Standard K100rs tyre sizes

[Andrew2]

  Just a simple question. What are the standard tyre sizes for my '87 K100rs please. It currently has a 100/90-18 Sport Demon front and a 11 year old 130/90-17 rear which I want to replace with a matching Sport Demon.
   The manual gives me a range from 130/90 to 140/80. The shop wants to sell me a 130/80-17. I'm looking at the 130 so is it an 80 profile or a 90 profile or doesn't it matter too much. I'm currently to the edge of the front with a good 15 mm left on the side at the back so was thinking a flatter 80 profile rear might even things out a bit. I'm asking in case there have been handling issues in the past with fitting a 130/80-17.


  Cheers
  Andrew

[rbm]

You can use a tire - rim sizing chart to determine the range of tire fitments that are compatible with the rim width of your wheel.  For example:





The tire profile ratio (eg. 130/80) will determine how far out your speedometer reading is from your actual speed.  The recommended ratio for the rim type (snowflake or three-spoke depends) gives the optimum accuracy on the speedometer reading.  There is a program called K-diag on the download section which will allow you to play around with different tire - rim combinations on various K-bike types and see their effect on the speedometer and odometer.

[Laitch]

Just a simple question. What are the standard tyre sizes for my '87 K100rs please.

Here is a simple answer. It's from the 1988 BMW K75/100 workshop manual available here as a download from the Repair Guidance section.


Your shop is selling you that tire because that tire is probably the only one they have to fit your bike. It will mount; it will roll. Your "even out things a bit" strategy eludes me, but a new tire should widen your margin of safety a bit. There are titanic threads on this site about tire size and performance. Paste this search term into your browser's Google search window and take a look. tire size site:motobrick.com

[Andrew2]

  Kind of condescending eh?. Did your read my question or just read the thread title. I referred to the manual and it gave me a couple of options .I also did a thorough search but if you type standard tyres etc you get a "titanic" amount of tyre threads which I spent some time going through but was not finding the info I was after so a "simple" question is all I asked. I always search before I ask. It would have taken you longer to type what you did than give a simple answer.
  By evening things out I mean a matching profile front and back where you get an even amount of use to the edge. My shop has the full range of sizes but I thought I would ask the opinion of experienced K riders before I bought one. Maybe I was wrong. I ask questions to learn and not make the same mistakes others have.
  I may be new to K series bikes but I've been riding for over 40 years and currently own 6 bikes ( 4 Ducatis and 2 BMW's ) and have done a lot of sport, touring and outback riding. I ride every weekend and also ride a bike for a living.

 Cheers
 Andrew

[Laitch]

I referred to the manual and it gave me a couple of options .

The manual gives you standard tire sizes. Popular tire sizes are a different consideration.

[Andrew2]

You can use a tire - rim sizing chart to determine the range of tire fitments that are compatible with the rim width of your wheel.  For example:





The tire profile ratio (eg. 130/80) will determine how far out your speedometer reading is from your actual speed.  The recommended ratio for the rim type (snowflake or three-spoke depends) gives the optimum accuracy on the speedometer reading.  There is a program called K-diag on the download section which will allow you to play around with different tire - rim combinations on various K-bike types and see their effect on the speedometer and odometer.

  Thankyou RBM :2thumbup: