Increased Wheel Diameter w/ Stock 2.1L Engine

[alanmacleod2]

I'm looking to get some new (taller) wheels for 16" rims (want cheep increase to highway gearing) with a stock 2.1L engine.

Can anyone tell me what diameter wheels (inches or revolutions/mile) they are running with a stock motor and has there been a significant reduction in power.

Thanks in advance,
Alan

[dhaavers]

Wheel diameter will not necessarily affect power to the pavement, but TIRE diameter will:

I recently moved to 5% taller than stock tires on my stock steel wheels, with
a (predictable) 5% loss in power & RPM at any given speed. IOW, less hill-
climbing power but lower engine RPM @ any given highway speed.

Easy to calculate, given your current tire size. Please share...???

- Dave
_________________
86 White Wolfsburg Westy Weekender
"The WonderVan"
<EDITED TO PROTECT INNOCENT PIXELS>

[alanmacleod2]

Yes, you are correct - I mis-spoke.

I am looking to get taller than stock tires for new 16" rims. I am currently running 185/14s (appox 820 revolutions/mile ?) and am looking for people's real-world experience regarding going to a taller tire with a stock 2.1L engine.

I'd like to get feedback as to what tire diameter (revs/mile) the power loss becomes an issue.

Thanks for your reply.

Alan

[dhaavers]

So noted. Personally I'm comfortable that 5% can be dealt with by additional RPM's in lower
gears (& comparable hit in MPH) but 10% could be too much for the stock 2.1 in extreme
conditions ( >6% grades for long climbs, or >8% grades even for moderate climbs)...

You could be putting yourself in real danger depending on traffic conditions, ambient speed, etc...

YMMV...literally...

- Dave
_________________
86 White Wolfsburg Westy Weekender
"The WonderVan"
<EDITED TO PROTECT INNOCENT PIXELS>

[tencentlife]

Under about 6-7% I doubt you'd notice the power reduction most of the time. Up to about 9-10% it's a good trade-off, over that I think you'd wished you'd done less, and mileage may actually get worse if you have it floored too much and the engine's running open-loop.


Here's the math to figure any tire size to compare, there are variances but this will get you into +/- 0.25" or so:

Metric P or LT sizing is, for example, 205/70-16.

205 is the tread width in mm.

/70 is the aspect ratio, that is the sidewall height as a percentage of the tread width, so 205 x 0.7 is 143.5mm

-16 is the wheel diameter in inches (funny hybrid system isn't it?)

25.4mm in one inch

(143.5 x 2) + (16 x 25.4) = 693.4mm

693.4 / 25.4 = 27.3"

The stock 185 tires don't usually print the aspect ratio but diameter is usually about 24.5"

27.3 / 24.5 = 1.114, or an 11.4% increase in dia.

To get that down, choose a lower aspect ratio like 60 or 65, then do the math.

You can apply a percentage across the board, so your rpms will change by the same amount in any particular gear with a standard trans.

Go to town.
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Experience is kryptonite to doctrine.

[Robw_z]

Also remember that the the lower the sidewall profile of the tire, the harder it is to find a good load rating. It is possible to get a 16” tire that is equal in diameter to factory, but load your van up, take a sharp turn and it’ll blow.

-Rob

[E1]

We have a stock 1.9L -- a powerplant known as The Ripper if you didn't know -- and went from your tires and wheels to 16s.

Is dirt in your future? I ask as we're running 215/65-16 at 27" high and do lots of backroads. It works for us because we went from a stock 4.83 ring & pinion to a 5.43, meaning we're turning about 12% more revs at a given speed, roughly. That was key for us, but we're full-timers so weigh a hair above GVWR. If you want to configure for longer trips and have more weight, I think you'll notice the bigger tires, though certainly not a disaster like some might say.

Conclusion..... it's slow either way.

Point is if doing a dirt setup again I may have gone with 15" wheels with taller sidewalls, better grip and flex on dirt but sloppier handling needing more pressure on pavement. Priorities... General handling of our van on pavement is now very, very good, mostly because the tires are D-Rated and we put whatever air in the tires holds the thing up under duress.

At the recommended, 1984 pressures, it handles just like in 1984 and feels like you're on flats, which might happen if the tire debeads from having 36 lbs. and avoiding an elephant or something. Beware: others will disagree.

Maybe a consideration on wheel choice... if a granny rebuild is in your near future -- Edit: Don't touch Granny, instead, rebuild your tranny -- use that as a good time to get it all right. In retrospect I'd have done a 5-speed if I could have.
_________________
‘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

[Love My Westy]

i've been running oversize tires for so many year I can't remember what the stock 185 x14 tires were like. I do know this, that the bigger, stiffer tires make the van handle so much better (along with shocks and heavy duty sway bar) that it was worth it for me to go to the larger tires.

I currently run 215 75 x 15 BFG's and am happy with them. I still have my stock 2.1 and it is slow going up hills, I probably shift into 3rd gear sooner, but so what, I'm driving my van and it will never be as fast as all the newer cars that pass me. Dangerous? If your really concerned about the speed of your van, may you should do an engine conversion instead of just tires. I think the handling with skinnier tires and stock suspension are scarier then going a little slower up the hills.

[E1]

My God Man, you can pull 3rd gear like UP a hill???!!!!!!!

<<< Bookmarked >>>


_________________
‘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

[IdahoDoug]

Quote: "I think the handling with skinnier tires and stock suspension are scarier then going a little slower up the hills"

Hmmm, so your suspension and tire changes make your Vanagon handle better than stock? I would be interested to run a stock version side by side and see if that is so. Be careful mixing and matching aftermarket parts, larger tires and making claims like that. I'd be willing to bet you're slower around laps, less stable on slippery conditions and in the wind, and have some emergency handling issues you'll only know when you are in an emergency. Atop that, you're likely getting less fuel economy and have less available power.

So, where's the better handling part come in?
_________________
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

[E1]

On the track, when works for you?

Near Ennis now.

Are you suggesting that bigger tires hold less weight than small tires of the same model? Surely you're not.
_________________
‘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

[IdahoDoug]

Heh - no, not suggesting bigger tires carry less weight. Hope your journeys are going well!!
_________________
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

[E1]

Whew, that was close...

Good Doug, Thanks!


By "carry less weight," I mean "less tire mass to grip with in corners."

If disagree, call 1-800-DRAGBUS.

Sorry, wrong threat: 1-800-BUSGRIP
_________________
‘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

[alanmacleod2]

All,

Thanks for the replies/information.

It sounds as though a taller tire (increased circumference) up to approximately 765 revolutions/mile (+ 7%) should get me almost 5 mph faster at the current 60 mph engine rpms without losing a significant/dangerous amount of engine power.

I believe this would include the following tires:
225/60-16 (757 revs/mile)
215/65-16 (747 revs/mile)
205/65-16 (761 revs/mile) - pushing it

Any all weather recommendations (So. Calif - mostly street, some dirt roads, no off-road).

Thanks,
Alan

[crazyvwvanman]

Those rev/mile numbers are pretty far off. Don't use those for your calculations.

Look up what Nokian gives for their tires in those sizes.

215/65-16 _ 770 rev/mile
205/65-16 _ 785 rev/mile
225/60-16 _ 780 rev/mile


For comparison with the 2 stock 14" size,
185R14C about 810 rev/mile
205/70R14 about 820 rev/mile

I've been running oversize tires on my Vanagons for 30 years.
I find that 750 rev/mile is the upper limit before the loss of power is too great for me. I prefer slightly less loss, and now run 770 rev/mile. I'm talking about stock power level vans, or close to it.

Mark

[SSWesty]

On my westy with a 2.2 wbx engine I am running 27x8.5 14 Grabber ATs which are spec'd out at 26.5" diameter and 784 revs per mile. This gets me 3,200 rpms at 60mph which is about where the torque curve starts to flatten out. Once in awhile I tow a boat so this is about as tall as I want to go. I could see going a little taller but not much.

Also take into consideration that the wider the tire you'll probably get more road noise.

[jimf909]

[Waldi]

[82westyrabbit]

I hesitat to comment on this at all as my van is vary different. Air cooled transmission=higher gear and a Tiico inline four engine. I use to run 23 inch tall tires to help lower my gear ratio 205/60 14. I am now running 15 inch tires that are 26 1/2 inches tall if I remember correctly. Now the van is geared vary high 3200 rpm’s at 70 mph witch is not a big problem as I can climb hills at 65 or 70 in the 4500 rpm range in third gear. The real problem is first gear is higher than I would like it to be and now I am unhappy with the brakes that are also less effective than they were. I am not recommended against larger tires. I feel the larger handle better and ride better. But if I wanted to go off road I would definitely have to regear the transmission. My only point is that less power is only one of many things that happen with larger tires. Good luck with your choice most people are happy with the larger tires. John

[E1]