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Always in the wrong gear
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I’ve really come to the conclusion that RAD just doesn’t work for me.
I have a degree in biomechanics, and am a sports/ortho physical therapist, so I can follow the logic of what Lee says, but neither of my bikes are even in that same zip code as my calculated RAD.
I’m 5’9”, my measurement with the marker in hand on the wall is IIRC 735mm. Both my FS and my hardtail have a RAD of something in the low 800s! Neither has a long reach- the HT is a 450 reach, the FS is a 445. I’m running 50 and 55mm stems with 780 bars. To get my bike fit down to the suggested RAD, I’d be in my 5’5” wife’s bike, or I’d be running a 32mm stem with flat bars, and I’d be slamming my knees into the dropper lever.

I’ve done the ladder-test and the bars are juuust short of being comfortably in hand, I’m also really comfortable on both my bikes, so I don’t sweat it.
 

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I’ve really come to the conclusion that RAD just doesn’t work for me.
I have a degree in biomechanics, and am a sports/ortho physical therapist, so I can follow the logic of what Lee says, but neither of my bikes are even in that same zip code as my calculated RAD.
I’m 5’9”, my measurement with the marker in hand on the wall is IIRC 735mm. Both my FS and my hardtail have a RAD of something in the low 800s! Neither has a long reach- the HT is a 450 reach, the FS is a 445. I’m running 50 and 55mm stems with 780 bars. To get my bike fit down to the suggested RAD, I’d be in my 5’5” wife’s bike, or I’d be running a 32mm stem with flat bars, and I’d be slamming my knees into the dropper lever.

I’ve done the ladder-test and the bars are juuust short of being comfortably in hand, I’m also really comfortable on both my bikes, so I don’t sweat it.
Did you do the wall test with your legs straight? They didn't explain it in the video but once you get into your riding foot position, straighten your legs.
 

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2020 Santa Cruz Tallboy C
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Interesting the timeliness of this topic. I bought a new mtb back in January, a 2020 SC Tallboy C V4 size large. I was able to take it for a brief test ride and found it fit very well. Shortly after that I start seeing this topic of RAD on Joy of Bikes and a few others. I'm somewhat OCD and this sent me into analysis mode. I found my new bike was bigger than my RAD. I only had a couple of rides on it and starting thinking my re-entry to mtb after some years away was already flawed. I'm pretty anal about my fit and tried a shorter stem (40mm vs 50mm) which made my bike very twitchy. I decided to ignore this RAD stuff and just ride and find my skills are coming back, albeit slowly. I had the opportunity to ride a bike that was my RAD size, I hated the fit, it felt very cramped. I am 5'11" and have 33.5" inseam and a very big wingspan.

Just like all the other formula driven bike fits it doesn't work for everyone. I'm sure some of you read Greg LeMond's book back in the 80's and set their seat height to inseam*0.883. I know I did until my knees told me otherwise.
 

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Always in the wrong gear
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Did you do the wall test with your legs straight? They didn't explain it in the video but once you get into your riding foot position, straighten your legs.
I did. I’ve watched most of JoBs videos, a bunch of LLBs, and even a few random YTers making videos about JoB.
Even Assuming I didn’t straighten my knees, and stayed in the ‘slight-crouch’ attack standing position, it doesn’t come close to account for the near 100mm discrepancy.
It’s bizarre.
 

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I’ve really come to the conclusion that RAD just doesn’t work for me.
I have a degree in biomechanics, and am a sports/ortho physical therapist, so I can follow the logic of what Lee says, but neither of my bikes are even in that same zip code as my calculated RAD.
I’m 5’9”, my measurement with the marker in hand on the wall is IIRC 735mm. Both my FS and my hardtail have a RAD of something in the low 800s! Neither has a long reach- the HT is a 450 reach, the FS is a 445. I’m running 50 and 55mm stems with 780 bars. To get my bike fit down to the suggested RAD, I’d be in my 5’5” wife’s bike, or I’d be running a 32mm stem with flat bars, and I’d be slamming my knees into the dropper lever.

I’ve done the ladder-test and the bars are juuust short of being comfortably in hand, I’m also really comfortable on both my bikes, so I don’t sweat it.
I'm 5'8" 30 inseam and my RAD measured ~80cm. Are your arms super long or legs super short?😁

My GF at 5'6" 30 inseam measured at ~78mm.

I had to measure myself a few times because I kept bending at my waist to see the mark.

All my bikes are mediums with 50mm stems. All of my bikes are fairly short in reach. The RAD on all four measure between 79 and 81cm. One measured exactly at 80cm.
 

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Always in the wrong gear
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I'm 5'8" 30 inseam and my RAD measured ~80cm. Are your arms super long or legs super short?😁

My GF at 5'6" 30 inseam measured at ~78mm.

I had to measure myself a few times because I kept bending at my waist to see the mark.

All my bikes are mediums with 50mm stems. All of my bikes are fairly short in reach. The RAD on all four measure between 79 and 81cm. One measured exactly at 80cm.
I dunno. I just measured it again. I’ve got on my Specialized Rime shoes, my feet are 320mm apart, as if standing on pedals. My shoulders are back and down, elbows extended, arms along my thigh, a marker in my fist. I make a dot on paper. 742mm.

¯\(ツ)
 

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2020 Santa Cruz Tallboy C
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I'm 5'8" 30 inseam and my RAD measured ~80cm. Are your arms super long or legs super short?😁

My GF at 5'6" 30 inseam measured at ~78mm.

I had to measure myself a few times because I kept bending at my waist to see the mark.

All my bikes are mediums with 50mm stems. All of my bikes are fairly short in reach. The RAD on all four measure between 79 and 81cm. One measured exactly at 80cm.
I was just reading yours and your girlfriends RADs. I am 5'11" with 33.5" inseam and 73.5" wingspan. My calculated RAD is 80cm and my actual body RAD is 78cm. That would put me on the same bike size as you and your GF.
 

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always licking the glass
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I was just reading yours and your girlfriends RADs. I am 5'11" with 33.5" inseam and 73.5" wingspan. My calculated RAD is 80cm and my actual body RAD is 78cm. That would put me on the same bike size as your and you GF.
The point of the RAD measurement is to get people to size down one or two sizes, so you’re not wrong.

I rode an XS at 5’5” based on that. Too twitchy, and I was way too crunched up. Now i get way ledgy trails were particularly nerve wracking.

Two years ago got on a medium and my riding has improved significantly. Body feels much better, and my bike handling is much better too because the twitchiness is gone.
 

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Rippin da fAt
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The point of the RAD measurement is to get people to size down one or two sizes, so you’re not wrong.

I rode an XS at 5’5” based on that. Too twitchy, and I was way too crunched up. Now i get way ledgy trails were particularly nerve wracking.

Two years ago got on a medium and my riding has improved significantly. Body feels much better, and my bike handling is much better too because the twitchiness is gone.
Any time one can be on a bike that is relaxed in terms of fit as opposed to knees in front of the bar or reaching to the next door neighbors front door, the ride experience will be superior.
Now it would get down to what caster angle is comfortable for you and forget everyone else, not to mention STA and how that affects your spin and power production range.
Remember, you are the one writing the check, you are the one tasked with riding it. Fitment should be a pleasure, not a chore.
 

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I was just reading yours and your girlfriends RADs. I am 5'11" with 33.5" inseam and 73.5" wingspan. My calculated RAD is 80cm and my actual body RAD is 78cm. That would put me on the same bike size as you and your GF.
The RAD measurement is nothing more than the measurement from the crank spindle to the virtual center of your grips. It for the full range of motion. You can get the same RAD on a medium and a large. Most bikes are designed around a 30 to 50mm stem. I can get a small and use a longer stem...or a medium and use a shorter one. Its a consistent number that can me moved from bike to bike depending on the handling characteristics you're looking for. Your fit will be similar across multiple bikes. He's not a bike company trying to sell you a bike. He's just basing it on his experiences as a MTB coach.

People are going to have their preferences regardless of what anyone says. Do what makes you happy.
 

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The RAD measurement is nothing more than the measurement from the crank spindle to the virtual center of your grips. It for the full range of motion. You can get the same RAD on a medium and a large. Most bikes are designed around a 30 to 50mm stem. I can get a small and use a longer stem...or a medium and use a shorter one. Its a consistent number that can me moved from bike to bike depending on the handling characteristics you're looking for. Your fit will be similar across multiple bikes. He's not a bike company trying to sell you a bike. He's just basing it on his experiences as a MTB coach.

People are going to have their preferences regardless of what anyone says. Do what makes you happy.
I understand the concept. I can't get my size large Tallboy set to a 78cm RAD but I have tried another bike that was a medium that measured 78cm RAD. When I set my seat height for my legs the bar drop was uncomfortable and to get the bar height up it would have gone over RAD. I rode the bike and found my legs hitting the bars on standing pedaling and I was leaned over the bars quite a bit.

I'm not saying this fit doesn't work for some but it is not a universal thing. My Tallboy measures 84cm RAD and gives me the room I need for my legs and arms. The cool thing is the human body is remarkably adaptable. The best thing is a comfortable bike is one you like to ride. That makes me happy. :cool:
 

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I think the body measurements, aside from your height, are too easy to mess up. Is the pen level, are your hands the right distance apart, are you knees straight, are your shoulders packed? Etc etc. Just do the step ladder test with your bike if you feel like it is hard to pump, jump, turn, or your back hurts after a few hours riding. If you are mostly an XC, non technical rider, this stuff doesn’t apply as critically, same if you are a more passive rider, looking to sled down the hill.
 

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always licking the glass
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I think the body measurements, aside from your height, are too easy to mess up. Is the pen level, are your hands the right distance apart, are you knees straight, are your shoulders packed? Etc etc. Just do the step ladder test with your bike if you feel like it is hard to pump, jump, turn, or your back hurts after a few hours riding. If you are mostly an XC, non technical rider, this stuff doesn’t apply as critically, same if you are a more passive rider, looking to sled down the hill.
The RAD does not take into account seated pedaling. Enduro and XC both do it, and for me, that’s where it kills me. My RAD is a lot smaller than where I’m comfortable uphill or seated pedaling.

It also doesn’t work for me because it forces me into a much more cramped position that my spine seriously objects to, even on the pump track.

I wouldn’t say DH riders are necessarily passive either—RAD is a fine that works for some folks, but it’s not for everyone.
 

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The RAD does not take into account seated pedaling. Enduro and XC both do it, and for me, that’s where it kills me. My RAD is a lot smaller than where I’m comfortable uphill or seated pedaling.

It also doesn’t work for me because it forces me into a much more cramped position that my spine seriously objects to, even on the pump track.

I wouldn’t say DH riders are necessarily passive either—RAD is a fine that works for some folks, but it’s not for everyone.
Your analysis is spot on.
I'm in the northeast (NY/NJ area) so undulating and technical (rocks and roots) are everywhere. Not a lot of long downhill or uphill but for some reason there seems to be more uphill than downhill.
 

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always licking the glass
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Your analysis is spot on.
I'm in the northeast (NY/NJ area) so undulating and technical (rocks and roots) are everywhere. Not a lot of long downhill or uphill but for some reason there seems to be more uphill than downhill.
It's crazy how many people take this as gospel. I've seen people ride with 30 and 50mm bars ridden upside down to meet their RAD, rather than fit the bike to them, they force themselves into a RAD. Lee thought of this back 5 years ago or so, where bike geometries were so different than they are now. It hasn't evolved at all, and as the bike change, it makes it really difficult for this to apply to everyone over the years. Even you and I, both riding different types (more park and DH for me, more XC for you), it doesn't work for us. A few of my other friends have had to readjust from it too--neck and shoulder issues from what I remember. Not worth getting hurt to match some numbers on the internet so I squish into them.
 

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Seems to me that as bikes getting longer, RAD is more important if you are trying to do the things that require you to have leverage over the front end. If you are not able to generate a ton of torque on a BMX, that's fine only a small amount of torque is needed to pull a manual. Modern geometry enduro with 180mm travel bike, If you want to have more control over the front end, more ability to "PULL UP", manual, wheelie, drop off ledges with control at slower speeds. Having that leverage makes it require less energy to accomplish. If you're bombing smooth downhills holding on for dear life, that's different.

Also the "it doesn't feel right" argument is sometimes flawed imo. We get accustomed to a bike and then that feels right, change geometry, stem length, spacers, where the levers are... feel is impacted. Decide you like it for one reason or another it will feel right over time. Decide you don't like it for one reason or another and "it doesn't feel right".

Pick up something with some weight off the floor close to your feet. Now try to do it with it gradually further and further away from your feet. Leverage decreases as that distance increases plain and simple. If you have enough leverage to pop up tough climbs, manual without exerting everything you can, yank a J hop you are proud of, u good. Riding a bike giving you enjoyment, NICE!
 

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Agree, feel means almost nothing, not buying the "RAD is too short for my spine and climbing." I've shortened my RAD from what thought it should be before to the measured distance of about 30mm closer to me, and the bike climbs great. Now I can corner more confidently and lift the bike more easily. With steeper seat tube angles (or virtual STA by sliding your rails forward), it's not necessary to weight the front end as much and you can climb in a position that handles better.

Lee rails about super-long reach these days, but I wish he'd also mention that reach used to be much too short. There's nothing good about a bike with a 90mm-120mm stem--something was wrong with bikes a few years back, and now they're much better fits.
 

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The RAD does not take into account seated pedaling. Enduro and XC both do it, and for me, that’s where it kills me. My RAD is a lot smaller than where I’m comfortable uphill or seated pedaling.

It also doesn’t work for me because it forces me into a much more cramped position that my spine seriously objects to, even on the pump track.

I wouldn’t say DH riders are necessarily passive either—RAD is a fine that works for some folks, but it’s not for everyone.
Yeah, there are too many variables to make one formula work every time, and this one isn’t focussed on seated pedaling.

I think the step ladder test is a good starting point for people who don’t feel quite right on their bike, since a professional fit might not work out either, and can be expensive, but perhaps better informed.

The sled comment is not aimed at DH riders, who can be very active and mobile on their bikes, but was more of a lazy way to say, sizing down won’t work for people who feel really tied to the longest wheelbase they can work. Personally, I haven’t sized down on my modern bike, just tweaked my reach and stack down a bit, and widened my handlebars at the same time, which can counteract the steering effect if simultaneously going to a shorter stem.
 

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Curiosity got the best of me. I bought his guide and will play around with it later. Though I suspect it's going to be tough with my build. I'm 5'11" with a 6'6" wingspan and I suspect no calculator out there is going to work with that.
 

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Curiosity got the best of me. I bought his guide and will play around with it later. Though I suspect it's going to be tough with my build. I'm 5'11" with a 6'6" wingspan and I suspect no calculator out there is going to work with that.
Wow, that is a wingspan! Are your legs long as well? That would be an interesting fit.
 
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