Tire size & Frame Geometry

[RAT900]

2002 Monster 900ie

Ok so I changed out my tires from 170/60 rear to 180/55

front tire stayed the same went from 120/70 to 120/70

To what extent have I altered the weight distribution/ride height at the rear?

dropping 5 points on the rear aspect ratio (60 to 55) has, I am assuming, lowered the rear of the bike in relation to the front of the bike.

should I compensate for this change by moving the tubes up in the triple tree? or conversely raising the ride height adjustment rod at the back?

I guess what I am getting at is "what is the ideal "horizontal plane" (loaded or unloaded if that is more relevant) geometry of the machine?"

Am I looking for the bike to have a dead level ground clearance front to rear...let's say if I used the bottom seam of the crankcase as the index/measuring point to the ground surface

would I want the bike to measure XXXmm at the front of the crankcase seam as well as at the backend/rear of the seam?

would this be the starting point for subsequent setting of sag and preload etc?

[stopintime]

In theory, your change lowered the rear by 3mm.
I'd assume raising it accordingly is a good idea.

It's not required to have a level bike. Forward orientation makes the steering quicker/more nervous and invites you to have more weight over the front - both of which are usually good ideas on a Monster. Unless you're a cruiser wannabe...

When I got my new suspension, I suddenly had a much better geometry (better handling) - from that experience I always preach to have our bikes professionally set up for ourselves.

[RAT900]

In theory, your change lowered the rear by 3mm.
I'd assume raising it accordingly is a good idea.

It's not required to have a level bike. Forward orientation makes the steering quicker/more nervous and invites you to have more weight over the front - both of which are usually good ideas on a Monster. Unless you're a cruiser wannabe...

When I got my new suspension, I suddenly had a much better geometry (better handling) - from that experience I always preach to have our bikes professionally set up for ourselves.

I couldn't agree more on having the bike set up properly hence the posting....certainly not a cruiser wannabe...I'd buy a pavement scraper and beanie helmet if I was into all that

but you do get what I speak of regarding weight distribution...hell anyone who has carried a heavy object up a stairs with someone else knows they don't want to be at the low-end of that carry...so distribution of the mass has much to do with the static angle the bike sits at

My point is I kind of want to understand where the bike needs to start from geometrically before I start fiddling with increasing or decreasing pre-loadings to distribute the introduction of the additional weight of my carcass...

or am I chasing a ghost here that is immaterial and I should just start preloading/unloading (which I do not think is the right way to set-up a bike because I believe loading should really be inherently compensatory only for the rider weight and style of riding)

I understand there are more variables that play-in such as distance of the rear wheel from the pivot point, clip-ons vs. bars, etc

[Raux]

if you have the height adjustable rear. just raise it 3mm

[stopintime]

but you do get what I speak of regarding weight distribution...hell anyone who has carried a heavy object up a stairs with someone else knows they don't want to be at the low-end of that carry...so distribution of the mass has much to do with the static angle the bike sits at

True, very true. During my years in removals I learned that part of physics very well
That's why the bike should be set up with you on it, in your spirited riding position, with your unique weight distribution, foot pegs and grip position etc

My point is I kind of want to understand where the bike needs to start from geometrically before I start fiddling with increasing or decreasing pre-loadings to distribute the introduction of the additional weight of my carcass...

or am I chasing a ghost here that is immaterial and I should just start preloading/unloading (which I do not think is the right way to set-up a bike because I believe loading should really be inherently compensatory only for the rider weight and style of riding)

IMO it's not a ghost and it's not immaterial. My bike has been lowered 10mm up front and raised about the same in the rear.
That was a welcome change for me. Not radical at all, just a little more cooperative and the steeper steering angle hasn't spooked me yet (it did while I had the totally worthless Marzocchi non-adjustables though)

I think you might as well start by changing the geometry to see how that effects your riding. Then set up the suspension and get some experience. From there on it's minor adjustments, which you may or may not need/like/want

[Speeddog]

If you liked the way the bike was handling in general with the 170/60, then raise the rear 3mm.

Likely the 170 was worn out, and the 180 is new, so your ride height is probably the same as it was before...

[RAT900]

If you liked the way the bike was handling in general with the 170/60, then raise the rear 3mm.

Likely the 170 was worn out, and the 180 is new, so your ride height is probably the same as it was before...

actually the 2002 dated 170 dunlop sport max looked nearly brand new...

had been heat cycled with usage by the prior owner

and the bike sat unused for 6 or 7 years...and the rubber was looking hard, somewhat weathered and not worth gambling on

[devimau]

My suggestion to you will be to ride it as is first and concentrate on how the bike handles, then rise it how it was and try to feel and understand what the difference was compared to before and then so on.
that's the best way to learn, you can expect a very stable ride when the rear is low but might not be quick into turns and the other way around when raised.
start from there and post your updates so we can all help you with your best set up.

[Speeddog]

Thinking about this a bit more.

3mm is a pretty small change, IMO.
It's about half of what the front ride height changes between a full and empty tank.

I suspect most folks wouldn't notice if you snuck in their garage and changed the ride height 3mm.
On a racebike, maybe folks would notice.

[MotoCreations]

also remember that say 180/55-17 is a "general figure".  If you get various tires from different manufacturers with all the same width/aspect ratio and wheel diameter -- all the overall tire heights will vary by +/-10mm or more.

Thus although looking at the numbers is a good idea -- physically measuring height (or circumference) is an even better method in regard to tires.

[devimau]

speeddog, the 3mm difference you mentioned with fuel tank full will be in sag and not in ride height.
I also think that 3mm change will be almost unnoticeable for us "humans".

Thinking about this a bit more.

3mm is a pretty small change, IMO.
It's about half of what the front ride height changes between a full and empty tank.

I suspect most folks wouldn't notice if you snuck in their garage and changed the ride height 3mm.
On a racebike, maybe folks would notice.