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August 13th, 2018, 03:45 AM   #31
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Originally Posted by Taffy View Post
6mm of OFFSET? offset should first and foremost allow the bike to roll around a radius of bends (either slow/hairpin, medium or fast), the three aren't mutually exclusive. the bars should remain neutral with no effort to steer.

if you imagine a corner a as rock face at say 45d and you are travelling across it, you don't want the bike to climb up the corner because this will cause the bike to break traction or to want to ride straight ahead (down the rockface) 'out' of the corner.

the 2004-2008 SMs handle best with 16,17,18mm offset. the 2001-2003 SMs handle best with 18, 19, 20mm offset. so where does 6mm offset come from?

all that means, like a tea trolley, you lay it on its side and the wheels turn at 90d to the trolley, the front wheel of a bike tries to climb up the corner to the inside but of course it scrubs and you lose the front end.

https://www.google.co.uk/url?sa=i&so...34167547303697

the guy in the link/photo above has obviously just 'lost it' but if he was to corner with 6mm of offset and just gently hold the bars like we all do then this would be the effect. the front end went to turn in like a tea trolley wheel.

all you have to do is take a tea trolley and push it over on to two wheels and the front wheel will pivot round to 90d.

you can do the same by standing behind a bicycle or a motorbike. the steering always turns into the corner.

luckily, the rear tyre is driving the headstock forwards just like we push the trolley and there's an element of it pulling the wheel straight again (the wheel has trail so like the tea trolley being pushed it straightens up).

The FE570 dirt bike had so much trail at 16/18mm that i went to 20mm and then 22mm. word had it that Joachin Lungren had asked for 24mm offset but the factory refused so he said; "well i want to race the 2T for 2011 instead then" and so they let them.

but that is 24mm, i wanted 24mm. how the hell can you ride with 6mm?

Taffy
FFS you twit! Can go down to 4mm if you wish!

https://www.computrackboston.com/KTM...0-190-5-bk.htm
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August 13th, 2018, 03:47 AM   #32
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Originally Posted by Alan View Post
FFS Taffy you twit. Jacking the rear wheel or lowering the front will change your rake. This isn’t how you change your trail.
Actually a primary effect of changing rake is the change in trail.

However, there’s another property which is changed by canting the bike backwards and forwards on the suspension: Balance.

Therefore, the same bike setup with a smaller offset yet equal trail will have a more forward-biased weight distribution.
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August 13th, 2018, 04:06 AM   #33
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Originally Posted by tourist View Post
Actually a primary effect of changing rake is the change in trail.

However, thereís another property which is changed by canting the bike backwards and forwards on the suspension: Balance.

Therefore, the same bike setup with a smaller offset yet equal trail will have a more forward-biased weight distribution.
Thatís right but you wouldnít change rake to change your trail or any other part of your geometry unless that is what you are looking to achieve.
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August 13th, 2018, 08:49 AM   #34
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Originally Posted by Alan View Post
FFS Taffy you twit. Jacking the rear wheel or lowering the front will change your rake. This isnít how you change your trail.
he asked me the ways that you reduce the trail. so I'm far from a twit, i told him some of the ways. if you want to add more ways of reducing the trail then by all means put them up.

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August 13th, 2018, 08:57 AM   #35
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Originally Posted by tourist View Post
Therefore, the same bike setup with a smaller offset yet equal trail will have a more forward-biased weight distribution.
except that this isn't possible except with a change in rake. if you don't change the rake then the above is impossible.

if you change the offset, then you have changed the trail. and as for weight distribution changes it is a very small factor when dealing with 2mm of offset.

and Alan, just because you CAN doesn't mean you SHOULD buy those clamps!!!!

the 570 is a heavy bike and not everyone will appreciate being fecked by a gorilla after two laps.

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August 13th, 2018, 09:25 AM   #36
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Originally Posted by Taffy View Post
except that this isn't possible except with a change in rake. if you don't change the rake then the above is impossible.
Agreed.

Originally Posted by Taffy View Post
if you change the offset, then you have changed the trail. and as for weight distribution changes it is a very small factor when dealing with 2mm of offset.
I'm prepared to be wrong, but I believe we'd get at least somewhat significant weight redistribution by canting the bike forward on the suspension. At least when going from around 20mm to 6mm offset and lots of trail, and then canting forward (front lower on forks, rear higher on shock) to get trail back to what it was (by virtue of the rake changing).

Last edited by tourist; August 13th, 2018 at 09:29 AM.
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August 13th, 2018, 09:57 AM   #37
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oh it makes a difference changing the pitch, I know that, it changes things for sure in the suspension but it effects too many other things which you can set to work on beating but you would only change the springs F & R if they were near the edge anyway so if you had .46 fronts and you were always edging towards say a set of .48s then this would tip you over and you would need them. but you are never more than 2mm away from the correct set up.

when i changed the headstock angle on the BEARUP I changed it what...5d? and the TCs went from 22mm offset down to 12mm offset. so that is 10mm for 5 degrees. 2mm per degree and the ethos of the bike was the same otherwise so it is a fair comparison to say that 1 degree needs 2mm change in offset.

but nobody ever changed from 20 to 6. that's like a dream. mind you, if i'd sold my dirtbike to Alan in Oz and he took my 22s off and put in his SM wheels i guess he'd be putting in 6mm offset clamps.

fact is though, these were raced back in 2009-2013 at their peak and they didn't use 6mm offset then and they therefore wouldn't need it now. the correct offset can't have changed because the bike hasn't changed. the other thing to recall is that until 3 years ago the fork legs were the same distance apart and now KTM have them 10mm further apart to facilitate more steering lock. going from old to new therefore presents headaches.

not all bikes are the same but after a time it is tested and proven and noted what they like best.

I work a lot with ScX (sidecarcross) and we change wheel sizes (say 20 up to 21) and then have to get the trail back. by moving the front loop forwards in one of a choice of 3 holes at the foot of the solid forks, each hole change is an incredible 15-20mm. the problem is the shocks that were vertical on the front are now kicked forwards 15-20mm and so they are shorter so now you changed the pitch and the trail again! we have to change one spring (heavier) to get the pitch of the bike back up.

i use the term pitch a lot but you won't hear anyone else talk about it. just me.

I also don't believe in 'on the wheels' sag. just wheels free, race sag and the preload. that's all.

Taffy

Last edited by Taffy; August 13th, 2018 at 10:05 AM.
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August 14th, 2018, 02:05 AM   #38
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Originally Posted by Taffy View Post
I also don't believe in 'on the wheels' sag. just wheels free, race sag and the preload. that's all.

Taffy
Thank you! I have never understood the reason to care about "on the wheels sag" as I can't see the importance of it.
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August 14th, 2018, 02:13 AM   #39
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it is an indicator that your spring is too hard or too soft but it is better to check how much the spring is preloaded. i.e. if it came 260mm long and it is now 245mm then that is far too soft. the spring on a PDS system wants to be around 2-8mm crushed wheels free or in the vice if you like.

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August 14th, 2018, 02:38 AM   #40
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Originally Posted by Alan View Post
FFS you twit! Can go down to 4mm if you wish!

https://www.computrackboston.com/KTM...0-190-5-bk.htm
Holy thread Hi jack

You sure that spec referenced doesn't refer to adjusting the standard offset by 4 or 6mm ?

On the KTM tard I had, the offset was adjusted by 6mm
WAS 20mm
IS 14mm via billet clamps.

I think there was also 22mm offset standard with 16/18 as an option (again adjusted by 4/6mm)

Worked a treat, although had to be gentle on the big 576 stroker whiskey throttle and all :-0

Last edited by 383hq; August 14th, 2018 at 02:45 AM.
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