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Old 15th November 2004, 19:07   #76
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Quote:
Originally Posted by [b
Quote[/b] ]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.
i actually said that at a given engine rpm the wheel rpm will remain the same, irrespective of tyre diameter. So, speedo read shouldn't change either. U should check the rpm using a ECM reader. Never trust the cars dials when you seek accuracy.

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Old 15th November 2004, 19:31   #77
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Quote:
Originally Posted by [b
Quote[/b] ]but 1st gear can not utilize the whole of the 106bhp... so the rest still remains potential.
Who says so? The car will use 106 bhp in every gear, that revvs to 6800 rpm.



Quote:
Originally Posted by [b
Quote[/b] ]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!
Dude, by changing the wheels, the mass of the car doesn't change. It's only the weight of the wheels that have to be added to the overall weight.

Quote:
Originally Posted by [b
Quote[/b] ]wheels are nothing for the engine!!...
When you're doin top speed , fighting against all sorts of resistances and running out of power.......each n every kg will make a diff. Ofcourse wheels do make a diff.

Quote:
Originally Posted by [b
Quote[/b] ]USING?
ok.. how about a car in neutral gear.. parked. revved to 6800rpm. its using 106bhp for sound? or for heat?
When a car is doin it's top speed in 5th, it is using up all the power the resistant factors allow it to. if the gear is engaged in neutral, the engine is still producing 106bhp at 6800 rpm. Only diff is, that now it's being wasted.

But power isn't useable once you've crossed that rpm mark. At 6500, if a car produces 104 bhp, it has only 2 more useable bhp left, beyond that point (considering that it maxes at 106 bhp @6800 rpm.)

Look, u wanted a qualified member to answer this question. Dom said top speed will readuce and still it's not enuf to satisfy you. It makes no sense.

Neither can you provide us with any authenticated material saying your're right. So what do we make of it?

I've shown you articles where they've said small wheels reduce top speed.And, I have a qualified member who is backing my point of view.

Theories that can't be proven cannot exist. That's the rule.

So....small wheel have to reduce top speed, if the weight of the wheels remain the same.

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Old 15th November 2004, 21:02   #78
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Quote:
Originally Posted by [b
Quote[/b] (Shan2nu @ Nov. 15 2004,17:01)]Who says so? The car will use 106 bhp in every gear, that revvs to 6800 rpm.
Sorry, but you have no physics base!

Quote:
Originally Posted by [b
Quote[/b] ] Dude, by changing the wheels, the mass of the car doesn't change. It's only the weight of the wheels that have to be added to the overall weight.
No comments

Quote:
Originally Posted by [b
Quote[/b] ]When you're doin top speed , fighting against all sorts of resistances and running out of power.......each n every kg will make a diff. Ofcourse wheels do make a diff.
How many times did we agree to keep the weight same?

Quote:
Originally Posted by [b
Quote[/b] ]Look, u wanted a qualified member to answer this question. Dom said top speed will readuce and still it's not enuf to satisfy you. It makes no sense.
I am sure he didn't get the problem properly.
And why do you want me to question member's 'qualifications'.

Anyways, my problem is : I see very clearly 'how' you are thinking.

anyways don't reply. neither would I
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Old 15th November 2004, 21:11   #79
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So, that does it then. Smaller wheels reduce top speed. If you can't prove it then, there's no point trying to prove the rest of the world, wrong.

How can you expect people to believe theories that cannot be proved??? It's never happened before and it ain't happening today!!!

Anyway, this is more than enuf info. Let someone else read our posts and reply. Until then, we don't discuss it.

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Old 15th November 2004, 21:28   #80
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Quote:
Originally Posted by [b
Quote[/b] ]Sorry, but you have no physics base!
so wats ur base (slk)?
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Old 15th November 2004, 21:40   #81
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hi, guys this is rahul im a new member ive been readin this thread for the past 2 days & a big missunderstanding going around here . its a known fact that using smaller wheels increases acceleration but reduses top speed of the vehicle .
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Old 15th November 2004, 21:46   #82
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Quote:
Originally Posted by [b
Quote[/b] (Sujit @ Nov. 15 2004,18:58)]so wats ur base (slk)?
my base?... well not much! but yeah.. physics..was my thing till I was in that stream.

But you seem confident enough to have a strong one! So probably you can read the last 5 pages and comment on the subject here.


hey shan2nu, whatever you say is right. cool!... (doesn't matter if I am not convinced)

anyways was waiting for rehaan to comment.... maybe he comes up with some.. different point to convince me
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Old 15th November 2004, 22:02   #83
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Quote:
Originally Posted by [b
Quote[/b] ]hey shan2nu, whatever you say is right. cool!... (doesn't matter if I am not convinced)

anyways was waiting for rehaan to comment.... maybe he comes up with some.. different point to convince me
I'm just waiting pal, any time, any where, from any one. Just wanna see how your theory makes sense.

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Old 15th November 2004, 23:04   #84
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Quote:
Originally Posted by [b
Quote[/b] (Rxinxs @ Nov. 15 2004,19:10)]its a known fact that using smaller wheels increases acceleration but reduces top speed of the vehicle .

The top speed has to reduce coz the wheels will travel shorter distance in the same given time as compared to the bigger tyres.
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Old 16th November 2004, 00:24   #85
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Quote:
Originally Posted by [b
Quote[/b] (shravan316 @ Nov. 15 2004,20:34)]
The top speed has to reduce coz the wheels will travel shorter distance in the same given time as compared to the bigger tyres.
You are right.... but.. unfortunately.. that isn't the subject of the thesis we are writing here... *

ps: I am not participating!.. just putting it back on the track!



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Old 16th November 2004, 17:50   #86
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lets put it like this a larger tyre will have more centrifugal force than a smaller tyre due to larger radei.now the larger tyre at lets say (X) rpm and (y) power going through it movin a car at (z) with given power loss due to drag at that speed.now the smaller wheel will use up more power to cover the same distance as the bigger wheel to (cover the same distance in the same time that is).now this intern will strain the engine that much more and make it rev higher to generate the req power plus now the pwer which was earlier available to fight drag will also get used.requiring more power to fight drag the poor engine will have to strain more.so finally what u get is a net loss.
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Old 7th April 2008, 15:28   #87
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Default The impact of a car's tyre size on its parameters

We all know that a wider tyre will give more comfort, less mileage.
And that lower profile tyres give better handling and worse ride comfort.

What about the tyre size?

All other factors being equal, does a bigger tyre size give
  1. Less torque? (dont quite know how to explain this)
  2. Better top speed? (radius is bigger, so for the same number of revolutions, the car will travel faster??)
  3. More mileage? (same reason as for point 2)
Expanding on the above hypothesis,

For a car with more torque (new Safari, Endy, Getz Crdi and the likes), increasing the tyre size will increase the topspeed and mileage at the cost of torque.

For a car with more BHP and comparatively less torque (OHC Vtec and some other petrol cars) decreasing the tyre size will result in decreased topspeed and mileage and increased torque.

These are all my thoughts and are not from any website\book.

How do you think changing the tyre's size will affect the cars performance? (All other factors being equal fo course)
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Old 7th April 2008, 23:14   #88
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50 views and no replies.

Some related links:
WikiAnswers - Does rim or tire size change mileage
Tires: Tire size effect on gas mileage
Tire Size Vs Gas Mileage

Last edited by Proxima : 7th April 2008 at 23:15.
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Old 8th April 2008, 07:45   #89
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Let me correct some of your terminology as well as abuse the "theory of relativity" in my explaination below. lol

Quote:
Originally Posted by Proxima View Post
We all know that a wider tyre will give more comfort, less mileage.
Do we??
According to some, a wider (wider tread width) tyre will give less comfort because the larger contact patch goes over more undulations(pebbles/cracks/rough patches) in the road.
If you mean higher profile - then yes.

Quote:
Originally Posted by Proxima View Post
And that lower profile tyres give better handling and worse ride comfort.
Correct.

Quote:
Originally Posted by Proxima View Post
All other factors being equal, does a bigger tyre size give :
Im guessing you mean to say "larger overall diameter (OD)" or "larger circumference".

Quote:
Originally Posted by Proxima View Post
  • Less torque? (dont quite know how to explain this)
  • Better top speed? (radius is bigger, so for the same number of revolutions, the car will travel faster??)
Yes. You can find the explaination of this in gear ratios.
Think of the tyre as a small gear which in turn is turning a much larger gear (the earth)
If you increase the size of the drive gear (the tyre) it will deliver less torque, but the driven gear (the world) will turn faster under it (i.e the car will travel faster - assuming the engine has enough torque).


Quote:
Originally Posted by Proxima View Post
  • More mileage? (same reason as for point 2)
This one is tricky - whether it will give MORE mileage will depend on what speed you are going, in what gear, and what you engine's toqrue curve is like etc etc.
The change in tyre OD will shift the *sweet spot* for best milage a bit. Whether this would be to your advantage or disadvantage would change from case to case.

Quote:
Originally Posted by Proxima View Post
For a car with more torque (new Safari, Endy, Getz Crdi and the likes), increasing the tyre size will increase the topspeed and mileage at the cost of torque.

For a car with more BHP and comparatively less torque (OHC Vtec and some other petrol cars) decreasing the tyre size will result in decreased topspeed and mileage and increased torque.
Neglecting the "mileage" point - yes.
But keep in mind that a LOT of work goes into chosing the right sized tyres for these cars by the manufacturers. The choice not only affects the drive ratio (drivability, FE, pickup, etc), but also stability, ground clearance, suspension, handling etc etc.

The concept you are playing with here is essentially changing the gear / drive ratio.
Changing gears its self could be thought of as changing tyres (assuming the ratios in your drivetrain were constant). Really tiny tires for 1st gear, really huge tyres for 5th gear etc etc.

cya
R

Last edited by Rehaan : 8th April 2008 at 07:57.
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Old 8th April 2008, 08:20   #90
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Note from Mod : Proxima's thread merged into an existing thread.

Also check out this link for an explaination of RPM and gears :
http://www.team-bhp.com/forum/techni...s-up-rpms.html (What's up with RPMs?)

And here is a real world example of changing the overall drive ratio :
http://www.team-bhp.com/forum/modifi...e-my-jeep.html (Higher final drive in my Jeep!!)

cya
R
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