Tire Specs & Options

Side wall height is an important consideration in selecting tires.  Tires to be used off road should have a high profile, or tall side wall.  VW specifies 80 series tires for the syncro this reason (e.g., 185R14 or 205R16).  The taller the side wall, the more cushion the tire provides to absorb bumps and rocks, and the less likely the wheel is to be damaged.  VW does, however, specify a 65 series tire (205/65/15) for the 15" wheels that come on the South African T-3 (Microbus), but this appears to be due to gearing considerations.  Extra caution should be used with 65 series tires in rugged off road terrain. 

Tire width is also an important consideration.  VW specifies 185 - 205 mm widths for the syncro.  There is a reason for this.  First, wider tires are heavier.  This increased mass affects suspension  and steeriing.  It also affects acceleration.  A heavier tire/wheel combo will tax the damping of the shocks and degrade suspensipon performance.  It will also tax the steering system (including steering rack bushings) and put added stress on all of the components, even the CV joints and the transaxle. 

Tire pressure has a big effect on tire performance, suspension and handling.  VW specifies that the rear tires have higher pressure than the front tires by several pounds (see your door jam or owners manual for details).  You can fine tune steering by adjusting this differential.  It is well worth the little time it takes to try different tire pressures to see how they affect handling.  Tires for the syncro require 40 p.s.i. pressure capability.  Several of the tires availablke for the syncro will take up to 65 p.s.i.  There is no one air pressure good for all vehicles at all times, so none will be offered here.  However, for off road use (and driving in snow), airing down greatly increases traction and provides a softer ride.  In sand, it is not uncommon to go down to 10 p.s.i., but the tire can come off the rim if pressure is too low.  Higher pressures should be used in rocky terrain.

Wheels

Syncro owners soon learn that wheels are a complex subject.  The syncro can be shod with 14," 15" or 16" wheels.  VW initially sold a 14" and 16" version of the syncro.  The 16" model was not available in the US and some other markets, and very few were made.  VW also sold T-3s in South Africa with 15" wheels as standard equipment.   So, there are stock VW steel and alloy 14" and 15" wheels available, and steel 16" wheels.  Derek Drew  imports a 16" alloy wheel that meets or exceeds VW specs and  is lighter than most of the 15" wheels.  This discussion will be limited to these specific wheels, all of which have the proper off-set, are the poroper size and have the proper load-bearing capacity.  For info on other wheels possibilities, see BenT's Wheel Photo page.

14" VW factory Alloy Wheel: 30 Offset, 18lbs      16" VW Factory Steel Wheel: 30 Offset, 28 lbs. 15" VW Rhein Wheel 30 Offset.  23 lbs. 15" VW Starburst Wheel 30 Offset.  19 lbs. 16" CV 900 Wheel 30 Offset.  21 lbs.

One reason wheels are a complex subject is that changing the overall diameter of the tire changes the gearing.  Most syncros are underpowered to start with and do not handle taller gearing well at all.  A syncro with higher than stock gearing and a stock engine will suffer certain performance degradation in all environments except perhaps flat interstate.  The bigger the diameter of the tire, the worse performance will be.  Tires with a shorter sidewall to compensate for the larger wheel can be obatined, but no additional ground clearance would then be gained from the bigger wheels, and the shorter side wall would mean poorer off-road performance and increased risk of wheel damage (pic).  The only gain going to larger wheels would provide then would be the ability to use the larger 15" brakes, and perhaps cosmetic gains. 

Thus, in order to obtain the benefits of bigger wheels without suffering unacceptable loss of performance, the only course of action is to first change the ring and pinions in the transaxle and front differential to adjust the gearing to the tire size you have carefully determined you would like to use.  It is best to do this when the transaxle is out for a rebuild.  The new parts will range from roughly $1000 to $2,500, depending where they are obtained and whether new or used.  There are four different R&P sets, 4.86 (stock 14"), 5.43 (SA 15"), 5.86 (16") and 6.18. 

The first step in the process is to determine what tire size you want to use.  This will dictate what gearing changes to make.  The only reliable way to make these determinations is by having available the Revolutions Per Mile spec for each tire size of interest.  This spec is universal across manufacturers, unlike the tire size specs the manufacturers use, which is very unreliable.  Once tire size(s) has been determined, the data can be plugged into the Gearing Calculator Tim Smith and others developed, and you can instantly see what final gearing various tire and ring and pinion combinations will provide, and compare them to the stock set up.  This way you can carefully choose tires and R&P ratios that will provide final gearing that is no higher, and preferably lower, than the final stock ratios.  

The syncro is already geared on the tall side for the stock engine.  One way to obtain a definite performance enhancement is to go down in final drive gearing a bit.  This will provide for quicker acceleration, better hill pulling ability with less need to down shift and better off-road gearing.  The trade off is a loss of a few miles per hour cruising speed on top (4 MPH loss is not much, but provides valuable gains elsewhere).  It is not a bad trade off.  For those who spend most of their time on back roads and dirt roads, or who are content to cruise at 65-70 MPH, it provides a significant performance gain and no performance downside at all (except higher gas consumption).

Below are links to the magical wheel-gearing calculator and to other discussions and info on wheels and gearing:

Tire & Gear Calculator (xls)

• Photos of Porsche front & rear disc brakes fitted to the syncro hubs.