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How to make a chassis into British Superbike spec

Published: 22 April 2002

Updated: 19 November 2014

The chassis on Suzuki’s GSX-R1000 is good enough to keep even the most demanding rider happy… or so you’d think. But when you’re using one to defend the British Superbike title, a stock one simply isn’t up to the job.

" With the grip from modern tyres and the way the top men ride, you’d be amazed what happens, " said Steve Harris of Harris Performance, the firm which adapts the frames for John Reynolds’ Suzuki team.

" I’ve seen bolts with 4mm of clearance between the engine and frame leave an imprint in the rails because a chassis flexes so much. "

So what can you do to improve its performance when the new-for-2002 superbike rules insist you use a production-based chassis? It’s simple, as Harris explains:

1: Headstock:

Harris says: " The power of modern brakes means there’s a lot of movement at the headstock when a top rider is pushing hard. A bit of sideways movement is OK, but I won’t even try to explain that! You need the wheels to stay true to each other, but a chassis flexes. We add a gusset behind the headstock, which fixes to the frame rails, to spread the load and avoid a pressure point. We then add a thicker beam under the main rails, from the headstock to beyond the cylinder mount points. "

2: Engine mounts

Harris emphasises that precision is vital on a race bike. He said: " On a production bike, the frame is designed to be bolted together quickly. That’s not suitable for a race bike. We need the engine to fit exactly in the frame. It’s vital it doesn’t move about.

" So we bush all the holes in the frame to make the bolts fit precisely. What we’re doing is removing the production tolerances, so one specific engine fits one specific frame.

" All the bolts we use are made from titanium for strength and lightness. Steel works fine, but we also need to consider the weight. "

3: Swingarm mount:

Harris isn’t impressed with production swingarm mounts. He says: " They’re just welded on to the end of the frame rails and in a race the bike flexes around points like this. At the back of the frame, where the shock mounts, there’s a box-shaped rail. We close that in – a closed box with six sides is far stronger than an open one. We also add a gusset from each frame rail to the cross rail to spread the load. "

4: Swingarm:

" We normally chuck the production swingarm away, " says Harris casually. " We make a £2000 replacement, which the rules allow. We add bracing it so it’s far stiffer than the original to keep the wheels where you want them. The spindle is lightweight and the adjusters are quick-release so you can take a wheel out and the brake caliper stays in place.

" The adjusters are super-accurate and there’s twice as much adjustment as a stock bike. When you stiffen the suspension, you effectively shorten it. The swingarm lets you recover that length, which is vital for stability. "

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