Hi all,
I'm completely new to biking, and to motor vehicles in general. I've found several web pages talking about different kinds of bikes (sports, tourers, etc), but what's still confusing me is the numbers - can someone explain what the difference (as in, when you get it on the road, what is different) between, say, a 125cc, a 600cc and a 1200cc bike is? Riding a 125 at the moment I appreciate that it's got a top speed presumably cos the engines small, but is more cc = more speed? From what I've read on here a 600cc bike is plenty big enough to go out and do scary speeds on, so if this is the case I'm puzzled why bikes any bigger cc than that are made. As I say, I am completely new to this so I'm sure I may have misunderstood what I've read already.
Whilst we're at it, can you explain what is meant by "low down torque"?

If this is all reinventing the wheel plz do point me in the right web page direction.

Ta!

Hey matey... welcome to the forums!

I'm not too hot on the science of all of this, but my basic understanding is this:

CC is cubic capacity, this is quite simply the size of your engine. The bigger the CC's the more fuel can be pushed through your cylinders and the more power can be thrown out

Torque is basically how well a bike 'pulls'. I.e. you twist the throttle, the higher the torque the more your pushed forward. This also depends a lot on the gears and rev's your at, hence most specs will say measure it by a certain benchmark.

When we refer to 'low down torque' we are saying the amount of power lower down in the rev range. i.e. some sportsbikes (i.e. an R1) have all their power in the higher rev range, meaning you have to keep the bike revved to get the benefits of its power... some other bikes (i.e. my thundercat) will pull you forward even at lower revs.

As far as i know, the bhp is a measure of the power the engine alone will kick out... before it gets applied to the gear box etc. this is why you often hear people say its got a certain bhp 'at the back wheel' indicating the true power of a bike after the power has been applied.

This is my understanding and i am no means anything close to a mechanic.... its probably all completely wrong

For my twopenceworth :

CC is the cubic capacity of the engine.

BHP and Torque are insignificant 'Top Gear' phrases that mean nothing as long as you enjoy your bike

They are specifically designed for Power Rangers to discuss when they have ridden 10 miles to a cafe on a sunny Sunday afternoon

G2M is close, CC is actually cubic centimetres, so 500cc is half a litre, 1000cc is a litre.

Because of how an engine works, it makes you go faster in "pulses" (These pulses happen so fast that we cant feel them, but they are still there nevertheless).

Torque is a measure of how "strong" each pulse is, RPM is basically how many pulses there are in a certain amounty of time. and Power is these 2 numbers multiplied together.

Basically if you think of a ball sitting on a table, you could give it one big push and it would roll a certain distance, but you could also give lots of little pushes and it would roll the same distance. So the power in both cases is the same but one case its done with one big push (Large torque, Low RPM) and the other case is lots of little pushes (Low Torque, High RPM)

Now you could have 2 engines that both produce the same power, one is a big torquey low down revving engine, the other is a high RPM screamer. On the roads you will find the low down torquey engine easier to use, it doesnt matter where you are in the rev range, the torque is there for when you want to accelerate. The High RPM screamer on the other hand, you need to be a lot mare careful and change gears more often to keep it within the rev range that the power is produced, otherwise you open the throttle and nothing happens.

So looking at that, you might be wondering why you would want an engine that is a high RPM screamer, rather than a low down torquey engine that will be easier to use ?

Well since power is a torque x RPM, the easiest way to increase total power is to increase RPM. Due to the way engines work, as you increase RPM (how fast the bits are moving) you tend to reduce the torque that it can produce so thats why you get either high RPM screamer, or low down torquey grunter, you dont really get both.

So basically if you want the most power you can have out of an engine size, you have to have a high RPM screamer, if you want it more usuable then you have to sacrifice total power for more torque and more imporantly more low down torque.

It also means you might have 2 bikes, one is a 600cc and the other a litre bike. The 600cc might produce more total power than the litre but it only produces it above 10,000RPM, the litre bike might produce less total power, but its torque will be much more and will start much earlier, maybes even as low as 2000RPM.

On the road the litre bike will accelerate far quicker and be far easier to use, while the 600 will need a lot of work to keep it in the correct gear so that the power is available when needed. However the 600 will still have more power (so probably a higher top speed) despite being almost half the engine size.

BHP is just a measure of an engines power normally taken flat out, so on the road this figure is not too important.

Torque is a measure as described previously of how strong it is Ie if you have lots of low down torque the slightest wiff of throttle will have you wipping of down the road with out having to thrash the thing or change gear a lot.

Different sizes and styles of engine can give you a different power delivery..and yes as a very rough rule of thumb bigger is faster.... but not always

People want 600cc bikes plus because they want more acceleration..top speed might be similar on a 600cc as an 1200cc but it's how fast you get there that counts

Thanks for the info guys. The rpm/torque stuff makes sense, it rings vague bells from my a-level physics days
So would I be right in saying that you could have a 600cc bike that is low-down torquey (i keep thinking of fawlty towers when I read that ), and then a different 600cc bike that has all the power in high revs?
I'm trying to get it clear in my mind cos I keep looking at bikes that I might like to get once I do my test, but the whole cc business has perplexed me. I've read the other threads about newbies buying sporty bikes - but is it the fact they're sporty rather than they're 600cc that makes it easier to get such high speeds on them?
I'm not that interested in buying a sports bike, more something that I can get some serious miles in comfort on - does that in itself define the kind of cc capacity that I'm looking for, or does it depend on each model what it's defined for?
Cheers!
Robin.

Well i'll give you 3 actual bike examples which might make it clearer (I wouldnt say this was the way to choose your bike, just trying to explain it so you might understand the differences better), all are 600cc's so all have the exact same engine size

Suzuki Bandit 600
Kawasaki ZZR 600
Yamaha R6

The bandit is the "low down torquey" one out of these three and the manufacturers specs give
Power 77.50 HP (56.6 kW)) @ 10500 RPM
Torque 54.10 Nm (5.5 kgf-m or 39.9 ft.lbs) @ 9500 RPM

The ZZR is middle, so its kinda half way between the other two with manufacturer specs of
Power 98.00 HP (71.5 kW)) @ 12000 RPM
Torque 61.00 Nm (6.2 kgf-m or 45.0 ft.lbs) @ 9500 RPM

The R6 is the most focused high revving out of the 3 and has manufacturers specifications of
Power 120.00 HP (87.6 kW)) @ 13000 RPM
Torque: 68.00 Nm (6.9 kgf-m or 50.2 ft.lbs) @ 11500 RPM

Now all 3 of those bikes are japanese 4 cylinder 600cc bikes, so they have the same number of cylinders and the same size of cylinders, the only real difference is how tuned the engine is. If you look at the total power produced by each engine you will see as you go down the list it increases but also the RPM at which its produced is also higher.

What this doesnt show of course is the torque curve which is why its so important to test ride and not just go from manufacturers specification. By this I mean that althought the R6's peak torque looks higher than the bandit, you will find that through the rest of the rev range and especially low down in the rev range, the bandit has higher torque than the R6.

What that equates to in real life is if you are just trundling along at say 4000 revs in top gear and open the throttle to overtake - the bandit will actually accelerate quicker, the R6 you would have to drop down a few gears to get the RPM into that peak torque/power figure and THEN it would leave the bandit in its dust.

The most important thing is to try a few bikes and see what you prefer. Some like the ease of use of soemthing like the bandit, while others actually like the "work" required in keeping the engine in peak revs.

Lol.... very well put Finn

Bit like a car has a 1.2 engine in other words its a 1200cc.

Hi

Finn could not put it any better....


I used to have a Bandit 600 and changed to a Bandit 1200...

the B6 has about 78Hp and the B12 about 100Hp.... only about 25% more,
and not that much more top speed...... for twice the size of the engine

the difference is,, it pulls from just above 2000rpm,,,,,,and it makes no difference if you got a pillion or not,, it just pulls like a tractor...

Not saying it is best ,,, it depends on what you like,

but it suits my ridding better......

Not really much to add to that lol

But very good question!!! I reckon there are quite few people out there who just nod nd agree when these things are discussed, but dont really understand. Good on ya mate!

Nice one Finn!!!!