Airhead specials - Suspension

fok

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My Paralever PD with 48mm WP (KTM) forks is having a suspension service and at the same time I'm thinking of reducing the length of stroke of the forks as it sits a bit chopper-like, even with an extended rear shock.

I appreciate that geometry is going to affected by the lower offset of the KTM yokes, balance of front to rear height, blah blah blah, but I'd like to ask those of you who've built or modified your airhead GS and switched the forks, is there an optimum length that you worked to? i.e - Top yoke to axle centre. I've done loads of internet reading so have an idea, but you can't beat real world experience.

Thanks in advance
 
I’ve not, but advice from three who should know recommended the WP usd forks I have, set with bottom of the top caps flush to the yoke.

I can measure tomorrow if that’s helpful?
 
Nin said:
I’ve not, but advice from three who should know recommended the WP usd forks I have, set with bottom of the top caps flush to the yoke.

I can measure tomorrow if that’s helpful?
Click to expand...


Nin, if yours are forks off a KTM EXC enduro bike they will have 300mm travel. The same fork fitted to 690 enduros and 990 adventures had travels ranging between 250mm and 275mm. The forks I’m using on mine are 250mm travel. Whatever travel fork you use it’s important to fit the right weight springs
 
Yep mine are from a 2004 EXC so 300mm.

I had them built by Mark Hammond (MH Racing) who was suspension tech on the Cagiva Dakar team. I don’t know what springs he put in but the static sag is bob on.
 
Thanks guys, can you measure overall length, top yoke to axle centre please.

I'm pretty sure mine are 300mm travel but I have the opportunity to reduce length when they're apart. I know they need it but I wondered by how much.

Cheers
 
Measured mine from top cap to axle centre and they are 885mm (2008 690 Enduro)
 
Top man, thanks.

I've changed my mind about reducing the stroke, I'll do it by dropping through the yokes a little if neccessary, I'm guilty of liking the tall front "stance" reminiscant of 80's desert racers, regardless of it not really being conducive to good road manners.
 
fok said:
Top man, thanks.

I've changed my mind about reducing the stroke, I'll do it by dropping through the yokes a little if neccessary, I'm guilty of liking the tall front "stance" reminiscant of 80's desert racers, regardless of it not really being conducive to good road manners.
Click to expand...

Out of interest, are you using KTM yokes? They give poor geometry for an airhead.
 
I’d get some bespoke yokes with the correct offset before doing anything else.
The last bike I rode with the standard ktm forks /yokes was absolutely lethal.
Hitting a cats eye on the road at 40 mph + would create a violent tankslapper.
In addition to that the incorrect ride height with it’s raked out front is not favourable to the forks actually compressing when hitting bumps.
Another thing worth considering when addressing the rear ride height is ,a longer shock or shortened torque arm will reduce the wheel base.
This won’t help the stability of the bike at all.
IIRC the ktm yokes have @15 mm of offset
A para GS has @ 36mm
 
mikeyboy said:
I’d get some bespoke yokes with the correct offset before doing anything else.
The last bike I rode with the standard ktm forks /yokes was absolutely lethal.
Hitting a cats eye on the road at 40 mph + would create a violent tankslapper.
In addition to that the incorrect ride height with it’s raked out front is not favourable to the forks actually compressing when hitting bumps.
Another thing worth considering when addressing the rear ride height is ,a longer shock or shortened torque arm will reduce the wheel base.
This won’t help the stability of the bike at all.
IIRC the ktm yokes have @15 mm of offset
A para GS has @ 36mm
Click to expand...

Great info thank you. Yep, I get the feeling that they feel a bit harsh as they're not compressing correctly.

@Mad Hatter..........You mentioned yokes from Roy Martin at BilletBikeBits in your build thread. Are these the sort of thing that mikeyboy is talking about, with more of an OEM offset?
 
fok said:
Great info thank you. Yep, I get the feeling that they feel a bit harsh as they're not compressing correctly.

@Mad Hatter..........You mentioned yokes from Roy Martin at BilletBikeBits in your build thread. Are these the sort of thing that mikeyboy is talking about, with more of an OEM offset?
Click to expand...

Yup, exactly that. Roy made me a set with the same offset and the BMW GS yokes but with holes to suit 48mm KTM forks. SWT sell a set, HPN do, Gletter do etc. but Roy was about half the price and the quality is excellent
 
Mad Hatter said:
Yup, exactly that. Roy made me a set with the same offset and the BMW GS yokes but with holes to suit 48mm KTM forks. SWT sell a set, HPN do, Gletter do etc. but Roy was about half the price and the quality is excellent
Click to expand...

Beautiful thanks.
I'll have a word. It makes sense to start there.
I appreciate all the input chaps.
 
Why would you 'shorten fork travel'? I thought more fork travel would iron out bigger bumps. :nenau

I don't know the ins and outs of motorcycles, I just get on them and ride them. With Mikey saying they wobble if you hit a cats eye - well don't hit the cats eye then! That is my way of riding. :D
 
King Rat said:
Why would you 'shorten fork travel'? I thought more fork travel would iron out bigger bumps. :nenau

I don't know the ins and outs of motorcycles, I just get on them and ride them. With Mikey saying they wobble if you hit a cats eye - well don't hit the cats eye then! That is my way of riding. :D
Click to expand...

If you've a lot of travel, you need long forks, which, if the back end is still standard will rake the forks out making it (probably) steer very slow, not want to turn. If you go the other way, too short it'll make the forks steeper and the steering really quick and unstable. There are many other variables which have the ability to make you go through a hedge, instead of going round the corner, or have the front wheel flapping like a shit castor on a shopping trolley, chucking you up the road whilst pursuing the quest for perfect handling that you don't have to think about.
Then there's tyres, weight distribution, wheelbase...............
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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