The Big wheel Gearbox debate

[GordyT6]

Hi peeps. Look I know everyone has an opinion on this. But I have my 20's on my T6, a few warned me about it screwing my gearbox, then others say no I wouldn't, we've been and done that now but to a mere fool that I am. Can anyone answer me why VW think big wheels do the gearbox in? Surely my 22's have the same rolling radius of a set of standard wheels with bigger walled tyres. So therefore they'd be no more torque to turn the wheel? Or am I wrong. Keep it simples please. Lol

 

[DaveBos]

20" wheels on my T5 with the correct load rated tyres had a larger diameter than the standard 16" steels and also weighed at lot more, maybe this is the reason???? Definitely noticed a difference in the gearing with the 20's.

 

[Pauly]

Following the debate the other day I had a google around on this and couldn't find anything 100% conclusive either way.
What I did find was a detailed experiments/comparisons of wheel and tyre packages tested in the real world and the main conclusion was that is does have an effect, going to 17/18 inch wheels made little difference but moving up to 19 inch wheels and beyond resulted in lower fuel economy and reduction in power output
Rolling circumference will be increased when you reach a certain increase in wheel size depending on starting size, it's worth noting those figures are from tests based on a car (VW golf) so will vary a bit for CVs

Effects of Upsized Wheels and Tires Tested - Tech Dept.
Circumference comparison tool for tyre sizes
Will They Fit - Online Wheel and Tyre Fitment Calculator

 

[Peec]

It's gotta make a difference if the rolling radius has changed.

Each turn of the engine will be moving the van further forward than it would on the stock wheels, so the gearbox loading increases in every gear.

Don't get me wrong, I swapped my VW 17" alloys to 19" Diewe Trina's three days after delivery. Before doing this though, I did a ton of research about wheel loading, rolling radius, tyre loading etc and with the help of an excellent local wheel and tyre dealer, found a setup that looked great, but complies with the load rating for wheels and tyres (T32 so needs to pass a class 7 MOT). My setup does increase the load on the gearbox, but only by 3%...thats as good as I think you can get on a T32 with 19" rims.

 

[GordyT6]

Interesting reading.
It was just a thing bouncing in my mind after the chat the other day ( for you didn't see it, it's in the show us your van section, and in team Chestnut)
Thanks @Pauly @Peec @DaveBos

 

[CRD]

The way I look at it is, the gearbox and driveline is designed to take the weight of the van plus a tonne approx of payload. Running the van lightly loaded on 19" wheels probably isn't going to stress things too much. However, if your van is frequently fully laden, the oversized wheels may not be such a good idea long term

 

[Peec]

Agreed. I had a quick read of the @GordyT6 's thread in the other forum, and by my calcs he's actually 0.6% under loading the gearbox! Definitely not a problem there. I'm guessing he has a T30. There's so much more choice on the Wheel & Tyre combinations if you don't have to comply with the T32 Class 7 stuff

 

[GordyT6]

@Peec can you redo the calcs cos mines the T28 ta

 

[Peec]

I really don't think you have anything to worry about @GordyT6. VW sell the T6 from the factory with 1 of 5 wheel / tyre combinations. The rolling radius of your setup is well within the spread of those VW originals so you wont be putting any more load on the gearbox than those original wheels would.

From what I have been told by my local Class 7 MOT tester, the load rating of the wheels is not a checked requirement for a Class 3 MOT (The std one and the one you'll need), unlike the T32's which will be checked in a Class 7 MOT.

The load rating of the tyres is checked on a Class 3 and I think you can be failed on it. The T28's come with an axle weight sticker (somewhere), but I don't know what the weights shown would be. (You can't just take the max laden weight / 4 as the front and rear axles will differ). The simplest check would be to look at the original tyres and make sure your new ones have a load rating the same or higher. If you don't have the originals, then you will need to find the axle weight sticker, then Google Tyre Load Ratings and look up which rating is the first one above the weight shown on your van.

 

[Pauly]

Axle weight sticker is stuck to offside bulkhead in engine bay in front of driver
Heres mine for a T32, the numbers after the 1- & 2- are the front and rear ratings

 

[former member]

Is it really worth it on a £30k+++ brand new van just for a bit of vanity?!
Heavier (and it's unsprung weight which is far worse), far less choice of good tyres, much more prone to kerbing, likely to tramline, worse mpg, slower, possible gearbox issues, kills almost any off road ability - the list goes on.

I just don't (and will never) get it - smallest wheels that fit the brakes for me - 16s on the Subaru, 17s on the van, 18s on the M135i.

 

[Caravellet6]

Is it really worth it on a £30k+++ brand new van just for a bit of vanity?!
Heavier (and it's unsprung weight which is far worse), far less choice of good tyres, much more prone to kerbing, likely to tramline, worse mpg, slower, possible gearbox issues, kills almost any off road ability - the list goes on.

I just don't (and will never) get it - smallest wheels that fit the brakes for me - 16s on the Subaru, 17s on the van, 18s on the M135i.

I'm with you on this @Polzeylad call me risk averse but I'm staying with standard wheels.

Yes I had 19" wheels and wide tyres on my t3 but that was 25 years old and fairly sure not under warranty lol

 

[Mojo]

Interesting stuff!... Are there documented cases of gearbox problems due to non-standard wheels? The demonstrator I drove at Leeds VW before ordering mine had 20' Fondmetals and a 40mm drop!

 

[Walski]

Interesting thoughts and advice on this thread. I think it helps people make their own choice on wheel and tyre size combination when they can consider these options. There will always be people who want to stick with standard and those that want to push the boundaries......
If I can get away with my long running garage height issue on mine, I'll be getting 19s, but only if I can keep a sensible 45 profile tyre that essentially keeps the rolling radius (therefore speedo) consistent with factory 16s with 65 profile. If I can't get 19s and 45s then I'll be going to 18s.
This thread has made me query the weight difference of the new wheels vs standard though.

 

[former member]

It's really hard to find tyre weights but I did get info on my old BMW 335d which had 17" alloys.
I compared the weight of the wheel and tyre to a 19" BMW M sport one; 19kg for mine; 29kg for the 19" (which were s fair bit wider).
That's a HUGE difference and in unsprung weight too.

If you look at all race Caterhams, they are on 13s. Only the flashy road versions have 15s.

I really don't get the big wheel thing at all!

 

[CRD]

Is it really worth it on a £30k+++ brand new van just for a bit of vanity?!

The same argument could be made that spending £30k+ on a VW is vanity in itself. Surely we don't just buy them for their reliability and performance?
I'm quite upfront on the reason for buying a T6 is 'image'. My business has 2 other vans, a new model Vivaro biturbo which is quite frankly brilliant and a Citroen Relay which is a bit 'meh', both of which can be had for half the price of a T6.

So it's 19" wheels for me (in the summer at least)

 

[RattyMcClelland]

Bigger wheels and tyres will cause the gearbox to turn slower as the rolling radius is bigger.
Smaller wheels are underdriving the gearbox making it spin faster.
All of which passes through the final drive which has the biggest influence on the gearbox.
If anything I would say heavier wheels have the biggest influence and the bigger the wheel the more weight is going to be on the outside so more inertia again putting a bit more strain on driveshafts.

Im only speaking from my experience I have had the 16" steels, 17" banded steels, 17" borbets and currently 19" 3sdm's.

I found the most straining to drive on was the 17" banded steels. They were 19kg per wheel before the tyre was on.

The 16" steels were most responsive and felt great but very spinny and quick gearing causing an higher mpg.

The current 19" offer my the best ride and accurate Speedo reading but are more sluggish than the 16" but getting better millage on fuel.

But the heavy banded steels definitely felt like they were more straining.

Both my 5 speed gearbox and drivers driveshaft have failed but that was due to the genetic elite flashed remap and wrong torque curve for my gearbox eventually failing the diff. (The weak point)

I think anyone will be fine with big wheels on these gearboxes from my experience and I'm putting my 3sdm's into my t6 when it arrives. That will see 140k miles over the 5 years I intend to own it with 19s and 275/40/19s.

 

[Walski]

What 3sdms you got @RattyMcClelland??? Put up a piccie

 

[RattyMcClelland]

0.05 9.5" all round

 

[Walski]

Nice Where's your chips away patch??