Wheel size versus maximum speed

[Toadranger]

Hi gang-

Upgrading wheels and tires for 1988 tintop 2.1l automatic. She came with 15" Mercedes rims with 205/65 R15 Kumho Solus tires. The Gowesty 16X7.5 Alloy Wheels ET23 just arrived.

I have had recommendations from friends from 205/65R16, 215/60R16 to 215/65R16 and want to be careful not to add too much stress the tranny and stock motor. I have made tweaks here and there but nothing to add much HP.
Just hoping for a better cruising speed/efficiency for level terrain, perhaps not to exceed 27" diameter.

I live in TN with mostly modest hills but will need to cross the Appalachians on occasion.

What have others done/experienced in this scenario? Any particular brands/models with appropriate load ratings?

Thanks for your time and advice...dw

88 tintop Wolfsburg Evangeline

[?Waldo?]

[dobryan]

[chrissev2]

[jimf909]

[DuncanS]

205 65 16s--4% increase in diameter over stock wheels. At the time of the accident, they were stock 14" rims and tires.

Duncan

[dobryan]

If you cannot lock up the brakes then the BMW brake booster may give you the extra assist you need.
_________________
Dave O
'87 Westy w/ 2010 Subaru EJ25 (Vanaru) and Peloquin TBD

"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson

MD>Canada>AK>WA>OR>CA>AZ>UT>WY>SD
https://www.thesamba.com/vw/forum/viewtopic.php?t=620646

Building a bus for travel in Europe (euroBus)
https://www.thesamba.com/vw/forum/viewtopic.php?t=695371

The Western Syncro build
https://www.thesamba.com/vw/forum/viewtopic.php?t=746794

[DuncanS]

OK, going out today and will try to lock the brakes. 3400 pound, '91 tarptop (47" x 77" of steel replaced with canvas--only the drivers seat aboard.)

There was one time when in a dire emergency, I stomped as hard as I could. Don't remember any tire squeal and after I had calmed down and got out to look, there were no skid marks on the pavement. New rotors, pads, drums, shoes, brake lines at the time. But before the top came off and I had 1000 pounds of tools and gear aboard. The final stop was abrupt, but because of an earth berm, not the brakes. Abrupt enough that the A/C, without the side supports in place, came down.

Duncan

[IdahoDoug]

Or, he's using larger than stock tires and reducing his ability to brake? Yes, you should be able to lock the tires on dry pavement of a car you are operating on the public roadway.

It may well be that you are also simply a good driver and can't recall ever having locked the tires because you pay attention, drive wisely, don't get into situations with too much speed, and a Vanagon is a bit of a slug and doesn't encourage sporty driving (!). But if tomorrow you TRIED to lock them, I'd hope you could.

And agree it's nothing to do with rim size - the factor that affects power, braking, and handling is the larger tire diameter.
_________________
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

[?Waldo?]

You are the common denominator of those 7 or 8. That doesn't make it impossible, just not something you have been able to do. It could be a matter of reduced foot pressure or a matter of maintenance.

[DuncanS]

Opps--Posted to the wrong topic. Sorry. Interesting you can lock your brakes. I never have been able to any of my 7 or 8 T3s.

Duncan

[?Waldo?]

[DuncanS]

Sorry, hit "submit" instead of "preview".

So, note the difference in size between the discs in the bike. Why is there a bigger one on the front wheel?

The reason for this is to get better braking on the front wheel. If what the guy says in the video is correct, then why do they use a bigger brake?

And this one also from the video. Stock passenger car on top and race car on the bottom.

Scaling off the pics, I measure 23mm for the stock car and 30 for the racing car in terms of distance from the center of the wheel to the point where the brake pads make contact. This is a 30% increase and thus a thirty percent increase in the length of the lever arm. For the sake of argument, let's assume the pressure is identical. But what is different, is the effective ability of the brakes to stop wheel rotation? Say, for example, the torque on the stock brake is 200 foot pounds. For the race car it would be 260 foot pounds. If you can lock the wheel at 200, then for the normal guy, that's good enough. Our problem is we can't. And thus, any way to get more torque on the wheel is necessary. In fact on a Vanagon, it's vital--especially in a loaded Westy or a tin top filled with tools, rocks, or a 400 HP marine diesel engine.

Duncan

[?Waldo?]

Why can't you lock up your brakes? How hard have you actually tried?

In a panic stop I've locked up all four tires on dry pavement with stock brakes, 27" tires and ~1000 pounds of tools in the back. Granted I was literally standing on the brake pedal...

[DuncanS]

Watched the "Why trigger brakes won't stop you faster" video.

Completely disagree for Vanagons. First of all we can't lock up brakes as there isn't enough pressure to seize the wheel. So this means adhesion to the road surface and the explanation of size of the pad don't mean anything. There are two ways to increase the braking effectivity for Vanagons. One would be to increase the pressure on the brake cylinder so there is greater friction on the disc/drum. The second is to increase the disc diameter--i.e. bigger brakes.

Take a look at these two screen shots taken from the video

[?Waldo?]

With the automatic trans it might have a more significant effect than with a manual as will not only affect the power for a given speed but will also affect the accelerator position required for a given speed/load, and the accelerator position is used as an input for the trans in determining shift points.

[chrissev2]

[jlrftype7]

[?Waldo?]

Why do you keep talking about rim sizes? As others have mentioned, the rim size is irrelevant to the gearing. The tire circumference is what affects the gearing. A larger rim size with a smaller tire circumference (shorter sidewall) can result in shorter overall gearing than a small rim size with a larger tire circumference (larger sidewall). I personally prefer larger rims with shorter sidewall tires as it reduces sway at the expense of a slightly (almost imperceptibly) harsher ride.

For example, one van of mine has 16" rims with 26.5" diameter tires and another has 14" rims with 27" tires. Obviously the 14" rims with 27" tires result in TALLER gearing than the 16" rims with 26.5" tires despite the 14" rims being two inches shorter.

[chrissev2]