Few questions for 2017 stick shift owners

[nextcar]

Originally Posted by Tcoat

Probably the least of the concerns with this thread really.

[Borchert97]

Originally Posted by Tcoat

Again not a great way since they can vary even more than GPS or the speedometer. Those signs are just designed to be in the general ballpark and are not a precision device.

Nah the ones I've seen are all fairly accurate, they use similar equipment to what cops use, and considering the only number that matters is the one the cops get, I'll gladly use it as my benchmark instead of the speedo or some GPS.

[Tcoat]

Originally Posted by Borchert97

Nah the ones I've seen are all fairly accurate, they use similar equipment to what cops use, and considering the only number that matters is the one the cops get, I'll gladly use it as my benchmark instead of the speedo or some GPS.

How do you know they are "fairly accurate"?
They are not even remotely close to what the cops use.

[strat61caster]

Originally Posted by nextcar

And you guys are aware that the final drive ratio varies by country, and in the US at least was changed for manual transmission cars in 2017, right?

Well I didn't give a specific number, so unless it's 3.5k+ on the 17 I am confident the answer I gave is not wrong.

[billwot]

Originally Posted by nextcar

You sure about that? Not the wheel speed sensors used by the ABS system?

Even if that's correct, its reading rotation...its recording the RPM of a rotating component. The tire size will not alter the rate of rotation.

No speedometer actually records linear travel, it only estimates it based on reading the rotational speed of a rotating component.

[Gil Scott Heron]

Originally Posted by billwot

Even if that's correct, its reading rotation...its recording the RPM of a rotating component. The tire size will not alter the rate of rotation.

No speedometer actually records linear travel, it only estimates it based on reading the rotational speed of a rotating component.

If a smaller diameter tire has to rotate faster to achieve the same automobile speed, wouldn't that indicate a higher speedometer readout, given that the sensors are from the output shaft to the rear wheels?

[nico_rsx]

Originally Posted by Gil Scott Heron

If a smaller diameter tire has to rotate faster to achieve the same automobile speed, wouldn't that indicate a higher speedometer readout, given that the sensors are from the output shaft to the rear wheels?

Yes. If you have smaller diameter tires (not wheel diameter), or very worn tire, your speedometer readout will be higher than reality.

[humfrz]

OK, maybe I missed it ....... but what component is measured for our car to calculate its speed .......??


humfrz

[nextcar]

Originally Posted by humfrz

OK, maybe I missed it ....... but what component is measured for our car to calculate its speed .......??


humfrz

Wheel rotation

[humfrz]

Originally Posted by nextcar

Wheel rotation

Well, OK, then, so, the only variable that would effect the linear speed reading (besides the rotation speed of the wheel) would be the circumference of the tire ....... right ..... ??


humfrz

[billwot]

Guys...the speedo reads the rotation of some component in the drive train Different tire circumferences will effect actual speed, and will effect a discrepancy between actual speed and the speed indicated on the speedo, but the tire circumference will not change the speedo reading.

If a 10 inch wheel is turning at 1000 RPM, or if a 20 inch wheel is turning at 1000 RPM, the speedo will still read the same. The only "data" the speedo sees is rate of rotation. You can jack it up and take the wheels off, and the speedo will still read the same.

Tire size alters actual speed. Tire size has no effect on speedometer reading.

[mjanmohammad]

Originally Posted by curiosul

Actually thinking about getting one. I test drove one (see my impressions here) but I didn't have time to notice/check everything.
Questions:

1: What rpms do you get at 70 mph?
There's no youtube video of someone cruising (or even accelerating) in 6th gear. Maybe some one can post a youtube video of cruising, 1/3 throttle accelerating from 60 and WOT accelerating from 60 in 6th gear?
2: How accurate is the speedometer (compared to GPS)?
All the old cars I've had were doing around 67 when 70 was indicated.
The newest car I have (a 2016) is SPOT ON.
3: What kind of cruising MPGs do you get (flat road, no AC, 70mph, stock)?
4: How accurate is the indicated fuel consumption?
5: For "early adopters" (people who bought it in early fall) did you notice a big difference in fuel consumption between summer and winter blends of gas?
6: How do you get the high beams with the new headlights?
Is there a separate bulb (that I can't see in pictures) or is the whole assembly twisting up? Is it blinding for the incoming traffic or just a tad brighter than low beams?

Thank you!

2017 BRZ here

1. Around 3k rpm
2. Haven't tested, but its always 1mph lower than my radar detector's speed indicator when an alert goes off
3. Display shows 27.4 mpg on mine (75% highway and some joining around). Fully shows 25mpg average since I bought it a month ago
4. See above.
5. Not applicable (but I do see a difference between certain brands of gas)
6. It's built into the housing for the headlights. Much brighter than the stock lamps

[nextcar]

Just because I cannot resist...

At 70MPH, a north america 2017 manual transmission 86/BRZ with stock tires will be at 3153 RPM. Change the model year to 2013-2016 and hold every other constraint and the answer is 3007 RPM.

Because math. Relevant data:

2013-2017 stock tire diameter: 24.62 inches.
2013-2017 MT 6th gear ratio 0.767
2017 NA MT ring and pinion: 4.30
2013-2016 NA MT ring and pinion 4.10

[Tcoat]

Originally Posted by billwot

Guys...the speedo reads the rotation of some component in the drive train Different tire circumferences will effect actual speed, and will effect a discrepancy between actual speed and the speed indicated on the speedo, but the tire circumference will not change the speedo reading.

If a 10 inch wheel is turning at 1000 RPM, or if a 20 inch wheel is turning at 1000 RPM, the speedo will still read the same. The only "data" the speedo sees is rate of rotation. You can jack it up and take the wheels off, and the speedo will still read the same.

Tire size alters actual speed. Tire size has no effect on speedometer reading.

I think that is the point of what people are saying that the wheel size does change the actual speed vs what the speedo is reading so that is the variation.

What seems to be the common belief is that the wheel size has a huge impact on on the difference between the two. You need to have a huge increase/decrease in size of the wheel to really make that big a difference. It takes a 2 or 3 inch increase to show a 5MPH between actual and gauged speed and the little bit of change a worn tire will give is in the fractions of a MPH. All in all not as big a deal that people are making it out to be.