Club 80-90 Forums

OK, will have a go in a quiet moment (I can clamp a bar to a machine table and use a bit of PTFE as a bearing, nice an slippery)

We currently a Jaguar SS100 gearbox to finish tomorrow for a German chap (who has Turns 8 & 9 of the Nordschleife named after him) that is rather urgent...

Just got around to weighing some wheels ...



The MB W126 7x15 ET25 steel wheel on the right weighs 9 kgs and the Ronal 7x15 ET33 on the left weighs 7.4 kgs. According to Busschmiede the Mefro 6x15 weighs 11 kgs

Whilst i was up at Aidans recently we realised there was quite a range of wheel/tyre combinations available so took the opportunity to measure and weigh them.

In diameter size order from smallest to largest they are:

185 R14C on an original steel - 635mm
205 R14C on an Alloy - 680mm
215/75/R15 on a Mefro steel - 720mm
235/85/R16 on a Mercedes ML Alloy - 800mm

And now the weight measurements:


185 R14C on an original steel - 20kg
205 R14C on an Alloy - 20kg
215/75/R15 on a Mefro steel - 27.5kg
235/85/R16 on a Mercedes ML Alloy - 30.5kg





And here's a shot just to compare the two Mud Terrains next to each other:

This should be made a sticky .... well the last bit should!

That is a rather large one....

I really want that tyre on my van, I also want to keep the 16" arches. What want will win my brain argument?.. Would it devalue a 16"?..

That 16" 235/85 wheel tyre is just bonkers for a Syncro. 30% heavier than standard and 6 1/2" larger in diameter has to have a detrimental effect on brakes, shocks and everything in the transmission! Crazy.

I'll have to weigh my wheel and tyre combo, the merc rims are super light

That 16" 235/85 wheel tyre is just bonkers for a Syncro

Works quite nicely with a Tdi though.

That's 50% heavier not 33% SPaddy.

So the MoI is probably 2 x or 100% greater. .

HarryMann wrote:That's 50% heavier not 33% SPaddy.

Or 30% .... !!

Its difficult at my age to see the keys without my glasses.... difficult to see most things actually!

I would also concur that the MoI is twice what it should be and even with a built in safety factor without mods to the entire drive train those big wheels are bonkers on a Syncro - TDi or not!

Can you guys explain for everyone what you're talking about?

MoI = Moment of inertia is a property of a body that defines its resistance to a change in angular velocity about an axis of rotation.

Now you know !!

If you ever wondered why you are shearing drive shafts and bursting CV joints whilst off road, now you partially know! Its to do with a change in angular velocity about an axis of rotation and if the 'body' has twice the 'property' and tries to suddenly change its angular velocity ...... crunch! There are other factors as well ...

if the 'body' has twice the 'property' and tries to suddenly change its angular velocity ...... crunch!

Yup, that's definitely a very good description of what happened last time i sheared some drive shafts, however i think that was more to do with my rear difflock engaging suddenly whilst a wheel was spinning. Lesson learned in there, never try anything stupid unless you are positive that the difflocks are engaged already!
However, i didn't have these tyres back then. I was running a size which is very close to a standard 16" size, admittedly the 16" vans run thicker drive shafts/cv joints to compensate for the heavier wheels/tyres etc and i thought about having larger shafts made up but decided i would rather the shafts were the weak point in the system.
Much cheaper to replace one of those than a gearbox and CV's even!

Aidan was telling me the other day that it was possible to get a 16" with 7.50 16" tyres, something to do with NATO wanting to run that tyre size (makes sense). Which actually means that my current tyre size isn't very far away at all from something specced from the factory. Not even sure if the 7.50 16" would even be any lighter, given the kind of steel most of the military tyres have in them.

I definitely would like some shocks with different damping though, but it drives surprisingly well considering the shocks are built to deal with a lot less weight flying about underneath them!