Fork Yokes (Triple Trees)

Carbonfibre · Mar 7, 2011

I don't think there would be enough difference between yokes that you would really notice, you would need a drastic change in castor angle to make any significant difference. I've just been reading an article about a modified Bonneville, the guy who built it reduced the rake to 24° to run modern tires and suspension, although to compensate he also lengthened the swingarm.

I found the specs for my 94 Speed Triple, it has a huge (for a modern bike) rake of 27°, I believe this is due to the fact that the bike is top heavy, the increased rake would add to the stability.

Now, to continue looking for those featherbed specs

Webby[/quote]

A change to the geometry of the yokes alone, allowed factory Norton race bikes to lap the IOM 1/2 minute faster, so maybe its something you would notice even on a road bike?

Jeandr · Mar 7, 2011

Carbonfibre said:
A change to the geometry of the yokes alone, allowed factory Norton race bikes to lap the IOM 1/2 minute faster, so maybe its something you would notice even on a road bike?

Maybe they had it wrong from the beginning on the race bike which is very different beast. It also depends on rider style when racing. These guys have to run at 100% to win so every little change will help to get closer to perfection.

Don't forget you mention a change in the yokes, nowhere in your statement is it said what that change was, so going to early yokes on late frames may improve things no?

Jean

Carbonfibre · Mar 8, 2011

Changes to production Commando yokes were carried out after race bike lap times improved drastically, and after the changes had been given the ok by factory test riders on stock road machines. For the Peter Williams article on this see this months "Classic Bike Guide". Finally its worth remembering that the early Norton race bikes were essentially heavily modified road bikes, and provided useful feedback and development information for the road going machines.

Webby03 · Mar 8, 2011

Thanks for all the input guys,
But has anyone found the specs for the rake and/or trail for a Commando or any Featherbed framed bike?
If we knew the changes Norton made, we could then get into the details of what made the bikes faster round the IOM.
I've looked everywhere and I can't find sod all :?:

Webby

Jeandr · Mar 8, 2011

Webby03 said:
Thanks for all the input guys,
But has anyone found the specs for the rake and/or trail for a Commando or any Featherbed framed bike?
If we knew the changes Norton made, we could then get into the details of what made the bikes faster round the IOM.
I've looked everywhere and I can't find sod all :?:

Webby

They were faster because the riders had big cojones

Jean

Webby03 · Mar 8, 2011

Jeandr said:
Webby03 said:

Thanks for all the input guys,
But has anyone found the specs for the rake and/or trail for a Commando or any Featherbed framed bike?
If we knew the changes Norton made, we could then get into the details of what made the bikes faster round the IOM.
I've looked everywhere and I can't find sod all :?:

Webby

Click to expand...

They were faster because the riders had big cojones

Jean

Was that because of the heavy braking and the tank strap toggle :mrgreen:

Webby

Webby03 · Mar 8, 2011

OK, thanks to Mr. i phone I now have something to measure angles with.
I can confirm that my Speed Triple has a rake of 27° measured at the fork slider. (as per spec.) I've no idea how much of this is due to the yokes as I don't have access to the head stock.
My 71 Bonnie has a rake of 30° at the fork slider, this is with the bike completely level which is due to the shorter shocks I've got fitted, I guess standard would be 28°- 29°. Measuring from the headstock, It would appear that the yokes have no castor built into them.
The Norton measures 24° at the headstock, again this is sitting level. It will be interesting to see if there is any castor built into the Norton yokes.

Webby

Carbonfibre · Mar 15, 2011

In general the older the bike the more rake its likely to have, so its surprising that a Commando has the same steering angle as most modern sports bikes.

Webby03 · Mar 15, 2011

Hi Carbon,
The angle I measured was a Featherbed frame, not a Commando. Mind you I was surprised that it had the same angle as a modern bike!
I still haven't found the steering angle of a Commando, I know the 750 has about 1° more rake than an 850, but the 850 yokes have a negative trail of 1.5°, I assume this was to increase stability as this modification would have kept the wheel base the same but increased the trail by a couple of mm.

Webby

Webby03 · Mar 15, 2011

I received a set of 750 Commando yokes yesterday (thanks Tim

)
Now, it turns out these are 71 - 73 yokes with an offset of 2 13/16", standard Featherbed yokes (and pre 71 Commandos) have an offset of 2 1/4". I've roughly calculated that this increased offset will result in a decrease of trail by about 15mm, the yokes have no castor angle built into them, so the forks fix parallel to the head stock. This, in theory will either quicken up the steering or turn it into a tank slapping beast!

So, tonights stupid question is what do you think a decrease in trail of 15mm would have on a Triton with a steering angle of 24°?
(If I choose not to use them, at least they give me an excuse to buy a matching Commando :mrgreen: )

Thanks

Webby

mcvic750 · Mar 16, 2011

Hi Webby
I’ve been following this thread as I’m trying to get the front end of my ’71 commando sorted out. The yokes on my bike are off a pre ‘71where the stem is connected to the bottom yoke rather the top yoke and it does not have the steering stops on the bottom yoke. The top yoke has the mountings underneath which I think were to take the early Halo headlight ring. Have to admit I do not know what the offset is, but if you can explain the measurements in terms that a Neanderthal man would understand then I can maybe work it out. If they would work for you and yours would work for me wondered about a swap? Mine are powder coated black and in good condition.

These are photos I already had, I can take more if needed.
Let me know, I’m in the UK (The nice bit at the top with all the whisky and salmon! :lol: )

Thanks
McVic

Jeandr · Mar 16, 2011

mcvic750 said:
Let me know, I’m in the UK (The nice bit at the top with all the whisky and salmon! :lol: )

And the salty air making things rust :wink:

Where did you get the exhaust nuts :?:

Jean

mcvic750 · Mar 16, 2011

Jeandr said:
mcvic750 said:

Let me know, I’m in the UK (The nice bit at the top with all the whisky and salmon! :lol: )

Click to expand...

And the salty air making things rust :wink:

Where did you get the exhaust nuts :?:

Jean

It’s not salty air it’s just all the rain! If it’s only raining lightly my wife and I go out for the day and take advantage of the good weather

! PO fitted exhaust nuts so can’t tell you sorry.
McVic

Webby03 · Mar 16, 2011

Hi McVic,
I'm from over the water, the other place where it rains constantly and has great whiskey and salmon, Not to mention a good excuse to get p*ssed tomorrow

Looking at your photo I'd say those yokes are pre 71 Commando, you should find your offset is 1 1/4" (about 56mm). To measure this, take a straight edge and set it in the centre of the fork stanchion holes, now measure from the straightedge back to the centre of the yoke stem.

My yokes are in good condition and I think they should fit your bike, although I'm missing the stem. I'll have a look and see how much a new one costs from RGM.
I'd be more than happy to do a deal, but remember the 71-73 Commando allegedly had dodgy handling (a high speed weave I think) so do a bit of research before you make a decision, you may find you might be better off with a set of 850 yokes. I'm in no position to comment as I know sod all about Commandos, in fact I know sod all about Nortons ! :mrgreen:

I'll post a couple of pics once I've finished stuffing my face

Webby

Webby03 · Mar 16, 2011

Hi McVic,
Here's the pics of my yokes with the measurements of the offset (in inches and mm)
If you're interested, I can get them bead blasted and painted black (maybe silver, I'd need to ask) at work. Regarding the stem, I've looked in the RGM catalogue and I can't find one, you may need to find a second hand one or get one turned up.

Let me know what you think.

Thanks

Webby

mcvic750 · Mar 16, 2011

Hi Webby,
Ah a fellow Celt, have a great day tomorrow, I will do some measuring and come back to you when you are sober again……………..in July :lol: !! Paint the town green.
Cheers
McVic

Webby03 · Mar 16, 2011

Sober, what's that? :mrgreen:

Carbonfibre · Mar 17, 2011

Webby03 said:
Hi McVic,
Here's the pics of my yokes with the measurements of the offset (in inches and mm)
If you're interested, I can get them bead blasted and painted black (maybe silver, I'd need to ask) at work. Regarding the stem, I've looked in the RGM catalogue and I can't find one, you may need to find a second hand one or get one turned up.

Let me know what you think.

Thanks

Webby

That amount of offset will mean very slow steering, and can be contrasted directly with modern sports bikes which have considerably less, and in most a steeper head angle as well. I would imagine the the 71/73 bikes which supposedly had "dodgy" handling, were fitted with the alternative fork yokes referred to by Peter Williams in CBG, which reduced lap times in IOM by 1.5 minutes! Thing is though that a bike with quicker handling isnt as easy to ride, and after a few less experienced riders have crashes, they very quickly get a reputation for poor handling...........which seems to be what PW was suggesting in his magazine article.

Be interesting to compare the different yokes though, and I would imagine those fitted to the better handling 71-73 bikes almost certainly had alternative caster angles.

Webby03 · Mar 17, 2011

Hi Carbon,
I believe the opposite is true, if you increase the offset you decrease the trail, therefore making the bike more unstable. So this would lead to (in my case) either a nice fast steering bike, or one that goes into a tank slapper at a certain speed!
This would be why modern bikes have almost no offset, the steering would be fast enough with the steeper headstock angle.
It's all explained here http://www.spiritchopshop.com/techpages ... il_101.htm

I too would assume that it was these yokes that Peter Williams refers to, as they would indeed speed up the steering at the expense of some stability, as the Commando has a rake greater than a featherbed (I'm guessing around 26°) it would already have less trail than a featherbed even when both are fitted with 1 1/4" yokes.
This is why I'm considering giving these yokes a go, I would still have more trail than an early Commando, so they should work.

What do you think, give em a go or get the correct ones?

Webby

Webby03 · Mar 17, 2011

Carbonfibre said:
Be interesting to compare the different yokes though, and I would imagine those fitted to the better handling 71-73 bikes almost certainly had alternative caster angles.

Sorry Carbon,
I forgot to mention, I compared the casting numbers of the yokes I have to several previous threads here and they are indeed from a 71 - 73 year bike. These have no castor angle built into them, this has been confirmed by my measurements and others on the forum.
As I mentioned earlier the 850 yokes have a negative castor angle of 1.5° built into them, this would have helped compensate for a further decrease in trail caused by the increase in the headstock angle.
Confused yet? I am! :mrgreen:

Webby

Fork Yokes (Triple Trees)

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