Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Horse Power to hit 150mph ?

drag is the killer, maybe even more than frontal area.i dont know how to calculate drag without a wind tunnel, but i think its possible to look at a motorcycle and decide what makes more drag than what doesnt.

on my own race bike, i think im close to as much horsepower as i can get, or very near anyway.

i keep thinking of where i can reduce drag, and on an unfaired machine im not sure what i can do

Brilliant !! thanks

Narrower tyres.

I found out about drag a couple of years ago. shut the throttle and put my head above the fairing at over 190mph, it caused the bike to dance about a bit.
I was hitting 194-195 all day, I saw a photo of me crossing the finish line and my elbows were alongside my knees. I shuffled my bum back a bit so my elbows tucked in front of my knees, my speed on the next couple of runs was 198.
Last year without the cross wind 200.5, 2 run average 200.064

On an unfaired bike, cardboard and gaffer tape to put a taper behind the fork legs, Keep the headlight shell but turn it backwards. Put the footrests in the region of the rear wheel spindle so your lower legs are horizontal

200mph, that's going very well for a 350 Greeves.

i ran a set of 2.5 x 17, but destroyed a wheel bearing at 130 mph. i havent had a chance to have the machine shop look over the problem. that is in the works for 2023.





^^^this configuration gives me more sprocket choices than the stock 43 or 46.

In the early 50's Moto Guzzi did a lot of work on drag. You'll remember they had their own wind tunnel so could explore it to their hearts content.. Fergus Anderson, one of their factory riders of the day wrote about it in one of the weeklies of the day (I think the Blue'un) and described how he spent days trying various riding positions and seeing what efffect moving about on the bike had. He even found the position of his feet on the footrests made a measurable difference.
Looking at racing Guzzis of the day you'll notice some had oddly shaped tanks. These were all the result of windtunnel tests with the rider aboard, not just what someone thought might work but what did work with the rider draped over them.
Full streamlining was somewhat controversial at the time. It was seen as giving factories an unfair advantage over the private rider who couldn't afford it. Guzzi were having a bit of a bet each way as their bikes didn't wear streamlining but much discreet effort had been put in to reduce drag on a naked bike. It didn't last of course. Streamlining won the day and bugger the little bloke.
Anyway, given the above discussion it may be useful to hunt out those old Fergus Anderson articles and give them a once over. It certainly seems the Guzzi work on drag has been lost in time.
After all, reducing drag is free power isn't it.
Chers,

most of that was with dustbins, wasnt it?

Andy, I'm wondering what you were riding and where? I see you have a Kawasaki ZZR1400 "Kuro No Senshi" so probably that one, but where can you ride it that fast in England?


Although Ignoramus does not mention land speed racing, what you're suggesting puts the bike in Altered Partially Streamlined class for the events we participate in. Which is OK, but you'll encounter way more streamlined bikes in that class than just fork leg fairings and rear set footpegs.

Tom

not available for me in the modified class.

i dont think anything up front has as much effect as closing the air behind. i suspect re-configuring the pipes so that they dump in front of the rear tire, lowering the machine by returning to the 17-inch wheels, and adding pizza pans for wheel discs is about as good as i can get.

I woulnt go with narrow tyres on a beach straight liner ....you want to have SOME chance if you hit a soft spot .

I was thinking more of double rear wheels like the Austin 7 powered Brough Superior they made for side cars. NOT spaced much so no smart arse will say "cant you ride a 2 wheeler yet"
For Tyres i was thinking about those bulbous things u see on bicycles used on soft sand. I am going to get one and run it up to 2800 rpm with a 3 phase motor just so i can know if the tyre will shred at high speed ...

Koncretekid Yes I was riding my ZZR1400 at Elvington airfield. The runway is just shy of 2 miles, the top speed traps are at 2KM from a standing start, there are also other traps to record standing 1KM flying 1KM, flying 1/4 mile and flying 1/8 mile.

I also rode my Ninja H2 the same weekend and exceeded 209mph, the guys stood across from the finish line said they couldn't hear the exhaust, just the sound of the air being pushed aside

I have found a delightful Asian lady whose hobby is making strange things out of bamboo.

" Me make long tube you sit in, be very strong for you" "have friend who put cloth on it with special can of stuff .... keep wind off you"

I am getting her to see if she can get another lady to paint a furious looking fire breathing red dragon on it hhahahahah

So i could definitely claim some type of record for ***MPH with 1950s lawnmower engines . spruce components and a bamboo streamliner

Bamboo could be quite good as it is very strong and light .

It just predates the full streamlining dustbin era, Kevin. Fergus Anderson started to ride for Guzzi in 1950 just beforehand. FIM, the governing body was wary about streamlining and tippy toed around it for years. Everyone knew the theoretical advantages of streamling but how to do it whilst maintaining a rideable and controllable motorcycle was a foreign country. Hence the inelegant attempts in the early 50's with beaks in front, tanks moulded to body shapes, semi enclosed rear wheels and so on.
Everyone knew streamlining was coming but how did you do it effectively and stay within the rules?
Finally the FIM came to the party and we entered the dustbin period. They were gorgeous bikes. I saw them racing at Bandiana here in Oz and have never forgotten them. I was a new apprentice and attending my first real road race meeting with a factory racing team and international riders and all. Those dustbin Guzzi flat singles made a big impression on a gormless lad and to this day remain my ultimate ideal of a proper motorcycle. I've been a sucker for lightweight Guzzis ever since.

Andy, ran a ZZR1400 through the online calculator that was included in a previous post. Found rear wheel HP and wet weight on Wikipedia, added a 170 pound rider, guestimated frontal area, and adjusted coefficient of drag to achieve end result of 200 mph.

Calculate HP For A Given Speed
Coefficient of Drag .46
Frontal Area of Car 7.3 Sq/Ft
Weight of Car 770 Lbs
Velocity of Car 200 MPH
Calculate
Using your vehicle Speed of 200 MPH takes 183.39 HP to overcome air drag.
Rolling resistance is 5.34
For a total of 188.73 HP to run 200 MPH

I have 214 RWHP

The calculation would change if the CofD was changed from .46 or the frontal area from 7.3 sq/ft. I arbitrarily selected those values.

Redid with same arbitrary values and adjusting MPH to achieve your RWHP. Yielded 209 MPH
Calculate HP For A Given Speed
Coefficient of Drag .46
Frontal Area of Car 7.3 Sq/Ft
Weight of Car 770 Lbs
Velocity of Car
209 MPH
Calculate
Using your vehicle Speed of 209 MPH takes 209.28 HP to overcome air drag.
Rolling resistance is 5.58
For a total of 214.86 HP to run 209 MPH

I think the racing Tridents made about 80 HP and did better than 150 mph.

Black Bart Racing has been campaigning this Rob North Triple at Loring for years, always chooses a different class to try to set a new record. This photo taken in 2022 but with the full fairing on, his best record in the 750 APS-PG class (750cc A class because it was originally a race only model), Partially Streamlined in 2018 was 152.872 mph. Interestingly, in the Loring record book, my record directly above his at the same event in 650 APS-PG is 152.866 mph. I only have about 60 hp, but I have a lower coefficient of friction with better streamlining.



Tom

fwiw.... round is a very un-aerodynamic shape. not as bad as square, but not too much better.

From poster "Porkpie" on landspeedracing.com about wind drag: "It doesn't matter how you open the hole, it's how you close the hole."

about all thats available in modified production is a kamm tail

from what i have read, kamm tail design is a lot more subtle than just putting a box behind the seat

I doubt the heat wrap will do anything meaningful. On a data logger it was 5hp, not much and it rusted stainless pipes before I pulled it off. When I say 5hp it is a lot when you are chasing it, but not much different just riding around. It was the easiest restoration of 5hp taking it off.

I guess that's a limited test, but cured me.

Also, because one Triple did over 170mph at Daytona doesn't mean they all did or will.