Triple clamp musings.

[Lucky Phil]

37 minutes ago, motortouring said:

O yes, you are right. This is because the steering head and fork are not parallel.

And I finally understand the difference between offset and rake.

[docc]

On 2/2/2022 at 10:19 PM, Lucky Phil said:

So here's my calculation docc. A std 1100ie Sport 26deg/45mm offset combination has approx trail of 96mm. If someone has the guaranteed actual figure let me know. Working on the same assumptions for fork length and front tyre OD a std V11 Sport with a 25deg/40mm offset triple also has 96mm trail. Now if you use a set of 1100ie Sport triples with 45mm offset on the V11 Sport so you get a 25deg/45mm offset combo you end up with 90mm of trail. A significant difference towards the "sharper steering" end of the spectrum. My 1198 has 30mm offset aftermarket triple clamps down from the std 36mm offset so it steers better on the track and doesn't push the front on corner exit on the throttle. That 6mm on the Ducati makes a lot of difference to the steering so 5mm offset and 6mm trail on the Guzzi V11 is a significant change to the steering and stability. I think this is probably whats happened back on the early bikes. We'll know for certain when I pull the triples on my bike after I get the replacement forks sorted and I can measure the supposed "cant" on my bikes original triples. 

If you had a std V11 Sport 25/40 set up and canted the triples 1/2 deg you'd go from 96mm to 103mm trail. If you instead opened the head angle to 25.5 you'd go from 96mm to 99mm trail.

If you had 1100ie 45mm triples on a V11 sport and you "canted" the triples 1/2 degree you'd end up with 97.5mm trail from 90mm. Seems to me the most likely scenario is they started with 1100ie Sport triples at 45mm offset and then due to customer/journalist feedback increased the trail from 90mm to 96mm by virtue of 40mm offset triple clamps to bring the figures back to the same as a std 1100ie Sport.

Ciao     

 

 

On 5/24/2022 at 1:29 AM, Lucky Phil said:

Ok so I've had to delete my last post on this because it was wrong. I have established without doubt that the later V11 sport triple clamps are indeed "canted" or more correctly have a built in negative rake. You can fairly easily check what your bike has by a measurement insitu. I have a new set of the later black triples and you can confirm by measuring the steering stem hole location in the bottom clamp. If you measure from the edge of the stem hole OD to the front and aft edges of the oval flat face the newer raked clamps measure  11mm and 16mm respectively where the older 0 rake forks measure 13mm and 14mm. So Guzzi have moved the stem forward 2mm in the new lower triple clamps effectively steepening the angle in the lower clamp and left the top clamp the same. So 40mm offset on the top clamp and 38mm for the lower. They have of course machined the fork leg bores at a fractional angle to allow for this so you cant mix and match new and old clamps.

Here's an image of a later clamp base and you can see the stem hole is obviously off set on the machined flat face. The earlier lower clamps have the stem hole more centred by 2mm. The effect of this negative offset is to give the bike more trail. How much I don't know but it may also clear up some of the wheel base question marks as well between the bikes which I think have been discussed aside from the long/short frame variations.

 

And so, the plot thickens . . .

Now we can say there was more than one change to the V11 fork geometry.

1) Very early V11 Sport, 1999 to very early production 2000 (before March 2000) may have been fitted with 45mm offset triples from the Sport 1100/ 1100 Sport-i. The resulting short trail, along with the short "RedFrame" and tire selection (soft, triangular profile Pirelli Dragon Corsa) were a formula for instability.

2) 40 mm offest triples were introduced (as early as March 2000 production) that corrected this issue.

3) The LongFrame (with braced subframes and wider rear wheel tire) was introduced 2002. "Perhaps" along with this, the lower triple tree has 2mm decreased offset that further increases trail/stability, but required machining "the fork leg bores at a fractional angle."  (the "canted" triples!)

Can we determine these mixed offset upper/lower triples and the canted bores began with the LongFrame?

 

[Lucky Phil]

4 minutes ago, docc said:

 

And so, the plot thickens . . .

Now we can say there was more than one change to the V11 fork geometry.

1) Very early V11 Sport, 1999 to very early production 2000 (before March 2000) may have been fitted with 45mm offset triples from the Sport 1100/ 1100 Sport-i. The resulting short trail, along with the short "RedFrame" and tire selection (soft, triangular profile Pirelli Dragon Corsa) were a formula for instability.

2) 40 mm offest triples were introduced (as early as March 2000 production) that corrected this issue.

3) The LongFrame (with braced subframes and wider rear wheel tire) was introduced 2002. "Perhaps" along with this, the lower triple tree has 2mm decreased offset that further increases trail/stability, but required machining "the fork leg bores at a fractional angle."  (the "canted" triples!)

Can we determine these mixed offset upper/lower triples and the canted bores began with the LongFrame?

 

Good question docc, I don't know. I also don't really know why the earlier 40mm lower triples have a different casting number because they look the same dimensionally although mine are still fitted to my bike so I haven't been able to measure them and look in detail at them and the later ones I have on the bench. Interestingly the Cafe sport, Copa Italia and Balabios, IE all the bikes that use traditional handlebars instead of clip ons have a different P/N lower clamp to the Le Mans bikes with Marzocchi forks although they all have black clamps so it's not a colour thing.

 

[docc]

That we found the hold-over 45mm offset triples on an actual, early V11 Sport at a South'n SpineRaid with a Sport 1100-i present for comparison was revealing.

That @Lucky Phil has verified this differential offset (from top to bottom) in the later triples is epic.

Welldone, Sir!

 

[docc]

TechSession fodder for the Eighteenth South'n SpineRaid !

The difference in offset is actually enough to see visually without calipers. Now that we know what to look for!

[Pressureangle]

Metric 150mm scale - check
Magnetic angle meter - check
Digital caliper - check 

Ride height also plays a part in rake, a little less in trail. We'll have to find a way to assure ride height is a standard; the easy way would be to measure the top of the spine with the tank off. 

[Pressureangle]

Figured I'd toss this out there, was burrowing through 'Access Norton' ancient posts.
 

 

[Lucky Phil]

So here is the definitive answer to the triple clamp offset question. Twenty years in the pursuit. This is what you get when you use a later top clamp on an early lower clamp with fork tubes fitted. The stem doesn't line up with the stem bore due to the different lower clamp offset. 

Another difference between the later and earlier lower clamps is the steering damper lug is 7mm longer on the later clamps so you need to machine that amount off the later clamps for the steering damper to fit correctly.

[docc]

1 hour ago, Lucky Phil said:

So here is the definitive answer to the triple clamp offset question. Twenty years in the pursuit. This is what you get when you use a later top clamp on an early lower clamp with fork tubes fitted. The stem doesn't line up with the stem bore due to the different lower clamp offset. 

Another difference between the later and earlier lower clamps is the steering damper lug is 7mm longer on the later clamps so you need to machine that amount off the later clamps for the steering damper to fit correctly.

So, this conundrum is down to change in "offset" and not "angle" or "cant?"

[Lucky Phil]

4 hours ago, docc said:

So, this conundrum is down to change in "offset" and not "angle" or "cant?"

Well if you change the bottom tree offset and leave the top the same then the fork leg bores need to be bored at a slight angle so they align. So now on the later forks the stem and the fork legs are not parallel. Just like an RC30 Honda and others for example.

So the top and bottom triples are a matched set between the earlier and later. 

 

Phil