Improving the BMW R80G/S and R100GS

While BMW’s original pioneering large-capacity trail bikes are excellent machines, there’s plenty of scope for improvement, and if you intend to use yours for Adventure Touring, serious trail riding or even competitive events like the Classic Paris-Dakar or Tuareg Rallye - then you should certainly be considering some changes!

When modifying a production bike to meet your own needs, remember that every change you make will have a knock-on effect in another area. We have developed the Moorespeed GS into a total package: and one that works. If you want to upgrade your own bike in your own way, then that’s fine – but you will find pitfalls along the way and need to find your own solution. That’s why we have standardised our components and made them available to those who prefer the DIY approach.

Front suspension

The original front forks have their limitation, and increasing the engine power makes this all too obvious with flexing, poor damping and limited travel for off-road use. The front brake is another area of concern, and with the standard forks you have few options to upgrade.

There are plenty of front forks available from more modern motocrossers that will provide more travel and adjustability with greater rigidity – but remember that they will have to be thoroughly overhauled and set-up correctly to suit the weight of a road-equipped trail bike. An extra bonus is that these forks usually have mountings for modern Brembo calipers, so you now have the possibility of a decent front brake!

The Moorespeed BMW R100GS uses either Paioli/Kayaba or Marzocchi 46mm upside-down forks. If you have a set of similar forks, we can fit a new steering stem to the lower yoke and supply new bearings so that these forks can be used with the GS headstock.

With new suspension in place, your old wheel will no longer fit. While it would be possible to make new spacers/spindle etc to suit , you have to bear in mind that the old wheel is just that: old. By the time you have totally rebuilt the wheel and sorted a new disc to suit the Brembo caliper – not to mention solving the problem of mounting the new disc and the new spindle – it is more cost-effective to replace the front wheel/disc too.

With the Moorespeed R100GS, we have settled on a Talon hub and disc brake intended for a Honda motocrosser, laced to an Excel rim. If you have purchased secondhand forks, then try and secure the wheel, disc brake and caliper too. Talon make a vast range of hubs to fit most motocross forks, so if the hub you have is below par, there is an easy fix. If you need advice, just ask.

Main frame

Please note that if you do fit long-travel front suspension, then the frame must be suitably braced around the headstock or failure in this area should be expected.

In fact, we brace not only the headstock but also the swing arm pivot area and the top tube/twin rear down tube area. That makes for one REALLY strong frame: overlanders need not fear a frame breakage en route!

If you are making this a solo bike, then the bulky right-hand pillion footrest mount can be removed.

Swing arm/drive shaft

If you want more rear wheel travel, then simply adding a longer travel shock absorber is not the answer... the rear end would be jacked-up far too high, the wheel would hit the subframe, and the shaft drive’s universal joint would soon fail due to the extreme angles it would be forced to work through.

Our solution is to use a Wilbers shock absorber made to our specification with its lower mount moved from the from the rear hub to the swing arm. We prefer to use the monolever swing arm as it is lighter and stiffer than the paralever – but it is also shorter… that’s why we lengthen the swing arm by 50mm if you want the same overall length swing arm as before, or 100mm if you want even more suspension travel and have plans for extreme riding conditions.

Of course, a longer swing arm needs a longer drive shaft, so we take a pair of (totally rebuilt) monolever shafts, jig them to ensure perfect alignment, then weld them together in an inert atmosphere before shot-peening. As an added bonus, your drive shaft now runs in an oil bath: no more premature failures.

Rear wheel and bevel box

Time to consider your budget and aspirations here.

The standard R100GS has a 17-inch diameter rear wheel which can use a tubeless rear tyre. It runs on a 4-stud hub. That is fine – but there is a much wider choice of suitable 18-inch diameter tyres (including competition tyres for those who take off-roading seriously), while the extra diameter gives a bit more ground clearance. Further, a conventional 18-inch rim can be re-spoked with the centre line offset, allowing a wider section tyre to be used.

Unfortunately, you cannot just lace a conventional 18-inch rim to a BMW hub designed for a tubeless rim: the angles drilled in the hub for the spokes are aligned to point to the outside of the rim, rather than the centre. Offsetting the hub only makes the problem worse.

If you want to run an 18-inch rear wheel (which will cosmetically match the front if you have upgraded the suspension) then the solution is to use the hub from a BMW R80G/S or ST, which uses a conventional rim.

Only snag there is that these hubs run a 3-stud hub…

Again there is a solution: change the bevel drive for the G/S items – or any other monolever hub, then change the crown wheel and pinion. While doing this you can choose the best gearing ratio too. If you find any or all of these items secondhand, budget for a rebuild – they are up to 30 years old after all. Fortunately, BMW can still supply all these items new, albeit at a price.

Rear subframe

If you have increased rear wheel travel, then you will need a rear subframe that physically allows the wheel to achieve this movement.

Those with the skill and equipment may be able to adapt the existing subframe, but if you look at its design, you can see its limitations: all of the rider’s weight (plus pillion and luggage) is carried by two not very substantial struts, the webbing brace is only welded on one side, and the length is excessive. Look at where the webbing ends on the inside (at the rear) and you will probably see that the paint is cracked. Wonder why?

The Moorespeed rear subframe is based on the shorter item originally supplied on the R80 Basic, as this is much stronger than the standard subframe, being made with tubing that is a full 3mm thick. This is then extensively modified by adding an extra support arm either side, moving the front cross brace and incorporating a neat rear carrier, plus adding the necessary lugs for the rear indicators. The standard seat mount can no longer be used...

The mudguard mounts (we prefer UFO plastics) are raised/repositioned to allow the wheel to achieve full travel.

Battery box and battery

If you have fitted the Moorespeed 50mm extended swing arm, then you will have to fit a smaller battery/battery box – the standard items will foul the rear wheel. These new items save a lot of weight (and space) so are well worth fitting anyway

Frame sundries

Longer travel suspension means that your centre stand is now too short and will need lengthening accordingly. If you have changed from paralever to monolever swing arm, then a spacer is required to fit on the rear brake pedal pivot, where the paralever strut used to fit.

Longer travel suspension (and the necessary new rear subframe to accommodate the increased wheel travel) also means that your saddle will need to be cut away on the underside and shortened, which in turn means recovering. You might well want to re-shape it too at this stage.

Of course, now that you are sitting higher, you will need to raise the handlebars. The original bars are heavy and easily bent – so now’s the time to choose your favourite style – and mount them on risers for maximum comfort whether sitting or standing on the pegs.

Engine performance

Moorespeed has developed a number of engine performance parts, from free-flowing air filter system through to specially-developed high-compression pistons, larger valves and long con-rods, to a complete free-flowing exhaust systems and replacement carburettors. If you want more performance (and we can deliver up to 50% more power and 40% more torque at the rear wheel!) look at the Moorespeed BMW parts section – or call to discuss the full range of options. A full engine rebuild service is also available.

Transmission

A higher top gear ratio – either + 6% or +10% - can be fitted to your gearbox for more relaxed cruising – especially useful if you have increased the power output over stock. A lower first gear (-6%) option is available too, while a 6-speed gearbox is yet another option. Even if you are happy with the ratios you currently run, it’s a good idea to get the box rebuilt.

Fairing

This is all down to personal choice – and certainly sets the style for your machine. There are plenty of aftermarket fairings available if you want to look different (but you will have to sort out your own mounting system), or we can supply HPN’s ‘classic’ Paris-Dakar style with 7-inch headlight.

On the subject of headlights, there is a again plenty of choice from a range of aftermarket concerns – from tiny projector lamps to high-power HiD units.

Instrumentation

The stock GS instrumentation is rather basic – and heavy.

If you want to compete in Desert Raids and similar events, then a competition-style ‘road book’ would be the best solution, but otherwise there are a number of digital-style speedos available – some better than others, and not all have a good after-sales reputation.

We recommend the Koso unit (and stock it with full back-up): a high quality multi-function digital speedo/tachometer which features a large analogue-style 0-10,000rpm tachometer, digital speed read-out and twin trip recorders. It also displays time, oil and/or cylinder head temperatures, and has owner-defined gear change indicators, temperature warnings and distance indicators… all in a very neat and attractive console.

1989 BMW R100GS Engine.