The real deal on top speed!

[Bowlsie]

I went out last night to solve this top speed theory on our cars once and for all. I took my Garmin GPS unit and velcroed it to the dash and went out to the most desolate straight stretch I know of (2 1/2 miles long) Let me say I unleashed hells fury. In 6th gear which what looked to be at about 7k rpms (keeping my eye on the gps, the speedometer, and the road) I was doing 138 mph and it still had pull. From what I could see looking back and forth my GPS and my speedometer were dead on. My speedo was almost pegged at the 140 mark and the gps was saying 138. So I don't think there is any, maybe 1mph difference variation in actual speed and what the speedometer reads. Not once did I feel any kind of limiter kick in. And for all of you safety fans out there I did not pass nor see another car in sight. I took this into my own consideration and knew what the consequences could be. And yes you can still feel the lift at this speed! SWEET!

[NovaResource]

The real deal is this: GT tops out a 129, period. This has been validated by numerous car magazine tests. GPS is not an accurate way to test speed. A calibrated radar gun or acceleratomer is the only way. End of discussion.No if you were going down hill or had a tail wind, a few more MPH can be had since the 129 speed is due to drag. Lessen the drag (with a tail wind) will raise that number.

[Celtic_Curse]

Holy that is fast, whats the top end for the base if anyone knows?

[NovaResource]

quote:Holy that is fast, whats the top end for the base if anyone knows?GT = 129BAse = 115

[Bowlsie]

Well say what you will but I find it hard to believe that the GPS and the speedometer were within such a close distance and neither were right. Guess I will have to try a couple more things and try again.

[satur9]

why would that gps be innaccurate ,it must have a accellerometer in it or something to track speed. my http://www.mrdyno.com has accellerometers(?) in it. so if i took that out for a test would you accept that top speed.sombody here has to have a cop buddy with a laser gun. those magazine figures are always off, its like they pick the worst places and drivers.

[NovaResource]

quote:why would that gps be innaccurate ,it must have a accellerometer in it or something to track speedNo, it doesnt. It samples your position at various times and averages you speed by calculating the distance traveled over a period of time.quote:those magazine figures are always off, its like they pick the worst places and drivers.And I'm sure you're a better driver.

[Robert G]

Top speed of AWD?

[Bowlsie]

This is quoted directly from a link at Garmin: GPS Speed: How accurate is it? How fast can I go? How HIGH can I go?GPS receivers display speed and calculate the speed using algorithms in the Kalman filter. Most receivers compute speed by a combination of movement per unit time and computing the doppler shift in the pseudo range signals from the satellites. The speed is smoothed and not instantaneous speed. HOW ACCURATE IS THE SPEED READING? From the NAVSTAR GPS User Equipment Introduction document Section 3.7: GPS receivers typically calculate velocity by measuring the frequency shift (Doppler shift) of the GPS D-band carrier(s). Velocity accuracy can be scenario dependent, (multipath, obstructed sky view from the dash of a car, mountains, city canyons, bad DOP) but 0.2 m/sec per axis (95%) is achievable for PPS and SPS velocity accuracy is the same as PPS when SA is off. Velocity measured by a GPS is inherently 3 dimension, but consumer GPS receivers only report 2D (horizontal) speed on their readout. Garmin's specifications quote 0.1mph accuracy but due to signal degredation problems noted above, perhaps 0.5mph accuracy in typical automobile applications would be what you can count on. HOW FAST CAN I GO AND HAVE MY GPS READOUT MY SPEED? All Currently manufactured CONSUMER GPS receivers we know about will measure speed to 999 miles per hour. Garmin (uniquely as far as we know) manufactured the G-38, G-40, G-45, and the G-II (not PLUS) units which had a 90 mph speed readout limit. These units are manufacturing discontinued and we know of no other manufacturer who made a unit which would not go to 999mph. HOW HIGH CAN I GO AND HAVE MY GPS READOUT ALTITUDE? Defense department regulations prohibit standard consumer GPS receivers from functioning above 60,000 feet and 999mph (simultaneously). Most GPS receivers seem to set hard limits at EITHER 999mph or 60,000 feet. Not being a smartass but I think you are a little off on your facts.

[NovaResource]

I haven't seen a writeup on the AWD but I would think it's close to the base. Maybe 2 or 3 mph slower due to the added weight and restructive exhaust.

[NovaResource]

Calculating speed is different from measuring speed and not as accurate.

[Bowlsie]

I still don't see how the speedometer and the GPS unit are both wrong. I guess I will have to call the guys over at Car and Driver to come by my place and do a top speed runout. I know drag can hold a vehicle back but with the engine in the GT at high revs this car pulls. I know I was still pulling when I let off. And like I said before my speedo was almost pegged on 140. Oh well.....

[NovaResource]

Well, a theoritical top speed based on gearing would be a max of 145-mph. That's a GT at 8200-rpm in 5th gear (top speed is usually not reached in 6th gear because it is so overdriven). Now, does the GT have the power to go faster than 129-mph? I don't know because I've never tested one with the correct equipment so I go with the info provided by respected testers (Motor trend and Car and Driver are just 2 or a few that claim the 129-mph top speed). I know you say you got 140 and it was still pulling but the max you could have gotten in 5th gear at the 8200-rpm redline is only 145-mph.quote:In 6th gear which what looked to be at about 7k rpms (keeping my eye on the gps, the speedometer, and the road) I was doing 138 mph and it still had pull. From what I could see looking back and forth my GPS and my speedometer were dead on. My speedo was almost pegged at the 140 mark and the gps was saying 138.You numbers are off. At 7000-rpm in 6th gear you should be doing 157-mph. That number is based on the engine rpm, 6th gear ratio, final drive ratio and tire circumference. 157-mph is not obtaiable. You can't get a GT to 7000-rpm in 6th gear.

[Bowlsie]

It did still have pull. And like I said earlier I looked and it seemed to be at 7k rpm's. Even an overdrive ratio will still pull. Especially if you are in the meat zone. In the vibe you have 180 horsepower at that engine rpm. The difference in gear ratio between 5th and 6th is meager. I know what my GPS said and I know what my speedo said. I could be off on my tach stats because I really wasn't paying close attention to that. I was worried more about the speed number. Next time I try this I will take a friend with me and actually take some photos to prove it. I can't right now though because im on my 5th Coors lt I don't think that would be very safe.....

[esjones]

quote:Calculating speed is different from measuring speed and not as accurate.They are the same thing, except for the basis of your calculations. If you use a radar gun, you are calculating speed based on the time differential of the radar echo return. If you use a calibrated fifth-wheel, you are basing your calculations on the time it takes the wheel to make a rotation. GPS, using doppler shift, etc. is just another calculating device. Now, I think what you are trying to say is that, if you travel one mile in exactly one minute, and that is the only information known, it tells you little about what happened in that minute. For 30 seconds, you could be traveling far faster than 60 MPH, and for the other 30 seconds, you obviously would be going slower, in order to complete the course in one minute. But if you have only those two data points, you would conclude that the car's speed was 60 MPH.It seems to me that all speed calculation/measurement is based on averages over intervals, and the description of the GPS measuring algorithms seems sufficiently large numbers of data points over sufficiently small intervals to yield a reasonable estimate of top speed. As O'Reilly says, "Tell me where I'm wrong."

[rasermon]

Some info. on Doppler shift GPS. http://www.racelogic.co.uk/vbox/gps.htm http://www.racelogic.co.uk/vbox/aboutvbox.htm

[mu_ohio]

quote:The real deal is this: GT tops out a 129, period. This has been validated by numerous car magazine tests. GPS is not an accurate way to test speed. A calibrated radar gun or acceleratomer is the only way. End of discussion.No if you were going down hill or had a tail wind, a few more MPH can be had since the 129 speed is due to drag. Lessen the drag (with a tail wind) will raise that number.The only thing that I wonder about the speed posted in those two mags is if they tested it or used numbers from manufacturers. I'm not sure if the GT truely tops out at 129 because I have neither a personal drag strip or radar gun, but I can see it being in that area. I'm sure it's also possible to raise the number by lowering a car and removing things like the roof rack, or I could add a huge wing and hit only 85

[philndz]

quote:Next time I try this I will take a friend with me and actually take some photos to prove it. I will hang tight for the pictures but what i can say is that as a long time user of GPS equipment, both in and out of the car (and in my plane too), I have always found it to be dead on. In the car the GPS matches the speedo at any speed....if im doing 20 on the speedo...the gps shows 20.....40 on speedo, gps = 40.....and so on....so why should it then be inaccurate at 138?

[Faultline]

quote:Holy that is fast, whats the top end for the base if anyone knows?GT = 129BAse = 115I can vouge for the top base speed, I have a base , and now with a turbocharger on it....the base has a govenor on it...the fuel cuts off at 115 mph... ..I live at 3000 ft elev...before the turbo, I huffed and puffed to get to 115mph in 4th gear...along a lonely faultline road, that got me into the notion of needing a turbo.....with the turbo, I arrive at 115mph in 4th or fith gear easily.....if the govenor was not there, then I do belive I could pull , all the way to the 6500 rev in fifth gear..in 4th for sure....but I dont know what theoretical speed that would be....and then what if I had a celica ecu whose rev limiter is 7000 rpms...what would that speed be....???hmmm???,,..thank God for govenors...it is a sensless way to die...