Rep Power: 419

I have an LX. Stock it has 185/70-14's. I've maxed out at 115mph. The engine was climbing up to 115 steadily, but then it stopped all of a sudden. That's how I know it's some sort of speed governor and not the car's true maximum speed. Okay, now I put on a set of aftermarket wheels and tires. The new size is 215/45-17. According to the calculator that's 1.62% slower than stock. Now, my new maximum speed is 113mph. This is what I don't understand. I guess the speed sensor does not work off of axle rotation?

You see, 1.62% of 113mph plus 113mph gives us the true speed of the car. That's 114.8306mph. I guess my needle on the speedometer must have been just past 113mph, but I didn't notice this small difference. Anyway, this part makes sense. What doesn't make sense is how the freakin' car measures speed. I thought that it was by axle rotation... The car should have still gone a maximum of 115mph on the speedometer, but it would have really been going 1.62% faster than that. Does anyone know what the hell is going on?

Is my thinking off somewhere, or does the speed sensor work some other way? I can't imagine how since the speedometer seems to work off of axle rotation. Does the stupid speed governor work some other way? Maybe it's not a speed governor? Maybe it's just an rpm limiter? Did I mention that I can't take it past 6,100rpm in 4th when I'm going 113mph? I guess it's an rpm limiter for each gear dependant on speed? WTF is going on? Does anyone have any insight?

 
Rep Power: 311

Its all computer controlled... Honda calls it an engine speed limiter.. ack! But I think the speed based of of various sensors like the VSS. So tire size probably doesnt really matter that much to the computer. Just a guess..

 
Rep Power: 419

VSS = Vehicle Speed Sensor [IMG]i/expressions/face-icon-small-confused.gif[/IMG]
Do you happen to know how the VSS measures your speed...

 
Rep Power: 311

I havent looked at how our cars VSS works, but some cars use a magneto setup that triggers the VSS signal to the ECU. The magneto setup is typically found in the tranny or transaxle. I'll look at my Helm service shop manual tonight and see if it has anything related..

 
Rep Power: 419

Thank you muchly! [IMG]i/expressions/face-icon-small-smile.gif[/IMG]

 
Rep Power: 311

I looked at my Helm manual, but it doesnt really give details on how the VSS works but more of how to replace the sensor. I noticed that the VSS has a gear on the end of it that meshes inside the main tranny housing o some other gear. So it doesnt look to be magneto based, but instead gear driven. Basically as the gear from the VSS spins off of some other gear in the tranny, it send a signal to the ECU.

I assume that this signal and probably other systems are then used to set limits plus other functions that are based off of vehicle speed.

EDIT: This is all based off of my assumptions on how things may work.. not to be taken as factual information as I'm not a Honda Tech!

 
Rep Power: 403

well the 1.62 means your speedo is off by about 2 miles per hour so lets say you are going 30 mph, that means you are really going like 28 because the wheel and tires you have are bigger than stock. so it takes longer for the car to make a compeat tire rotation than you would with your stock wheel tire combo... and flotsamm is right, there is a sensor in the tranny which measures the rpm to gear ration then does something in the ecu. then sends it to the speedo... ever since i got my reverse gauges in my rpm and speedo are off, then when i put on my V-AFC i see now that the rpm on my gauges are about 250 rpm off from what the true rpm is. i don't feel like fixing it...

 
Rep Power: 0

ummm don't you mean take 1.62% from 115 which is 1.863.... so subtract 1.863 from 115 and you get 113.137.... so you're right when you say your max speed is now 113.... you just did the math wrong [IMG]i/expressions/face-icon-small-tongue.gif[/IMG]

 
Rep Power: 419

Who? Me? No, I know. I was going backwards though. Since my speedometer is off now I max out at what looks like 113mph to me. So... Since my speedometer is actually 1.62% slower than what the actual speed of the car is we can derive the actual speed of the car. (113mph / 100) * 1.62 = 1.8306 1.8306 + 113mph = 114.8306mph That's about 115mph (the true maximum speed of my car). I guess the 115 - 114.8306 = 0.1694 difference is due to the fact that when I looked at my speedometer and saw 113mph I couldn't tell the difference betwean 113mph and a little more than 113mph.

 
Rep Power: 403

yes, and that is what the tire calc is for, to show you the diffrence of your stock tires to your newer tires/rims