Why are RPMs shown rather than torque?

[psycho22]

I reckon I can change gear in around a second, it's not that hard. Just back off the throttle at 18,000RPM, slam it into gear and nail the throttles straight away.

I'd say thats about average for most bikers.

Besides unless you're racing on the track or going down the drag strip it's not going to make any difference whether you change gear in 1 second or .5 of a second.

[tigertim20]

May sound like a damn silly question on it's own but the real question is why do both cars and bikes show RPMs as a read-out as opposed to torque?

Most lay people, such as myself, look to RPM as an indicator of "fast" (as in higher means "faster" in both terms of acceleration and cruising speed - when gear ratio taken into account). However, having just read a thread from another forum of optimum places to change up (in RPM terms) it seems to strongly allude that change up points are best selected for the points where torque is strongest (calculated both in the current gear and the next gear).

So, if acceleration is best judged by torque, why do bikes/ cars not have a torque read-out (either in addition to, or instead of, RPMs)?

Are bikes and cars just working on old technology instrumentation read-outs? And, if a dyno machine can measure torque at any point, why can't a modern automobile?

Lots of questions but I am genuinely interested in the reason behind why torque is not displayed.

tourque isnt a necessary readout. you can feel how much the thing is pulling when you wind her out.
rpm on the other hand, well its certainly handy to know where red line is, and how much you are stressing the engine

[LBD]

Right, to answer the first question...Unlike RPM, too mush torque does not make a hand grenade of your motor.

Peak power is just below the red lineusually but peak torque is often 50 to 70% of the max RPM.

Power does not accelerate, torque does.

Re screwing the ring off it for fastest acceleration....it is not the max engine torque that counts, it is the maximum torque at the gearbox output shaft or rear wheel so what you need to do is...

1) Get the engine torque curve for your bike
2) get a list of the gear box ratios for your bike
3) Get MS XL and learn how to make graphs
4) Column 1, list the torque values at 50 rpm increments to the red line
5) Column 2, multiply the engine torque values by the 1st gear ratio
6) Column 3, Multiply the engine torque values by the 2nd gear ratios
7) So on for 3rd, 4th, 5th and 6th.
8) Then make a pretty graph of all the torque values after the gearbox ratios

Still with me?

9) now if you study the graphs you will note that after peak torque is reached, it then begins to drop off.

10) at some point the graph of the dropping of value meets the rising torque value of the next gear up....that is the optimum gear shift point, between those two gears.

11) do this for 1st to 2nd, 2nd to 3rd, 3rd to 4th ect. you will find the optimum shift up point will shift slightly for each.

And that is how you calculate the fastest acceleration shift points.

[avgas]

This all lead me onto re-examining what the point of the tacho was. It isn't for acceleration purposes that is for sure, hence why a torque gauge would be useful, in addition to the tacho gauge.

Errr actually it is.
You are looking at the result, and expecting the equation to equal it. e.g. x = y
If you were given a torque gauge, you understand it is a curve right......so how would you know if you had hit the peak for that particular gear?
That is where the rev counter comes in - as you ride more, you learn more about where the sweet spots are according to engine revs. These may not be the actual peak torque points - but ranges as to where to ride in each gear. e.g. In the street triple you mention below 1st would have a ideal range of say 1,000-4,000, 2nd 2,000-5,000.....
say we call each one of these ranges a1, a2, a3..... for each gear. Now using this tool (rev counter) you have an appropriate time to change gears.
y = ax (where a can be substituted for what ever gear you in).
Where as trying to do this directly via torque gauge will be like playing a round of blackjack.....how high do you go before changing. Change to low and you never get peak torque, however if you go to high - you break 21 and sorry you missed the peak.

Ok the fact I just had to explain to you how to ride a bike has convinced me this is too hard for you......get a scooter. Most people figure this out in the first week on a bike.

[kinger]

....it's not going to make any difference whether you change gear in 1 second or .5 of a second.

It can make a huge difference if you're carrying a pillion.
Clutchless changes aren't difficult, have a learn.

[marty]

a torque-o-meter would be simple to create.

a shaft that twists under load with 2 pickups - 1 at the driven end, one at the drive end. the split between the two pickups measures the torque output.

[BASS-TREBLE]

Pretty sure I read somewhere that the new six cylinder 1600 BMW has an available torque display instead of of a tacho.

Perhaps you could Google it and see what they say?

I too have read that and I'd imagine it makes cruising on them even easier since you know exactly where to change without thinking about it

[nadroj]

Concentrate on the road not the guages. Experience will tell you when to change gears thru sound and feel.

[Bass]

a torque-o-meter would be simple to create.

a shaft that twists under load with 2 pickups - 1 at the driven end, one at the drive end. the split between the two pickups measures the torque output.

What you say is true and strain gauges would measure the twist very well. However, where are you going to mount it in the drive train so that it doesn't have to go round and round?
The signals that the measuring devices produce are very small so that commutators/slip rings etc screw them up completely.

[imdying]

Maybe because using too much of your torque won't destory the motor, but too many RPMs will?

[psycho22]

It can make a huge difference if you're carrying a pillion.
Clutchless changes aren't difficult, have a learn.

I ride with a pillion a lot and I actually happen to use clutchless changes too.

However a quick gear change, clutchless or not, doesn't necessarily make it a smooth one.

But anyway I was talking in terms of acceleration rather than smoothness.

[marty]

What you say is true and strain gauges would measure the twist very well. However, where are you going to mount it in the drive train so that it doesn't have to go round and round?
The signals that the measuring devices produce are very small so that commutators/slip rings etc screw them up completely.

luckily, I'm just an ideas man - someone else can figure out how to make it work

[schrodingers cat]

a torque-o-meter would be simple to create.

a shaft that twists under load with 2 pickups - 1 at the driven end, one at the drive end. the split between the two pickups measures the torque output.

Close but no cigar. Ford (MoCo) developed a driveshaft steel in the late 90's which gave an altered resistance figure dependant on the amount of force twisting it. It did required a trasmitter and reciever but that sort of electronics is ho-hum these days.
Lots of cool tricks you can do with that technology i.e Measure input shaft force and output shaft force, apply gearing mutiplication math and then weep as you see how inefficient the gearbag is

Elegant engineering also just to actually measure what interests you rather than apply endless bullshit to the equation.

Gear shifting: on a sequential gearbox a slow shift would be 0.2 sec.
0.1 if you were trying hard, 0.15 sec without much thought

If using an ignition cut flat shift, typical cut times are around 11 thousanths of a second. The 'dog' only needs the force off it momentarily to disengage. Re-engaging sorts itself out as the there are a few degrees rotation availible between front face and back face engagement. The undercut does the rest.

Torque - o -meter
Once you know the torque curves absolutes become irrelevant as variances due to external factors is less than 3%. It is sufficient to have a target RPM plus or minus 100 rpm.
Unless RPM is measured from a crank angle sensor it is at best a guide anyhoo.


The theory is all very wonderful for cluttering up the interweb. What you you really want to achieve and how much are you prepared to spend to learn it?

As for me? I'll just be riding mine.

[LBD]

On an electronic engine torque can be calculated electronically ie:
X amount of Torque can be produced at a given RPM, the torque being produced will be a calclation of actual fuel injector pulse width divided by maximum pulse width available at that same RPM, you then would know what % of the available torque you are using

[schrodingers cat]

On an electronic engine torque can be calculated electronically ie:
X amount of Torque can be produced at a given RPM, the torque being produced will be a calclation of actual fuel injector pulse width divided by maximum pulse width available at that same RPM, you then would know APPROXIMATLY what % of the available torque you are using

Fixed that for you. Engineering requires precise language