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is the civic's speed limited by a governor on the indicated speed on the speedo.... or is it limited by a certain rev point in 5th gear.
if you saw 140 on your speedo, then it's probably limited by revs in 5th gear.
and you'd be amazed how off your speedo is up at those speeds. in a stock civic, if your speedo says 130mph, chances are you are only going about 121-125mph.
tires flex exponentially and directly in variation with the speed you are going, particularly as they reach their maximum speed rating. this causes a huge difference in indicated speed vs actual.
so yes, seeing as you have larger tires than stock, chances are at those speeds, your speedo is actually reading a good 15+mph OVER what you are ACTUALLY going.
My tires overall diamter are actually slightly smaller than stock... I've set both side by side, and the tire calculator on this website says so also.
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actually i was just going to edit my post, but you beat me to it.
that makes perfect sense now.
when you DECREASE the overall diameter from stock, your speedo will read a FASTER indicated speed than what you are actually going.
if you INCREASE the overall diameter, obviously your indicated speed is SLOWER than what your actual speed is.
so yes, considering the tire flex at those speeds, i'm willing to bet had you kept going, you'd have quickly found your speed limiter, which i'm guessing is done by engine speed, not indicated speed on your speedo.
so yes though your speedo said 140mph, i'm willing to bet you were only going 125 or less. if you want, give me your original tire size, and your new tire size, and i can calculate roughly what your indicated speed vs actual speed would be at those speeds.
On a side note for S2000man01... If you look at my video in my gallery. My speedo shows I hit right around 100mph at the time I passed the 1/4mile on the track....my time slip for that pass if I remember correctly clocked me at lik 96mph... thats about a 4-6 mph difference in speed. Therefore my thoughts are this...your 15+mph speedo inaccuracy idea does not seem to make sense to me.
I'm betting that my speedo is off by 3-6 mph and I dont see how that margin of error can change regardless of what speed I'm traveling at. If it can change at all due to tire flex, I dont think it is going to change by very much if any at all.
number one, you'd be amazed how much tire flex changes your speedo reading. think about this. let's say your tires are a normal diameter of 20 inches. let's say that at 100mph, your tires rotate 40 times per second.
now, increase your tires to 20.7 inches. (rough estimate of tire flex) now, at 100mph, essentially your tires would be spinning only about 38 times per second. that's a HUGE difference. that's roughly 40 less inches you are traveling every second compared to your normal rate of speed.
if you were to continue at that speed, after 1 hour, that equates to almost 5 FULL MILES. this means from tire flex alone, your indicated speed is 5mph faster than actual. as you get faster, the tire flex increases, and of course, the variance grows. assuming the tire didn't flex any more, just think. at 150mph, that would be 7.5mph difference.
trust me, tire flex makes a much bigger difference than you think.
number 2, keep in mind, trap speed is measured by how long it takes you to cover the last 60 feet of the 1/4 mile. it's fairly accurate, but not as accurate as say radar or laser would be. there is probably about a -/+ 2 mph variance with trap speed vs actual speed.
i'm not making this stuff up. trust me, tires can flex even up to or greater than a full inch at higher speeds. especially tires that aren't rated for high speeds. plus throw in the fact that you are running a slightly smaller diameter than stock. i'm willing to gaurantee if i did the calculations (which i can do later when i have time) that your indicated 140mph is closer to an actual of around 125mph.
If the stock tire stands 1 inch taller than my 17s when you set them side by side then that should make up for that .7 inches worth of flex? Hmmmm You're still talking a 15mph difference on the speedo man, thats a huge difference. A very hard difference to believe...I dunno man.
i should state that the lateral flex caused by traveling at higher speeds causes your speedo to read faster than you are actually going. you are confusing overall tire diameter with the lateral flex caused by rotation.
on my old truck they put too small tires on the back...
it made my speedo read faster than I was going...
at 30mph it said 32
40 it sed 45 and so on.
so s2000 man is right on that...
but if you are chipped to remove the governer you dont have to worry about it. anything over 15mph over the speed limit is jailtime regardless in most states...
__________________ Wait a minute! What am I doing.? I am far too sober for this.
i should state that the lateral flex caused by traveling at higher speeds causes your speedo to read faster than you are actually going. you are confusing overall tire diameter with the lateral flex caused by rotation.
how is the lateral flex of the tires' rotation that you're talking about going to cause the speedo to give a faster reading than what is actual when the flex is causing the over all diameter to increase, thus causing rpms of the wheel decrease for the same distance?
ok i did the calculations. these are all WITHOUT tire flex.
at 100mph the stock tires spin 72.7 times per second. that means in one second, the car covers 1,760 inches. with your smaller diameter tires, you only cover 1,704 inches per second. over a one hour period, that's a 201,600 inch difference. etc etc, that equates to a 4mph difference in your speedo at 100mph vs actual speed from stock.
now, as we already know, cars in general in stock form, always show an indicated speed that is higher than your actual speed. on average, at 100mph, the difference is about 4mph. so, take the original 4mph, now add your 4, and your car is showing a total difference of 8mph so far at 100mph.
so... speedo on stock civic reads 100mph. actual speed is 96mph. your civic would be at 92mph.
now throw in any equation for lateral flex, plus the fact that at 140mph this difference is even greater. in fact, it's almost another 5mph. so now you're at an indicated 140mph, and your speedo is showing a difference of 14mph, meaning your actual is around 126mph.
