RFL

[Corvus]

Gromit said "Said friend was slightly baffled at this but it's simple - as BnB said, bikes' aerodynamics are pretty dreadful. Above 100mph, a huge amount of the engine's oomph is taken just to battle against the drag of the air. Cars win back very convincingly. "

30 HP on a motorcycle will comfortably get you to 100mph, especially with decent fairing, would you agree?

It would take a VERY aerodynamic car to get there on 30 HP.

50 HP on a bike will get you north of 120mph, yes? I can't imagine a car with 50 HP would get past 90mph? Our car, with 67HP, would probably top out at 110mph.

[Gromit]

Gromit said "Said friend was slightly baffled at this but it's simple - as BnB said, bikes' aerodynamics are pretty dreadful. Above 100mph, a huge amount of the engine's oomph is taken just to battle against the drag of the air. Cars win back very convincingly. "

30 HP on a motorcycle will comfortably get you to 100mph, especially with decent fairing, would you agree?

It would take a VERY aerodynamic car to get there on 30 HP.

50 HP on a bike will get you north of 120mph, yes? I can't imagine a car with 50 HP would get past 90mph? Our car, with 67HP, would probably top out at 110mph.

With respect, you're forgetting the power to weight ratio in this equation - let's take for example the old RD250LC, a good one would put out itro 35bhp and the bike would just about scrape a genuine 100mph (I know that because I owned one many moons ago). The LC weighed around 140kg ie power to weight is approx 250bhp/tonne. That sort of p/w is pretty high for any car - my old Caterham 7's (145bhp/500kg) was approx 290bhp/tonne and that would hit 120mph on a good day. A very light car, but its aeros, like a bike's, were atrocious hence its poor top speed - saying that, 100mph in it was scary enough. Into a headwind it would knock 10mph off it, despite its great p/w. You could actually feel the car fighting the breeze. Add a passenger (someone who weighed around 100kg like me) and the top speed wouldn't change as it's still the barn door aerodynamics killing the speed, not the p/w.

The Caterham 21 - a slippery bodied Caterham 7 - had far worse p/w (it was a good 250kg heavier) but was considerably faster top speed-wise. Its engine didn't have to waste power just fighting the air.

Back when the new Audi 100 was introduced (around 1982/83 I think?) the company made a lot of noise about the new car's fabulous drag co-efficient. At our local Audi dealer (Vindis in Sawston) the chap from Audi did a short presentation, during which he explained the relevance of aerodynamics and how they have a massive effect on the top speed of a car - and therefore how hard a car has to work. I remember being truly amazed at the examples he gave, admittedly it was mostly marketing spin but the maths made perfect sense. The Audi 100 would reach 100mph (for example) on less bhp than a considerably more powerful (in terms of p/w) car. The Audi was making better use of its bhp, even though it had a lower p/w. It also used a lot less fuel.

[Corvus]

Gromit said: " Add a passenger (someone who weighed around 100kg like me) and the top speed wouldn't change as it's still the barn door aerodynamics killing the speed"

(Very much with equal respect and ready to accept I'm getting it wrong, but......)

That's what I've been saying!

We shouldn't get hooked up on the weight when looking at top speed. Weight VERY MUCH matters when looking at acceleration for a given amount of available power. But it matters not a jot with regard to top speed, unless it affects area or rolling resistance (which it will, to a degree, all else being equal).

It seems to me that a bike is like a knife compared to a car. Won't this more than compensate for its relative lack of slipperiness? It seems to.

Bikes, even with their lack of recent technology as applied to car engines with the aim of improving mpg, are more fuel efficient. Surely they always will be?

[Gromit]

It seems to me that a bike is like a knife compared to a car. Won't this more than compensate for its relative lack of slipperiness? It seems to.

One would've thought so, but even stuff with high p/w and good - for bikes - aeros (the Hayabusa for example) they simply don't have the same top speed potential as cars with lower p/w and excellent aerodynamics. I'd bet the 'Busa has a much higher p/w than a Veyron but it certainly won't hit 250mph.

Bikes, even with their lack of recent technology as applied to car engines with the aim of improving mpg, are more fuel efficient. Surely they always will be?

Agreed - for the performance available that is beyond any doubt. Whilst my Blackbird's not cutting edge (prehistoric more like - it runs carbs) in terms of engine-tech, it'll happily achieve 50mpg on a gentle-ish run on dual carriageways/A-roads. Caning it, it'll drop to around 40mpg. For the sort of performance on offer, I can live with that.

Back on track - my RFL reminder arrived in the Post today aswell.

[Corvus]

It seems to me that a bike is like a knife compared to a car. Won't this more than compensate for its relative lack of slipperiness? It seems to.

One would've thought so, but even stuff with high p/w and good - for bikes - aeros (the Hayabusa for example) they simply don't have the same top speed potential as cars with lower p/w and excellent aerodynamics. I'd bet the 'Busa has a much higher p/w than a Veyron but it certainly won't hit 250mph.

Bikes, even with their lack of recent technology as applied to car engines with the aim of improving mpg, are more fuel efficient. Surely they always will be?

Agreed - for the performance available that is beyond any doubt. Whilst my Blackbird's not cutting edge (prehistoric more like - it runs carbs) in terms of engine-tech, it'll happily achieve 50mpg on a gentle-ish run on dual carriageways/A-roads. Caning it, it'll drop to around 40mpg. For the sort of performance on offer, I can live with that.

Back on track - my RFL reminder arrived in the Post today aswell.

Talking top speed at this point, not mpg...

What power does the veyron have?

Forget the weight. The drag coeficient equation doesn't take account of weight. Don't get me wrong, I hate equations. I feel faint at the sight of brackets and Greek symbols. But I've looked and I can't see weight mentioned.

I suspect it is the veyrons' power and its drag coefficient that count here the bike will have less than a quarter of the power I guess? Give the bike the same power......

[slparry]

1184 bhp for the super sport one .... 987 bhp for the slow old sports tourer version

http://en.wikipedia.org/wiki/Bugatti_Veyron

[Corvus]

Gromit, looking back over the last few posts, we seem to be saying the same thing. Except with respect to the effect of weight on top speed.

[Corvus]

1184 bhp for the super sport one .... 987 bhp for the slow old sports tourer version

http://en.wikipedia.org/wiki/Bugatti_Veyron

Thank you.

Doesn't seem to be a fair comparison in my eyes. A good comparison to prove a point perhaps?

[Gromit]

Gromit, looking back over the last few posts, we seem to be saying the same thing. Except with respect to the effect of weight on top speed.

Pretty much.

We can, as you say, largely discount weight from the equation when we're talking top speed. As the Audi bloke said, the biggest enemy to speed potential is the wall of air we're trying to push the vehicle though. The more efficiently we can do that, the quicker we can go for the same amount of power.

Looking at the Veyron's performance figures they're pretty outrageous for a car. Would love to have a go in one...something I very much doubt will happen.

[Corvus]

Gromit, looking back over the last few posts, we seem to be saying the same thing. Except with respect to the effect of weight on top speed.

Pretty much.

We can, as you say, largely discount weight from the equation when we're talking top speed. As the Audi bloke said, the biggest enemy to speed potential is the wall of air we're trying to push the vehicle though. The more efficiently we can do that, the quicker we can go for the same amount of power.

Looking at the Veyron's performance figures they're pretty outrageous for a car. Would love to have a go in one...something I very much doubt will happen.

Hee Hee. Me too.

Not sure we reached any new conclusions there but it gave the old grey matter a workout. I need another beer.

[slparry]

You can all have a go in mine when I win the lottery

[Corvus]

You can all have a go in mine when I win the lottery

If I'm honest, in spite of the impression I might give, I'm perfectly happy on a little bike down a decent backroad. Very happy in fact.

I'll still blag a drive in the veyron though.

[Corvus]

Tune a car engine to 100bhp / litre and see what that does to economy.

Then try taking it to 180bhp / litre, as we get from a modern supersport bike.

If you put a 180bhp 1litre engine in a car, the economy would be awful.

(there are some really shocking figures coming back on the Ford 1litre 'ecoboost' with 125bhp - with many owners reporting 35mpg averages)

That seems to ring true to me.

[Corvus]

Just to change tack slightly, I read earlier (on parliament.uk) that "the tax disc was introduced in 1920, and the tax charged at a graduated rate of £1 per horsepower".
Interesting. I wonder how that would go down today?
http://www.publications.parliament.uk/p ... /90705.htm

Not bad, if we apply the horsepower/litre figures of the day. I think they categorised a one litre engine as 10hp or some such?



Ps) sorry for the number of posts on here. I didn't read the thread when it first appeared and there's some interesting and very debatable aspects arisen. I'm catching up!

[Corvus]

Corvus said: "Bikes, even with their lack of recent technology as applied to car engines with the aim of improving mpg, are more fuel efficient. Surely they always will be?"


Twinspark said: "What does a Boxer do? - 40mpg on average? - my BMW 120d is doing 50mpg with nearly twice the BHP and 3 extra seats."

My little theory is looking shakey, to say the least, based on that evidence.

Am I simply wrong?