Low tyre pressures?

[Biggles08]

can to low tire pressures in a front tire cause the suspension to shake under hard braking from speed??.
I have just put a set of ah12 dunlops on my race bike and ran 27r and 27f hot last weekend at ruapuna for the first time and noticed the front end shake\pogo a little under brakes at the end of the straight under brakes.
I ran the front at 25 yesterday on the b track to see if i could get more grip and thinking about it now i was getting a little shake into the hairpin.
Just wondering if the pressures are to low and deforming the tire badly under brakeing causing the chatter.
I diddnt notice anything like that with the power ones i had on before at 27 hot front.

Shaking under braking is usually caused by your front discs being warped...I have had very few race bikes in which the brakes don't shake a bit from hard braking...if its not too bad just ignore it. Also, 'pogo' or a heavy 'shake' under very heavy braking is probably you bottoming out your suspension on the rubber...when you don't have enough preload you will use all your fork travel and bottom out making your front tire start to give instead of your front suspension...this can feel somewhat un-ideal. Does it reduce shaking when you let the brakes off a bit when its doing it? If so this is the culprit.

On Dunlop 211GP's I was running rear 20Psi and front 28Psi hot off the track. 27 both front and rear isn't too low I wouldn't imagine...but I don't know what ah12 Dunlops are so couldn't comment.

[kiwi cowboy]

Shaking under braking is usually caused by your front discs being warped...I have had very few race bikes in which the brakes don't shake a bit from hard braking...if its not too bad just ignore it. Also, 'pogo' or a heavy 'shake' under very heavy braking is probably you bottoming out your suspension on the rubber...when you don't have enough preload you will use all your fork travel and bottom out making your front tire start to give instead of your front suspension...this can feel somewhat un-ideal. Does it reduce shaking when you let the brakes off a bit when its doing it? If so this is the culprit.

On Dunlop 211GP's I was running rear 20Psi and front 28Psi hot off the track. 27 both front and rear isn't too low I wouldn't imagine...but I don't know what ah12 Dunlops are so couldn't comment.

Hey Biggles, thanks for the reply,

no its not the brakes i dont think as i have had that befor and it comes through the lever.

This seems to come on after i have been on the brakes for a second or so and i didnt notice this with the power one i had on before.

I only had 25-hot off the track and with the a12h being a harder carcase tire i wonder if that was too low and made the tire deform under stress from braking and crinkeled on the sides causing shudder.


Its hard to explain but it isnt there "bang" when i hit the brakes but sort of comes on after being on them for maybe a second and then it sort of comes in from just noticeable to a shudder and come right after i let the brakes go so maybe suspension but then why did i not get this problem with other tires?.

[Ocean1]

Just a thought, check your steering head bearings, a bit of play there can cause this.

If that's OK it might be a disk or pad issue, and they can be hard to nail down. Big thing is to change just one thing at a time eh? Take the disks off and lightly sand them all over. Clean 'em with brakeclean and test ride. If there's any change you're in the right area, if it's different but still not OK then clean the disks again and try different pads.

Luck mate.