Type R LE 0-290 km/hr

tinyman392

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Assuming it’s on level ground, I think it’s speedo error, which is very common on all makes of cars. 2% sounds well within reason for normal street driving.

Regarding power loss from weight, I don’t think that will make a difference in top speed. The power loss that people measure is due to the difference in measured acceleration on a dyno and that certainly reflects in how the car accelerates. However, at top speed, you are no longer accelerating. Instead, you are in a static situation where the torque at the wheels is balanced against friction. At that point, the weight of the wheels doesn’t matter. Heavy or light, they’ve already accelerated to speed and are no longer influencing things.
So the top speed of the car is limited by drag. Specifically this means that the negative acceleration from wind drag is balanced in an equilibrium by the forward acceleration of the wheels, and thus no more acceleration is possible.

Typically the you’ll need 4x the amount of power to get 2x the top speed of a vehicle from this perspective (which is why it’s very difficult to go faster as the power required is huge). So, if you increase the power/torque (they’re increasing one technically will increase the other for a given RPM), you will be able to accelerate just a little bit faster which means you’ll be able to “beat” more of the negative acceleration due to drag just a little bit more. This, in turn, will increase the top speed ever so slightly.

The thing is, with the loss of weight in the wheels, it’ll amount to what, 5-10 HP (if that)? That definitely won’t be enough to add 10 MPH to the top speed (maybe 1-3 MPH using similar math below). A tail wind, slight downhill, and speedometer error certainly could though.

Getting the car to 180 MPH (290 KPH) would be a total increase of 6.5% in top speed. In order to get this, you’d need 1.065^2 the amount of total power the car puts out or about a 13% increase in power. Say the stock car makes 300 WHP, then you’d need about 340WHP to get to 180 MPH with identical conditions to the original test (and a transmission/tuning that will allow the overrev to hit said speed).

Something else has to be going on to hit that 180-ish MPH mark on top of the speedometer error. A downhill grade of a tail wind certainly could help explain it.

Edit: let’s say the car is hitting 177 MPH (redline of the Type R), then it would probably need about 329 WHP to do that (again, identical situation to the original 169 MPH test).
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RedGiant217

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I'm still questioning how there's 2% error in the calculation between engine/transmission speed and vehicle speed...are the 2 numbers not calculated from the same sensor?
 

tinyman392

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I'm still questioning how there's 2% error in the calculation between engine/transmission speed and vehicle speed...are the 2 numbers not calculated from the same sensor?
I do know in the US it’s mandated that the speedometer cannot read lower than the actual speed you’re traveling (this is to prevent speeding I think). So a lot of car manufacturers will actually have their speedometers set up to read slightly lower (by 1 or 2 MPH) than the car is actually traveling. Mine is typically off by 1-2 MPH from the factory. My Camry I had before this Civic would generally be about 2 MPH slower while the Sentra I had before that was off by 3. This is all legal, BTW, since the speedometer reading was higher than I was actually traveling.

Other things that can affect the speed reading is the actual diameter of the tire. That technically varies too. Not only between tire models (same specs/size) but also as it wears. For example the if you run down a set of the stock Conti’s to 4/32, then the tires diameter is technically ~1.2% smaller than it was stock. Granted doing the same to the Cup 2s (LE stock if I’m not mistaken) it would be ~0.7% smaller. If I took the PS AS3+ then it would be ~1.7% smaller while the AS4 would be ~1.4% smaller.

Edit: I should also note that in a lot of cars, the vehicle speed sensor can read differently than the speedometer for whatever reason. Granted this is more common with analog speedometers as they begin to break. We shouldn’t have the same issues, but it is possible that Honda keeps them separate for whatever reason.

Edit 2: I should probably mention that I know how far off my speedo is due to a few things. GPS and the speed trap sensors police setup. Either the GPS and all the speed guns I’ve passed are off by the same amount, or my speedo is off by said about. I feel like it would be the latter (former is far less likely).

Edit 3: So lets say that the LE was traveling 177 MPH, add in the 1.5 MPH higher due to factory stuff, it would read 178.5 MPH. Let’s say that the tires were worn down to 4/32 on Cup2s, so multiply the 178.5*1.007 = 179.7 MPH ~ 289 KPH. It’s not totally far fetched... assuming of course the car can even get that high (assuming it's stock, if it's not then it shouldn't be an issue). Even with weight reduction (F=MA) and rotational weight reduction (more power), I don’t see it happening. Though if it was going downhill with a tailwind... Still... Very weird phenomenon.
 
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RedGiant217

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@tinyman392 thanks for the detailed explanation. I appreciate your analytical approach to things. I had not thought of any intentional speedo error to prevent displaying lower than actual speed.

As far as tire/wheel size goes though, I don't see how that plays into displayed speed vs RPM. Things like that will affect actual vs displayed speed, but my question is, shouldn't the car always display the same speed at a given RPM?

Even if the sensor has some error in calculating transmission speed, shouldn't the equations for calculating engine rpm and vehicle speed still end up displaying the same speed at a given displayed RPM for every Type R (unless something like gear ratios in the equation were different)?
 

tinyman392

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@tinyman392 thanks for the detailed explanation. I appreciate your analytical approach to things. I had not thought of any intentional speedo error to prevent displaying lower than actual speed.

As far as tire/wheel size goes though, I don't see how that plays into displayed speed vs RPM. Things like that will affect actual vs displayed speed, but my question is, shouldn't the car always display the same speed at a given RPM?

Even if the sensor has some error in calculating transmission speed, shouldn't the equations for calculating engine rpm and vehicle speed still end up displaying the same speed at a given displayed RPM for every Type R (unless something like gear ratios in the equation were different)?
I don't feel like our speedometer is hooked to our drive shaft, transmission, or anything of that nature. If it were, our speed would rocket up when we spin the front tires in 1st or 2nd (along with our RPM). It's been a while since I actually spun the tires quickly, but I never remember the speed shooting up, just the RPM.

I want to assume that the car uses one or more of the wheel speed sensors that are part of the ABS system to compute vehicle speed. I kind of wish I knew more though. I do know that if any of the wheels have a different overall diameter than the driven wheels (which themselves can differ), assuming the driven wheels aren't used entirely to track speed, then it's possible for the speedometer to read something different than what the gear ratios say it should be reading. But it would be reading differently than what I stated above (differences in tire wear would be causing the error vs tire wear itself). At the same time, the TPMS system would go off if the error was large enough.

So I guess I really don't know why it's reading differently than what the drive shaft says it should be. I do know it definitely can read different. Someone on FB posted a photo that showed an FK8 going 177 MPH at around 6600 RPM while the video posted by the OP shows it hitting 177 MPH at around 6750 RPM (the video showed the car hitting 175 around 6600 RPM). Unless there's a conspiracy going on I believe what I'm seeing.
 


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I think Honda has improved a few small things in the FK8 LE:
- Less aero drag, small aero changes, this helps increasing the top speed.
- Less weight (-47 kg Euro spec), lowers the drag at wheels etc. a little bit.
- Less drag at engine because they removed the A/C + pulley.
- Maybe increased the engine power a little big?
- longer final gear reduction?
 

RedGiant217

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Ah. If speed is calculated from the wheels and RPM from the transmission or somewhere else, that could allow for some variation between the 2.

Note that I'm not really questioning the validity of the video(s). Just not willing to let go of the idea of new gear ratios yet.
 

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Tire size is the same: 245/30R20Y Michelin Pilot Sport Cup 2.
 

CTR1633FK2

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This guy is able to reach 297 km/h with 420 HP.
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