7k RPM 3rd gear speed

[stangman638]

Noticed something strange the other day on my 2019 GT, my speed at 7k RPM was roughly 70MPH when using the paddle shifters... On my 2018 I was in the low 90's in 3rd at 7k ish RPM ... ???? Am I crazy? the 2019 has the 3.55's but thats a 20+ mph gap

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[GregP27]

Depend on what gear you were in at the time (and the ratio). It wasn't top gear. Also depends on what tires you are running. You said 3.55, right. So, you are running a 10-speed auto, at least of it is a 2019 model.

 

[stangman638]

Depend on what gear you were in at the time (and the ratio). It wasn't top gear. Also depends on what tires you are running. You said 3.55, right. So, you are running a 10-speed auto, at least of it is a 2019 model.

Same tires.. only difference is the 18 had 3.15 and the 19 is PP1 with 3.55's ,,, Both in 3rd gear from 2500rpm to 7kish . I didnt think there would be a 20mph difference.

 

[EFI]

It shouldn't be 20mph, so my guess is you weren't in the same exact spot in the RPM range.

To be exact, it's about 11mph difference...so maybe try to log speed vs rpm with something and report back on the difference.

 

[stangman638]

It shouldn't be 20mph, so my guess is you weren't in the same exact spot in the RPM range.

To be exact, it's about 11mph difference...so maybe try to log speed vs rpm with something and report back on the difference.

Yeah you are right... 2018 non PP 3.15 83mph at approx 7200 and 2019 PP 3.55 78mph I think I was remembering speed at 7500+ RPMs on the 18..

 

[GregP27]

We can calculate the theoretical speed easily. Need tire size, transmission gear, and differential. You already said 3.55 diff. If you have a manual, third should be 1.42. If you have and Auto, third should be 2.15. That assumes 5.0 V8 ... different for Ecoboost. If you have the stock 275/40R-19 tires, the circumference is 86.901 inches. Sidewall height = 40% of 275 = 110 mm = 4.331 inches. Diameter is 19 inches for wheel and 2 times sidewall height to give 27.66 inches. Circumference is 86.901 inches.

So, assume 6-speed manual. Third is 1.42, Diff is 3.55, tire circumference is 86.901 inches. Then 7,000 rpm SHOULD give you 114.27 mph. Conversely, 70 mph should give you 4,288 rpm.

If you have an auto, tires are the same, diff is 3.35, third gear is 2.15. 7,000 rpm will give you 80 mph. 70 mph would be 6,127 rpm.

I'm guessing you have an automatic transmission, but would not care to speculate in engine or tire size.

If anyone is interested, I can post the Excel file when I get home from vacation, so you can do your own calculations.

Cheers.

 

[stangman638]

We can calculate the theoretical speed easily. Need tire size, transmission gear, and differential. You already said 3.55 diff. If you have a manual, third should be 1.42. If you have and Auto, third should be 2.15. That assumes 5.0 V8 ... different for Ecoboost. If you have the stock 275/40R-19 tires, the circumference is 86.901 inches. Sidewall height = 40% of 275 = 110 mm = 4.331 inches. Diameter is 19 inches for wheel and 2 times sidewall height to give 27.66 inches. Circumference is 86.901 inches.

So, assume 6-speed manual. Third is 1.42, Diff is 3.55, tire circumference is 86.901 inches. Then 7,000 rpm SHOULD give you 114.27 mph. Conversely, 70 mph should give you 4,288 rpm.

If you have an auto, tires are the same, diff is 3.35, third gear is 2.15. 7,000 rpm will give you 80 mph. 70 mph would be 6,127 rpm.

I'm guessing you have an automatic transmission, but would not care to speculate in engine or tire size.

If anyone is interested, I can post the Excel file when I get home from vacation, so you can do your own calculations.

Cheers.

Did you mean 3.55 (instead of 3.35)?

Stock PP tires, 3.55 Rear Diff 10r80 5.0 engine in 3rd gear .. 7k RPM speed would be?

 

[GregP27]

AFAIK, stock rear tires are 275/40R-19 for PP1, PP1 Auto is 3.55 Differential, and gears have 10 ratios, but 3rd is 2.150.

With these numbers, Speed is 75.47 mph at 7,000 rpm.

Conversely, 70 mph would show up as 6,482 rpm.

 

[Pero]

If anyone is interested, I can post the Excel file when I get home from vacation, so you can do your own calculations.

@GregP27: I'm interested in your Excel file for theoretical speed calculation.

 

[GregP27]

OK, here it is. Sorry, I didn't design this for public consumption. I originally did it just for me.

1) The 2019 diff ratios and transmission ratios are shown to the left.
2) You enter you Diff ratio and the gears you are interested in.
3) To the left below the gear stuff, enter the driven tire size (where it says 275 / 40 - 19).
4) You enter an rpm or a mph you are interested in and it calculates: 1) the mph for rpm of interest and 2) rpm for mph of interest.

I could dress this up and make it for more public consumption, but you get the idea.

This stuff is fun! Cheers!

 

[Idaho2018GTPremium]

Factory shift points at redline in the PP1 w/ 3.55 and A10 equate to:
1st: 35 mph
2nd: 55 mph
3rd: 77 mph
4th: 94 mph
5th: 109 mph
6th: not sure

So I'm guessing you mis-remembered (I see you noted that). The difference between 3.15 and 3.55 is about 13%.

It's interesting to me how close 4th and 5th gears are.

 

[Condor1970]

I think I was going about 110mph... or there-about. I was too busy looking at the road.

Oh wait, I have a Manual. Nevermind...

 

[Zinc03svt]

I have plenty of logs I could look at to see what the speed is @ that rpm.

 

[frank s]

I'll see if I can upload don_w's tire/gear/rpm/speed xls files, one copy zipped. It was made for S197s through 2009, but even with my near-absent Excel understanding and skills I was able to translate the formulas to cover through my 2014 automatic. It took finding a chart of the gear ratios and extending the calculations by substituting the new and additional information. I haven't done the S550, lacking the motive and concentration I had earlier. Someone here will undoubtedly have the interest and ability to update this really useful appliance; when he does, I'd surely like to have access to it. And I thank him profusely, in advance.

I'll keep trying to give access to the files. Plenty of trial-and-error going on here.

Well, then: I rediscovered the most recent version of the Excel RPM v. MPH file, and my DropBox account. Click on the link, then select Download to go into Save As mode. There you have it, I hope.

https://www.dropbox.com/preview/Public/!B_ADD_AUTORPM_vs_Speed~16SpeedAddedOrigA_B.xls?role=personal

 

[frank s]

I'll see if I can upload don_w's tire/gear/rpm/speed xls files, one copy zipped. It was made for S197s through 2009, but even with my near-absent Excel understanding and skills I was able to translate the formulas to cover through my 2014 automatic. It took finding a chart of the gear ratios and extending the calculations by substituting the new and additional information. I haven't done the S550, lacking the motive and concentration I had earlier. Someone here will undoubtedly have the interest and ability to update this really useful appliance; when he does, I'd surely like to have access to it. And I thank him profusely, in advance.

I'll keep trying to give access to the files. Plenty of trial-and-error going on here.

Well, then: I rediscovered the most recent version of the Excel RPM v. MPH file, and my DropBox account. Click on the link, then select Download to go into Save As mode. There you have it, I hope.

https://www.dropbox.com/preview/Public/!B_ADD_AUTORPM_vs_Speed~16SpeedAddedOrigA_B.xls?role=personal

There you have it, I hope.

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