Hello! Log in or Register   |  Help  |  Donate  |  Buy Shirts See all banner ads | Advertise on TheSamba.com  
TheSamba.com
 
Bigger tires, changing gearing.
Page: Previous  1, 2, 3, 4, 5, 6, 7, 8, 9  Next
Forum Index -> Vanagon Share: Facebook Twitter
Reply to topic
Print View
Quick sort: Show newest posts on top | Show oldest posts on top View previous topic :: View next topic  
Author Message
IdahoDoug
Samba Member


Joined: June 12, 2010
Posts: 10239
Location: N. Idaho
IdahoDoug is offline 

PostPosted: Sun Aug 19, 2018 9:38 pm    Post subject: Re: Bigger tires, changing gearing. Reply with quote

Lifting a vehicle causes it to displace air above it that would have been otherwise undisturbed. The higher you go, the more it affects fuel economy.

As for air going under the vehicle. Air pushed under a vehicle causes far more resistance than air going along the sides or top. Various protruding objects, the tires, the higher pressure of the air, etc. That is one reason front air dams and those side spats (long aero devices along the trailer sides) on semi trucks and race cars pay dividends. It's better to push it around the vehicle than let it go under and collide with the aerodynamically dirty underside. For racing, it has other advantages that accrue to handling.

So, you can measure these differences quite readily. One model of the LS400 I worked on had an air suspension that dropped it lower at higher speeds. We measured better fuel economy though it was only a small height change.

So yes, lifting a vehicle costs you fuel economy
_________________
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
Back to top
View user's profile Send private message Gallery Classifieds Feedback
E1
Samba Member


Joined: January 21, 2013
Posts: 6379
Location: Westfalia, Earth
E1 is offline 

PostPosted: Sun Aug 19, 2018 9:44 pm    Post subject: Re: Bigger tires, changing gearing. Reply with quote

For Doug especially:

Not a trick question, in fact you eluded to it...

If one drops the front really low, raises the rear high, and seals in the air underneath with side panels reaching from van to ground, what would you have?

(Think "discovered by Colin Chapman, 1978")
_________________
‘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
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
IdahoDoug
Samba Member


Joined: June 12, 2010
Posts: 10239
Location: N. Idaho
IdahoDoug is offline 

PostPosted: Sun Aug 19, 2018 9:49 pm    Post subject: Re: Bigger tires, changing gearing. Reply with quote

A wedge? Or Kamm-esque shape? Or a vortex generator?
_________________
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
Back to top
View user's profile Send private message Gallery Classifieds Feedback
E1
Samba Member


Joined: January 21, 2013
Posts: 6379
Location: Westfalia, Earth
E1 is offline 

PostPosted: Sun Aug 19, 2018 9:51 pm    Post subject: Re: Bigger tires, changing gearing. Reply with quote

World's first ground-effects Vanagon.

(sort of, meaning not an efficient one) Wink
_________________
‘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
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
IdahoDoug
Samba Member


Joined: June 12, 2010
Posts: 10239
Location: N. Idaho
IdahoDoug is offline 

PostPosted: Sun Aug 19, 2018 10:07 pm    Post subject: Re: Bigger tires, changing gearing. Reply with quote

Ah - heh. Yeah, I have a Wolfsburg Edition, which means I have from what I know the only Vanagon ground effects piece of OEM equipment - a front air dam. This model also has the lowest springs of the lot, I think. The air dam had been off since I first dragged her nonrunning carcass onto my trailer 5 years ago or so. I needed that bit of extra clearance to get her on. Maybe I should put it back on in honor of Mr. "design in lightness" hisself!
_________________
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
Back to top
View user's profile Send private message Gallery Classifieds Feedback
E1
Samba Member


Joined: January 21, 2013
Posts: 6379
Location: Westfalia, Earth
E1 is offline 

PostPosted: Sun Aug 19, 2018 10:34 pm    Post subject: Re: Bigger tires, changing gearing. Reply with quote

IdahoDoug wrote:
Maybe I should put it back on in honor of Mr. "design in lightness" hisself!

Yeah, but you'd be breaking suspension bits just going a mile for coffee and donuts.

(It'd be a quick mile, though)
_________________
‘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
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
IdahoDoug
Samba Member


Joined: June 12, 2010
Posts: 10239
Location: N. Idaho
IdahoDoug is offline 

PostPosted: Sun Aug 19, 2018 10:48 pm    Post subject: Re: Bigger tires, changing gearing. Reply with quote

No, no - my van is stock and these are factory Wolfsburg springs. I do like the sound of coffee and donuts, however. My wife and I have a houseful of guests, but we got up before the house did and snuck off for breakfast at our little spot. It was worth it!
_________________
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
Back to top
View user's profile Send private message Gallery Classifieds Feedback
E1
Samba Member


Joined: January 21, 2013
Posts: 6379
Location: Westfalia, Earth
E1 is offline 

PostPosted: Sun Aug 19, 2018 11:01 pm    Post subject: Re: Bigger tires, changing gearing. Reply with quote

Haha, meant if Colin had done the work on this, your Vanagon 19.

(Oh no, more code-speak!) Laughing
_________________
‘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
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
Waldi
Samba Member


Joined: February 28, 2014
Posts: 1752
Location: Germany
Waldi is offline 

PostPosted: Mon Aug 20, 2018 8:05 am    Post subject: Re: Bigger tires, changing gearing. Reply with quote

?Waldo? wrote:
Hopefully you adjusted your mileage calculations for the larger size tires and did not go off the odometer, as the odometer is skewed to a lower reading of miles traversed when larger tires are fitted. Regardless stock tire size is usually fairly well matched to stock vehicles so it doesn't surprise me that one would get lower fuel economy when going to either larger or smaller tires.


Come on Waldo,
who measures the mpg with the odo in times of GPS ?
Atleast everybody knows the difference of his odo.
Also there is no need to know the exact mpg, just if it is more or less with larger tires.

Just came back from Italy 650km over the alps with 1000kg less but 6,50-16 tires instead of 205/70-14 on the way ldown. What do you think where i used more fuel ?

Alot of confusion here.
Mpg on constand speed ? Are we speaking about theorie or real life ?
Higher mpg on tdi conversion with stock gearing than with 10% taler gearing of a JX ? Sure with the same weight but not with a 2t trailer, everybody knows it that a 1,9er dont rev as high as a shoe rt huber 1,6.
Lower mpg due to more mass of wheels ? You can read it in every forum.

Ask yourselfe why nobody try to get better mpg with taler tires on a 50hp van.

Here in EU the mpg is a 3/3 mix. 1 city driving, 1 1ane overland, 1 highway at 130kmh

Excuse me, but US car/motorcycle ingeneers are not known as very good in fuel saving.
Where does the trend of tall wheels come from ?

As for the wind resistance on higher vans.
Ofc it effects the resistance. Check wind channel pics. The air cannot go withour resistance under the car.
A spoiler increases the front aera, but it gets better results, as less air is being presst and revolved under the car. The van do not have a plan flor like Ferraris.

The increased roling resisstance of taler and mostly wider tires and the need of more fuel during accelaration and climbing reduces the mpg far more than the gain of 500 revs less. In practical driving, not dreaming on theories and perfect conditions.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
E1
Samba Member


Joined: January 21, 2013
Posts: 6379
Location: Westfalia, Earth
E1 is offline 

PostPosted: Mon Aug 20, 2018 8:56 am    Post subject: Re: Bigger tires, changing gearing. Reply with quote

Several people have gotten better mileage on bigger tires because it -- perhaps accidentally -- changed gearing enough to do so... on their vehicle, at their weight, with their engine, and their style, at their speed, and their hair color.

Your disputing that is the very sort of theory you're now disclaiming from others' actual experience. Like they're too dumb to get the math right.

Kinda Silly, Eh?

When speaking reality as pure; if one finds the optimum tire for mpg, and mpg can never possibly be improved per all above factors, and then one adds tire height or width which add drag or more rotating mass, then Yes, you are correct. It is impossible for that to be incorrect when all else is equal.

So I again think we're not all able to distinguish facts from principles of Physics here, in considering all others' actual experience, including you, and worse, distinguishing from opinion based upon random principles inconsistent with a point anyone else is making based on another method entirely. Whew.

So in the end, what could have been a learned discussion benefitting the unknowing has left them more confused than when they opened the thread.

We can do better, and we owe it to them to do so and speak the same language -- the language of understanding, which in of itself has to remain simple to help anyone.
_________________
‘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 9:14 am; edited 1 time in total
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
Waldi
Samba Member


Joined: February 28, 2014
Posts: 1752
Location: Germany
Waldi is offline 

PostPosted: Mon Aug 20, 2018 9:13 am    Post subject: Re: Bigger tires, changing gearing. Reply with quote

E1 wrote:
Several people have gotten better mileage on bigger tires because it -- perhaps accidentally -- changed gearing enough to do so... on their vehicle, at their weight, with their engine, and their style, and speed, and hair color.

Your disputing that is the very sort of theory you're now disclaiming from their actual experience. Kinda Silly, Eh?


No, i dont.
Read my posts and try to understand.

Edit after your edditing:

I have 3 Syncros running, i own 5 different tire sets, i have tryed all gearings. Changing tires and gearing cost me only time.
Do you think i choice something that costs me more money for 30k km a year ?
Back to top
View user's profile Send private message Gallery Classifieds Feedback
E1
Samba Member


Joined: January 21, 2013
Posts: 6379
Location: Westfalia, Earth
E1 is offline 

PostPosted: Mon Aug 20, 2018 9:21 am    Post subject: Re: Bigger tires, changing gearing. Reply with quote

I did, and I am. Read mine and note many points are consistent with yours.

All I'm saying is your last paragraph I mostly replied to seems to disclaim the idea that a tire size can even accidentally find a sweet spot of mpg, as many claim.

Or are you agreeing with my "all was at very-best mpg until I added tire size and screwed it all up?" Because if you're disagreeing with both, you are claiming knowledge of a physical impossibility. As mentioned a few times now I do not think we're all coming from the same angles on Physics vs. other factors.

And please know I bring this up for other readers, not at all to argue. Very Happy

Edit after yours: No, I do not think that.
_________________
‘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
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
Waldi
Samba Member


Joined: February 28, 2014
Posts: 1752
Location: Germany
Waldi is offline 

PostPosted: Mon Aug 20, 2018 9:58 am    Post subject: Re: Bigger tires, changing gearing. Reply with quote

E1 wrote:
I did, and I am. Read mine and note many points are consistent with yours.

All I'm saying is your last paragraph I mostly replied to seems to disclaim the idea that a tire size can even accidentally find a sweet spot of mpg, as many claim.

Or are you agreeing with my "all was at very-best mpg until I added tire size and screwed it all up?" Because if you're disagreeing with both, you are claiming knowledge of a physical impossibility. As mentioned a few times now I do not think we're all coming from the same angles on Physics vs. other factors.

And please know I bring this up for other readers, not at all to argue. Very Happy

Edit after yours: No, I do not think that.


I am not contra your 2nd line.
As i was showing with the TDI.
They may be savings in fuel with taler tires in some cases, but in this cases there would be more saving with longer gearing.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
E1
Samba Member


Joined: January 21, 2013
Posts: 6379
Location: Westfalia, Earth
E1 is offline 

PostPosted: Mon Aug 20, 2018 10:00 am    Post subject: Re: Bigger tires, changing gearing. Reply with quote

Perfect, and Thanks. Cool
_________________
‘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
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
Waldi
Samba Member


Joined: February 28, 2014
Posts: 1752
Location: Germany
Waldi is offline 

PostPosted: Mon Aug 20, 2018 10:06 am    Post subject: Re: Bigger tires, changing gearing. Reply with quote

And as a side note:
The only broken teeth on a 7-teeth pinion with a good bearing i have seen on heavy highroof syncros with 225/76-16 tires and stronger engines.
Whatever that meens.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
E1
Samba Member


Joined: January 21, 2013
Posts: 6379
Location: Westfalia, Earth
E1 is offline 

PostPosted: Mon Aug 20, 2018 10:24 am    Post subject: Re: Bigger tires, changing gearing. Reply with quote

As you know, it's slightly more stressful to add bigger tires and I fully concur.

I also think in general that people are way too demanding on these vans. Kid Gloves avert mechanic's gloves. Smile
_________________
‘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
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
IdahoDoug
Samba Member


Joined: June 12, 2010
Posts: 10239
Location: N. Idaho
IdahoDoug is offline 

PostPosted: Mon Aug 20, 2018 11:09 am    Post subject: Re: Bigger tires, changing gearing. Reply with quote

I think what Waldi is saying about the unlikelihood of larger, heavier, or wider tires (or all 3, usually as they are related) producing higher fuel economy is accurate. Physics dictates that adding rotating mass has the highest reduction in fuel economy. So purely by chance, adding larger tires and finding this "sweet spot" (a theoretical thing itself, by the way) that gives you better fuel economy is simply highly unlikely. How unlikely? Dunno. 100:1 against it? Dunno.

Think about what he and I are saying. You are driving down the road in your Vanagon at a steady state on stock 24.5" tires and getting 16.5MPG at 60mph and the HP required to do this is 45hp. A helicoptor comes along and lifts the van while 4 mechanics swap to 27" wider tires and lets go of the vanagon.

Now the Vanagon is 1.25" taller, weighs 12lbs more, 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?

One issue that always comes up with internet MPG claims is this - accurate measurement. It takes a lot of work and change to an existing vehicle to increase MPG even a very small amount - say .5MPG. There are so many variables when operating a vehicle that would affect this measurement, that anybody claiming to have accurately measured it (even with a GPS) to the level of accuracy needed for the claim to be valid is probably wrong. It takes a team, special facilities, special equipment, and statistical analysis to do this.

Since the physics is against this theory being true, then it immediately calls into question the measurement technique. Ordinary roads, wind, load, temperatures, elevation changes, a slightly dragging brake, etc could EACH introduce a larger change in the data than the measurement errors itself. So people's observed MPG improvements is more likely to be measurement errors due to the measuring ability itself, or variables not controlled for. And there is a significant physics headwind AGAINST being able to increase fuel economy by installing taller, heavier and wider tires.

Is it possible? Sure, there may be a steady state speed under certain road, load, temperature, elevation, wind speed and direction such that in a narrow range of 63-64.5 mph there is a "sweet spot" where you are getting .223mpg better than the stock tires. But that is not the same as a blanket statement that "I'm getting better fuel economy now that I put taller, heavier, wider tires on my Vanagon."

If someone would like to bet me pink slips (that's the title to their car here in the US, Waldi) and we'll both fill up and drive together until one runs out of gas, I'd love to own another vanagon with larger, wider, heavier tires on it.
_________________
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
Back to top
View user's profile Send private message Gallery Classifieds Feedback
E1
Samba Member


Joined: January 21, 2013
Posts: 6379
Location: Westfalia, Earth
E1 is offline 

PostPosted: Mon Aug 20, 2018 11:22 am    Post subject: Re: Bigger tires, changing gearing. Reply with quote

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 --

Very Happy
_________________
‘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
Back to top
View user's profile Send private message Send e-mail Gallery Classifieds Feedback
?Waldo?
Samba Member


Joined: February 22, 2006
Posts: 9752
Location: Where?
?Waldo? is offline 

PostPosted: Mon Aug 20, 2018 11:42 am    Post subject: Re: Bigger tires, changing gearing. Reply with quote

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 produce 10% more torque at that lower RPM in order to generate the same power and propel the vehicle at the same speed (load).* If the BSFC is better at that new RPM you will save fuel, if it is worse your fuel economy will suffer. 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.


Last edited by ?Waldo? on Mon Aug 20, 2018 12:06 pm; edited 1 time in total
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Waldi
Samba Member


Joined: February 28, 2014
Posts: 1752
Location: Germany
Waldi is offline 

PostPosted: Mon Aug 20, 2018 11:52 am    Post subject: Re: Bigger tires, changing gearing. Reply with quote

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 --

Very Happy


You could order the van with 5,43 or 5,83 ratio. Many construction companies did so for heavy weight or offroad use.
If somebody buys this kind of van and use it as a camping car, the mpgs will increase usually with for example 205/80-14 or even 205-65-16 tires.
But it would make more sense to change the box to 4,85 on the next ocation.
Its economicaly nonesens to spend 500 or more on tires or gear change.
How long does it take to get the money back ?
Most economic way to save fuel is to drive slower.
But it does not look good Wink
And the industrie and politics dont like it.
Back to top
View user's profile Send private message Gallery Classifieds Feedback
Display posts from previous:   
Reply to topic    Forum Index -> Vanagon All times are Mountain Standard Time/Pacific Daylight Savings Time
Page: Previous  1, 2, 3, 4, 5, 6, 7, 8, 9  Next
Page 5 of 9

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum

About | Help! | Advertise | Donate | Premium Membership | Privacy/Terms of Use | Contact Us | Site Map
Copyright © 1996-2023, Everett Barnes. All Rights Reserved.
Not affiliated with or sponsored by Volkswagen of America | Forum powered by phpBB
Links to eBay or other vendor sites may be affiliate links where the site receives compensation.