tires on R80RT?

[sbosbach141157]

I have recently purchased a lowered 1983 R80RT where the upper attachment point of the Koni shocks were moved forward two inches, front forks slid up in the triple tree 5/8 inch. The bike came fitted from the PO with a Dunlop 491 (110/90 B18 61H) rear tire in combination with a Metzeler Marathon 110/90 57H 19 front. I measured the actual widths and profiles of both tires fully inflated with no weight on them. Actual widths were 112 and 102 mm respectively. Actual profiles were 85 and 77mm respectively. Both tires have tread depth around 2-2.5 mm and are only a couple of years old. I'm running 37 PSI rear and 35 PSI front with two up.

OK, so much for background. My riding from years ago on Honda's tells me the bikes handling is not right. There is a strange disconnection from the road feeling, as if the bike was "skating" or slipping around momentarily. This seems especially noticeable by my passenger, enough so that she is leery of riding two up until I get this fixed. I also have a leaking steering damper, but there is no sign of head shake or wobble, just a vagueness about the directional line, as if the bike were not firmly planted on the pavement.

Being new to BMW, I need some experienced opinions before I go replacing tires and parts.
Steve Bosbach in Austin, TX

 

[shire2000]

Well, a good start might be to reattach everything back where it started. i.e., Forks back to proper height, and move the shocks back to proper placement. With the shocks leaned forward, it will definitely alter the handling characteristics.

Once done, take the bike out for a ride to see if the problem persists.

If it does, then check out all suspension parts. Forks, Fork oil, etc. Rear shocks and springs. I would almost bet the problem is the rear shocks.

I had a similar issue with my R100RT in that the back end felt like it wanted to go it's own way. Was especially a problem in the wet and corners. I replaced the old shocks with some nice new Progressives and now it handles like it is on rails. What a huge difference.

Good luck and take it one step at a time.

 

[grumpyone]

Definately

We found it is a real issue with the suspension on these girls. We had a R 80 that would handle like it was on water from the shock just being set to light I cant even imagine what the ill effects are from re positioning it in the frame
Remount and restore to original and Id say your probally going to have to spend a couple $ and replace the spgs and shock.
Good luck ; we all need it on these girls but their worth it
Jim and Esther

 

[35303]

Also look for dried steering head bearing grease and adjustment.

 

[sbosbach141157]

Thanks for the suggestions. I will make one change at a time and sort this out. The bike came with Koni's on it already, but they are leaned forward two inches and set at their softest setting. I'll try some pre-load first and see what happens. Then I'll start putting things back in their original locations. Thanks again.
Steve
83 R80RT

 

[sumran]

I wonder what the arc of the swingarm looks like against the original shock mounting position. I suspect that if you took a piece of wire and put one end at the swing arm pivot and one end at the lower shock mount, that it would go to the original upper shock mounting if you pivoted it up. If that geometry changed at all, you would be moving the shock around instead of compressing it. Not a happy circumstance.

 

[lkchris]

There is a strange disconnection from the road feeling, as if the bike was "skating" or slipping around momentarily.

Perfect description of the Dunlop 401--worst tire ever made.

Of course, the frame configuration modifications don't help either, and should be returned to original.

 

[sbosbach141157]

Kent,
Thanks for the confirmation that it might be the rear tire. The Dunlop is a 491, and I just posted another thread asking about date codes. The Dunlop is easy to read, but the Metzeler dot code ends with X101d. Do you know how this should be read? The Dunlop ends in 0201, so the tire will be swapped out.
Steve

 

[boxerkuh]

When I bought my 86 a couple of years ago, it had the wrong tires on it front and rear. I had a bad wobble. Once I mounted the correct tire size, new tires and checked the head bearings, all went away. It was like a new bike. That said, our airheads don't like frame, suspension changes that may lead to different angle's in the motor, tranny, shaft, and rear-end... I would put everything back to stock, and new rubber and you will have a whole new bike. Best of luck.

 

[jforgo]

Avon AM26's are available in the correct sizes as per your owners manual - and are also designed for dealing with both rain and rain grooves.
I bought a bike with freshly-shod Kenda's on it - rode into a downpour - they performed very poorly.