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tjet 
Samba Member
Joined: June 10, 2014
Posts: 3533
Location: CA & NM
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 Posted: Mon Aug 20, 2018 11:55 am Post subject: Re: Bigger tires, changing gearing. |
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| IdahoDoug wrote: |
| ., I'd love to own another vanagon with larger, wider, heavier tires on it. |
I met a guy selling a Syncro that has 31" tires. He is getting 25-27 MPG because he installed an AHU & kept the stock Syncro final drive & 4.86 R&P.
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Waldi
Samba Member
Joined: February 28, 2014
Posts: 1752
Location: Germany
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| Posted: Mon Aug 20, 2018 12:10 pm Post subject: Re: Bigger tires, changing gearing. |
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| ?Waldo? wrote: |
| IdahoDoug wrote: |
| Physics dictates that adding rotating mass has the highest reduction in fuel economy. |
Rotating mass is nowhere near the biggest impact in fuel economy. The heavy hitters are coefficient of drag, frontal area, engine efficiency, and rolling resistance. Rotating mass only affects fuel economy during acceleration.
| Quote: |
| the engine is pushing against a 10% longer lever (requiring it to generate 10% more power/fuel burn) and spinning heavier wheel/tires. How is it burning less fuel? |
Tire size does not affect the amount of power the engine needs to produce to propel the van at a given speed aside from the very slight changes in aerodynamic drag or in rolling resistance. Your 10% taller tire does not cause a 10% increase in the power the engine needs to produce. The change of the size of the tire 'lever' has absolutely zero impact in the power required to propel the vehicle. What it does change is the RPM of the engine at that given speed. Levers NEVER change the power required to perform work, they just change the force (torque) and the distance (RPM) over which that force needs to be applied and those changes are always reciprocal and always cancel to result in the same power required. Because of the reduction of engine RPMs from the larger tires, the engine needs to produce proportionately more torque at that lower RPM in order to net the same amount of power for the same speed. A 10% taller tire will essentially reduce the engine RPM by 10% causing the engine to need to prcoduce 10% more torque at that lower RPM in order to generate the same power and propel the vehicle at the same speed (load).* THAT is what physics dictates.
*Note: please excuse the mathematical inaccuracy introduced by the fact that 10% more and 10% less are not equal amounts. |
What do you do driving in city or mountains or curvy roads ?
Accelarating and breaking and accelarating and ...
Power meaning HP is not the right word, but lets say engine load.
No more load without more fuel. Does the engine need more fuel driving downhill or with wind with 5k or uphill, against wind with 4k ?
Yes i know the engine runs most effitient where the torque curve cuts the hp curve on full throttle.
But if you decrease revs from 4500 to 4000 you are still far away from it.
So you gain maybe 3% effciency driving on flat without wind on constant speed, but loose on rolling resistance and all other situations. |
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Waldi
Samba Member
Joined: February 28, 2014
Posts: 1752
Location: Germany
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| Posted: Mon Aug 20, 2018 12:29 pm Post subject: Re: Bigger tires, changing gearing. |
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| tjet wrote: |
| IdahoDoug wrote: |
| ., I'd love to own another vanagon with larger, wider, heavier tires on it. |
I met a guy selling a Syncro that has 31" tires. He is getting 25-27 MPG because he installed an AHU & kept the stock Syncro final drive & 4.86 R&P.
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Nice example.
I am geting 31 with 5,43x0,78 and 215/70-16 on my orange syncro mAFN.
Highway at 110 900km trip. Some short sprints 5km with over 140 to annoy 2wd t3s 
Driving 1 lane streets overland i can go 1000km with one tank. |
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jackbombay
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Joined: October 19, 2007
Posts: 2723
Location: Eastern Idaho
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| Posted: Mon Aug 20, 2018 1:17 pm Post subject: Re: Bigger tires, changing gearing. |
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| IdahoDoug wrote: |
One issue that always comes up with internet MPG claims is this - accurate measurement. |
I doubt that you know anybody that measures their MPGs more accurately than me, there may be some exceedingly awesome people out there that measure their MPG's as accurately as me, but not more accurately
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Last edited by jackbombay on Mon Aug 20, 2018 1:24 pm; edited 1 time in total |
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jackbombay
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Joined: October 19, 2007
Posts: 2723
Location: Eastern Idaho
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| Posted: Mon Aug 20, 2018 1:21 pm Post subject: Re: Bigger tires, changing gearing. |
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| E1 wrote: |
Understand and agree with all, or most, of that.
Case Study, Dateline Bombay:
Guy lost 400 RPMs in TD. Van was revving too high and thus wasting fuel. Tires changed rev like gearing would. Result, no more high revs beyond the necessary, mpg improved.
-- The End --
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Exactly.
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IdahoDoug
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Joined: June 12, 2010
Posts: 10251
Location: N. Idaho
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| Posted: Mon Aug 20, 2018 2:23 pm Post subject: Re: Bigger tires, changing gearing. |
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Agree JB - I've seen your anally retentive posts!! Heh...
My point is the tiny changes in MPG possible from mechanical bolt ons vs the similarly significant changes in MPG possible from temps, wind, load, elevation, etc, vs the measurement errors possible (warm fuel vs cold fuel volumes, evaporation from the tank on a hot vs cold vs 30 year old evap gear, old fuel vs summer fuel vs winter fuel) are all in the same size range and impact on the "conclusion" enormously. The measurement errors on the tested for variable (MPG) equal or exceed the expected changes from the testing itself.
The expected range of changes to fuel economy through out the normal speed, acceleration, etc of normal full driving cycles (not steady state) with essentially a "final drive" ratio change would be expected to be very small. You'll lose some MPG here, gain some MPG here. That puts a premium on extremely precise measurement to end up with meaningful and certain data.
So, just pointing out the difficulty in a bunch of guys making a conclusion like that. And further pointing out that with instrumented testing, the MPG direction is negative for larger, wider, taller tires.
I guess draw your own conclusions.
On rotating mass like wheels, I believe that even on steady state driving there is an energy penalty. You are still "accelerating" the mass against its desire to slow down without further energy burned, and centrifugal forces are increased, so more fuel is burned. Further, as Waldi points out, claiming that if a steady state at a single narrow RPM range gives you better fuel economy means you are going to burn less fuel in every day driving is untrue. Sweet spots are just that - single spots on a curve.
And finally, there is the "common sense" comment.
Don't you "larger, wider, heavier tires get better fuel economy" folks think that tire companies would be advertising the heck out of this remarkable suspension of physics if it were true? I can just see the ad copy "Install these larger, wider and heavier tires on your car and get 2% better fuel economy!" Right? During the energy crisis were people frantic to put larger, heavier, wider tires on? Take a look at vehicles designed for maximum fuel economy. See any heavy, large tires on them? Or do you see small, light tires and wheels? That is because auto manufacturers do research and instrumented testing. They know that you can't put larger, heavier, wider tires on a vehicle rated at X MPG and expect X+ fuel economy.
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader |
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E1
Samba Member
Joined: January 21, 2013
Posts: 6562
Location: Westfalia, Earth
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| Posted: Mon Aug 20, 2018 2:43 pm Post subject: Re: Bigger tires, changing gearing. |
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| IdahoDoug wrote: |
Agree JB - I've seen your anally retentive posts!! Heh...
So, just pointing out the difficulty in a bunch of guys making conclusions like that. |
Which is absolutely identical to a bunch of other guys making a conclusion like yours.
So here's the Rub. To us who've made the eggregious error of determining we got better mileage from a gear change -- Uh, I mean, a tire change -- the posts flat denying any possibility of that happening are beyond just starting to sound like one or all of:
-- You guys are wrong
-- You guys are too dumb to calculate mpg
-- You guys just wanna argue
-- You guys are lying about your mpg quotes
-- You guys just don't understand
I am all ears to hearing any other obvious conclusions that We the Wrong should make here. Please tell us what you really think. 
On any communication level, this simply isn't opinioned debate anymore. We may as well be speaking Vulcan to each other. 
_________________
‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman
Last edited by E1 on Mon Aug 20, 2018 3:22 pm; edited 1 time in total |
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?Waldo?
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Joined: February 22, 2006
Posts: 9752
Location: Where?
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| Posted: Mon Aug 20, 2018 3:18 pm Post subject: Re: Bigger tires, changing gearing. |
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| IdahoDoug wrote: |
| On rotating mass like wheels, I believe that even on steady state driving there is an energy penalty. You are still "accelerating" the mass against its desire to slow down without further energy burned. |
Interesting. Consider that the Earth keeps on spinning in space without any thrusters 'accelerating' its mass against its 'desire to slow down'. If more mass required additional force to 'accelerate it against its desire to slow down' then the Earth would have stopped spinning eons ago. A rotating body will continue rotating due to inertia unless there is a force acting on it to slow it down. A wheel obviously has friction at its wheel bearings and the drive train has frictional losses throughout it but those frictional losses are the same whether the wheel is tall or short.
| Quote: |
And finally, there is the "common sense" comment.
Don't you "larger, wider, heavier tires get better fuel economy" folks think that tire companies would be advertising the heck out of this remarkable suspension of physics if it were true? I can just see the ad copy "Install these larger, wider and heavier tires on your car and get 2% better fuel economy!" Right? During the energy crisis were people frantic to put larger, heavier, wider tires on? Take a look at vehicles designed for maximum fuel economy. See any heavy, large tires on them? Or do you see small, light tires and wheels? That is because auto manufacturers do research and instrumented testing. They know that you can't put larger, heavier, wider tires on a vehicle rated at X MPG and expect X+ fuel economy. |
By the exact same token, don't you think the tires would be getting smaller rather than larger if smaller tires always increased fuel economy and taller tires always hurt fuel economy?
You keep saying "wider, heavier, and taller", lumping the three characteristics together. I haven't seen anyone say that heavier tires or wider tires can ever increase fuel economy. By lumping all three characteristics together, you are using what is called the 'straw man' logical fallacy. |
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IdahoDoug
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Joined: June 12, 2010
Posts: 10251
Location: N. Idaho
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| Posted: Mon Aug 20, 2018 6:32 pm Post subject: Re: Bigger tires, changing gearing. |
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OK, so now we're using planet rotation in this discussion?
No, I'm not accusing anyone here of misrepresenting your results. That would be unfair. What I said is you don't have a well designed test that produces accurate results. There is a difference and I hope you understand it.
Before posting again here, I decided to do something. I used the following in a Google search: "Can larger tires improve fuel economy?" Check out the answers and see what you think.
As for the larger, heavier, wider tires - yes, I am assuming that unless one of you states you are using a larger, wider, lighter tire. Good luck with that.
Doug
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader |
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?Waldo?
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Joined: February 22, 2006
Posts: 9752
Location: Where?
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| Posted: Mon Aug 20, 2018 6:59 pm Post subject: Re: Bigger tires, changing gearing. |
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| IdahoDoug wrote: |
| OK, so now we're using planet rotation in this discussion? |
The physics of rotating bodies is universal. Do you have a problem with that?
I have certainly fit taller tires that were not any wider than those that I replaced. I have also replaced a steel wheel tire combo with an alloy wheel tire combo that was simultaneously taller, the same width, and lighter all at the same time. To believe that taller always means wider and always means more rotating mass is not correct. Assuming that taller, wider, and more rotating mass all have the same effect on fuel economy is also not correct.
Why don't you link the most accurate and insightful article that you found on google? The top hits I saw were comical and yet still stated that in some cases taller tires can improve fuel economy. I didn't see any remotely credible links that said that taller tires always result in worse fuel economy. |
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IdahoDoug
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Joined: June 12, 2010
Posts: 10251
Location: N. Idaho
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| Posted: Mon Aug 20, 2018 7:26 pm Post subject: Re: Bigger tires, changing gearing. |
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OK, I'll noodle around a bit and see if I can find something of use to all of us in the discussion on Google. It's actually remarkable the breadth of things that can be found. I'll take a look.
On the GM/Allante/tire size study, I confess I got the ladder out, tried not to fall on the Supra on blocks under the shelf which I can't move, and got to the top of the ladder. I quietly swore to myself that one day I am going to clear out decades of old Easter decorations, random college textbooks, and other debris and have all my car spares organized. But the shelf is 8 feet deep(!) and clear at the back is whatever crap from my career I have after 5 moves. But today's not the day and there are probably spiders back there from the Carter administration that would gang tackle me.
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader |
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E1
Samba Member
Joined: January 21, 2013
Posts: 6562
Location: Westfalia, Earth
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| Posted: Mon Aug 20, 2018 7:33 pm Post subject: Re: Bigger tires, changing gearing. |
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If only Waldo took me off Ignore, he'd see I'm mostly backing him up, Bwaaaaahahaha!
_________________
‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman |
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Pcforno
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Joined: October 14, 2014
Posts: 575
Location: Santa Fe, nm
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| Posted: Mon Aug 20, 2018 7:36 pm Post subject: Re: Bigger tires, changing gearing. |
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For those that keep responding to IDoug, please see his previous “discussions” of the VC and bigger brakes, and how many keystrokes were wasted, then decide for yourself if further discussion is warranted.
Those discussions are excellent descriptions of every type of logical and argumentative fallacy one would learn in philosophy 101 |
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E1
Samba Member
Joined: January 21, 2013
Posts: 6562
Location: Westfalia, Earth
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| Posted: Mon Aug 20, 2018 7:41 pm Post subject: Re: Bigger tires, changing gearing. |
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I hear Ya, but he's a good guy so it's all okay.
Plus I only made it to Philosophy 100.9 on my FM dial anyway.
_________________
‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman
Last edited by E1 on Mon Aug 20, 2018 7:47 pm; edited 1 time in total |
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IdahoDoug
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Joined: June 12, 2010
Posts: 10251
Location: N. Idaho
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| Posted: Mon Aug 20, 2018 7:47 pm Post subject: Re: Bigger tires, changing gearing. |
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Wait, the viscous coupling? You mean that device that is NOT a differential which can split torque to two output shafts? Ever find it funny/notable that the VC has only two shafts where a differential has 3 - one input and two outputs?
Heh...
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader |
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Pcforno
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Joined: October 14, 2014
Posts: 575
Location: Santa Fe, nm
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| Posted: Mon Aug 20, 2018 7:48 pm Post subject: Re: Bigger tires, changing gearing. |
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| I’m sure he’s a great guy! As are all of you. But I’ve found for some people discussions become more about proving oneself right than listening, responding, and understanding opposing viewpoints. For these situations I usually politely concede “you are right” and change the subject |
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Syncronoid
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Joined: January 21, 2012
Posts: 1111
Location: Stanford, CA and Bend, OR
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| Posted: Mon Aug 20, 2018 8:14 pm Post subject: Re: Bigger tires, changing gearing. |
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OK, I'm back, what'd I miss?
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E1
Samba Member
Joined: January 21, 2013
Posts: 6562
Location: Westfalia, Earth
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| Posted: Mon Aug 20, 2018 8:18 pm Post subject: Re: Bigger tires, changing gearing. |
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You missed saying Thanks for people trying to help you.
_________________
‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman |
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E1
Samba Member
Joined: January 21, 2013
Posts: 6562
Location: Westfalia, Earth
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| Posted: Mon Aug 20, 2018 8:22 pm Post subject: Re: Bigger tires, changing gearing. |
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| Pcforno wrote: |
| I’m sure he’s a great guy! As are all of you. But I’ve found for some people discussions become more about proving oneself right than listening, responding, and understanding opposing viewpoints. For these situations I usually politely concede “you are right” and change the subject |
Yep, it can be really tough to interpret written words sometimes.
But yeah, most people here are pretty darned cool.
By the way, How's your weather? 😂😂😂
_________________
‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
— Colin Chapman |
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jackbombay
Samba Member
Joined: October 19, 2007
Posts: 2723
Location: Eastern Idaho
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| Posted: Mon Aug 20, 2018 8:32 pm Post subject: Re: Bigger tires, changing gearing. |
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Hey, I spent the last 7 hours determining which bar is equidistant to all of us, and crazy as it seems, it turns out "The Royal Wolf", which is only 1 mile from my house, is equidistant from all of us, we should all meet up there for further discussion. Does tomorrow at 7 pm work for everyone?
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