How fast is your car in 2nd gear?

67LS1 said:

73 mph

Based on a 6800 rpm redline, 2.37 ratio 2nd gear, 3.07 rear end and 26.6" tall tires.

Reminds me of a Click and Clack article (may have been transcript) I read where a guy wrote in with a 911, noting that his speedometer read correct at normal speeds but was low for the RPM at 180mph.  They were going on about how there must be a problem with the speedometer because there's no way the tires were spinning at those speeds.

Um.

Pneumatic tires work by traction, and traction has a degree of slippage.  Slippage increases with power.  Peak grip may occur at over 10% slip.  So, given that the mechanical speedometer got its reading from the front tires, YES, the tires were in all probability slipping enough to account for the discrepancy.

My swaps (rx8 with t5 and 4.44 rear gear) does like 49 in 2nd gear.

The rx7 swap with t5 and 4.10 rear gear...  also does like 49 in 2nd gear.

18s versus 15s.

Top speed in both is right around 130 gear limited.

Both gm 60degv6 swapped.  Rx7 with a 3500.  Rx8 with a 3900 swapped.

No speedo on my track cars, so I dunno, slower than third.

frenchyd said:

Keith Tanner said:

145 mph or so in first.

Which Teasla do you have again? 

Model 3 Dual Motor. The Performance is faster :)

Pete. (l33t FS) said:

67LS1 said:

73 mph

Based on a 6800 rpm redline, 2.37 ratio 2nd gear, 3.07 rear end and 26.6" tall tires.

Reminds me of a Click and Clack article (may have been transcript) I read where a guy wrote in with a 911, noting that his speedometer read correct at normal speeds but was low for the RPM at 180mph.  They were going on about how there must be a problem with the speedometer because there's no way the tires were spinning at those speeds.

Um.

Pneumatic tires work by traction, and traction has a degree of slippage.  Slippage increases with power.  Peak grip may occur at over 10% slip.  So, given that the mechanical speedometer got its reading from the front tires, YES, the tires were in all probability slipping enough to account for the discrepancy.

Or, more likely, at 180 mph the tire diameter has increased more at the lightly loaded front, especially if there's some front end lift going on.

Or, customer doesn't notice a 1 mph discrepancy at 60 mph but can see a 3 mph discrepancy at 180.

In reply to Keith Tanner :

It was something like 10mph off.  Less than 10% but more than the error at low speed.

I give it a wash, use GPS if you're that particular   At 180, your actual speed doesn't matter much.

This thread made me realize that I have no idea where my Volvo is at the top of 2nd gear.  I don't feel very comfortable spinning something with a 95.5mm crank up at 6750.  Or hitting a rev limiter.  Or risking another transmission pump failure, which occurred very shortly after hitting the rev limiter the first time.

I know the one RX-7 does 70ish in 2nd on asphalt, about 45-55 on dirt, even when it is grippy dirt.

frenchyd said:

AnthonyGS (Forum Supporter) said:

In reply to frenchyd :

Which one?  You think most people here have just one car......

Fair enough, which ever one you'd like. 

About 60, but when I'm going that fast in 2nd I'm pretty busy looking at things that are not the speedometer.  
 

70ish, again kinda busy looking at other things.  

Pete. (l33t FS) said:

67LS1 said:

73 mph

Based on a 6800 rpm redline, 2.37 ratio 2nd gear, 3.07 rear end and 26.6" tall tires.

Reminds me of a Click and Clack article (may have been transcript) I read where a guy wrote in with a 911, noting that his speedometer read correct at normal speeds but was low for the RPM at 180mph.  They were going on about how there must be a problem with the speedometer because there's no way the tires were spinning at those speeds.

Um.

Pneumatic tires work by traction, and traction has a degree of slippage.  Slippage increases with power.  Peak grip may occur at over 10% slip.  So, given that the mechanical speedometer got its reading from the front tires, YES, the tires were in all probability slipping enough to account for the discrepancy.

I'm not exactly sure which you're suggesting, but the front tires aren't slipping unless they're being powered. And if you've got 10% (or really any) rear tire slip at 180mph your day is about to get really really bad.

Modern porsches for whatever reason have optimistic reading speedometers. I'm not totally sure if it's a fixed offset or proportional, but if it's proportional then that barely noticeable 2mph at 60mph becomes 6mph at 180. Similarly most things that affect the reading are proportional and are going to have a bigger impact at higher speeds. And that's also making some assumptions about tach accuracy, especially reading at the end of its range versus the middle.

Pete. (l33t FS) said:

67LS1 said:

73 mph

Based on a 6800 rpm redline, 2.37 ratio 2nd gear, 3.07 rear end and 26.6" tall tires.

Reminds me of a Click and Clack article (may have been transcript) I read where a guy wrote in with a 911, noting that his speedometer read correct at normal speeds but was low for the RPM at 180mph.  They were going on about how there must be a problem with the speedometer because there's no way the tires were spinning at those speeds.

Um.

Pneumatic tires work by traction, and traction has a degree of slippage.  Slippage increases with power.  Peak grip may occur at over 10% slip.  So, given that the mechanical speedometer got its reading from the front tires, YES, the tires were in all probability slipping enough to account for the discrepancy.

 

Not sure about slippage at 73 mph? My cars converter does lockup in 2nd through 6th gears. But my car has no speedo so that's why I was only able to extrapolate my speed in second gear. And if a I did have a speedo in my car it would be driven from the ECM that gets its data from the transmission output shaft. Or I suppose I could get a gps speedo.

In reply to Keith Tanner :

That's impressive!   

Forte tuned was 68ph. Pre-tune 62. Rio is 59 on stock wheel/tire combo. 56 in the race tires. 3rd is 95/90.

To contribute a bit to the Porsche discussion:

"European law (ECE-R39) says speedometers cannot show speeds less than the actual speed, and they must never show more than the 110 per cent of actual speed plus 4 km/h."

It's really, really against the rules to read low, but there's lots of space above, so German speedos are always optimistic.

I came across a tidbit (from a legitimate source) years ago that the NA Miata speedo was optimistic to the fullest extent of the law, to heighten the sensation of speed. Someday I'll come across it again, it might have been in the Yamaguchi books. Definitely pre-Facebook. If you've spent much time with Miata speedometers, it has the ring of truth.

Also, the tachs are optimistic when they're moving fast but seem more accurate when they're moving more slowly. On a rip through the gears, you can see 7500 indicated on a 7300 rpm fuel cut. Or 8000 on a 7800.

Pete. (l33t FS) said:

In reply to Keith Tanner :

It was something like 10mph off.  Less than 10% but more than the error at low speed.

I give it a wash, use GPS if you're that particular   At 180, your actual speed doesn't matter much.

This is true. I once, took my friends '06 R1 to the limiter in the 6th gear. I think the speedometer showed just under 200, which gives credence to speedo's reading high, since the factory limiter is supposed to be 186. 

In reply to AnthonyGS (Forum Supporter) :

I really dig that 4th gen.

This hoopty o' mine (w211 E55) shifts outta 2nd at 82. 

Surprisingly, 76 mph at max rpm (7000) with stock 15" tires. Data is for a 1958 MG.

My '18 Mazda 3 is rev limited to 60 mph in 2nd. I imagine this was done intentionally to enhance the 0 to 60 time for the spec book.  

64

My Camaro will do 97 MPH at my 6500 RPM shift point or pull to 105 or so if I let it hit the 7,000 RPM rev limiter.  Based on gearing and RPM alone it has a theoretical top speed of 220 MPH against the redline but I'm sure that it takes more than 640 HP to push a second gen Camaro through the air at that speed. I suspect that it really tops out at around 170 or so.

My Formula Ford has a quick change gearbox so it can, depending on what gears are installed, theoretically be whatever I want up to the 135 MPH or so top speed of the car.

APEowner said:

My Camaro will do 97 MPH at my 6500 RPM shift point or pull to 105 or so if I let it hit the 7,000 RPM rev limiter.  Based on gearing and RPM alone it has a theoretical top speed of 220 MPH against the redline but I'm sure that it takes more than 640 HP to push a second gen Camaro through the air at that speed. I suspect that it really tops out at around 170 or so.

My Formula Ford has a quick change gearbox so it can, depending on what gears are installed, theoretically be whatever I want up to the 135 MPH or so top speed of the car.

The 1975 Jaguar XJS shifts at 110 mph into high gear which tops out at 155 mph. 
  My 2016 Ford F-150 pickup shifts at 12 mph from 2nd gear to third. 
 My 1953 MGTD redlines (5000) at 28mph In 2nd gear. 

Opti said:

In reply to AnthonyGS (Forum Supporter) :

I really dig that 4th gen.

Thanks there is quite a bit more info about it in my poorly named build thread.  This long weekend will be used to do a lot on it.  It's about ready for its first run at CAM.  I'm seriously considering a 24x conversion soon too.  It's a real 96 SS and had all the SLP options (yes all).  It's a slick top 6 speed to boot.  

...

You know, I am slightly relieved that this has not come up yet.  But only slightly.

I only know my stock 2007 Cayman S was 106 in 3rd. I trapped at 107mph in the 1/4mile but had to shift at the trap or i'd hit the rev limiter (which makes you want to vomit as you'll hit it and it cuts everything so it feels like you blew a $26k motor).

Race me on a mexican street and you'll probably be in top gear when you egg me on and I will be in 3rd ready to blow your doors off. I cannot say no.

In reply to preach (fs) :

LS1 Camaros with the T56 could hit about 106 in 3rd.

The funny part is, the convertibles were speed limited to 108 because of the tires/suspension.  So they'd hit the speed limiter in 6th, 5th, 4th, and almost 3rd.