Wheel size versus maximum speed

[chrissev2]

So interesting experience this weekend.

I tried out some 17 inch wheels on the diesel Vanagon (1.9AAZ with a 3.27 RP automatic tranny).

The wheels took the tire height from 22.7 inches up to just over 25 inches.

So I figured, that is only about 2.5 inches in tire height. This couldn't make all that much of a difference.

The difference, though, was quite a lot.

The Vanagon would not go past 80km/hr and had trouble getting there. It lost all of its power.

The "sweet spot" in the transmission, where it shifted up from second to third at just past 60km/hr, and had power all the way up to about 110km/hr, was gone.

It is amazing how much difference wheel size makes on these old vans. When I put the 14 inch wheels with the 185 60 14s back on it again, the power was restored and it was the old Vanagon again, able to get up to about 110km/hr without difficulty (and struggle past that, but I usually don't go past 110km/hr as it is an old van (1986) and I don't really like how it sounds going past that).

I guess these things were meant to be run on 14 inch rims. Everyone will tell you different, but larger wheels in my experience meant all my power was gone, I could hardly get it to 80km/hr and it was a horrible driving experience.
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2024 GLI Jetta 6spd manual
2023 VW Atlas 3.6 VR6 Highline
1978 Volkswagen super beetle convertible
1992 Eurovan 2.5 5spd westfalia

[jimf909]

Experience is a good teacher.

Keep in mind that the tire dimensions determine the revolutions per mile and the change in gearing you experienced. Wheel size has less to do with revolutions per mile because a high profile tire on a 14" wheel can have a greater circumference than a low profile tire on a 16" wheel.

Experiment with different wheel/tire combinations here:
https://www.tacomaworld.com/tirecalc

Regardless, larger tire diameters can rob a Vanagon of its zip.
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- Jim

[DuncanS]

This is the size you would need. I don't even know if such a size exists.

Duncan

[jlrftype7]

I kept the stock 25” overall diameter in mind when swapping to 15” rims from the stock 14” rims on our ‘84 1.9.
I’d watched too many people put lifts and over sized tires on a stock vehicle over the years for off roading, only to be surprised at what their larger tires got for them when daily driving on the road.
Then, they start talking about final drive changes….
It is a wake up call when you drive a modified vehicle sometimes.
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'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto

[IdahoDoug]

Chris,

Thanks for being open and honest about your experience. As most know, for decades I have been an advocate for stock rims and tire sizes to get the most out of your Vanagon. But there are always people who've spent $3000 on new larger rims and over size tires that insist they are getting better ride, better MPG, better traction, and even that their hair is growing better.

The loss of power (and braking power!) is the ratio of the new diameter vs the old. Yours was over 10% so you had a loss of both braking and acceleration power of 10% on a car already in marginal territory for power.

Thanks for providing a real life experience all the young whippersnappers can see and read...
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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, 1993 Toyota LandCruiser, 2002 BMW 325iX, 1982 Toyota Sunrader

[PDXWesty]

Yes, it does happen.

Keep in mind that wheel size really has nothing to do with this. It's overall tire diameter that affects power and braking. You can have 16" wheels with smaller diameter tires that would be the same as stock.
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89 Westy 2.1 Auto

[?Waldo?]

Power = Torque X RPMs

A larger diameter tire reduces engine RPMs for a given speed and that reduction in RPMs means that the engine will produce a proportionately lower power for that given speed. The max power that the engine will produce at a given RPM is unchanged, you have just changed the RPMs for all given speeds. In other words, the power that the engine produced at 45 MPH, is now what the engine will produce at a higher speed (e.g. 50 MPH). That can certainly have a significant effect as wind resistance increases exponentially with increases in speed. Given the Vanagon's relatively poor aerodynamics and large frontal area, the effect of wind resistance is more dramatic than it is for most vehicles and because of that, it is remarkably easy to overgear these vehicles and reduce top speed and performance for no actual gain.

[DuncanS]

[VicVan]

Weight of the turning object (the wheel, i.e. rim+tire) can also affect performance. I don't know if its significant compared to a difference in overall diameter.

What is the weight difference between a stock wheel (14 in) and a 16 in wheel?
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'90 Little Blue Truck, 2WD auto, FAS GenV 2.0 NA (AVH)

[skills@eurocarsplus]

[fxr]

[atomatom]

i have 16" rims but the same tire diameter as stock, so my 16" tires have much shorter sidewalls. net result is same power but a lot more stability.
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84 Vanagon Westy, 1.9L, California raised but defected to Canada.

[DuncanS]

[Alaskaberrys]

[do.dah]

[VicVan]

Thanks for these figures. So weight is not a factor, or at best it helps...
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'90 Little Blue Truck, 2WD auto, FAS GenV 2.0 NA (AVH)

[chrissev2]

[do.dah]

I think by the mid to late 80's, no vehicle manufacturer was using 14 inch wheels on their trucks/vans besides VW.

[syncrodoka]

[chrissev2]