Duplicates of Corse racing yokes

Diesel

I was certainly under that impression as well until I started doing some measuring. I am lead to believe the 25mm offset may have some front wheel clearance issues under full compression! So many Corse may have been changed to 27 or even 30 to offer some relief in this area. I know the standard SP4 and SP5 is 30mm off set. The early Corse and SPS was different?

the 30mm off set also makes the 888 a lot easier to turn-in! for road use, apparently!!

Mr.R

Road bikes had 30mm offset yokes, the Corse models had 27mm (or possibly 28mm?) to speed up the steering.
Later Corse motors had the exhaust rocker box shaved back to give more clearance under braking and possibly use a lower profile front tyre like a 120/60X17 against the road bikes 120/70X1717.
A mate's SP(4)S has worn right through the fairing V piece.

Steve R

Jasper

Mr.R wroteRoad bikes had 30mm offset yokes, the Corse models had 27mm (or possibly 28mm?) to speed up the steering. Later Corse motors had the exhaust rocker box shaved back to give more clearance under braking and possibly use a lower profile front tyre like a 120/60X17 against the road bikes 120/70X1717. A mate's SP(4)S has worn right through the fairing V piece. Steve R

My tyre is VERY close to the front of the fairing.!

duc904red

If l were to make these what would we go for 27mm or 30mm
Regards Steve

Diesel

IMO. For general use, with a bit of track, riders of our ability (yes, admit it!) would only ever need 30mm off set and avoid potential damage to V-pieces. I really dont think any of us will be pushing our old Girls that hard we would get the benefit of a 27mm OR 25mm off set.

However, if someone wants ORIGINAL Fitment (like me, despite the consequences) I will want the 25mm. ( Thank you Guy 😄)

If Iam going for a spirited ride, I will take V piece off to avoid damage.😁

marvin

duc904red wroteIf l were to make these what would we go for 27mm or 30mm Regards Steve

IMHO there is no reason to make 30mm offset yokes. There are lots of stock 30mm offset yokes out there. 27mm seems to be the corse offset of choice which slows the steering down and makes the bike more stable. 25 may be going too far IMHO (stock carby Monster yokes are 25mm if you want to try them). I made a set of 27mm yokes and love them. With the stock 30mm the 851 would "drop" in a slow speed corner unless you were on the throttle (very much a pucker factor!). With the 27mm it is no longer a problem. BTW it seems as though some of the European yokes (mainly for WP forks I think) are 25mm offset.

Pompey

Excuse my ignorance but how is the offset measured? I presumed that having a steeper (more upright) position for the forks made it tip in quicker... which is why people drop the yoke down the forks to bring the back wheel closer in thus quickening steering sacrificing a longer wheelbase for stability? When I was racing we used to try to counter it by having a longer chain and pushing the rear wheel back as far as possible to emulate a longer swing arm bringing the wheel base back to a stable distance keeping the sharper steering angle.😳

duc904red

Looks like 27mm is going to be the way forward
I still might do a corse look alike top yoke at 30 mm to go with the std bottom yoke
Regards Steve B

Diesel

Pompey wroteExcuse my ignorance but how is the offset measured? I presumed that having a steeper (more upright) position for the forks made it tip in quicker... which is why people drop the yoke down the forks to bring the back wheel closer in thus quickening steering sacrificing a longer wheelbase for stability? When I was racing we used to try to counter it by having a longer chain and pushing the rear wheel back as far as possible to emulate a longer swing arm bringing the wheel base back to a stable distance keeping the sharper steering angle.😳

Off set is measured; centerline of Forks to centerline of steering stem. Roughly like this....

Pompey

Ahh. That explains it. Love learning new stuff. I thought it was the angle in degrees, not the distance in mm with the same rake. So even a 27 mm yoke would have the same effect as a 30 mm one if the chain was coming to the end of its life and adjusted more then 3 mm back. Which is the norm right? Although having the shorter distance would mean the centre of gravity be further forward for the whole mass thus turning in quicker. Or you could race with the misses on the back! Solve 2 problems in one... more rear grip and shut her up for 30 minutes. Cheers Diesel.😄

Diesel

Meant to also say, the off-set is one of the variables that change the 'Trail'. Fork height in the Yoke also has an effect on the Trail measurement and wheel base.

marvin

Less ofset means more trail=more stability=slower steering=more weight on the front wheel. The offset of the top clamp is the same as the bottom clamp. (AFAIK a different system than the later 916 series bikes). Yes, move the rear axle rearward as far as possible which also puts more weight on the front wheel and a longer wheelbase. That's why Corse bikes have a longer swingarm.

Mr.R

Now I might be wrong here?
But I think that reducing the offset of the yokes/triple clamps from 30mm to 27mm would speed up the steering/turn in.
Making the bike's steering faster but less stable, which is why the Corse bikes had a steering damper fitted as standard and later on had longer swinging arms to counter act the instability?

Steve R

Diesel

Mr.R wroteNow I might be wrong here? But I think that reducing the offset of the yokes/triple clamps from 30mm to 27mm would speed up the steering/turn in. Making the bike's steering faster but less stable, which is why the Corse bikes had a steering damper fitted as standard and later on had longer swinging arms to counter act the instability? Steve R

I tend to agree with this statement, based on my experience. I didnt want to be an arse as I am new around here!!

Less off-set will make the initail turn-in effort harder, but a more agressive (faster). Less off set can also have the added benefit of losing rear end mechnical grip and creating a perfect high-side situation !!!😎

Pompey

ahh. Good, thought I was going nuts and forgotten the lessons of youth on the track.😏

Phil911

Mr.R wroteNow I might be wrong here? But I think that reducing the offset of the yokes/triple clamps from 30mm to 27mm would speed up the steering/turn in. Making the bike's steering faster but less stable, which is why the Corse bikes had a steering damper fitted as standard and later on had longer swinging arms to counter act the instability? Steve R

---> 100% correct !!!
In 888 racing era, numerous riders complained with offset yokes settings.
An italian team decided to fit the Magnesium steering yokes from the Cagiva 500 -V.591- which offered the opportunity to adjust from 25 to 30 mm, thanks to an excentric axle, the correct offset in accordance with the pilot's ridding style.
Few years back, I've had the opportunity to get an alloy copy made for 888s and I confirm all the validity of that idea, after have tested myself on tracks, the different settings those yokes offered.
To be honnest, I didn't expect such a huge difference, according to the choosen
offset with ... a 24°30' steering column angle !!!
With the shortest offset and the long swingarm, the bike immediately fell down at the entrance of the curve and made me ... scared !!! Out of the curve with full throttle open, I felt the bike dancing which made me scared a second time.
Scared twice in a single curve made me understand it was time to change immediately the settings.
With 30 mm, I felt the bike long, long as a truck, and 27 mm made me much more confident ...
Recently questionned by myself about the subject, a mechanic from that period told me :
"Did you pay attention that in early 90's, all 888 racing bikes on tracks didn't have the long swingarm ???
With mag. yokes, some riders said that their bike was too rigid, reason why we succesfully tested that solution !!!"
On the racing frame 93/94, with a steering column designed at 22°30' angle, the offset yokes at 27 mm, I dare to say that the reactivity of the bike is similar, compared with my (ex ...) 916 SP.3 with the adjustable shortest offset !!!

I do not pretend I'm a pilot, no, no, simply my personal feedback ...

Phil911

marvin

Mr.R wroteNow I might be wrong here? But I think that reducing the offset of the yokes/triple clamps from 30mm to 27mm would speed up the steering/turn in. Making the bike's steering faster but less stable, which is why the Corse bikes had a steering damper fitted as standard and later on had longer swinging arms to counter act the instability? Steve R

That's opposite from what I've read. My 851 with the 27mm offset and the axle as far back as possible is extremely stable at high speed and no longer drops in slow tight corners.

MarkT

Thanks Phil for your experience on the effect of offset/trail changes. Your feeling that the 30 mm offset with the shorter trail making the bike have slower turn-in versus the 27 mm offset with the longer trail seems to match the experience of other members. For me the difference between a 30 mm offset and the 27 mm is not as clear cut.

Back in '96 I was tracking an '89 851 with an 888 kit and SP1 cams in a stock frame- but I did have the later Showa forks on the bike. The next year I installed a 27 mm mag yoke and Ohlins. I was fully expecting the steering to get a bit more lazy because as Marvin pointed out that in theory , a longer trail will tend to produce a slower steering and thus a more stable motorcycle. I had to ask myself why would Ducati want the Corse to have slower steering then their street bike which have to contend with the bumps and imperfections on the street where you want the self correction (caster affect) that longer trail gives you- but on smooth tracks you would think less trail would provide quicker turn in thus faster lap times.

I knew that while the 27 mm yoke provides more trail and in theory slower steering (really turn-in)--- more trail also shortens the wheel base a bit which is the same thing as moving the engine forward and putting more weight on the front tire- which should make the bike's turn-in feel lighter, increase front end feel, both which helps it turn in.

Conflicting theories.

One extra thought I had about the factory perhaps wanting more stability over quick turn-- many of the track in Europe are fairly flowing and high speed so more trail and stability is a good thing--- and these riders are FAST-- and much much more agressive. So when we mere mortals are talking about turn in feel- these guys know how to get through a corner fast at speeds that a bit more stability is desirable at the limit of their tires. Who is to say that the factory did not change offset yokes from track to track?

So as far as turn in quickness it could go either way-- AND while trail numbers greatly affect turn-in turn-in is also affected by a few other little items such as fork height in the triple tree, rear end height, swing arm angle, rear axle position, tire diameter and profile-- and the rider.

Assuming that there is an inverse 1:1 relationship between offset change and trail--and keeping every item the same on your bike-- changing from a 30 mm to a 27 mm offset you can expect about 3 mm increase in trail. So assume that the 30 mm triple has 94 mm trail and the 27 mm has 97 mm trail which is the ball park of currently used trail numbers, will a good street rider feel the difference?

In my case I changed nothing on the '89 except installing the mag triples and the Ohlins. I cannot swear but I believe that the front end was the same height as when I had the Showa's.

The first thing that was most noticeable (this at boomer track Mosport) was how great the Ohlins felt over any bump on the track- the bumps just went away. The second thing I noticed was- well not much difference going into the turns- not any slower or faster-- but then again this was the third year of being on the track and I was not all that good and my motor was pretty mild.

For my skill level 3 mm change in trail did not make a noticeable difference back then and even after these many years of tracking these bikes I am not sure if even now I could tell the difference. For me how the motor performed and how the power affected the chassie is what got my attention as I got Corse's with factory motors.

A year latter I restored a '93 AMA Customer Corse with G cams. This customer frame has the same 24º 30' rake as the street bike. Now I had a motor that would accelerate the bike big time down the straight and lighten up the front end enough to see why you would want more stability--the bike was nervous in a straight line and the front end would come up between shifts-- I mean every shift. Fun but hard for me to ride fast- spinning up in turns and nervous in the straights over 150 mph. To keep the front end from being light I pulled the rear axle as far back as I could-- and the turn in got perhaps a bit slower but I was not jittering down the track. When I went with 421 intake cams the front end calmed down a bit since there was no big rise in the torque curve a 8K rpm.

In the same period I had the '93 on the track I built my own bitsa Corse using a '94 frame with the 22º 30' rake-- and factory spec of 102 mm trail. If this factory specification is correct (although steeper rake with more trail could be desirable) then something else must have changed like tire diameter because I get a trail numbers much closer to 97 mm keeping everything on the bike the same as my '93.

I can say that the '94 frame bike has a paddok turning radius like a bus, I can scuff the front head with heavy braking even with the flat mill off-- but it does have quicker turn in-- still does not "drop into turns" and is stable at high speeds unlike my '93 and earlier frames--- but I also have a very mild 984 motor in it. For this bike I increased the rear ride height to prevent squat which changed my rake even more. Still not a quick drop in - just a bit less force required.

In a nutshell--for me all these bikes have to be muscled a bit into turns no matter if you have a 27 or 30 mm offset or the 24º 30'/22º 30' rake. The trail with the current higher profile front tires (original were 120/60 17") will be even more then the factory specification so you will have to play with the front and rear set up a bit to adjust these bikes to your liking.

Phil911

MarK, you know what ???
Sometimes, I dream to provide correct and detailed technical explanations as you usually do ...
Each reply is a great "Ducati moment" and I warmly thank you !!!

At 52 y.o.a, I think it's time for me now to sell my bikes in order to pay a "devoted english teacher" !!!
Thus, I might be, around ...85 y.o.a, understood by the whole of the forumers !!! 😏

Phil911 ... a lost French among all of you !!! 🙁

Jasper

I had 20mm spacers on my suspension hoop to quicken the steering on my SP5. I then got some corse yokes and took them off. The bike was incredibly "tippy", literally fell on its side in a corner,roundabouts were a nightmare and unnerving. I messed with the eccentric, to no avail. I moved the wheel back in the swing arm,again to avail.

In a last resort, contrary to everything I thought, I put the spacers back in,which jacked the back up by 20mm. I thought the bike would be so unstable as to be unrideable.

The change was a revelation. The bike turned sweet,was stable and the tippy feeling was gone.

Yet I presumed by raising the rear,it would have made it worse! Go figure.

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