The speedo can be WAY off so I wouldn't go by that. It's possible the governor is RPM based and you weren't quite at that RPM, but the speedo was reading much higher.

You really need to be looking at your RPM and use your gear ratios and tire heights to back your way into your speed. And verify things with GPS (which also has a margin of error).

This is what Tire Rack has to say about speed ratings:

Speed Rating

In Germany some highways do not have speed limits and high speed driving is permitted. Speed ratings were established to match the speed capability of tires with the top speed capability of the vehicles to which they are applied. Speed ratings are established in kilometers per hour and subsequently converted to miles per hour (which explains why speed ratings appear established at "unusual" mile per hour increments). Despite the tire manufacturer's ability to manufacturer tires capable of high speeds, none of them recommend the use of their products in excess of legal speed limits. The maximum operating speed of a vehicle must be limited to the lowest speed rated tire on the vehicle.

Speed ratings are based on laboratory tests where the tire is pressed against a large diameter metal drum to reflect its appropriate load, and run at ever increasing speeds (in 6.2 mph steps in 10 minute increments) until the tire's required speed has been met.

It is important to note that speed ratings only apply to tires that have not been damaged, altered, under-inflated or overloaded. Additionally, most tire manufacturers maintain that a tire that has been cut or punctured no longer retains the tire manufacturer's original speed rating, even after being repaired because the tire manufacturer can't control the quality of the repair.

Over the years, tire speed rating symbols have been marked on tires in any of three ways shown in the following examples:

225/50SR16 225/50SR16 89S or 225/50R16 89S


Each of these was an acceptable method of identifying speed ratings.

Early tires had their speed rating symbol shown "within" the tire size, such as 225/50SR16. Tires using this type of branding were not to have been produced after 1991.

225/50SR16 112 mph, 180 km/h
225/50HR16 130, 210 km/h
225/50VR16 in excess of 130 mph, 210 km/h


Beginning in 1991, the speed symbol denoting a fixed maximum speed capability of new tires must be shown only in the speed rating portion of the tire's service description, such as 225/50R16 89S. The most common tire speed rating symbols, maximum speeds and typical applications are shown below:

L 75 mph 120 km/h Off-Road & Light Truck Tires
M 81 mph 130 km/h
N 87 mph 140km/h Temporary Spare Tires
P 93 mph 150 km/h
Q 99 mph 160 km/h Studless & Studdable Winter Tires
R 106 mph 170 km/h H.D. Light Truck Tires
S 112 mph 180 km/h Family Sedans & Vans
T 118 mph 190 km/h Family Sedans & Vans
U 124 mph 200 km/h
H 130 mph 210 km/h Sport Sedans & Coupes
V 149 mph 240 km/h Sport Sedans, Coupes & Sports Cars


When Z-speed rated tires were first introduced, they were thought to reflect the highest tire speed rating that would ever be required, in excess of 240 km/h or 149 mph. While Z-speed rated tires are capable of speeds in excess of 149 mph, how far above 149 mph was not identified. That ultimately caused the automotive industry to add W- and Y-speed ratings to identify the tires that meet the needs of new vehicles that have extremely high top-speed capabilities.

W 168 mph 270 km/h Exotic Sports Cars
Y 186 mph 300 km/h Exotic Sports Cars


While a Z-speed rating still often appears in the tire size designation of these tires, such as 225/50ZR16 91W, the Z in the size signifies a maximum speed capability in excess of 149 mph, 240 km/h; the W in the service description indicates the tire's 168 mph, 270 km/h maximum speed.

225/50ZR16 in excess of 149 mph, 240 km/h
205/45ZR17 88W 168 mph, 270 km/h
285/35ZR19 99Y 186 mph, 300 km/h


Most recently, when the Y-speed rating indicated in a service description is enclosed in parentheses, such as 285/35ZR19 (99Y), the top speed of the tire has been tested in excess of 186 mph, 300 km/h indicated by the service description as shown below:

285/35ZR19 99Y 186 mph, 300 km/h
285/35ZR19 (99Y) in excess of 186 mph, 300 km/h


As vehicles have increased their top speeds into Autobahn-only ranges, the tire speed ratings have evolved to better identify the tires capability, allowing drivers to match the speed of their tires with the top speed of their vehicle.

most speedos read 12-25% high. pretty easy to verify with a GPS unit.

Wait i dont get it... I read your posts after and you are saying it is rev limited, yet you also say its drag limited.... Every car is drag limited once the rev limiter is off... If it is drag limited then why were my rps not even close to redline at 154MPH?

electronically limited from the factory to ~155mph.

It is drag limited to about 165, give or take.

to the bolded part--drag limited means you can't run the car to redline because there isn't enough power to overcome the drag....

I think you're just misunderstanding me.

In terms of real world top speed (with the speed limiter removed) it is drag limited to around 168 mph. At that speed there is simply too much drag for the engine and gearing to overcome.

In stock form, the car is limited to around 155 mph. This could be a rev limit *IF* that's the type of governor used... where the ECU says "I'm going to cut fuel at X RPM in top gear where X RPM = 155 mph or thereabouts."

okay gotcha, i see what you mean now

I've only hit 110mph in my Z, so Im still a ways away from finding out what she'll do, theres not many roads around here to open her up..

ive hit 150 in my auto, forgetting to upshift in manuel mode to the 7th gear lol

Come visit Maine, ill show you some! :driving:

Not that I ever would outside a track, or on a track for that matter, but it's nice to know the RE070s I got are (Y) rated. FWIW, a stock 370Z will do ~175mph on the old Mulsanne straight at Le Mans...in Forza 4 :driving:

:icon18: I love that track to test out all my cars.

This sunday after few weeks take my baby to highway. Outside temp were really low - 2'C and winter tires on 18" wheels.

The Vmax by speedo reached were 270 km/h!!!! the 255 km/h on 5th gear (but limiter is higher). It was first time with speed exceeding 200 km/h for longer time and I'm really nicely surprised :driving:BTW: RON95 used for few last tanks.

135 to 150mph is kinda slow to get to. The Z definately needs bolt ons for a smoother-quicker ride to 155mph. But this car sure feels crazy above 140mph in spite of the kinda laggy accel up high.

Went just shy of 155, and the car kept going.. Friend of mine said it would be limited to 110, but that was disproven :)