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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 03-14-2009, 02:11 PM   #1 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 19,374

Blackfly - '98 Geo Metro
Team Metro
90 day: 65.31 mpg (US)

ForkenSwift - '92 Geo Metro EV
Last 3: 95.68 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 38.25 mpg (US)
Thanks: 2,005
Thanked 4,718 Times in 2,363 Posts
tire width vs. drag (Cd)

The question of the effect of tire width on drag seems to come up once in a while. So here's more data to add to the pile, from Hucho, 1998.

---

Influence of the tire width on drag, lift, and yawing moment, after H Kerschbaum Fig 5.72



CD --- tire & rim size (for a 1991 BMW 318i)

0.293 --- 155 R 15; 5 1/2 Jx15 St. with wheel covers
0.294 --- 165 R 15; 61 2 Jx15 St. with wheel covers
0.297 --- 175/70 R 15; 6 Jx15 St. with wheel covers
0.305 --- 185/65 R 15; 61 Jx15 St. with wheel covers
0.311 --- 205/60 R 15; 61 2 Jx15 St. with wheel covers
0.314 --- 205/60 R 15; 7 Jx15 LM
0.319 --- 225/55 R 15; 7 Jx15 LM

Keep in mind the increase in Cd comes with an increase in A (frontal/projected area) too, so you're getting a double whammy.

Add to this from Phil's notes:
  • 1986, wind tunnel development work for Subaru XT show a drag increase of 5.1 % when tire size is increased from 155 to 185 series radials.
  • 1984-1987 HONDA CRX shows jump from 165 to 185 series radials increase drag 9.3 %.
Phil's notes also point out that the increased drag from wider tires can be partially offset by managing the airflow ahead of them (dams/spats).

Attached Thumbnails
Click image for larger version

Name:	BMW_318i_91-98_front.gif
Views:	67
Size:	35.2 KB
ID:	7380  
__________________
Latest mods test: 15 mods = 15% MPG improvement: A-B test, 2007 Honda Civic 1.8L, 5-speed
Ecodriving test:
Manual vs. automatic transmission MPG showdown: Nissan Micra 1.6L



EcoModder
has launched a forum for the efficient new Mitsubishi Mirage
www.MetroMPG.com - fuel efficiency info for Geo Metro owners
www.ForkenSwift.com - electric car conversion on a beer budget
  Reply With Quote
The Following 7 Users Say Thank You to MetroMPG For This Useful Post:
aerohead (10-17-2012), ausias (10-17-2012), California98Civic (03-18-2011), Cd (11-21-2010), EngineeringStudent (12-06-2009), landsailor (11-20-2010), mikeyjd (07-01-2013)
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 03-14-2009, 09:54 PM   #2 (permalink)
(:
 
Frank Lee's Avatar
 
Join Date: Jan 2008
Location: up north
Posts: 11,862

Blue - '93 Ford Tempo
Last 3: 27.29 mpg (US)

ShWing! - '82 honda gold wing Interstate
90 day: 33.65 mpg (US)

F150 - '94 Ford F150 XLT 4x4
90 day: 18.5 mpg (US)

Sport Coupe - '92 Ford Tempo GL
Last 3: 69.62 mpg (US)

Moon Unit - '98 Mercury Sable LX Wagon
90 day: 21.24 mpg (US)
Thanks: 1,337
Thanked 2,826 Times in 1,804 Posts
Wow, I wouldn't have guessed the CRX' drag to go up that much.
  Reply With Quote
Old 03-14-2009, 10:03 PM   #3 (permalink)
38 time NHRA/IHRA Champ
 
ATaylorRacing's Avatar
 
Join Date: Jul 2008
Location: Fishers, IN
Posts: 305
Thanks: 1
Thanked 10 Times in 8 Posts
Couldn't a low rolling resistance tire that takes much higher air pressure cancel out the CD loss of a larger foot print? I am throwing that out there because the 13's on my 96 Geo 1.0 call for a max of 35 psi (I put in 39) while the 195/50/15 size that I want to put on in the distant future has a max reading of high 40s.
__________________
42 time NHRA/IHRA drag race champ

05 SRT4-12.17@117 mph on DOTs-31.0 mpg-SOLD
96 Geo Metro-3 banger-60.1 mpg-SOLD
95 BMW M3-13.41 @ 106 mph-31mpg-SOLD
77 Chevy Monza with 350/350-FOR SALE
84 Horizon-1880 lbs-29 mpg
95 Neon-43 mpg
99 Z28-10.80 @ 127 mph-27.1mpg
2011 Prius-62.1 wife's
  Reply With Quote
Old 03-16-2009, 05:37 PM   #4 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 8,277
Thanks: 10,029
Thanked 4,316 Times in 2,389 Posts
Couldn't

Quote:
Originally Posted by ATaylorRacing View Post
Couldn't a low rolling resistance tire that takes much higher air pressure cancel out the CD loss of a larger foot print? I am throwing that out there because the 13's on my 96 Geo 1.0 call for a max of 35 psi (I put in 39) while the 195/50/15 size that I want to put on in the distant future has a max reading of high 40s.
When I went from a 35 psi 165 70R-13 all-season steel radial,to a wider 175 60R-14 Michelin MXV4 Green-X 44-psi all-season radial,There was no loss in mpg,so I know,at least for the CRX,that the relationship worked.The ride improved,wet and dry traction improved remarkably,and tread is supposed to go 83,000 miles.From a safety aspect,I think it's a good way to go.And with fairings and strakes you can still probably compensate for the increase in frontal area.Net gain.
  Reply With Quote
Old 12-05-2009, 01:27 AM   #5 (permalink)
Master EcoModder
 
Join Date: Jan 2009
Location: Maui, Hawaii
Posts: 813
Thanks: 5
Thanked 32 Times in 25 Posts
I'm skeptical about the impact of wider tires on fuel use. A wider tire with the same contact patch as a narrower one is also deforming less, which has to count for something.
  Reply With Quote
Old 12-05-2009, 08:07 AM   #6 (permalink)
Tire Geek
 
CapriRacer's Avatar
 
Join Date: May 2008
Location: Let's just say I'm in the US
Posts: 637
Thanks: 0
Thanked 231 Times in 150 Posts
Quote:
Originally Posted by winkosmosis View Post
I'm skeptical about the impact of wider tires on fuel use. A wider tire with the same contact patch as a narrower one is also deforming less, which has to count for something.
Me, too! But rather than just wonder, I pulled out my Excel spreadsheet and did some calculations.

According to the first post (not sure where the data came from!) The average for a 10mm increase in tire width was 0.003 or about a 10% change in Cd.

According to US Department of Energy, the effect aero has on the EPA fuel economy test is 3% for the Urban cycle and 11% for the highway cycle. (For rolling resistance of tires it's 4% / 7%)

That means the effect on fuel economy of a 10mm change is 0.03% to 0.11% - wider being worse.

Smithers reported to the California Energy Commission on a study of tire sizing and its effect on RR. From that data, the effect a 10mm increase in width has on RRC is about 3% (if you assume there are no other changes)

So if you combine that with the effect RR has on the EPA test, then a 10mm increase in tire width DECREASES the fuel economy by 0.12% to 0.21%, which is significantly larger than the effect caused by aero (0.03% to 0.11%)

This means the aero effect of the width of tires is more than offset by the improvements in RR.

This may seem counter intuitive as wider tires ought to have more RR, but most of the effect is coming from the less deformation as winkosmosis suggested.

Last edited by CapriRacer; 12-05-2009 at 08:23 AM..
  Reply With Quote
Old 12-05-2009, 09:18 AM   #7 (permalink)
Master EcoModder
 
basjoos's Avatar
 
Join Date: Dec 2007
Location: Upstate SC
Posts: 1,032

Aerocivic - '92 Honda Civic CX
Last 3: 70.54 mpg (US)

AerocivicLB - '92 Honda Civic CX
Team Honda
90 day: 61.34 mpg (US)
Thanks: 6
Thanked 526 Times in 257 Posts
I always wondered how Fred Flintstone was able to propel his car with just his feet. I guess those ultra-wide tires on his car produced some really low RR values.

I'm sure the width vs. RR curve has a point of diminishing returns.
__________________
aerocivic.com
  Reply With Quote
The Following User Says Thank You to basjoos For This Useful Post:
aerohead (10-20-2012)
Old 12-05-2009, 10:45 AM   #8 (permalink)
Master EcoModder
 
Join Date: Nov 2009
Location: Leadville, CO
Posts: 509

Maroon Ballon - '98 Chrysler Town & Country LXI
90 day: 26.42 mpg (US)

MaEsTRO - '95 Geo Metro 5spd hatch, 3 cyl
Thanks: 47
Thanked 54 Times in 38 Posts
Quote:
Originally Posted by basjoos View Post
I always wondered how Fred Flintstone was able to propel his car with just his feet. I guess those ultra-wide tires on his car produced some really low RR values.

I'm sure the width vs. RR curve has a point of diminishing returns.
I think I saw something about extremely low RR for stone tires (not Firestone), and a significant flywheel/gyroscopic effect once in motion.

I think wind tunnel test are done with the wheels stationary. A spinning wheel wouldn't show a change in frontal cA, but there must be a dynamic change in cD for an eggbeater style of wheel. Any quantitative studies on this?
  Reply With Quote
Old 12-05-2009, 12:45 PM   #9 (permalink)
Master EcoModder
 
Join Date: Jan 2009
Location: Maui, Hawaii
Posts: 813
Thanks: 5
Thanked 32 Times in 25 Posts
Quote:
Originally Posted by CapriRacer View Post
Me, too! But rather than just wonder, I pulled out my Excel spreadsheet and did some calculations.

According to the first post (not sure where the data came from!) The average for a 10mm increase in tire width was 0.003 or about a 10% change in Cd.

According to US Department of Energy, the effect aero has on the EPA fuel economy test is 3% for the Urban cycle and 11% for the highway cycle. (For rolling resistance of tires it's 4% / 7%)

That means the effect on fuel economy of a 10mm change is 0.03% to 0.11% - wider being worse.

Smithers reported to the California Energy Commission on a study of tire sizing and its effect on RR. From that data, the effect a 10mm increase in width has on RRC is about 3% (if you assume there are no other changes)

So if you combine that with the effect RR has on the EPA test, then a 10mm increase in tire width DECREASES the fuel economy by 0.12% to 0.21%, which is significantly larger than the effect caused by aero (0.03% to 0.11%)

This means the aero effect of the width of tires is more than offset by the improvements in RR.

This may seem counter intuitive as wider tires ought to have more RR, but most of the effect is coming from the less deformation as winkosmosis suggested.
So that's a typo? Wider tires really do decrease rolling resistance? I knew it...

Got a link to an article about the width/efficiency?

Edit: Is this it? Tire Fuel Efficiency Consumer Information Program | Federal Register Environmental Documents | USEPA

Last edited by winkosmosis; 12-05-2009 at 12:59 PM..
  Reply With Quote
Old 12-05-2009, 03:18 PM   #10 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 8,277
Thanks: 10,029
Thanked 4,316 Times in 2,389 Posts
case-specific basis

Quote:
Originally Posted by winkosmosis View Post
I'm skeptical about the impact of wider tires on fuel use. A wider tire with the same contact patch as a narrower one is also deforming less, which has to count for something.
I don't know if sweeping generalities serve the greater good.Certainly exceptions will abound as soon as any claim is made about any topic.
With respect to my experience,Michelin's claims about fuel-savings were so clever,I went for the bait.
And after spending $1,000 (US) for their tires and 14-inch wheels to put them on,I was rewarded with Zero-mpg gain!
The only reason I didn't immediately blow my brains out was that I rationalized that I had gained excellent dry and wet traction,a quiet smooth ride,and long tread life AT NO EXPENSE to mpg,in spite of the aggravated frontal area.
It could have been different for a different vehicle,different tires.With a 345,000 mile data base on the CRX I'm pretty confident with my numbers.

  Reply With Quote
The Following User Says Thank You to aerohead For This Useful Post:
mikeyjd (05-26-2014)
Reply  Post New Thread


Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
CdA list Daox Aerodynamics 152 03-18-2017 12:06 PM
Top 5 most fuel efficient tires (Lowest Rolling resistance: LRR) blackjackel General Efficiency Discussion 144 01-25-2016 11:39 PM
aero mods-data-% change or Cd change ( installment # 7-Wheels/Tires/Wheelcovers/etc. aerohead Aerodynamics 5 06-04-2014 12:14 PM
Sources of Aerodynamic Drag in Automobiles and Possible Solutions SVOboy Aerodynamics 12 02-17-2010 02:09 PM
Tire Engineer here - concerned about hyperinflating tires CapriRacer Introductions 48 09-26-2009 09:25 PM



Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com