OK peeps, I would love to try and get my head around the pros (and cons?) of running reduction boxes on stock(ish) campers? I was hoping this might end up being a useful reference thread on the subject?

My very basic understanding of them is that they were designed to give the heavier bus (compared to a beetle) more bottom end torque. However this was at the expense of getting higher top end power and speed? Does this sound about right?

So with a standard 1600 engine, you might realistically get say 60-65mph as a top speed if using reduction boxes? Is fitting twin carbs on a 1600 that runs though reduction boxes a waste of time in terms of adding any real benefits to the engines performance?

Can any issues with the reduction in top end power/speed be addressed through:

1) Gearing/gearbox
2) Engine size

* please correct me as and where necessary on any/all of this?

Hopefully Spence might pop by, as I know he seems to understand the whole reduction box/gearing/tyre size subject pretty thoroughly!

your concentrating too much on top end speed, you can stick a 'tuned engine ' on RB's and it'll go like a bat out hell...till it maxes out, but who really needs to be going much more than 65 in a splitty anyway ????

maddison wrote:your concentrating too much on top end speed, you can stick a 'tuned engine ' on RB's and it'll go like a bat out hell...till it maxes out, but who really needs to be going much more than 65 in a splitty anyway ????

True, but is it not better to be doing, say 65mph, without having things maxed out, as I'm assuming that at that kind of speed on a stock set-up, the revs are going to be pretty high?

.....so do 55mph

i just done 70 on stock set up and that was not reving to much at all

Nothing wrong with rgb's at all but I do no more than 55 in mine. Goes nice up the hills and the engine spins fast enough to keep it cool.

I`ll try and keep this brief...

Pros - Virtually bullit proof, virtually maintanance free, very very strong and gives excellent ground clearance.

Cons - None. Unless the bearings are worn - then they are noisy, so replace barings and problem solved. Or if you want to lower the bus then RGB`s are the worst transaxle set up for this application.

Top Speed - this has absolutely NOTHING to do with the reduction boxes themselves, but has everthing to do with the final drive gearing of the complete transaxle. This is calculated using size of forth gear, size of ring gear, size of RGBs (if fitted) and rolling diameter of the wheel/tyre combo.

News Flash - RGBs in no way limit or affect the achieveable top speed , it`s just another B.S VW urban myth, a bit like when people used to say you can "upgrade" to a 009 mechanical adbance distributer.. . Many high horsepower sand rails and even drag buses use RGBs. The RGB gears are much bigger/stronger than the gears in the gearbox itself and in these applications its been proven that the gearbox internal gears will strip out under heavy force long before the RGB gears do.

You can do 100mph all day long with the RGBs if you so chose. To make this possible you will have to make sure that the final drive gearing is suitable for the speed you wish to achive verses the engine rpm you will be having to run to obtain this speed. Simple.

This can be achieved in many ways and applies equally to all vehicles with or without RGB`s. The best way is to first select what tyre size you wish to run, for me this is a 195/80/15 as it`s the closest rolling radius radial to stock and aesthetically fills the arches very nicely. Leave all the gear ratios in the gearbox well alone - VW got them spot on. You then just type the info you have into a gearing calculator. I.E you know you are running (in my case) a stock .82 fourth gear, (rgb gearing size if fitted) rolling radius of wheel/tyre choice and what ring gear (diff) you are running and hey presto - it will calculate your RPM`s at any given speed.

To alter the gearing you then just change the ring gear size (smaller for highergeared , bigger for lower geared) to suit whatever speed/RPM combo you wish to run. There are lots of different ring gear sizes to suit everyones needs. It really is that simple folks.
Obviulsy if you want to cruise fast, say higher than 65mph - 70mph then you`ll need a bigger motor than stock in order to produce enough torque/horsepower to physically have enough grunt to force the weight of the bus through the air at that speed, but again thats only limited by motor HP and not RGBs.


In answer as to why they were fitted in the first place I think it was 85% to do with the fact that they couldn`t get the ground clearance they needed with the beetle staight axle set up and had to invent a new 2staggered axle" set up in order to achieve this. The fact that bus doing so also enabled them to creat a reduced gearing set up at the final drive point in order to help a gutless engine produce more torque at the wheels to help pull 9 people amd their luggage up a hill with 30hp avaiable was no doubt seen as a huge bonus too!

Thanks for that Spence, very helpful!

So with the higher/taller gearing, are you referring to the 'freeway flyer' type of box (was this an original VW spec box, or a later aftermarket incarnation?)

Did someone say stock

passion4 wrote:Thanks for that Spence, very helpful!

So with the higher/taller gearing, are you referring to the 'freeway flyer' type of box (was this an original VW spec box, or a later aftermarket incarnation?)

Yes, "Freeway Flyer" is a nickname coined in the USA that is given to RGB gearboxes that have been rebuilt using a taller (smaller) ring gear (diff).

Stock ring gear size in a late spit bus is a 4.37. Freeway Fliers are generally built with a 4.12 or a 3.88. A 4.12 is the tallest you`ll pull with a stock 1600 motor. For a 3.88 you`ll need at least a 1776 and preferably something considerably larger still. A 1776 actually still works very well with the 4.12 box.

There are even smaller ring gears available but you`d need a simply HUGE motor to pull that kind of gearing...

All the above info is based on the assumption you are using using stock late big nut RGB`s and stock rolling radius wheels/tyres and a stock gear cluster with a 0.82 fourth gear.

Obviusly by changing the diff you raise ALL the gears, 1 through 4, but you maintain the relationship between the gears so you don`t end up with large jumps between the gears - this happens when people change out 4th gear for a smaller one but leave all the other gears/diff alone. The result is too larger jump between 3rd and 4th and a vehicle that is miserable to drive - do not do this!

By changing out the ring gear and leaving everything else alone you don`t mess with the ergonomics of the gearing and everything works in the harmony that VW designed it to do. By changing out the ring gear you can achieve any final drive gearing you desire - whether you have enough power in your motor to pull that kind of gearing is another matter! As I said, with a stock motor a 4.12 diff is all the gearing you`ll ever need.

And finally, no. The "Freeway Flier" was never offered by VW as an option but something that came about with people putting bigger motors into buses in the States and wanting to keep the RGB`s for their excellent off road/camping capabilites, reliability and ground clearance but at the same time also wanting to wind up to 70mph cruising for long freeway runs with the motors not revving their tits off - and so the freeway flier was born

Got to agree with the other rgb pro comment s,just navigated the A39 through Porlock, Contisbury and Lynton or a new 1776 with reduction boxes and even the meet the fockers RV that stopped in front of me 1/3 of the way up Porlock hill couldnt prevent the bus flying up it I never wanted speed as the Jack Brahbam cornering is not a thing the wife likes 55/60 is ample, bump for hills etc... Love rgb's unless your drag racing them and lowered,that funny

There`s one point I don`t think i made clear in my last post on FF boxes - You don`t need a Freeway Flier box to get a good cruising speed with a stock engine , it`s really not necessary and if the bus is fully loaded the stock 4.37 diff is actually probably best overall.

I`ve got a 4.12 freeway flier box and I`ve also got a stock 4.37 box. I`m currently using the 4.37 box as most of the miles in the camper are done almost fully loaded up for holidays etc and especially round hilly areas I prefer the 4.37 box. The 4.12 does come into its own on the smooth french motorways however.

My gearing is still higher than stock though. This is because although I`m running the stock 4.37 box with the late (higher geared) big nut RGB`s in my `61 I`m still running the early stock 15" wheels with full profile tyres. The late big nut RGBs came in in `64 when VW switched over to using the smaller 14" wheels across the splitscreen range. So if you use the early larger 15" wheels with the late higher geared "big nut" Rgbs you get instantly higher gearing across the whole gearbox, in much the same way you would by changing out the ring gear, but this way is much cheaper/quicker and to be honest creates a gearing that is as high as the stock engine can cope with if you`re loaded uo with family members/camping gear etc. I would always recommend trying this set up first before forking out for a Freeway Flier box as 90% of the time this gearing is perfect for most people

FYI - this set up allows me to cruise at a genuine GPS 65mph with a bit more speed if needed for overtaking etc. This can even be achieved fully laden if the road is smooth/flat. I don`t see how it would be achieveable to get a better cruisng speed out of a stock engine with any other type of transaxle set up, Ive certainly not found one and I`ve driven pretty much ever configuration going over the years...

Sweet Rides wrote:There`s one point I don`t think i made clear in my last post on FF boxes - You don`t need a Freeway Flier box to get a good cruising speed with a stock engine , it`s really not necessary and if the bus is fully loaded the stock 4.37 diff is actually probably best overall.

I`ve got a 4.12 freeway flier box and I`ve also got a stock 4.37 box. I`m currently using the 4.37 box as most of the miles in the camper are done almost fully loaded up for holidays etc and especially round hilly areas I prefer the 4.37 box. The 4.12 does come into its own on the smooth french motorways however.

My gearing is still higher than stock though. This is because although I`m running the stock 4.37 box with the late (higher geared) big nut RGB`s in my `61 I`m still running the early stock 15" wheels with full profile tyres. The late big nut RGBs came in in `64 when VW switched over to using the smaller 14" wheels across the splitscreen range. So if you use the early larger 15" wheels with the late higher geared "big nut" Rgbs you get instantly higher gearing across the whole gearbox, in much the same way you would by changing out the ring gear, but this way is much cheaper/quicker and to be honest creates a gearing that is as high as the stock engine can cope with if you`re loaded uo with family members/camping gear etc. I would always recommend trying this set up first before forking out for a Freeway Flier box as 90% of the time this gearing is perfect for most people

FYI - this set up allows me to cruise at a genuine GPS 65mph with a bit more speed if needed for overtaking etc. This can even be achieved fully laden if the road is smooth/flat. I don`t see how it would be achieveable to get a better cruisng speed out of a stock engine with any other type of transaxle set up, Ive certainly not found one and I`ve driven pretty much ever configuration going over the years...

Thanks for the extra info Spence, that does sound like an ideal set-up!

For my build I was looking at the different gear ratios of small nut vs big nut RGB’s and centre boxes.
I had always assumed that the big nut boxes had a higher ratio to match the increased power of the 1500cc engine when it became available. This is true to an extent although there is not a huge difference in the final drive ratio between big and small nut drive-trains. What I hadn’t realised was that the centre gearbox of a big nut transmission actually has a lower output ratio than the small nut box.

I was looking for a higher final drive ratio to make the most of my 1776 that had been built with torque in mind not bhp.

Below is a calculation table of the different combinations of centre box and RGB’s


Of course this is pretty crude as it doesn’t take into account increased wind resistance at speed etc, so I rekon you could take at least 5mph of the 4th gear speeds.

My ideal cruising rpm will be between 3000 and 3500 - I'm not interested in flying but at least maintaining a 'reasonable' motorway speed when needed.
So I'm going to be trialling a ‘hybrid’ transmission with OE 27” diameter tires.

My post may be a bit premature as I haven’t driven it yet! – if its lousy I’ll edit this post. Seems to work well for a number of people on thesamba.com though.

monkey knuts wrote:For my build I was looking at the different gear ratios of small nut vs big nut RGB’s and centre boxes.
I had always assumed that the big nut boxes had a higher ratio to match the increased power of the 1500cc engine when it became available. This is true to an extent although there is not a huge difference in the final drive ratio between big and small nut drive-trains. What I hadn’t realised was that the centre gearbox of a big nut transmission actually has a lower output ratio than the small nut box.

I was looking for a higher final drive ratio to make the most of my 1776 that had been built with torque in mind not bhp.

Below is a calculation table of the different combinations of centre box and RGB’s


Of course this is pretty crude as it doesn’t take into account increased wind resistance at speed etc, so I rekon you could take at least 5mph of the 4th gear speeds.

My ideal cruising rpm will be between 3000 and 3500 - I'm not interested in flying but at least maintaining a 'reasonable' motorway speed when needed.
So I'm going to be trialling a ‘hybrid’ transmission with OE 27” diameter tires.

My post may be a bit premature as I haven’t driven it yet! – if its lousy I’ll edit this post. Seems to work well for a number of people on thesamba.com though.

^^^^This is a VERY useful post and what an excellent little reference chart!

The "hybid" you refer to in your chart is what the americans call a "freeway flyer" as expalined in my post above. Essentially you are combining the higher geared late RGBs with the smaller (higher geared) early 4.12 ring gear and the early higher geared 27" diameter tyres.

I own this exact set up and have driven it many thousands of miles - you will not be disappointed! It works brilliantly with a 1776 motor - it`s absolutely the perfect gearing for it! You re going to be well pleased!