[Closed] Top speeds

I once did an inverted negative-g pushover with a Mig.

I just worry that something might fall off over a certain speed (30ish) - it never has but it's always in my mind - not useful.

Happy to do 40++ on a waterski, snow skis and the like - for some reason they feel safer (?!). A very nasty MTB crash a while back doesn't help.

I've "calibrated" my bike computers by measuring the exact distance to an object a mile away so they should be pretty accurate.

fastest i have gone is 48 on my road bike legs wouldnt go fast enough to go any faster,

think we need to start some other willy waving topic, maybe who has jumped the furthest. i once jumped so far i went all the way round the world!

Happy to do 40++ on a waterski, snow skis and the like

Never had any idea about how fast on skis, but have always been interested.

It generally feels much faster than mountain biking...

My top speed down Radford Bank is nearly as fast as the average speed in the Tour de France.

I don't think I've ever been down a hill that was steep as well as straight?

We used this:

http://www.streetmap.co.uk/map.srf?X=269240&Y=361350&A=Y&Z=120

Had to ride up first and open a few gates.. plus there's a main road and a stone wall at the bottom so you have to brake ON the hill.

This one is where we got 48mph laden:

http://www.streetmap.co.uk/map.srf?X=291000&Y=321995&A=Y&Z=120

Must be one of the highest density of chevrons anywhere on the OS maps?

I once rode so fast I caught up with time itself and appeared to be standing still. Then I fell over.

Sam Hill says he does [url= http://www.dailymotion.com/video/x5vwvp_mtb-sam-hill-vs-subaru-impreza-wrc_auto ]80-90km/h[/url]

That's because I was travelling both faster and slower than you, got there 1st or possible never arrived and then pushed you over both before and after you had arrived.

Time travel is fun.

Never had any idea about how fast on skis, but have always been interested.

With waterskis - usually mono at 30+ knots boat speed. Flinging yourself across the wake as fast as possible adds a lot to this number. It hurts if you fall in but you never break anything. I find speed over water usually feels quicker - 40 knots in our boat (just over 40mph) feels like about 90 in a car!

For snow skis - done timed runs on ski slopes of a known distance then worked it out (did a race once too) - I'm not a great skiier but easily reach 40++mph.

48.9 twice on the same bit of hill (Pendle Hill Clitheroe side). Once on a lightweight HT with knobblies and once on a converted hardtail with 1.5 slicks. Both recorded with a Cateye Strada Wireless (which is very reliable and one of the least prone to interference) backed up by a slight lower reading from a GPS (GPS always seems to read lower).

I think at these speeds it is everything to do with drag, wind resistance, length of run and weight and has very little to do with fitness or gearing.

It does seem high forties is the max realistic speed for standard two wjeel bike, higher on a tandem makes sense as there is more weight for relatively less drag, therefore greater acceleration.

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That's because I was travelling both faster and slower than you, got there 1st or possible never arrived and then pushed you over both before and after you had arrived.

(GPS always seems to read lower).

Don't GPS measure your horizontal speed? Therefore, down a hill, the GPS would measure lower then a wheel magnet computer.

Sorry to jump this thread with a serious question but shouldn't 29ers have a higher (theoretical) top speed?

stumpyjohn - on the tandem with 4 sets of panniers we topped out at under 40 mph on glencoe road. You could just feel it hitting a wall of wind resistance. The panniers acting as air brakes effectivly.

What goes faster, a monster truck or a f1 car?

I think at these speeds it is everything to do with drag, wind resistance, length of run and weight and has very little to do with fitness or gearing.

Weight is like 80%. Getting aero is 15%. Type of bike 5% perhaps.

111MPH http://connect.garmin.com/activity/37649713

or more realistically when I moved from iPhone to Garmin Edge 500 for GPS

42.7MPH on Sunday http://connect.garmin.com/activity/40077854

I'm now very much looking forward to getting my old road bike up and running again...

53/39 on the front. The 20mm Conti GP tyres always felt quite skittish at speed though.

Did a very short test ride at the w/e and all seemed to work, although it was a very useful ride to tweak positions on bars / saddle etc. Hasn't got a working speedo at the mo. Waiting for delivery of a spare mount so I can use my mtb speedo on it.

I told you it would

Weight is like 80%. Getting aero is 15%. Type of bike 5% perhaps

That feels like it's all the wrong way around...!?

Certainly weight has a big impact on initial acceleration when you first point downhill. At 15-15.5st I really notice this, especially when skiing. I can easily out accelerate far better skiiers from start, and carry momentum easier / further across flat sections (if I get right down on the skis).

Type of bike and air resistance will be more important for sustained speed, surely?

40 on the mountain bike, on a straight road hill going into High Wycombe (some-one else's computer, which must be the dodgiest claim ever)

high 40/ low50 ish on the road bike, on a very long gentle slope (pedal like mad) followed by a short sweeping drop into a village, keep off the brakes, take it wide, hope no cars are coming the other way. It's a rush...

@nickc - Which hill into HW, assume it must have been Amersham hill or Marlow hill? Used to-do Amersham hill on a regular basis (ride into work) on my old early 90's rockhoper with canti brakes. But was always concerned about some twonk opening a door or turning right across me to go too fast.

I managed 49.9mph on a mtb down Old Wyche Road in Malvern once; I was gutted that I couldn't manage just 0.1mph faster. Normally it was somewhere in the region of 40-45mph down that road.

On the cross bike I seem to have a terminal velocity of about 38mph unless I'm draughting something; I just can't go any faster however much I may try to pedal or crouch. Down the same hills our brick-shaped van will still be accelerating to much higher speeds due to gravity alone, it's not fair!

lowey - Member
Around the 50mph mark coming down from Drum mountain into Llanfairfechan.

I went past this guy with the GPS.

Scared myself shitless when I hit the brakes.

About 55 mph on the road bike and someone overtook me

I managed 50mph in the Peaks once down a gravel farmers track. Wired computer (never had wireless). 50mph on the road bike is much easier. Depends a lot on the wind round here though.

Don't know why people might think 40mph+ must be "fantasy", it's pretty easy in hillier areas without much trouble. I always try to get the maximum though by spinning out top gear. I used to run a 50/12 on the MTB when non compact chainsets were the norm. It was ace!

I feel ashamed... I've not even managed to get the "30 mph zone" sign to tell me that I am going too fast as I enter my village down a decent hill.

If some little scrote hadn't knicked my gps mount, I'd be able to tell you the exact depth of my shame.

Early to mid 30's. But then I *am* honest. I also start to feel like death himself is standing over my shoulder.

Interesting that people are mentioning gear ratios; I find that top speeds normally occur above the speed that you spin-out, so pedalling is irrelevent. 😉

For the record, I've clocked* 53mph three times on three seperate bikes, [url= http://www.multimap.com/s/PV9SxMd6 ]here.[/url]

The 18mm-tyred road bike maxed-out at exactly the same speed as the nobbly-tyred singlespeed - probably because the limiting factor on that road is how late you dare leave the braking for the corner at the bottom, and road brakes are cr@p in comparison to those on MTBs... 😀

I must take the recumbent up there at some point...

* which may or may not be accurate, but the computers used seemed fairly good elsewhere and riding the same route on a motorbike I 'feel' that the speed wasn't wildly inaccurate.

58 mph down East Chevin Road in to Otley, based on my bike computer which is accurate to my car at 30mph. It doesnt really feel that quick to me, but once my sun glasses came off and just stuck to my chest.

PhilO Gearing makes a huge difference. If I was to go down the same hill without peddling like mad on the top section I doubt I would get above 45mph.

You really know when your shifting when you need to start planning ahead in your mind and slight movements catch the air etc etc. On skis 70mph plus gets to be fun!

Got 60.4mph on my wired cycle computer going down the Varaita valley in northern Italy last week.

I'm inclined to believe it, partly because I'd cycled up the valley prior to descending it and partly because my freehub gave up the ghost at some point on the descent. It went from a screeaming wail to screaming silence in a very worrying way and caused me a few moments of distraction whilst I checked the wheel was still rotating - merely a reminder about how badly and how quickly it can all go wrong.

TBH I was more interested in keeping my wheels out of the subsidence cracks in the road than I was about what speed I was going.

Also, I find have difficulty judging what speed I'm going at on a road bike once above 35mph - it's just shades of very fast as far as my brain is concerned.

Interesting that people are mentioning gear ratios; I find that top speeds normally occur above the speed that you spin-out, so pedalling is irrelevent.

On my normal routes I have very little road space between spinning out the gears and having to hit the anchors...

I went so fast in three weeks time that I pedalled back in time to come here and tell you.

Weight is like 80%. Getting aero is 15%. Type of bike 5% perhaps.

Weight makes no difference to downhill speed (or a very very small amount of difference). Type of bike makes a big difference just because you can get more aero on a road bike.

Above about 30mph it is all about aerodynamics. Above about 50mph on the road, on a decent descent it starts to become less efficient to pedal than just to tuck and freewheel, as the turbulence created by your moving legs slows you down more than they are putting in (you've typically spun out so you're not putting in much effort).

With the right hill (long, steepish, not too tight corners), 80km/50mph on a road bike is just about hanging on, there's no real skill or fitness to it. One hill we used to ride when I was in New Zealand was pretty crazy though - very very fast and not too tight for the first 2km or so, then suddenly dropping down, adding extra speed, for about 500m, until a sharp bend (signposted as maximum speed 20km/h). Trying to hit high speeds on that was scary as it basically involved braking for the corner as late as possible - the one and only time I've done a skid at 70km/h (thank goodness I stayed on for that one!).

Joe

Sorry to jump this thread with a serious question but shouldn't 29ers have a higher (theoretical) top speed?

No. Why would they? Once you've gone beyond the top pedalling speed, there is no major difference (rolling resistance maybe, but then that is going to be so small compared to aerodynamics).

Joe

PhilO Gearing makes a huge difference. If I was to go down the same hill without peddling like mad on the top section I doubt I would get above 45mph.

I can see that it might make a difference on some hills - I assume that your favoured hill has a gentle run-in and a steep but short section towards the end? IME most good hills allow you to reach terminal velocity before you run out of road, no matter what your launch speed (see my experience of the SS equalling the road bike on my local hill). YMMV, however... 8)

Certainly weight has a big impact on initial acceleration when you first point downhill. At 15-15.5st I really notice this, especially when skiing. I can easily out accelerate far better skiiers from start, and carry momentum easier / further across flat sections (if I get right down on the skis).

Type of bike and air resistance will be more important for sustained speed, surely?

Weight makes no difference to downhill speed (or a very very small amount of difference). Type of bike makes a big difference just because you can get more aero on a road bike.

I'm 8.5 stone. Even on my road bike that is about 3 sizes too big for me, where I can put my mouth on the stem very easily, I still get left for dead on descents. Long, straight descents are where its most obvious, I'll pop it into top gear, thrash it until I spin out, then get super aero, and everyone else comes past me freewheeling, on the hoods. Its annoying, but its the laws of physics.

Getting more aero on a road bike? Not necessarily, as mountain bikes usually have a lower top tube, so when you sit on it (under the saddle), you can probably get as, or even more, aero then a road bike.

Basically, if you sit someone on a road bike, and send them off down a hill, their speed will increase if they tuck in, but not as much as if they suddenly ate an entire greggs.

On my roadbike downhill 40mph scares the death out of me when cars pull out 😀

i think these suggestions that weight affects acceleration and speed down hills go against a fundamental law of physics. obviously assuming that things like bearings resistance and rolling resistance impact negligibly on different rider weights.

[url=

hammer and the feather[/url]

Potential energy = mgh. Two riders at the top of a hill, the fat one has more potential energy.

They start going down the hill, the potential energy gets turned into kinetic energy. mgh = 0.5mv^2

The feather hammer thing works because the masses cancel, to give gh = 0.5v^2

But you have to take in air resistance.

Gravity provides 9.8N acceleration per kg. ma = F

The fat rider will have a bigger F then the slim rider. The air resistance difference will be very small.

So someone 100kg will have 908N pushing him down the hill. Someone 50kg will have half that, 454N. Take away maybe 30N for the slimmer rider from air resistance, and 40N from the fatter rider, then divide by their masses.

Fat rider has acceleration of 8.68ms^-2

Slim rider has acceleration of 8.48ms^-2

you've confused me with science, there. 😆

now i want to believe you because you have used letters in place of words, which always looks convincing. but i don't know what to think. 😕

I realised I hadn't really explained myself properly, I've edited, have another look.

This is based on real world experience, and I then proved it using physics to myself.

60mph on a road near Hawes on me HT, (combination of long hill and cat'n'mouse drafting with chums). Low 50's mph offroad on a track in Plymbridge, (combination of big rings and youthful exuberance).

There's also a road near Lopwell Dam where if can hit 25mph on the first corner and hold it, you'll freewheel to 50+ without trying. Huge run off as well.

The force pushing you down the hill is due to your weight and the incline. Without wind resistance your size wouldn't matter.

However wind resistance is proportional to speed.

Terminal velocity is when you are going fast enough that the wind resistance is equal to the force produced by your weight

if you double the weight of a person you do not double their wind resistance - hence they reach a higher terminal velocity.

theflatboy - if you need convicing turn the argument around.

Who goes [i]uphill[/i] quicker - heavy rider or light rider??

If I have to carry laptop and / or files on my commute, the climbs are significantly more strenuous, but the bike wants to run away more on the downs

ETA, which of course only reflects the energy required to get the heavier mass to an elevated posn - ie higher potential energy position, but ignores the air resistance effects encountered going DH, as very clearly explained by TJ.... which also explains a tandem's rapidity of descending!!