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The Internet Was Wrong: Short Chainstays Suck*

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3/11/2019 6:38 PM

ninjichor wrote:

Sounds like you convinced yourself that you didn't have to adapt to the bike's geo, and felt the negative traits of heavy weight bias up front, which I expected.


Sounds like you made up your mind a long time ago and won't hear anything to the contrary.

Build your bikes, try them, and see what works for you. I've done the same and, for now, I'm happy with my current geometry - which is similar to your diagram in front-centre and rear-centre, except with more reach and a steeper head angle.

Thank you for the discussion; I now plan to discontinue our conversation.
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3/11/2019 6:51 PM
Edited Date/Time: 3/11/2019 8:21 PM

R-M-R wrote: ninjichor wrote:

Sounds like you convinced yourself that you didn't have to adapt to the bike's geo, and felt the negative traits of heavy weight bias up front, which I expected.


Sounds like you made up your mind a long time ago and won't hear anything to the contrary.

Build your bikes, try them, and see what works for you. I've done the same and, for now, I'm happy with my current geometry - which is similar to your diagram in front-centre and rear-centre, except with more reach and a steeper head angle.

Thank you for the discussion; I now plan to discontinue our conversation.

That escalated quickly.

I'm saying that your "contrary" account has facts that are agreeable. The difference is the interpretation of the facts. The big picture usually has perspectives coming from multiple angles. I'm not denying yours, I'm adding to it in a manner that can coexist, just with different subjective "judgement".

Who's questioning your current geo? FC and RC is what is the subject here. How you get the FC is secondary. If I wanted to fit a shorter person on the same wheelbase as your bike, I'd give them a shorter reach and slacker HA (and possibly a longer fork and steeper STA), in order to maintain the same FC and RC. I dunno if a taller person than you would accept a longer reach, steeper HTA, and possibly slacker STA and shorter fork in order to fit on a bike with the same wheelbase, FC, and RC (basically describing a shorter travel bike).

By planning to discontinue conversation, you're the one that won't hear anything, contrary or not.

Wasn't weight bias part of the topic too? If you went from driving a loaded pick-up truck across a slippery/icy route, and dropped off over half the load, would you say you'd be fine driving back with the remaining load distributed willy nilly? Cab full, and a little left in the bed? That may be how you usually load in fairer conditions, and it's fine for that, but when stability and control is at its limits, would you not want to shift some of that weight to make it so weight more evenly distributed over all wheels (shifted to the rear to compensate for the front being weighted by the engine and cab)? Perhaps a little extra for the rear if you wanted a bit more traction for propulsion (and didn't mind a bit of understeer)?

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3/13/2019 2:46 PM

What I posted is not a Dengfu frame; not sure where you got that idea.

In any case, I'm now considering building up a 97.5 bike (aka "reverse mullet") on a frame with 425mm chainstays and 450mm reach on a medium frame.

Many are saying it's a dumb idea but I personally think I'm better at math than them so we'll see. wink

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3/13/2019 11:14 PM

Guessing they're saying it's a bad idea if you're going 27.5 to mixed. Not much to F up if you go 29 to mixed.

I'm picturing the Kona Process 153 29 in med as a good candidate, that fits your specs.

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3/14/2019 12:52 AM

ninjichor wrote:

Guessing they're saying it's a bad idea if you're going 27.5 to mixed. Not much to F up if you go 29 to mixed.

I'm picturing the Kona Process 153 29 in med as a good candidate, that fits your specs.

Yes, it does. With its really short chainstays and high-ish bb, it's almost begging to be built up as a 97.5er.

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3/16/2019 3:02 PM
Edited Date/Time: 3/16/2019 3:22 PM

Verbl Kint wrote:

Yes, it does. With its really short chainstays and high-ish bb, it's almost begging to be built up as a 97.5er.

Not only that, but I'd go as far as arguing that short CS and short wheelbases are more suited to smaller wheels, since there's a synergy for where/how they likely to be ridden (tight techy trails).

I still keep a 2013 Stumpjumper FSR EVO in my quiver, with a 27.5 on its front, but wish it had a longer reach and steeper STA, which newer bikes like that Process have. It rides with great balance out of the saddle, is super fun due to its acceleration and quick responsiveness, but is a bit nerve-wracking when speeds hit mach silly, unless I run big tires and big suspension.

Having a seated position that's less different/rearward than the standing one fixes issues like spring rate setup. Do you calculate rear sag when you're standing, or when your seated? When you're seated, there's so much weight on the rear that it sags a bunch. I did the scale test on my bike, and found that it had a ~68% rear bias when seated, compared to ~56% rear bias when standing straight. Makes you wonder when someone else says they like 33% (seated) or 25% (standing). Is there any downside to reducing the weight bias difference between sitting and standing?

Maybe part of the problem is that 26er geo is being put on big wheeled bikes, since consumers demand it. The demand comes from familiarity, rather than considering if big wheels work better with longer wheelbases, to please the kind of high speed riding people are interested in nowadays (on "trail" bikes).







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3/19/2019 12:32 PM
Edited Date/Time: 3/19/2019 12:35 PM

ninjichor wrote:

I'm confused by how my post could be read so different from its literal wording. Pay attention to the caption under A, and relate it to the last line in the post. It's all about rider positioning, and why it must adapt that way to the geo.

This thread has answered the question regarding why the Dengfu geo will put you into the position of A in a corner, repeatedly. Simply put, it's because the wheels are essentially being moved rearward relative to the BB, compared to a modern bike. The "balance/stable" point of the bike also goes rearward. If you don't also shift body weight rearward, you're going to have a lot of weight on the front, making the front wheel risk stalling out if it hits an obstacle it can't roll over, possibly leading to an OTB.

How about this picture:

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The confusion is occurring because you're making wild exaggerations to underscore your point. You might also observe that you're the common variable in every bit of contention on this thread so far; perhaps the resolution has less to do with correcting others.

The numbers on that open mould frame (Dengfu or whatever it is) would not result in hanging your ass off the rear wheel to keep it from flipping over, that is hyperbole on your part. We can use your equation (WB/2-CS) or Steve's (FC:RC) but either way the numbers suggest it would ride very similarly to the Nukeproof Mega 290 in terms of rider weighting balance, front to rear.

AKAIK, the 290 has the longest RC on the market and the lowest FC:RC, and while it hasn't received much attention, nobody has reviewed it and suggested anything out of the ordinary beyond it feeling a bit harsh for its travel rating. The only noteworthy aspect seems to be how "balanced" it feels. Imagine that.

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3/26/2019 1:12 PM
Edited Date/Time: 3/26/2019 1:18 PM

ninjichor wrote:

@Big Bird, can I see picture of your bike with super short CS and a the longest front you got? And can you give me an idea of how you like to ride it?

@Jeff/JFL: I'll tell you ahead of time that 50:50 is cruiser bike territory. Current examples of it include entry level 29er HTs in smaller sizes, on the compact end of the spectrum, and emtbs on the scaled up end of the spectrum. Enduro bikes are closer to 60:40 (more weight on the rear).

JLF1200 wrote:

I'm looking for bikes that sit close to the 1.7 FC:RC mark (or, a chainstay that is ~ 60% of the front-center). I haven't done the dual scale test to see what the weighting results are from that arrangement. I just know that bikes with that relationship have always felt faster in corners, predictable in chaos, and maneuverable with less body english than all the new, long front-end/short-cs bikes I have now.

ninjichor wrote:

That math scales absolutely horrendously. No wonder you are so prejudiced about long wheelbase bikes. I suggest another method.

May I suggest one that uses a fixed # to determine how forward the center point between the axles is in front of the BB? It scales decently, but doesn't account for suspension compression affecting the CS/WB:

(WB/2) - horizontal CS length

For this to work, you need to determine your target #. The larger the #, the more forward/aggro you are on the bike. The smaller the #, the more rearward/defensive you are on the bike. Modern bikes are increasing this number, by lengthening the front (forward geo), and also moving the seated position forward with longer reach and steeper STA.

I suggest you find a bike that you feel is dialed, out-of-the-saddle, and find its #. I found that 140-150mm FS bikes around 175-185mm were pretty nice, for someone of my height. I found that a 130mm HT around 155-165mm felt pretty nice. I imagine a Pole/Geometron-like bike, with even slacker front, more travel, and steeper STA, would maybe feel dialed with an even higher # (180-195?).

The issue with this formula is that it basically highlights the whole fixed CS length across sizes fiasco.

And regarding the equations to find balance (FC: RC vs WB/2-RC)... there are not large differences in these approaches. Why you think a literal ratio scales "horrendously" is still beyond me, because that's what it does by definition. Your equation, OTOH, either gives results that vary by each size, or calls for extreme chainstay lengthening across sizes to maintain a consistent result. My understanding is you admit it needs to change across sizes, which makes it a pretty useless tool in assessing geometry WRT to scaled sizing.

These are all size medium unless otherwise noted. You'll see that the ranking for WB/2-RC very closely tracks FC:RC with few exceptions. If we were to run the numbers across sizes, you'd see that a consistent FC:RC number calls for longer stays on bigger bikes, which is the whole point of this thread. Your equation produces a length taht seems like it needs to vary across sizes. That might be useful once you figure out your ideal number, but it's not something we can generalize.
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3/26/2019 1:55 PM

In terms of scaling, I was considering how well it applies to NORBA XC geo ~42 inch wheelbase (1050mm in med) and smaller (DJ, trials, road), and Geometron geo 1325mm wheelbase and bigger. I was afraid that people would "round" the ratio to fewer digits. Both methods are an oversimplification. I don't have any attachment to the WB/2-RC, even if I brought it up. It just related to how I analyzed side shots from pics, looking at only the FC and RC--in the pics I look at many more factors.

If you ran the same calcs on those bikes in their largest sizes, you'd recognize why there's demand for longer CS. If you ran the same calcs for those bikes in their smallest sizes, you'd recognize why there's critics against long CS. The smaller the calc'd #, the more rearward a rider's CoG should be in relation to the BB, and vice versa.

A designer can tune the geo to guide that rider's CoG to the ideal point. If the rider CoG needs to be moved forward, they'd push the grips forward, such as through extra reach and steeper STA. A rider who doesn't know better, relies on the designer's tuning to determine their "fit".

This is why I specifically recommend certain bikes in certain sizes. I'd say that Fezzari La Sal Peak works better in size large, because it has a steep STA and long reach, and you have to consider sag shortening the FC and lengthening the RC based on the axle paths (slack HA and low pivot geo change, vs steep HA and high pivot). Say for instance you were deciding between a SB150 and SB130, and usually always ride L. I'd more likely suggest the SB130 on geo alone.

When you consider how designers plot a rider CoG location in their suspension software, you will notice that a lot of values like AS and AR are calculated based off of it. I take that into consideration when I think of the ideal "central" and "balanced" position, when I judge geo good or bad:

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3/26/2019 2:51 PM

BTW, in another post, I posted a table that suggested that with the usual sizing method of increasing FC by ~20mm per size through reach, I'd generalize the CS should grow by 4.5mm to balance that out to have similar weight bias. That's not extreme, compared to people who were saying that the Pole and Geometron long wheelbase bikes should have a CS of 480? From a starting point of 430mm CS matching with 1200mm WB relating to a CoG point slightly in front of the BB, that'd suggest that 400CS goes with 1050WB and 455CS goes with 1325WB.

Considering that taller riders have greater range of motion, able to move further back than a shorter rider, the 2 oversimplified methods for calculation proportions won't have a fixed # that is ideal. It just depends on other factors... gotta consider relativity... factors such as fore/aft weight shifts affecting the shorter WB bike more than they would on the long WB bike.

If I could have my way, I'd prefer to do an actual weight bias test for every bike. I'd putting a rider on a bike, with each wheel on a scale, and measuring weight bias. If the scales read 90 lbs up front and 90 lbs in the rear when standing straight up, and then 75 lbs F and 105 R when sitting (42F:58R), I would take that data and try to relate that to their riding style. I'd consider what they complain about and what they want, and perhaps try to optimize/improve capability, confidence, comfort, attitude, and just general impression of fit. If they're a defensive type, I'd optimize by making the geo put more weight on the front, so they can stay comfortable and confident in their rearward position. I wouldn't put them on a Doctahawk, unless they were like the guy who designed that bike.

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6/12/2019 1:17 AM

Being on the tall end of the spectrum myself I decided to whip together my understanding of a balanced, scaled geometry for my size and actually ride it. So far its the smoothest turning bike i rode and i gets me into trouble quick, considering its a hardtail. Of course it being a hardtail required even more compromised decisions but it turned out great.
Its supposed to be a trailbike but i am riding with guys on 160mm fs bikes so it usually gets choppy.



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9/14/2019 11:45 AM
Edited Date/Time: 9/14/2019 12:13 PM

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Privateer 161 - CS length proportional to WB length

Reputedly dialed to handle well with the rider staying centered. I totally believe them, seeing their numbers.

I also like the fact that Santa Cruz has been including CS length adjustment chips on their releases, which makes each bike size possibly work out to be dialed for far more people.

I still stand by my estimate table, to find bikes that appeal to me: 430mm CS 1210mm WB, 435 1230, 440 1250, 445 1270, 450 1290 (further simplified compared to before)... rather than going by ratios found with RC/FC or whatever. I used to like the idea of WB/2 - RC = ~175, but this only applies to bikes with WB of close to 1200. The sweet spot value rises as the WB grows over 1250mm, and vice versa. Same with the FC/RC ratio, where a ratio of 1.80 might only appeal to me if the bike's WB is about 1200mm, and I'd want a higher ratio if the WB is longer.

Not surprised to see brands evolving to tell that riders to choose between 2-3 sizes, based on preference, rather than recommending a certain size to a certain height range. Example: 2020 Spec Enduro 29

Another industry trend that should be picked up would be to follow in Cannondale's concept of size-specific susp kinematics, and make bigger sizes have more anti-squat, to account for the higher CoM of a taller rider and bike.

P.S. Sam Hill went to 29 and dramatically longer. The whole belief that Sam Hill is riding what's dialed, rather than what he simply got well adapted to, is up for question now that his proto is getting closer to what Pole has been doing.
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9/16/2019 7:44 AM

Banshee's new Titan slots in with 17.8" chainstays:

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10/16/2019 12:48 PM

I just got the Banshee Rune V3 and the 17.2" chainstay isn't necessarily super long, but compared to my 18' Transition Scout (16.75 CS) the difference feels significant, mostly in a good way. I think the Banshee's steeper seat tube angle is also a big contributor to the more centered between the wheels feeling the Rune has, and doesn't require the more pronounced forward weight shift I was used to making with my Scout when looking to plant the front tire. I only have a few rides in at this point, but the Rune certainly feels more stable through loose and flat corners. Conversely, the longer rear end will take some getting used to in terms of small jumps where I notice it takes more effort to pick up the rear end for lining up on transitions.


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10/16/2019 7:05 PM

17.2" is 437mm

Rune V3 WB with 27.5 wheels: S 1188, M 1214, L 1243, XL 1273

A Transition Scout is 425mm with WB: M:1189, L 1218, XL 1247

A Fezzari La Sal Peak has 435 and 1235 in L. This is the model that stoodout for Fezzari, getting acclaim that it competed with the likes of the SB150.

A SB150 in M has 433 and 1223, L 1248. Pinkbike liked the SB130 more than SB150. Well, Levy likes short travel bikes, but Kazimer seems to be a geo connoisseur sorta. They both ride size L. SB130 in L is 433 and 1230.

I simplified what I consider my sweet spot CS-WB proportions to be 425/1190, 430/1210, 435/1230... if the WB is any longer such as if you upsized, you would need to put extra weight up front (ride aggressively, or just love backwheel). If WB is any shorter, you'd need to shirt weight rearward for balance (ride defensively, or prevent OTcool.

Guessing your Scout and Rune are both size L? I would say the Rune is what I'd prefer in size L too, and would have predicted that kind of balance on the L Scout.

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10/17/2019 7:03 AM
Edited Date/Time: 10/17/2019 7:04 AM

Wow. Lots of nerdery here!

While I appreciate where ninjichor is going, I do think a lot of this needs to be taken with a grain of salt, as there are a few variables missing from the equation, most notably being the rider's proportions and style.

Ultimately, the best way to know if a bike fits with respect to weight distribution is going to be on the scales. We don't have enough data in this department to parse out some magic ratio for everyone otherwise.

What we really need is more adjustment, which we're starting to see. Something to get us "close" for each size. I know we'd all cringe to go to horizontal dropouts but man, it'd be the best way to give us the adjustment we *really* need. No special machining of dropouts (Greg's V10). No fabricating new seat/chainstays. Just slide the wheel back and forth to find what works for you, anecdotally or on the scale.

My real dream is a fit system built around weight distribution. It'd be killer.

Oh, and just a fun side point, I've been spending a lot of time on a bike with 435mm CSs and a 487mm reach and it handles AWESOME with great weight distribution o nthe scales.

...but how!?

HTA is 67.5 and it has a 44mm offset fork. Its an XC race bike, and super fun.

No one number will tell the whole story...

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10/17/2019 4:42 PM

What's awesome mean? To me, that would be meeting all my expectations, which are many:
- doesn't slip excessively when climbing out of the saddle
- doesn't require a lot speed or perfectly timed/executed manuals to ride drops
- doesn't get excessively sketchy up front when on the brakes
- flies naturally off of jumps, leveling out and landing with both wheels simultaneously
- generally just handles well-of-the-saddle

I imagine people don't expect these things from a XC bike, perhaps thinking that I'd want a longer travel bike for that. They'd be more focused on seated comfort and efficiency on the climbs, seeing if they can get up the hill with less effort.

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10/18/2019 6:43 AM
Edited Date/Time: 10/18/2019 6:45 AM

ninjichor wrote:

What's awesome mean? To me, that would be meeting all my expectations, which are many:
- doesn't slip excessively when climbing out of the saddle
- doesn't require a lot speed or perfectly timed/executed manuals to ride drops
- doesn't get excessively sketchy up front when on the brakes
- flies naturally off of jumps, leveling out and landing with both wheels simultaneously
- generally just handles well-of-the-saddle

I imagine people don't expect these things from a XC bike, perhaps thinking that I'd want a longer travel bike for that. They'd be more focused on seated comfort and efficiency on the climbs, seeing if they can get up the hill with less effort.

That is a lot!

My goal was more simple when I brought this up, neutrally weight the bike between two wheels when descending. EG: Allow the rider to ride (descend) more from his/her legs than forcing the rider to move their mass forward and ride through their arms to properly weight the front tire. The idea is to reduce upper body fatigue, and allow the rider to be quieter on the bike. Less body movement = less fatigue, more consistency, less crashes, more fun.

I want to reiterate something from way back when, many bikes in smaller reach sizes already do this. Longer reach there are very few that will have the same weight distribution as say a medium Nukeproof Mega (I bring this one up for a reason wink )

I keep verifying my own experience on scales so I have something quantitative, not just feel or by doing some math in a vacuum. I want my own proportions to be taken into account, scales are the only way I can do this.

As far as tire slip while climbing, manual-ability, sketchiness when on brakes, flying flat etc - all of those have other variables involved as well, such as your suspension settings, your ability to manual, your ability to modulate your braking, your tires, your core strength, your bar height, head tube angle, seat tube angle etc etc etc.

If we are trying to make something better we first must define a very specific problem.



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10/18/2019 7:08 AM
Edited Date/Time: 10/18/2019 7:19 AM

Is there an echo chamber here? I've been preaching that all along. Got even more time on my proto and only more convinced. Forbidden and Privateer already putting things into commercial production. Plenty more room to go for other brands to consider weight balance... Norco is cute with their attempt, but I don't think they use scales, just #s in a vacuum. They're just lucky to have L dialed, with 435 and 1230ish WB on their latest Optic release (and 426 and 1190ish with their Revolver in L). I have enough measurements to be quite confident in my predictions.

Regarding reach, I find short reach forces me back in the saddle. I have 490mm reach on my proto (note I'm 5' 7") and I put on a 70mm stem since I find there's room to go longer. I admit that the ETT is a bit shorter than I'm used to (570mm), but I do like the position I have now, because my back is no longer relatively flat/level, and my arms and back make more of an A frame shape, rather than have arms angled straight down..

Need to get rid of some stigmas, like steep HA bikes are outdated, 80+ STA is too extreme, and/or I only like an ETT of precisely X and am not that flexible (+/- 10mm). Would be good to have people open up to 650+ stack too. Steep HA is one of the few ways to keep WB lengths under control and gain stack height.

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10/18/2019 7:46 AM

jeff.brines wrote:

That is a lot!

My goal was more simple when I brought this up, neutrally weight the bike between two wheels when descending. EG: Allow the rider to ride (descend) more from his/her legs than forcing the rider to move their mass forward and ride through their arms to properly weight the front tire. The idea is to reduce upper body fatigue, and allow the rider to be quieter on the bike. Less body movement = less fatigue, more consistency, less crashes, more fun.

I want to reiterate something from way back when, many bikes in smaller reach sizes already do this. Longer reach there are very few that will have the same weight distribution as say a medium Nukeproof Mega (I bring this one up for a reason wink )

I keep verifying my own experience on scales so I have something quantitative, not just feel or by doing some math in a vacuum. I want my own proportions to be taken into account, scales are the only way I can do this.

As far as tire slip while climbing, manual-ability, sketchiness when on brakes, flying flat etc - all of those have other variables involved as well, such as your suspension settings, your ability to manual, your ability to modulate your braking, your tires, your core strength, your bar height, head tube angle, seat tube angle etc etc etc.

If we are trying to make something better we first must define a very specific problem.



Jeff - can you say more about how you use the scales to measure? I’m intrigued to try this too. I think you explained early in the thread but this thing is long now!

What scales do you use (are cheap analog bathroom scales workable)? How do you make sure it’s relatively level ground and repeatable?

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10/18/2019 8:05 AM
Edited Date/Time: 10/18/2019 1:23 PM

Allen_Gleckner wrote:

Jeff - can you say more about how you use the scales to measure? I’m intrigued to try this too. I think you explained early in the thread but this thing is long now!

What scales do you use (are cheap analog bathroom scales workable)? How do you make sure it’s relatively level ground and repeatable?

Good question.

I use freight scales from amazon (digital). Obviously, you need two of them. I've verified their accuracy vs a more precision calibrated instrument by weighing myself. Its probably accurate to the tune of 0.5 pound for my 200 pounds.

The ground is level, verified using a level (garage floor).

From here all you do is put the bike on the scales with someone helping you balance by holding the front wheel steady. Yes, your helper can impact the test so you have to be a little careful, but its not that hard.

Go ahead and bounce up and down, get the suspension to settle. Then get into your normal riding position. There is a LOT of wiggle room here, so you need to be consistent. Really try and replicate where you want to ride from, and what feels most natural. The best way I do this is by starting seated, then rising straight off my saddle weighting my feet in an "attack" position with a light feel through my arms. (enough to steer, but I'm not trying to support my body weight).

Now read the scales, write them down and do some math.

For fun, I did this with my dirt bike, too. Moto companies have spent so much time trying to nail weight distribution in we'd be silly not to pay attention.

In a perfect world, we'd have onboard telemetry that can more accurately measure this when riding. We're probably 5+ years out of that one (for hacks like us!)...



EDIT: Those wondering, yes, I've tried to do this with one scale and a piece of wood that is roughly the same height as the scale. (scale under one wheel, wood under the other) This just adds a variable that starts to get in the way of doing any meaningful testing around this concept. Point I'm making is if you want to dial your bike in this way, order two scales...its well worth the extra $30 or so you end up spending.

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10/19/2019 2:13 PM

What position are you using when you're measuring? I personally like the "Universal Athletic Position", which is like a partial squat, that follows the heavy-feet and light-hands riding style, and what I base my sweet spot balance on.

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