Thanks! It seems I hit a nerve here :) I will play around with my seat position and handle bar height. I have noticed that I spend a lot of time looking at the ground when I go downhill...that could magnify the effects of the speed considerably.

Come on. I can sprint up to 30 on the flat on a vintage roadie. I'm pretty sure I could do it on my IXFS if I had the gearing. Heck, even with the gearing I've got, I could probably spin it with a supreme effort. Give me better tyres and about 85 gear inches, and I'm certain I could.

The top speed for a folder is 88 mph. After that point, fire erupts from your tires and you start hearing Huey Lewis tunes.

http://www.brinkleys.org/users/tsl/Files/btf.jpg

Speed really has nothing to do with the size of your wheel. It's largely a matter of fitness and enough gear inches. With that said, I know I can sprint faster than 30 mph on a flat for a short distance. I couldn't maintain it for a long period of time, but that's why they call it a sprint.:) I will tell you one thing-my twenty easily weighs 29lbs so if iknow I'm going out on a fast group ride, I would sooner grab my 18lb road bike.

People are muddling two issues here.

How fast you can ride on the flats in low windspeed conditions? That depends on your fitness, technique, aerodynamic positioning and bike design.

How fast you can safely ride on a steep downhill before the bike becomes too hard to control? That depends in large part on the stability of the bike at high speeds. This is what the OP wanted feedback on.

:eek::eek:Rocket pacing! That's insane! :eek::eek:

Sure would like to try it some time :o...

I think this relates to if you can ride the bike without hands. Am I wrong assuming that the bike is safer in high speeds if you can ride it without hands in low speed on a level road? I’m thinking of this scenario: you ride 50 km downhill – you must take your other hand from the handle bar – the front tyre hits a small pebble.

I don't think I'd let go of the bars cruising downhill at speed. But there's probably some truth to what you say. Bikes with less twitchy steering, ie, that have a large positive trail and thus are easy to ride 'no hands', are possibly safer at hgh speed than bikes with quick steering. However, high speed bike wobble is poorly understood and difficult to predict.

The maximum safe speed for a folder on British motorways would be 70mph and 30mph in residential areas. Same as cars really. Sammyboy is a threat when at full pelt in residential areas of Southampton or London. He would need a Dahon Speed Pro to be allowed on the motorways.

People have been seen breaking these speed limits after seeing Sammyboy riding naked behind them on his Downtube FS-FS (Full Suspension-Fully Starkers!) Unfortunately it did not trigger the speed cameras much to the anger of the local police in Hampshire.

I do know that an orange Downtube FS exceeded 70mph yesterday quite safely. It was in the back of Snafu21's not so green 4x4 returning after a Hyde Park Folding Society meeting :D

i went almost 60km/h when going down a steep and long slope on my mod dahon vitesse..still stable but not advisable..i don't think any of the brakes on a stock foldy is able to stop the bike in time..especially with 20' wheels..

Gentlemen, we need to settle this ONCE and for all.....I propose we all meet at the top of some insanely steep mountain road, somewhere in Bolivia or Columbia and see who can reach the fastest speed while negotiating impossibly crazy hairpin bends...that don't have guard rails. The winner is the rider who doesn't plunge to their death. :bike2:

You mean like Bolivia's highway of death?

http://bp2.blogger.com/_BqWviijUrNw/...ighway-8-1.jpg

http://bp2.blogger.com/_BqWviijUrNw/...ighway-6-1.jpg

only time ive had a wobble was on a scooter on a sandy beach, it wobbled becuase of big ripples in the sand and i ended up flying off face planted myself in the sand and whacked my shin on the scooter. and i did this when i was 10 LOL, ive never experienced a wobble on a bike but i think i would be able to controll it. If you just keep your bike in a straight line then you should have no wobbles, and before coming to a turning or w/e then slowly put pressure on the breaks instead of whacking them on when you meet the corner or you might end up faceplanting yourself (yes i have done this aswell :)) so i have learned from my experiences :D

No problem doing that downhill on my Brompton lol!

sammy, also i think you could not do 30mph on a flat straight on a folder, once i get a new folder ill buy a speedo go down the big hill i was talking about and see how fast i go, ill also peddle in top gear downhill all the way.

I hit about 45 on a very steep (although not that long) hill on my Friday. That's about as fast as I have any need or inclination to go. As far as the wobble goes, the WORST thing you can do is hold the bars tight. That just makes it worse. The trick is to carry most of your weight on the pedals and hold the bars loosely. I've had a wobble at about 30mph in a crit where there was a big crash right next to me. I clamped down on the bars and got a big wobble. I just had to force myself to let go, and the wobble went away. Nothing like a speed wobble during a sprint finish to get your heart rate up!

+1, great advice. Use your abs to hold your body up so you don't put too much weight on the bars.

With any wheeled vehicle, I use the following formula to figure out what is a safe speed...

Density Of Surroundings (include people, traffic etc.) + Road Conditions (how well kept up) + Bike Conditions (brake condition, regular tune-up, whether or not I own the bike) = Right Speed To Ride.

Since I figured out this formula, I have had no major or overly scary problems-even suprises-cropping up.

Speed Kills!

;)

I don't like going fast on my Strida at all... talk about wobbly... it's almost impossible at speed. I think this is why the excellent disc brakes were put on it!

5 mph on Stelvio tyres at 100 psi, on gravel. At 6mph, it threw me off.

I agree, Nice formula! :D

Regards

That's exactly what I'm talkin' about, but notice how the other weenies have avoided commenting?

Sounds like fun!! Is there a prize (besides still being alive :P )?

Those pics have been distorted to exaggerate them. See this is the corrected one:

LOL, still doesn't look good!

Ya had ta spoil the effect, didn't ya Jur ;)

However, I have to say that after reading the huff 'n puff about how quick some fodder....(oops, I mean folder), riders claim that they can ride, I'd like them to meet my challenge....so it's Bolivia, yes?

As for the prize?........Well, Owlmaster08, if you were one of the lucky ones to survive, a choice of one of Jur's folders is your's....take the Swift!!

Funny thing is, I can't get the image outa my head of scores of folder riders disappearing over the edge....screaming in vain.....

Be careful and never go faster than you feel comfortable or faster than the conditions allow. Many factors come into play. Visibility, road surface, run out, wind, fatigue. etc. Naturally a bike with larger wheels feels more predictable at high speeds going downhill.

The fastest safe speed is very personal. But, I think, generally an individual will feel more comfortable going downhill at higher speeds with larger wheels, but it's been a long time since I ridden a large wheeled bike.

Edit: Second thoughts ;)

Dahon Speed D7 downhill (44ish mph):
Brompton downhill (42mph):

Mach 0.8 in a 747-400 @ 30,000 feet.

Documented upper limit of the Dahon Speed D7: 44mph?

Lowering the handlebars is the key ingredient (see post #3 of this thread): More mountain climbing fun on a Dahon folding bike (pics & video) .

"I lowered the bars as far as they would go. The next day's descent...was much smoother, so I was able to go as fast as gravity would take me."

BTW Based on the daredevil antics of that poster, maybe that site should be renamed Team Testosterone. She has more balls than most guys do! For safety's sake, if you were brave/crazy enough to do the same kind of stunt, I'd follow her lead and ditch the fenders, too.