Here's something i saved from good old itpro =) actually, i have quite a bit of his stuff saved =P lol anyway, here it is, hope it helps, Thomas......
There IS no simple answer..... except to say.... "where it gives you the best weight distribution".
Put crudely, if you are tall but fat and short legged (like me) then your seat needs to be further forward and lower for ideal weight distibution than it is for a short stick insect (typical quick karter's shape)! Damn what the 'books' tell you!
This is only MY way of doing it.... others will disagree but here's an answer I wrote for someone else, long ago:-
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Simply FORGET the concept of 'corner weights'. It simply does NOT work for karts! Period!
Even if you COULD do it properly, you'll find that moving just you HEAD while in the seat alters the 'corner weights' DRAMATICALLY. It would be GREAT....... if you sat STILL in the kart but you DON'T!
However, I have long argued that front/rear weight distribution is THE key to getting the kart to work. By all means, use your 4 scales and use the COMBINED total of the fronts and the COMBINED total of the rears. The general 'rule' is somewhere between 45%:55% and 40%:60%, favouring the 'heavier front' in the WET!
It's EASY to set your seat in the RIGHT place to give that distribution.
1) Place the kart on your scales
2) Place a STRONG board which EXACTLY covers the 'hole' in the chassis rails where you seat will go.
3) Place the seat ON that board
4) Disconnect the pedal cables and loosen the 'stops' so you can place your feet where it is MOST comfortable REGARDLESS of where the pedals are NOW!
5) Get INTO the seat fully kitted up! Place you feet where it feels most comfortable. I you are using a ‘flat bottom’ seat, it can be ideal to make sure that the ‘flat bit, is ‘flat’ on the board. That will give you an angle which will best protect the seat from ‘grounding’’.
6) Get someone to watch the scales and MOVE your seat ALONG the board until weight distribution is where you choose (e.g., 42.5% and 67.5% as a ROUGH guess)
7) if you are tall (and fat) like me, then you will NEED to rotate your seat BACKWARD to lower you CofG and that will need you to move the BASE of the seat further forward! Make sure the seat is where you want it with regards to 'twist' and 'left right' alignment!
8) FORGET about how your feet fit the pedals or how you like to hold the wheel: we adjust THOSE later!
9) Now get your team mate to mark an EXACT VERTICAL line on the seat (with a good felt tip) directly in line with the SIDE-seat-mounting-holes of the seat brackets. (We'll bother about the front ones later.) That will show you the EXACT line on which the mounting holes will be drilled when we have the seat at the right height
10) Now, remove you, your suit, the board, etc... Place a board on the floor about 3cms thick or MORE, UNDER where your seat will go. Place the seat IN the 'hole' and ON that board and sit back in the seat. Make CERTAIN that the seat mounting holes remain aligned with the newly marked vertical lines and that you are leaned back at EXACTLY the same angle you chose before (remembering that WILL make the felt tip line absolutely VERTICAL!)
Be CERTAIN that you are as comfortable with the 'position' as you can be and that it's STRAIGHT, centrally positioned (as much as possible) etc.
11) Now get your friend to mark the seat THROUGH the seat-mount-holes with the same felt tip. MAKE CERTAIN that the new marks are ON the vertical lines you drew or else it will NOT be at your chosen weight distribution! Now remove the seat and drill those two holes!
The height that you chose for the board sets the 'ground clearance' under the seat. We have ALLOWED for the 'sag' that will happen when you put your weight in it and we have allowed for a bumpy track as the whole thing usually 'droops' by about 1cm to 2cms when the seat, and you, are 'mounted'!
Many people make their seats remain ABOVE the lowest part of the chassis rails. That's fine for 'skinny short' little b*gg*rs but not for us 'more substantial' people! If you want to do that, make your board SMALLER than the hole in the chassis so it can 'stick up' through the 'seat hole' by about 1cms to 2cms. That will drop it to being 'level with the rails' when you have mounted it and then get IN it!
So, choose the 'seat ride height' that YOU want CAREFULLY! Us tall-fatties like it lower (to keep the CofG lower) but it CAN cost you the bottom of your seat if you go 'kerbing'
12) Fit the seat bolts to the sides of the seat and then you can put the kart on your stand to make the next bit easier.
13) The seat will now 'swing' from its side bolts. Set the angle of the seat so that your 'vertical line' is VERTICAL again. Lock-off the side-seat-bolt-nuts so that the seat REMAINS at that angle.
14) Now CAREFULLY, get below the chassis and feed your drill UP through ONE of the front seat-mount-holes. The seat will probably be a LONG way from the seat mount as we will (probably) need to 'pack' the bolt to get the front-height right
15) Make CERTAIN that the drill meet the seat where it touches at EXACTLY (and I do NOT mean NEARLY) 90 degrees to the point of contact Don't worry that it is meeting a 'curved shape'. Just make sure it is perpendicular to the point of contact. If it DOESN'T, the seat bolt and washer will cut a neat HOLE through your seat when you tighten it up at a VERY nasty angle!
15) Now, cut the spacers or combine pieces of MORE than one spacer to fit over your FIRST front seat bolt until the angle of that (now famous) vertical line is vertical AGAIN! (You'll find seat spacers here:
http://www.spellfame.co.uk/acatalog/Seat_Accessories.html
I can't find a supplier of the BEST packing washers. They used to be fat and thick walled black plastic 'tubes' about 5cm in length which you cut to length and angle as required. What the HELL has happened to these? I am glad I have plenty in stock!
16) Now fit that ONE side and then drill the OTHER in exactly the same way!
You will now have your seat mounted EXACTLY at the right ride height AND weight distribution!..... so long as you've been careful!
17) Now, set the pedals by using the 'stops' to fit your chosen 'leg length', etc.. Re fit the cables at EXACTLY that position moving the steering wheel as required, too.
If you have done it RIGHT, then your weight distribution SHOULD be correct as will you ground clearance and CofG!
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Many people will TELL you that seats SHOULD be mounted where the manufacturer SAYS! That's just PERFECT...... if you are the standard, top-line-driver, skinny, short little 'runt', but most of us ARE NOT! My 'method' has worked since I was a kid and that was a LONG time ago!
Ian
(phew!)
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Tillett Seat positioning by 'Crashlanding' (12 Nov 2009 @ 16:40)
