[Shan2nu]

I found this article on the net and this is what they had to say...

Changing from a larger to a smaller diameter will increase the gap from the top of the tire to the bottom of the fender well. A large gap will give the appearance of a four-wheel drive truck, which is not a bad thing if you have a four wheel drive truck. Acceleration will increase as the gearing is increased numerically, while top speed is reduced. Speedometer readings will be higher than the actual speed and miles on the odometer will pile up faster.

Click on the link above to go to the site.

Shan2nu

[SLK]

I absolutely understand what you are saying! - that only true if you are redlining for the top speed with current tyres.
so u reduce tyre size you have less top speed.

but.. i'll give it another try .. to explain my point to you - When you are not able to redline for top speed (as in 5th gear)
why is that 5th gear does less speed than 4th? Just b'coz 4th has a higher ratio.
now if you reduce tyre size the new 5th gear will have a higher ratio than the original one.
SO you are bound to have a higher top speed in the 5th.
but yes this is not applicable.. for down sizing from 13" to 3" tyres.

[Shan2nu]

Originally Posted by [b

Quote[/b] ]but.. i'll give it another try .. to explain my point to you - When you are not able to redline for top speed (as in 5th gear)
why is that 5th gear does less speed than 4th? Just b'coz 4th has a higher ratio.
now if you reduce tyre size the new 5th gear will have a higher ratio than the original one.
SO you are bound to have a higher top speed in the 5th.
but yes this is not applicable.. for down sizing from 13" to 3" tyres.

That is true to a certain extent. You're right, that using a smaller wheel will make the 5th gear rev to 6500 rpm, compared to the 6000 rpm with bigger wheels. But, at 6500 rpm the smaller wheels will be covering the same amount of distance per min, as that of the bigger wheels would, at 6000 rpm. So, where's the increase in speed?

Increase in revvs does not count as increase in speed when comparing a small wheel with a big one.

If the engine was to revv to 6500rpm with big wheels then yes, top speed has to increase.

So, while you gain more revvs in top gear, the speed of the car will remain unchanged. 2ndly, the smaller wheels will help revv the engine to 6500 only if they prove to be lighter than the bigger ones. If the overall weight of the car remains the same, then the car wont be able to revv to 6500 and will have to make do with 6000 rpm, thus reducing top speed.

Shan2nu

[SLK]

... where's the wall... not the AW.. but a concrete wall so that I can bang my head onto it!!

Originally Posted by [b

Quote[/b] ]But, at 6500 rpm the smaller wheels will be covering the same amount of distance per min, as that of the bigger wheels would, at 6000 rpm.

Perfect till this point.
But here we have a Vtec... which produces a peak at 6800rpm... so the small wheels will allow it to go to 6800rpm at least if not further!.

=====
One more theory for you.
forget the wheels. and gears
say its flying in air!!.
how much propelling force does the Honda city body (includes its weight / aerodynamic ability) needs to reach 200kmph. say 106bhp
how much propelling force does the Honda city body (includes its weight / aerodynamic ability) needs to reach 190kmph. say 100bhp

so in case 1 when engine is producing 106bhp it can go till 200.. and in case 2 its till 190. Bcoz its producing less bhp.

=====
Back to tyres
the smaller tyres allow the engine to produce its 106bhp.. so it will do 200kmph. (no no not on the speedo - the car doesn't even have a speedo anymore)

[Shan2nu]

Show me one authenticated article where they say your theory is right. This is just not possible, not even therotically.

If the weight of the car and the resistant forces remain the same. There is no way a car with smaller wheels can have a similar or higher top speed. You can't go against the "Laws of Physics".

Search the net for a few hours and see if you can find data that can back you up. I bet they'll all say that smaller wheels will have a faster rotational speed but, not the speed of a car.

Shan2nu

[SLK]

man.. if someone.. isn't clear he needs backup!... I am crystal clear in my head.

Even if.. you conduct a poll on team-bhp.. and.. 100% vote against what I am saying. I still know I am right.

I just don't have to convince you, I just know what I know. Thats it.

its a 3 dimensional thing... you can't see the 3rd dimension "the power". can't help it any more!

[Shan2nu]

Originally Posted by [b

Quote[/b] ]Even if.. you conduct a poll on team-bhp.. and.. 100% vote against what I am saying. I still know I am right.

That xplains a lot.

But in anycase, this discussion is still incomplete, as long there is no documentation backing your theory. Life isn't that easy, you have to prove your theories.

Originally Posted by [b

Quote[/b] ]its a 3 dimensional thing... you can't see the 3rd dimension "the power". can't help it any more!

Power has always been there, it's not a 3rd dimenssional thing.

Shan2nu

[speedsatya]

hey slk and shan,
then how does changing tire OD change the speedo rdg.
do u mean to say that the speed rdg will not chnage but the odo reading can change.

attack guys

[SLK]

Well I quit, from this topic for now.
I would like to see the more "qualified" members of the forum comment. but only after reading all the 3 pages.

have a good time

Originally Posted by [b

Quote[/b] ]Life isn't that easy, you have to prove your theories.

Its not my theory!... its a fact derived from 'understanding'. I have tried to explain it but if somehow you aren't able to understand : It won't make it wrong. ....
Its all cool.. chill out

[mayur]

Hmmm

I tend to agree with SLK here. What he says may not be practical , but i dont understand why he cant be theoritically right.

Forget for a moment that the engine is wasting power in revving the wheels. Assume the only work the engine is doing is moving the weight of the car, AND doing work against air resistance.

Original topspeed of Vtec = true 195 kph in 5th gear at 6000rpm ( 100bhp) . so here ,100bhp in 5th gear = air resistance at 195.

Now, wheel diameter has been decreased and gearing has become shorter( nothing else has changed).
now at 6000 rpm in 5th gear,car is doing true 185kph . Engine is producing 100 bhp which can easily fight air resistance at 185 kph and CAN accelerate the car to more than 185.

NOW, assume it can go to 195 kph. here its at 6500 rpm (104 bhp) . Air resistance is same as ORIGINAL but power available is more(104 bhp opposed to 100).

So, the car MIGHT THEORETICALLY be able to go past true 195 kph.

My way of explanation is largely the same as SLK's. Iam probably thinking on the same lines as him. And , i dont have much technical knowledge about cars, so i could be wrong.

But i will use another explanation here ........

Assume a hypothetical car( max power 100bhp at 6000 rpm ) hitting the top speed in 4th gear(gear ratio 1.2) 170 kph at 6500rpm(revlimit). 5th gear is pretty tall( gear ratio 0.7) . it does only 160kph at 4500rpm.

Theoretically there exists(unless that gear ratio is 1.2, here assume 1.2 is too short) some gear ratio between 1.2 and 0.7 which gives higher top speed than 170. Say that gear ratio is 1:1(giving top speed of 180).

Fix a tyre which is pretty small dia, so that 5th gear ratio becomes 1:1 from 0.7:1.

So the car now reaches 180 in 5th gear

Hope i made sense.

Regards,
mayur

[Shan2nu]

Originally Posted by [b

Quote[/b] ]So, the car MIGHT THEORETICALLY be able to go past true 195 kph.

The car cannont go past 195kmph bcoz the 4 bhp is being used to gain that extra 500 rpm, while the speed of the car is tha same, the rotating parts of the car have to turn that much faster.

It's not that 6000 rpm produces 100 bhp. It's the 100bhp that helps it reach 6000 rpm in the first place.

Originally Posted by [b

Quote[/b] ]Theoretically there exists(unless that gear ratio is 1.2, here assume 1.2 is too short) some gear ratio between 1.2 and 0.7 which gives higher top speed than 170. Say that gear ratio is 1:1(giving top speed of 180).

So i ask you, why not the 0.7? if 1:1 can increase top speed, then 0.7:1 should increase it even further. That is where the AW comes into account. Gear ratios can help increase top speed only to a certain extent.

And generally, all cars will have gear ratio that is equal to or close to 1:1. Vtec's 4th gear is 0.9:1 and that is where it hits top speed.

Originally Posted by [b

Quote[/b] ]hey slk and shan,
then how does changing tire OD change the speedo rdg.
do u mean to say that the speed rdg will not chnage but the odo reading can change.

Changing OD of the tyres will affect both, the speedo as well as the odo. You SM and OM are cliberated such that, it increases the speedo read with the increase in wheel rpm. At 100kmph, the wheel is supposed to rotate at a rpm (irrespective of wheel size). Now, it's common sense that a wheel with smaller OD will cover a lesser dist for every roatation as compared to the bigger one.

If the wheel rpm remains the same at 100kmph (speedo), then the smaller wheel covers lesser dist, for a given interval of time.

Shan2nu

[SLK]

Originally Posted by [b

Quote[/b] (Shan2nu @ Nov. 08 2004,23:36)]It's not that 6000 rpm produces 100 bhp. It's the 100bhp that helps it reach 6000 rpm in the first place.

ya thats why even the maruti 800 touches 6000rpm. but its only has 45bhp!! the remaining 55 is on rent from the Vtec.

its not the bhp that comes first ...bhp is the output ... rpm comes before bhp.

ps: I am trying to remain out.. but can't help it sometimes!

[Shan2nu]

Originally Posted by [b

Quote[/b] ]ya thats why even the maruti 800 touches 6000rpm. but its only has 45bhp!! the remaining 55 is on rent from the Vtec.

The M800 is also considerably lighter than the Vtec. If the M800 engine was to be fitted in the vtec it wouldn't even hit 4000 rpm in 5th.

It's all interconnected. Less powerful engines need the car to be light as well.

Shan2nu

[SLK]

Originally Posted by [b

Quote[/b] (Shan2nu @ Nov. 09 2004,00:22)]The M800 is also considerably lighter than the Vtec. If the M800 engine was to be fitted in the vtec it wouldn't even hit 4000 rpm in 5th.

I have a perfect explanation/solution or clarification or whatever you might want to call it, even for this. but never mind!

[Shan2nu]

All i ask for is one certified article, which proves your theory, or if you wanna call it a fact, lets call it that. See if you can find something that says "smaller diameter tyres on a car with all other variable unchanged, will increase top speed."

If not for your satisfaction, then atleast for mine. Coz personally, i found nothing of that sort on the net.

When the 4th gear ratio of the Vtec is already less than 1:1 how can you expect smaller wheels to increase it's top speed, *with the conditions remaining the same.

Either the car has to be made lighter, or the resisting factors (wind, friction) have to be reduced or the engine output has to increase. If these don't change, then i'm afraid the car wont go any faster.

Plus smaller wheels offer more rolling resistance compared to bigger ones, so a part of the engine power will be wasted there too.

Shan2nu