Here's a question I get asked a LOT,I've had a few emails about the subject too. "D'ya know if an xyz's forks fit a an abc bike?". Short answer, in most cases, Dunno!. Legends exist for example, that RGV250 forks fit the GS range etc but in practice it's not always true.

So let's assume that ye want to swap the front end on yer bike. Ye fancy a nice set of upside doonys on yer fizzy or CG125, hmmmm. Sit down, have a cold bath, throw a stick for the dog, just take a bit of time and think it out. All I can do here is pass on some experience and tips on the process.

In this example me mate Marty decided he hated his ZX-10 rat but loved his XS650 hardtail chop but had gone in the huff with it's crap front end with single teflon disc and brake calipers which didn't even have enough grunt to make ye smile if ye bunged yer knob between them.

As happens, Marty turns up at my door and grins, the grin ye recognise that is going to lead to one of those, "Ho Al, can ye make a ZX-10's forks fit ma XS, grin, grin", aye well.... c'mon in, ah'll put the kettle on.

First Get yer precision measureometer out, rule, tape, metre stick, cat, tesco poppy seed baguette in order of accuracy of course.

A "very near" gauge or "vernier", it's posh sunday name, would be useful too.

I'll tell ye what to measure in a moment but first.

There are three scenarios that are possible here, each posing different challenges.

1. The headstocks of both bikes are the same length and both bearings are the same....... look d'ye see that squadron of pigs up there at 50000ft, If this happened I'd go buy a lottery ticket. Ye might get this if the forks and frame are off the same bike, or model. e.g. Bandit 6 and 12.

Before worying about bearing sizes..............

2. The headstock is longer than the yoke spindle. Bugger, this will mean that ye need a new yoke spindle, this involves pressing out the spindle, getting a new one turned, threaded and pressed in, or find yokes of the right length that will take yer diameter of forks. This is a hassle.

3. The headstock is shorter than the yoke spindle. Wohoo, do the dance of the whirling dervish round the shed, yer luck's in. This is the case for this example.

First up, the yokes from the ZX-10,

measure the length of the spindle, which was 210mm,

measuring the headstock of the XS showed it to be 171mm.

The Top and bottom XS bearings were 25mm ID(inside diameter/ 48mm OD(Outside diameter)

The ZX10 spindle bearing surfaces were 25mm top and 28mm bottom.

The upshot of this was

1. The XS headstock was shorter than the ZX10 spindle therefore a bearing cup extension had to be manufactured to take up the space.

2. The top bearing from the XS could be used in it's existing bearing cup.

The brown line indicated where the part fits into the existing bearing cup of the XS headstock

Ther ye have it, a nice new front end which has brakes that actually stop the bike, the return on investment being made through cleaning costs of underpants caused by the previous single disc/piston arrangement which would get you from 60-0mph in about the same time as getting the cellophane off a packet of chewing gum when ye've bitten all yer fingernails off.

In a nutshell, if ye still want to swap front ends then go to a breakers/mates/showroom and get measuring, make it as easy as you can for yourself.