R6R forks - doable?

[RJ2112]

I don't think the trail has been affected, assuming the fork tubes are the same length. If you take a plumb bob and mark where the center of the axle is, that's the end point of the trail measurement.

When you move the axle 'back' (because the forks are moved 'back') the end point of the trail calculation moves back an equal amount. If the fork angle doesn't change, the rake doesn't change.... the point the measurement starts from also moves back an equal amount. In algebraic terms you've subtracted equally, from all parts of the equation.

The only number that would change, would be wheel base, which is measured from axle centerline to axle centerline. Bringing the fork tubes 'aft' will cause the axles to be that much closer together.

 

[krushnuts]

I don't think the trail has been affected, assuming the fork tubes are the same length. If you take a plumb bob and mark where the center of the axle is, that's the end point of the trail measurement.

When you move the axle 'back' (because the forks are moved 'back') the end point of the trail calculation moves back an equal amount. If the fork angle doesn't change, the rake doesn't change.... the point the measurement starts from also moves back an equal amount. In algebraic terms you've subtracted equally, from all parts of the equation.

The only number that would change, would be wheel base, which is measured from axle centerline to axle centerline. Bringing the fork tubes 'aft' will cause the axles to be that much closer together.

I've heard from several different sources that trail is measured using the angle of the neck/yoke of the frame. Your saying it's measured using the angle of the forks?

However, *if* trail is measured using the angle the yoke is at - that has not changed. The part that has changed position is the axle, which moved back towards the bike, lengthening the trail.

I'm going for a bit of a buzz around my suburb and will see how it feels.

Here's my shopping list, everything is in AUD:
1. 2006 R6R forks, brake lever & master cylinder, brake lines and calipers - $650, a bit less than 1/2 of that was the USPS shipping charge. Anyone know what brand forks they are?
2. Rotors & new pads, local manufacturer, MetalGear - $600
3. R6R top triple clamp - $260
4. R6R front fender and associated washers, nuts, bolts and two high tensile bolts for the calipers (I lost a set... lol) - $350
5. Dave Kellett Moto Engineer handle bar risers, installation and frame straightening - $700

$2560 all up. Woah... Thankfully spread out over nearly two months, flying the whole time under me missus's radar :spank::rockon:

She thinks it looks great and understands that it will help keep me from getting too close to Mr Bitumen.

 

[RJ2112]

Bless her heart, LOL.

 

[RJ2112]

I've heard from several different sources that trail is measured using the angle of the neck/yoke of the frame. Your saying it's measured using the angle of the forks?

However, *if* trail is measured using the angle the yoke is at - that has not changed. The part that has changed position is the axle, which moved back towards the bike, lengthening the trail.........

I've re-thought this... I agree with you that the trail is now longer as a result of the fork tubes coming back towards the steering neck. The measurement has to be made from the steering neck, rather than the fork tubes themselves.

Is the steering 'slower' as a result? Higher effort at low speed, a bit more 'floppy' when you lean it at slow speeds?

 

[MRGM]

You say that the fork legs got closer to the frame, but I think that's just because they are much larger in diameter. I did a little research on the geometry differences in the bikes.

The R6 triples run 30mm of offset, while the FZ6 is about 28mm. So the swap is reducing you trail. Due to the rake angle difference, that should put us with less trail than the R6 since the Yamaha website lists both bike as running 3.8" of trail (they are probably not exactly the same).

If you want to get closer to the R6 rake angle, raise the forks in the triple and buy the height adjustable Ohlins rear shock. Of course, raising the forks will increase the trail compared to what we have right now.

The other key factor between the bikes is the greater wheelbase of the FZ6. While raising the forks in the triples will have the effect of reducing wheelbase, we already increased it by adding offset to the forks. None of these changes will do much anyway because there is a 2.5" difference between the bikes.

I'm hesitant to modify the swingarm to reduce wheelbase, as that will start to put the center of gravity closer to the rear wheel, which makes the bike want to wheelie more. This all depends on the relative center of gravity between the FZ and R6, which I don't have a way of quantifying. I might check it out on my bike over the winter and see if I can do a little machining to get the ability to change it. Though it will require removing a link from the chain.

 

[krushnuts]

You say that the fork legs got closer to the frame, but I think that's just because they are much larger in diameter. I did a little research on the geometry differences in the bikes.

The R6 triples run 30mm of offset, while the FZ6 is about 28mm. So the swap is reducing you trail. Due to the rake angle difference, that should put us with less trail than the R6 since the Yamaha website lists both bike as running 3.8" of trail (they are probably not exactly the same).

If you want to get closer to the R6 rake angle, raise the forks in the triple and buy the height adjustable Ohlins rear shock. Of course, raising the forks will increase the trail compared to what we have right now.

The other key factor between the bikes is the greater wheelbase of the FZ6. While raising the forks in the triples will have the effect of reducing wheelbase, we already increased it by adding offset to the forks. None of these changes will do much anyway because there is a 2.5" difference between the bikes.

I'm hesitant to modify the swingarm to reduce wheelbase, as that will start to put the center of gravity closer to the rear wheel, which makes the bike want to wheelie more. This all depends on the relative center of gravity between the FZ and R6, which I don't have a way of quantifying. I might check it out on my bike over the winter and see if I can do a little machining to get the ability to change it. Though it will require removing a link from the chain.

My aim wasn't to try and replicate the geometry of the R6, I just wanted the forks on my bike. Now I'm trying to find out what effect the new geometry is having lol, a bit backwards I spose, but there was no other way...

Yeah, I was thinking that changing the height of the rear of the bike could help compensate. The height adjustable ohlins rear shock is on the shopping list. The weight distribution is another consideration, 49/51 percent (rear/front) on the FZ6 I think. Dono about how it's distributed on my bike now, something else to work out.

I have the FZ6 triple here, so I made a stencil of the fork & steering shaft holes. I found the center of the holes by drawing several chords inside the circles and extended a perpendicular line from the center of each chord - where the lines cross over is the center of the circle. I connected the two center points from the fork holes then measured the distance from the center of the steering shaft hole. It measured 33 mm. The R6 triple is on the bike now, so can't measure it accurately.

If the R6 triple offset is 30mm looks like the forks have moved 3 mm closer to the bike... Is that enough to make a difference?

The bike 'feels' like it's a tiny bit harder to turn, like I have to push harder on the 'bars to get the bike to start turning. When I say harder, it's a really small amount, but enough to notice.

Could it be the weight difference? I'm just trying to find an explaination for the change in the feel of the bike. Of course it has something to do with the conversion, but I'd like to find out what.

I'm going to take it up to the local dealership, who has a stock FZ6 which is owned by one of the mechanics. I'll see if he'll oblige and help me compare the two - perhaps some answers will be found :thumbup:

 

[krushnuts]

I've re-thought this... I agree with you that the trail is now longer as a result of the fork tubes coming back towards the steering neck. The measurement has to be made from the steering neck, rather than the fork tubes themselves.

Is the steering 'slower' as a result? Higher effort at low speed, a bit more 'floppy' when you lean it at slow speeds?

Hmm, yeah I think so, It's a bit hard to quantify, it certainly seems harder to turn it, ever so slightly. For example, when I pull into my driveway, I come in straight and turn the bike into the front yard, then reverse it back onto the driveway to reverse into where I park it. I used to make the turn smoothly and only need to put my feet down when I stop to reverse, but now the bike seems to be 'flopping' over and I need to put my foot down to stabilise it during the turn.

Also taking corners, doing about 60 kph I need to push a little harder on the 'bars and adjust my shoulders more into the corner.

 

[MRGM]

I believe your measurements over mine. I took them off my bike, which is together...

It makes sense. If you want the same trail on the FZ with an extra degree of rake, you need to run more offset.

Since that is the case, I would definetly recommend you raise the forks in the triple.

 

[krushnuts]

I believe your measurements over mine. I took them off my bike, which is together...

It makes sense. If you want the same trail on the FZ with an extra degree of rake, you need to run more offset.

Since that is the case, I would definetly recommend you raise the forks in the triple.

Cool, I wanted to find an explaination for the different feel. I'm much more comfortable and confident with it now I think I know what is causing it!

I've been thinking about the rear suspension. Just now, I changed the preload from the factory setting of 3 up to 5 (harder) and re-set the forks to factory and well... It feels easier to turn, the bike used to want to run wide a lot of the time and that feeling has gone too. :Flash:

This has inspired a world of confidence on top of your confirmation MRGM. For even sharper turn-in I will see how it feels with the forks raised 5mm.

Thanks loads for your help and input, it's great to have confirmation from 3rd parties. :thumbup:

Days nearly over here, so I'll have a tinker with the forks tommorrow and report how it goes.

MRGM, will you still be going ahead with your fork isntallation?

 

[MRGM]

Yes, I'm still going to do that swap. I'm going to draw everything out in CAD and figure the amount we need to raise the forks, and raise the rear of the bike to achieve the same trail that we started with. Either that or somehow change the offset with different bearing cups... Eh, that would be too much work

 

[bmrandrews]

WOW

I will have to do this :rockon:

I've heard from several different sources that trail is measured using the angle of the neck/yoke of the frame. Your saying it's measured using the angle of the forks?

However, *if* trail is measured using the angle the yoke is at - that has not changed. The part that has changed position is the axle, which moved back towards the bike, lengthening the trail.

I'm going for a bit of a buzz around my suburb and will see how it feels.

Here's my shopping list, everything is in AUD:
1. 2006 R6R forks, brake lever & master cylinder, brake lines and calipers - $650, a bit less than 1/2 of that was the USPS shipping charge. Anyone know what brand forks they are?
2. Rotors & new pads, local manufacturer, MetalGear - $600
3. R6R top triple clamp - $260
4. R6R front fender and associated washers, nuts, bolts and two high tensile bolts for the calipers (I lost a set... lol) - $350
5. Dave Kellett Moto Engineer handle bar risers, installation and frame straightening - $700

$2560 all up. Woah... Thankfully spread out over nearly two months, flying the whole time under me missus's radar :spank::rockon:

She thinks it looks great and understands that it will help keep me from getting too close to Mr Bitumen.

 

[crofz]

How did you solve steering stop points at the lower triple tree to get correct steering angle? Any photo of that?

 

[Hellgate]

How did you solve steering stop points at the lower triple tree to get correct steering angle? Any photo of that?

Stick on wheel weights work well for that. Just stick them on the stock stop points. Or you can drill and tap a hole in the stop and screw in a bolt. Wheel weights are much easier.

Sent from my MB508 using Tapatalk

 

[crofz]

Maybe I didn't ask right question...I was thinking on this as pointed on the picture.

 

[Hellgate]

I see, thanks.

 

[yoshiki]

grind off the steering stoppers.

 

[crofz]

grind off the steering stoppers.

Yes...I got that, but how to make it work again?
I'm out of ideas and I find it little difficult to weld new stops because of the difference in shape between those two triples...