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Author Topic: "Wobbly" DR650 - Is it the tyre?  (Read 607 times)

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Offline swartspan

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"Wobbly" DR650 - Is it the tyre?
« on: November 14, 2010, 10:10:23 am »
Morning guys and girls

I took delivery of my DR650SE yesterday after shopping around like crazy.

I had new tyres fitted and chose the Mitas 07's after reading about them on the forum.

When I reach 120km/h now, the bike's handlebars starts wobbling like crazy (really scary) and keeps at that until I slow down to 100km/h again.  It also gets progressively worse if I do not slow down (throttle down).

Can it be the tyres?

The problem is that I have nothing to compare it to, meaning I only got it yesterday.

Should I worry?

SwartSpan
 

Offline columbus

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Re: "Wobbly" DR650 - Is it the tyre?
« Reply #1 on: November 14, 2010, 10:28:28 am »
By wobble, do you mean tank-slapping? If its tank-slapping try adjusting the rear suspension lower.
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Offline NoobRider

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Re: "Wobbly" DR650 - Is it the tyre?
« Reply #2 on: November 14, 2010, 10:31:42 am »
It could be the tyres but I suspect you have to much pre-load on the rear shock or not enough on the forks. I would try reducing the pre-load on the shock. if that does not help get some pre-load spacers make for the forks.
 

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Re: "Wobbly" DR650 - Is it the tyre?
« Reply #3 on: November 14, 2010, 10:37:57 am »
Is your bike lowered?  The lowered DRs often experience head-shake.

You could try reducing the tyre pressures to 1.5 or 1.8 bar and see if that makes a difference.

Oh, are the tyres properly seated?
 

Offline Wolweseun

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Re: "Wobbly" DR650 - Is it the tyre?
« Reply #4 on: November 14, 2010, 11:41:09 am »
By wobble, do you mean tank-slapping? If its tank-slapping try adjusting the rear suspension lower.
That would be a wobble a tank slap is violent and is what happens just before you hit the ground

Check tyre pressures
Get someone to setup your suspension properly setting the rear sag is one of the most important initial suspension settings
Try your original front tyre
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Offline swartspan

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Re: "Wobbly" DR650 - Is it the tyre?
« Reply #5 on: November 14, 2010, 01:11:51 pm »
Thanks guys

I guess "tankslapping" is what I experience

I did have the rear suspension upgraded before taking delivery due to my "size". - guess - should have the front done as well then?  The shop delivering the bike forgot the manuals so how do - adjust the front suspension?
 

Offline Rocstompa

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Re: "Wobbly" DR650 - Is it the tyre?
« Reply #6 on: November 14, 2010, 07:15:56 pm »
Same problem with the E 07 it feels as if you have a flat tyre am going to try running them harder or re balanced.
 

Offline bike bum

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Re: "Wobbly" DR650 - Is it the tyre?
« Reply #7 on: November 14, 2010, 07:29:15 pm »
Had the same issue with new Heidi front tyre. was sorted after 500km, don't ask me why.
 

Offline Roof of Africa

Re: "Wobbly" DR650 - Is it the tyre?
« Reply #8 on: November 15, 2010, 04:59:02 am »
Have the same with my BMW X Challenge and it is really bad since I put a Dunlop knobbly on the front, You can  normally "ride through" it. ie it disappears after about 140 but it is a bit scary the first couple of times!
 

Offline swartspan

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Re: "Wobbly" DR650 - Is it the tyre?
« Reply #9 on: November 15, 2010, 06:11:24 am »
Eisch!!!  Ride through it??!!

@#!!;@@#. Fark!!!


 

Offline lecap

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Re: "Wobbly" DR650 - Is it the tyre?
« Reply #10 on: November 15, 2010, 07:56:37 am »
Primary suspect rear shock. I assume it was you asking me about the spring?
Which spring did they end up putting in and how did they set the preload?

I'd recommend to get the rear shock setup sorted first before checking and modifying anything else.

Re. the front end: The OEM springs are quite lekker progressive (precisely spoken twin rate) ones and work well for the average rider.
Do NOT use additional preload spacers on twin rate or progressive rate springs unless you really know what you are doing (means unless you've calculated the spring)! Not for the OEM ones and also not for aftermarket ones!
The twin rate spring is supposed to work primarily on the soft part when riding normally. The soft part of the spring goes coil bound just below your normal supension sag making sure your ride is comfortable and the nose does not dive excessively when you drop anchor.
If the springs are too soft and you increase the preload on the spring the soft part will go coil bound too early, you basically convert the spring into a linear rate one. Not what you've paid for :-\
You can calculate the takeover of a twin rate spring where the soft part goes coil bound. Ideally your sag should be some 30% whilst yourt takeover of the spring should be at about 40% - 50% compression. Preloading the spring will not only reduce the sag (this is what you want) but also take the takeover further up (this is what you don't want assuming the spring is correctly sized for the bike).

If your front is too soft you have various options:
Linear rate springs: Cheapest. Relatively easy and quick to get. (you can often find and adapt suitable MX bike fork springs).
Disadvantage: You have to go relatively hard with the initial setup to keep the bike from bottoming out and diving excessively. Not an issue with an MX where lap times & best match of spring and damper count but somewhat less than ideal on a DS bike which you might wish to ride all day and over 100's of km's.

Progressive / twin rate aftermarket. I've been selling them for close to 20 years and still have to see a bike where they don't make an improvement.

Progressive / twin rate custom build in the unlikely case that the above does not work. IMHO this will only be the case if the rear is too stiffly sprung and you can't get the preload set correctly.

One more thing about preload spacers and fork springs:
Always calculate the block length of your spring & spacer assembly and make sure it's less than the space between the bottomed out damper piston and fork cap. If it isn't and you bottom out your forks you will convert them into scrap metal. You will most probably destroy your damper rod and damper piston in this bottom out, the forks will with all likelihood not rebound and about 0.3 seconds later you will be able to see your rectum from the inside :-\

A few more notes:
It is not true that low suspension setting DR650SE's are tendencially wobbly. Not if you follow procedure and lower the bike according to factory spec / the workshop manual. Most workshops don't and that's where the problem starts ::)

Check the steering head bearing on your new DR650SE. All my seven DR650's came fron the factory with grossly overtightened steering heads. This wioll cause poor handling and lack of steering precision, high speed instability and it will destroy the bearings within 10,000km - 15,000km. And yes they are expensive and expensive to replace.

Ride knobblies a bit harder than factory spec especially at high speeds and on hardpack and tar. I found 1.7 bar (front) and 2 bar (rear) to work very well on my DR's. Keeps the bike stable up to top speed and helps tires to run cooler and last longer. I don't run my DR's softer than 1.7 bar at all as I don't do endless and bottomless sand. Works well for me and I never dinged a rim. Use it - don't use it. If you're big (I think you are) you can go a tad higher with tire pressures to account for more wheel load (1.8 / 2.3bar).

If all the above is set and in spec. and the bike still wobbles check if the front wheel is fitted correctly (tighten axle first then tighten clamp), the rear wheel is fitted straight (both issues I would recommend to check on a new bike ::) ) and that the wheel bearings are ok (no issue on a new bike).

Don't think "ride through it" is the solution to suspension problems.
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Offline Rooikat

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Re: "Wobbly" DR650 - Is it the tyre?
« Reply #11 on: November 15, 2010, 08:56:46 am »
I had the same experience on my CB900F after fitting a new front tyre. Used to ride
through it, would settle after 160 km/h, but really scary. No trecommended. Took me
a couple of weeks to find out that the wheel spacer hadn't been tightened enough,
allowing just 1/2 mm free play - too much.
Check the seating of the tyre - most likely cause. If that doesn't work, follow lecap's
advice. Good luck!
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