AirCooledSuzuki

My first post but really after a biggy.....

1981 1100 kat has bandit 1200 front and rear end. I made extensions for forks ( of course including extension of damper rod to suit etc) all looks good with offset sprockets Koni twin shocks ( height same as original) etc.
However I have removed the extensions as they made the bike look too high (made 110 mm long). On my test ride the bike was fine in straight line and did not feel unstable. However when turning even extremely carefully felt like it was about to "tuck under" and had to inch my way round turns till I got home. It must of course be related to rake,trail etc but jut wondered if you could give any input to assist progress. I intend to put the extensions back in and gradually drop the forks. I can then remove if a suitable length is found and get machined down so I don't have loads sticking thro. The bike was still showing this tendency even with the full length in so I don't think this will be the complete answer as the trail must have been massive. Any ideas or any measurement I can give you to help?
Original kat: forks 81cm, offset of top yoke approx 5cm, front tyre radius 33cm, rear radius 33cm
Now: forks 77cm, offset of top yoke 3cm, front tyre radius 29cm, rear tyre radius 31cm
Running Pilot roads 120/180 inflated to 34psi
rear end Bandit with twin shock Konis giving standard ride height

I looked in the "RP Racing site" and put in the info to their calculator and it looks like the trail without the extensions actually increases by 3mm, which is probably due to the reduction in offset. This has now totally baffled me.
By these calculations and reading other descriptions on "chopper sites" it looks like the forks are too long as the bike flops into corners as decribed on many dodgy chopper conversions - Help
I appreciate any help you can give, as even though I am an engineer my maths is crap
I will endevour to measure the actual trail on the bike but am at a total loss for the moment.
The best possibility I can think of is that the ideal area lies somewhere between the 100mm extensions (hoping 50mm) and the bandit forks with no extensions and that I have crossed from one extreme to the other with a sweet spot in between
I also wonder wether the wide back wheel causes slow lean with the front then comparitivly diving as narrower.
The original; Kat front19"/back 17" actualy end up the same diameter due to tyre preofile were as in the Bandit case the back is a larger diameter
I really dont want to change wheel size (have just spent out on repaint and new tyres) and yes I could use dropped yokes but these give me exactly the same action as extending the forks

Ideally I am looking for someone who has done the same conversion and can give me fork length or yoke step dimensions.
also would be glad of some reassurance.

If you got this far thanks for bearing with this- why ask foir a little when I want the lot!
Thanks
Mark

TBH i know a lot of folk use the bandit front end ..but apart from adjusting the leg hight in the yokes it does lack adjustment...

i recall reading your question of face book ..and no one mentioned .

1) the kat engine is a lot heaver than the B12 unit.....so more mass on front end...."forks will need revalving and better springs "in my opinion"

2) the B12 arm is slightly shorter than the OE Kat one......and a shorter rear tends to turn quicker....

i ran my EFE on a K4 Radial front end .."it was very soggy" But once revalved with better springs it transformed the handling"

I have also ran a 1100K RWU front end on an EFE and that was the same ..untill "i put stiffer springs in it".....

Thanks for reply.
I do have uprated progressive springs on the front .
Hagon technician advice on stiffness related to weight .
The swingarm is only a few mm shorter so would be very suprised if this would cause the bike to try and nosedive when leant over.

Hi how you doing. What are you reffering to when you mention extensions?
Im no expert when you talk about rack etc. I can say if you ride modern bikes dont try to compare them to the Kats. I fitted a bandit front end to my wifes kat, i fitted a gsxr1100J 18" front wheel. Kept stock 330mm kat shocks and arm. I fitted a 600 bandit rear wheel with a 160 tyre. Compared to stock it handles much much better.
Ive just fitted bandit front and rear to my turbo Kat. See project section. I have used the bandit arm with shock lugs mounted and connected to gsx1400 shocks. We set the swinger at 9 degrees which is the same as the gsxr1100l i have. Aint rode it yet but it looks like it will handle.
FBJ

The extensions basically screw into the fork tops then the original fork tops are screwed into the top of these extensions.
The damper rods are extended to suit with the spacer and washer in origial location . This results in a longer fork with exactly the same action/mechanism inside. I think it is a far better method than using dropped yokes when wanting to keep clipons.
You seem to have gone down a similar track to one of my lines of thought - a narrower back tyre with a larger front wheel.
Your other project sounds very similar to what I have done ( bit more adventurous with the turbo etc tho) in relation to set up so I will have a look at it in the project section.
I really don't want to change my wheels- if I was after spending more dosh I would rather have a dabble at the engine like yourself but ho hum if needs must.
Thanks for the reply, I will check yours out
Mark

katanamak1 wrote:Thanks for reply.
I do have uprated progressive springs on the front .
Hagon technician advice on stiffness related to weight .
The swingarm is only a few mm shorter so would be very suprised if this would cause the bike to try and nosedive when leant over.

Well you seam to have answered that question then.....

i would check the head race bearings are ok and not to loose...and possibly look at a steering damper...

Oh well, it looks like I had better start strip down at the weekend again.
Used to be enjoyable but getting a tad tedious now.

Back end looks really low. Are they 330mm long? The tyre looks very low profile to.

Probably just because of the angle
Standard length shocks mounted were they should be/area like yours
Back tyre 180/55
Front 120/70. Both standard bandit
Love the look of you bike by the way

Just got home and have some more measurements.
Wheels spindle to spindle 150cm
Swing arm pivot to rear spindle (as adjusted for chain in approx centre of adjust) 56cm
Shocks are 335mm long. The pivot point/shock bolt centres are 9cm from the end of the arm
If you're not all sick of this thread by now any comparisons welcome.
I seem to be manopolising FBJ time at moment for which I am gratefull.
I do seem to end up with some wierd problems at times, having just sorted out some partially running led's that gave me problems that I only found one guy in the US had come across.
Considering I work on aircraft perhaps you should all change your travel plans