Frame size and "fit"

[Chief]

1 hour ago, mack_turtle said:

Interesting that you bring that up.

https://youtu.be/xMXlKED32uo

That's how he got started down the rabbit hole😂

[mack_turtle]

Lenosky weighing in on bike fit with RAD theory. I feel vindicated that this is catching on. for the past few years, people have bought into the idea that the longest bike possible and ten-foot wide handlebars are the solution to everything. just like JNCOs and giant smart phones, it turns out that moderation and individual needs have to be considered.

 

[TheX]

1 hour ago, mack_turtle said:

 ten-foot wide handlebars 

I cut mine down from 800 to 740 and suddenly liked the bike more.

[Jessica]

I'm 5'4" with a 29 inch inseam. 

I ride a medium Santa Cruz HighTower with a 29er setup and a 54cm Specialized Sequoia.    

Some bike shops wouldn't size me on these sized bikes, but it I feel cramped in smaller bikes.  My previous bikes were smaller and hurt my posture on longer rides.  Barry does spec all my parts and did put really short stems on both bikes, but I find the handling of shorter stems preferable on squirly and DH shit. 

Arm length- reach and inseam make a big difference on some bikes.  I literally can't stand over a Gorilla Gravity medium frame with the tires inflated.  

Always demo a bike on a reasonable ride. 

[ATXZJ]

5 hours ago, mack_turtle said:

 just like JNCOs and giant smart phones, it turns out that moderation and individual needs have to be considered.

 

everything in moderation, including moderation

[Barry]

3 hours ago, Jessica said:

I literally can't stand over a Gorilla Gravity medium frame with the tires inflated.  

Dude, that GG Trail Pistol was a small!

[attaboy]

Thanks mack-turtle. Super helpful. Combining the PVD stuff made RAD make sense. Thing missing was how you could have same RAD with different lengths/heights on the other two sides of the triangle, so to speak.

A while back, noticed how reluctant I was to stand and pedal on steeper tech. Bar felt too far back when standing to get good leverage on bars when pulling up. Recently lengthened stem (committing new geo heresy) and lowered bar, keeping RAD the same, but really improved bike feel especially on technical ups when out of the saddle. Your spreadsheet helped explain this.

[AntonioGG]

2 hours ago, attaboy said:

Thanks mack-turtle. Super helpful. Combining the PVD stuff made RAD make sense. Thing missing was how you could have same RAD with different lengths/heights on the other two sides of the triangle, so to speak.

A while back, noticed how reluctant I was to stand and pedal on steeper tech. Bar felt too far back when standing to get good leverage on bars when pulling up. Recently lengthened stem (committing new geo heresy) and lowered bar, keeping RAD the same, but really improved bike feel especially on technical ups when out of the saddle. Your spreadsheet helped explain this.

This is exactly what I’m thinking I need to do on my full suspension.  I’m measuring RAD on all my bikes and measuring myself as well to see what I come up with.  Good to read it helped you!

[mack_turtle]

12 hours ago, Barry said:

Dude, that GG Trail Pistol was a small!

I've heard from folks at GG that their frames are big. that's by design and following a design philosophy that they have embraced. obviously that works for some riders on certain kinds of terrain. they're in Colorado, so that makes sense, but at 5'9", they recommend a "size 2" with an itty bitty stem and it still sounds too big for my liking. of course, a test ride would make a huge difference. I think the pendulum might swing back the other way in the coming years. on the other hand, the bicycle industry has a severe lack of bikes for shorter riders. a 5'4", I would think that most "small" sized bikes should fit you but GG doesn't seem to make bikes that are actually small.

[Barry]

6 minutes ago, mack_turtle said:

I've heard from folks at GG that their frames are big.

The reach was just fine on the GG. The problem was just the standover as she couldn't stand over the top-tube without being on her tiptoes. It turned out they measured stand-over at the lowest point on the top tube (under the saddle), and not at a place you can actually stand. Over. Of course we found this out after I built up the bike and not during the 70 or more emails I exchanged with GG including every imaginable body measurement. They did pay for the return shipping and fully refund the purchase.

But! This was on their old aluminum frames with the silly up-sloping top tube. It looks like they may have fix'd that issue with their carbon frames. 

[ssorgs]

16 hours ago, ATXZJ said:

everything in moderation, including moderation

'Too much of everything is just enough.'

[rockshins]

Just checked the RAD on my bike and based on Lee Mccormacks guide it is slightly too short for me. This is helpful because the bikes does feel a little short and now I know I am not crazy. Going to try out a 60mm stem, I really love the feel of shorter stems so not loving the idea but we’ll see how this works!

[AntonioGG]

4 hours ago, ssorgs said:

'Too much of everything is just enough.'

"Keep Balance all Life" --Mr. Miyagi

[mack_turtle]

Interesting way to test RAD fitting theory on the bike rather than with abstract numbers:

Find a pair of picnic tables. (If you have two low step ladders, that works too.) Suspend your bike by it's pedals on the table tops. If you're in a public park, try not to gouge up the tables. Step up onto your pedals and test your range of motion. When the bike is as close to upright as it can get with your handlebar in your lap like you've just reached the top of a deadlift.

Drop your shoulders and straighten your arms and wrists. Ideal RAD will set your grips right in your hands. There's a range that works for everyone. This serves as a good reference point. I believe most riders will have a RAD that is quite a bit longer than that, so the grips will be at your wrists or higher. Lee calls this "RAD plus" and might work well for gravity-assisted riding. Grip below your knuckles is RAD minus and might better suit riding twisty trails with lots of trials-y stuff that we think of as East Coast riding.

Being a giant dork, I did the picnic table experiment in Dick Nichols Park a few years ago. My RAD for that bike was a little long, but a short stem and sweety bar got it within range to serve as a good reference point.

[attaboy]

This recent article presents a different take on this, a bit of a departure with RAD as something static across frame sizes; addresses the issues of fit across riders of differing heights. https://www.pinkbike.com/news/importance-of-handlebar-height-mountain-bike.html

[mack_turtle]

Just saying: I've been using the terms "effective reach" and "effective stack," and trying to get people to think in terms of RAD/ spread/ room/ effective down tube in the same context for years. Since no one lists EDT on bikes, I have an old spreadsheet comparing several frames I was considering at the time, partially based on calculating the EDT as a starting point. I have bike fit paperwork from 2017 where I had Frank at ATX Bike label the "eR" and "eS" on my fit labeled. Glad to see it's finally catching on.

Saddle-handlebar drop is indeed mostly poppycock. Hot take: Most people have their handlebar too high so they can sit up high and pretty like a beach cruiser. Take that or leave it. But if you ride with me and I smoke you on a climb, it's not all the fiber in my diet that's doing the work. Maybe the farting gives me a boost.

I can't seem to get my handlebar low enough to be confidence-inspiring!

Edited June 4, 2021 by mack_turtle

[hurronnicane]

On 4/5/2021 at 12:18 PM, ssorgs said:

'Too much of everything is just enough.'

You cannot know what is enough until you know what is too much.

Edited June 4, 2021 by hurronnicane
Error

[TheX]

15 minutes ago, hurronnicane said:

You cannot know what is enough until you know what is too much.

Wisdom, seriously.

[ssorgs]

11 hours ago, hurronnicane said:

You cannot know what is enough until you know what is too much.

That's how I make lots of adjustments! Go too far and dial it back...

[AntonioGG]

This is more oriented toward road/gravel and endurance MTB riding (i.e. more seated pedaling).  For me, hip and knee angles are critical, but I had also wondered about femur velocity and this guy talks about it which is really cool.

 

 

[mack_turtle]

I used the ultra slo-mo video feature with my phone, with an app called Angulus to measure my knee and hip angles to get a better fit on my gravel bike.

Hip pain is how I determined that my 175mm cranks were too long, video is how I learned that 170s were better. confirmation came with the subsequent lack of hip pain. Put another way, "You cannot know what is enough until you know what is too much."

Edited September 21, 2021 by mack_turtle

[AntonioGG]

So you did video with both 175 and 170 cranks?  What angle difference did you get?  I like that this video offers an alternative of changing setback and seat height to change femur angle before going through the expense of new cranks.

[mack_turtle]

There's a lot of trial and error that goes into any aspect of bike fitting. I put the cleats in a position that feels most stable to me, which is pretty far back on the shoe. then I set the height based on my measured PBH. then set fore-aft based on what feels the most balanced to me. Steve Hogg and John Weirath do a good job of explaining this method. then you look at knee and hip angles to determine if crank length is appropriate, or if a change in handlebar position might accommodate a slightly different saddle position.

for angles, I found some guides that recommended a bent-knee angle of 68-74°. with 175mm cranks and everything set in a place that felt good for bike handling, the high angle was much more than that, like 76°. my knee was bending too much at the top of my pedal stroke, so it was forced to flare out. raising the saddle would result in a over-extended knee at the bottom of my pedal stroke. I took slo-mo video and screen shots, but I can't find the images any more. must have deleted the photos of myself in my living room, wearing lycra so they would not fall into the wrong hands.

I traded the cranks, so getting shorter cranks didn't cost me anything but gas money. if you're not super picky about cranks, it's not difficult to find something that works. the chainrings didn't matter because I have a single ring on this bike. 

this seems like a lot of work, but if you spend a lot of time on the bike, it seems like time well spent instead of $200-300 on a pro fit. I paid a few bucks to download the complete guide from https://bikedynamics.co.uk/shop.htm and that helped a lot. understanding bone structure and exactly where body parts move around on a bike makes a lot more sense now. 

Edited September 21, 2021 by mack_turtle

[AntonioGG]

Don't get me started on Hogg and his rants on plastics that affect proprioception.  🙂 

I think we've done this dance before.  I've done the video and angles thing and the bike fitters thing.  Probably spent $1k on bike fits before I paid ~$5 for the the Bike Dynamics guide (highly recommend it to the rest of you.)

I also start at the cleat like the guide recommends, but I'm 5-10mm behind the ball midline.  I would consider more mid-foot placement but for toe overlap problems.  Is this where one of us posts the Keith Bontrager KOPS rant? 🙂  

My seat/pedal/crank/cleat tweaks are very small like @AustinBike is finding, but I've still not nailed the whole RAD thing and I think I could benefit from it.  Been riding too much road the last few months.

[mack_turtle]

20 hours ago, AntonioGG said:

Don't get me started on Hogg and his rants on plastics that affect proprioception.  🙂 

I think we've done this dance before.  I've done the video and angles thing and the bike fitters thing.  Probably spent $1k on bike fits before I paid ~$5 for the the Bike Dynamics guide (highly recommend it to the rest of you.)

Yeah, Hogg is really out there on some stuff. What is he smoking? his perspective on a saddle height that does not allow your hips to rock and a fore-aft position that feels balanced instead of some KOPS magic makes a lot of sense though. Weirath's videos under "bike fit advisor" on YouTube do a better job of explaining it.

that book is worth every penny if you want a solid baseline fit on a road bike. I think it needs tweaking for mountain bike fitting though, because mountain bikes fit differently to handle terrain well. I don't think they claim that their fitting method applies directly to mountain bikes, but I've seen fitters use the exact same approach to road and mtn bikes. it makes customers feel confident, but doubt that the approach is a good one.

Edited September 22, 2021 by mack_turtle