Wobbly handling - K-Bikes.com - Excellence in Motion
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post #1 of 8 (permalink) Old Jul 11th, 2010, 4:09 pm Thread Starter
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Wobbly handling

I picked up my new K75RT last Thursday and my initial impressions are that the bike feels "wobbly" - lacking directional stability - nothing making it unrideable 'tho.

The rear BT 45 tyre is down to 3mm wear limit in the centre .... do you think that is causing the problem?

Apart from that I love it!

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post #2 of 8 (permalink) Old Jul 11th, 2010, 5:10 pm
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post #3 of 8 (permalink) Old Jul 11th, 2010, 8:09 pm
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Tires are the primary suspect. Steering head bearings also can cause wobbleness, if either they're too loose or tight, or "notched" in the straight ahead position (then they need replaced)
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post #4 of 8 (permalink) Old Jul 12th, 2010, 3:38 am Thread Starter
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The head bearings seem to be OK...let's hope the new tyre does the trick!


If I had posted this sort of question on my favourite GS forum the stock answer would ahve been "they all do that"!
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post #5 of 8 (permalink) Old Jul 16th, 2010, 3:09 am
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Carefully check tyre pressures, too.

Mine behaves badly if pressures are out!
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post #6 of 8 (permalink) Old Jul 25th, 2010, 12:01 pm
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definitely check the pressures against the tyre manufacturer's recommendations - they'll probably be quite different to the one's BMW put in the manual 20-something years back.

Bridgestone say 36f 40r for BT45 on K75rt.

But as always the simplest way to improve a new old bike's handling is to ride it a lot..
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post #7 of 8 (permalink) Old Aug 12th, 2010, 9:21 pm
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Question.... Is it a wobble felt from the rear or from the front of the bike?

BTW :: Got my '88 K100RS back from my attorney and took if for a 486 mile one day ride this last weekend.

Reason I ask is because the feeling coming from one end of the bike or the other makes a great starting point to look for problems. Over pressured tires cause problems if they have been run too low on pressure and develope the odd wear pattern. (i.e. feathering, cupping, chop, and of course ridging due to wear on the outer edges and less on the center.) Also watch the tire pressures cold and not hot. Air expansion on a hot run then topping off actually leaves you underinflated. Tread depth differences change steering geometry and can make a bike feel a little wobbly.

Worn or mis-adjusted rear shock can cause problems. Too tight will cause the rear to push around on uneven surfaces. Too loose and the back sags thus taking the bike out of it's engineered suspension geometry. Fork springs worn out do the same thing. Worn fork bushings can cause the front tire to track or pull. Low/un-equal fluid in the forks will cause individual fork response different. (Thank God BMW puts fork braces on the tubes from the factory.)

And the steering head bearings being dry and/or loose can cause a wobble as well.

I found it best to start at square one with my K100RS when I got it, and make the mileage at time of purchase my start point for services and maintenance. Clymer has a nice schedule to follow for tires, lube, and general maintenance. I guess what I'm trying to say is perform as many of the checks and maintenance items as possible and see how the bike handles from there.
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post #8 of 8 (permalink) Old Aug 13th, 2010, 5:30 am Thread Starter
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I've put on a new rear tyre, changed front fork oil (10W) and ridden the bike more.

Whilst the steering/handling is a little top heavy in comparison to my GS the K75 seems to get very unsettled on bumps and this leads me to think that rear damping is shot?

I've been taking it easy until the new tyre is scrubbed (and waiting for some dry weather!)
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