How fast - on 50cc?!

[xwhatsit]

After listening to the sound of a Honda RC110 (see Who needs porn?), a 50cc GP bike from 1962, I decided to read up a bit more about this 50cc GP class. Wikipedia, as usual, has the goods (http://en.wikipedia.org/wiki/50cc) (http://en.wikipedia.org/wiki/50cc%29).

Anyhow, what fascinated me was this;

By the end of the season, with the addition of rudimentary streamlining and the increase of carburettor size to 17 mm, the 9 hp (http://en.wikipedia.org/wiki/Horsepower) four-speed two-stroke (http://en.wikipedia.org/wiki/Two-stroke) bikes could top over 85 mph.<sup id="_ref-Kreidler.2C_Strassen-Rennmaschinen_von_1959-65_100_0" class="reference">[4] (http://en.wikipedia.org/wiki/50cc#_note-Kreidler.2C_Strassen-Rennmaschinen_von_1959-65_100)</sup>

What the. Apparently eventually Honda's four-stroke RC110 made 10hp, more than the two-strokes, but that's not the story here.

85mph is more than 135kph. How is it, that I'm struggling to hit 140kph in a 26hp machine, and these 9hp things were almost getting there? Even bikes like the GPX250, with fairings, and substantially more horsepower are only hitting about 160kph.

I'm going to rule out streamlining as a reason; surely modern production bikes have better streamlining than the `rudimentary' streamlining on these GP bikes in the 60s. Weight is a factor here; obviously these things weighed next to nothing, with a 50cc engine and very lightweight frames. Skinny tyres, too. But all that doesn't seem to add up to more than doubling the horsepower. Does it?

[gamgee]

probably a combination of the gearing, and making an engine which is made to perform at extremely high revs

[McJim]

How much torque were they generating?

[marty]

maybe they actually knew how to ride?

[thehollowmen]

At one time suzuki (?) had a 50cc 2stroke racer with a narrow powerband and 17 speed gearbox. They didn't have the restrictions then that we do now

I'll try and look it up.

A derestricted RS50 will do over 70 mph (112 km/h)

Then again my DL650 doesn't go much faster than 180km/h

Edit - nine speed ones here: http://en.wikipedia.org/wiki/50_cc

This still wasn’t enough to compensate for the machines relative lack of power and three weeks later at the Isle of Man TT, nine gears were fitted and the rev limit increased to 17,000 rpm with output now up to around 10 hp.[8] Sometime during the season, the machines designation was changed to RC111, but Honda’s records are unclear as to what precise change in the development this signified or when it was used.[9]

In contrast, the Suzuki team were committed to two-stroke technology and their single cylinder RM62 machine featured rotary valve induction and an 8-speed transmission and produced about 10 hp at 12,000 rpm

[James Deuce]

Quite simply it comes down to power to weight, jockey-like riders, and superb technique.

A good RG50 will do 100km/hr

[Kickaha]

They were also very light and ridden by midgets, there are guys racing in world GP at the moment who have a family history dating back to those bikes

The Suzuki RK67,50cc GP bike was a twin cylinder,revved to 17,500, had 17 gears and would supposedly do 170km

NZer Hugh Anderson won world 50cc championships in 63/64 on Suzukis

[James Deuce]

NZer Hugh Anderson...

Speaking of midgets.

[nudemetalz]

My wee RG-50 I had a number of years ago would go to 120km/h (indicated), however only on a really long straight and also only if one of the 4 other RG-50-shod riders didn't put his foot over the exhaust to choke it !!!!!!!!

[Kickaha]

There's 50cc GP bikes on here
http://www.suzukicycles.org/history/history_04-race-1960-1967.shtml
you'll see the 50cc triple RP68 that they built,the rules were changed to restrict them to 1 cylinder before it was raced


Some more about them
http://www.juen.com/racing50cc/

I've seen the one Hugh Anderson won his championship on in real life back in the late 1970s at a display in King Edward barracks in Chch

[Bass]

I'm going to rule out streamlining as a reason; surely modern production bikes have better streamlining than the `rudimentary' streamlining on these GP bikes in the 60s.

Tain't necessarily so!
Also, some of these guys would ride lying flat on the seat, feet out behind and changing gear with their left hand.

[James Deuce]

Actually bike aerodynamics in the '50s and '60s were much better than now, at least in regard to top speed, and the Dustbin or Porpoise fairing allowed 50-60HP 500cc machines to get close to 200mph.

The problem with motorcycle aerodynamics is that bikes roll about an axis and the moment they move off vertical the aerodynamic properties of a fairing that works well from a top speed perspective, change drastically. The Dustbin fairings were banned because there were fatalities that may have been caused by those fairings generating lift at high lean angles and speeds and literally lifting the wheels off the ground.

Motorcycle aerodynamics are still very poorly understood. What works well at one track may be a liability elsewhere. Rossi demanded a bigger fairing for the first RCV211V, but had to return to the small fairing because of the massively negative effect on turn-in the bigger fairing had.

HRC have changed the design of the rear hugger on the RC212V throughout this year. Looking at the shape after the initial photos were published for the RC212V I theorised that the shape of the hugger was developed to meld aerodynamics to rear suspension action and to create a vortex generator to deny a draft to a following motorcycle. I think it probably had a deleterious effect on top speed as the little pointed spoiler disappeared from the hugger. A flat topped hugger with spoilers on each side at the rear, angled at roughly 45 degrees to horizontal has appeared since, possibly to improve lateral grip in high speed corners.

[Coyote]

maybe they actually knew how to ride?
Knowing how to ride doesn't increase top speed in a straight line. Any chimp can wind the throttle up

[xwhatsit]

Interesting to hear about the aerodynamics. It's funny how much difference that can make to a bike -- I know that first hand; my bike will do 130-135kph in a normal riding position (albeit with clipons), however if I lie flat on the tank the speed instantly begins to climb, slowly. Yep, I can see why it'd be a very tricky job doing aerodynamics on a bike. In cage racing there's issues even with the tiny roll angle they have when cornering fast sweepers (leaning the other way, though), so 45 degrees or so is going to be a headache.

Do the gears make that much difference? I would've thought they'd let it get to the top speed much faster, but would they actually add much?

I had no idea weight played such an important role in straight-line speed. Acceleration, cornering speeds, but sheer top speed? Interesting.

[Timber020]

Knowing how to ride doesn't increase top speed in a straight line. Any chimp can wind the throttle up

With some bikes, especially ones that require some nursing, you do need to know how to ride to get the best out of them, just winding the throttle up isnt always enough.

My 2 RG's have been good for over 100. The one I have currently got will do 120kmph if I get a draft or downhill for the gap in powerband between 5th and 6th! Once at that speed and in the band it will hold it. New piston and rings might fix that issue or another tooth on the rear sprocket. The other was lower geared and would do 110. Bloody good fun having to work them so hard. 82 gear changes between karori and island bay! (and thats with a clear run!)

[Ivan]

THe 17 gears was crucial because crank case compression was altered it had a high crankcase compression and made the engine to peaky and unrideable they needed more gears for a better power spread.
Porting of the 2 stroke engien also weaves good power
Internal gearing defines your gear setup then your final drive gearing, plus the frame weight rider ability,

Its all part of it

Id struggle to see a 50cc Honda GP get near 200 the speed of there 125GP bikes??????

[lb99]

85mph is more than 135kph. How is it, that I'm struggling to hit 140kph in a 26hp machine, ?

your bike should smoke 140, more like 150+ with big balls down a bit of a hill, CB250rs is a prtty quick single, maybe yours isn't making 26bhp? :Pokey:

[Coyote]

With some bikes, especially ones that require some nursing, you do need to know how to ride to get the best out of them, just winding the throttle up isnt always enough.

My 2 RG's have been good for over 100. The one I have currently got will do 120kmph if I get a draft or downhill for the gap in powerband between 5th and 6th! Once at that speed and in the band it will hold it. New piston and rings might fix that issue or another tooth on the rear sprocket. The other was lower geared and would do 110. Bloody good fun having to work them so hard. 82 gear changes between karori and island bay! (and thats with a clear run!)
Interesting, I've yet to ride such a bike

That's one of the great things about the small light bikes, it's rewarding when you get the shifts just right

[eliot-ness]

The first pic is the RC110 minus fairing, this was not the factory racer but was very close. It was produced as a limited edition over the counter racer in 1962. Specs. DOHC 4 stroke single cylinder. Bore 40.4mm Stroke 30mm. HP. 8.5bhp. 8speed gearbox. Weight. 62 kgs Top speed 88mph. Cost in 1962. 380 pounds. Value now Approx 25,000 pounds.

The second pic is Ricardo Tormo onthe Bultaco, 1975 Two stroke with monocogue frame. After 1969 rules were changed. 6 speed boxes were the limit. The Japanese had pulled out leaving the field open to the Europeans. The Bultaco was originally a Dutch bike, but after a brief move to Italy was bought by Bultaco who, with rider Angel Nieto in 76/77 and Ricardo Tormo 1978 won the world championships. Bulaco went bust but had built a few replicas, one of which won the 1981 championship with Tormo aboard. These bikes had a race average of over 100mph at tracks like Spa. In order to keep the engine within it's 13,000 to 16,000 power band corners had to be taken almost flat out, only backing off when the tyres started to roll on the rims. Cornering speeds were higher than the 250cc class. Not all riders were midgets. Hailwood rode the Kreidler at the IOM in the mid 60s
Bultaco specs. Water cooled rotary valve 2 stroke single. Bore 40mm, stroke 39.5mm. BHP 18. Gearbox, 6 speed. (cassette type). Weight, 55.5 kilos.
Top speed, Approx. 118mph

[Kickaha]

, but after a brief move to Italy was bought by Bultaco who, with rider Angel Nieto in 76/77

The Nieto family is still very much involved in GP racing

[speedpro]

In NZ I think Pete Sales still holds the 50cc land speed record on his GT50 at something like 85mph.

[quickbuck]

In NZ I think Pete Sales still holds the 50cc land speed record on his GT50 at something like 85mph.

He may well do.
I do know of somebody (that lives quite close to me) who wanted to break it using an old aircraft drop tank....
Not sure if that project is still underway though.

[nudemetalz]

I raced an RD-50 at about 1988-89. Clocked at 110-115km/h from memory. Weighed virtually nothing. It had a very peaky powerband and needed lots of clutch work out of corners

Here's a couple of pics of it.
That second shot is me on the sweeper onto the straight at Levels. I was nearly at maximum speed there, so you can imagine the poor wee engine pulling 12,000rpm all the way. I had problems with it nipping up on me, unsurpisingly !!!

[nadroj]

yeah Pete still does though I'm sure I could beat him with some decent gas & some comprewssion, shit this keypoad is crapy. Ivan I wa just wondering if you were dead as haven't herardmuch of you & no show at Brooklyn.


anyway hello from the KB gathering, guess-who & hello Mike.,, Hope things are going well with the new job,

PS this isn't my log on, just free for all on someone elses at the rally

[xwhatsit]

your bike should smoke 140, more like 150+ with big balls down a bit of a hill, CB250rs is a prtty quick single, maybe yours isn't making 26bhp? :Pokey:

Down a hill, yeah, I imagine I could get close to 150kph. On the flat though, 140kph is where it tops out (convenient for avoiding licence suspension lol). I wouldn't be surprised if it's a little bit down on power, the valves need a better seal, and either the ignition is over-advanced or it's running lean, so there's potential for improvement I think.


The first pic is the RC110 minus fairing, this was not the factory racer but was very close. It was produced as a limited edition over the counter racer in 1962. Specs. DOHC 4 stroke single cylinder. Bore 40.4mm Stroke 30mm. HP. 8.5bhp. 8speed gearbox. Weight. 62 kgs Top speed 88mph. Cost in 1962. 380 pounds. Value now Approx 25,000 pounds.

The second pic is Ricardo Tormo onthe Bultaco, 1975 Two stroke with monocogue frame. After 1969 rules were changed. 6 speed boxes were the limit. The Japanese had pulled out leaving the field open to the Europeans. The Bultaco was originally a Dutch bike, but after a brief move to Italy was bought by Bultaco who, with rider Angel Nieto in 76/77 and Ricardo Tormo 1978 won the world championships. Bulaco went bust but had built a few replicas, one of which won the 1981 championship with Tormo aboard. These bikes had a race average of over 100mph at tracks like Spa. In order to keep the engine within it's 13,000 to 16,000 power band corners had to be taken almost flat out, only backing off when the tyres started to roll on the rims. Cornering speeds were higher than the 250cc class. Not all riders were midgets. Hailwood rode the Kreidler at the IOM in the mid 60s
Bultaco specs. Water cooled rotary valve 2 stroke single. Bore 40mm, stroke 39.5mm. BHP 18. Gearbox, 6 speed. (cassette type). Weight, 55.5 kilos.
Top speed, Approx. 118mph

Beautiful, mate, both those bikes. The non-factory racer RC110 was the CR110, wasn't it? That's the one they recently made a reproduction of (with a 100cc+ engine though, to get the same performance as the 50cc without crazy rebuilds), and are selling in Japan for ludicrous amounts.

Why did this class disappear? Did it just become irrelevant? Wiki says the reason they started racing was that there were heaps of 50cc bikes just lying around and in production, so it was very cheap to get involved in. Not really the case today, I'm sure the amount of technology they'd use today wouldn't come easily, but it would still be cheaper than maintaining a 125 or 250 at race spec.

[kensuem]

http://www.vintagebike.co.uk/
go to the above site and click on 'Sounds',then look for the sound of the 50cc pack.there are also some other great sounds there.when i did the video of my GN250,I tried dubbing the sound of some of the classic racers on to my Gn tape,but decided no one would believe me!On my way to school as a 15year old,I used to pass a bike shop which sold Itom 50cc bikes.The great Bill Ivey used to work as a mechanic in that shop,and his Itom race bike was often on show in the window.I was too big a build for a 50,but ended up buying an A7 Shooting Star from them instead.

[Bass]

In NZ I think Pete Sales still holds the 50cc land speed record on his GT50 at something like 85mph.

Where is he these days?
I used to know him quite well but I haven't seen him in 30 years or thereabouts.

[Forest]

Knowing how to ride doesn't increase top speed in a straight line. Any chimp can wind the throttle up

A good rider can alter the shape of his back to help smooth the air-flow over the top of the bike. It takes some skill to do this well.

[speedpro]

Where is he these days?
I used to know him quite well but I haven't seen him in 30 years or thereabouts.

Total Motorcycles just south of Palmerston Nth.

[N4CR]

cagiva mito 125 gasses zxr250 in top end most of hte time 200kmh with the right setup wtfpwnd. 7 gears of ***. go get a refund on your rg50's. rs50 4tw

2

[90s]

In the mid-90s I did a little work with Rabasa Derbi in Catalunya, Spain. Like many of you, I did not really know this company beforehand. It seems they have a great GP history, but pretty much all with 50cc-250cc bikes, but really specialising in the smaller stuff. Barry Sheene started out racing small bikes with them, and their 50cc bikes really can fly.

Many of your are surprised that a 50cc can hit the high speeds. But if you ride one you will see how they managed to accelerate slowly at speeds above 100k (which is why streamlining becomes so important), and how much of a (fun) effort it is to whip these bikes up to 100k in the first place.

Even 50cc honda mopeds I used to ride with modified exhausts could crack 90k with a bit of a heads-down, but it was an experience I would hope not to repeat.

As the yanks say, there's really no substitute for cubes.
(metric version - more cc = more grin, Jim)

For more on Derbi:
"The 'Red Bullets' were a global success in the small cylinder categories for 40 years, collecting an incredible 81 Grand Prix victories in the 50, 80, 125 and 250cc classes, as well as 18 World titles. Ten individual crowns won by Angel Nieto (5), Jorge Martínez 'Aspar' (4) y Manuel 'Champi' Herreros (1) were added to by eight manufatcurers' titles, with two other legendary 500cc World Champions also having begun their careers with DERBI - the late Barry Sheene and, later, Alex Crivillé.

DERBI returned to the 125cc class of the MotoGP World Championship in 1999 after an eight year absence. Within five years the factory have picked up 11 victories and finished runner-up in the championship on two occasions with Japanese rider Youichi Ui. During this time, DERBI has also left their mark on the championship with a series of technical innovations, such as being the first to use double front brake discs, as well as a winning spirit exclusive to the great factories and earned over four decades of effort and, above all, passion for motorcycle racing."

[Blackflagged]

Aprilia Rs50,in the USA http://www.apriliausa.com/njb_dettaglio.asp?id=303
Bonneville salt flats.160k+
Stock derbi & Aprilia`s do 110kph (takes awhile)with eu3 mufflers and tiny carbs

[slopster]

Remember their 9hp is probably measured at the rear wheel. While your 26hp is probably measured at the crank with most of the engines ancilliries removed and then honda probably added a few for good measure anyway.

[ajturbo]

I raced an RD-50 at about 1988-89. Clocked at 110-115km/h from memory. Weighed virtually nothing. It had a very peaky powerband and needed lots of clutch work out of corners

Here's a couple of pics of it.
That second shot is me on the sweeper onto the straight at Levels. I was nearly at maximum speed there, so you can imagine the poor wee engine pulling 12,000rpm all the way. I had problems with it nipping up on me, unsurpisingly !!!

luke has been clocked on his rg-50 around taupo at over 120..!!!!.. not bad for a bike that has nothing done to it...

[vifferman]

I read some time back (but no doubt it's still true) that a Honda 50 engine from the 60s still holds the record for the power/litre for a naturally aspirated four-stroke engine.

[xwhatsit]

I read some time back (but no doubt it's still true) that a Honda 50 engine from the 60s still holds the record for the power/litre for a naturally aspirated four-stroke engine.

I read that recently, except I'm not totally sure it was the 50cc GP engine. 22,000RPM in 1963 -- damned impressive.

Meanwhile, I hear Hondas are for fags :sunny:

[eliot-ness]

I read some time back (but no doubt it's still true) that a Honda 50 engine from the 60s still holds the record for the power/litre for a naturally aspirated four-stroke engine.

Not 100% sure but I think that honour goes to the 5 cylinder 125 honda of 1963. From memory (not always reliable nowadays) it developed around 30bhp or 240bhp per litre. That really was something to listen to

[xwhatsit]

Not 100% sure but I think that honour goes to the 5 cylinder 125 honda of 1963. From memory (not always reliable nowadays) it developed around 30bhp or 240bhp per litre. That really was something to listen to

<hints id="hah_hints"></hints>Yep that sounds like the information I read... did you see my other thread on http://www.honda.co.jp/SoundofHonda/ ? Got a recording of that and many other Honda GP bikes.

Also kensuem's link was pretty cool -- not such high quality recordings, it sounds like they've been taken off LPs, but they're from actual races. You can hear Hailwood go into the pits, and then a short while later run down the pits and bump start the bike. What a roar out of such a tiny engine!

The 50ccs sound cool too, you can hear the Honda screaming away, sounding quite bizarre next to the two-stroke Yamahas; the same frequency as the two-strokes (revving twice as high!) but with a four-stroke exhaust sound. Odd.

[eliot-ness]

<hints id="hah_hints"></hints>Yep that sounds like the information I read... did you see my other thread on http://www.honda.co.jp/SoundofHonda/ ? Got a recording of that and many other Honda GP bike

Heard the 125 Honda and Suzuki live on the short circuits. Three times every race, Once in the pits, again off the start line, and then again half a dozen laps later when they lapped me, but for sheer noise level the MV 125 had them beat. Shattered both eardrums and had hearing problems ever since.