Rear tire wear = Front end wobble/shimmy on the Forza 300?

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MBMyer
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Rear tire wear = Front end wobble/shimmy on the Forza 300?

Post by MBMyer »

I'm just going to tell this story in case anyone else has had a similar thing happen. I'm wondering if this is known lore or whether I still have a second issue that I need to find.

I've been riding the Forza for 18 months now, but only have about 4650 miles (7500 km) on the odo. Despite my Iron Butt days, I'm clearly just a commuter now, which is exactly why I downsized to the NSS300. Back in September, when I had ~3700-3800 miles on it, I started to notice a front-end wobble (or shimmy) at around 25 mph (40 kph). Since the road on which I live is marked at 25 mph, and since my 5 mile (8 km) commute to work involves streets flagged for 25 (40), 30 (50), 35 (55) and 40 (65) mph (kph) and lots of turns/corners, I have often found myself this semester having to apply a bit of pressure to the handlebars in order to fight the wobble when making a turn, since they normally happen at around 25mph/40kph. As the semester has gone on, the wobble started happening down as low as 15 mph / 25 kph.

Also during the semester, I noticed that the center of my rear tire (stock Dunlop) was going bald. So I knew that I was going to have to swap it out. I read the experiences with various tires of people here on the forum, and settled on trying the Michelin City Grip in a 150/70-13 size, but had to find the right time to get the thing changed. (Finding time to do things / get things done is not easy on a teacher's schedule here in The States.)

The front end wobble on the Wing was a design problem that was ameliorated (but never entirely eradicated) by replacing the upper & lower steering stem ball bearings with tapered bearings. But the wobble on the Forza was getting worse as time went on. In my head, I was running through a whole list of things I was going to have to try over Christmas break to get rid of it.

But then, just a couple of days ago, I had my thoroughly worn-out rear tire changed (stock Dunlop at 4613 miles / 7427 km). And now the wobble is gone. The handlebars stay straight & steady at all speeds from 0-75 (0-120), even when I lock the throttle and take my hands off of them.

So, there it is.

Has anyone else had this experience? Does your front end develop a wobble as your rear tire wears out? Is this a weird design artifact native to the Forza that I can use to tell me when a rear tire is dying? Is it something particular to the way a rear Dunlop for this bike dies? Or should I be looking for some other factor on my particular bike that ought to be corrected?

Curious,
Michael
Current ride: 2014 Forza bought new in mid-2015 with only 15K on the clock
Traded in: 2003 GL1800 with 152K and several IBA rides on the clock
6 other previous bikes
nearly 3/4 million miles logged
now just commuting instead of touring
davenowherejones
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Re: Rear tire wear = Front end wobble/shimmy on the Forza 30

Post by davenowherejones »

I would check the bolts at the top of the forks. I think the factory spec is not quite tight enough. But there is supposedly a problem if they are too tight. I just use a short wrench and get them weakling tight so that they no longer turn.

Also check the air pressure in the front tire. The pressure is on a sticker inside the seat case.

My front wheel has a slight dent in the front wheel from the previous owner. It does not appear to be a problem after 36,000 km.

I also had a spacer put in the front forks. I THINK it helps?

Supposed to snow tomorrow so I don't no if I get my Sunday breakfast run?
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Re: Rear tire wear = Front end wobble/shimmy on the Forza 30

Post by gn2 »

MBMyer wrote:Has anyone else had this experience? Does your front end develop a wobble as your rear tire wears out? Is this a weird design artifact native to the Forza that I can use to tell me when a rear tire is dying? Is it something particular to the way a rear Dunlop for this bike dies? Or should I be looking for some other factor on my particular bike that ought to be corrected?
Yes, its perfectly normal for worn out tyres of all brands to misbehave and my Forza has also done this.
Relax and enjoy the ride.
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Re: Rear tire wear = Front end wobble/shimmy on the Forza 30

Post by Ole »

Do you have a top case on your Forza? If I put too much beer and groceries in my top case, my front end gets wonky on a rough stretch of road nearing my home. If I put the beer and grub under the seat, the bike handles fine on the same piece of road.
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Re: Rear tire wear = Front end wobble/shimmy on the Forza 30

Post by gn2 »

Ole wrote:If I put too much beer and groceries in my top case, my front end gets wonky on a rough stretch of road nearing my home. If I put the beer and grub under the seat, the bike handles fine on the same piece of road.
Again, that's exactly as you would expect.
Heavy items should never be put in a top case.
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Re: Rear tire wear = Front end wobble/shimmy on the Forza 30

Post by davenowherejones »

I am surprised how little weight in my top case affects my Forza riding. Mind you my 55 litre top case is way behind my rear wheel.

The handling changes so much that I have decided I am never going to put a girl on the back of my motorcycle. It is just not worth it.

Snowing today, ride safe.
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Re: Rear tire wear = Front end wobble/shimmy on the Forza 30

Post by gn2 »

Girl on the back won't affect it as badly because the weight will mostly be between the axles.
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Re: Rear tire wear = Front end wobble/shimmy on the Forza 30

Post by you you »

Ditch the beer and groceries. Keep the girl.
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