unstable at high speeds - MVAgusta.net
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post #1 of 16 (permalink) Old 04-24-2010, 09:43 AM Thread Starter
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unstable at high speeds

i hope somebody can help me with this question:

i recently put new tires on my brutale 910 R, Pirelli Diablo Supercoras SP; 120/70 front and 190/55 rear. now before i was using for a long time the 190/50 michelin power pilot. now the bike feels unstable with the front tire at speeds above 200 km/h (it feels the sameway as is the front tire is about to wheely). is this the just the new tires, or can be something wrong with the mouting/balancing of the front tire.
and what are the best solutions?

- lowering the bike in the back to compensate the "higher" tire?
- steering damper?

thanks all for the help.
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post #2 of 16 (permalink) Old 04-24-2010, 10:03 AM
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I would consider a full control and check if all has been mounted correctly; or might be just a wrong balancing

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post #3 of 16 (permalink) Old 04-25-2010, 02:24 AM
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Check tyre pressures, I have found so many blokes fit a tyre and leave it on silly high pressures, for the road to start at 32/34 psi will do, I used to run the front at 30psi on my Brutale and about 34psi at the back.

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post #4 of 16 (permalink) Old 04-25-2010, 03:13 AM
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Definately start with a balance re-check. If slightly off you wont feel a thing until you reach the speeds you mentioned.
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post #5 of 16 (permalink) Old 04-25-2010, 04:52 AM
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Id check they have been fitted correctly, the correct rotation and balanced- its ball ache but better safe than sorry.

I run exactly the same tyres....

Mine felt as thought the rear was washing under me so iv tried all sorts of pressures to rectify this-

The pressures that work on my F4 750s are 34 front 39 rear- it may sound high but its stable as and im scrubbing right to the edges. The front tyres saved my ass a few times- super sticky rubber

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post #6 of 16 (permalink) Old 04-25-2010, 03:47 PM Thread Starter
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thanks all for the advice. i am running exactly the recommended tire pressure by pirelli for this tire and bike; which is 33.3 psi (2.3 bar) front and back. so i will check back with the shop for balancing, as i am planning a track day, but really dont feel safe to hit the high speeds.
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post #7 of 16 (permalink) Old 04-25-2010, 04:11 PM
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Quote:
Originally Posted by firedancer View Post
i hope somebody can help me with this question:

i recently put new tires on my brutale 910 R, Pirelli Diablo Supercoras SP; 120/70 front and 190/55 rear. now before i was using for a long time the 190/50 michelin power pilot. now the bike feels unstable with the front tire at speeds above 200 km/h (it feels the sameway as is the front tire is about to wheely). is this the just the new tires, or can be something wrong with the mouting/balancing of the front tire.
and what are the best solutions?

- lowering the bike in the back to compensate the "higher" tire?
- steering damper?

thanks all for the help.
lowering the back will raise the front making it more unstable, is it not that the tyre profile is now that of a new tyre and you had become accustomed to the slower steering profile of a worn tyre?

My thoughts are this is what you are experiencing

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post #8 of 16 (permalink) Old 04-26-2010, 05:32 AM
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Quote:
Originally Posted by Badger View Post
lowering the back will raise the front making it more unstable, is it not that the tyre profile is now that of a new tyre and you had become accustomed to the slower steering profile of a worn tyre?

My thoughts are this is what you are experiencing
Actually the opposite: Lowering the back increases rake. This has the effect of slowing the steering...i.e. more "stable", but harder to turn in.

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post #9 of 16 (permalink) Old 04-26-2010, 06:54 AM
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Getting tooo technical guys

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post #10 of 16 (permalink) Old 04-26-2010, 07:21 AM
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Actually the opposite: Lowering the back increases rake. This has the effect of slowing the steering...i.e. more "stable", but harder to turn in.
Me bad, yes it does make it more stable, it had been a long day yesterday and me brain was not working as it should, i meant to put across that it will want to run wide on corners, thanks for the correction mate

Still reckon the tyre profile is a probability

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