Question about tires size. (not tire thread)

[georgesgiralt]

Hello !
I've bought a set of Michelin Pilot Activ for my R65.
The rear is an 4.00 H18 but the front does not exist in Imperial size. So I bought a 90/90 H18 size.
I find the handling peculiar. The bike seems to fall when I'm cornering and I've to force it up when returning on strait trajectory.
So I wonder if it is wise to mix Imperial and metric sizes ? Or is it something else ?
Many thanks in advance for your help !

[Bob_Roller]

Do you have an R65 owners manual ??
I've checked the three owners manuals I have and the BMW shop manual and they all have 3.25-18 for front and 4.00 -18 or the rear tire .
No metric sizes .
I do know, that the narrower the front tire, the handling becomes more sensitive .
You may have to experiment with tire pressures, to see if that may help .

[Barry]

My guess would be it's the effect of 90/90 on what is a narrower than optimum 1.85 is rim. The usual fitment charts show a 2.15 being optimum for a 90/90 chart. True the same chart shows 2.15 being optimum for a 3.25 as well but there may be subtle differences in the shape of the mounted tyres.

What I'm suggesting is there is not much difference in width between the tyres (my 3.25 measures 95mm wide) but when mounted on a 1.85 rim they may be different enough in shape for the 90/90 to feel likes it's falling into bends.

[georgesgiralt]

This may explain why it was so difficult to mount !
There is no 3.25 H18 tire in the Pilot activ range.
This is why I bought a 90/90 -18 ...
(but there is a 3.25h19 ...)

[R65Guy]

I'm running Avon RoadRiders in the 4.00 and 90/90 combination and am very happy with the turn in and exit.  A little crisper turn in than the original but it still tracks great all the way through to the exit.  The last time I had vagueness in the turns I tracked it down to some minor stiction in the front forks.  Good luck sorting it out.

Neal

[DadsR65]

Hello !
I've bought a set of Michelin Pilot Activ for my R65.
The rear is an 4.00 H18 but the front does not exist in Imperial size. So I bought a 90/90 H18 size.
I find the handling peculiar. The bike seems to fall when I'm cornering and I've to force it up when returning on strait trajectory.
So I wonder if it is wise to mix Imperial and metric sizes ? Or is it something else ?
Many thanks in advance for your help !

A word of warning...I could never get a Pilot Active to seat on my rear rim (neither could a shop).  I tried two different tires and finally gave up and put on a Avon Roadrider (took 10 minutes to install).

I left the Michelin on the front.  It was tough to seat, but worked finally.

[georgesgiralt]

Well, I was luckier. The rear seated at once and perfectly. But it took me two tubes and the help of a machine to have the front properly installed and the tube not pinched dead...
Both where easy to balance, though maybe it has to do with quality control or better manufacturing process ?
As they said, you mileage may vary !

[MikeFossl]

I usually notice "quicker" steering when switching out my front tire.  The rounder profile of a new tire seems to have that effect but it quickly disappears after you get used to it.