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grandpa pete
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jaransonT3 
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Joined: January 01, 2005
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Location: Dearborn, MI
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 Posted: Mon Aug 08, 2016 4:52 pm Post subject: Re: Tallest tire ; Squareback |
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It is not that simple....unfortunately.
The 205s I am running on the back of Sophy are 205/55R16. These turn out to be 24.87" in diameter which is actually smaller in diameter than the stock 165R15s which are 25.39" in diameter.
The 205 is the width of the tire. For the height you need to consider the side wall aspect ratio and the rim/wheel diameter. You also have to consider your ride height.
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grandpa pete
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Nate M.
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Joined: August 11, 2003
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Location: Anacortes, WA U.S.A.
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| Posted: Mon Aug 08, 2016 5:53 pm Post subject: Re: Tallest tire ; Squareback |
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Mileage is not necessarily a function of simply reducing RPMs by running a larger diameter tire. If it were, all those big trucks rolling on 38"+ tires would be mileage kings,. . . aaaaaand they're not!!
Larger diameter tires increases the load placed on the engine just like a higher gear in a transmission. Higher loads require more fuel as a rule of thumb. So it's balance between speed and load.
Driving style plays a huge part in your mileage too and can't be overstated.
A perfect example of this was when I drove my bus on a trip a few years back and blew the trans input shaft seal. This wetted down the clutch with tranny oil and forced me to drive no more than 3K rpms in 4th and with only a light load in ALL gears or the clutch would free-wheel. It took forever to get home (doubled our driving time). The positive thing though was that my fuel mileage went up by 40%. Typically I would cruise @ 65-75mph and get around 22-23mpg with a full bus pulling my singlewheel trailer. On the way home, we couldn't go faster than 50mph and *any* incline reduced our speeds massively. We got just over 29mpg coming home!!
It's all about load and your driving style.
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eyetzr
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Joined: October 09, 2013
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Location: Toronto, Ontario. Canada
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| Posted: Mon Aug 08, 2016 6:17 pm Post subject: Re: Tallest tire ; Squareback |
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The big trucks have some crazy gear ratios, so the big milage works with better driving style. I have some 225R6015 for the rear of my square on 15X7 weld wheels with a 4 7/8 back space. Big tire but heavy. Tire diameter is the thing to measure as John pointed out. You could fit up to 29 inches in the rear, but you will not be hauling too much weight. My porch wheels are 17 with 245 55 tires.
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Bobnotch
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Location: Kimball, Mi
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| Posted: Tue Aug 09, 2016 8:33 pm Post subject: Re: Tallest tire ; Squareback |
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| grandpa pete wrote: |
Early smoothie 15 inch rims ;
I've been to the tire calculators that give the tire heights but I don't know how much room there is ....
Someone has figured this out before me ........ |
Pete, your biggest issue IS rim width. You can safely run a 205-65-15 with your trans (it'll be in your tire calculator for gearing size), but it won't fit on your narrow rim. You have to have at least a 5" or better rim width. I'm running 205-65-15's on the back of my Notch with no issues (they equate to the 165-80-15 in height), and they are at least a 5.5 inch wide rim.
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raygreenwood
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Location: Oklahoma City
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| Posted: Tue Aug 09, 2016 9:19 pm Post subject: Re: Tallest tire ; Squareback |
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Actually...tire circumference is key...not tire diameter. Its rolling inches per revolution per mile....and then add in the friction from wider tread if mileage is the issue.
The object if handling is the issue....is to get a tire that is wider than stock....but with a,sidewall profile ratio that keeps the tire close to stock total height for bot height settings and to keep your speedometer accurate.
I think I need to publish my tire profile vw diameter vs circumference list.
Being a "205" does not......as mentioned. .....automatically make a tire taller. Side wall profile is a multiple of treadwidth. For example.....a 205/60....means that the side wall of the tire on each side of the rim is 60% of the tread width. So a 205/60-15...without weight load/crush kn it.....has a side wall of 123mm....which is 60% of 205mm.....on each side of that 15" rim. 123mm = 4.842".....so the total tire height is 4.842" + 4.842" + 15" = 24.684".
A stockish 185/80r-15 is 26.653" tall. Ray |
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Nate M.
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Location: Anacortes, WA U.S.A.
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| Posted: Wed Aug 10, 2016 6:10 am Post subject: Re: Tallest tire ; Squareback |
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| raygreenwood wrote: |
Actually...tire circumference is key...not tire diameter. Its rolling inches per revolution per mile....and then add in the friction from wider tread if mileage is the issue.
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Tire circumference increases with increased diameter; it cannot decrease as it's a mathematical impossibility so it's kind of a moot point.
Adding width does increase rolling resistance and drag down the mileage significantly. You can offset that some by adding tire pressure, but your ride comfort suffers and it also adds road noise.
You will notice that many delivery box trucks use small diameter drive wheels. This increases the fuel mileage in stop & go traffic by lowering the final drive of the heavy truck and thus decreasing load when accelerating from a stop (which kills MPG). Getting up to speed quickly with the least amount of load helps in the MPG numbers for around town driving.
Hwy cruising you could see a benefit to slightly larger diameter rear tires to lower the RPMs, but not so low that you have to floor it to go up any incline.
Still I contend the biggest single factor is driving style period. A perfectly tuned car with a lead foot behind the wheel is going to get crappy mileage compared to the same car driven by grandma. 
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Nate M.
Squarsche build
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For heaven's sake, put a type4 and a Porsche 5-speed in there. . . It's the right thing to do!! |
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raygreenwood
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| Posted: Wed Aug 10, 2016 6:44 am Post subject: Re: Tallest tire ; Squareback |
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| Nate M. wrote: |
| raygreenwood wrote: |
Actually...tire circumference is key...not tire diameter. Its rolling inches per revolution per mile....and then add in the friction from wider tread if mileage is the issue.
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Tire circumference increases with increased diameter; it cannot decrease as it's a mathematical impossibility so it's kind of a moot point.
Adding width does increase rolling resistance and drag down the mileage significantly. You can offset that some by adding tire pressure, but your ride comfort suffers and it also adds road noise.
You will notice that many delivery box trucks use small diameter drive wheels. This increases the fuel mileage in stop & go traffic by lowering the final drive of the heavy truck and thus decreasing load when accelerating from a stop (which kills MPG). Getting up to speed quickly with the least amount of load helps in the MPG numbers for around town driving.
Hwy cruising you could see a benefit to slightly larger diameter rear tires to lower the RPMs, but not so low that you have to floor it to go up any incline.
Still I contend the biggest single factor is driving style period. A perfectly tuned car with a lead foot behind the wheel is going to get crappy mileage compared to the same car driven by grandma. |
Sure....but my point,was.......the sidewall profile multiplier has the most effect....on diameter and circumference.. It appears some people are not fully getting that. While you are correct that diameter is a function of circumference and vica versa......its far easier to SEE the point,when you break it down to inches/feet of travel per each rotation.
Meaning.....how many feet per mile, per minute, per second does that tire turn for each rev or at any given rpm.
Just saying that ......."I have factory 165-80R-15s and now I am going to a 205 tire"...does not instantly mean that the 205 is going to be bigger in diameter/circumference.
You have ro ask....."205 what"? The stock 165 tire which is an "80" series will be 25.397" in diameter...or height viewed from the side. If one were to install a 205/55 series.....diameter or height viewed from the side will be 23.85".....a good deal lower than the smaller tread width stock tire. It will also need to turn more revolutions per mile to go the same distance.....so will require more engine rpm.
Also ehat is not being mentioned....and some of this will depend on tire construction and air pressure......the narrower 165 tire will generally have more sidewall flex....so will also sit slightly lower than the wider 205 tire which will "generally" have a stiffer sidewall.
If ride height and fender clearance is what you are after....all of this must be taken into account. If gearing/rpm/speedo reading change is the worry ....diameter/and circumference are the big worry. Ray |
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Komissar
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| Posted: Wed Aug 10, 2016 8:04 am Post subject: Re: Tallest tire ; Squareback |
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I think the best mileage will be obtained by using 155 SR15 tires on stock wheels. The narrow contact surface will ensure getting the least friction. Also, when selecting tires look for the highest supported tire pressure possible and inflate the back tires to that max pressure (without going over) and front pressure lower (as aircooled rear engined volkswagens require, use the tire inflation chart as a guideline to deduct the proportion of pressures).
Another wild thought would be using some older narrow 16" rims with adaptors - things like Split 16" rims, but those are very rare.
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Erik G
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| Posted: Wed Aug 10, 2016 8:33 am Post subject: Re: Tallest tire ; Squareback |
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| Komissar wrote: |
I think the best mileage will be obtained by using 155 SR15 tires on stock wheels. The narrow contact surface will ensure getting the least friction. Also, when selecting tires look for the highest supported tire pressure possible and inflate the back tires to that max pressure (without going over) and front pressure lower (as aircooled rear engined volkswagens require, use the tire inflation chart as a guideline to deduct the proportion of pressures).
Another wild thought would be using some older narrow 16" rims with adaptors - things like Split 16" rims, but those are very rare. |
but 155 was never stock for a type 3 - so why would you go smaller than stock?
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Komissar
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| Posted: Wed Aug 10, 2016 8:54 am Post subject: Re: Tallest tire ; Squareback |
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From what I see in Europe the preferred "stock equivalent" (so to speak) is 155 SR 15. Roughly speaking 155SR 15 are the same width as the original tires and the 165s are the same height. That's because modern radials have inherently shorter sidewalls than old bias play tires. ( Bear in mind, that we are talking about 155 SR 15 = 155 82 R 15 and not the shorter 155 used in Smart Fortwo cars).
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raygreenwood
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| Posted: Wed Aug 10, 2016 8:58 am Post subject: Re: Tallest tire ; Squareback |
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| Erik G wrote: |
| Komissar wrote: |
I think the best mileage will be obtained by using 155 SR15 tires on stock wheels. The narrow contact surface will ensure getting the least friction. Also, when selecting tires look for the highest supported tire pressure possible and inflate the back tires to that max pressure (without going over) and front pressure lower (as aircooled rear engined volkswagens require, use the tire inflation chart as a guideline to deduct the proportion of pressures).
Another wild thought would be using some older narrow 16" rims with adaptors - things like Split 16" rims, but those are very rare. |
but 155 was never stock for a type 3 - so why would you go smaller than stock? |
 Waaaay back in the day....like high school when I had my first 411 four door....my first car.
Of course you do not have much cash working sacking groceries....so I had to buy new tires and all I could find that fit and I could afford...new....were 155/SR-15...bias ply tires made by Mohawk. I think they were about $35 a tire in 1978.... 
Ho-lee crap those were some squirrely fast wearing tires!
No way would I run even radial 155's even if I could get them. Just not enough tread on the ground and very high sidewalls versus how much tread on the ground.
Stock 165/80-15's theoretically have 165mm of tread width and 132mm of sidewall height on each side of the rim.
A 155/80-15 has 124mm of sidewall on each side of the rim but with so little tread on the ground...just 6.1".....that was ugly. On basic wet pavement...I "ski'd" through several intersections trying to stop.
As for gas mileage....there is something to be said for less tread on the ground. There will be less friction and rolling resistance....however there will also be less friction available for handling and braking.
Last summer I got new tires for my 2012 Golf. I was not out to buy low rolling resistance tires. But actually one of the top rated tires for wet, dry and snow weather handling for a touring tire....also happened to be a low rolling resistance rated "eco" tire.
The handling in all weather has been superb...and yes....there was a noticeable across the board...tracked all this year..increase in fuel mileage on many of my regular long distance runs....of about 2mpg.
With the modern low rolling resistance tires it is a combination of tread design and tread compound chemistry. Not all of them are created equal. Some of the super low rolling resistance tires (like those specified for a hybrid car) ...actually are too low in friction and can have handling issues.
I mention this because if you are looking for better gas mileage from a tire...look for a modern low rolling resistance tire designed to do that. Don't go compromising safety and handling by searching for a skinnier tire.
These are the tire...Continental Pure Contact with EcoPlus technology....if you could use a 185/65-15...this is a superb tire.
http://www.tirerack.com/tires/tires.jsp?gclid=CJrr...10155324:s
Its interesting...according to the Continental tire finder on line....165-15's are available in several series.....but in Europe. Ray |
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Erik G
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| Posted: Wed Aug 10, 2016 9:00 am Post subject: Re: Tallest tire ; Squareback |
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nope.
Stock for a type 3 was a 6.00x15. thats about 165R15
stock for a bug or ghia was 5.60x15 = 155R15
everybody uses 165's (165R15 or nowadays 165/80-15) for a bug because that's what has been available. I havent seen 155SR15's for 20 years (other than the replicas that are now available) And you can see the rub marks on the front trailing arms from the 165's being slightly too big for a bug
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raygreenwood
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Location: Oklahoma City
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| Posted: Wed Aug 10, 2016 10:14 am Post subject: Re: Tallest tire ; Squareback |
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| Erik G wrote: |
nope.
Stock for a type 3 was a 6.00x15. thats about 165R15
stock for a bug or ghia was 5.60x15 = 155R15
everybody uses 165's (165R15 or nowadays 165/80-15) for a bug because that's what has been available. I havent seen 155SR15's for 20 years (other than the replicas that are now available) And you can see the rub marks on the front trailing arms from the 165's being slightly too big for a bug |
Well...and this is the question to me...is a 165 rubbing on a bug because of the width...or the height? I am assuming the width.
The 155 being 24.76 high and the 165 being 25.38" high...of course before sidewall compression from weight. Still the difference from tire to tire is the same as shown. Ray |
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Erik G
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Donnie strickland
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| Posted: Wed Aug 10, 2016 11:16 am Post subject: Re: Tallest tire ; Squareback |
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I don't know if this was just for the US market, but my 1971 glovebox sticker shows the radial size as 165 SR 15.
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Erik G
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| Posted: Wed Aug 10, 2016 11:34 am Post subject: Re: Tallest tire ; Squareback |
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| Donnie strickland wrote: |
I don't know if this was just for the US market, but my 1971 glovebox sticker shows the radial size as 165 SR 15. |
yes - this is correct for type 3's regardless
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Komissar
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| Posted: Wed Aug 10, 2016 12:10 pm Post subject: Re: Tallest tire ; Squareback |
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| Erik G wrote: |
| Width. And the above reply was in relation to Komissar thinking 155SR15 was the right tire for the type 3. It's not. thats a bug tire |
Sorry, my mistake  . I drive my bug more than I drive the type 3.
But the idea remains - if mileage is what you are after, narrow stock tires are the answer.
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KTPhil
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| Posted: Wed Aug 10, 2016 12:24 pm Post subject: Re: Tallest tire ; Squareback |
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Tires won't do that much for you. Best advice for better mpg is simply to slow down.
Data is for a bug (from the owners manual), but on a relative basis, just as applicable to a Type 3:
Over about 40 mph (45-50 in a higher geared Type 3 maybe?) consumption increases drastically.
Also, shift as soon as you can be at 1800-2000 rpm in the next gear, and don't floor it after you shift... ease into it as the best torque range in reached. |
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