Go Back   EcoModder Forum > EcoModding > Off-Topic Tech
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 08-28-2012, 05:09 AM   #11 (permalink)
German Hypermiler
 
Join Date: Aug 2012
Location: Springe, Germany
Posts: 5
Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by mcrews View Post
You need to define 'smaller'

What you mean is narrower. Smaller means smaller diameter.

Smaller would prove for worse mileage.
Narrower would provide such a small gain that I would not concider the lose of handling and comfort.
Have you aired up the tires to 40-45psi?
Sorry, my fault. I meant narrower tires, with same diameter.

Both tires are stock recommended sizes. 175/80R14 is the narrowest regular size for this car, 195/65R15 is the most sold tire in germany, and also stock recommended. In size 175 there are only an few different tires to buy, but in 195/65R15 there are about 300 different profiles and a lot of LRR-tires to buy.

In the moment i´m driving very bad all-weather tires from the last owner of my car. So i need to buy some new tires and rims for summer.

I´ll drive the tires at maximum sidewall pressure, but actually the mounted tires are so bad, i wont try it with them...

Kind regards

Benny

__________________
ecomodding in germany, with prices of more than 8$ per gallon....
  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 08-28-2012, 08:45 AM   #12 (permalink)
Tire Geek
 
CapriRacer's Avatar
 
Join Date: May 2008
Location: Let's just say I'm in the US
Posts: 794
Thanks: 4
Thanked 388 Times in 237 Posts
Bigger is better!

The best information I have been able to dig up is that bigger is better - no matter how you define "Bigger".

That said, the effect is small - especially compared to the differences between tires.

In other words, spend your time researching tires and very little researching tire size - but if you have the opportunity, go larger.
__________________
CapriRacer

Visit my website: www.BarrysTireTech.com
New Content every month!
  Reply With Quote
Old 08-28-2012, 10:47 AM   #13 (permalink)
Exceptional Member
 
YukonCornelius's Avatar
 
Join Date: Jan 2011
Location: Pennsylvania
Posts: 166

Crapolier - '98 Chevrolet Cavalier base
90 day: 34.81 mpg (US)

05 CTS-V - '05 cadillac cts-v
90 day: 33.01 mpg (US)

95 Accord - '95 Honda Accord
90 day: 38.06 mpg (US)

11 CTS-V - '11 Cadillac CTS-V
Thanks: 27
Thanked 15 Times in 14 Posts
Not a direct comparison. However my 95 accord with 185/70/14s and lowed CoD does not roll with EOC nearly as well as my 98 Cavalier with a high CoD and 195/65/15s. Both are around 50psi in the tires. Also, my accord is a death trap in the rain with those skinny tires and no ABS.
  Reply With Quote
The Following User Says Thank You to YukonCornelius For This Useful Post:
mcrews (08-29-2012)
Old 08-28-2012, 02:37 PM   #14 (permalink)
live, breath, Isuzu-Ds
 
trooper Tdiesel's Avatar
 
Join Date: Mar 2011
Location: oregon
Posts: 231

puddle jumper - '93 Suzuki sidekick base model

energizer bunny - '86 isuzu trooper base model

Clifford the big red dog - '84 GM S-10 durango
Thanks: 1
Thanked 20 Times in 17 Posts
wasn't there some one that tested the idea of using 4 space saver tires on a auto and lost some mpg.
__________________
1 86 T\D trooper with rare GEN 3 rods TRANS FIXED NOW DD
1 86 4WD 5sp pup is 2.3L gas, but plan on 2.2L diesel repower
1 91 trop, long term plan is a group buy of imported Isuzu 4JB1-T 2.8L I-4 engines, hoping to get price down to 2K not 3K plus
1993 sidekick my MPG toy, epa rating 26.
i get 29/31 with stock drive train.
  Reply With Quote
Old 08-28-2012, 02:47 PM   #15 (permalink)
Master EcoModder
 
mcrews's Avatar
 
Join Date: Oct 2009
Location: Texas
Posts: 3,523

The Q Sold - '02 Infiniti Q45 Sport
90 day: 23.08 mpg (US)

blackie - '14 nissan altima sv
Thanks: 2,203
Thanked 663 Times in 478 Posts
Quote:
Originally Posted by trooper Tdiesel View Post
wasn't there some one that tested the idea of using 4 space saver tires on a auto and lost some mpg.
Oh please dont bring that back.....It didnt work/wont work.
__________________
MetroMPG: "Get the MPG gauge - it turns driving into a fuel & money saving game."

ECO MODS PERFORMED:
First: ScangaugeII
http://ecomodder.com/forum/showthrea...eii-23306.html

Second: Grille Block
http://ecomodder.com/forum/showthrea...e-10912-2.html

Third: Full underbelly pan
http://ecomodder.com/forum/showthrea...q45-11402.html

Fourth: rear skirts and 30.4mpg on trip!
http://ecomodder.com/forum/showthrea...tml#post247938
  Reply With Quote
Old 08-28-2012, 03:05 PM   #16 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,513

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 52.71 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)

Appliance car - '14 Mitsubishi Mirage ES (base)
90 day: 60.16 mpg (US)
Thanks: 4,058
Thanked 6,957 Times in 3,602 Posts
I compared the rolling resistance of 4 space saver donut spares on the car against various other tires in my fleet of various sizes. The donuts were the worst of the lot: http://ecomodder.com/forum/showthrea...uts-19094.html



from: http://ecomodder.com/forum/showthrea...e92-19126.html
__________________
Project MPGiata! Mods for getting 50+ MPG from a 1990 Miata
Honda mods: Ecomodding my $800 Honda Fit 5-speed beater
Mitsu mods: 70 MPG in my ecomodded, dirt cheap, 3-cylinder Mirage.
Ecodriving test: Manual vs. automatic transmission MPG showdown



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
Old 08-28-2012, 04:43 PM   #17 (permalink)
Master EcoModder
 
Join Date: Jul 2008
Location: Silly-Con Valley
Posts: 1,479
Thanks: 201
Thanked 262 Times in 199 Posts
Barry/Capri, can you please help me understand the coefficent of RR versus the RR force?

To me it seems that we have a fixed weight (to a close approximation) of vehicle, so we would be putting a fixed load on a tire. I would also assume (and it may be a bad assumption) the same inflation pressures in each case. And for comparison we also need to assume the same construction, rubber compounds, etc. In that case, the lower RR force for narrower tires would seem to mean that those tires would coast farther.

Why is it the coefficient, which you have to multiply by the load, which actually shows you which tires would coast further?

-soD
  Reply With Quote
Old 08-29-2012, 08:46 AM   #18 (permalink)
Tire Geek
 
CapriRacer's Avatar
 
Join Date: May 2008
Location: Let's just say I'm in the US
Posts: 794
Thanks: 4
Thanked 388 Times in 237 Posts
Quote:
Originally Posted by some_other_dave View Post
Barry/Capri, can you please help me understand the coefficent of RR versus the RR force?

To me it seems that we have a fixed weight (to a close approximation) of vehicle, so we would be putting a fixed load on a tire. I would also assume (and it may be a bad assumption) the same inflation pressures in each case. And for comparison we also need to assume the same construction, rubber compounds, etc. In that case, the lower RR force for narrower tires would seem to mean that those tires would coast farther.

Why is it the coefficient, which you have to multiply by the load, which actually shows you which tires would coast further?

-soD
Rolling Resistance Force (RRF) = Rolling Resistance Coefficient (RRC) X load on tire.

When tires are tested for RR, they are tested at a particular load and inflation pressure. The result is a Force. If you divide by the test load, you get a dimensionless number (a coefficient) that applies to that particular test fixture and that particular test procedure at that particular inflation pressure.

If you want to compare tires, you need to run them all at the same time, at the same place, and under the same conditions.

Questions:

1) Do the values vary according to the test fixture? Yes, but a correlation between test fixtures (and therefore test facilities) could be done so they could be compared. I'm not going to go into what it would take for that to happen but it is considerable!

2) Do RR values vary according to the test method? Yes, but a correlation between tests can also be done. Again a considerable coordinated effort would need to take place.

3) Is RRC constant for a given tire? No. Not only does it vary according to inflation pressure, but it varies according to load. The best information I have is the variation due to load is small enough to ignore (but it is something to keep in mind)

Coming back to the same tire in different sizes, I think the reason the data shows that "Bigger is Better" is that an increase in tire width of (say) 10mm increases the width of the tread a fraction of that (say 7 mm), but the increase in load carrying capacity is pretty close to the increase in width. The net effect is that there is slightly less material in comparison to the load.

And did I mention that while the sidewalls only play a small role in RR, every tire only has 2. Changing the tire size doesn't change how many of them there are.
__________________
CapriRacer

Visit my website: www.BarrysTireTech.com
New Content every month!

Last edited by CapriRacer; 08-03-2014 at 07:12 AM..
  Reply With Quote
Old 08-29-2012, 10:15 AM   #19 (permalink)
home of the odd vehicles
 
rmay635703's Avatar
 
Join Date: Jun 2008
Location: Somewhere in WI
Posts: 3,874

Silver - '10 Chevy Cobalt XFE
Thanks: 495
Thanked 863 Times in 650 Posts
I think what is being lost here are the effects of rolling mass and aero.

So when driving down the road which trumps which
Rolling Mass + Aero or Rolling resistance by itself.

Obviously crap tires made of bias crap compounds won't score well.
  Reply With Quote
Old 08-29-2012, 10:19 AM   #20 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,513

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 52.71 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)

Appliance car - '14 Mitsubishi Mirage ES (base)
90 day: 60.16 mpg (US)
Thanks: 4,058
Thanked 6,957 Times in 3,602 Posts
Short answer: it depends.

You can find a good discussion of aero losses vs tire width in this thread: http://ecomodder.com/forum/showthrea...g-cd-7475.html

You can also use the aero/rolling resistance calculator to estimate effects of changes to Cd/A & RRC from tire changes: http://ecomodder.com/forum/tool-aero...resistance.php

__________________
Project MPGiata! Mods for getting 50+ MPG from a 1990 Miata
Honda mods: Ecomodding my $800 Honda Fit 5-speed beater
Mitsu mods: 70 MPG in my ecomodded, dirt cheap, 3-cylinder Mirage.
Ecodriving test: Manual vs. automatic transmission MPG showdown



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
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com