1.4T highway cruise RPM

[RichieRocket]

I wanted to get an idea of what the RPM would be at highway speeds. I found the Sonic transmissions gear ratios online and the axle ratio was on the Sonic options sheet.

I listed out the gear ratios for the three transmissions, then multiplying by each axle ratio, you get the 'overall drive ratio' for each. So for the 6-spd manual, in first gear, the engine turns over 14 times for one rotation of the wheel. In 6th gear, the engine only turns 2.23 times for one wheel rotation.

For the 195/65-15 tires, the rolling diameter is 25"

At 70 mph, the 25" dia tire spins at 941 RPM

The overall drive ratio in 6th gear is 2.23, so

Engine RPM = 2.23 X 941 RPM = 2100 RPM @ 70 mph

The low-end torque of the turbo engine really allows the highway cruise RPM to be really low!

For comparison, my '98 Civic turns 3000 RPM @ 70 mph

 

[Stic5]

that's pretty impressive... both your math and the Sonic's cruising rpm.

 

[tainopayute]

I wanted to get an idea of what the RPM would be at highway speeds. I found the Sonic transmissions gear ratios online and the axle ratio was on the Sonic options sheet.

I listed out the gear ratios for the three transmissions, then multiplying by each axle ratio, you get the 'overall drive ratio' for each. So for the 6-spd manual, in first gear, the engine turns over 14 times for one rotation of the wheel. In 6th gear, the engine only turns 2.23 times for one wheel rotation.

For the 195/65-15 tires, the rolling diameter is 25"

At 70 mph, the 25" dia tire spins at 941 RPM

The overall drive ratio in 6th gear is 2.23, so

Engine RPM = 2.23 X 941 RPM = 2100 RPM @ 70 mph

The low-end torque of the turbo engine really allows the highway cruise RPM to be really low!

For comparison, my '98 Civic turns 3000 RPM @ 70 mph

What Sonic did you use to get these RPM numbers, the LTZ or the RS? I ask because on my RS my RPM's are 3,100 at 70 mph.

 

[The Champ]

The final drive ratio of a non RS Sonic 1.4LT with automatic is actually 3.23, not 2.23.

6th gear is .75 - so the actual effective 6th gear ratio is 2.42.

Transmissions
Hydra-Matic 6T40 6-speed automatic (1.4L Turbo)
Fifth: 1.00
Sixth: 0.75
Reverse: 2.94
Final drive:3.53 (Sonic RS) 3.23 (Sonic)

So RPM with a 25" tire at 70 MPH calculates to 2279 using a standard RPM calculator:

Engine RPM Calculator

This correlates to my actual indicated RPM at 70 - which displays about 2300.

Doing the same calculations for an RS automatic that has a final drive of 3.53 the calculated RPM is 2491.

Actual tire size and tire inflation will affect the numbers.

 

[ScarabEpic22]

What Sonic did you use to get these RPM numbers, the LTZ or the RS? I ask because on my RS my RPM's are 3,100 at 70 mph.

Not our RS 6MT, that sounds about right for my car too. 4.18 final drive kills the mpg at high speeds, wish 6th was a really high (low numerically) OD gear to compensate.

 

[The Champ]

Not our RS 6MT, that sounds about right for my car too. 4.18 final drive kills the mpg at high speeds, wish 6th was a really high (low numerically) OD gear to compensate.

Automatic would have a 3.53 and .75 6th gear vs. your 4.176 and a .74 6th gear.

RPM calculator puts 70 MPH at 2910, which is 69 RPM less than my '64 GTO at 70...

 

[black granite sonic]

I have a RS with auto trans, When I'm rolling at 82 mph my tach reads 3 grand even when doing 95 the auto trans is around 3600.

 

[perrymk]

2100 RPM @ 70 mph

That sounds about right. Just glancing while driving mine is 2100-2200. I noticed because it seemed awfully low, but then I figured that's why it gets decent fuel economy. I average 39 MPG overall.

2014 Sonic Hatchback
1.4T, 6 speed stick

 

[tainopayute]

In my RS with a manual transmission, my RPM's in six gear at a highway speed of 70 mph is 3,100... does that sound about right to anyone?

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[zippypcs]

In my RS with a manual transmission, my RPM's in six gear at a highway speed of 70 mph is 3,100... does that sound about right to anyone?

Sent from my SM-G920T using Tapatalk

yes that would be correct for an R/S stick

 

[tainopayute]

yes that would be correct for an R/S stick

Thanks for your reply bud. That's a relief. I was beginning to think that sometime was wrong with my Sonic.

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[zippypcs]

My LTZ 6 speed does 2100 rpm @70 My buddies R/S 6 speed does 3100 rpm @ 70. We have swapped cars overnight a few times.
He also does not get the 40 plus mpg I get on the freeway more like 37-38.
Also I like the gearing in the LTZ vs the R/S just seems more drivable.
The R/S does feel a bit quicker out of the hole though.

 

[Dogz]

zippy, seeing as you have driven both is there a noticeable difference with in gear acceleration, 5th gear from 50 to 70.

 

[zippypcs]

Both have a tune. My LTZ has DDm intake and ZZP cat back.
R/S pulls harder in 5th gear 50-70. When I step out at 50mph in LTZ, I drop back to 3rd. It pulls quite hard there. Both have their good or sweet spots. The LTZ @ 50 mph and in 5th gear is meh.

 

[Natesriv]

4K RPM in an 1.4T is the sweet spot... Hit it in 4th, and you're gone!

 

[tainopayute]

My LTZ 6 speed does 2100 rpm @70 My buddies R/S 6 speed does 3100 rpm @ 70. We have swapped cars overnight a few times.
He also does not get the 40 plus mpg I get on the freeway more like 37-38.
Also I like the gearing in the LTZ vs the R/S just seems more drivable.
The R/S does feel a bit quicker out of the hole though.

That's exactly the comparison that I have been looking for. Thanks for posting this information bud...

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