Tire tips

Autors: Knut Anders, Ralf Burde, Wolfgang Nicklich,

Michel Thevissen

Translated by Per Lindgren <mailto:lindgre@online.no>


Re-equipment of tires on the Syncro 16”

NOTE!!!!!! Readers of this article will also wish to read a companion All About Vanagon Wheels (Including 16" Wheels)


...faces it’s own problems, as the Syncro 16” no longer is in production, and there is no commercial interest in making parts for the few vehicles on the market. In addition, it is for many unknown, that there even is a version of the VW Bus with bigger tires, and that existing approvements for the vehicle is available, as most people only know of the 14” and the TÜV requires papers of approvement. When replacing rims, one is best to cooperate with the [German] dealer; that is why I will in this document mainly tell about the possibilities over installing bigger tires on the stock wheels, 5½JKx16 H2 ET34, what works and what doesn’t.


From either VW or Steyr-Daimler-Puch, one cannot obtain apprevement for tires larger than 205R16. The tire manufacturers or –importers gives quite willingly so-called approvements, as long as the corresponding numbers for rim size (see further down), top speed and load index (which is in the vehicle reg. Papers) are within the current frames. Many TÜV stations still don’t find this sufficient, and require approvements. To get a single approvement made costs quite a lot of money, and the positive result is unknown.


The only thing that helps is to collect different approvements from different TÜVs and possibly making clear with one approver what needs to be done. Since the company Projektzwo no longer finds the T3 Syncro market lucrative, is the following two companies good partners even for eccentrical modifications:


Off Road Center Meisen

Schlagbaumer Str. 102

42653 Solingen


Phone: 0212/546630




Sport und Geländewagentechnik

Otto-Wels-Str. 5

42111 Wuppertal


Phone: 0202/270650


Here are modifications made, mostly with Borbet aluminum wheels design CD from CW Fahrzeugtechnik offered, which are available for the Syncro in the sizes 7Jx15 and 7Jx16 ET30 (KBA 43312) The bolt circle is drilled from the customer’s wishes. The load capacity of these wheels is quite high.


When mounting other wheels one needs to be cautious, e.g. the Ronal R9, a 5-spoke wheel for Mercedes, earlier offered for the Syncro by Projektzwo and in the pictures in the press. One day, the cast broke at the manufacturer, and they decided that the wheel that was out of fashion was not to be produced again. In addition is the fact that the load capacity of an expedition-equipped Syncro in terrain did not increase, so when the rumor of the broken cast came around, Projektzwo decided to only offer the wheel only in relation with downgraded load capacity. So anyone with a damaged wheel is out cold and can no get a replacement.


Upgraded springs for increased ride height is offered by company


Auto Seikel

Industriestr. 5

63579 Freigericht (Altenmittlau)


Phone: 06055/5282


The Eibach/Seikel springs have a spring constant of 140 kg/cm front and 120 kg/cm rear compared to the stock springs at 75 kg/cm. With these springs, the vehicle will be 1 cm taller when empty, and 3-5 cm taller when loaded [PerL: I cant see how this can be, there must be a mistake here] These springs have several satisfied users in the IG Syncro 16”. The comfort is of course somewhat less than stock. The use of Seikel springs make place for larger wheels,  when the spring compression under high load is severely reduced. Rubbing of the tire against the wheel wells are prevented. There are less body modifications needed too.


It is of course a matter of taste, how deep in the wells the wheels will travel. Those who never take the Syncro off road and never expect extreme wheel positions, can of course also mount bigger tires. The nose dive can also be regulated by mounting extra rubber bump stops on the shocks. The opinions are then differed from what works and what doesn’t.


It is also important in this situation to know that the front wheel moves towards the rear when the suspension is compressed. This also shows from the situation of the control bar, it is connected to the front of the lower wishbone and adjusts the caster angle of the suspension. The control bar is not mounted horizontal, rather in an incline towards the front, to achieve the effect of the suspension. If the vehicle is equipped with taller springs, there will be more room behind the wheel. Theoretically, one can also achieve more room behind the wheel by tightening adjusting the control bar towards the front. Then the caster will be bigger. The caster controls the “flatness” of the steering, and on a car with drive on the front wheels, too much caster can have negative effect too. The 2,5º caster on the Syncro is much less than what it is on 2wd Vanagons. If you are to adjust the caster on the Syncro, you can win up to 1 cm of space on the rear of the wheel. It would be interesting to hear the comments of a wheel alignment specialist.


As I myself is no acknowledged approver in this area, and have no means to test whether certain tires for the regular street traffic can be approved, is the following versions purely technical legally binding and should in single cases be discussed with a TÜV approver. My personal experiences is with a Transporter Type 251-299, how the same example is with a Doublecab, I do not know. When you touch the edges of possibilities, it all will also depend o the tolerances of the vehicle and the wheel/tire and the differences between the different tire manufacturers. In the table I have gathered manufacturers information over such tires that can be compared equally. One can see that there are quite some differences. Of course, I do not depend blindly on the manufacturers specifications. There is also the possibility that what fits on my vehicle, can not fit on another. Even between the left and right sides of the vehicle, there can be millimetres of differences. Everyone must check the clearance of the wheel, the general thumb rule is that 5 mms of air between tire and body is enough. One must also not forget that on an off road vehicle, stones can get caught in the thread of the tire, and scrub the body when there is not enough space; the wider the thread, the larger stones.


One other aspect is the “bellow” of the body; the underside of the wheel wells extend far into the body. When the front wheels see heavy nose dive, the tire can rub the body in the front or rear.


Space problems


Then  it is time for the problem areas, which is sorted in order. E.g. if #3 is a problem, #1&#2 should also be sorted out.


1.      One corner of the battery box under the front seats can cause tire rubbing when the steering is towards the outer limits of travel, and nose dive occur at the same time. This corner is already cut on the Syncros [PerL: 16”s?]; further modification is possible, and should get you 1 cm more clearance, to keep enough space for the battery. More than 1 cm is also not necessary as the tire will rub the upper fender edge of the wheel well. In extreme situations, even the 205R16 can rub; every increasment of the tire size will affect the problem negatively. Practically, it will only occur when driving onto a curb; when you are driving even with low speed, there should be no problem. Those who like to  compete in rallies, must have taller or stiffer springs.


2.      The front black fender extensions are the next hindrance. They must be grinded in the lower edges or removed, or else even light turned front wheels will rub.


3.      Also the footsteps are a bit protruding into the front end of the wheel well, they have no structural function, and can be modified freely.


4.      The vertical rear wall of the wheel well, with the horizontal wedge shaped reinforcement on the lower end has clearly a structural carrying function, and can not simply just be removed. Independent of the suspension, the tire will rub at heavy steering. Narrow tires are an advantage. To achieve more space, one can bend the horizontal reinforcement down, and dent the vertical wall with a hammer.


5.      On the rear wheels, the fender flares are once again the first problem. There are still more space here, so according to tire size, the possibility of installing snow chains is present.


6.      The absolute limit concerning tire size is the rear trailing arms, because it is not possible to alter these. Not even HD springs help here. One must still note that the trailing arms on the Syncro 16” is 25 mms longer than the arms on the Syncro 14”, to be able to install the larger tires.


Independent of the aspects mentioned above, wider tires will introduce a set of problems of its own. With tires wider than 245 mms, there can be problems opening the sliding door, so a longer hinge is necessary. (from MY 84, expensive ~1000 DM). The offset (ET) plays a big role here, with wider tires rims with deeper offset is often installed, but then you get problems with 2, 3 and 4. It is better to choose a big offset (limited by the suspension), then you’ll have less problems with the sliding door. The stock 16” wheels have ET 34, with smaller offset the wheel will sit further out. With tires 245/75R16 on rims 7,5Jx16 ET 30, the door will rub slightly, with 7Jx16 ET 30 you will have 3 mms of space between the tire and door. The total width of the General Grabber  ST on 7” rims is exactly 245 mms. From here, it is no problem to calculate that the distance from the door to the brake drum is 95 mms. Everybody can measure this themselves.


There will also be problems on the inner side of these tires, the tire collides with the suspension. The tires 245/45R16 on rims 7,5Jx16, the tire will rub on the upper arm in front, and the space between the tire and rear trailing arm is zero, the tire can also rub the bracket for the brake line. The optimal offset is between 30 and 34 mms. If wider tires are to be installed, the choice must be made with a smaller offset and the tire further out in the wheel well, where the tire will rub the outer parts of the well, and the clearance and movement of the tire will be severely limited.. The above mentioned combinations will dive in the wheel well, not on it.


If you limit yourself to the narrow 5,5” stock wheels, one can not just mount wide tires. From the information of a tire importer, there is especially on American made tires strict directions in how wide rims the tires is supposed to be mounted on. It is recommended that the tires are no more than 2” wider than the rim. That would be 190 mms!! Wider than 3” is not approved. That is a width if 215 mms. In theory, 215/85R16 is the biggest tire one can have approved on the stock rims. Here in Germany, this is clearly not looked at as that narrow. Semperit has an approvement on the size 225/75R16. For the BFGoodrich All- and Mud-Terrain, there is approvements from RW TÜV (FZTP 91/1773/03/37) for the size 235/85R16 and even 245/75R16 (!) on Mercedes G-class with 5,5R16 rims. Also for other reputable tire manufacturers, there are similar approvement papers, and according to the Mercedes Off Road Center in Munich, the sizes 225/75R16 and 235/85R16 can be mounted on 5,5Jx16 rims. On the other side, I have been told of one Syncro owner that argued his way to get the size 245/70R16 on stock 5,5 rims approved by TÜV. With such tire combinations, one must expect quite mushy steering and handling. The conclusion must be that the reasonable tire width is 215 mms on stock rims, and the upper limit is 245 when bringing space into consideration.


Tire dimensions


The classical tire dimension 7,50R16 can with some mods be mounted on the Syncro (See story from M. Thevissen), but all 6 points will be tight. In addition, the circumference will be more than 8% bigger on most makes, so TÜV will demand new exhaust tests. One can probably not get it approved by the TÜV either. This goes just further for the metric equivalent of the tire, the 235/85R16, which is a bit wider.


More realistic is the fit of the next-lower size, the 7,00R16 or the metrical equivalent 215/85R16. The latter is wider, and thus a bit smaller in diameter. 7,00R16 is not much smaller than the 7,50R16 but this means that the Fuldaflex 7,00R16 on point 4 only rubs slightly in original version. The extremely narrow pattern is just an added bonus. On point 5, one can easily modify. The supplied circumference is exact, this is then the reasonable upper limit of the circumference. Interesting is that in the original VW parts catalogues, there are exchange parts for the speedometer drive for the 7,00R16. Was this size supposed to be mounted from the factory? Unfortunately, the Fuldaflex is a real truck tire, made for heavy loads (2570 kg per tire). For distinct desert-fans, the Pirelli Scorpion Dakar is the tire. In the size 7,00R16 it is a matter of a straight competition tire, and not to be found in the Pirelli standard program. The measurements is about the same as the Cooper Discoverer 215/85R16 (I’ve measured it myself)


The 215/85R16 is probably by many tire manufacturers the economical version of the 235/85R16, so one can not find any high performance tires in this dimension. The selection is not big in this size (see tire table from OffRoad 8/97); if you want an all round tire, the Cooper Discoverer LT is almost the only choice. The Goodyear Wrangler AT 215/85R16 is still in production in USA, but no more sold in Europe. Interesting is the new Fulda Tramp 4x4 Tour, which fills this gap. For the Stratton Traction King one receives a quite wide formulated approvement, and should be able to be approved by a cooperative TÜV approver.


On the Cooper, you only need to take notice of the points 1,2 and 3. The wheel wells can be modified to leave enough space for this tire. Point 1 is still a problem, though. Rubbing is unavoidable; with careful driving, even a trip to Iceland made no damages; stiffer springs are still recommended. The Cooper tires comes out quite narrow on all tables, the fact is that the pattern on the 215/85R16 is narrower than the stock Semperit 205R16! The circumference is only ca. 2360 mms. A speedometer adjustment is advisable, e.g. at VDO Kienzle. The Cooper with stock rims weighs 28 kg.


The same diameter but more width offers the 245/75R16, a regular size with large selections of makes. On this dimension, it all depends much more on the individual tolerances of the tire and the vehicle! Points 1 to 4, possibly also point 5 must be modified, point 4 is the real limit. The huge tires fills the entire front wheel wells, and it looks quite angry when fully loaded. The look is much more friendly when the Seikel springs are mounted and the vehicle is 4 cm taller, which also should be done with these tires. In combination with the stock rims, the ride is very soft; only in a few approvements, there is the possibility of this combination. It is advised that a wider rim is chosen. The offset must not be too small, and the rim not too wide, as the space will be even tighter. 7Jx16 ET 30 is a reasonable dimension, the sliding door will still open too. The Grabber ST with the CW Borbet CD rim weighs 29 kg.


Even wider is the tire 31x10,5x15, comparable to the similar 255/75R15, offered by Projektzwo on Mangels steel rims, 7x15 with the very small offset 23 mms. The suspension is not in the way here. The wheel is very far out, and will collide with the fender. In addition, Bus models needs modified hinges for the sliding door. What more than needs modifications, is to me unknown; I would love to see a Syncro with this setup. I do believe however, that the 255/75R15 on a rim 7x15 ET32 would be just as good, and the door should clear the wheel too.


The next smaller wheel when measured in the diameter is the 225/75R16. Even here you have a quite large selection. Problems with clearance applies only to point 1. The diameter is almost the same as the 6,50R16, so you do not need any speedometer modifications.


On even smaller sizes, there is hardly any clearance problems. What problems you might see if you stick to small, wide tires, e.g. 245/70R16, I do not know, but the width concerns are the same as above.


Some 15” wheels can also be mounted on the Syncro 16”. As far as I know, this will not cause immediate disclosure from the IG Syncro 16”. If the brakes get the cooling they need, is to me unknown. In any case, an approvement for the wheels is necessary for the TÜV to approve them. Many TÜV approvers react quite suspicious when smaller wheels are fitted to a vehicle than what the manufacturer fitted. In addition, most 15” tires are too wide or have too small diameter. Under the already mentioned 31x10,5x15 is the 30x9,5x15 or the bit smaller, metrical equivalent 235/75R15. This is almost the same as the 225/75R16, just a bit wider. Except point 1, maybe even 2 and 3, there should be no clearance problems.


30x9,5x15 is probably one of the biggest tires that fit without modifications. From Mickey Thompson, there is even a 30x9,5x16 with the same outer dimensions, so there is a possibility to use it on the stock rims.


Tire-type size rim dia. width circ radius.

Norm- 225/75 744 225 2269 324

maße 235/85 806 235 2460 365

215/85 772 215 2355 346

245/75 774 245 2360 355

7,50 802 210 2445 375

30x9,5 750 240 2276 348

31x10,5 775 268 2364 355

Cooper 205 5,5x16 734 - 2245 330

Discoverer 225/75 6,0x16 744 158 2273 345

LT 245/75 6,5x16 780 165 2384 361

215/85 5,5x16 772 155 2360 358

235/85 5,5x16 808 155 2461 373

7,50 5,5x16 811 144 2476 376

30x9,5 6,5x15 744 175 2273 345

31x10,57,0x15 767 201 2342 356


Fulda 245/75 6,0x16 774 - 2361 342

4x4 Tour 215/85 5,5x16 772 - 2355 346

Fuldaflex 7,00 5,0x16 784 140 2390 364


Pirelli Dakar7,00 - 780 162 - 374


Goodyear 225/75 6,0x16 747 162 2276 330

Wrangler 245/75 6,5x16 780 183 2377 343

AT 215/85 5,5x16 775 157 2363 340

235/85 6,0x16 805 173 2457 353

7,50 5,5x16 810 162 2472 356

30x9,5 6,5x15 749 183 2286 328

31x10,57,0x15 775 203 2363 338


General 225/75 6,0x16 744 171 2268 343

Ameri 245/75 6,5x16 770 189 2344 353

550AS 215/85 5,5x16 772 163 2351 356

235/85 6,0x16 806 177 2455 368

Grabber 205 5,5x16 735 156 2233 319

AP 31x10,57,0x15 775 211 2361 353

ST 245/75 6,5x16 774 185 2351 338


Comments for the table: The fact that a tire is listed above, does not necessary mean that the tire is recommended or even fits the Syncro, rather I have collected for you, a maximum number of data , from which every one can make their own key. The single columns mean


Size: Nominal size-description on 16” wheels; the sizes 30x9,5R15 and 31x10,5R15 requires 15” wheels.


Rim: Minimum width of the rim (in inches), according to the manufacturer.


Diameter: Tire diameter in millimetres; important for the available space in the wheel wells.


Width: The section width of the tire (in mm), must not be confused with the total width in the size designation; important for available size in the wheel wells. On norm sizes, the total width is still given.


Circumference: The circumference (in mm) is mostly important for the rpms, the speed of travel, and the speedometer accuracy.


Radius: The tire’s radius (in mm) gives the ground clearance and height of the vehicle.


Almost all the data’s from the manufacturers are unchanged. If you do a close study of the table, you might find errors, mostly because of misprint and different methods of measurement.


My special thanks for valuable tips go to Knut Anders, of Solingen.


Another tip comes from Ralf Haarpaintner, about the jack which is too short even for the regular Syncro 16”, and after a tire change is almost only to consider as dead weight. The jack for the VW LT has the right height, and is stronger, but does not fit in the Syncro’s jack hole. However, one can remove the rod from the stock jack, and weld it onto the LT jack. Then, one can yet again look calmly towards a tire change.


Last, yet another entry to the discussion over the subject flat tires. I’ve already had two flats while driving, because the (tubed) tires had a defect, was damaged to the unrepairable and needed replacement. This is my theory: the big disadvantage of the Syncro system for those who travel far distances is that because of the lack of pressure, the circumference will be shorter, the tire spins faster, but will be forced to spin in the same speed as the other wheels because of the relatively stiff power transmission in the Syncro system. From the high stress on the tire, the tire core will be damaged to the unrepairable. That is my theory, it would be interesting to know, whether other people have similar experiences, or I was just plain unlucky.


At the BRW offices, Geländewagenmagazin (former Auto-Off or Off-Road), Am Sportplatz 1, 82041 Deisenhofen, Germany one can order a tire test from the magazine Geländewagenmagazin, cost DM 10,-.


<Wolfgang Nicklich>




Tire change to Michelin 7,50R16


1.      With 1200 kg permittable axle load, on can run tire pressures of 1,3 bar off road, and 0,6 bar on sand; with 1600 kg axle load, one should run 1,9 bar off road, and 0,9 bar on sand. The tire diameter, mounted on stock steel wheels 5,5x16 is 80 cm vs. 72 cm with Semperit 205R16. The net height increase is 4 cm (1,6”). Price in Belgium is ca. DM 400,- each, including sales tax. The width of the road surface of the tire is only 160 mm, the circumference is 2510 mm vs. 2245 on the Semperit.

2.      Can only be used outside Germany (No TÜV approvement possible) [PerL: Same goes for Norway, and possibly other countries in Europe]

3.      With Semperit 205R16, when the engine speed is 3000 rpm in 4th one is doing 80 km/h. With the Michelin 7,50R16, the speed will be 88 km/h in 4th @ 3000 rpm. The speedometer shows too little, so one should drive by the rpms.

4.      One loses about 10% pulling power; one notices when starting (a bit slower) and just inconsiderably when going up long 5% hills. In G-gear, I have not noticed any change.

5.      The ground clearance on my vehicle (with 500 kg load) is front 32 cm, and rear over 32 cm (I do not know exactly, the measurement was done with two broken rear springs).

6.      Turning circle 11 m vs. 10,5 before, the tires rub the battery box when pulling the steering hard. No problems though, as the max. steering is only used when going slow.

7.      The diesel consumption is about 10% higher; it is quite normal, as the regular engine speed @ 3000 rpm is about 10% higher now. On my car (with 115.000 km on the engine), the consumption is about 9l/100km (all combined, asphalt, sand, off road)

8.      Noise: A bit louder than the Semperits, but not disturbing.

9.      The tires have a bit more rolling resistance over the normal tires; I guess about 10-15%.

10.  Higher total weight: the tires and rims weigh 32 kg, one can feel that when mounting them on the car.


Modifications on the vehicle



The fender flare exceeding 8 cm length must be grinded down towards the wheel arch, about 5 mm into the plastic. Between the tire and the well, there is about one fist size of free space. The tire has never rubbed on my Syncro. Between the tire and the trailing arm, there is about 5 mm clearance. The tire has never touched the trailing arm. One can hear small rocks and gravel bounce off the tires, after it is stuck in the thread. An inspection after 10.000 km shows no damage to the trailing arm.



1.      The fender flare, in front, exceeding 20 cm must be completely removed, the metal edges must also be removed and repainted.

2.      The middle part is to remain intact.

3.      The rear end of the flare must be removed (single piece) but can be reinstalled when using normal wheels. Metal edges over 25 cm must be removed and repainted. There is about one fist size between the tire and the well.


After driving 10.000 km (about 1.500 km on rocks and some sand), I am satisfied, especially when the extra high ground clearance is needed. The underpinnings have not been rubbed once, that is a comforting feeling.

It is possible that there is need for only little or no modification to install the smaller brother Michelin 7,00R16 4x4 OR 108N XZ2. I guess the ground clearance will be only about 2 cm taller, and maybe even get the blessing from the TÜV.


<Michel Thevissen>



Tire change for the Syncro 14”


In general, the tips for the Syncro 14” are similar to those for the 16”. Even here, one should talk to TÜV and control the clearance. The body clearances are the key factor here. When controlling clearance, one should fully load the vehicle, and control the clearance by all steering angles. At extreme circumstances, as several potholes after each other, bottoming out the springs, the clearances can be even smaller.


The tight spots at the 14” Syncro:


The #1 limit is the rear trailing arms, as those are 25 mm shorter than on the 16”. There are supposedly 14” Syncro’s with the 16” arms fitted from the factory.


The front wheel wells are also a limiting factor, as long as they are not modified. It is possible to make it similar to the 16” by installing the fender flares. There are normally no problems with large tires in the rear, because of the short trailing arms.


Of the tight spots, that are described further in the part about the 16”, the battery box needs some attention. Even only when you install the largest tires possible with the rear trailing arms.


It must also be mentioned, that Syncro drivers that want to put on snow chains, especially on the 14” one quickly reaches the limit concerning the rear trailing arms. The condition is also that you use a chain with small links.


For the basic 185R14 and 205/70R14, the easiest upgrade is the 205R14, and even TÜV should have no problem with this tire (one must always ask though, each approver sees things differently) Speedometer adjustments can be necessary. Bodywork is not necessary.


The following upgrades, based on 205R14 is theoretically also possible on the 185 versions, but the final drive can be a bit long. In addition to the lowered acceleration, it also affects the off road abilities (climbing abilities, and by heavy uneven terrain) Ground clearance is not all there is to it. It must be noted that heavy vehicles may need modifications to the suspension system, e.g. stiffer springs.


On the regular 14” rims, the tire alternatives are 215R14 or 225R14. The choice of larger tires for the 14” rims is very limited.


On 15” rims (E.g. Mangels 7x15), the tire assortment is a bit larger. Approvements (e.g. Projektzwo) are available for 225/70R15, 235/70R15 and wider (fender flares are necessary from 215 upwards. Should be declared with TÜV. From 225, It may be necessary to have a longer arm for the sliding door). Also possible to mount on 15” rims: 215/75R15, 215R15, 225/75R15.


On regular 5,5x16” rims, the tire options are 195/75R16, 195R16, 205R16.


There are surely other possible tire combinations too. In any case, the clearance on the rear trailing arms must be controlled on circumferences larger than 2200 mm. The front wheel wells may even be tight with smaller tires at 2150 mm (even dependant on vehicle weight, modifications are possible, see above)


Also limitations can be found at TÜV concerning tire manufacturers and types; speedometer adjustment may be necessary. Syncro 14”s with 205R16, but without any modifications on the body are observed. TÜV have even approved some of these.


When doing a tire/rim swap, one must also observe the load capacity of the tire and rim. What good is a Syncro camper with wide and tall tires, when the wheels don’t stand up to the load? Also the bigger tires are heavier to stop, and take a larger toll on the brakes. This can lead to problems at TÜV. The Syncro 16” has larger brakes, as a general rule.


Interesting lecture is always to be found in tire tests and on exhibitions in the regular off road magazines. In addition, there are books about wheels and suspension to be found in large bookstores and libraries.


So far so good, ya’ll have fun with your new tires.

<Ralf Burde>




Relations between Differential ratio, Speedometer calibration, Transmission codes and tires.


¨The circumference of the tires can easily be decided by one self, when one knows the code  of the rear axle. This code is found in the sticker in the service book, a similar sticker is found near the fuse box in the drivers cabin. A built in trip counter and a known distance is necessary, e.g. Highway with kilometre markings. The accuracy of measurement is increased with the length of the measured distance, and is only accurate depending of the accuracy of the markings along the road. The needed vehicle data’s is provided by the following table. The table may not be accurate in single cases, as the trip counter may be slow after tire changes. When it is only a little slow, it is not necessary with speedometer adjustments, because the speedometer is set a bit too fast from the factory. The adjustment can be set by swapping the speedo drive gears in the front axle. Still, an external speedo adapter (from e.g. VDO-Kienzle) seems to be a better way to me. This is easily mounted between the front diff and speedo cable.





RA Code

FA Code



37:6x 8:21






37:6x 7:19







35:6x 8:19









35:6x 8:20








35:6x 8:21






35:6x 7:19






38:7x 9:20












38:7x 9:21








38:7x 9:22






38:7x 8:20







38:7x 8:21







34:7x 8:18







34:7x 8:19







32:7x 8:18






Source: VAG Parts Catalogue © W. Nicklich


Explanation of the table:


Axle: The ratio between the axle and intermediate shaft, e.g. 37:6 = 6,17:1

Speedo: The ratio between the intermediate shaft and the speedo cable in the front axle unit, Za:Zb where Za = 7, 8, 9 is given by the axle code, and Zb  18,…., 22 can be replaced to achieve the desired number. Beware: the gears for e.g. 7:19 and 8:19 are different.

Circ.: Circumference of the tire in mm by exact km counter, e.g. 37:6 x 7:19 = 2272 mm. This simple relation goes when the km counter counts 1 km and the speedo cable is doing 1000 revolutions (identifiable on the number 1000 on the speedo). If the circumference of the mounted tires is substantially bigger than the given number, it could be advisable with a speedo adjustment.

FA Code: The ID code of the front axle unit.

RA Code: The ID code of the rear axle unit.

Tires: The tires specified by the factory, for the different transmission combinations. The circumference is always smaller than the number in the table.


Transmissions with diff lock are underlined.

With this, the explanation of the front diff unit is complete, except a small uncertainty on the ADM.


The use of the table is explained in an example:

-         Chosen tires: General Grabber ST 245/75R16

-         Tranny code AND

-         Original tires 205R16

-         Front diff lock

From this the front code AOM shows, and can be checked from under the car. Compare this to the tire table, and it shows that the circumference of the chosen tire is 2351 mm, considerably larger than the standard tire’s 2272 mm; a speedo adjustment is necessary. With original parts, it is only possible to replace Za from 7 to 8, i.e. rebuilding the entire diff unit, or replacing the unit with a ANB unit (not to be advised here).

To find the circumference, you have to travel a distance with the chosen tires: measured distance: 60 km, the meter shows 57,9 km. The circumference adds up to 37:6 x 7:19 x 60:57,9 = 2354 mm. If you can not identify the front diff, you can alternatively try the ANB: 2349 x 60:57,9 = 2434 mm. Compared with the tire table (2351 mm), it shows that this case is to be ruled out.

The transmitted circumference includes also the slip of the tire, the number is a bit lower than the true circumference. How much the slip interfere with the result, depends on how much power the viscous coupler transmits to the front wheels. To disconnect completely, one must either travel slowly or remove the intermediate shaft.

<Wolfgang Nicklich>


-S.3- Stand: Juli 1997 © Ig syncro 16“