1992 K75rt - 140/80 instead of 130/90?

[georgethegoat]

new to the forum,

so far best i've found out there.

i've read a few places that people are using 140/80-17 in the rear and 110/80-18 in the front on the k75 instead of the stock recommendation.

why? does it matter whether the bike is RT or not for this switch?

also i'm coming of of a pair of lazertecs and thinking about switching to BT45s. any $.02 on this are appreciated in advance.

[frankenduck]

One reason to do it is to run radials instead of bias ply tires.   You can get a Michelin Pilot Road 2 or Bridgestone 023 for the front and an Avon Azaro rear.

I'm about to switch my K75 to a Bridgestone BT023 front and Avon Azaro rear next month. (From Michelin Mac 50s.)

[georgethegoat]

awesome, thanks for the quick response.

is this tire pairing any better or worse for long trips? i'm doing coast to coast this summer maybe more.

thanks again your wisdom is invaluable.

[frankenduck]

awesome, thanks for the quick response.

is this tire pairing any better or worse for long trips? i'm doing coast to coast this summer maybe more.

What is this "tire pairing" of which you speak?

thanks again your wisdom is invaluable.

I have several ex-girlfriends who would disagree with you. :nono  (I used to be a lot more Type A when I was younger.)

[conybeare]

Does this switch to wider/lower profile tires require the newer style 3-spoke wheels? It looks like the 3-spokes are a bit wider than the older style wheels, as least in the rear... Front wheel looks to be the same width. I have the older style and I'm interested in making this switch/upgrade.

[frankenduck]

Yes, you'll probably want to get the 3x17 rear 3-spoke that came on the later K100s and the K1100LT.

[conybeare]

Paul Glaves says that using a 110/80 on the front would "slow down" the steering on the front a bit (http://www.bmwmoa.org/forum/showthread.php?t=9824) - has anyone noticed that? Just curious...

[frankenduck]

I'm running that combo now on my K75(Mich Mac 50 bias plies soon to be replaced by a BT023 and Azaro radials) and it rides just fine.

I'd guess Glaves' theory is that a tire with a lower aspect ratio will have a slightly larger contact patch and therefore take a smidgen more force to turn but  I doubt you'd even notice it. .I don't.


The wheels on my K75 are from a K1100LT:

Front: 2.5 x 18 running a 110/80-18
Rear: 3 x 17 running a 140/80-17

[CRASH]

I'd guess Glaves' theory is that a tire with a lower aspect ratio will have a slightly larger contact patch and therefore take a smidgen more force to turn but  I doubt you'd even notice it. .I don't.

Concur, "theory" being the operative word here.  Yes, physics says it will slow down your steering, now much and how noticeable depends on a lot of variables.  Since the Duck has actually done it and is not therorizing, I would tend top believe it would present minimal risk.

I have played with tire widths my entire life ... the only reason I could see even bothering to change to something non-specified is to take advantage of new technology (eg. Radials) or to deal with tire sizes that have been obsoleted.  If you don't go crazy on over sizing, handling is really not much of an issue for most.

[lukeman]

Does this switch to wider/lower profile tires require the newer style 3-spoke wheels? It looks like the 3-spokes are a bit wider than the older style wheels, as least in the rear... Front wheel looks to be the same width. I have the older style and I'm interested in making this switch/upgrade.

I run the 140/80V-17 on the older wheels without any problem as do other people.

[Scott_]

Just a word of warning to remember, be careful of a taller tire up front on a stock rim so you don't rip it up with the fork tree cover screw. (for those of you that have it)

[Roy S.]

One reason to do it is to run radials instead of bias ply tires.   You can get a Michelin Pilot Road 2 or Bridgestone 023 for the front and an Avon Azaro rear.

I'm about to switch my K75 to a Bridgestone BT023 front and Avon Azaro rear next month. (From Michelin Mac 50s.)

Looks like a good combo. Clearances look a little tight for a 3 x 17 wheel and tire (http://www.sporttour.com/shopexd.asp?id=1102 ) for the rear of an K75RT. Do you suggest any modifications? Such as shims to the wheel for frame clearances, or grinding off some of the center stand?