Chris SFor a multitude of reasons this is not a good idea,
Front tyres bigger than rears,
1) It is physically impossible for the VC unit to turn the rear wheels faster than the front which it must do to provide rear wheel drive,
Congratulations, you now have a 2WD Syncro.
2) You are also now relying on the freewheel mechanism to allow for the difference in rotation speeds, and as this is now working 100% of the time and will fail early, thats very early btw.
All the broken off hardened steel pieces from the freewheel mechanism will then be chewed up by the diff and spat into bearings, oil seals etc, and its new diff time
Rear tyres bigger than Fronts
1) As the rear wheels are larger they will rotate slower, the VC unit will sense this and attempt to transmit power and drive them at the same speed as the fronts which of course it cant as they are rotating slower to cover the same distance.
This stresses the complete drivetrain out and rapidly leads to failure, usually by breaking the VC unit in half or blowing one of its end plates completely off, it is now scrap and its new VC time.
Congratulations you now have a zero wheel drive Syncro.
no such userYou should normally fit a full set of five new tyres to a Syncro vehicle, but sometimes this isn’t possible. In this situation you should try to buy a pair of new tyres, of the same size and (if at all possible) brand and tread pattern. This ensures they are as close as your existing tyres in rotational size.
When fitting a pair of new tyres to a Golf Syncro (or T4) they must be fitted to the front and only fitted provided there is not a substantial difference to the wear point vs the rear tyres. When fitted to the front these tyres will wear faster and even up quickly. While they are ‘evening up’ the freewheel on the T4 and Golf will ensure there is no transmission wind up and you should not suffer any mechanical breakages because of this.
You should only ever fit a complete new set of tyres to a T25 Syncro – there is no freewheel in the drivetrain and thus no way of ‘taking up the slack’. You will break things if you do not fit tyres as a complete set.
jinx82I’ve just bought an ’90 Golf Mk2 syncro. However I have (previous Mk2) BBS’s RM in 8 + 8,5″. All tires are 195/45 R15. Will there be any problem with syncro as the difference (little) because of different width of the rims?
Thanks!
Marino
no such userYou absolutely MUST run same-width rims front and back and same make, size and preferably wear-point tyres. If you were to fit your existing rims then you will put a constant slight drive through the VC, so it will go stiff and then tear your drivetrain apart.
All the system needs is a little difference and you’ll start breaking stuff.
Don’t do it – get same-size rims and same-size and wear-point tyres.
Chris SI have two sets of wheels for my syncro, 1 set is fitted with summer tyres and the 2nd set has M+S winter tyres, when I change over from one to the other I put last years fronts on the rear and move the rears to the front, I find that this equalises the wear out quite nicely. [
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Chris SJust a thought btw if you have a spacesaver spare wheel,
It is a different size to the 2WD Golf spacesaver spare, and the 2WD spacesaver spare should NOT be used on the 4WD Syncro as it will damage the drivetrain [xx(]
optimus234I asked on vwvortex about tire sizes. I have 7 inch wide wheels on the front and 8.5 inch wide wheel on the rear. They said there can be a 1% Circumference difference in tires sizes. So I bought 215/45 17 for the front and 235/40 17 for the rear giving me 77.31 in the front and 76.65 circumference in the rear. I was told this would work because there is less then a 1% difference. Will I be ok?? I already bought this stuff and really dont want to have to try and get new wheels but will if I really have to.
This is for a 92 passat syncro.
Thanks,
Kevin
no such userHow much have you spent on your transmission?
You got to ask yourself is it worth junking hard to find bits just so you can run a totally inappropriate wheel combination?
Unlike Porsches and other rear-drive cars your car is front-drive biased. This means you should run the wider tyres on the front, as that’s where you need more grip, not the rear. Thing is, if you did that style-wise (which has to be the only reason you’re so hung up on these wheels) you’d look like a moron. The sound advice delivered on here still stands – stick with same size wheels and tyres front to back. Sitting at the side of a road with broken drivetrain parts will make you look like more of a moron than running wider front wheels, in my opinion, anyway.
ld50What compounds the issue is that (as far I was concerned) the syncro tended to understeer so adding *more* grip to the back might look cool but would make it handle more like a fwd which is counter-productive imo.
Out of interest, other than it looking a bit odd is there any reason (legal or otherwise) why one couldn’t run wider wheels on the front? I’ve seen it done on fwd draggers and was thinking about this particularly with regard to sideways action like drifting and the occasional santa pod run. I figured it might be possible to accentuate the oversteer like by stiffening the rear damping etc.
I’m assuming a theoretical situation here where all the rolling radii are the same so my point isn’t about blowing VCs to bits.
Hungry_Horse_1955Chris,
You say you are running M+S tyres on your second set. What size are they and what make?
The Country I have bought has a set of winter tyres, but these are snow tyres. I would like to fit M+S or ATs to them. Does anyone have any suggestions for suitable sizes and make?
Clive
FrankthecampervanmanChris,
I have fallen foul to the VC/rear diff problem and, when checking back, realised that the occurrences were after punctures where one (winter tyres) or two (summer tyres) were replaced. I have been working with a differential engineer and cut open the rear differential in an effort to finding out what is going on.
The conclusion for larger (i.e. new) rear tyres is how you describe. There will be a permanent speed differential in the input and output plates of the VC which will cause the silicon oil to heat up, which means the input tries to drive the output faster than the speed dictated by the rear wheels. The resultant torsional wind up manifests itself by breaking the weakest point in the transmission, in my case the bevel gears and VC itself.
With larger front wheels I can’t see how the engaged freewheel would fail. The system is similar to motorcycle starter clutches (but with eleven pins, not three), and motorcycle starter clutches spend almost all their working life in freewheel mode. Can you explain the reasoning as I was going to just fit the new tyres to the front?
There are also open questions I was hoping you may know:
1. I find it hard to understand that VW engineers did not foresee this problem, given the testing that is carried out. I have seen nothing in handbooks or workshop manuals explaining the tyre issue. Is this problem therefore a by-product of oil deterioration in the VC which alters the characteristics? Normally oils get more viscous (runny) with heat, which should mean a lower inclination of the input plates to drive the output. In other words, should I fit a brand new VC?
2. The manual states that the freewheel engages automatically when the brakes are applied. I see no automatic function. Any idea why the manual makes this comment, given that they are derived from VW worksheets?
Oh, and hello to everyone.
golfmk3i’ve got a 1989 standard Golf Rallye and do about 2000 miles a year in it
I am looking at fitting some 16″ Borbet ‘A’ 7.5in front and 9in rears with 225/40/16 tyres all round.
Is this going to cause any issues?
cheers
86 Syncroquote:
Originally posted by golfmk3i’ve got a 1989 standard Golf Rallye and do about 2000 miles a year in it
I am looking at fitting some 16″ Borbet ‘A’ 7.5in front and 9in rears with 225/40/16 tyres all round.
Is this going to cause any issues?
cheers
Someone hasn’t been paying attention…
YES! This WILL cause issues!!!