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Old 17th March 2005, 17:25   #16
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Please go through the link I have provided for transmission losses I think it will help clear a few more doubts (even for the 1/4 mile).
From your link it seems they're talking about how efficient the transmissions are in transferring power. We all know that by the time the engine power reaches the wheels it's reduced by a certain percentage.

But, how does that affect top speed in relation to gear ratios? We're not bothered how much power is being transferred, our discussion is about clutch slip.

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Old 17th March 2005, 17:59   #17
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Guys I give up, but the way I understand this topic is very simple

Top speed is limited by many factors and not just the number given by the gearing and tire circumference. Some of the factors that I am aware of are:

1) Transmission Losses (Energy loss, clutch slippage etc)
2) Aerodynamics (Drag Co-ef)

I also said that "This may lead to clutch slippage at higher speeds than 150kmph" if you guys can continue to educate me on this thread or otherwise I would be thankful.
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Old 17th March 2005, 18:09   #18
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Top speed is limited by many factors and not just the number given by the gearing and tire circumference.
We all agree to that. Though my car is geared to do 248kmph. It can't bcoz the kind of power that is transferred to the wheels is not enuf to fight the wind resistance offered beyond 185kmph.

This has nothing to do with clutch slip. If the wind resistance is further increased, the car will obviously slow down but, that will also reduce the engine rpm, in relation to vehicle speed.

If clutches could slip that easily then, things like burnouts, powerslides and bike wheelies wouldn't have been possible. Heck, i've even seen cars do wheelies.





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Old 17th March 2005, 18:19   #19
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hey guys, i would like to point out that psycho is right, that top speed, or vehicle performance, for that matter, depends upon a lot of factors other than just overall gearing, like coefficient of drag, transmission losses, rolling resistance of the tyres and as such.
but like shan2nu pointed out, clutch slip due to wind isn't a factor, because, if my calculations are correct, a car travelling at speeds of 150 km/h has to face winds at an velocity of about 195km/h , which i don't think will affect the clutch of that car in any way.
clutch clippages occur due to mechanical reasons, of which wind isn't one of, and i agree with shan2nu on this!!!!
p.s-by the way shan2nu, how did u upload those pics(and so fast!!)?

Last edited by veyron1 : 17th March 2005 at 18:25.
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Old 17th March 2005, 18:28   #20
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hey guys, i would like to point out that psycho is right, that top speed, or vehicle performance, for that matter, depends upon a lot of factors other than just overall gearing, like coefficient of drag, transmission losses, rolling resistance of the tyres and as such.
Yes, we never said there is just one factor. All the other factors do affect top speed but, clutch slip cannot be taken into account. Engine rpm rises and falls with respect to the selected gear and vehicle speed.

And even if you take clutch slip into account, it will have to be a very weak, old and worn out clutch.

Shan2nu

Last edited by Shan2nu : 17th March 2005 at 18:31.
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Old 17th March 2005, 21:51   #21
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veyron i dont think auto transmissions are more efficient than manual ones. in auto transmissions slip very much exists. the fluid coupling which is used can not operate at 100% efficiency. if i my memory is right the slip is pretty high in the auto trannies.
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Old 18th March 2005, 00:24   #22
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Originally Posted by Shan2nu
Heck, i've even seen cars do wheelies.
We thats not due to the clutch but due to a torque bar.

As for dragster's we do not have telemetry tools avialable that easily to monitor vehicle performance but dragsters do check clutch losses by logging data on engine RPM vs. Driveshaft RPM.(Well they do use centrifugal clutches though.)

And here is another bit of info that you might find useful

"When a clutch starts to slip, the slippage will be most noticeable when the engine is under load, as when lugging at low speed in a high gear, when driving up a hill, when accelerating to pass another vehicle or when towing a trailer. The more the clutch slips, the hotter it gets and the more it wears. This accelerates the problem even more and may result in additional damage to the flywheel and pressure plate. "

I got this bit at

http://www.autopn.com/autoparts/clut...utch_info.html
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Old 18th March 2005, 02:15   #23
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Quote:
Originally Posted by Shan2nu

If i had clutch slip, my 4th and 5th gears would have redlined with the top speed still staying at 185kmph (which doen't happen).

Shan2nu
Talk about nail on the head...
perfectly right.
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Old 18th March 2005, 14:54   #24
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harrie, that's what i said-auto trannies aren't more efficient-if you read my post completely..
Quote:
if what psycho says is true, then at least theoretically, automatic transmissions should be more efficient, as there is no clutch, and power is transferred through fluid flywheel.as said above, manual transmissions should lose their advantage after a certain velocity .
but this is not true, as you can see in case of the new honda cr-v, as an example. both the manual and automatic versions of the car have 5-speed ratios, but still, the manual manages a better top speed, and is more efficient
also, no powertrain is 100% efficient, manuals included-there's always a loss in transmission of power- upto 0-5%(from the flywheel to the clutch to the gearbox input/driven shaft) . the clutch slip is one factor in this- but that's due to the friction coefficient of the clutch, not wind-like you said earlier..
and guys, like everybody pointed out in their different ways, the clutch of any performance car DOES NOT slip at speeds above 150 km/h due to wind: but only due to the friction coefficient of the clutch, which means that a car might achieve an top speed of 200 km/h with one clutch, but may achieve 205 with a high performance one-again, wind isn't a factor-like i said earlier..!but nevertheless, a certain amount of slip is necessary.......
also, the centrifugal clutches used in drag cars are designed to attain a certain amount of slip, as the transmission is not designed to take the 6000 horses+ from the flywheel of the methanol-powered engines at one go- when the clutch doesn't slip, or doesn't slip as planned, you see engine blowouts, and powertranny damage(one of the many reasons) . also, the drag cars wheelie because of improper/non- clutch slippage- if the clutches didn't slip, the cars would flip backwards- that's because the tyres are designed for high grip, and are made of vulcanized sulphur-compound high-traction rubber-which results in much more traction than required. you must have seen, that in some drags, the drag cars do flip backwards, which happens due to non-slipping of clutch- all the power is sent to the wheel at once-causing the mishap

Last edited by veyron1 : 18th March 2005 at 14:58.
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Old 18th March 2005, 15:32   #25
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I give up on the wind affecting clutch part....

a few more points...

1) Auto trannies arent efficient as they come from the factories because of the stall converter and Torque Multiplier settings. The stall converter is supposed to lock up at a certain RPM and transfer all the power to the torque converter, this is however more efficient than a manual gearbox if it is calculated correctly and built, which is not possible here in India.

2) Drag cars do not have gears hence do have to rely on clutch slippage which is controlled either cetrifugally or hydraulically to transfer all the power to the final drive over a fixed time / RPM. You are right about the tranny blowout causing a car to flip backwards but an engine blowout causes a car to fold down and break. Theoritically it is possible for the pro dragsters to flip because of premature clutch lockup but this is rare as they are wheelspinning for the first 60' ft.

3) The flips that you see in Pro-Dragsters are primarily due to lack of enough downforce at the front wheels. and once the front is up it causes enough drag to flip a car over. However the street dragsters like the ones Shan2nu has posted lift due to the use of a torque / lift bar at the rear wheels to transfer all the power to the rear wheels while launching this is mostly done on leaf spring type rear suspensions.

And Shan2nu you are right when you say if clutch slipped the you would redline at close to a constant speed however this would only happen on a worn out clutch.
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Old 18th March 2005, 21:06   #26
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well, psycho, what can i say..you read my mind....!!
and yeah, there aren't conventional gerboxes in dragsters-what i meant by the transmission was engine to clutch-differential combo.
and no, autos aren't as efficient as manuals-like i said earlier-at least not fixed ratio types anyway. which is why i stated the example of the honda cr-v manual and auto.
the only automatics that are (slightly) more efficient than the manuals are CVTs(Continuous Variable-ratio Transmission) with computer programmed selective shift mechanism-with pre-programmed shift points for various load applications at different ratios.
also, the torque converters with lockup are used in some cars in india-mercedes E270 cdi-it's a cbu import-as an example.and the torque converters are used to multiply torque being sent to the gearbox-this is to counter the loss in power due to the hydraulic setup.
and also, automatics aren't that useful anyways(except in traffic), as they are more cumbersome to maintain-they can't be push-started in case of any failures(battery being one).plus the oil level has to be maintained constantly.
i agree with you on the engine blowout part of the pro dragsters-that's what i meant.
and yes, some pro-dragsters do flip backwards due to premature clutch lockups.
i agree with shan2nu as well on the clutch slip part.
and by the way, i forgot to mention....

Last edited by veyron1 : 18th March 2005 at 21:11.
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Old 19th March 2005, 02:12   #27
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Hey,

Just to chime in -

1. Clutch slip - Sounds quite likely that it does happen, and naturally it happens more as the (wind) load increases. However, when we say slip, (unlike what harri calculated) we dont mean slip to failure ie input=xyzRPM output=0RPM. Its more like there is 1 lost revolution per ever 100(hypothetical number) of revolutions, and naturally this ratio changes as load changes.

2. Now about calculating the exact speed using "engine rpm, gear ratio, final drive ratio and wheel circumference", personally i feel that tire slippage & deformation would be a larger issue than clutch slippage if you are trying to be so specific.

Eitherway, +/- 10km/h makes no difference to me. Lol.
cya
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Old 19th March 2005, 08:26   #28
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1. Clutch slip - Sounds quite likely that it does happen, and naturally it happens more as the (wind) load increases. However, when we say slip, (unlike what harri calculated) we dont mean slip to failure ie input=xyzRPM output=0RPM. Its more like there is 1 lost revolution per ever 100(hypothetical number) of revolutions, and naturally this ratio changes as load changes.
Nobody said it doesn't happen. But the amount of force needed to slip the clutch cannot be achieved by doing 185-200 kmph, especially in modern cars which are designed to reduce drag.

If a car was designed to have a top speed of 250kmph, the manufacturer sees to it that the clutch can withstand those speeds without slipping or malfunctioning.

Quote:
2. Now about calculating the exact speed using "engine rpm, gear ratio, final drive ratio and wheel circumference", personally i feel that tire slippage & deformation would be a larger issue than clutch slippage if you are trying to be so specific.
True, thats why, in my calculations thread i've mentioned +/- 3%. So far, i'm yet to see an error bigger than that.

And when i say error, i don't mean between the calculated speed and the speedo read. It's the error between calculated speed and actual true speed.

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