RPM's at highway speeds

GlocksRock · #1 (**permalink**) 03-08-2002, 11:31 PM

What RPM's are you guys getting at highway speeds, say 60 to 80 mph, on your stock size tires (265/70/16) with your 4x4 V8? At 60 mph I am at exactly at 2K rpms. I remember reading stuff on this subject on the forum before it crashed, and it seemed others were around 70 mph at 2K, but I thought all the 4x4 V8 Tundras had the same gear ratio.

Thanks

arkie6 · #2 (**permalink**) 03-09-2002, 07:31 AM

I'm running about 61-62 mph at 2000 rpm. All Tundra V8s get the same axle gear ratio of 3.91 (rounded off). Each truck could have a slight variation in the tachometer and/or speedometer calibration. These are just electronic devices that take electronic pulses and convert them to an indication of RPM or MPH. They are not perfect devices and the calibration from one unit to the next is likely to vary a little.

Tire size will have no effect on your indicated speed if all the other components are stock. The speedometer is measuring how fast your transmission output shaft is turning. It doesn't know what size tire you have on. It is calibrated though for the Dunlop P265/70R16 tire size, at least on my truck. I have checked my indicated speed numerous times against various measures (timing between mile markers and police radar units) and my indicated speed is always within +/- 1 MPH of actual.

matttom · #3 (**permalink**) 03-09-2002, 06:10 PM

Mine does 63 MPH @ 2000 RPM

Larry Lawton · #4 (**permalink**) 03-09-2002, 06:12 PM

Kikyou,

Of course it's right, buddy. We all just KNOW adding Flowmasters lets you go 100 MPH at only 1500 RPM.

My Tundra goes about 61 or 62 at 2000 RPM. That's a 2001 4X4 limited, so it's got a 3.91 rear end. If our friend really went 100 miles an hour at 1500 RPM -- well, you do the math, but that's an axle ration never before seen on Detroit iron, IMNSHO.

Acura_Bossman · #5 (**permalink**) 03-09-2002, 07:45 PM

My Tundra does 12,000 RPM at 60mph in 4.79 sec flat. Mines equipped with 3 Hayabusa engines put together to exactly 4.7 liters. I like this mod the best.

Larry Lawton · #6 (**permalink**) 03-11-2002, 01:52 PM

You were RACING a Chevy and doing 60MPH, with only 1950 on the tach? You're pulling our legs, right?

If I were racing, I sure wouln't be in high gear at 60 -- which is where you'd have to be to see 1950 RPM.

TundraGuy · #7 (**permalink**) 03-11-2002, 02:13 PM

I think he was joking, because his tach shows 5000 RPMs and his speed is only 70mph, so he must have been in 2nd gear.

Sean

Larry Lawton · #8 (**permalink**) 03-11-2002, 04:49 PM

Toy, I'm sorry. I didn't carefully read your post.

In your first paragraph, you referred us to a picture of your instruments while racing. As others pointed out, that shows your tack 'way up there, your speedo at 70 MPH.

The second paragraph is on a different subject, and responds to an earlier question: How fast your truck goes at 2,000 RPM.

I will now go sit in the corner, put on that TALL pointed cap, and write fifty times:

"Paragraphs are used to separate different ideas while writing."

BirdDog0 · #9 (**permalink**) 03-12-2002, 07:04 AM

I'm with Hovismo here. At 2K, my normal highway speed, I register right around 68 mph, figuring a 5% error for the 285 BFGs, I'm actually travelling around 71-72 mph for 2000 rpms.

And YES, tire size, DOES make a difference in what you read on the speedo....

ra1nman · #10 (**permalink**) 03-12-2002, 07:13 AM

Here's a little somthing i'm throwing out that'll help calculate your speed with 2 different size tires..
http://www.csgnetwork.com/lttrucktireinfocalc.html

oneslackr · #11 (**permalink**) 03-12-2002, 01:09 PM

Here is another good site that helps w/tire sizing, gear ratios, & speedometer error.

The site below just reminded me - I sold my C5 back on Feb. 8th. Sure miss it. Hope the new Tundra puts a smile on my face when it arrives.

Oneslackr

www.c5-corvette.com/tirecalc.htm