2WD mismatched tire sizes

[VisPacem]

Hello

Over the last ~ 3 years I have owned my latest Vanagon, I have read most if not all the wheel/tire threads here, (yes, including the Sticky)

Unless I missed it, I did not see a post/thread addressing the possible mixing of different size tires front/rear. Now I am talking about regular Vanagons 2WD of course. Not them fancy pants power monsters ready for the Daytona 500 or the Nürburgring or the Paris-Dakar.
It would seem, and I stand to be corrected, that the Vanagon weight distribution favors the front. However, being, thankfully, a rear wheel drive vehicle would there be an advantage in running bigger tires**
- in front ?
- in the rear ?

Or just stick with the same size all around.

I am running 215-70-15 at the moment and thinking for my next set of going 205-70-15 in the front and 225-70-15 in the back ...
or ... would there be an advantage in dropping to 65 profile tires ?

The extreme accuracy of the speedo does not concern me, I use a gps.

** Without ANY body modification and allowing "normal" operation of all OEM components including the sliding door.
_________________
LG aka VisPacemPB, *The* party Pooper

No Regrets (Nothing to do with Vanagons)

[vanagonagon]

I've got 27/8.5/r14s on the rear and stock size yokohamas on the front and can't notice any difference in the sliding door operation or anything else for that matter. It's not a huge size difference either.

[Vango Conversions]

I had stock 185R14 tires in the front and 225/70R16 in the back for a while.

The reason I did it was to get the largest diameter on the rear wheels to lower the RPM. There is no reason you can't mix tire sizes front to rear in a 2wd. The large tires can rub in the front and lower profile tires in the front can keep the speedo close to accurate and handle better.

[VisPacem]

[j_dirge]

I ran taller wider tires in the rear of my 2WDfor 4 yrs.
185/85r14 in front... 225/70r14 in the rear.

It handled fine... brought down rpms.
Did not give better mpgs, but less rpm was noticeably quieter at 65mph

The added width in the rear gave quite a bit more traction off pavement, too.

Gave the van a retro look.
_________________
-89 GL Westy, SVX.. finally.

-57 pan f/g buggy with a 67 pancake Type 3 "S"
"Jimi Hendrix owned one. Richard Nixon did not"
-Grand Tour, Season 1, episodes 4 and 5

[teej]

How do you do tire rotations? Or not?

[j_dirge]

[Wildthings]

It all depends on how the tires match up. When I bought the first set of replacement tires for my Multi I only bought two as I was short on funds and two of the old tires still had acceptable tread. The remaining two OEM 205/70R14 just plain out handled the two replacement truck tires making the van very squirrelly. I had bought the two truck tires just before leaving on a trip of a few hundred miles and ended up going ahead and buying two more of the truck tires two hundred miles down the road because the handling was so poor.

Presently have regular truck tires up front and 27/8.5R14 studded tires in the back. The handling isn't quite balanced but close, the 27/8.5R14 are just a little stickier than the narrow overly stiff truck tires.

[piruvan]

I'm running slightly larger 225/R70 in rear and stock 185/R14 in front on my 2WD. No probs. Won't be rotating since the fronts are new and the rear seem to wear faster (prob due to weight) Gives the van a slight rake. You know, like the A-Team van.
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'89 Vanagon GL "Whitestar" Wolfsburg edition. 4-speed, 2.1L
'06 Accord EX-L 5-speed

[IdahoDoug]

Not to put too fine a point on it, but different size tires can have very big impacts on emergency handling. On a sedan, it would be an issue but on a top heavy short wheelbase van, it could be serious. This is not something you'll feel on a daily basis but in an emergency. Also say you increase the diameter on one axle by a mere 1.4 inches. That means brake power on that axle just diminished by 10% to create quite an imbalance as well.

So, some deterioration in safety to consider.
_________________
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

[Wildthings]

If you are referring to the difference in size between a 27/8.50R14 and a stock tire size, the difference is closer to 1.2" in diameter which works out to only around 5 % difference in braking power. For most this is probably not an issue.

[IdahoDoug]

My purpose in pointing this out is that either larger tires, or 2 different tire sizes creates a pretty big change in what happens in the pre-crash phase of trying to avoid an accident. I have been part of studies of max braking, low coefficient handling, mixed coefficient handling, ad nauseum. So when I read of people changing or mixing tire sizes "with no issues" it makes me want to stand up and shout "That's crazy talk - it's a dangerous thing to do, plain and simple!".

Precisely when you want your vehicle to help you out, you have handicapped it by altering important variables. This vehicle, like any German vehicle, was carefully tested as to its emergency handling. Repeatable tests were run to decide the optimal tire pressures to prevent uncontrollable over or under steer, to absorb road variations in hard cornering, and to provide acceptable steering response and braking stability. Engineers studied pages of data, tire slip angles, cornering behavior, etc, had meetings as to a couple pounds of air pressure here and there, and how it changed things around in statistically valid distributions of data. They then signed off on those variables as well as the shock damping rates and spring rates and a myriad of other variables.

Then along comes an owner who casually tosses on wider tires and rims with an improper offset. If tested by VW, the handling and other stock variables would measure so far off the original and safe behavior that they wouldn't have even been in the consideration set when final vehicle parameters were decided upon.

Add to that the inevitable deterioration of a 25 year old vehicle's springs, suspension bushings, brakes and steering and you may have no idea that you are driving a vehicle that could be flipped on flat, dry pavement with a few flicks of the steering wheel in the right combination.

So I guess I'm making a point that this forum should err on the side of caution when someone asks if its OK to run two different sizes of tires on their van. I'm impressed that people here make a big deal of having the correct load rated tires even though they're very difficult to find in stock sizes now. I like that - because that load rating is a very big deal. But it's worth noting that the hazard from overloaded tires would take quite some time to become a danger such as a long highway trip on a hot day at max GVW. By contrast something like different size tires could cause you to flip your Vanagon on the way to the corner market avoiding a deer or similar.

I don't want to rain on anybody's parade, but I feel this is an important topic. Anytime you stray away from stock offsets or tire diameters or mix diameters you are entering dangerous territory that will only become apparent when you're already in trouble.

DougM
_________________
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

[Wildthings]

I am perhaps more aware of my vehicle than most and have been around a while to boot. I remember back when they were first coming out with radial tires and it was common knowledge (actually the law in some states) that if you only ran two radials mixed with your bias ply tires the radial had to be run on the back axle. Well I acquired a couple of radials eventually and dutifully installed them on the back. The car became almost undriveable, you couldn't keep it in its lane and barely on the road. I pretty quickly picked up a couple more bias ply tires for the rear and relegated one of the radials to use as a spare. Sometime time down the road I got a flat on the front and had to install the radial spare. After the experience I had had with the two radials on the rear, I was petrified to drive with that one radial tire installed on the front. I slowly crept up to around 35mph and started working my way home with the intention of coming up with another used bias tire to install before I continued with my weekend trip.

I found the car handled pretty well at 35, so I tried some evasive maneuvers and things felt okay so I picked my speed up some more and kept testing the handling as the road would allow. Even at the full legal speed the car was handling better than it had ever handled before and never got squirrelly at all. I kept that radial on and eventually installed the other radial on the other side of the front and drove it that way for the full life of those tires. The bad understeer problem that I had had with the bias tires all around was gone, and now I had a well balanced car with better steering and braking.

Engineers, in this case German ones, are not always right. They at times design things that leave lots of room for improvement. I certainly am not above running two different tires if it improves or at least doesn't significantly harm the steering and braking.

[Vango Conversions]

I guess I should have started my last post with, "Perform at your own risk!" disclaimer, but I didn't have any problems with the taller size in the back, no problems with the sliding door. I considered the possibility of screwing up the brake bias but it seemed to stop and handle fine.

I did it because I was about to drive across the country in my newly converted subaru 2.5 powered van and I wanted to drop the RPM as much as possible and I had limited time and funds and I didn't think the 225/70R16 tires would fit in front.

Now I'm running a matched set of snow tires, but come spring I'm going back to 225/70R16 in the back and I think I'll try 225/55R16 in front to avoid hitting the top of the wheel arches while turning over bumps.

[j_dirge]

[wvukidsdoc]

I wouldn't make any hard and fast guesses or conjectures on diameter vs braking efficacy. The immediate thought to me is that running tires of greater diameter is likely also meaning wider and also going to be changing contact patch, which is where it all comes down to, where the rubber meets the road and friction coefficient of that contact. Sure you increase the lever arm (tire radius) by 1.5 inches or so you'll decrease the resisting load to get the same braking torque by 8-9% as I calculate it. However if that load is over an effectively 5-6% larger contact patch say, probably a wash. And I'm so rusty from being 20 years out of engineering that I'm not even sure I'm thinking clearly this is a problem. If it takes less force at the contact patch to get the same braking torque, is that a good or bad thing, can I apply more absolute braking when all is said and done before slip? A first year engineer who is still and engineer can answer this. And then throw in the compensation on the rear, and who the heck knows.

I'm not saying to do it, but I've bought lots of bays and vanagons running larger tires in the rear, hell at times is seems you can hardly find a split that didn't have its rear hogged out for massively oversized tires somebody ran in the 70s. I think the point about how it actually handles with your combination of tires is real, real, valid. I've had vans with all 4 185R14s where the brand (all good C-D load raters) of tires was different front to rear and they handled frightfully, and others with massive difference, and big probably not really up to LTs in the rear and they handled beautifully. I too have had bias snows on the rear and radials on the front on buses I've bought that handled just find despite VW prescribed warnings. YMMV.

YMMV.

[WestyBob]

We used to drive splitties and bays all the time with mix-match tires including bias-ply and retreads but that's because we couldn't afford anything else. Was it safe ? Naw. Did we all die ? Naw. But if you can afford to be safe then do it regardless of sticking with same or mix.

Super higher speeds with the subie ? Better do some testing with mixing prior to any road trip. Cruising at 75-80 mph when an antelope/deer hops out ? Better check the handling ahead of time.

[?Waldo?]

I've driven many years with stock vanagon tires on the front and 27.5" diameter tires on the rear (almost as large as will fit on a 2WD w/ stock trailing arms). I have been in a couple of harrowing driving experiences due to idiots on the road and have found the van to handle and brake better than with stock size tires all around. YMMV.

[VisPacem]

It would seem that some of us are no Ariadne or Theseus, as the thread was tires of different sizes.

Not different brands
Not different pattern
Not different construction
Not bias vs radials
Not snow tires vs slicks

But it's ok, it's New Year we are all entitled to a (or several) shot of JD or XO

Thanks for the comments, opinions and recommendations
_________________
LG aka VisPacemPB, *The* party Pooper

No Regrets (Nothing to do with Vanagons)

[WestyBob]

When was the last time you saw a longer thread stay on track ?