That Jason Perez dork

[bladderhead]

I saw a bloke in London go over a hole so big that his light flew off and smashed.

 

[paco1961]

You're right that this road is rather smooth but what it has are lumps(the smooth dark spots you see) and in my experience at these speeds lumps are crazy dangerous on a bent. On a DF bike you float on your hands and toes going down so your body absorbs the jolts from lumpy roads. On a bent you whole body weight charges the frame with a bunch of stored energy when you hit the lump and as you go over the frame rebounds and releases that energy sending you into the air or at the very least your legs which influences the steering on a cruzbike heavily. At 5:50 you can see me take some rather odd lines over the next part because if I were to take the normal line I would get my legs tossed around over the black stuff and end up in the barb wire. Really only an issue for me when going faster then most rider are willing to go so it's a mute point for most people. If I'm not mistaken I took the KOM on in that video which ain't bad considering how highly contested that road is with local racers.

I think the stuff you worry about at 60mph is the stuff most of us mortals worry about at 30mph. Not sure why but for me descending at speed is much more terrifying on the CB. Never thought twice descending at 40-45mph on a DF but on the CB at 30 I'm feel like i'm going twice that speed. I've only been on the S40 for 4 months or so and gaining speed all the time but that applies to flat and climbing speed, not descending. Was out last night with the usual group and blew past the whole line at 26/28mph on 4 mile a 1-2% climb but they all blew past me on the 8% descent on the other end while I was on the brakes keeping it under 30 . . .

 

[bladderhead]

I am very confident in handling the bike at all speeds, but I cannot stop worrying about the road surface. Also, I cannot bring myself to trust the tyres in the high-speed, leaning-over turns. It amazes me how the motorbike racers lie it flat at 100mph.

 

[RojoRacing]

I am very confident in handling the bike at all speeds, but I cannot stop worrying about the road surface. Also, I cannot bring myself to trust the tyres in the high-speed, leaning-over turns. It amazes me how the motorbike racers lie it flat at 100mph.

you can't compare the two, a motorcycle has worlds more grip and are infinitely more stable in a corner than a bicycle.

 

[Patrick Bateman]

I think the stuff you worry about at 60mph is the stuff most of us mortals worry about at 30mph. Not sure why but for me descending at speed is much more terrifying on the CB. Never thought twice descending at 40-45mph on a DF but on the CB at 30 I'm feel like i'm going twice that speed. I've only been on the S40 for 4 months or so and gaining speed all the time but that applies to flat and climbing speed, not descending. Was out last night with the usual group and blew past the whole line at 26/28mph on 4 mile a 1-2% climb but they all blew past me on the 8% descent on the other end while I was on the brakes keeping it under 30 . . .

That phenomenon has narrowed the speed gap between my Catrike 700, my Silvio and my DF road bike. Basically the Catrike is the slowest up the hills, but I feel bulletproof going down hills, due to a combination of stability and really great brakes. On my Silvio I generally go down hills sitting upright, so that my body increases the wind resistance and I don't have to ride the brakes so hard. (My Silvio has conventional brakes, my Catrike has disc brakes.) A few years ago I blew a tire by riding the brakes too hard (rim was hot as a frying pan) so I'm always a bit wary of long downhill descents.

 

[Balor]

That phenomenon has narrowed the speed gap between my Catrike 700, my Silvio and my DF road bike. Basically the Catrike is the slowest up the hills, but I feel bulletproof going down hills, due to a combination of stability and really great brakes. On my Silvio I generally go down hills sitting upright, so that my body increases the wind resistance and I don't have to ride the brakes so hard. (My Silvio has conventional brakes, my Catrike has disc brakes.) A few years ago I blew a tire by riding the brakes too hard (rim was hot as a frying pan) so I'm always a bit wary of long downhill descents.

I hate to sound like a broken record, but this is a problem of not enough control over the front end - short wheelbase with CG very close to steering axis require needle-sharp control over the bars, and on MBB it is heavily compromised by steering inertia and 'two-fold' wheel flop.

Motorcycles, being much heaver, also have a lot of inertia and flop - but like Jason said, they indeed have a TON more grip and, hence, a ton more trail force - because trail self-centring force depends on tire grip.

Trail force, (that serve as steering damping), is crucial for control over the bars (because control over the bars is, basically, damping of steering overcorrections), a bike with no trail or, much worse, negative trail is much more 'squirrely' and feels unsafe at speed, because the higher the speed, the faster and more precise the steering must be, and the greater the requirements for NOT to overcorrect. It is very good that trail force increases with speed, otherwise most bikes would also feel less stable at speed, not vice versa.

French designs go for slack angle and lots of trail - they are quite stable at high speed, but really unstable at lower speeds due to flop. Flevobikes (45 deg steering angle) correct the flop with elastomer return-to-center spring somewhat, but their 'leg steering' prevents me from ever riding one, I suppose, I just don't do leg steering, not after 10k miles on MBBs even.

I'd recommend installing 20" rear wheel to test how slaker angle and much more trail affect your steering, but I suspect that combination would be barely rideable because you'll not be able to see the road due to seat not being adjustable..

Of course, 'control of the bars' is subjective and depends on your ability. Jason is very gifted - I'm extremely clumsy.

Yet, with zero flop and plenty (about 6cm) trail and 30cm steering axis-BB distance my latest MBB is rock sold at 43 mph - I just don't have hills steep enough to try to go faster... and the is despite front end weighting as much as Vendetta itself!
It felt absolutely stable from the first ride, while going over 35mph stayed terrifying on my previous MBBs for 10k kilometers.

Patterson's paper is crucial for understanding this phenomenon (though he omits MBBs in particular):

http://www.bicycle.tudelft.nl/ProceedingsBMD2010/papers/patterson2010application.pdf

"Df bike geometry" simply does NOT work for MBBs (as in - not optimal. Making a truly unrideable bike is a serious engineering challenge - some people are just that good).
It does not even work all that well for NON-MBB bents due to, usually, different weight distribution, hence Patterson's bikes have more trail and steeper steering angles and are noted for great stability. Science, it works... you know
It would also make DF bikes more stable, but negative offset will make the bike dangerous due to great foot overlap. Plus, you don't need a 'perfect' geometry - you need something 'good enough'. Just like Burrows said, 'best steering angle is vertical' - any alterations from it are due to ergonomics and other design constraints (even aesthetics play a role.. unfortunately).