Gents,
There's a few things at work here & some of them are contradictory, so its a little more involved/complex than most people realise.
If you reduce offset, (ie have more trail) you get more of the centre-ing effect which tends to make slightly heavier feel to the steering. It should also cause less headshake.
It would give more stability too, except that you've also reduced the wheelbase which tends to reduce stability. Hence something of a contradictory effect. (Headshake is not the only issue in stability. There's also the tank-slapper effect, which is increased w shorter wheelbase)
But less offset also affects weight distribution, putting more weight on the front wheel, which tends to make the front wheel stick better in cornering. ie better steering. (This probably explains the issue w CRF450 steering mentioned in an earlier post. More weight on front wheel from less offset gives better steering, but the corresponding shorter wheelbase gives less stability).
It seems to me the change in weight distribution is the biggest factor/effect, & the one most often overlooked. Compare vintage Maicos. They were the best steering bike in MX, yet their rake & trail (overall offset) were exactly the same as many other VMXers. (I've measured many of them) The difference was the weight distribution. They had longish wheelbases, w motors & seating position well forward. So plenty of weight was on the front wheel giving very precise steering. When you sit on them it almost feels like the forks come out of yr hips! (Even a bikes ergonomics affects steering.)
Also compare Bultacos - the early ones washed out rather terribly, but the later ones (post Mk6 pursang) steered much better. The difference was in the triple clamps. The later ones had reduced offset & as far as I can tell, that was the only difference. This is particularly interesting since the later ones (Mk6-7) had considerably larger trail than any other bike of the era, but they steered fairly well cos they got the weight distribution/balance right & the front end stuck reasonably well. (Tho they could be even better w the tank & seat a little further forward, like an Ossa Phantom/Pioneer)
Now compare vintage Huskies. They ran very short wheelbases, with raked out front ends to get some stability, but they didn't steer too well (cos of the rake & consequent rear-ward weight distribution) & had the famous husky-hop (cos of short wheelbase). History shows those early Huskies didn't have the right combo, & it was a common mod to extend the swingarm/wheelbase & reduce the fork-offset to make them work better. That's effectively what the factory itself did. The 74 MAG Husky steered better than earlier Huskies cos of longer swingarm/wheelbase, & 75-76 USA works bikes ran reduced-offset triples as well as longer wheelbase.
Gary Flood further improved the steering of his Bultacos by adding 30mm to the swingarm (according to an early VMX mag). That's entirely consistent w what I'm saying. He would also have improved stability.
If you increase offset, you reduce the centre-ing effect, which makes slightly lighter feel to the steering (& can cause more headshake), but because yr moving the front wheel further forward it tends to cause front-end washout because of less weight on the front wheel. That can be offset by extending yr swingarm, even if only by chain adjusters (& another link or 2 in yr chain) because that restores some of yr weight distrbution/balance.
There is also the effect of raising/lowering yr forks in the triple clamps. On a typical VMXer of about 55" wheelbase, raising/lowering the forks 1" changes rake by about 1 degree. But what is most often overlooked is the larger effect on wheelbase & weight distribution/balance. Most people don't realise that a 1" change (sliding forks up or down) on a 30deg rake is a 0.5" change to yr wheelbase & weight distribution. ie Yr front wheel is either 0.5" closer to you or further away from you, depending on which way you slide the forks in the triples.
That is why, when people extend their forks w travel extenders (or simply longer forks or damping rods from a later model) using the same triple clamps they often find the bike now steers poorly w more front end washout. It can be corrected (or at least compensated for) to some degree by extending the swingarm, &/or reducing the offset w different triple clamps.
As you can see, there are many variables involved & many effects of changing the offset. Its not just different trail. But in general if yr front end washes out, bring the front wheel in closer to you &/or move the rear wheel further rearward. Even 5-6mm (or 0.25") makes a fair bit of difference.
As mentioned in an earlier post, the discussion in Foale & Willoughby is excellent. However most discussions on steering in 70's bike mags only concentrated on rake & trail in isolation which is of limited value - & frankly is often misleading. Hence bikes w the same rake & trail can steer entirely differently as Brent mentions above comparing the RH to the early version of his project bike.
Clear as mud?? It could be muddied further if you consider the effect of wheelbase on cornering. In general a shorter wheelbase is better for cornering. But cornering is different to steering in my view (tho there is of course some overlap). eg On Gary Floods Bultacos, they would have steered better (more weight on front wheel) but not cornered so well (longer wheelbase corners slower). Another contradictory effect.
Finally, getting back to MX250s original post, the H6 enduro came stock from the factory w straight forklegs, whereas the VB came w offset axle foklegs. The H6 legs were also shorter. That explains the diff offset in the triples. Some people just put offset axle forks in straight-forkleg triples if the fork dia was the same. Very bad move. It completely stuffs up the steering cos it stuffs up the weight distibution. It would also have a potentially bad effect on head-shake. Probably very bad!
I hope this has added further understanding to the discussion
