Relationship between Rim Width, Sidewall Height, & Stability

[TheArmand]

Hey everyone,

Lurking for a while now, finally found a topic I could not resolve through relentless searching. These forums are amazing! Thanks for contributing and being a part of it.

Issue: Stock 14" steelies/alloys suck. The combination of LT load rating, sidewall height, and 5.5-6" rim width contribute to instability and overall sub-par ride.

Solution: Upgrade to 15 or 16" rims, obtain shorter sidewall height, wider tread width support, and a selection of higher quality tires. This combination results in a more stable, comfortable, and predictable ride.

The Discrepancy: When looking to switch to 15/16" wheels, many of the popular wheel choices out there offer these larger diameters, but some do not offer any wider of a rim width compared to stock. Granted, this is mostly regarding steel wheels, where it is common to find both 15 & 16" wheels with 6-6.5" width.

The ever popular Mefro wheels for example, are 6" in rim width for both 15 & 16" sizes. Yet many Syncro owners, for example, or rocking Mefro's with enormous tire sizes, like 225/75/16, or some with even 235 width. Despite the ratios of rim width to tread width being equivalent, or sometimes greater, compared to stock wheel & tire sizes, an improved ride is noted. It seems safe to say, that sidewall height is the main contributing factor to the improvements in ride quality when changing to 15/16" wheels.

The Question to Answer: How relevant is rim width?

For every 1/2" change in rim width, a tire's overall tread width changes by 5mm. If one were to mount a 215/65/16 tire on a 16x6 Mefro vs a 16x7 S.A. Steelie, would a 10mm difference in tread width create a noticeable difference for the average Vanagon driver? Another example is GoWesty's Euro wheel, sized 16x7.5. Is that additional 1-1.5" enough to really make a typical tire size, such as 215/60/16, the best it can possibly be?

If you have experience with utilizing the same tire size on different rim widths, please chime in!

[dobryan]

I cannot answer your questions but another variable you must consider is sidewall stiffness. Not all tires are created with the same sidewall stiffness. The load rating does affect sidewall stiffness too....
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[Mellow Yellow 74]

[Ahwahnee]

[0to60in6min]

[Merian]

yup - also what is the age of your tires?
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....

[IdahoDoug]

Hammer,

For many people, putting larger tires on creates an enormous placebo effect that provides reviews of better ride, better cornering, greater stability, etc etc ad nauseum. I can tell you from years of instrumented testing as a vehicle developer that wider and larger tires almost invariably deteriorate ride AND several handling aspects (hard braking and turning, etc). We also documented many instances of SLOWER lap times when we took a car fully and properly developed with X size tires and put wider tires on it. Yes, I said slower lap times.

So what you are proposing is no easy task and I would say your odds of improving the ride with wider tires are near zero, improving "stability" (you have to define this to me better) is also in the 15% range. You will improve curb appeal at 90% however.

Better explain what you are trying to accomplish, and what the tires and pressures and other questions asked above currently are and how those are not meeting your needs.

PS - I still don't think anyone else is getting your name....

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

[rubbachicken]

scroll 3/4 of the way down this page http://www.carbibles.com/tyre_bible_pg4.html you will see a tire size calculator, you put in your existing tire size, and the size you are thinking about, it will compare them and tell you how much bigger / smaller, the % difference either way, bigger or smaller, there's also an offset calculator on the same page, you tell it rim width of present, and future wheels, and it will tell you if you are going to catch or not.
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[TheArmand]

This is more of a generalized discussion. The "issue" I've presented is moreso an echo of the Vanagon community rather than a personal problem, albeit reading it again describing it as 'sub-par' may have been a bit too much. Nothing is inherently wrong with the stock wheel/tire size, until you start comparing it to the wheels/tires they're being replacing with. I've heard it over and over, not only online but in person as well, of the various improvements these larger sizes create in dealing with cross winds, big rigs passing, road feedback, etc etc.

I'm simply trying to get more detailed feedback from more knowledgeable & experienced Vanagon folk. I feel like there are some missing bits of information with all these different variables. Who knows, at the end of the day were probably just shooting the ____, as it's all anectodal feedback without controlled variables. Gotta start somewhere right?

I'm interested in the topic as I'll be both lifting and high topping my van by the end of the month. I've experienced what it's like driving in strong cross winds, and keeping the steering wheel clocked a couple hours to one direction to maintain a straight line for miles on end isn't ideal, to say the least. I know wheels/tires are not the only factor, and that the above will be improved greatly when I replace bushings/shocks/springs. Yes I'm running correct psi and proper tires, just stock steelies.

[TheArmand]

[Steve M.]

Don't need to be a prophet to see where this thread is going.

[0to60in6min]

http://www.roadhaus.com/tires/guideline.html

http://www.roadhaus.com/tires.html

[Ahwahnee]

[IdahoDoug]

So here's the physics against putting wider tires on to make the Vanagon "handle better", "track better", or "corner better".

A tire's contact patch is the exact same square inches in touch with the ground if the tires are at the same pressure - whether it's a stock 185R 14, or a 225/50 16 GroundPounder Super Duper Deluxo Racey Tire. Same square inches of total ground contact. Same PSI. Same amount of grip.

What changes when you put the GroundPounders on is the shape of the contact patch. It goes from oval with the long axis in the direction the vehicle travels, to an oval with its long axis at 90 degrees from the direction of travel. Guess which one is more stable - meaning which contact patch shape will keep the vehicle tracking straight down the road in cross winds, uneven road undulations, around a curve with a bump in the middle? If you guessed the contact patch of the 185R 14 with its contact patch in the direction of travel, go to the head of the class.

If you drive down the road with the GroundPounders on, and you hit a bump with one edge of the tire, it can bump steer the vehicle much more easily because there is so much tire contact patch far away from the center line of the contact patch. Simple leverage. Hit the same bump at the edge of the stock 185, and you'll hardly feel it twitch the van around - the contact patch is long and narrow.

There's pages of information on this, and it flies in the face of the cosmetics of having wide tires, so it always loses in Internet discussions. But the truth is that stock tire size tires will be more stable and ride better and brake straighter, etc than wider tires.

I get the "better choices of tires" argument, however and that's definitely an issue.

As a data point, my Vanagon tintop on correct Michelin 185R 14's (what - 82 profile?) on stock alloys with good shocks, a brand new steering rack, a recent alignment and the tires properly inflated runs down a windy interstate quite well. It also carves mountain roads beautifully, rides well and has a delightful "light on its feet" feel that frankly makes motoring fun.
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[zak99B5]

Excellent post and info, Doug--I learned a bit.

It reminds me of all the people who buy coil overs and lower their cars and rave how much better it handles, when in most cases they have ruined the suspension geometry and their cars have less roadholding than with the stock suspension. Physics be damned, marketing wins.
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[Ahwahnee]

[Zeitgeist 13]

Most of us don't have access to solid data-logging equipment, so we have to rely upon anecdotal evidence, which is always problematic. Nevertheless, in my experience with Mercedes, Audis and Vanagons, stepping up from 15" to 16" in the former two vehicles and from 14" to 16" in the latter has significantly improved cornering ability by reducing sidewall flex. The trade-off can often be a harsher ride, since the reduced sidewall flex forces more of the road impact to be absorbed by the suspension. I've also stepped one of my Mercedes up to 17" and the cornering effect is even greater, as is the harshness and bumpsteer.

I think 16" is the largest diameter rim I would recommend for most passenger vehicles where the aim is to retain the same or similar wheel/tire diameter. If you want oversize tires, then that adds a whole lot of other variables.

My van is currently setup with 8" 225/50 rear rims/tires and 7.5" 205/55 fronts. The front track is setup to be wider than the rear (to clear big brakes). The cornering on that combo and stock Carat springs and suspension is really quite stellar. I'm about to experiment and raise the height by adding stock early model springs and 225/70 rear and 215/70 front tires. I'm nervous to see how badly my cornering takes a hit with that combo. I strongly suspect that I'll need to invest a shit-ton into suspension improvements in order to gain back some of my overall stability and handling.
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[IdahoDoug]

Yep - glad you recognized the challenge going into this project. Objectivity is the key as you seem to grasp.

That change is going to be a challenge - one direction I can suggest is to put quality shocks on with those springs - like factory Boge's, etc.
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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

[blackfilmguild]

I am riding on Hancook 205/70/14 and they are working out great. I have read that some people are choosing the Hancook 185/14 LT (light truck). Do you get better handling from the 185 and less bulb in the sidewall with 185 LT vs 205?

[E1]

I’ve never run Hankooks, but some observations…

Both our vans started life on 14” alloys. Van 1 came with Big O offroads, C-rated, the old and loved 27x8.5 size, decent on dirt but otherwise they were spongeballs.

Replaced with 27x8.5 rears but BFG ATs, the style before KO2s. Much better. A few months later we couldn’t find 27x8.5s anymore (2014), so put smaller 185/14s on front, but they were D-rated KO2s. HUGE benefit on turn-in despite being significantly smaller than the rears, mostly because the 8-ply sidewalls were MUCH stiffer than the Cs.

We wore these all out over time, and replaced with BFG KO2 all around — but on 16” wheels. 215/65R-16 size. It’s nothing short of mind-blowing going to 16s and their stability, but especially when having stiffer sidewalls from the D-rating.

The downside is unless having something with more power than a Wasserboxer, you almost have to change the ring and pinion to make up for the re-gearing the taller tires do — and there's no getting around it and the drag of more rubber and heavier wheels atop that.

I never choose tires based entirely on Load Rating (Edit: I meant Load Index — the posted numbers like “98” or “102” or whatever). Those really are guidelines mostly to demonstrate safety values per corner weight, legalese in a sense, so people don’t overload tires. But otherwise most dealers or customers have little knowledge of tires, honestly.

Even with dealers, the lack of practical knowledge is frightening. Don’t believe me? Look at the crap pressure gauges most of them rely on, for one.

Specific to your sizes is this:
https://www.tacomaworld.com/tirecalc?tires=185-70r14-205-70r14

Between these, I see the advantage going to the 205s, and their slightly wider tire patch per diameter.

MY MAIN POINT IS THIS:
If all else is equal, on these vans, the best handling you will get is on D-rated tires. The sidewall stiffness and higher air pressure holds more weight on cornering, situations that have soft sidewalls and less air simply collapsing under high-grip demands.
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