How to uprate your fork internals

IT’S ironic that the only company today to use an alternative to telescopic forks is the same one which introduced them first on production bikes.

BMW’s R12 and R17 had the first telescopics in 1935, and since then no alternative has been found which is better for high-performance sports bikes.

Modern forks are far more sophisticated than those early versions, but that’s not to say they can’t be improved upon. Inevitably, there are limitations imposed by mass production and cost, but also the forks of the majority of sports bikes are set up to suit all types of road conditions and users around the world.

So inevitably they’re a compromise, especially in the UK, where riders of this type of bike tend to use them harder than in many other countries.

There are two types of fork, conventional and inverted, but both use the same basic principles.

Each consists of two concentric tubes, one of which slides inside the other with a spring to support the weight of the bike, keep the forks extended and allow movement as the bike rides over bumps. That movement needs to be contained, otherwise the forks will oscillate up and down after every bump – enough for the bike to go out of control, which is where damping comes in.

The exact amount of this damping is crucial to the performance of the forks, determining how stable the front is and how evenly the tyre is held against the road surface which, in turn, affects grip. But it needs to be altered to suit different weights of rider and riding styles, which is why many forks feature the facility to alter the amount of damping. But this alone is not always enough as many riders still find the forks on superbikes too soft and too prone to bottoming-out (where the forks run out of travel by compressing as far as they can go). This happens especially under heavy braking and upsets the whole bike, as well as reducing the braking available by causing the front wheel to skip across the surface.

There is an easy and relatively cheap route to improving the performance of forks, and that is to fit new internals. Ohlins makes kits available for most modern superbikes, so we spoke to Harris Performance’s Richard Brendish, whose CV includes working with Kevin Schwantz, Eddie Lawson and a host of British Superbike teams, to find out whether the gains are worth the investment.

He says one problem with modern sports bikes is that they all use progressive springs. This means it takes less weight to compress the spring a certain amount in the first part of its travel, then slightly more in the middle area of its movement and more again to compress it in the final part of its travel. For example, a weight of 0.75kg will compress the spring 1mm in the first third of its movement, then 0.8kg to get it to compress 1mm when it’s in the second third and 0.85kg to compress it 1mm as it approaches the end of its travel.

” This gives you a very plush ride, ” says Brendish. ” It’s very good at dealing with potholes, helping the wheel drop in quickly. But if you just touch the brakes you’ll immediately use up something like 30 per cent of the travel. As a first stage in improving your forks, the progressive springs should be removed and replaced with linear rate springs. ”

This reduces the dive under braking, meaning the bike doesn’t pitch forward so much and it remains more stable when the brakes are used hard. The forks are also less likely to bottom-out, all of which improves wheel control and hence grip, plus stability. It’s not expensive, either, with a pair of Ohlins springs costing around £68 a pair. On many bikes, such as Honda’s FireBlade and SP-1 or Suzuki’s GSX-R600, fitting them is easy, too, and well within the scope of the home mechanic, though on others, such as the R1 and GSX-R1000, Brendish describes it as ” a pig of a job! ”

Take your forks to a dealer and budget on around an hour’s labour, and it’s only that quick because he’ll have the special tools required to cope with the heavy pre-load (and even then it’s a two-man job!).

This already makes a big improvement, which is noticeable on the road and which many riders say transforms their bikes on track days. But there’s more which can be done.

Stage two is to change the original 5W damping oil for a heavier 10W oil (these ratings apply to specialist fork oil). According to Brendish, this is effective on a lot of road bikes, especially the R1, but it’s not that easy on inverted forks, which have to be removed and then turned upside-down so the old oil can be pumped out. It should then be replenished to the recommended level.

” With the linear springs, this will bring the damping adjusters back to the middle of their range, ” said Brendish. ” Otherwise, a lot of riders find with the 5W oil they have the adjusters wound up fully, right on the limit of their damping for the forks to work properly. ”

The damping action can be improved further using revalving kits. The damping works by an internal piston forcing oil through a stack of shims at each end of the fork. Ohlins produces kits to replace the pistons and shim stacks with more finely-machined and calibrated ones. The firm won’t sell the kits on their own in the UK because fitting them is such a specialist job – the potential for damaging the forks is considerable. But the cost is still not excessive.

Take your forks to an official Ohlins centre and for most superbikes the cost is around £350 (with a two-day turnaround time), though R1s and R6s cost around £400 as they also need to have a rebound piston holder fitted.

The pistons used are the same as those fitted to the 1997 Ohlins superbike racing forks, while the shim stacks are carefully calibrated by Ohlins technicians. You’ll then have forks identical to many used on the current Superstock race bikes, which means front-end control and grip is transformed.

For a list of Ohlins dealers, call Harris on: 01992-532506.