Top speed and transmission theory - Civinfo

 
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post #1 of 3 (permalink) Old 16th February 2017, 22:28 Thread Starter
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Top speed and transmission theory

So something which struck me, to be a bit strange were Hondas figures for top speed on the 1.5l turbo. The car is more powerful, has a claimed better drag coefficient and yet it should only reach 220 kph or even 200 kph with the CVT.

Some real world tests with the CVT are reaching 208 kph (not in hatchbacks as far as I've seen, but they shouldn't be too far off). For the 6 speed manual, I haven't found any real world tests just yet. Only 0 to 60 mph tests, which aren't that helpful in this regard.

So, theory time with Arsenal it is. I'm not that sharp when it comes to car mechanics and stuff, but I think I've grasped some of the basics for top speed and stuff.

So I'm basing this on the following:
6200 rpm max, 17 inch wheels with 235/45 and the gear ratios given in the brochure: 3.642; 2.08; 1.361; 1.023; 0.829; 0.686; 4.105

And the results are the following:
1st Gear (mph): 31 1st Gear (kph): 50
2nd Gear (mph): 55 2nd Gear (kph): 88
3rd Gear (mph): 84 3rd Gear (kph): 134
4th Gear (mph): 111 4th Gear (kph): 178
5th Gear (mph): 137 5th Gear (kph): 220
6th Gear (mph): 166 6th Gear (kph): 265

So a lot quicker than the Honda figures. Of course the top speed is also limited by power. So my 8G 103kW diesel goes up to around 230 kph. The air drag will be the most important factor here. The force required is 103kW/230kph = 1620 N. With this I can calculate the Cd*A of the 8G Civic to be 0.661 m². Now each generation is said to be aerodynamically improved, but let's just take this figure and move on.
With this and another nice formula a 8G Civic with 134kW (180 hp) should reach 250 kph.

So it could be that a manual transmission 10G reaches more like 245-250 kph instead of the 220 kph.

As for the CVT, the theoretical maximum speed is (gear ratio: 0.405 and 4.810): 240 mph or 386 kph. So clearly: the numbers are wrong or (more likely I think) the top speed is electronically limited at 200 kph.
I wonder why they do that. Sure adjusting it to go all the way to 386 kph is complete nonsense, but why not to 220 kph like in the manual transmission? Do you think someone will mod the CVT in a way to reach a higher top speed? Is the CVT not able to handle all the power from the engine, so they had to limit it to make sure it lasts?

Yeah, I know, looking at the top speed is stupid considering how often you actually reach it (in Germany I have at least the chance to do so ). But artificially limited devices nag me.
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post #2 of 3 (permalink) Old 17th February 2017, 10:36
 
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Some late night tinkering. Love it.

I think top speed listed in the manual is a worst case scenario.

Top speed of my 8G 1.4 for example is 175 kph, although I did 190 at one time with 4 people and their luggage for 2 weeks. YMMV...
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post #3 of 3 (permalink) Old 17th February 2017, 16:48
 
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Quote:
Originally Posted by Arsenal View Post
So something which struck me, to be a bit strange were Hondas figures for top speed on the 1.5l turbo. The car is more powerful, has a claimed better drag coefficient and yet it should only reach 220 kph or even 200 kph with the CVT.

Some real world tests with the CVT are reaching 208 kph (not in hatchbacks as far as I've seen, but they shouldn't be too far off). For the 6 speed manual, I haven't found any real world tests just yet. Only 0 to 60 mph tests, which aren't that helpful in this regard.

So, theory time with Arsenal it is. I'm not that sharp when it comes to car mechanics and stuff, but I think I've grasped some of the basics for top speed and stuff.

So I'm basing this on the following:
6200 rpm max, 17 inch wheels with 235/45 and the gear ratios given in the brochure: 3.642; 2.08; 1.361; 1.023; 0.829; 0.686; 4.105

And the results are the following:
1st Gear (mph): 31 1st Gear (kph): 50
2nd Gear (mph): 55 2nd Gear (kph): 88
3rd Gear (mph): 84 3rd Gear (kph): 134
4th Gear (mph): 111 4th Gear (kph): 178
5th Gear (mph): 137 5th Gear (kph): 220
6th Gear (mph): 166 6th Gear (kph): 265

So a lot quicker than the Honda figures. Of course the top speed is also limited by power. So my 8G 103kW diesel goes up to around 230 kph. The air drag will be the most important factor here. The force required is 103kW/230kph = 1620 N. With this I can calculate the Cd*A of the 8G Civic to be 0.661 m². Now each generation is said to be aerodynamically improved, but let's just take this figure and move on.
With this and another nice formula a 8G Civic with 134kW (180 hp) should reach 250 kph.

So it could be that a manual transmission 10G reaches more like 245-250 kph instead of the 220 kph.

As for the CVT, the theoretical maximum speed is (gear ratio: 0.405 and 4.810): 240 mph or 386 kph. So clearly: the numbers are wrong or (more likely I think) the top speed is electronically limited at 200 kph.
I wonder why they do that. Sure adjusting it to go all the way to 386 kph is complete nonsense, but why not to 220 kph like in the manual transmission? Do you think someone will mod the CVT in a way to reach a higher top speed? Is the CVT not able to handle all the power from the engine, so they had to limit it to make sure it lasts?

Yeah, I know, looking at the top speed is stupid considering how often you actually reach it (in Germany I have at least the chance to do so ). But artificially limited devices nag me.
Nicely calculated but you are missing something:
Top speed could be electronically limited (for example most high performance German cars are limited at 250 kph). The reasoning here is that especially cars with very good Cd numbers generate a lot of lift at high speeds which is problematic for high speed stability.

For example my 9G 2.2 i-dtec reached 230 kph downhill but you got a pretty unsafe feeling from 215 and up because you could feel the car getting lighter and lighter whereas my 9G Type R with all the aero drives like a tank even at 260+ kph.

Because the top speed is such a round number (220) I'm really expecting a limiter in place.

The CVT may be slower to limit wear on the transmission like you said - CVT's don't like torque so getting them working with a high torque turbo engine might necessitate some limits there (Driving with high torque applies usually only for a few seconds to get up to the desired speeds. So a top speed drive over German autobahn with high torque for minutes could damage the transmission so they limit the speed so even at the top speed the engine isn't sending max power through the CVT).

Last edited by Helmigurt; 17th February 2017 at 16:51.
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