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 Fully suspended MBB with 90 deg steering angle

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T O P I C    R E V I E W
Balor Posted - 06/11/2018 : 16:18:50



130cm wheelbase, 90 deg steering angle, 5cm trail (about 6cm with sag), 30 deg seat, just enough seat to BB distance for a 174cm man to fit into with standard cranks, can fit tires up to 26" 2.0 - offroad capable.

Since I'm no builder, it is being fabbed by an other recumbent enthusiast from Russia from my blueprints (he made only FWD-TC recumbents before). The project is pretty much complete, and I think is a great success:

Builder hopped on and rode off right away, went for an 50 km offroad test ride next day with no fuss and was consistently faster than on MTB... he swapped bikes with his buddy and same was true for him as well. Suspension works great and does not seem to bob much (6cm of pure vertical travel, 35mm rearward axle path)

It would be not faster than true 'racing' bents (plus it is heavy) obviously, but the goal was to have a replacement for MTB for long offroad rides and brevets where there is really bad asphalt.

Once I'll actually receive it, I'll post updated impressions.
24   L A T E S T    R E P L I E S    (Newest First)
Balor Posted - 08/28/2018 : 12:28:05
Well, that's what I meant by 'lateral Center of Pressure'.
If you even the areas out, you'll get neutral CoP and 'zero aerodynamic trail'.

With negative offset you are getting 'positive aerodynamic trail' that might actually be better than a strictly centered CoP, because you'll get a combination of unequal tire friction and air resistance force as return-to-center force exactly when you need it most - at high speeds, instead of vice versa!

Plus, on MBB your CoP is already shifted to the front of the steering axis quite a bit.
Ideally, one would require a wind tunnel and dynamometric stand to measure force of those effects - it might much more minor than I think. Still, I highly suspect that at high enough speeds quadratic air resistance forces are going to 'overrule' linear trail-related fiction force and make a bike with conventional offset behave like a bike with negative trail... a VERY scary thought.
Runxner Posted - 08/27/2018 : 19:18:59
quote:
Originally posted by Balor
main fault of front disk is not increased lateral area per se, or even lateral CoP, but 'negative aerodynamic trail' when combined with conventional positive offset.

That was even explained on your own site in Brown articles:
http://www.recumbents.com/wisil/brown/airdragformula.htm


and before that
http://www.recumbents.com/forums/topic.asp?TOPIC_ID=2463

Team Low-Life
Lowracer Test Pilot/Evangelist
Balor Posted - 08/27/2018 : 03:51:24
I did test the front disk on my 'test loop' and imporoved my KOM by 4 sec.. I suspect what was gained in aerodynamics mostly lost in rolling resistance on a rough road.

After puncturing front tire on a railway crossing on my way back (100 psi in a 23mm tire with 90 kg normal load is way underinflated I presume), I've ditched the disk wheel for now (cannot fit a larger tire, and disk benefits don't really shine with a fat tire).

Finally went for a longer ride (nice and flat), 190 km, nearly averaged 30 kmh:

https://www.strava.com/activities/1798895310

Again, not impressive, but a couple of miles faster than my previous bents and I've finally beat my DF niner average speed (though with half the climbing).

Some roads were truly brutal and I was very happy to have full suspension.
Balor Posted - 08/23/2018 : 06:36:40
Rode about with dual disks today:
https://www.strava.com/activities/1791724701

Wind a bit less (about 15 mph), I've felt 'steering effect' only once when I've been hit by a gust when exiting 'cover' of the building, and effect was pretty slight. For some reason, it felt like steering impulse was OUT of the wind, despite negative offset! It seems like COP is actually in front of the steering axis due to transmission + legs. Or some other thing is going on...
Again, you do have to lean into the wind, a bit harder this time.

We don't usually have winds stronger than those. I'll try riding in traffic next and see how passing trucks will affect me.
Balor Posted - 08/22/2018 : 08:51:11
(If CoP was really at fault, than MBB bikes would be unrideable in gusty winds because your legs are connected to steering and contribute to shifting CoP WAY forward, I daresay more than any disk wheel).
Balor Posted - 08/22/2018 : 08:48:14
Maybe, but with one disk I've notice pretty much nothing of the sort.
I suspect that main fault of front disk is not increased lateral area per se, or even lateral CoP, but 'negative aerodynamic trail' when combined with conventional positive offset.

That was even explained on your own site in Brown articles:
http://www.recumbents.com/wisil/brown/airdragformula.htm

"With a shallow steering angle of 50 degrees, a disk wheel really gets blown around. However, some experimental remote steering bicycles that people have been building, with a steering axis around 90 degrees and a reversed fork, would be excellent geometry for a front disk wheel."

I have exactly that and I intend to test it :).
warren Posted - 08/22/2018 : 07:58:41
Your bike is looking good, Balor.

You will notice a front wheel disk makes you get pushed around by side winds. Because of that I prefer a deep dish aero rim rather than a full disk in the front.
Balor Posted - 08/22/2018 : 07:33:05
By the way, does side wind really slow you down?
Theoretically, if you are airfoil-shaped, you will generate lift force when leaned into wind and hence your rolling resistance will be reduced... just make sure you don't generate too much to take off :)
Balor Posted - 08/22/2018 : 07:05:40
Rode about in a 20 mph wind, didn't notice anything 'unusual' with a rear disk. You need to lean into the wind a bit, but it is not that much of a bother.
Dual disks next, I'll see how it turns out.
Balor Posted - 08/20/2018 : 04:53:43


After fairing rear wheel and installing better tires, I've gained about 1 mph on my 'training loop'.

https://www.strava.com/activities/1780701670
Given poor condition of the road, I think I'm might average more on a better one.
Balor Posted - 07/26/2018 : 10:33:27
Admittedly, those passing trucks provide a permanent tailwind (this is a rather busy highway), it gets me 1 mph extra at the very least. Plus, it's flat:
https://www.strava.com/activities/1725029972

I'm working on finally getting rid of that extra weight (300 pounds overall is a LOT, and the bike makes only a small fraction of it), I'm simply crawling up any hill worth it's name.
MBB seem to work very well for me - no feeling of 'inefficacy' and low BB totally solves my numb feet problem, but my speeds drops to below 10 mph on moderate hills even with respectable (250 watts or so) power output...
warren Posted - 07/26/2018 : 08:06:06
Very cool that it's working well for you. 24MPH average speed is very fast!
Balor Posted - 07/25/2018 : 08:09:35
After adapting to new (very open) pedalling position and short cranks, I'm significantly faster than on my previous bents - I've managed ~24 mph (nearly 39 kmh) average speed on a highway for 50km (looped track), something I've managed only on a road bike with aero bars before.
I know it is not at all impressive for bent veterans, but I daresay it is cool for a bike you can turn into a quite capable MTB by a swap of a tires, and I didn't try narrow tires and disk wheels yet - should be practicable even up front due to negative offset, resulting in 'aerodynamic trail' effect, wide bars with a ton of leverage... and the fact that I'm very heavy.
In Soviet Russia, YOU buffet passing trucks, lol.
Balor Posted - 06/29/2018 : 16:45:11
Maiden voyage!
https://www.strava.com/activities/1670046779



I daresay it is fast enough for a FS bent with body position (low BB) and crank length I'm not familiar with yet.
"Cruzbike cockpit' with 'seagull bars' is great and short cranks allow for comfortable arms position without my knees hitting anything in the process.
I should note that road on that track is very bad, with lots of potholes and rough, weathered asphalt. Funny enough, front suspension seems much 'smoother' than the rear - likely due to heavy front weight bias (hence much larger suspended mass) and rearward axle path.
Among 3 MBB bents I've tested (Zorkra Clone, MBB with negative angle and this one) - this is the most easily steered bike, despite front triangle weighting a ton. One-handed operation is trivial, riding no-hands is ALMOST doable even for an oaf like me! I bet I'll get the hang of it eventually.
Basically, ride has a 'relaxing' quality that my previous MBB bents sorely lacked. You don't feel like being from one small hand twitch from lying in a ditch :) Yet, you can 'swing the boom' for power and pull the bars and stomp the pedals and get rewarded with feel of power NOT being lost anywhere.
I should note that suspension does NOT bob at all at least when cruising on flat ground - something that came as a surprise for me, actually.
Balor Posted - 06/28/2018 : 08:40:49
Well, it seems it weights about 49 pounds when assembled, so color me surprised :)

Ok, I've got it, assembled with one gear (33x11) and one brake and went for a short night ride (otherwise I'll not get any sleep :)).

So, how it handles? Lugging it around is still a pain due to heavy and somewhat floppy front triangle (real steering angle turned out about 88 deg or so), but once you sit down and push the pedals the beast transforms.

Steering is absolutely rock-stable at any speed past snail pace, mentioned wheel-calf conflict is not noticeable with 40mm tires. It does not feel like your typical MBB at all - even pedal steering effect is barely noticeable at speed! (color me surprised again - likely due to longish tiller)

I'll need to try this on one guy that tried my previous bents before and did not like them, whether he'll 'ride off' this time :)


Suspension works wonderfully and allows one to simply fly over huge potholes that my neighbourhood supplies in abundance :).

Low BB feels and pedals great.

Fit... is tricky though, like I suspected the builder made the frame a bit larger than I asked for, and given very limited tolerances it feels I'm overextending a few mm even on 150mm cranks. I actually have cranks as short as 140mm, but those are road double and it will result in rather 'virtually tall' gearing with cranks that short.

I'm contemplating cutting a notch in my seat to move it forward those missing few mm.

Pictures after I'll finish assembly.

As for the 'showel' hint - our parents actually have a titanium showel (it was a gift), ehehe.
Unfortunately, that's way out of my budget.

Aluminium - maybe, but I think I'll leave the suspension parts steel, make the frame from basalt fiber and boom from aluminium - Cruzbike.
carolina Posted - 06/25/2018 : 21:11:10
That g. Hill guy is really sompin:) Still modding lowracer, cut frt off again.

velosRus.com
Garrie L Hill Posted - 06/25/2018 : 20:49:08
Hmmmmmmmmm......



Garrie "carbon based lifeform" Hill
HPRA Co-Dictator of the East
for pics of some of my time and money sucking projects
http://s58.photobucket.com/albums/g277/cfbb/
and videos
http://vimeo.com/5513519


SpiderMonkey Posted - 06/25/2018 : 11:40:02
Having taken delivery on a fully-suspended, 47-pound 'bent recently, I'm always surprised at how much the weight matters when you're carrying it around. I notice it so much less when I'm riding it (even uphill. Sure it's slow, but it's geared LOW.)

That is one nifty-looking machine.

--SpiderMonkey
Balor Posted - 06/22/2018 : 11:17:38
quote:
Originally posted by PUGZCAT

Balor you are a design genius. I like the clean effective design, from Frankenstein-ing full suspension "Walmart" mountain bikes. Good handling, smooth riding and fast, checked all boxes got the job done.



I'll be very surprised if it turn out to weight less than 50 pounds, so 'lightweight' box remain soundly unchecked.

I actually kind of enjoy designing around constraints like that, but I bet I will not be too happy to actually lug it around :) Plus you may call me a genius once I'll manage to cram in remote steering and all wheel steer (and make it rideable to boot without weighting even MORE). Otherwise the concept is pretty simple :)

Also, I'm yet to ride it, it is still 'in the mail' and should arrive sometime next week.

As for new developments, we've added a head tube gusset (just in case) and I've ordered a 'cruzbike type boom' that is compatible with superman bars clamp:



Should be stiff enough yet MUCH more adjustable than cruzbike arrangement.
If I like it, I may design an other bent around that concept, but not with adjusability, but light weight in mind. My bad back actually complains about lugging 50+ pounds up stairs, I don't have a ground level garage.
PUGZCAT Posted - 06/22/2018 : 10:45:04
Balor you are a design genius. I like the clean effective design, from Frankenstein-ing full suspension "Walmart" mountain bikes. Good handling, smooth riding and fast, checked all boxes got the job done.
Balor Posted - 06/13/2018 : 14:26:22
quote:
Originally posted by warren

Looks very cool! I love the bent tube!



Well, it's a bent. It should feature a bent tube! :)

Admittedly, when using wide tires and manuevering offroad, there is 'calf interference' issue according to the builder, which I'm familliar with but kinda forgot about (because it is not a problem at all during normal riding with 40mm tires on a bike with similar negative offset).

I'll see how actually bad it is, if bad enough I have a 'backup plan' of 24" front wheel and 165mm instead of 150mm shock - it should preserve geometry, but decrease offset and tire of smaller diameter should not interfere as much.

I really want an 'offroad bent', actually I've been wanting one since 2014 when I got my first one, but Azum max clone didn't work for me at all (numb feet onset - half an hour), and offroad LWB is way to unwieldy.
warren Posted - 06/12/2018 : 10:36:58
Looks very cool! I love the bent tube!
Balor Posted - 06/12/2018 : 03:14:47
A mount for QR rack, I've had a similar arrangement on one of my first bents and liked it:

Garrie L Hill Posted - 06/11/2018 : 18:34:33
Very nice! What is the short post behind the shoulder area of the seat?

Garrie "carbon based lifeform" Hill
HPRA Co-Dictator of the East
for pics of some of my time and money sucking projects
http://s58.photobucket.com/albums/g277/cfbb/
and videos
http://vimeo.com/5513519



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