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Old 9th November 2004, 03:59   #46
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Quote:
Originally Posted by [b
Quote[/b] (Shan2nu @ Nov. 09 2004,00:50)]When the 4th gear .......
how can you expect smaller wheels to increase it's top speed......
4th gear if its redlining then I AGREE it is not possible to increase top speed with smaller tyres.

I have mentioned this before that i am talking about a gear where the car is not able to redline. as IT HAPPENS IN 5th.
here you can get more speed than what you are getting NOW by using smaller tyres. (I am not calling it the TOP speed of the car but just the top speed of the gear has increased) now do we agree?

If we do. then taking mayur's example in a situation you can get the 5th gear to give out more speed than the 4th ever did. So eventually getting 195.1kmph from the 5th is the new top speed!

Shan2nu lets leave it for the others to comment. We are just repeating ourselves in every post we make.

Maybe I am overlooking some factor... so that might be the end.
But for now I can see from here what you are overlooking.

Why won't we find an article on the net?
Thats b'coz this is impractical. the 5th gear was supposed to be an overdrive. Why would one use it for top speed.
If anyone wanted to get a perfect top speed he'll rather tune his gear ratios to those which allow his car to be at the max power producing rpm (not redline) and no more rpm than that, when the car hits top speed. Its an equilibrium kind of thing.
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Old 9th November 2004, 04:52   #47
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Quote:
Originally Posted by [b
Quote[/b] ](I am not calling it the TOP speed of the car but just the top speed of the gear has increased) now do we agree?
Now, you're saying the speed of the gear will increase and not the speed of the car, that's exactly what i was trying to tell ya.

Quote:
Originally Posted by [b
Quote[/b] ]Why won't we find an article on the net?
Thats b'coz this is impractical. the 5th gear was supposed to be an overdrive. Why would one use it for top speed.
If anyone wanted to get a perfect top speed he'll rather tune his gear ratios to those which allow his car to be at the max power producing rpm (not redline) and no more rpm than that, when the car hits top speed. Its an equilibrium kind of thing.
So, any gear with a 1:1 ratio should technically give a car it's top speed at an rpm where the engine produces max power. Lets say the Vtec can revv to only 6800 rpm in 4th and has a speed of 195kmph at that point. It's already hit the AW in 4th and can't redline. So how will smaller tires help here?

Maybe they will help the car redline in 4th gear but at 7100rpm, the smaller tyres will be covering the same distance as the bigger tires were at 6800.

Smaller tyres give the gear the ability to revvv higher, but the speed of the car wont increase.

Anyway, i'm willing to see what others feel about it.

Use this calculator to see for yourself.


Top speed calculator


Use the following variables.

1. Engine speed - 6800

2. Tire Size - 175 - 65 - 14

3. Gear ratio - 0.937

4. Final drive - 410

Calculated top speed should read 121 mph

Now, keeping everything else the same reduce the wheel size from 14 to 13. Top speed will automatically reduce to 115.7 mph.

Lets say that even if the small tyres revv the engine to 7000 rpm, top speed will still be at 119.1 mph.

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Old 9th November 2004, 14:27   #48
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Shat2nu... we'll argue abt this weekend to weekend
I was on leaves for few days.. now I am back to work so won't get much time.

Till then think about the original example - I mean put it into the calculator.
6000rpm with 14 inch wheels.
6500rpm with 13 inch wheels.

but again this calculator doesn't consider the bhp.. and expects you to put the rpm it'll revv to, manually.
So its not as simple as it looks.
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Old 9th November 2004, 15:02   #49
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This is pretty accurate. it says in 2nd gear the Vtec will max out at 99 kmph at 7100 rpm. An infact it does, at 98 kmph. So the error is minimal, less than 1%.

Quote:
Originally Posted by [b
Quote[/b] ]6000rpm with 14 inch wheels.
6500rpm with 13 inch wheels.
Dude that's a therotical revv increase i used as an example. In reality it wont increase by that much. Domnic, who is a car tuner has tested diff cars with diff wheel sizes and hes say the revv might rise to 6250 rpm max.

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Old 9th November 2004, 23:22   #50
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Quote:
Originally Posted by [b
Quote[/b] (Shan2nu @ Nov. 09 2004,12:32)]Domnic, who is a car tuner has tested diff cars with diff wheel sizes and hes say the revv might rise to 6250 rpm max.
Hey Dom, tell me this.

Since you agree the car will be able to revv-up to 6250rpm to attain the same speed (call it X).

It wasn't able to cross the 6000rpm mark earlier with bigger tyres. Since the engine wasn't producing enough power to take the physical mass of the car past the X speed mark. But now our engine is giving out more power so it'll be able to go past the X speed along with revving a bit more.

remember the given car has its peek power at 6500rpm

did I say anything materially wrong?
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Old 10th November 2004, 02:13   #51
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Hi,
*Man this is a heated debate

Well, SLK, the car will be able to revv upto 6250rpm with smaller dia, but cannot reach the top speed attained by the 14" at 6k

Now here is a table:
Tire Diameter 1: 23(175/65-14) inches
RPM * * * 1st * * * * 2nd * * * *3rd * * * *4th
5500 29 49 74 99
6000 31 53 81 108
6500 34 57 88 117
*All in MPH

Tire Diameter 2: 22(175/65-13) inches
RPM * * * 1st * * * * 2nd * * * *3rd * * * *4th
5500 27 46 71 95
6000 30 51 77 103
6500 32 55 84 112
*all in MPH

Basically the cars acceleration will definitely increase, but top speed will reduce, reason as the engine will have to rotate the wheels more to attain the top speed (and hence will need more power to do it) which is not possible, as Power at the crank will remain the same with smaller or bigger wheels. Only the power delivered at the wheel will be different. *
and note power will not increase only the power band will be shifted.


Cheers
Dom



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Old 10th November 2004, 02:35   #52
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Quote:
Originally Posted by [b
Quote[/b] ]Since you agree the car will be able to revv-up to 6250rpm to attain the same speed
Let me make that a bit more clear. A smaller wheel will not increase engine revvs in 5th if the weight of the car and the resistant factors remain unchanged.

What engine power was being used to fight wind resistance at 195kmph, "6000 rpm" , is now used to overcome the rolling resistance the smaller (equally weighted) wheels offer.

Lets say, at 6000 rpm engine speed, the smaller wheels make the car top at 190kmph. ofcourse wind resistance at 190kmph is less than that at 195kmph, but the engine has another resistance that has popped up with change in wheel size, "rolling resistance". Reduced aerodynamical resistance is compensated with increased mechanical resistance. "Every action has an equal and opposite reaction".

So, the engine will max out at 6000 rpm "engine speed" as before but, since the wheels r smaller now, they cover lesser distance per min.

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Old 10th November 2004, 03:34   #53
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ok guys.. so you mean to say... if you increase the wheel size of the V-tec.. the top speed will increase. cool .. try that... but in 5th gear remember

Domnic I think you are making the same mistake.
I say when you talk about 14" wheels 6500rpm isn't available. So counting that top speed.. is.. not the right thing to do here.

Quote:
Originally Posted by [b
Quote[/b] ]but the engine has another resistance that has popped up with change in wheel size, "rolling resistance"
Now, Rolling resistance increases with smaller dia wheels!!!
I don't think.. so... as it will always reduce.
but since we are not putting very small size tyres here... we can assume it to be same.

try this http://www.legslarry.beerdrinkers.co.uk/tech/GS.htm


Does anyone agree that the top speed of Maruti Esteem can be increased by proper gearing?
Now if this change in gearing is done through tyres... any problem with that?
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Old 10th November 2004, 04:16   #54
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Quote:
Originally Posted by [b
Quote[/b] ]
Does anyone agree that the top speed of Maruti Esteem can be increased by proper gearing?
Now if this change in gearing is done through tyres... any problem with that?
Using a taller overall gearing will surely increase it's top speed marginally. Slower acceleration though. This is the same as fitting bigger wheels, the overall gearing bcomes taller.

Quote:
Originally Posted by [b
[/quote]


Been there, read that, long ago. These tests were done using diff compounds and brands of tyres. ofcourse, each brand of tyre will have it's own rolling resistance. But in our case, we're using the same brand of tyre, with the same compound and the same psi without even changin the width of the tyre. In this case, the bigger wheels roll better.

Quote:
Originally Posted by [b
Quote[/b] ]ok guys.. so you mean to say... if you increase the wheel size of the V-tec.. the top speed will increase. cool .. try that... but in 5th gear remember
In 5th gear, it wont really make a diff as the car hits top speed in 4th. But if you do this on a car that redlines in 5th then surely bigger wheels will increase top speed.

Quote:
Originally Posted by [b
Quote[/b] ]Domnic I think you are making the same mistake.
I say when you talk about 14" wheels 6500rpm isn't available. So counting that top speed.. is.. not the right thing to do here.
He's not saying it'll hit 6500 rpm, he's just made a calculation. See the speeds at 6000 rpm, they will be lesser. I don't see the point in trying to attain top speed in 5th when the car infact, maxes out in 4th.

In 5th gear i feel speed wont really be affected.

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Old 10th November 2004, 12:06   #55
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Quote:
Originally Posted by [b
Quote[/b] ]Domnic I think you are making the same mistake.
I say when you talk about 14" wheels 6500rpm isn't available. So counting that top speed.. is.. not the right thing to do here.
Hey dude,
Im not making any mistake, its a calculation i made, and i surely know thats impossible, i just wanted to show the charts to make it simpler. My software will generate charts upto 20,000rpm.

Cheers
Dom
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Old 10th November 2004, 13:16   #56
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Here's an article which explains rolling resistance better.

<a href="http://hea-www.harvard.edu/~fine/opinions/wheelsize.html#answer" target="_blank">This means that for any given forward speed of the bicycle (v), the energy required just to get the wheel up to speed is greater for larger radius wheels. And this relationship is linear, e.g. a wheel that is 50% larger (in radius) will require 50% more energy to reach the same speed (note that this is only wheel rotation energy, not the much larger amount of energy needed to accelerate the bike and rider).
So this issue is finally settled, right? Unfortunately not. It takes this much energy to get the wheel up to speed, but once it's there, you only need to add more energy to make up for what has been lost to friction, and here the larger wheel wins.

Larger wheels have less rolling resistance, for several reasons. First, they won't drop (as much) into a smaller hole as a smaller wheel would. Second, They have greater leverage for lifting the wheel over bumps. Third, there is less deformation of the tire at the contact patch on the ground. Fourth, smaller wheels require faster chain speeds, which will have higher frictional losses. Fifth, for similar reasons they will have higher hub friction.
</a>

So, bigger wheels need more energy in the initial stages, that is why bigger wheels retard acceleration, but once you're up to speeds, the bigger wheel (with the right air pressure) will roll better.

Note that, he's also taking into consideration, frictional losses and hub friction. These things add up to the total resistance a smaller wheel offers.

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Old 11th November 2004, 02:03   #57
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Quote:
Originally Posted by [b
Quote[/b] (Shan2nu @ Nov. 10 2004,01:46)]I don't see the point in trying to attain top speed in 5th when the car infact, maxes out in 4th.
hmm.. I see... It isn't really helping.
I say this every time that we are NOT talking about the top speed of a car, which is maxing out in any gear what-so-ever.

If its maxing out then the only way MAYBE to increase top speed is bigger wheel size.

What I mention in my posts is.. that the gear is not optimized for top speed (in other words its taller) ..

the car can have its top speed at almost 1:1 gear ratio?

here our car has 1.3:1 gear ratio with wheel size 14&quot;. now we increase the wheel size to 16&quot; to modify the final drive ratio to get a overall ratio of 1:1.
Then we get our top speed (call it speed X).
(before this the car was maxing out at a lower speed)

now this car was sent to Domnic's workshop where he modifies the gear box to give a gear ratio of 0.7:1 considering the 16&quot; wheels. then we get our top speed (call it Y)
Now we decrease the wheel size back to 14&quot; to modify the final drive ratio to get back overall ratio of 1:1.
Then we get our top speed (call it speed Z).

Now what I am saying is the speed Y is less than Z. (thats all)
What I always agreed upon is Speed X is more than Z.

now about the concept of modifying the gear ratio (the final drive) by tyre resizing... is not.. far fetched. you can search for that if you want to!

ps: I still doubt that you'll agree.
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Old 11th November 2004, 03:56   #58
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Every car, has it's gear ratios set according to it's top speed. It's not that they set the ratios first and and check top speed later. Before the car rolls out, every possible gear ratio is taken into consideration, such that the car attains the top speed, it's engine and body design allows it to.

I'll really be surprised if i can find a car in production, with your kind of gearing.


Quote:
Originally Posted by [b
Quote[/b] ]now this car was sent to Domnic's workshop where he modifies the gear box to give a gear ratio of 0.7:1 considering the 16&quot; wheels. then we get our top speed
A gear ratio change was never a part of this discussion. Only wheel diameter changes are taken into account.

2ndly, Domnic would never do such a thing if he knew what he was doing, which he does.

Ok, lets say that you convice Dom into changing the gear ratio of your car with 16&quot; wheels to 0.7 and you fit it with 14&quot; tyres. Now, that the gearing has come close to 1:1 again, it should revv higher in 5th. Is that right?

But, if you calculate the top speed using a GPS system, it'll still be slower than running the car on 16&quot; wheels using a .7 ratio. The smaller wheels are turning faster, the revvs are higher but the dist covered per min is still slower or similar, but not more. it just can't be. Diff in circumference, between a 175/65 R14 and a 175/65 R 16 is 15.9 cm or 8.71%.

How much the gear ratios change we don't know. I doubt it'll change from .7 to 1:1.

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Old 11th November 2004, 04:20   #59
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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.

As long as resistance remains the same, taller gearing can only retard accleration, but it cannot affect top speed (provided the gear doesn't redline). What auto mags do, is that they drive th car in 5th for a few secs or a min or 2 and say that &quot;this is as fast as it goes&quot;.

Plus, it's just not possible to keep wind resistance in check as wind speed and direction keep changing. So, it can be said that under those circumstances and conditions, the Vtec was able to hit 195kmph in 4th gear. Another top speed test in another part of the country could fetch a slightly diff top speed figure.

It's only the acceleration that is getting affected here, the cars ability to slice through air is still the same.

So, why break our heads with top speed. It'll never be consistant.

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Old 11th November 2004, 04:43   #60
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Quote:
Originally Posted by [b
Quote[/b] (Shan2nu @ Nov. 11 2004,01:26)]Every car, has it's gear ratios set according to it's top speed. It's not that they set the ratios first and and check top speed later. Before the car rolls out, every possible gear ratio is taken into consideration, such that the car attains the top speed, it's engine and body design allows it to.
Well, again.. I always mentioned.. that this is impractical.
Did I ever say some one would do this in a practical situation?
Smaller wheels??? .. come on!!... it'll be a compromise in many areas..

There is one car the Maruti Esteem!.. the gearing of this car is not.. right at all. You can compare its gearing to Diablo!

Quote:
Originally Posted by [b
Quote[/b] ]2ndly, Domnic would never do such a thing if he knew what he was doing, which he does.
Why? B'coz that car is owned by some poor guy called SLK and he needs some fuel economy! Is that such bad a thing?

Quote:
Originally Posted by [b
Quote[/b] ]But, if you calculate the top speed using a GPS system, it'll still be slower than running the car on 16&quot; wheels using a .7 ratio. The smaller wheels are turning faster, the revvs are higher but the dist covered per min is still slower or similar, but not more. it just can't be. Diff in circumference, between a 175/65 R14 and a 175/65 R 16 is 15.9 cm or 8.71%.
Now thats where you just won't agree!.. how can I help it?
You are just implying that you can put a bigger wheel and get a better speed without bothering about the gear at all!.

I don't understand, at team-bhp we don't have more than 4 members who can even comment on this topic!
Whether right or wrong they might be able to give me some other point of view... so that I can re-consider, what Dom &amp; you are not able to convince me for!

Quote:
Originally Posted by [b
Quote[/b] ]How much the gear ratios change we don't know. I doubt it'll change from .7 to 1:1.
Yes its difficult to say... but it'll depend on the actual gear ratios... how much a change in tyre affects them.

But why bother about this since what you are saying is in a way gear doesn't make a difference!.
bigger the better!

ok just for fun ( not a part of the actual discussion )
we remove your Vtec's fenders .. and put 25&quot; 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 &amp; 5th gears!
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