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Old 11th November 2004, 04:51   #61
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Quote:
Originally Posted by [b
Quote[/b] (Shan2nu @ Nov. 11 2004,01:50)]What i feel is, if the Vtec is given loads of time to accelerate in 5th. It might just hit the same top speed as it did in 4th. It may take mins or even an hour, but technically, it should hit the same top speed.
If this fact is right!!!!.. Which i doubt.
Then its done... I'll agree with you.. game over.

We bang our head here or not!... this wasn't a bad discussion at all... as I am sure you also got a lot to think.

and all that has been put down.. does make some sence... if any other members are interested!
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Old 11th November 2004, 06:41   #62
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Yup i agree, it was pretty good. i did spend a lot of time finding info on this and learnt a lot in the process.

Ofcourse a little more participation from others would have been better. Rehaan is busy with his work, or else he would have surely come up with something. With illustrations!!! hehe

Quote:
Originally Posted by [b
Quote[/b] ]ok just for fun ( not a part of the actual discussion )
we remove your Vtec's fenders .. and put 25" wheels. And we also remove all extra stuff.. so that there is no weight increase in the car.
Do you think top speed will increase? consider both 4th & 5th gears!
Well, like i've said before, if the weight of the car and resistant factors remains the same. Top speed has to increase. Practically speaking, we will have to weigh the bigger wheels and make sure they have the same weight as that of the smaller ones.

Let me give you an example :
Take a 6 ft iron rod. Hold it with your hand at one end. Try and lift it, you maynot be able to. Now move your hand closer to the center of the rod and try the same excercise, lifting it will be easier now. Now, the place where you're holding the rod is the hub/center of a wheel and other end of the rod is the circumference.

So smaller the dist between the hub and the circumference, lesser input of torque is required to turn it. But here's the catch. Though a smaller wheel would require less torque, the weight of the wheel also makes a diff. If the 13" wheel is as heavy as the 16" wheel, then the requird torque will remain the same, inspite of the smaller diameter.

Lets take the iron rod example again. We found that by hold it near the center and not at one end, reduces the amount of energy required. That is bcoz, when you're gripping at the centre the weight of the rod bcomes half of wat it was, as you no longer have to worry about the other half of the rod.

But if you take another rod which is twice as heavy as the first one and grip it at the center, it'll still require the same amount of energy which was needed to lift the lighter rod by holding it's end.

Shan2nu
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Old 12th November 2004, 16:30   #63
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Well, it depends on where the max power is being produced..
and I feel SLK is right....

For starters...this link will make this more easylink
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Old 12th November 2004, 18:17   #64
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Quote:
Originally Posted by [b
Quote[/b] (Shan2nu @ Nov. 11 2004,04:11)]Though a smaller wheel would require less torque, the weight of the wheel also makes a diff. If the 13" wheel is as heavy as the 16" wheel, then the requird torque will remain the same, inspite of the smaller diameter.
ya, you can say that.
But thats about the wheels.

And we have a mass of 1000kgs to move here.

I'd say 1% of the power of the engine goes into rotation of the wheels (only wheels). and the 99% is going to move the mass of the car.

RPM * * * Total Bhp BW-1% *Bodypush SW-1.25% BodyPush
6000 * * * 92.4 * * * 0.92 * * * 91.48 * * * 1.16 * * * 91.25
6100 * * * 94.1 * * * 0.94 * * * 93.16 * * * 1.18 * * * 92.92
6200 * * * 95.8 * * * 0.96 * * * 94.84 * * * 1.20 * * * 94.60
6300 * * * 97.5 * * * 0.98 * * * 96.53 * * * 1.22 * * * 96.28
6400 * * * 99.2 * * * 0.99 * * * 98.21 * * * 1.24 * * * 97.96
6500 * * * 100.9 * * *1.01 * * * 99.89 * * * 1.26 * * * 99.64
6600 * * * 102.6 * * *1.03 * * * 101.57 * * *1.28 * * * 101.32
6700 * * * 104.3 * * *1.04 * * * 103.26 * * *1.30 * * * 103.00
6800 * * * 106 * * * *1.06 * * * 104.94 * * *1.33 * * * 104.68

*BW - big wheel
SW - Small wheel
I have made this.. rough table... So let me give a disclaimer first - its not perfect - assumes Vtec has a flat torque curve 6000 through 6800.

Lets say I agree with you that.. smaller tyres would waste more power and use 25% more power to rotate on account of 1) Higher rpm 2) rolling resistance *

Then the 99% power left is for pushing the car's weight/body. And in case of Small tyres this force is 98.75%.

So ... assuming that the change in wheel size causes the peak rpm to shift from 6000 to 6200. the car's body gets 3 additional bhp. So it'll accelerate further till it reaches its new equilibrium.

Now 2 things..
1st you can say.. how can I split 1% and 99%?
- Well only tyres don't even require that much power. So 1% is a safe bet.
2nd what is this equilibrium?
- there is some fixed amount of power the Vtec body will need to reach certain speed i.e. beat the gravity and the air.
say the table looks like this

kmph * Bhp required
180 * * *92.00
185 * * *94.50
190 * * *97.50
195 * * 101.00
200 * * 105.00

ahhh... *



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Old 13th November 2004, 14:41   #65
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Quote:
Originally Posted by [b
Quote[/b] ]So ... assuming that the change in wheel size causes the peak rpm to shift from 6000 to 6200. .
How many times do i have to say that if the weight of the wheel remains the same. The engine rpm wont rise to 6200 in 5th. So there's no question of increased power. It'sll still max out at 6000 rpm.

Quote:
Originally Posted by [b
Quote[/b] ]the car's body gets 3 additional bhp. So it'll accelerate further till it reaches its new equilibrium
It's not getting 3 additional bhp, it's using 3 additional bhp. If there is no increase in rpm, engine power will remain the same.

I know what youre trying to say, but that's technically not possible and will never happen.

Shan2nu



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Old 13th November 2004, 16:45   #66
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Quote:
Originally Posted by [b
Quote[/b] (Shan2nu @ Nov. 13 2004,12:11)]How many times do i have to say that if the weight of the wheel remains the same. The engine rpm wont rise to 6200 in 5th. So there's no question of increased power. It'sll still max out at 6000 rpm.
What weight of the wheels?
10kgs?
you don't see the 1000kg.. car?
just because its not in direct friction with the road?
wheels are nothing for the engine!!... its the actual MASS of the car that requires power to be moved!

Quote:
Originally Posted by [b
Quote[/b] ]It's not getting 3 additional bhp, it's using 3 additional bhp. If there is no increase in rpm, engine power will remain the same.
USING?
ok.. how about a car in neutral gear.. parked. revved to 6800rpm. its using 106bhp for sound? or for heat?
its not using, its wasting.. or rather its waiting for it to be used.
Its all available at the flywheel.
now here all the 106bhp is mechanical potential energy.
you put the gear in slot its converted into kinetic
but 1st gear can not utilize the whole of the 106bhp... so the rest still remains potential.
same way.. up u go more energy gets converted into kinetic.

then there is a time when the required is more than available.
Rest you can think - no use repeating.
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Old 14th November 2004, 01:34   #67
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Hey Shan ,Slk,Dom,

i have chnaged my tires and rims.from 145/80r12 to 155/65 r13 tubelss tires.
so according to all ur expert theories ,what shud be the difference in my performance.i.e my speeds and the top speed.
previously my car did 100kph at 3100rpm and 140 at 4300rpm and the top speed of 160kph on speedo at 5500rpm in 5th gear.
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Old 14th November 2004, 10:58   #68
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Quote:
Originally Posted by [b
Quote[/b] (ScarySkulls @ Nov. 12 2004,14:00)]this link will make this more easylink
Hey Guys,
did the link help u in any way...?
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Old 14th November 2004, 14:49   #69
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Hi Satya,
Here are a few approximations

With the changed size you have actually reduced the dia:
Original Diameter is : 21.1"
New Diameter is : 20.9"
So your correction factor is about .9905. So to get the actual readings multiply your present speedo reading by .9905

so:
62.137mph (100kph at 3100rpm) = Actual reading is 99.05 KPH with new tire dia
86.991mph (140kph at 4300rpm) = Actual reading is 138.67 KPH with new tire dia
99.419mph (160kph at 5500rpm) = Actual reading is 158.48 KPH with new tire dia

Cheers
Dom
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Old 14th November 2004, 15:22   #70
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Hey satya
I can't be sure.. but appart from the change in speedo readings as per domnic's calculations, your top speed might further decrease due to more friction. Just like they say wider tyres less FE. b'coz they have a wider contact patch.

So which tyres did you buy?.. and rims?
And how's the zen's ride after upgrade? Is it bumpy?
I am sure the steering now would feel much better / precise. With those 80% tyres it feels awful.
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Old 14th November 2004, 19:55   #71
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Quote:
Originally Posted by [b
Quote[/b] (SLK @ Nov. 14 2004,12:52)]Hey satya
I can't be sure.. but appart from the change in speedo readings as per domnic's calculations, your top speed might further decrease due to more friction. Just like they say wider tyres less FE. b'coz they have a wider contact patch.

So which tyres did you buy?.. and rims?
And how's the zen's ride after upgrade? Is it bumpy?
I am sure the steering now would feel much better / precise. With those 80% tyres it feels awful.
hey SLK,
i think Dom is right . .
as now my speedo shows 100kph a little before 3100.so maybe he is right that the speedo wud show a higher reaqding.
regarding the ride,i think its ok but now u can hear the tire noise when u drive and also every cut on a concrete road is more audible.
the grip seems to be better,but i also feel the car tramlines a lot more .
hehe also .i can sure that i can take aturns at more faster speeds as today i took a 90degree turn at about 20-30kph with much less understeer.and had a scooterist abusing me as he just got down from his scooter and jumped aside when he saw me turning. .
the tire does not touch anywhere as of now .

satya
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Old 14th November 2004, 20:12   #72
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Quote:
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Quote[/b] (speedsatya @ Nov. 14 2004,17:25)]hey SLK,
i think Dom is right . .
as now my speedo shows 100kph a little before 3100.so maybe he is right that the speedo wud show a higher reaqding.
of course he it right...
Now the zen will show you speeds a bit closer to actual
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Old 14th November 2004, 23:57   #73
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According to one of the posts in this same thread( i think that post was by Shan2nu)...

The speedo reading should be the same at 3100 rpm even AFTER the tyre change. but the car's speed is now lesser. In essence, for a given rpm, the car's speedometer SHOWS the same speed as before. Its only that the car is not going as fast as before.
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Old 15th November 2004, 02:02   #74
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Quote:
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Quote[/b] (mayur @ Nov. 14 2004,21:27)]The speedo reading should be the same at 3100 rpm even AFTER the tyre change. but the car's speed is now lesser. In essence, for a given rpm, the car's speedometer SHOWS the same speed as before. Its only that the car is not going as fast as before.


only that the error in the speedo reading will now be different.
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Old 15th November 2004, 15:09   #75
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Quote:
Originally Posted by [b
Quote[/b] (mayur @ Nov. 14 2004,21:27)]According to one of the posts in this same thread( i think that post *was by Shan2nu)...

The speedo reading should be the same at 3100 rpm even AFTER the tyre change. but the car's speed is now lesser. In essence, for a given rpm, the car's speedometer SHOWS the same speed as before. Its only that the car is not going as fast as before.
hey mayur,
the speedo rdg shows more speed at 3100rpm .now it shows 100kph a little before 3100rpm.
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