The Big wheel Gearbox debate

[brookster69]

so after reading all that, will range rover style 8 from the autobiography sport, size 20 x 9.5 inches
with an et45 and bolt conversion kit, running hanook 275/40/20 106xl fit on my t6 with or without a 5mm of 10mm spacer kit,
anyone tried, anyone got a picture of these fitted, or will they scrub on full lock .

 

[xpfloyd]

so after reading all that, will range rover style 8 from the autobiography sport, size 20 x 9.5 inches
with an et45 and bolt conversion kit, running hanook 275/40/20 106xl fit on my t6 with or without a 5mm of 10mm spacer kit,
anyone tried, anyone got a picture of these fitted, or will they scrub on full lock .

Use this site to check - www.willtheyfit.com

Type in the current setup details and the proposed. Pay attention to speedo error figure and how much in or out the new setup is compared to old

 

[brookster69]

thank you

 

[dubdub]

Please excuse me jumping in here but its a kind of related question... in an attempt to stop or at least reduce the rick of curbing my beautiful Bola xtr wheels AGAIN im going to replace the rear tyres from the 255 x 35 x 20 on at the mo for 275 x 40 x 20 to give a bit more side wall protection. As im only changing the rear tyres for larger ones making their rolling circumference bigger, am i right in thinking they wont affect gearing/speedo etc because they are not the 'driven' wheels in effect the rear wheels are just trailing wheels?

 

[chriscroft]

Please excuse me jumping in here but its a kind of related question... in an attempt to stop or at least reduce the rick of curbing my beautiful Bola xtr wheels AGAIN im going to replace the rear tyres from the 255 x 35 x 20 on at the mo for 275 x 40 x 20 to give a bit more side wall protection. As im only changing the rear tyres for larger ones making their rolling circumference bigger, am i right in thinking they wont affect gearing/speedo etc because they are not the 'driven' wheels in effect the rear wheels are just trailing wheels?

View attachment 15012

Certainly won't effect the gearing; speedo, not sure where the speedo drive is, but it certainly isn't on the back wheels, so right again. I guess Sorry to hear about your kerbing, ouch!!!
Do you feel the rear wheels are more prone to kerbing, than the fronts?

 

[Oldrat]

Ouchh!

Precisely why I chose ‘flat’ sided wheels which don’t hang outside of the rims.

 

[dubdub]

Thanks fro the reply yes the rears are more prone i think, I've 9.5 on the back but same width tyres as on the 8.5 fronts, so the front tyres cover better and give some protection but the rear wheel rims are just proud of the tyre wall so you have no chance. My hope is going to a 275 and a 40 profile i should have more rubber buffer. I squished over to let an ambulance get by and clipped the curb

 

[Lukavell]

Interesting thread guys. I can't help wondering why my (wife's) DSG Tiguan R-Line with the 2.0 EU6 150 TDI comes with 20" wheels from the factory but a T6 can't? I guess a T6 weighs more and the gearing will be different. Is it a case of the things bolted on to the engine/drivechain such as drive shafts being different or what?

 

[crackon]

I think Luke, that the Tiguan comes with 20's as they look really nice and it helps VW sell more R-Lines, simple as that. If enough van buyers wanted 20's to warrant the cost for VW you can bet they would do it too. Yep they weigh more and the gearing and attached gubbins will be different but it won't affect the gearbox. As mentioned before bigger wheels (and the increased rotational forces) impacts on the brakes, suspension and steering, the only things affecting the gearbox are the applied forces which are the engine's torque when accelerating and the brakes effectively slowing the driveshafts when decelerating, I can't see any logic in anything else, sorry, well bar the clutch maybe having a minimal effect. The gearbox warranty get out is just an excuse as far as I can see but obviously needs to be borne in mind.

 

[Lukavell]

I think Luke, that the Tiguan comes with 20's as they look really nice and it helps VW sell more R-Lines, simple as that. If enough van buyers wanted 20's to warrant the cost for VW you can bet they would do it

Ha, very cynical but probably right!! I agree on all the technical points, i think.

What it boils down to for me is that if the lump in a Tiguan can handle them then surely a T6 can, so if folk want to put 20s on their T6 then why not? Warranty issues excluded of course.

 

[ferrodo]

hi I'm new to the site I've just got a new t32 kombi and like the look of 20's. I have a t5 and I was going to put range rover storm alloys on it until I felt the weight of them, I agree with the thoughts on the gearing being higher and more weight to get going means more torque needed so more wear and tear and fuel ultimately. The brakes will also be affected, but I think the warranty issue vw has is prob more to do with the steering, as the wheel size goes up the tyre is much wider and has a bigger contact patch so puts more load through the steering. The differance between the Tiguan and the t6 would be it won't weigh as much loaded, also being its 4x4 off road crossover they would have designed the suspension and steering with more capacity to take the punishment off roading brings plus being that the Tigaun is a newer design it would have been designed with bigger wheels to begin with. Still don't know what size wheels to get.

 

[crackon]

An old favourite of mine this one! I'd like to see the logic, common sense and physics behind many of these claims, most are just opinions of a tyre guy or a gearbox guy based on anecdotal experience and not rooted in fact. I wouldn't mind betting that many of those changing to 20" wheels are less mechanically sympathetic and that has more to do with the loss of a gearbox than the wheels themselves (BTW I do have 20's on my T6 and I'd like to hope I was sympathetic, and I've not had a problem) . If you change the diameter of the wheel and reduce the tyre profile to keep the effective diameter the same then the torque needed is the same (for the same weight). If the weight of the wheel goes up then that will have the same effect as sticking a few bags of sand in the back of your van and VW don't penalise you for that, I reckon it's commonly used as a cop out by the dealers when a gearbox goes - they wouldn't dare say you're too heavy on your right foot would they. Admittedly heavier wheels would affect the suspension but gearbox, sorry nah, unless someone's got some empirical evidence to the contrary.

 

[DXX]

An old favourite of mine this one! I'd like to see the logic, common sense and physics behind many of these claims, most are just opinions of a tyre guy or a gearbox guy based on anecdotal experience and not rooted in fact. I wouldn't mind betting that many of those changing to 20" wheels are less mechanically sympathetic and that has more to do with the loss of a gearbox than the wheels themselves (BTW I do have 20's on my T6 and I'd like to hope I was sympathetic, and I've not had a problem) . If you change the diameter of the wheel and reduce the tyre profile to keep the effective diameter the same then the torque needed is the same (for the same weight). If the weight of the wheel goes up then that will have the same effect as sticking a few bags of sand in the back of your van and VW don't penalise you for that, I reckon it's commonly used as a cop out by the dealers when a gearbox goes - they wouldn't dare say you're too heavy on your right foot would they. Admittedly heavier wheels would affect the suspension but gearbox, sorry nah, unless someone's got some empirical evidence to the contrary.

The added mass of the 20” wheel / tyre is not the just the same as a few bags of sand in the back.
The added rotating mass affects the inertia / momentum when accelerating / decelerating, this is transmitted through the drive shafts to / from the gearbox. Whether this has any bearing on reliability who knows but I guess VW are well within their rights to say it does.

 

[crackon]

Thanks @DXX, with the greatest respect I agree and disagree.

I'm with you on the added rotating mass creating additional inertia, but this does not affect the driveshafts any more than the overall weight in the van when accelerating/decelerating. I'll hold my hands up and say I'm not 100% sure on this but have yet to see a convincing argument otherwise, but think on this - when you accelerate and the engine, via the gearbox, spins the driveshafts and wheels, do the drive shafts spin about the engine or the engine (and rest of the van) around the drive shafts? It depends where you are and we naturally assume the former, but if you're sat on the driveshaft it's the other way round. As I see it both the wheels and the van itself are being forced against each other in different directions, my few bags of sand analogy may be a little simplistic, as it will depend on the weight of the wheels, their speed and the number of bags of sand.

And when you brake, although the brakes act on the wheels, they have to reduce the kinetic energy (which is a product of the speed and total weight of the vehicle) of the whole vehicle (converting it to heat), which then results in the drive shafts slowing at a given rate, so it is the brakes that affect the force that goes back through to the gearbox. In fact, if you decelerate with heavier wheels (not using the brakes), the added inertia will prevent the vehicle from slowing so quickly and therefore will lessen the forces. So my take is that only bigger brakes will result in more stresses on deceleration.

As I said I'm not an expert on this, just using some schoolboy physics and trying to think it through. The reason this thread is a particularly interesting one is because we are yet to get a definitive technical view on this. I would love for a mechanical engineer to show us the maths on this to put it all into context. Maybe one will be along shortly

 

[DaveD]

Thanks @DXX, with the greatest respect I agree and disagree.

I'm with you on the added rotating mass creating additional inertia, but this does not affect the driveshafts any more than the overall weight in the van when accelerating/decelerating. I'll hold my hands up and say I'm not 100% sure on this but have yet to see a convincing argument otherwise, but think on this - when you accelerate and the engine, via the gearbox, spins the driveshafts and wheels, do the drive shafts spin about the engine or the engine (and rest of the van) around the drive shafts? It depends where you are and we naturally assume the former, but if you're sat on the driveshaft it's the other way round. As I see it both the wheels and the van itself are being forced against each other in different directions, my few bags of sand analogy may be a little simplistic, as it will depend on the weight of the wheels, their speed and the number of bags of sand.

And when you brake, although the brakes act on the wheels, they have to reduce the kinetic energy (which is a product of the speed and total weight of the vehicle) of the whole vehicle (converting it to heat), which then results in the drive shafts slowing at a given rate, so it is the brakes that affect the force that goes back through to the gearbox. In fact, if you decelerate with heavier wheels (not using the brakes), the added inertia will prevent the vehicle from slowing so quickly and therefore will lessen the forces. So my take is that only bigger brakes will result in more stresses on deceleration.

As I said I'm not an expert on this, just using some schoolboy physics and trying to think it through. The reason this thread is a particularly interesting one is because we are yet to get a definitive technical view on this. I would love for a mechanical engineer to show us the maths on this to put it all into context. Maybe one will be along shortly

I think you both make valid points but if I can throw something else into the mix.......
I think driving style is a major factor in how much stress is imposed on the brakes and transmission, whatever the size and weight of the wheels.
I hardly ever brake hard, I 'm often empty or with perhaps 100KG of tools in a van that can carry over 800KG.
I hardly ever accelerate hard, particularly in first gear, what's the point?
I think if you put bigger, heavier wheels on your van, load the van up near it's maximum weight and drive it like you stole it, yes, you might expect problems, but for the rest of us, no.
Just my opinion.

 

[drinfinity]

The torque required to add the extra angular momentum to a slightly bigger/heavier wheel will be trivial compared to that needed to accelerate the van. Imagine you put each wheel on the workshop floor, and give them a good shove. You will see them both accelerate fairly easily. Now fit them to the van, and give the van a shove. You probably can’t tell the difference between the wheels, because the total momentum of the system is overwhelmingly the van. The calculation is left as an exercise for the reader.

There is certainly a difference in the gearing. If you have a manual box, this only makes a difference when accelerating in first gear, or flat out in top gear - anywhere else and the driver will just select to change gear at a slightly different point. For an automatic, it could make a difference if you don’t tell the gearbox the gear ratios have changed. Either way, your right foot will have more influence.

Impact on suspension and steering could be an entirely different story, I won’t pretend to do the maths on that.

 

[paxter]

Will fitting 20" wheels affect my gearbox over time?