The 20 - 80 usable RPM rule

[Flyingpony]

So just what is the safe usable RPM range of an engine, this has always puzzled me. Some people say it's safe to go up to the red-line, but personally, the red-line is something I'd like to err on the side of caution and stay away from.

With that in mind, it turns out that keeping the engine between the 20-80% of the full rev range is best for the engine. Straying below the 20% mark can cause the engine to lug and struggle {note: higher gears will require higher percentages} while exceeding the 80% mark is placing it near the red-line zone and expensive damage zone.

Monitored my own riding habit recently, it turns out that when commuting it stays within the percentage band range 35-50%, and when out on the motorway 55-75% percentage range.

Obviously there are exceptions to this rule. Personally the 80% is one that I don't intentionally break but the 20% rule I will when stuck in traffic at snails pace in first or second gear, provided she's not stressed.

So what do you all think about the 20-80% theory?

[jonbuoy]

Depends I the type of engine I guess. No sense in flogging a VTWIN to the red line, in line fours love a good thrashing.

[Swoop]

I think V-Fours like a bit of welly from time to time as well...

[Nutter34]

The red-line is the manufacturers safe thrash limit. When they design engines, they run them to destruction and then add a percentage for reliability and longevity, which is where the red-line comes into play. You'll find that often the last thousand rpm is over-run anyway on most engines, they stop making power by then.... Have a look at most dyno graphs....
Then, most engines have limiters too, so if you do exceed the red-line, it'll cut the engine....
I agree riding lower revs may not be beneficial but thrash it like you stole it....

And when it comes to two-strokes, their power is determined by porting and pipes and a few other things. They operate best within a certain rpm set by the above mentioned parameters. If you change too early, you are actually riding the bike inefficiently and loading the engine more than it would be if you kept it in the power bands...
I suppose that theory applies to fours as well, coming on the cam it was called, I think...

[onearmedbandit]

With rev limiters on most modern bikes the chances of doing damage via high revs is pretty low, unless you drop it down too many gears. On the road I hardly ever see red-line (1st gear is enough to lose your license) but on the track I'll hit it often, even bounced off the limiter once or twice.

[Pwalo]

Horses for courses old chum. Depends on the layout of your motor.

Traditionally singles and twins tend to have a lower rev ceiling than triples and fours. It's all to do with piston speeds, piston stroke vs bore,reciprocating masses, and a few other factors. There are quite a few articles available which outline the different characteristics of differing engine configurations.

A four will always be able to be revved higher than a single or twin of the corresponding engine size, and needs to to produce it's power.

For a single or twin I reckon 40-80 rule sounds pretty reasonable, but with a four you're probably be looking at 60-90. Nothing worse than labouring an engine.

Running your FXR at it's redline probably isn't too flash an idea.

[bungbung]

That will depend on the specific motor and usage. It is pointless running up to redline on some applications. For the FXR you'll need to look at a dyno chart.

Bearing in mind that a) you'll need all of the power from a fxr b) you won't be running at full revs a high percentage of the time, so I wouldn't be so concerned about blowing it up.

Its a sympathy thing, some motors don't sound happy at the upper end of their range. I had a zxr250 that I felt bad about revving past 14k.

[Edbear]

The 20-80% guide is generally a good one for longevity, but my old girl, (bike not wife...), doesn't mind the odd thrashing at all, in fact I find I have to keep an eye on the revs as she just goes hard to the redline and doesn't seem to die away...

It certainly gets more urgency once it gets to 7k and from 9k it's pulling like a...a... shall we say proverbial...? Redline is 12k on mine.

Most posts here are pretty on the money. Some motors are more fragile than others, the air-oil cooled GSX's are almost indestructible. A modern bike is designed to rev and I haven't heard of anyone blowing one up lately, even racing them.

[inlinefour]

The redline is a fun place to be, however it requires a rebuild before the engine dies draMatically. As for the modern sport dunno, I'm usually holding on and watching where I'm going to have any idea A. what revs the motor is dong or B. what speed I'm doing. The DRZ does not have a rev counter, but I think Ive ridden it through the redline a couple of times, happens when you try to keep up with sportsbikes. Have a mx bike that I'm sure is at its best up by the redline. Remember, powerband can make you horney, does it for me, long time...

[kickingzebra]

I've not heard of an FXR blowing its lolly yet. They are pretty basic engine, and pretty bullet proof.
Hence, if it ain't on the redline, you aren't riding it hard enough!!
Mine copped a fair thrashing from just before the end of the run in period, till 30,000 kms later, when it had a run in of a different sort, and I damn near swear it was going better the older it got, and the harder I rode it. Provided services are kept up, and oil is nice and fresh, I doubt redlining it will damage it.

[bobsmith]

Hmmm strange... when I had my fxr... I almost never went below 5000rpm... (so that would be 45%)???

I figure with a small engine like that right up to the red line shouldn't do any damage... besides on open road you're crusing about 9-10k rpm anyway...

[Sketchy_Racer]

I've not heard of an FXR blowing its lolly yet. They are pretty basic engine, and pretty bullet proof.
Hence, if it ain't on the redline, you aren't riding it hard enough!!
Mine copped a fair thrashing from just before the end of the run in period, till 30,000 kms later, when it had a run in of a different sort, and I damn near swear it was going better the older it got, and the harder I rode it. Provided services are kept up, and oil is nice and fresh, I doubt redlining it will damage it.

Haha you think you thrashed you FXR....

My FXR has lived half its life on the rev limiter.....

Has been cart wheeled twice.

Lowsided so many times i cnat remember

Has had one oil change in its life. and the old was replaced with second hand oil.

And it still damn goes and stil goes damn hard for a 150 fourstroke!!

[Ixion]

I prefer the older rule, double 30/70. Keep both rpm and throttle bertwen one and two thirds.

The one third minimum throttle obviously must be bypassed in traffic. But running on a very small throyttle opening is not only inefficient it can be bad for an engine, especially a two smoker.

[Lou Girardin]

The manufacturers give you a redline and a warranty. They're not expecting them to go pop within those limits.
Then you've got proddie race bikes that live at the redline or more for extended periods and still live.

[Ixion]

Well, yes. But some of us do rather want the bike to last rather longer than the warranty. A LOT longer in fact.

EDIT: BTW did I ever tell you about my grandfather's axe?