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Author Topic: How Large of a Front Tire  (Read 1434 times)

Offline marcmax

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How Large of a Front Tire
« on: April 25, 2011, 03:05:52 PM »
I know I will probably incur the wrath of the BMW purists but hey " No Guts, No Glory".

I have an 84 LS that I bought as a rolling parts caddy for the 82 LS that I rebuilt. I was planning on parting it out when I was done but don't have the heart to take another one off the road. I also don't want to re-invest in replacing all the parts I used. So...

I am turning it into a bare bones ride. Frame w/wheels, engine/trans,  tank, handlebars, solo saddle, headlight and taillight. Nothing else. The airbox is gone, the battery has been replaced with a smaller one under the bump behind the seat.

What I would like to know if what limits the tire size in the front. I know a 110 fits the rear and a 120 will fit depending on brand and how much you want to fiddle with remounting the wheel. What I want to do is run the same size tire front and rear. Since there will be no front fender for clearance issues will a 110 or even a 120 fit the front wheel? Is the actual wheel narrower and not able to handle the larger size?
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Offline Lucky_Lou

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Re: How Large of a Front Tire
« Reply #1 on: April 26, 2011, 02:17:15 PM »
Thers a thread on the tech section that will answer all your questions.
Lou
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Offline Semper Gumby

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Re: How Large of a Front Tire
« Reply #2 on: June 13, 2011, 10:00:51 AM »
On the narrow 1.85 rim, putting some thing larger than a 100/90-18 on the front becomes problematic.  The bead takes up so much space that once you get it on it becomes hard to get it off without destroying the tire.

In search of stability on my overloaded R65 I had, at one time, a 110/90H18 Micheline macadam turned around back wards on the front.  You should have heard the cuss words that came out of the tire guys mouth when he took it off.

On a naked bike the most you really need is 100/90-18.  

The problem is the rim is too narrow.  In order to get the proper profile (round cross-section) out of a 110/90-18 front tire you need at least a 2.5 inch width rim which is not possible on a stock R65.  Also if you do try to shoehorn a 110/90-18 on the front you will need to move the fender up.  I elongated the fenderholes with a drill to get more clearence between the oversized rear tire and the front fender.

My solution to this was to change out the entire front end.  I bought a complete 1988 K100 front end and wheel off fleabay and bolted it up.  (The steering head bearings are the same part number.)  So now I have a perfectly round 100/90V18 front tire on a 2.5 inch rim with Brembo dual disks for fantastic stopping power -- The 41mm (?) forks are Rock steady and lightning quick handling at speeds I don't care to mention here.

« Last Edit: June 13, 2011, 02:13:01 PM by Semper_Gumby »
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Offline marcmax

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Re: How Large of a Front Tire
« Reply #3 on: June 13, 2011, 03:59:43 PM »
Thanks! That is exactly what I was looking for. I am not worried about fender clearance as there won't be any (fenders that is). I was worried about what the wheel width would carry. What I really want is to have the same size tire both front and rear. I have a 110/90 on the rear of my current R65 and haven't had any issues. I did find a set of 110/80 tires and a set of 100/90 and 100/80 tires as well (both front and rear). Based on your experience I will probably stick with the 100/90's front and rear.
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Offline Semper Gumby

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Re: How Large of a Front Tire
« Reply #4 on: June 13, 2011, 04:12:30 PM »
The Norton Guys put the same tire on front and rear due to 19 inch diameter rims (front and rear).  I am curious how doing that on the R65 will change the handling - Less unsprung weight aft for sure.

There is one person on this forum who put on 4.00-18 Dunlop K70s front and rear.  He also removed the front fender.  I think he was down under in NZ or OZ.  He really liked that set up...

Until I found the K100 front end I was thinking about putting a R65 laced hub on the front with a 2.5 inch alloy rim and heavy spokes.  Then I would have had matching rim width for and aft.  R65 laced hubs are hard to find though...

Curious.
« Last Edit: June 13, 2011, 04:19:23 PM by Semper_Gumby »
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Offline montmil

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Re: How Large of a Front Tire
« Reply #5 on: June 13, 2011, 07:38:29 PM »
Quote
... There is one person on this forum who put on 4.00-18 Dunlop K70s front and rear.  He also removed the front fender.  I think he was down under in NZ or OZ.  He really liked that set up...

Motu rocks the K70s with his very cool flat tracker-look R65 with his custom 2-into-1 exhaust plus a host of other mods. Ab fab all the way.

Monte
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1983 BMW R65
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Offline Semper Gumby

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Re: How Large of a Front Tire
« Reply #6 on: June 15, 2011, 11:37:54 AM »
That's who it was.  Looks good on the front as well.  I guess the K70 bead is not a thick as the Michelin Macadam.   ::)
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Bill Gould ?1980/03 R65 When at first you don't succeed....Moo!
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