Go Back   EcoModder Forum > EcoModding > Aerodynamics
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 11-26-2014, 01:42 PM   #1 (permalink)
Liberty Lover
 
j12piprius's Avatar
 
Join Date: Feb 2011
Location: central california
Posts: 587

pris prius - '12 Toyota plug in prius
90 day: 71.09 mpg (US)
Thanks: 417
Thanked 83 Times in 60 Posts
difference in drag during trips ~ aero or brakes?

On a long steep downhill, my previous top coasting speed was 49.1 mph which the car hit and maintained for 1/4 to 1/2 a mile. The top speed during the last trip was only 45.6 mph, a 3.5 mph difference. There was a similar difference in my mpg average for the trips in either direction.
Code:
                    october   november   difference
downhill coasting     49.1mph   45.6mph   - 3.5
east 125 miles        58.9mpg   54.2mpg   - 4.7
west 125 miles        60.1mpg   56.5mpg   - 3.6
What is the most likely cause of this? The only changes I made were (1) trimming the bumper cover and smoothing/covering the under part, (2) enlarging the vent, and (3) removing resistance from the brakes. However I'm still suspecting the brakes, maybe due to sticking front pistons. Two hours after getting home (I forgot right after), the temperature outside the front wheel covers was 4 degrees higher than in back. The setback is disappointing, and I'm wondering what to focus on next.

previous bumper cover


current bumper cover

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 11-26-2014, 02:13 PM   #2 (permalink)
Eco-ventor
 
jakobnev's Avatar
 
Join Date: Oct 2010
Location: sweden
Posts: 1,214

Princess - '92 Mazda MX-3 GS
House of Tudor
Team Mazda
90 day: 53.54 mpg (US)
Thanks: 49
Thanked 416 Times in 263 Posts
Send a message via MSN to jakobnev
Could be just lower ambient temperatures.
__________________




2016: 128.75L for 1875.00km => 6.87L/100km (34.3MPG US)
2017: 209.14L for 4244.00km => 4.93L/100km (47.7MPG US)
  Reply With Quote
Old 11-26-2014, 03:58 PM   #3 (permalink)
Liberty Lover
 
j12piprius's Avatar
 
Join Date: Feb 2011
Location: central california
Posts: 587

pris prius - '12 Toyota plug in prius
90 day: 71.09 mpg (US)
Thanks: 417
Thanked 83 Times in 60 Posts
ambient conditions

Temperatures were the same, in the 70s in mid afternoon.

I'd warmed the car up prior to starting, then driven 70 miles by that point.

Wind was negligible the previous trip, and slightly favorable during the last one.
  Reply With Quote
Old 11-26-2014, 04:28 PM   #4 (permalink)
Beating EPA Unmodded
 
Join Date: Oct 2014
Location: Oklahoma City
Posts: 143

Blue Eagle - '10 Honda Civic LX
Team Honda
90 day: 31.12 mpg (US)
Thanks: 4
Thanked 28 Times in 23 Posts
Could be the different types of fuel that the pump uses, since it is getting colder out, the gas stations have been switching to different types of fuel, which isn't good for fuel economy.
__________________

  Reply With Quote
Old 11-26-2014, 05:10 PM   #5 (permalink)
Liberty Lover
 
j12piprius's Avatar
 
Join Date: Feb 2011
Location: central california
Posts: 587

pris prius - '12 Toyota plug in prius
90 day: 71.09 mpg (US)
Thanks: 417
Thanked 83 Times in 60 Posts
I'm not sure about the differences in fuel, as I think they're not shown on the pumps, but that wouldn't explain the different speeds for dfco coasting down the hill, which felt like a major difference. The previous trip the car was going full blast, and the last time hardly moving along.
  Reply With Quote
Old 11-26-2014, 07:22 PM   #6 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 10,504
Thanks: 16,273
Thanked 5,586 Times in 3,339 Posts
difference

If you had full instrumentation and data-logging capability we might be able to figure something out.There's just too many possible variables which would have to be nailed down to find the signal in the background noise.
You'd also probably want to do at least 10-runs each time and average the numbers,just as in coastdown testing.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Old 11-26-2014, 09:50 PM   #7 (permalink)
Master EcoModder
 
JRMichler's Avatar
 
Join Date: Feb 2011
Location: Phillips, WI
Posts: 965

Nameless - '06 GMC Canyon
90 day: 34.17 mpg (US)
Thanks: 185
Thanked 391 Times in 252 Posts
Quote:
Originally Posted by johnlvs2run View Post
Temperatures were the same, in the 70s in mid afternoon.

I'd warmed the car up prior to starting, then driven 70 miles by that point.

Wind was negligible the previous trip, and slightly favorable during the last one.
Tire pressure?
Check brake disks/drums after driving several miles and coasting to a stop. They should all be at ambient temperature.
__________________
The vacuum gauge plus wheel covers helped increase summer 2015 mileage to 38.5 MPG, while summer 2016 mileage was 38.6 MPG without the wheel covers. Drove 33,021 miles 2016-2018 at 35.00 MPG.
  Reply With Quote
Old 11-27-2014, 12:14 AM   #8 (permalink)
herp derp Apprentice
 
Join Date: Oct 2008
Location: Lawrence, KS
Posts: 1,031

Saturn-sold - '99 saturn sc1
Team Saturn
90 day: 28.28 mpg (US)

Yukon - '03 GMC Yukon Denali
90 day: 14.4 mpg (US)
Thanks: 42
Thanked 315 Times in 226 Posts
Brake temps -
In diagnosing vehicles with a known but intermittent brake drag problem present, I have finally stopped using an infrared temp gun to try to help diagnose which wheel has the issue. It makes no sense to me why it doesn't help, but more often than not it will misdirect me.
  Reply With Quote
Old 11-27-2014, 03:00 AM   #9 (permalink)
Liberty Lover
 
j12piprius's Avatar
 
Join Date: Feb 2011
Location: central california
Posts: 587

pris prius - '12 Toyota plug in prius
90 day: 71.09 mpg (US)
Thanks: 417
Thanked 83 Times in 60 Posts
Tire pressure was 52 psi for both trips.

Quote:
Originally Posted by 2000mc View Post
Brake temps - In diagnosing vehicles with a known but intermittent brake drag problem present, I have finally stopped using an infrared temp gun to try to help diagnose which wheel has the issue. It makes no sense to me why it doesn't help, but more often than not it will misdirect me.
What have you found to be most likely causes of intermittent brake drag?
  Reply With Quote
Old 11-27-2014, 04:17 AM   #10 (permalink)
herp derp Apprentice
 
Join Date: Oct 2008
Location: Lawrence, KS
Posts: 1,031

Saturn-sold - '99 saturn sc1
Team Saturn
90 day: 28.28 mpg (US)

Yukon - '03 GMC Yukon Denali
90 day: 14.4 mpg (US)
Thanks: 42
Thanked 315 Times in 226 Posts
Caliper, flexible brake hose.
Do confirm where the problem lies before replacing components, I've worked on a guy's Colorado where literally everything in the hydrolic system was replaced except for the hard lines by another shop. Booster was the problem
Gm full size vans can get an unusually hard pull due to aftermarket pads, but they don't actually drag.


When you think it is actively dragging, is when you would want to be able to pick it up asap, to spin the wheel to check for the drag. Might not drag for whatever reason ( I think heat related usually ) if it sits very long.


Last edited by 2000mc; 11-27-2014 at 04:41 AM..
  Reply With Quote
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2019, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com