CARC

[Chris Wilson]

Hi Phil, 

I really don't want to argue, but please accept that Pete and I do talk and I was aware of the swing arm failure before this thread.

Anyhow, how does a single sided swing arm aid tyre wear?

Not heard of that one before and am genuinely interested.

Chris.

P.S. if it's the claim that chain adjustment  with a SSSA using a single eccentric cam tube adjustment ensures alignment, obviates twist and chain stretch giving excessive periodic torque then that's not a feature of SSSA's.

Ducati had a similar setup back in the 70's with double sided swing arms, the cam was a tube axle located inside of the swingarm pivot - a special tool was provided in the tool kit that keyed into the axle and adjusted both sides evenly provided you released the clamping bolts fully.

The exact same system could easily be used in a DSSA and it's the method of adjustment not the carrier that gives the benefit .

[Lucky Phil]

12 hours ago, Chris Wilson said:

Hi Phil, 

I really don't want to argue, but please accept that Pete and I do talk and I was aware of the swing arm failure before this thread.

Anyhow, how does a single sided swing arm aid tyre wear?

Not heard of that one before and am genuinely interested.

Chris.

P.S. if it's the claim that chain adjustment  with a SSSA using a single eccentric cam tube adjustment ensures alignment, obviates twist and chain stretch giving excessive periodic torque then that's not a feature of SSSA's.

Ducati had a similar setup back in the 70's with double sided swing arms, the cam was a tube axle located inside of the swingarm pivot - a special tool was provided in the tool kit that keyed into the axle and adjusted both sides evenly provided you released the clamping bolts fully.

The exact same system could easily be used in a DSSA and it's the method of adjustment not the carrier that gives the benefit .

Flex. A little flex makes life easier on the tyre. Cameron postulated if the benefit's of the Ducati mono arm were more than just marketing. The race history of the Ducati mono arm demonstrates it's not a liability.   

Ciao

[Chris Wilson]

Ah yes, agreed.

It would seem that the elastic nature of steel gives desirable handling qualities to frames rather than the all out rigidity of aluminium extrusions and castings.

So I gather that flex with a mono arm gives a semblance of rear wheel steer when it's most needed.

Thanks, Chris.

[Chris Wilson]

Phil, you seem to be in the loop with this so a quick question.

(It was explained to me by an engineer who built me a Bimota style perimeter frame back in the 80's that the flex to avoid in all cases was on the roll axis. Pitch is fine as it is thoroughly allowed by suspension and likewise yaw as it is catered for by steering. But roll takes the wheels out of plane.)

So the question is  how does a swing arm that uses a single cantilever spar resist roll? (I know bridging helps but that can be an aid to all swing arms).

Double sided spars would seem to be far superior in resisting roll.

Chris.

 

 

[Lucky Phil]

10 minutes ago, Chris Wilson said:

Phil, you seem to be in the loop with this so a quick question.

(It was explained to me by an engineer who built me a Bimota style perimeter frame back in the 80's that the flex to avoid in all cases was on the roll axis. Pitch is fine as it is thoroughly allowed by suspension and likewise yaw as it is catered for by steering. But roll takes the wheels out of plane.)

So the question is  how does a swing arm that uses a single cantilever spar resist roll? (I know bridging helps but that can be an aid to all swing arms).

Double sided spars would seem to be far superior in resisting roll.

Chris.

 

 

The key part in your post is "back in the 80's". Back in the 80's they thought anti dive was a good thing for a few years as well when in fact the opposite was the case and it was actually regressive and that's why it was abandoned 35 years ago. I made a mechanical system back then when I didn't think too much. Same for frame flex in the pitch axis, if it's flexing in the pitch it wont be stable on the brakes as the steering head moves the trail around like flexy fork stanchions. Controlled frame and swingarm flex is a massive and complex topic but one thing is certain, you need "some" lateral or roll flex. This is why modern GP bikes don't use cylinder head forward frame mounts anymore and use longer arms from the steering head area to the crankcases, the head mounted frames with no arms were too ridged and didn't allow any lateral flex. It's also probably why the Ducati Panigale isn't a more winning WSB. It uses cylinder head mounted box assembly for a steering head/frame support and there's not enough flex there so it works on some tracks but not on others because it's not rider friendly enough with less feel from the front tyre. This system was originally designed to use carbon as the material and you can tailor the flex with carbon but Rossi made Ducati abandon it. So we are stuck with the alloy beam frame for the most part. I'm actually wondering if wire spoke wheels will make a comeback on GP bikes in the future. In a much higher tech form than the past. You could possibly have different wheels with different stiffness depending on the track requirements and tyre carcase stiffness. You read it here first.

Ciao           

[Chris Wilson]

Aprilia applied for a patent on a mechanical anti dive system last year so maybe 'abandonment' is a harsh word.

Cheers.

 

 

[Lucky Phil]

2 hours ago, Chris Wilson said:

Aprilia applied for a patent on a mechanical anti dive system last year so maybe 'abandonment' is a harsh word.

Cheers.

 

 

For what sort of bike? On a sport/race bike it's precisely the last thing you need. Promotes rear wheel lifting under brakes and stops the trail reduction under dive which helps turn in. A lardy electric bike may benefit from some dive control, maybe. Manufacturers patent all sorts of stuff that often never sees the light of day. Sometimes patenting is used as a commercial road block as well.  

Here's my version from 1985

Ciao 

[Chris Wilson]

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.cycleworld.com/story/bikes/aprilia-anti-dive-fork-patent/&ved=2ahUKEwid4oyHz6P0AhWF63MBHUHAAvQQFnoECAMQAQ&usg=AOvVaw0R7KsnV6pnBE-tEToRVi_Z

 

I guess it's sport bike related.

Chris.

[Lucky Phil]

19 hours ago, Chris Wilson said:

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.cycleworld.com/story/bikes/aprilia-anti-dive-fork-patent/&ved=2ahUKEwid4oyHz6P0AhWF63MBHUHAAvQQFnoECAMQAQ&usg=AOvVaw0R7KsnV6pnBE-tEToRVi_Z

 

I guess it's sport bike related.

Chris.

Yes an enhanced version of the system I made. Can't see it being used or should I say providing any benefit as you want as much dive as you can get as soon as you can get it on a sports bike or race bike more or less. Thats what flattens out the contact patch and provides the grip, the weight transfer from compression of the suspension and loading the tyre. No fork dive no significant weight transfer and a reduced contact patch. Ever see the GP riders crashing at 5 deg lean angle almost upright? Thats what happens when you start the turn in on the brakes before you've compressed the forks and loaded the tyre and why anti dive isn't used on race bikes. Interesting though. Maybe Aprilias engineers are too young to remember the 80's. Boeing had the same problem with their Newbie structures engineers when they designed the new Horizontal stab on the 737's. The engineering knowledge from the past seemed to have been forgotten or ignored by the new generation of structures engineers until they started having issues. The reasons were obvious to the older engineers. 

Thinking about it this system looks more like "dive control" than "anti dive". Maybe a way to isolate compression damping from the dive control equation although the explanation of it's operation seems at odds with that as you want the maximum dive initially to load the tyre and stop the rear lifting without upsetting the chassis too much. Riders currently can't apply max braking force initially and need to wait a fraction until the forks have compressed and flattened the tyre before they can ramp up the lever pressure. Time will tell and we'll see if it moves onto winning MotoGP bikes. Thats the test.      

Ciao