Speedo dial with MPH as main and KPH secondary

[crxvtec]

Good point Ted - and this increase in pressure will also decrease the contact patch.

not really - pump your tyre from 31 psi to 31.3 psi and measure the difference... i am a big fan of just trying stuff out hands on.

The human body isn't sensitive enough to pick it up - but there will be a difference.

 

[tedg]

The human body isn't sensitive enough to pick it up - but there will be a difference.

Feel free to use a ruler, calipers, or perhaps even your speedometer

 

[crxvtec]

OK so let's test that by extending the concept a bit. Take a low-powered car with say 50bhp, average aerodynamics and narrow tyres. Say it's geared to 120mph at 6000rpm in top. Drive it flat out. Are you saying that the engine will rev to 6000rpm in top, with the wheels 'slipping' and the clutch slipping, and the car does say 90mph because that's as fast as it'll go, but it still pulls 6000rpm in top?

No I'm not saying that at all. Because a 50bhp car hasn't enough torque to pull 120mph so the car might make 90mph but the engine cannot keep up so you'd not be able to see the effects of what we've been discussing on such a low powered car.

But let's take my mate's old Pug 205GTi turbo technics, it's a 200bhp car with torque aplenty. Let's drive it flat out on a road: say it'll pull around 120mph at around 6000rpm in 5th. Now, if we gave the car some slicks, potentially it might pull 122mph at the same engine speed. And if we had slicks and put the car on a track, it might pull 123mph at 6000rpm. And we could eke an extra bit of speed out of it if we gave it some more downforce - e.g. body pan, faired in wheels.

 

[crxvtec]

The human body isn't sensitive enough to pick it up - but there will be a difference.

Feel free to use a ruler, calipers, or perhaps even your speedometer

All of these won't pick up the difference.

 

[tedg]

on your same website there is a link for speed vs. RPM... exactly what we are looking for 8)

here:
http://wahiduddin.net/race/speedrpm.htm

And guess what! the plots are linear :roll:

Not only that they provide calculation:

http://wahiduddin.net/calc/calc_speed_rpm.htm

Which is a linear calculation...... wow, they don't even mention the areodynamics adjusting the final drive/gears ratios. Perhaps you should email them?

But they do mention this about tyres:

There is a potential for error in these calculations with bias-belted tires due to centrifugal force expansion of the tire at high speeds, but that effect is generally negligible for radial-ply tires due to the circumferential belts used in their construction. To get accurate results, racers using bias-ply tires should check with their tire supplier to determine how much the tire radius will change at various speeds.

don't think many of us are running bias-plys

 

[crxvtec]

Good...now if the line on the graph was out by 1-2mph, do you think the line would look any less linear? That graph's a bad example because it's not fine enough (pixel resolution prevents us from seeing the slight variation we're looking for at the top end of the 5th gear line)

Centrifugal force expansion is completely different to increased pressure in the tyre...centrifugal force expansion by definition is related to wheel speed whereas increased pressure in the tyre is due to heat (as the wheel/tyre gets hotter, the air in the tyre will get hotter, thereby exerting greater pressure.

Also on the same site:
The available thrust from the engine is opposed by the rolling friction of the tires and bearings, the aerodynamic forces acting on the car, the mass (weight) of the car and the rotational inertia of the engine, drivetrain and wheels. Therefore, if you instrumented the car with a g meter, you would find that the car does not accelerate as much as the plot above shows, since the effects of the rolling friction, aerodynamics and rotational inertia were not accounted for.

Happy?

 

[crxvtec]

Look here:
http://www.cartestsoftware.com/cartest4.5/

Let me draw your attention to:
Display Power Loss Component Curves-

Plots losses from aerodynamics, tires, transmission, and road grade (if any) versus road speed.
Display Drive Power in Each Gear-

Plots the drive wheel force at the road in each gear versus road speed.
Determines optimum shift points.
Superimposed plot of total drive losses estimates top speed.
Display Speeds in Gears-

Plot theoretical road speed versus engine rpm in each gear.

Pic to follow (though feel free to use the software yourselves - they've got data for a DC2R)[/img]

 

[Evs]

It is impossible to achieve perfect transfer of kinetic energy in the real world. There's always a loss, and that loss increases with velocity.

Correct but it's not manifest in the way you are saying. By your argument, any system with gear teeth would not suffer frictional losses, but they do.

So your flywheel's spinning because you're engine's spinning, at say, 900rpm (idling speed). Your car is facing upward on an incline. By maintaining 900rpm, you stop your car rolling back. Why? because you can gauge at what point you can transfer just enough kinetic energy from your fliwheel to your clutch to balance the friction. By your argument, you'd always have perfect friction and a clutch would be like an on/off switch, either connected and giving a perfect transfer or unconnected and giving zero transfer. This is simply untrue.

No, what is happening there is that you're applying pressure to meter the amount of friction between the two clutch plates such that you hold them at slipping point. I'm not arguing that it's an on/off switch at all, just that a healthy clutch won't slip in the cirumstances we started with, and neither will the tyres.

Pressure of friction materials being pushed together does have an effect on the transfer of energy. Why do ice rally cars run narrow tyres? It's to increase friction by increasing pressure to the road. If they ran wide tyres, they'd lose friction and sit spinning wheels and not getting anywhere.

Ice rally cars run spikes, there's so little friction with any width of tyre that they'd just wheelspin anyway, because the properties of the surface. Completely irrelevant to the argument anyway. If we were talking about trying to do 150mph on ice then you might have a point, but we're not.

 

[tedg]

Good...now if the line on the graph was out by 1-2mph, do you think the line would look any less linear? That graph's a bad example because it's not fine enough (pixel resolution prevents us from seeing the slight variation we're looking for at the top end of the 5th gear line)

At this point I just can’t be bothered. Since I said it was a linear calculation (read the website yourself FFS) then it does not matter how much resolution you have, it IS a straight line.

At this point I am not sure if you are now just being augmentative as a matter of purpose, or that you have REALLY missed the point ..... or both....

Either way I will give up now, I feel like I am hitting my head against a really thick wall ](*,)

 

[Evs]

At this point I just can’t be bothered. Since I said it was a linear calculation (read the website yourself FFS) then it does not matter how much resolution you have, it IS a straight line.

At this point I am not sure if you are now just being augmentative as a matter of purpose, or that you have REALLY missed the point ..... or both....

Either way I will give up now, I feel like I am hitting my head against a really thick wall ](*,)

Totally agree mate. He has a partial understanding but has made incorrect assumptions and cited examples to support his arguments that are actually irrelevant (eg the Merc LM car, ice rally car, clutch balancing), and does not understand the basic physics of forces, acceleration and motion.

However he's convinced he's right so it's probably a waste of time arguing. I found it an interesting challenge for a while but now I've also come to the conclusion that I'm banging my head against a wall.

 

[crxvtec]

It is impossible to achieve perfect transfer of kinetic energy in the real world. There's always a loss, and that loss increases with velocity.

Correct but it's not manifest in the way you are saying. By your argument, any system with gear teeth would not suffer frictional losses, but they do.
Absolute breeze. Read what I said: "It is impossible to achieve perfect transfer of kinetic energy" gear teeth systems included. We are agreeing here, not disagreeing, however you've not been able to tell me how it IS manifested.

So your flywheel's spinning because you're engine's spinning, at say, 900rpm (idling speed). Your car is facing upward on an incline. By maintaining 900rpm, you stop your car rolling back. Why? because you can gauge at what point you can transfer just enough kinetic energy from your fliwheel to your clutch to balance the friction. By your argument, you'd always have perfect friction and a clutch would be like an on/off switch, either connected and giving a perfect transfer or unconnected and giving zero transfer. This is simply untrue.

No, what is happening there is that you're applying pressure to meter the amount of friction between the two clutch plates such that you hold them at slipping point. I'm not arguing that it's an on/off switch at all, just that a healthy clutch won't slip in the cirumstances we started with, and neither will the tyres.
First part is correct - that's what I said. But if you say that a healthy clutch won't slip in the circumstances, then you're implying there's perfect transfer of kinetic energy. There isn't, because we know that's not possible.

Pressure of friction materials being pushed together does have an effect on the transfer of energy. Why do ice rally cars run narrow tyres? It's to increase friction by increasing pressure to the road. If they ran wide tyres, they'd lose friction and sit spinning wheels and not getting anywhere.

Ice rally cars run spikes, there's so little friction with any width of tyre that they'd just wheelspin anyway, because the properties of the surface. Completely irrelevant to the argument anyway. If we were talking about trying to do 150mph on ice then you might have a point, but we're not.

Spikes aside, my point is to illustrate why they run narrow tyres as opposed to wide ones - to increase pressure to the road (the greater the pressure to the ice, giving the spikes a better chance of connecting with the ice, thus increasing friction)

Feel free to give up, but stating I have a limited understanding of physics doesn't resolve the debate.

 

[crxvtec]

Good...now if the line on the graph was out by 1-2mph, do you think the line would look any less linear? That graph's a bad example because it's not fine enough (pixel resolution prevents us from seeing the slight variation we're looking for at the top end of the 5th gear line)

At this point I just can’t be bothered. Since I said it was a linear calculation (read the website yourself FFS) then it does not matter how much resolution you have, it IS a straight line.

At this point I am not sure if you are now just being augmentative as a matter of purpose, or that you have REALLY missed the point ..... or both....

Either way I will give up now, I feel like I am hitting my head against a really thick wall ](*,)

Read the disclaimer off the same site - it's only linear cos they've not accounted for losses...I posted it for you but you've chosen not to read it.

 

[Evs]

Feel free to give up, but stating I have a limited understanding of physics doesn't resolve the debate.

My point is that we're not having a debate because your understanding is so limited - examples of clutch slip, transmission losses on rollers, cars with flat bottoms taking off over crests at 200mph, spikes on ice are all completely irrelevant. I frankly don't have the time it would take to go through all the basics and get you to understand. Just out of interest, what level of education in physics do you have?

Getting back to the point: You are stating that an average car will generate enough front-end lift to reduce the pressure on the tyres and the friction between the tyres and the road to the point at which the wheels will spin. And yet this car will presumably still be able to steer, using the same wheels that are spinning.

That is quite simply rubbish. You have not presented a logical argument for why it would happen, and it is not supported by experience.

 

[Suped]

you lot should really work for the governing body of scientific know-hows.!!!!

All this talk of measuring this, physic relating matters...?? Gordon Bennett, someone bring this lot a cuppa tea and a biscuit. :lol:

 

[crxvtec]

Feel free to give up, but stating I have a limited understanding of physics doesn't resolve the debate.

My point is that we're not having a debate because your understanding is so limited - examples of clutch slip, transmission losses on rollers, cars with flat bottoms taking off over crests at 200mph, spikes on ice are all completely irrelevant. I frankly don't have the time it would take to go through all the basics and get you to understand. Just out of interest, what level of education in physics do you have?

Getting back to the point: You are stating that an average car will generate enough front-end lift to reduce the pressure on the tyres and the friction between the tyres and the road to the point at which the wheels will spin. And yet this car will presumably still be able to steer, using the same wheels that are spinning.

That is quite simply rubbish. You have not presented a logical argument for why it would happen, and it is not supported by experience.

I see the point of confusion now - you believe I'm saying the wheels will be completely spinning, as if unconnected to the road - that is NOT what I'm saying. What I am saying is there is a component of the drive that is lost (a small percentage) through imperfect transfer of kinetic energy - a percentage of spin, as opposed to total spin. Does that make sense now?

 

[elgaz]

Dragging up an old post here ............... did anyone actually find anywhere that sells DC5 clocks showing both MPH and KPH, with mph as the main? Flew through my MOT this morning but failed on this one point, my clocks only show one rating and the law (at least here in NI) now stipulates that both MPH & KPH must be shown.

Thanks

Gaz

 

[crxvtec]

I bought mine from an Acura dealer in the US. Just get the clocks for the Type S model. It drops straight in and gives you an MPH readout

 

[big steve]

with all this research im suprised any of you have time to go out and enjoy your cars lol.

 

[qamvti]

Jack Daniels. Drugs are for losers and sick people.

Alcohol is a type of drug.

 

[stephen1612]

Dragging up an old post here ............... did anyone actually find anywhere that sells DC5 clocks showing both MPH and KPH, with mph as the main? Flew through my MOT this morning but failed on this one point, my clocks only show one rating and the law (at least here in NI) now stipulates that both MPH & KPH must be shown.

Thanks

Gaz

Didn't find any clocks with both, but....

I got sorted by getting a sticker from M Tech Graphics in Magherafelt.

Mitchell or Barney are the guys to speak to:

Telephone 028-79631895


He will require you to take the dials out, but this is very simple with the help from this thread :wink:

http://www.itr-dc5.com/forum/viewtopic. ... ht=#183898