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4/21/2018
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Edited Date/Time
5/11/2021 2:42pm
I might go out on a limb here, but let us entertain a thought. Or, rather some aspects that might be hidden in plain sight and some aspects that might be contradictory to what we he been told.
This idea first intrigued me after reading Paul Astons monster bike check a while back. And it was mister Aston BB-height of 375mm(maybe someone will convert it to imperial language in the comments). He said this was a good thing because the cranks was now above his axels height and that made the bike easier to tip over. In his reasoning, this was easier because he didn’t have to push through the line of his axels. If I get this right this is because the bikes tipping point, from side to side, will be at the height of the axels. And if you, and then your weight, is connected to the bike through a point that sits below this point, you must push through some leverage to tip the bike.
He then goes on to explain why we traditionally have low BB, for stability and cornering on shorter bikes. Now, since he is on a Nicoalai, and many other companies have solved this by making longer bikes, this point of low BB for stability is not valid anymore.
I have been thinking on this matter for some while, and tried to get some more information on the subject – but with no luck. But just the other day, Pole released a new version of their Evolink, with higher BB, and they said something to the effect that they did not need it for stability and they felt it was better.
This also have made me think of the mullet set up. When you lower the rear axle height and the line you have to push through have been lower in relationship with the crank, thus easier to tip over. Or that the line you have to push through will be more parallel to you as a rider then the ground. If that makes sense. But I think the cornering of mullet bikes might feel better, or is better for that matter, because of the change in how the leverage interacts with the bike when tipping it over into corners.
I might be writing this up with some bias, since I am riding a Nicolai and because of some travel adjustment on it, I ended up with a slightly higher BB at 360mm. Also set up as a mullet. I will test this in the coming months and see if I like it more. But then, I might not feel it, or I might like that I got more travel and think I like it because of the higher bb and mullet set up. Or it might just become a mess. But I have some faith in some of the reasoning her, though it is not main stream in the bike industry.
There are now questions here, but I think there is a lot to argue or thing to point out. I am not emotionally married to my point(s) here, so feel free to attack or spin of what makes sense. I think there might be a discussion here that could shed some light on the matter.
This idea first intrigued me after reading Paul Astons monster bike check a while back. And it was mister Aston BB-height of 375mm(maybe someone will convert it to imperial language in the comments). He said this was a good thing because the cranks was now above his axels height and that made the bike easier to tip over. In his reasoning, this was easier because he didn’t have to push through the line of his axels. If I get this right this is because the bikes tipping point, from side to side, will be at the height of the axels. And if you, and then your weight, is connected to the bike through a point that sits below this point, you must push through some leverage to tip the bike.
He then goes on to explain why we traditionally have low BB, for stability and cornering on shorter bikes. Now, since he is on a Nicoalai, and many other companies have solved this by making longer bikes, this point of low BB for stability is not valid anymore.
I have been thinking on this matter for some while, and tried to get some more information on the subject – but with no luck. But just the other day, Pole released a new version of their Evolink, with higher BB, and they said something to the effect that they did not need it for stability and they felt it was better.
This also have made me think of the mullet set up. When you lower the rear axle height and the line you have to push through have been lower in relationship with the crank, thus easier to tip over. Or that the line you have to push through will be more parallel to you as a rider then the ground. If that makes sense. But I think the cornering of mullet bikes might feel better, or is better for that matter, because of the change in how the leverage interacts with the bike when tipping it over into corners.
I might be writing this up with some bias, since I am riding a Nicolai and because of some travel adjustment on it, I ended up with a slightly higher BB at 360mm. Also set up as a mullet. I will test this in the coming months and see if I like it more. But then, I might not feel it, or I might like that I got more travel and think I like it because of the higher bb and mullet set up. Or it might just become a mess. But I have some faith in some of the reasoning her, though it is not main stream in the bike industry.
There are now questions here, but I think there is a lot to argue or thing to point out. I am not emotionally married to my point(s) here, so feel free to attack or spin of what makes sense. I think there might be a discussion here that could shed some light on the matter.
I would love to get some pictures up and illustrate this, but my technical skills in that field is not that good. I will give it a go tonight. Cheers for the feedback!
Thoughts on this?
No. The "tipping point" is the ground. Even if the BB is below the axles, there is no "leverage" to push through. It's just lower, and this has less distance to move laterally for a given lean angle. A higher BB moves further laterally for a given lean angle, which could be good or bad depending on corners (bermed, flat, off-camber).
Though my point is crumbling, i want to upload some pictures that might hive some room for further speculation.
Line through Axels are parallel to the ground.
Line through axels are slightly upwards, and if the bike is going down a hill, this Line would be more in sync with the position of the rider. Maybe?
Mr. Astons bike. High bb, and Linethrough Axels is upwards.
I feel that my idea is something, but my wording of it might be of. Would love if someone would Try to reword what i am pointing out is factors that could be in play.
And also, what are your thoughts and Poles last configuratoin of the evolink, with their comments on higher bb?
But as just6979 said, the further out you go from the ground, the longer your weight has to move side to side
.
*tin foil hat statement* the mullet set up will get this job done without going against the long, low and slack mantra of the industry. B/c you can say something like, the bike turns better b/c of the smaller arch of the rear wheel or something(though this would in reality be a really small change of arch. I think. Correct me if i’m wrong). Since higher bb is a thing of the past. And stability issues is now taken care of by longer bikes.
The point I'm trying to make is that BB height is a ways down the list on whether or not a mullet setup feels good. For me, the order of priority in finding a good mullet bike setup were:
1) does the travel front/rear balance remain reasonable?
2) does the HTA remain reasonable (~64ish)?
3) does the STA remain reasonable (~76ish)?
4) does the bike have a good suspension platform (progressive / pedal efficient)?
5) does the BB height not get crazy low (>335mm) or crazy high (<350mm)?
Chris Porter was saying that the lower a bb gets the more drastic the effect on a 29er. the gyroscopic effect of the wheels and the leverage point below the line makes it harder to initiate turns.
Also the radius of how the front and back wheel turn differs also.
It seems with the a mullet you have the best rollover and grip benefits of the 29 and then the 27.5 keeps that bb height in check as much as possible, it also in effect raised the pivot point which should improve rearward axle path movement, but this dependant on the design and very minimal and perhaps lost with the rollover performance a 29 offers?
I run a mullet Zerode. It would be interesting to see what a 26" on the back would feel like.
It would also differ depending on crank orientation; if the cranks are perpendicular to the ground it shouldn't matter what BB height you have since your levering off of a 165-175mm crank and that would almost certainly put it below the axle.
I haven't ridden a mullet setup and could be entirely wrong here. In the drop bar world, many new road bikes come with BB drops >75mm and would be more stable than a cyclocross bike with a BB drop <68mm down a fast descent - or at least that's what the roadies want to believe. CX bikes often have slightly longer chainstays than road bikes for tire clearance which could also play a role.
I believe cornering depends more on F and R weight distro. People like to think that having more weight on the front is a good thing, but I disagree. There is a very narrow sweet spot that allows me to pull off natural two-wheeled drifts, which I associate with excellent cornering. Sizing up and down between size M and L when demo'ing the latest and greatest bikes, I used to always favor the size L. On the smaller size, I had to get my weight a little further back to corner as well. The bigger size had less weight on the front, but it felt more intuitive to corner, taking less conscious effort to calculate the position to readjust the weight distro.
More BB drop led to a more planted feel. Not really sure if I'd want a mtn bike with zero BB drop.
Watching a rider like Kovarik on an Intense Carbine vs a DH bike, I'd blame the weight distro more than anything else to account for the difference in steeze. See which wheel breaks traction first. The Carbine's rear tire often breaks first in his promo vid. I know most prefer that over the front breaking traction first, but getting both naturally breaking at the same time is my personal preference.
Raising the BB makes manualling/bunny hopping easier, as any BMX rider can attest. It also makes cornering harder, because the vertical of the BB (the vertical component of the weight you put through the pedals) falls easily outside the "zone" connecting the contact patches of both wheels (trigonometry 101). This is essentially the main condition for an unstable equilibrium, and ultimately leads to loss if traction and skidding.
Running a smaller wheel at the back reduces its inertia moment and makes both acceleration and turning more agile. It also lightens/speeds cornering because you are placing comparatively more weight at the back of the bike, effectively avoiding a reduction of trail at the front wheel, given the fork compresses less.
Also, if you look at the principles Transition used to design their Speed Defined Geometry concept, the slacker the head angle gets, the shorter the fork offset must be, in order to avoid the dreaded wheel flap/slow steering associated with slacker head angles. Unfortunately, most fork brands offer their long travel models in longer offsets these days. Again, the bikes are leaning towards riding almost in a straight line, cutting through everything you can find in front of you. The trails consequentially are being designed to help the 29er monster trucks keep their momentum over the corners. Maybe mullets will change that and help us have more diverse/fun trails again.
TL/DR: bike design is a short blanket: if you cover your head, you'll leave your toes out to freeze.
Want to try it out? Just change the sag drastically, though that will change a lot of the aspects of how a bike rides...
As for gyroscopics, supposedly a bike with canceled out gyroscopic effects will tide just the same as a normal bike, I seem to remember reading the some tests were done on this matter.
Aside from cornering, the front to back balance of a mullet is more advantageous for gravity riding. Your BB will be higher in relation to your rear axle allowing for easier manuals and bunny hops, while your BB will be lower to your front axle which would give more confidence in steep section with less chances of OTBs.
Now in the real world a friend of mine mulleted his SB150 and couldn't really tell the difference despite him being a rather fast rider. So while it might be worth experimenting the advantage might be marginal or not noticeable if you are not focusing on trying to feel it. Hopefully I will get to experiment once a bike company have some bikes in stock.
A front 29er wheel feels better because it rolls over stuff much more easily, but also because its contact patch is larger. This combined with the more subtle weight displacement a LLS bike demands is the core of why they are more enjoyable on fast, open, although gnarly trails.
I would bring in Joe from straling cycles on some of the points put up in the last few posts. Take a look on his blog post in the subject of factors of wheels and wheel sizes:
Joe from Starling cycles
I tried the mixed wheel setup on a flow trail with the rear shock semi locked. I felt too high up and not inside the bike enough to really rail the berms. Tried it again with the shock fully open and it felt great.
So i like the slightly higher bb, but need the shock open for it to not be too high for aggressive DH.
And im amazed at how much tighter of a radius i can now turn since going mixed wheel. Id expect this more with a 29er dropping to 27.5 rear but also got the same result from bumping a 27.5 up to 29 in front.
At the time I had no idea why it worked better, but now I'd put it down to the rear wheel likely taking a smaller arc round corners than the bigger front wheel.
From day 1 I put a 29er wheel and 2.5 assegai. Rode well but vague cornering from the rear plus size 2.8 tyre.
Then swapped to a dissector in 2.3, holy crap just that change alone made the bike a demon in the corners, however BB was getting too low and pedal strike regular at 30% sag.
Eventually, the new 38's came out and I was onboard, the Axle to crown been that tad bit longer, and I went to a 170 fork this time (up 10mm in travel)
This was the sweet spot, raised the BB up that tiny bit, slackened H/A and wheelbase was nearing 1240mm for a bit more confidence at speed...
I am ready to transfer these findings to my Meta 29'er with some special yoke parts. Looking forward to it.
Obvious examples: Rear axle position seems to matter for manuals and wheelies, and the front tire contact patch position seems to matter for braking and turning traction. Talk amongst yourselves.
I agree with Primoz that contact patch is more important than axle position for cornering. But, if we assume that axle height doesn't affect cornering at all, then wheel size wouldn't matter for cornering. For instance, if axle position doesn't matter, a bike with 20" wheels and a bike with 36" wheels would corner the same if the contact patches were in the same place relative to the bb. I don't think that's true in practice.
And yes, I know a 20" tire and a 36" tire have different contact patch sizes and thus one would generate more traction, but that's not really what we're talking about here, so I oversimplified. For instance, no one is saying "I can't ride a mullet, I need my rear tire's contact patch to be 4% larger!!"
Different size wheels may have a slightly different shape contact patches, longer and thinner on bigger diameter wheels, but the area is the same. On a side note, the same is true of fatter tyres, a 2.2″ tyre with 20 psi has same contact patch as a 4″ tyre with 20psi. It’s just that the bigger volume allows you to run lower pressure without damaging your rims.
Rollover. Bigger wheels roll over bumps better, right? Well, no, not really. Realistically, I would consider a bump of 2” (50mm) in the realm of rollover. Anything much bigger and you need to start lifting the bike up and it’s not really rollover. If you consider where a 2” bump hits a wheel on both 29″ and 27.5″ wheels, you can see the difference in angle of attack is negligible, 1.14°.» from Staling cycles blot post.
But he goes on to what he thinks has a bigger effect on handeling.
« Gyroscopic stability. OK, this is the important one. Although there’s no change in angular momentum, there is an impact on the gyroscopic stability of the bigger wheels. This is because it is proportional to the diameter squared. The gyroscopic stability is the tendency for you wheel to stay ‘in-plane’ when rotating. Like the child’s toy, that stays upright when spinning, it doesn’t want lean over. Take your front wheel out of the bike and spin it up to speed holding it at the axle. Feel the forces to try and move the wheel out of plane.
Now imagine riding along on your bike and trying to lean it over, bigger wheels will make it harder to lean. But also, it means the bigger wheel will not be knocked off line as much by bumps. Anyone who has moved from smaller wheels to big 29″ wheels will have felt this affect. The big wheeled bike is harder to lean over, you need to put more effort in. But once it’s leant over, it’s more stable. People who are capable, will be able to tell you a 29″” is harder to whip off a jump.»
(This is sort of a double post, since i posted this link above. But these points need to be in the discussion, either to be further explored or picked apart)
Link is in a couple of post above.
I guess testing that would be simple, tie about a kilo of lead to either the top tube or around the BB and compare how the bike turns.
@SB14 regarding pressures, I'd say no, it's not the same area on a 2,2" and a 4" tyre at the same pressure. This is mostly gut feeling, haven't tested it, but we know for a fact that the tyre carcass plays a role here. But even with the exact same carcass, the diameter of the 2,2" tyre will be much smaller than the 4" tyre, so the support from the same pressure will not be the same. The effective shape-caused stiffness of that same carcass will be different. Lower pressures ran on bigger tyres makes me think the contact patch on the 2,2" tyre will actually be bigger due to more deformation. Maybe.
As for rollover, another benefit might (must?) be also rolling resistance. I see little other reason for modern EVs going to 20+" wheels and tyres, when we were happily chugging along on 15 to 17s just 10 to 20 years ago, not beating an eye. Higher weights and wider tyres to carry the load better might also have something to do with it too though...
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