The Place

Trying to help out a guy who's picked up a P5 machine thats been converted to F2. Apparently it has issues with severe understeer. I'm suspecting that some of the frame geometries may be out.

I have my short F1 to measure against (my bike handles fine) but no F2 dimensions as such. Is there a relatively common formula or set of dimensions that F2 chassis' are built to?

The dimensions I have from my F1 bike are:

62" wheelbase
42" track
26 degree headstock angle
1/4" trail
14" sidecar lead from rear wheel centre to chair wheel centre
26" from engine output shaft to front wheel spindle (for engine placement relative to the frame)
6 3/4" vertical offset from frame for swingarm pivot

I was going to use these as a base line to help correct his bike but would like to know if F2 dimensions vary much from these for any reason.

Doesn't sound too far off the mark. Is the engine as far as possible forward? What sort of rear shock/spring? If it's too soft it will squat too much & you'll get too much drive from the rear. Has someone experienced riding F2's had a ride on it? Sometimes another opinion can help sort stuff out.

The engine cold be moved forward another 1.5 inches or so (need to work out the steering clearance around the exhaust headers to be sure).

The frame was originally a P5 machine so had, I believe, a GSX1100 engine in it. When the conversion has been done, the new engine has been placed quite high in the cradle meaning there is a downward angle on the chain to the rear sprocket. I'm wondering if that could that be enough to upset the outfit under power?

I haven't looked at the springs too hard yet, but I will now.

He hasn't had anyone else ride it but thats a good idea before we go stuffing around too much.

I'd be moving the engine forward. I have a p5 with a GSX1100 which we recently measured up against a 2012 LCR and they were almost identical in all dimensions. I assume you meant that your engine is 26" from the crankshaft to the front wheel spindle. Both mine and the LCR we measured were 23"from the crank to the front wheel spindle. If this bike has had a Suzuki engine taken out and a modern 600 engine put in it's place. There is a huge weight difference between the two.

An update on what happened.

Shocks were okay as was the chassis and tyres. We ended up moving the engine forward 2" and down 1".

The difference was immediate. It steers like its on rails now. The lap times have tumbled during tuning sessions to a very competitive level. Looking forward to the next round to try it out in anger.

Thanks everyone for the help.