120/70 vs. 120/65

[Nitro]

I was wondering if any of you has switched to /65 and what was the result.

I did it on other bikes and I always found improvements; mainly quicker response.

Cool

[Rapt]

I haven't tried a lower aspect tire, but it makes sense that lowering the front makes for a faster steering bike because you've effectively steepened the head angle, also less sidewall means less flex in transverse loading.

Same effect without reducing ground clearance is acheived by raising the rear via a shorter paralever link.

[Eron Flory]

Going to a shorter tire will do three things that raising the rear won't do.

1. It will reduce the weight at the outside of the gyroscope that is the front wheel/tire assembly. This will quicken the steering and be more noticeable the higher the speed.

2. Lower profile front tires are usually slightly narrower than the higher profile front tire of the same width. This will change the steering characteristic when leaned over since the contact patch is closer to the centerline of the tire, this is generally better for neutral steering.

3. The slightly smaller outside diameter of the tire means that the brakes will have slightly more leverage (same brake rotor diameter, smaller tire diameter=more braking power).

I have run 120/70 and 120/60 and prefer the feel of the 120/60 in every condition I have ridden in.

Eron

[SpaCovers]

One more advantage will be the greater ease of bending the wheel! Isn't that great?! Then you can buy some great aftermarket wheels. You have to bend the old ones to get the new ones if you are married.

[Eron Flory]

Originally posted by SpaCovers
One more advantage will be the greater ease of bending the wheel! Isn't that great?!

That is true, but if your shocks are valved correctly then your wheels won't be bent unless you hit something really hard. If you want to have a discussion on shock valving we should probably start a new topic. That isn't to say that BMW doesn't have a tendency to manufacture soft wheels though!

Eron

[jclark]

Well I bent both front and rear using 70's...

I will go for 60's on track-only wheels in future.

jeff
$1300ish later...

I don't doubt what you are saying, but if a 120/60 is so much better, why do BMW fit a 120/70?

Andy

[SpaCovers]

I think because BMW got rid of Jaq. Nassar before he did something like that. He went to Ford and did wonderful things there for the tire dept.
These wheels are way to soft for 60's for street use. This is coming from someone who has made two sets of the BMW round wheels into BMW square wheels. By the way the round ones rolls much nicer and vibrate alot less, I don't know why but thats just the way it is.

I have to say I have always prefered round wheels. So are you saying that you wouldn't recommend a swap to 120/60 for street use.

Andy

[Rapt]

I like my wheels round too, but so far I haven't had any problems with "bending" them. However in light of the problems others have had I'd be very wary of making any significant departures from the factory spec to sidewall height or tire pressures.