Keith Code says the rear end of a bike rises under acceleration and suggests putting the front wheel against a wall and putting a little bit of power on to feel it happen.
Thing is, I can see my headlight go skywards when I accelerate.
What’s happening ? Is he talking about small throtle openings and I’m giving it a wrist full ? Can’t go and test it today, too much to do and wet and windy . . .
Thats confuddled me:hehe:
I was under the impression a bike squatted down at the back under hard acceleration. All except a Shaftie which comes up…yeeehaaaa:w00t:
That is a bit confusing. My old man described to me after a ride out we did with some of his mates about a year ago, all pootling on the motorway, he observed riding behind me that when I did full wind on acceleration the bike just seemed to squat for a split second, then bam, gone.
I thought it depended on the pivot point of the swingarm. When the chain pulls tight under drive it pulls the swingarm the easiest side of the pivot :blink:
Did that make sense? 
Surely your front still goes light due to weight transfer 
(just my opinion and I’m not a scientist :hehe: )
I’m trying to think what bike it was but there was one a few years ago that had the swinging arm pivot concentric with the gearbox sprocket. (May have been a bimota)It caused all sorts of odd things to happen with the rear end handling.
Thanks, Pete’s link does explain it pretty well. I need to read it several times before I think I’ve got it fully but it might mean that the rear sag on my bike is a bit too much, might need to adjust it for my weight, which hasn’t been done yet. Or it could be that KC is talking about a race bike that runs on perfect tracks not a road bike that needs to be a bit more compliant, or both :pinch:
Yslart - the idea behind setting static sag is to ensure that when you are sitting on the bike the suspension is in the correct “start position” ready to react to dynamic forces (bumps in the road and braking / acceleration forces)Symptoms of too much sag (Not enough preload applied) include:
The bike bottoming out over bumps.
Having to use excessive compression Damping to avoid the above.
At rear - ride height reduced making the bike turn slower.
HTH
I apologise for making several sensible posts. I’ve no idea what has come over me.
Thanks, that article suggests (if I’ve inderstood it correctly) that if the suspension is too low, so too much rear sag, the anti-dive aspect of the geometry won’t be working when it should, so the rear of the bike will dip under acceleration, just like a car. I’ve moved the mount point for the trailing arms on my car down 25mm to reduce the dip on acceeration and as Grim suggested the relationshop between the gearbox sprocket and the swing arm pivot is probably similar to that.
I think I need to try raising the back of my bike, which would make sense given it’s set for a generic 10 stone Japanse man and I’m considerably heavier
The front is also definately softer than it was last year, do forks bed in and get softer ? They’ve only done 10500 miles.
to adjust for your weight, you normally put a stiffer spring in the rear. jacking the rear puts more weight over the front (better turn in, but less high speed stability)
when you accel hard, the front forks extend, then the front tyre will lift off the tarmac depending on how hard you’re pinning it. if the rear is squatting, there will be an increased tendancy, but will happen either way
headlight will point up
Agree Johny, in the ideal world we’d all fit a spring weight to suit the rider, but how often does that happen with road bikes? I’ve only ever resprung one shock and one set of forks. So you are left with pre-load to adjust the sag.
Didn’t B sort your sussies out Slarty?
Would be not have set the sag for you?
There was a good article in Ride Mag a few months ago with a step by step guide to setting up your saggy bits. I’ve got it still and you are welcome to it if you want it.
true that, dont think most do, and I haven’t changed mine either, or changed the geometry really for that matter (got a 55 profile tyre on the back which raises things by 8-10mm i believe). not fussed to do it to the standard shock, maybe long term might upgrade mine to something flashy with the right spring in it for my heavy ass 
also need to be good enough to tell the difference (which i doubt i am yet 
)
think B ended up slapping the preload up nice and high on my r1 on the rear (think he said it didn’t really have a great range of adjustment and was still maybe a bit soft).
B did adjust my suspension and made it ride a lot better, I’m just trying to reconcile what I see happen with my bike (front rises under acceleration, rear sags) with what Keith Code says should happen. My bike isn’t reacting as KC says it should. Then again it’s a roade bike, not a track bike, but he’s adamant that I should see the rear rise under acceleration.
