Author Topic: K75S Wider Rear wheel and Radial Tyre  (Read 5777 times)

Offline aces59

  • Motobrick Curious
  • Posts: 46
K75S Wider Rear wheel and Radial Tyre
« on: June 12, 2017, 07:04:58 AM »
I’m sure this has been done before but this post is to document my fitting of wider wheel and radial tyre to a 1993 K75S
Old combination – 3 x 17 - 3 spoke wheel – Maxxis 130-90-17 tyre
New combination 4.5x18 - 3 spoke wheel – Bridgestone 160-60ZR18 tyre
I believe the new wheel is standard on K1100RS, K100RS and K1.
I had it powder coated and modified it to fit a right angled valve.
The new tyre is 20mm wider than the old one and 12mm smaller diameter (as the old one is very worn that’s probably nearer 20mm 
Theoretical sizes from a web based calculator (https://www.rbracing-rsr.com/tirediamcalc.html)
130/90/17 = 666mm   160/60/18 = 649  Which gives 17mm difference or about 2.5%
Also I believe the new wheel centreline is 12mm further away from the diff mounting face.
Comments on fitting.
Firstly and most important the new wheel and tyre bolts up and fits in place of the old one. There is about 4mm clearance between the swingarm and tyre when using the standard 2mm spacer.
The existing stand does not fit. A K1100 stand does not fit. In both cases the left hand leg needs modifying.
Stand Modification
I chose to mod the existing stand. Basically I bent the left leg out, cut a piece out of the bottom and welded it back up again. I chose to cut out the cross brace then weld a new one in afterwards. I would recommend you could probably get away without doing this and avoid issues re-aligning the top pivot bushes. Note you can take the opportunity to fit grease nipples by tapping the existing holes M6
I also moved the silencer out about 8mm by cutting its support bracket stubs and adding some washers. Again this might not be absolutely necessary.
You do not need to remove the brake caliper or lift the bike to fit the wheel. It’s far easier to remove the silencer. If everything is greased up with new clean fasteners it comes off easily.  Wheel slots straight in and wheel bolts are also easy to get at.
  • Bucks - UK
  • 1993 K75S, 1972 A65

Offline aces59

  • Motobrick Curious
  • Posts: 46
Re: K75S Wider Rear wheel and Radial Tyre
« Reply #1 on: June 12, 2017, 08:20:05 AM »
Here's a couple more photos.
Showing clearance between the stand and new tyre. Also showing the modified stand - with a standard K1100 one for comparison
Cheers
  • Bucks - UK
  • 1993 K75S, 1972 A65

Offline know_fear

  • Motobrick Curious
  • Posts: 31
Re: K75S Wider Rear wheel and Radial Tyre
« Reply #2 on: June 12, 2017, 12:09:34 PM »
How does the bike feel when cornering with that larger tire? Does the centerline  of the rear wheel being 12mm to the left cause any issues?

  • BC Canada
  • '85 K100RS, '69 Norton Commando
Know fear,have kids.

Offline aces59

  • Motobrick Curious
  • Posts: 46
Re: K75S Wider Rear wheel and Radial Tyre
« Reply #3 on: June 13, 2017, 02:57:17 AM »
I'm not an 'enthusiastic' rider so can't comment on life at the limit but it all feels fine so far - absolutely no discernible effect in terms of bias one way or the other
Steve
  • Bucks - UK
  • 1993 K75S, 1972 A65

Offline Blunderbust

  • Motobrick Curious
  • Posts: 27
Re: K75S Wider Rear wheel and Radial Tyre
« Reply #4 on: June 13, 2017, 05:12:41 AM »

Nice job, what are you doing with the K1100 stand? I am looking for one, for my bike. if it is for sale please let me know. Thanks.

  • Norfolk, UK
  • 1984 K100

Offline aces59

  • Motobrick Curious
  • Posts: 46
Re: K75S Wider Rear wheel and Radial Tyre
« Reply #5 on: June 13, 2017, 05:51:48 AM »
Sure - Do you want the sidestand strengthened?
Perhaps you could send a private message and we can sort it out
Steve
  • Bucks - UK
  • 1993 K75S, 1972 A65

Offline rbm

  • ^ Quintessential Motobricker
  • Posts: 2281
Re: K75S Wider Rear wheel and Radial Tyre
« Reply #6 on: June 13, 2017, 10:03:10 PM »
I've fitted Bridgestone T30 Battlax 110/80ZR-18 on the front and Bridgestone T30 Battlax 150/70ZR-17 on the rear.  Same rims I believe.  You'll come to regret fitting the right angle valves though.  I had multiple air leaks on mine until I replaced them with straight valves.
  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline aces59

  • Motobrick Curious
  • Posts: 46
Re: K75S Wider Rear wheel and Radial Tyre
« Reply #7 on: June 14, 2017, 03:02:21 AM »
Thanks for that comment Rob. Your rear tyre should be closer to the original rolling diameter.
I will watch the tyre pressures. Did you machine the rim to fit the valve? I couldn't fit one originally as the central spine got in the way.
Steve
  • Bucks - UK
  • 1993 K75S, 1972 A65

Offline aces59

  • Motobrick Curious
  • Posts: 46
Re: K75S Wider Rear wheel and Radial Tyre
« Reply #8 on: July 11, 2017, 10:29:19 AM »
Rob - Just noticed - not that it matters - You have 17" rear 18" front - Mines 18" rear 17" front
And for the record - My stand mod works OK except that its a bit more difficult to lift onto now.
Cheers
Steve
  • Bucks - UK
  • 1993 K75S, 1972 A65

Tags: