:eek: :eek: :eek: :cheers:

 

Just use a GPS---they don't lie. That's what we use in the boating world--not the speedos. By the way the speedos are always faster then the GPS speed. :yesnod: :cheers:

 

Adam Bruce:

Thanks for the analytical and factual information. Now if all the doubting Thomas's will just use your information, there should be unity regarding the top speed anyone can reach in any given gear combination. :D

And to whomever it was suggesting the problem was the speedo reading in Metric rather than English units for speed (Km/H vs MPH), max speed in 4th (with 3.42 gears) is about 141 MPH, the equilivant Metric reading would have been about 227 Km/H. Peace to you all :cool:

 

Redo your calcs too buddy because the side wall flex you are so quick to point out decreases the OD of the tire at a stop, but at 160MPH the OD increases. There's some serious centrifugal forces at work. :cheers: Go ahead and lean out the window the next time you are at 160MPH on your EMT's and measure them for me at speed. Thanks. :p:

-Jeremy



[Modified by Godspeed, 8:32 AM 4/5/2002]

 

Seanr, I believe 500+ RWHP and 373s is sufficient to pull in sixth gear over 170, But I will let you know for sure one day! :D
JB

 

For the record I have the A4. My car at full throttle will not hit high gear until 142mph! Just about 6600rpm. Have run up to 172mph before common sense got the better of me. Car was still pulling I have no idea however what the rpm was at that speed.

Bob


[Modified by 16Again, 2:46 PM 4/5/2002]

 

but how can I find anyone stupid enough to drive next to me at 150 MPH to see how far off it is?


I'd be happy to. Let me know when you're up for it.

Greg
:cool:

 

This may help clear things up. I was in 5th gear when I snapped this pic.
It was kinda hairy :eek:




[Modified by Loaded45, 5:11 PM 4/5/2002]

 

here's my "problem" - what's being discussed here isn't "which exhaust sounds better" or "which color looks better" or "which exhaust backplate shines more (LOL)" or "does the flameball shift **** lower my ET (LOL)", no, this kind of topic is a "hard" "technical" topic, and the fact is that if someone says (claims) they can do x speed at y rpm, then there is a very exact formula for determing if this is true. it has nothing to do with whether one wants their claims to be true or not.
speed in gears calc is
mph = (rpm * tire height in inches) / (trans gear ratio * final drive ratio * "the constant")

the constant is 336.1352, this is derived from PiRsomethingorother, it is correct, I and many many others have empirically validated this formula :)

this calc does not take into account overcoming wind resistance, so it is only accurate where a car can reach a given rpm in gear. ie most cars can not pull red line in top gear cause they can not overcome the wind resistance.

as to your car pulling 200 "with out a problem", that may be true with 550 rwhp (it probably is), but you'll need a pretty long straight-a-way in sixth gear to get to 4900 rpm, which is what you need for 200. in general it is not easy trying to turn that point five extreme overdrive top gear into the wind, where the power required to overcome the resistance triples with the square of the speed, few can do it (on stock tires get 4.8k rpm in 6th with 3.73's or 4.4k with 3.42's). the top speed of your car, with 3.73 rear and 295/35-18 tires and 6700 rev limit is 184 mph in fifth gear. and, as we all know, you will not be able to shift into sixth at 184, you will need to be in sixth at a much lesser speed before starting your top speed run. I do think you could do it but it's not a "no brainer". I'm not knocking you or your car, and I respect and admire your awesome machine.

I just want the "tech" aspect of this forum to be "real"

peace
David

my car can go faster than your car in 5th gear, nah nah :)

 

Yawn. How cute. but still wrong. every measurement of speed in gears for C5's on stock tires, especially the GM literature and reliable mag tests agrees exactly with the numbers I quote.
and btw - almost always when I go fast, I am not on stock wheels/tires..

 

:nono: NO NO NO NO.:nono: The tire height of a tire is :

tire.diameter = tire.width/25.4*aspect.ratio*2+rim.diameter

It doesn't matter if the tire is flat or has no deflection at all the Circumference is going to be the same. The tire does not grow circumference as centrifugal force spins it. It may ride up hire on the sidewall which might affect the height, but not the height for the speed @ gear calc. Which is.

current.mph=current.rpm*tire.diameter)/(selected.gear.ratio*rear.axle.ratio*336.1352398)

/* current.mph is the speed the car is going at current.rpm
/* with the current selected.gear.ratio (i.e. 4th gear)
/*
/* current.rpm is the RPM the motor is at when you calc the formula
/*
/* tire.diameter is the Actual height in inches of the tire
/* (Circumference and inches per mile per hour is calc'ed off the
/* constant of 336.1352398
/*
/* selected.gear.ratio is the gear you are in when you
/* calc the formula
/*
/* rear.axle.ratio is your axle gear (i.e. 3.73, 3.42, 3.23, 2.73 etc)
/*
/* 336.1352398 is the multiplier against time for inches of
/* circumference (i.e. in one rotation how many inches the tire revolves,
/* over how many times it revolves in a minute to the Rotation Per
/* minute (RPM) of the final overall ratio.

Hope this helps, and again, tire height based on how inflated the tire are will not change the circumference of a tire.

-Adam


[Modified by Adam Bruce, 9:16 PM 4/5/2002]

 

David, I fully understand there is a precise formula for calculating speed,gear,and RPM. I simply stated what my approximate RPM was and you said B.S. . You then stated that 171 in fifth is entirerly possible at 6250. You state that you respect my machine, how about alittle respect for the people on this forum. I don't make a habit of it, but I've pulled to 170 MPH a few times in a relatively short distance. I know I would have to make my shift to sixth before redline, but I believe given a safe area to do it, it would not be that hard to hit 200 MPH. My speedo has no hesitation as it pulls to 170MPH.
Respectfuly,
JB

 

In 4th, mine hits the stock rev limiter at 139 mph :cheers:
I have seen it many times on the MTI dyno.

 

I see 140 on the dyno before I get the shake that indicates your on the fuel cut-off.

I wasn't gonna post but after reading through both pages, I'm throwing in my $.02. You guys are just in bad moods tonight. If you had cut each other some slack I might have been through 5-6 other threads by now :lol:

Good discussion though. At least it wasn't another dude snapping a pic of his gauges during an ignition key cycle, saying wow dudes I'm do'in 190!

 

and what slack (pray tell) should I have "cut" and to "whom"?

this thread is a typical BS deterioration. lotta spouting, few "facts".

Adam Bruce says "no no no" to me, yet what has he added? he restates exacly what I said, with the same formula. tire height. yes, tire height.

jbsblownc5, I don't know "what you simply stated" that I so mangled, except a specific rpm and speed, so let's drop it. lemme know how two bucks feels and where you do it.

 

I've done 150-160 mph on the autobahn for more than a few seconds (more like a few miles) and she is getting close to red line in 5th. I don't think you did 160mph in 4th, you can't get past the gear ratio math unless you changed your rev limiter, no matter what your HP.

 

That's pretty cool. In my car with 26" tires and 3.08's at 4500 rpm in 3rd (1:1) my speedo said 180 km/h (111.8468 mph). According to this formula I was going 113. Pretty accurate for an analogue cable speedometer. :D

So then my run in 4th (0.72:1) at 4200 RPM which I had estimated at 235 km/h (146.0222 mph) from the position of the needle (numbers stop at 180) is pretty damn close to the calculated 146.4959 mph.

I always wondered if I was exagerating but I guess I wasn't. :)

 

:rolleyes: If you reread my post you will see that I was debunking that height changes as speed increases and even if it does, the proper way to measure tire height is based off that formula. Why do you want tire height? So you can figure out circumference of the tire. Why do you want to know that? So that you can figure for 1 revolution of the tire, how many inches of tire circumference just rolled across the ground (i.e. how “long” is that patch of tread the tire put to the ground in one revolution). Since RPM is a Revolutions per minute and you know based on how tall the tire is, what the circumference is, you know how many times he tire turns in a minute and thusly how many inches where traveled in a minute. Thus Distance/Time = speed.

So, the OD of the tire does NOT AFFECT the formula if the tire is flat the tire measures 24” or if it’s fully inflated and measures 26”. The Circumference does not change. Just because the tire gets flat it does not add or decrease the amount of tread on the tire. That’s why you should find tire height based on the tire height formula (listed above) or and even better way is to mark your tire, roll it one full revolution and figure out the length of your circumference.

-Adam

 

At least I don't run my mouth without backing it up jackbehind.

5th gear, 6600RPM - 180+ MPH in a f-body

 

Guys, please stop the bickering over something I said that was obviosly an error. No cure, you called me on it and proved my speedometer wrong. So now I have to get in contact with the original owner to see if he possibly had lower gears put in. No big deal. You have to understand, and you even said, that you can be a smarta s s. That's why some people here are taking offense to you. No one hurt, and again, no big deal.

Okay, to correct myself. My car wasn't doing 160 MPH in 4th gear. It couldn't have been. Either way it was flying and I had fun doing it! :)

I guess I should've titled this topic, 160 MPH in 4th gear???