Slow Riding - Torque and/or Power @RPM explained

Hi,

I would like someone to explain in plain english the use of the RPM of the power and torque while slow riding, riding in town, cruising on the A-road or motorway and/or riding fast.

Here are my spec for my SV650
Power 73.4 hp (54.7 kW) @ 8800 rpm
Torque 47.2 lbf·ft (64.0 N·m) @ 7000 rpm

1. When should I consider remaining under even though it requires changing gear or way below:
- 8800 rpm
- 7000 rpm

2. When should I consider keeping it exactly at:
- 8800 rpm
- 7000 rpm

3. When should I consider having it over e.g. while riding fast:
- 8800 rpm
- 7000 rpm

Thanks.

[Bibio]

none of the above, you are in the right gear and revs when you feel you are. there is no hard and fast rule. only thing i would say is dont 'labour' the engine which is pretty much keep it on above 4k revs but again its not a hard and fast rule.

dont look at the revcounter learn to listen/feel what the engine/bike is doing.

[Red Herring]

Different engine designs/configurations make their "power" in different ways.

Torque is the amount of turning force that the engine has, BHP is the measure of the total force that the engine produces.

I know this sounds a bit like the same thing but look at it this way. If an eighteen stone bloke came up to you and pushed you hard with both hands you would probably fall over, and that's because he's got a lot of weight behind the push. Now if a ten stone bloke came up to you and pushed you once you would move a bit, but if he immediately pushed you again, then again, and again you would keep moving and maybe go further than the one push from the big guy.... So the big guy has lots of torque, but the small guy may actually have more power, ie: he has moved you further.

Translating this to bikes each time a piston goes down the bore it produces torque, the more often it goes up and down adds up to the power. Now I know you are probably asking why we can't have the big bloke pushing us along repeatedly. Unfortunately big pistons (325cc each in the case of an SV) weigh more than small pistons and the more weight you have to stop and start the stronger (and heavier) everything else has to be, which is why an SV engine will generally only rev to 11k where a 600cc four cylinder bike (each piston only 150cc) will often go over 16k and therefore ultimately produce more "power".

Now add to this that there is an ideal rate at which a particular engine design can burn the fuel mixture that has been put into it. The more efficient the burn the more force available to push the piston down the bore, and the more torque produced. This is why an engine produces it's best torque figure at a particular RPM.

The best BHP (or power) is at a different engine speed because it also takes into account how often that torque is being produced so even though it is producing less torque at the higher RPM it is doing it often enough to do more work.....

A good engine has a nice flat torque curve, ie: it produces a decent amount of torque over a wide RPM range. Twins, like the SV, are good at this. It makes them easy to ride as you don't have to keep changing gear all the time. They are a good compromise between the big bloke who will shove you once and then have to regain his footing before being able to do it again (a single cylinder bike), and the little guy who you have to keep working hard to get you anywhere (the 600cc sports bike).

If you have read this far then I am truly impressed, like Bibio said just ride your bike and keep it somewhere in the middle of the rev range where it will be comfortable and you are getting the best from it.

[ChrisCurvyS]

That's an excellent explanation of a notoriously confusing area - as simple as it can be. Thanks RH.

Prob just worth adding that the smoothness of an engine and its tractability doesn't always correlate with layout and capacity - it's often down to that particular engine's design.

My Fazer 1000 has a straightforward four cylinder layout, is a heavy bike and doesn't have a huge capacity but is quite happy pulling from much lower RPMs than the SV, mainly because of the peculiarities of its design.

[aesmith]

It's worth adding that those figures, max torque at 7000 and max power at 8800, are for full throttle. At part throttle the maximum outputs will be at lower revs.

[Mauler]

Nice explanation, Red!

Originally Posted by laperlenoire

Hi,

I would like someone to explain in plain english the use of the RPM of the power and torque while slow riding, riding in town, cruising on the A-road or motorway and/or riding fast.

...
Thanks.

If you ride it flat out constantly you won't need to worry.

Originally Posted by Mauler

Nice explanation, Red!

+1

Originally Posted by laperlenoire

Hi,

I would like someone to explain in plain english the use of the RPM of the power and torque while slow riding, riding in town, cruising on the A-road or motorway and/or riding fast.

Here are my spec for my SV650
Power 73.4 hp (54.7 kW) @ 8800 rpm
Torque 47.2 lbf·ft (64.0 N·m) @ 7000 rpm

1. When should I consider remaining under even though it requires changing gear or way below:
- 8800 rpm
- 7000 rpm

2. When should I consider keeping it exactly at:
- 8800 rpm
- 7000 rpm

3. When should I consider having it over e.g. while riding fast:
- 8800 rpm
- 7000 rpm

Thanks.

Riding slow and around town, the SV650 is very happy at 3500 to 4000 rpm.
A-roads and motorways are nicely done in high gear. My SV runs about 5000 rpm at 70 mph and doesn't often need a downshift for passing at that rpm.
Riding hard on backroads and in the mountains, I generally run 4-7000 rpms, sometimes revving up to 8000 or a bit higher if I'm on a long fast uphill section.
On the track, I mostly shift at 8500-9000, only using the rest of the rpms when there's a long enough straight to need it in 6th gear, or when I need it to prevent shifting in awkward places on the track.
It's a very nice flexible engine with linear power delivery.
If you keep it in the meat of the powerband all the time, you'll use lots of fuel, wear out your tires (tyres) very quickly, annoy the town folk and accelerate engine wear. Probably attract the attention of the constables too.

[ophic]

Someone calculated the optimum change point for maximum acceleration on the SV a few years ago. Whilst I can't recall the exact results, the simple conclusion was, redline it in every gear.