpful....

    https://www.ridefatbikes.ca/fat-bike...and-reach#sr-1



    Modern length bike sizes vs RAD sizing-2019-ridefatbikes.ca-stack-reach-chart-94-frames.jpg

    -F
    It's never easier - you just go faster.

  21. #21
    mtbr member
    Reputation:
    Join Date
    Jun 2019
    Posts
    19
    @Harold I appreciate the advice. Here is some more info: I’m barely at 5’10”, 32.5” inseam, +1inch ape index, 185lb, good core strength (athletic but new to biking), fairly good flexibility.

    I ride various terrain in Northern California. I really like rocky, technical stuff (Rockville Park) at medium speeds, but I ride other trails as well, and even plan on visiting Tahoe and other parks with lifts and all that. I don’t do a lot of jumps and stuff as I don’t have the most bike “skills”, but in the future I could see myself being in the air more. What I really enjoy now and is clearing rugged, sketchy, rocky sections, both up and down.

    Anyway, your advice is well received. The bikes I’m currently considering are an Ibis Ripmo and the new Orbea Occam, but I’m really unsure about the size for either. I rented a large Ripmo and it felt great, just a little big on an uphill switchback. But I’m not sure if this would get easier over time, especially with a shorter stem.

  22. #22
    mtbr member
    Reputation: Dude!'s Avatar
    Join Date
    Mar 2004
    Posts
    2,182
    I have a theory on bike fit and geometry...more bike fit and control...

    I have been riding various flavors of newer geometry. I do like the newer geometry with respect to fit, but it doesn't always translate to riding better, particularly out of the saddle. I have difficult controlling the bike if the geometry gets too long.

    I believe the out of the saddle bike control is related to length of your legs. When Leo and SteveM debated about geometry, Leo said something that resonated which is you control the weight distribution of the bike by standing up or sitting down.

    I have very short legs and long torso so I like longer geometry because of my torso, but controlling the weight distribution with my shorter legs is limited. I have a buddy who rides a much longer bike with minimal issue, but he is the the opposite - very long legs and short torso.

    As I ride bikes with shorter front centers, I can really control the bike with legs and weight distribution. For me, I need to find a balance between geometry (reach, stack, RAD, diagonals, etc) and corresponding front center. The combination of the two allow fit and control.

    Anyway, I think leg length is overlooked in control, but is a major factor in changing weight distribution when riding!

  23. #23
    since 4/10/2009
    Reputation: Harold's Avatar
    Join Date
    Dec 2003
    Posts
    27,216
    Quote Originally Posted by Dude! View Post
    Anyway, I think leg length is overlooked in control, but is a major factor in changing weight distribution when riding!
    You're definitely on to something, but I'd say it's legs AND arms. Both have an effect on your overall range of movement, which absolutely affects your ability to control the bike.

    My leg length is fairly average for my height (32" cycling inseam at 5'8), but I've got a positive ape index. I can fit on quite a few large frames (and on some, I'm a solid large), but I feel like I get a much better range of motion on most mediums. This despite the fact that most manufacturers say I'm more likely to fit on a small frame than on a large one. Just nope.

    My wife is very much the opposite. She has pretty compact proportions for her height. As such, even though her height suggests she should fit on a solid small frame size, that's a definite nope for her. She can ride one, but she has zero range of motion when she's standing. She has had to size down to an xs frame, especially on more modern geometries. She needs a short ETT anyway.

    As mtb geometries have changed over the years, my impression is that arms and legs now play a larger role than they used to with regard to mtb fitting and handling.

  24. #24
    mtbr member
    Reputation:
    Join Date
    Jan 2016
    Posts
    1,397
    Just rent 5 bikes. That is what i did. Buy a 4-7 yo bike you might discover u like the tires or saddle or transmission, resell after 1-4 months close to paid price.
    You will figure geo and lots of stuff.
    I sold a Trek fat because i wanted 26 tires but i liked the transmission so much i bought a bike with that transmission. Do not think we can help you. Just switching a saddle might be important. You keep what you like, learning while pedaling. I have a saddle and seatpost from 2000, they do their job well.

  25. #25
    mtbr member
    Reputation:
    Join Date
    Jun 2019
    Posts
    19
    Yeah, looking for answers on the internet is probably a wasted effort. My intention was to make the post more general and just gather different info and opinions. I actually demo’d 4 bikes but they were on different trails, so it was helpful but difficult to notice a difference of 20mm here and there. The idea about buying a used bike for a month or two is interesting!

    I’ll probably go do a couple parking lot rides and narrow it down to a specific model, and then demo a Med and Large of that model on the same trail back to back. Thanks everyone!

  26. #26
    mtbr member
    Reputation:
    Join Date
    Apr 2010
    Posts
    130
    RAD = Revenue aiding dimension

  27. #27
    mtbr member
    Reputation: Dude!'s Avatar
    Join Date
    Mar 2004
    Posts
    2,182
    Quote Originally Posted by bikinson View Post
    Yeah, looking for answers on the internet is probably a wasted effort. My intention was to make the post more general and just gather different info and opinions. I actually demo’d 4 bikes but they were on different trails, so it was helpful but difficult to notice a difference of 20mm here and there. The idea about buying a used bike for a month or two is interesting!

    I’ll probably go do a couple parking lot rides and narrow it down to a specific model, and then demo a Med and Large of that model on the same trail back to back. Thanks everyone!
    I can have paralysis analysis with my bike geometries, etc. I am just wired that way and just curious, I have kept my paralysis analysis to myself these days and my friends. I have made spreadsheets did all of the calculations for comparing bikes.

    The RAD is basically an arc from the bottom bracket, which is quasi fixed because of stack and reach. Therefore to change the distance of the arc or the location of the arc this controlled by either spacers under the stem, stem length, and handlebar rise and sweep. None of these are going to overly change that distance. I learned this by doing the calculations and seeing the differences. There is a limit (using reasonable stems lengths, spacers, etc) to how far the BB can be to the handlebars. I believe RAD or the distance from the BB to the bars, provides a sense of comfort for being out of the saddle.

    The second most important item is front center - BB to front axle. This determines how much weight is required to drive the front of the bike.

    For me with shorter legs but a longer torso, I want a bike with a steeper head angle - this gives me the longest distance from the BB to bars (providing comfort), while keeping the front center relatively shorter (providing control).

    If you have longer legs, I believe you can get away with a longer bike with slacker head angles.

  28. #28
    mtbr member
    Reputation: Dude!'s Avatar
    Join Date
    Mar 2004
    Posts
    2,182
    Quote Originally Posted by Xlr8n View Post
    RAD = Revenue aiding dimension
    Haha - I agree. I did the calculations - it took about ten minutes. It just geometry and you can compute the RAD and RAAD.

  29. #29
    mtbr member
    Reputation:
    Join Date
    Dec 2013
    Posts
    2,236
    Quote Originally Posted by vikb View Post
    Asking for Reach without asking for Stack is pretty meaningless as Reach depends on Stack so two bikes can have the same Reach, but be different sizes due to varying Stack values.
    I just don't understand that. I've looked up the Geo charts to see what stack is, and I'm not saying you're wrong I just don't understand how it's that important. Stack basically just places a minimum height on your handlebars essentially right? Please advise.

    When I picked my current bike there were several features I was looking for but fit was the most important, because I found my previous bike to fit poorly and it was still the best I'd had yet. I knew where I needed my reach to be, my top tube length, my seat tube angle, and head tube angle, and I picked the bike that met these requirements iin combination with my desired travel and a history of peddling well and I nailed it. I didn't even consider stack. Between different stems, spacers under the stem, and different rise bars I just don't see why stack matters. I'm 5'11" on a Large Foxy 29 btw with a 490 reach, 654 ttl. Fit is beautiful. Performance is phenomenal. No regrets.

    Sent from my SM-G892A using Tapatalk

  30. #30
    mtbr member
    Reputation: Legbacon's Avatar
    Join Date
    Jan 2004
    Posts
    8,564
    2 bikes with 470mm reach but stacks of 610mm and 630mm. The one with 630mm reach will have a real reach because the one with 610mm has the top of the head tube closer to the BB. Look at a geometry chart and it will be obvious.
    Formerly Travis Bickle

    Team Robot. "modulation is code for “I suck at brake control.” Here’s a free tip: get better."

  31. #31
    mtbr member
    Reputation: jeremy3220's Avatar
    Join Date
    Jul 2017
    Posts
    1,998
    Yeah, two bikes with the same reach but different stack heights means that the bike with the higher stack is longer. What reach and stack really are, are Cartesian coordinates for the steering axis (at the minimum stem location). So the higher the stack for a given reach, the further away horizontally the steerer tube is. This is where RAD makes sense. It's a definitive measurement of how far away the steering axis is.

  32. #32
    mtbr member
    Reputation:
    Join Date
    Dec 2013
    Posts
    2,236
    But Reach is a horizontal dimension and therefore unaffected by stack height.

    If you are discussing the distance from the BB to the top of the head tube becoming longer because stack is taller, well yah, but so what? That's really just a bar height adjustment away. We have commonly available bars ranging from 0mm rise to 50mm. I run 40s.

    What am I missing here if anything?

    Thanks.

    Sent from my SM-G892A using Tapatalk

  33. #33
    mtbr member
    Reputation: vikb's Avatar
    Join Date
    Sep 2008
    Posts
    13,502
    Quote Originally Posted by Suns_PSD View Post
    But Reach is a horizontal dimension and therefore unaffected by stack height.
    Reach is defined by Stack so you can say it's unaffected by Stack.
    Safe riding,

    Vik
    www.vikapproved.com

  34. #34
    mtbr member
    Reputation: RS VR6's Avatar
    Join Date
    Mar 2007
    Posts
    5,029
    Doh...wrong thread.
    Last edited by RS VR6; 07-04-2019 at 05:00 PM.

  35. #35
    mtbr member
    Reputation:
    Join Date
    Dec 2013
    Posts
    2,236
    Quote Originally Posted by vikb View Post
    Reach is defined by Stack so you can say it's unaffected by Stack.
    I think you meant to say 'can't'. But yes, the stack is already in the Reach number since that's the point we measure to.
    The more you guys type the more i'm convinced that this stack number is fully reflected already in reach as well as top top length, meaning it's completely irrelevant. I guess it could be so extremely short or so extremely tall that your not able to get to your desired handlebar height with commonly available rise handlebars. But if they're all sort of in 'the normal range' that's a non issue.

    Sent from my SM-G892A using Tapatalk

  36. #36
    aka bOb
    Reputation: bdundee's Avatar
    Join Date
    Feb 2008
    Posts
    8,737
    Quote Originally Posted by Suns_PSD View Post
    I think you meant to say 'can't'. But yes, the stack is already in the Reach number since that's the point we measure to.
    The more you guys type the more i'm convinced that this stack number is fully reflected already in reach as well as top top length, meaning it's completely irrelevant. I guess it could be so extremely short or so extremely tall that your not able to get to your desired handlebar height with commonly available rise handlebars. But if they're all sort of in 'the normal range' that's a non issue.

    Sent from my SM-G892A using Tapatalk
    But the more you artificially raise the stack height by adding spacers and what not (the slacker the frame the worse it gets) the shorter your cockpit becomes.

  37. #37
    mtbr member
    Reputation: jeremy3220's Avatar
    Join Date
    Jul 2017
    Posts
    1,998
    Quote Originally Posted by Suns_PSD View Post
    But Reach is a horizontal dimension and therefore unaffected by stack height.

    If you are discussing the distance from the BB to the top of the head tube becoming longer because stack is taller, well yah, but so what? That's really just a bar height adjustment away. We have commonly available bars ranging from 0mm rise to 50mm. I run 40s.

    What am I missing here if anything?

    Thanks.

    Sent from my SM-G892A using Tapatalk

    So these bikes have the same reach but the green bike has a higher stack. So no matter what the steering axis of the green bike is further away. Raising the bars puts them further away from the steering axis which is the same as using a longer stem. What I'm saying is the location of the steering axis is what determines the intrinsic size of the bike. Bars, stems, etc are just cockpit adjustments.

    Name:  asset (1).jpeg
Views: 213
Size:  18.0 KB

  38. #38
    mtbr member
    Reputation:
    Join Date
    Dec 2013
    Posts
    2,236
    Quote Originally Posted by bdundee View Post
    But the more you artificially raise the stack height by adding spacers and what not (the slacker the frame the worse it gets) the shorter your cockpit becomes.
    I agree that adding spacers under the stem is not ideal unless you want to reduce reach. That's why I always slam my stem and run a tall bar that goes straight up.

    Sent from my SM-G892A using Tapatalk

  39. #39
    mtbr member
    Reputation:
    Join Date
    Dec 2013
    Posts
    2,236
    Quote Originally Posted by jeremy3220 View Post
    So these bikes have the same reach but the green bike has a higher stack. So no matter what the steering axis of the green bike is further away. Raising the bars puts them further away from the steering axis which is the same as using a longer stem. What I'm saying is the location of the steering axis is what determines the intrinsic size of the bike. Bars, stems, etc are just cockpit adjustments.

    Name:  asset (1).jpeg
Views: 213
Size:  18.0 KB
    I see your point here. Thanks for that.

    Sent from my SM-G892A using Tapatalk

  40. #40
    mtbr member
    Reputation: jeremy3220's Avatar
    Join Date
    Jul 2017
    Posts
    1,998
    Quote Originally Posted by Suns_PSD View Post
    I agree that adding spacers under the stem is not ideal unless you want to reduce reach. That's why I always slam my stem and run a tall bar that goes straight up.

    Sent from my SM-G892A using Tapatalk
    This has the same effect as using spacers and a longer stem. That's why I say steering axis distance is what matters and after how you get your grips where you want them doesn't matter. Stem angle, spacers, bar rise, bar sweep, stem length, etc... you're just moving your hands around the steering axis and the 'how' is irrelevant.

  41. #41
    mtbr member
    Reputation:
    Join Date
    Oct 2015
    Posts
    2,171
    Quote Originally Posted by jeremy3220 View Post
    So these bikes have the same reach but the green bike has a higher stack. So no matter what the steering axis of the green bike is further away. Raising the bars puts them further away from the steering axis which is the same as using a longer stem. What I'm saying is the location of the steering axis is what determines the intrinsic size of the bike. Bars, stems, etc are just cockpit adjustments.

    Name:  asset (1).jpeg
Views: 213
Size:  18.0 KB
    Great example of why stack is important in reach numbers.

  42. #42
    mtbr member
    Reputation:
    Join Date
    Feb 2007
    Posts
    108
    Of course the RAD number makes sense - and the size advice works well for me. People are so obsessed with reach that they completely forget about stack. Take stack and reach and calculate the missing thing - godd old Pythagoras- and you get the distance from BB to the headtube. Add things like spacers and bar height and you get this distance as effective measure. Other people measure the distance from the BB to the end of the bars - this makes absolutetely sense as well....

  43. #43
    mtbr member
    Reputation:
    Join Date
    Nov 2007
    Posts
    1,487
    Reach, stack, meh!

    Lee is on the right track with RAD. However RAD is about fit after you've added your cockpit components. When you're buying a bike, (usually) the frame front triangle is a rigid structure with a given geometry and there's precious little you can do after. Getting the main bit of metal (carbon) to be the right size is a big deal.

    Reach and Stack (as others have said) are interrelated. There isn't any way to get around needing two numbers to describe a point in horizontal profile view but the determination that reach and stack are "the" numbers is a matter of frame of reference only and while a major step ahead from ETT they are limiting too. "When you add spacers your reach gets shorter" is the classic example (except now we're confusing the reach the rider feels vs the hard numbers of the frame geometry)

    So back to frame of reference: You can go with reach and stack but then you're into approximation for jiggering about with stem spacers and stem length both having effects on the values. In engineering it is much more common for the distance of an axis from a point (steering axis from BB) to be described by the perpendicular distance. This gives us a single value that cannot lie describing the hard points of the geometry. We can see that stem length adds distance perpendicular to the axis also so we can add stem length and this value; spacers are along the line of the axis so do not change this value.

    We cannot line up a tape measure to verify the value reliably so it isn't as good as some of the other options. Given all the numbers we get in geo charts though it can be back calculated. Also to fully understand what is going on we need to know head tube angle before we can really tell very much about the bike fit. However, when we attach longer or shorter forks this number doesn't change (the rigid structure of the front triangle is fixed) and it just ends up changing BB height and head angle.

    Because this is how I deconstructed the geometry charts of all the frames I was looking at last time I went shopping I can tell you at 6'2" my sizing is 700mm (27.56") on a 65.5 degree head angle. This is XL in some brands and L in some others. What gets interesting is it shows up brands whose long low slack bikes aren't as long as they tell you they are because they have stuck with absurdly small head tubes (low stack inflates "reach"). This 700mm size isn't outlandish and in the case of my Norco Range XL it results in 483mm reach and 627mm stack.

    The easier to consume thing to do would be to have a standard stack height and give reach figures once you've spacered to the "standard size".

  44. #44
    battle stag commander
    Reputation: planetx88's Avatar
    Join Date
    Mar 2012
    Posts
    58
    Quote Originally Posted by petercarm View Post
    The easier to consume thing to do would be to have a standard stack height and give reach figures once you've spacered to the "standard size".
    I agree with this as far as what would be an ideal representation of sizing, and that reach/stack help us recreate or model how we find comfortable fit on an existing frame. The issue is how inconsistent geometry numbers are, and while we all sit around discussing millimeters, we ofter overlook that many companies dont measure static geometry, or that there is no standard for axle to crown lengths.

    I totally get it, and I do wish we could create more consistency, but ultimately, this will never happen. for me the best way to understand geometry is to really start by understanding how a company represents that information, or what I think might be missing. Then I generally look at ETT and seat angle, and try to put them in the context of the rest of the information provided. When companies then throw in the fact that these numbers I am looking at are taken at 32% sag or something, I get thrown off and really have trouble creating a mental model to compare things.

    In many ways, how a company decides to represent this geometry can be a great marketing tool, and they may want it to be unique. I think there is a reason there is pretty wide variability in what info is provided.

  45. #45
    mtbr member
    Reputation:
    Join Date
    Dec 2014
    Posts
    1,911
    Quote Originally Posted by Harold View Post
    . I don't dwell on numbers when it comes to fitting a bike. I focus on what feels right. So I haven't calculated RAD for any bikes I own. The whole concept seems rather contrived, anyway.
    So much this.

    Try a bike and pick the model and size that feels comfortable to you.

    People overthink this too much.

  46. #46
    mtbr member
    Reputation: mack_turtle's Avatar
    Join Date
    Jan 2009
    Posts
    9,635
    I wrote this and hopefully it will clear a few things up.

    https://www.cyclinghacks.com/mountai...ills-coaching/

    In short, Lee says the dramatic increase in reach on many modern bikes is a step in the wrong direction because it limits the full standing range of motion possible on the bike while wrangling the bike over terrain. Reach is getting longer and stems are getting shorter, but it's not balancing out. Bikes are just getting bigger, which puts the rider in the bike more than on the bike. This results in stability but limits control over the bike.

    My personal theory is that suspension and drivetrains are getting better, and riders are relying on this to make up for sloppy handling. My ability to out-ride many riders who are on fancy, long full-suspension bikes on my rigid singlespeed with a moderate reach and RAD fit somewhat backs this up, but that's not a scientifically sounds sample.

    My experience is that something closer to a RAD fit empowers me to master bike kung fu. The super-long limo bikes coming out make up for a lack of kung fu to some degree and it can manifest when the terrain overwhelms a rider's stunted skill level.

  47. #47
    mtbr member
    Reputation:
    Join Date
    Jun 2019
    Posts
    19
    While I agree that going off RAD may give the most biomechanical leverage and ability to handle the bike, I do not believe that necessarily implies it is the “best” all-around bike fit. What I mean is that there must be a trade off between the RAD biomechanical benefits (handling) and the benefits that physics tells us a longer wheelbase will provide (stability).

    For example, I recently demo’d a bike (L Ripmo) with a slightly longer reach and much longer wheelbase than my regular bike (L Rift Zone), and I was able to clear a very rough section relatively easy that I have only cleared once before and went OTB on twice before. Now I am definitely a beginner rider, and I’m sure that this added stability would not be as appreciated by a more advanced rider, but I don’t think that discredits my judgement that the longer bike was in fact “better” for this segment of trail.

    Lastly, I have a question. RAD refers to the distance from the BB to handlebars (basically), but what about the length of the wheelbase/front-to-center? I always assume RAD would dictate a shorter front-to-center as well, but I haven’t seen this stated. Are there disadvantages to a long front-to-center while having a shorter/appropriate RAD, or is it just a matter of leaning over the bars when necessary to weight the front end? If that’s the case, then one can just shorten the RAD of a longer, “modern” bike, with stem, spacers, and handlebar adjustments, and find a happy medium. Of course the bike will still be long, and thus a higher moment of inertia, but at least the rider will have max bio leverage.

  48. #48
    mtbr member
    Reputation:
    Join Date
    Dec 2007
    Posts
    6,661
    Quote Originally Posted by 33red View Post
    Forget about new, old.
    My legs are way too long.
    My bikes are way too long.
    I reverse seatpost to shorten the frame.
    When that fails, i cut frames then glue back.
    620 mm handlebars.
    Ya i am not average but with a good position i go up, down and turn.
    The idea is 95 % is about the rider, frame BS is if you hope
    your bike will turn u in an expert.
    Back when there was a place call Telemarktips, there was a poster who wrote like this, not sure if it's the same guy, I think he went by Telemon.

    620mm bars, now that is really narrow, do you ride one handed

    Bike design matters, it just doesn't matter to everyone.
    Guerilla Gravity Shred Dogg
    Fezzari Signal Peak (For Sale)
    Pivot Shuttle (wife's)

  49. #49
    aka bOb
    Reputation: bdundee's Avatar
    Join Date
    Feb 2008
    Posts
    8,737
    Quote Originally Posted by prj71 View Post
    So much this.

    Try a bike and pick the model and size that feels comfortable to you.

    People overthink this too much.
    But what if you want to order one and can't or not patient enough to wait for a demo? Numbers and reviews are all we have right? On a side note me and my wallet wish we had your patience

  50. #50
    mtbr member
    Reputation:
    Join Date
    Dec 2007
    Posts
    6,661
    Not just stack, but seat height also changes how a bike fits.

    It would be nearly impossible to say one "fit" works best for everyone, which is why people need to demo bikes and play with set up. Geometry tables can get you in the ballpark, then start tweaking from there.
    Guerilla Gravity Shred Dogg
    Fezzari Signal Peak (For Sale)
    Pivot Shuttle (wife's)

  51. #51
    mtbr member
    Reputation: jeremy3220's Avatar
    Join Date
    Jul 2017
    Posts
    1,998
    Quote Originally Posted by mack_turtle View Post

    In short, Lee says the dramatic increase in reach on many modern bikes is a step in the wrong direction because it limits the full standing range of motion possible on the bike while wrangling the bike over terrain. Reach is getting longer and stems are getting shorter, but it's not balancing out. Bikes are just getting bigger, which puts the rider in the bike more than on the bike. This results in stability but limits control over the bike.
    Which is great for everything except slow really tight trails and tech. Clearly the bikes from 7-10 years ago were too small. That's why DH racers looked like gorillas riding BMX bikes up until 2013 or so. I'd say bike length is just finally starting to hit the sweet spot.

  52. #52
    mtbr member
    Reputation:
    Join Date
    Jan 2016
    Posts
    1,397
    Quote Originally Posted by bdundee View Post
    But what if you want to order one and can't or not patient enough to wait for a demo? Numbers and reviews are all we have right? On a side note me and my wallet wish we had your patience
    I guess you know that reviews more often are just a form of disguised advertisement.

  53. #53
    aka bOb
    Reputation: bdundee's Avatar
    Join Date
    Feb 2008
    Posts
    8,737
    Quote Originally Posted by 33red View Post
    I guess you know that reviews more often are just a form of disguised advertisement.
    I speak of trusted rider reviews/gossip not advertising reviews. Been in this business long enough and have purchased enough bikes to know how it works but thanks for looking out for me.

    P.S. I was referring to riders reviews on sizing to keep with the theme of this thread.

  54. #54
    mtbr member
    Reputation:
    Join Date
    Jan 2016
    Posts
    1,397
    Quote Originally Posted by jeremy3220 View Post
    Which is great for everything except slow really tight trails and tech. Clearly the bikes from 7-10 years ago were too small. That's why DH racers looked like gorillas riding BMX bikes up until 2013 or so. I'd say bike length is just finally starting to hit the sweet spot.
    I will not say you are wrong. I happen to disagree. With an aging population the bikes should get shorter.
    I agree with mack_turtle.
    There is an obvious unwillingness to learn, improve, get better as a rider.
    Just reading posts it is obvious that many are looking for a better dropper.
    They waste $ on gadgets.
    They are addicted to new.
    They would do much better buying used proven stuff.
    I do not think they are a bunch of lazy.
    This is about the society we live in.
    Most people live in cities or suburbs disconected with facts.
    It is DisneyWorld, Oprah way, just wish it.
    A seat is to be used as a steering it is not a problem.
    We should not be in an expert trail too soon.
    Well with the credit habit people are unwilling to wait
    so they waste $$ on fullsuspension because they forgive.
    Well on my fourth year on fatbike and mountain bike i enjoy
    my HT, learning skills, practicing, improving.
    No i am not using a cell, i do not have one.
    No GPS, no idea about top speed, average speed...
    I just try to climb a hill untill i can.

  55. #55
    mtbr member
    Reputation: jeremy3220's Avatar
    Join Date
    Jul 2017
    Posts
    1,998
    Quote Originally Posted by 33red View Post
    I will not say you are wrong. I happen to disagree. With an aging population the bikes should get shorter.
    I agree with mack_turtle.
    There is an obvious unwillingness to learn, improve, get better as a rider.
    Just reading posts it is obvious that many are looking for a better dropper.
    They waste $ on gadgets.
    They are addicted to new.
    They would do much better buying used proven stuff.
    I do not think they are a bunch of lazy.
    This is about the society we live in.
    Most people live in cities or suburbs disconected with facts.
    It is DisneyWorld, Oprah way, just wish it.
    A seat is to be used as a steering it is not a problem.
    We should not be in an expert trail too soon.
    Well with the credit habit people are unwilling to wait
    so they waste $$ on fullsuspension because they forgive.
    Well on my fourth year on fatbike and mountain bike i enjoy
    my HT, learning skills, practicing, improving.
    No i am not using a cell, i do not have one.
    No GPS, no idea about top speed, average speed...
    I just try to climb a hill untill i can.
    Oprah, GPS, Disneyland, cellphones, suburbs, credit cards...got it.

  56. #56
    mtbr member
    Reputation:
    Join Date
    Apr 2010
    Posts
    130
    Quote Originally Posted by 33red View Post
    I will not say you are wrong. I happen to disagree. With an aging population the bikes should get shorter.
    I agree with mack_turtle.
    There is an obvious unwillingness to learn, improve, get better as a rider.
    Just reading posts it is obvious that many are looking for a better dropper.
    They waste $ on gadgets.
    They are addicted to new.
    They would do much better buying used proven stuff.
    I do not think they are a bunch of lazy.
    This is about the society we live in.
    Most people live in cities or suburbs disconected with facts.
    It is DisneyWorld, Oprah way, just wish it.
    A seat is to be used as a steering it is not a problem.
    We should not be in an expert trail too soon.
    Well with the credit habit people are unwilling to wait
    so they waste $$ on fullsuspension because they forgive.
    Well on my fourth year on fatbike and mountain bike i enjoy
    my HT, learning skills, practicing, improving.
    No i am not using a cell, i do not have one.
    No GPS, no idea about top speed, average speed...
    I just try to climb a hill untill i can.
    huh? So shorter bikes are somehow better for the elderly?

    New geometry bikes simply handle most terrain better and dropper posts make aggressive trail riding much less dangerous/much more fun....regardless of how long you've been riding.

    I started racing BMX in 1978 and transitioned to MTB in the early 90s'. For 40+ years now I've been offroad and I've now continued to improve my skills simply by riding a new bike with great new geometry that allows me to do more than ever on a 29" wheel. I'm hitting jumps and drops that I haven't taken in years.

    It's win-win for all. If you choose to ride older XC geometry with a fixed seatpost, by all means have at it, but please don't knock new innovation as though it's a short cut. It's an improvement.

  57. #57
    mtbr member
    Reputation:
    Join Date
    Dec 2014
    Posts
    1,911
    Quote Originally Posted by bdundee View Post
    But what if you want to order one and can't or not patient enough to wait for a demo? Numbers and reviews are all we have right? On a side note me and my wallet wish we had your patience
    Ha!!! Lots of number and reviews to look at. But nothing like riding the real thing.

    I may be making a Colorado trip this fall to try out a Spot. Hardtail is serving me fine at the moment.

  58. #58
    aka bOb
    Reputation: bdundee's Avatar
    Join Date
    Feb 2008
    Posts
    8,737
    Quote Originally Posted by prj71 View Post
    Ha!!! Lots of number and reviews to look at. But nothing like riding the real thing.

    I may be making a Colorado trip this fall to try out a Spot. Hardtail is serving me fine at the moment.
    I hate your patience, see ya later tonight!!

  59. #59
    mtbr member
    Reputation:
    Join Date
    Dec 2007
    Posts
    6,661
    Quote Originally Posted by 33red View Post
    I will not say you are wrong. I happen to disagree. With an aging population the bikes should get shorter.
    I agree with mack_turtle.
    There is an obvious unwillingness to learn, improve, get better as a rider.
    Just reading posts it is obvious that many are looking for a better dropper.
    They waste $ on gadgets.
    They are addicted to new.
    They would do much better buying used proven stuff.
    I do not think they are a bunch of lazy.
    This is about the society we live in.
    Most people live in cities or suburbs disconected with facts.
    It is DisneyWorld, Oprah way, just wish it.
    A seat is to be used as a steering it is not a problem.
    We should not be in an expert trail too soon.
    Well with the credit habit people are unwilling to wait
    so they waste $$ on fullsuspension because they forgive.
    Well on my fourth year on fatbike and mountain bike i enjoy
    my HT, learning skills, practicing, improving.
    No i am not using a cell, i do not have one.
    No GPS, no idea about top speed, average speed...
    I just try to climb a hill untill i can.
    Sounds like you are ready for cycling at it's most basic: Unicycle

    Seriously, it will change your life, brings a whole new perspective to riding.
    Guerilla Gravity Shred Dogg
    Fezzari Signal Peak (For Sale)
    Pivot Shuttle (wife's)

Similar Threads

  1. Wolf Tooth Goat Link vs OneUp RAD Cage vs Long B Tension Screw
    By aliikane in forum Drivetrain - shifters, derailleurs, cranks
    Replies: 42
    Last Post: 08-10-2017, 12:57 PM
  2. Help with A-C heights on modern forks and modern frames
    By Blatant in forum Shocks and Suspension
    Replies: 4
    Last Post: 05-28-2012, 05:24 PM
  3. Replies: 2
    Last Post: 10-13-2011, 07:34 AM
  4. 7005 Easton Tubing: FS RAD SL vs FS RAD DH
    By dandurston in forum Downhill - Freeride
    Replies: 3
    Last Post: 06-05-2006, 02:15 PM
  5. how do road bike sizes compare with mtb sizes?
    By journey in forum Bike and Frame discussion
    Replies: 3
    Last Post: 08-31-2005, 09:07 AM

Members who have read this thread: 247

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

THE SITE

ABOUT MTBR

VISIT US AT

© Copyright 2019 VerticalScope Inc. All rights reserved.