Slabbie frame bracing. Yes or No

[dupersunc]

  I know a few guys on here race Slabbies. What are your thoughts on frame bracing?

I'm currently collecting parts to build a 1216 powered 750G track/race bike. I'm not entirely convinced it's necessary with modern tyres and suspension, I've seen and ridden badly set-up moderns that handle like the have a hinge in the middle. I believe a lot of woes that in the past were blamed on flexi frames were more down to the limitations of tyres and dampers.

I'd be interested to hear the thoughts of those racing these bikes.

[kokolis]

Thin tubes m8, maybe what you say is true, but many do that, maybe is it between the ears....but if you are used to flexy frames that wouldnt be a problem..

[Leblowski]

Gonna race one next year 

currently gathering parts and start building the coming summer did some research spoke several people wich race a slabby.

They say brace it and race it

 

[Rene EFE]

Ask @YoshiJohnny 

Personal view; If modern tires and suspension did anything, is make the problem worse.

 

[Guest YoshiJohnny]

Canamant races week in week out with slingy wheels and an R1 shock... no bracing...he's quick.

I have braced mine a bit, nothing compared to the one we used at the Isle of Man which was MEGA braced...it handled very well with proper forks and a rubbish shock..

The standard frame is prone to cracking and the original welds were very poor....best checking for that before you brace it but in my humble opinion bracing will do no harm IF your ability outweighs the standard frame... I don't think my ability does ...yet

 

Edited January 26, 2016 by YoshiJohnny

[dupersunc]

3 minutes ago, YoshiJohnny said:

Canamant races week in week out with slingy wheels and an R1 shock... no bracing...he's quick.

I have braced mine a bit, nothing compared to the one we used at the Isle of Man which was MEGA braced...it handled very well with proper forks and a rubbish shock..

The standard frame is prone to cracking and the original welds were very poor....best checking for that before you brace it but in my humble opinion barcing will do no harm IF your ability outweighs the standard frame... I don't think my ability does ...yet

 

That's good to know, I've got Slingy wheels and a nos R1 shock, which I'll re-spring.   The frame I have needs a bit of remedial work, with the Tig, and will get a thorough going over before the build commences.   I'm inclined to beef the swing arm up though.

[Guest YoshiJohnny]

All will help it stop moving around and cracking

[dupersunc]

Where in particular do they crack johnny?

 

[cregnybaa]

A 750 g with a 1216 in it will be lively I think , good luck. what class are you thinking of racing in ?.

[Guest YoshiJohnny]

20 hours ago, dupersunc said:

Where in particular do they crack johnny?

 

mainly weak around the back and lower back main frame...if you are going to brace it and want to go mad have a look at Colins website that did our race frame..he went bananas but it worked.. 

http://www.tpeuk.com/GSXR 750F.htm

you can choose what you want to do but the headstock, rear upright filler and the casting plating is a good start

[Guest YoshiJohnny]

[markfoggy]

If you think about it, the performance gains on modern rubber are going to quite specific, you'll get a lot more braking from the front, trying to collapse the headstock, so bracing here is a good idea. In the corners you've got a load more lateral as well. Now a modern chassis get around a lot of this by using the engine as a stressed member and the engine itself is getting loaded a lot. so something in between the top rails should help to get that front tyre feeling anchored. Similarly, a little more between the down tubes wouldn't go amiss. 

At the back and especially with all that torque from a 1216, you'll start tearing lumps out of the chassis as modern rubber will grip so much better. I like the thinking on that swinger, a lot. Beware though, the stiffer you make the swing arm, the more that will transfer into the frame. That torque is trying to shorten the swing arm on the left even in RH bends, but for me I'd be putting that rear diagonal brace  in at 90 ^o to the one above. Now I reckon that you could gain quite a lot with rear and lower engine plates being heavier, as you'll load the cases better. After that, the traditional fillet from the swing arm pivot up to the upper frame rail is just common sense, that angle at the rear of the top rail was always awkward from an engineering perspective.

Edited January 27, 2016 by markfoggy
Left a bit out.

[Markz9]

I think I have seen that frame somewhere recently john !!!!!

 

[yann7/11r]

On 27/1/2016 at 8:01 PM, YoshiJohnny said:

Hope you don't mind me having a nosey...but I can clearly remember me, the old topic who explained the build from this fantastic bike, some years ago.
Can't remember what happened for the bike after the race. Dismantled ? 

If i can ask, of course.

[canamant]

Couple of ideas I have about 750 frames, bracing etc.

The 750 frame was good as it came out of the crate, nothing has changed with it, so it's still good.  What has happened is people's expectations, trying to ride it like a modern beam/stressed engine frame, and trying to make it feel like one by bracing everything up to high heaven.  These bikes are 30 years old now  so anyone under 50 will have started serious riding on later generation machines which do handle differently.  750 FGH do handle well without bracing if you ride them accordingly with high corner speed rather than standing them on their nose, squaring the corner off, then firing it out.

Any bracing put into a frame means that the stresses appear somewhere else.  That can cause a problem so you need to find out where and brace that too.  When all is done, the frame will be heavy, probably heavier than an 1100 frame. See later.

My opinion (and everyone has got one) is that the standard frame is more than good enough if you set it up properly and ride it accordingly.  These bikes were doing over 110mph laps at the TT /Manx in their day in standard trim and the Course gave the bikes far more of a battering then than they do now.  The stories of them wobbling and handling badly waere probably down to set up or rider style.  My bikes have done 3 Manx Grand Prix, one ran by YJ's team and two by me.  Yj's team fitted a high spec set of forks, shock absorber, and steering damper and finished at an average of 98.9mph with a fastest lap of 99.99mph.  In 2013 on my second go I averaged 96.8mph with a best lap of 98.5mph.  I had standard forks, no steering damper, R1 shock, and no 2nd gear from the start of the race.

So in my experience, the 750 frame is OK as is with up to maybe 115 - 120 bhp.  With a 1216, I'd forget about the 750 frame and build it into an 1100 frame.  The Classic TT/MGP rules allow 7/11s but no-one seems to go down that route. The 1100ishes all seem to be in 1100 frames or XR frames. There must be a reason.

[Guest YoshiJohnny]

2 hours ago, yann7/11r said:

Hope you don't mind me having a nosey...but I can clearly remember me, the old topic who explained the build from this fantastic bike, some years ago.
Can't remember what happened for the bike after the race. Dismantled ? 

If i can ask, of course.

I built the bike.after Colin at TPE braced the frame. It was raced at the Isle of Man Manx GP as it was, came 8th then was broken for Colin to keep the frame to make a road bike or race bike out of.

The frame is now owned by Mark Carels Watson who is gonna race it again.

I still have the motor and suspension etc from it.

[markfoggy]

@ canamant, has a good point here, what Yoshi were doing may well have been aimed at getting a particular advantage on track, or more likely targeting an area that they were loosing out in, on other bikes in the field. Would love to see their race notes. 

 

[markfoggy]

As it goes, I'm just about to start an email to a guy I know in the States who might know a little, though his work may have been a little later.

[HDTboy]

Tony Foale's website has some great articles on frame bracing. Some of the solutions he comes up with are aesthetically challenging though

[canamant]

hmm - old engineering saying was If it is right it will look right !!

 

[bernardo]

In reply to the question yes brace it. For what it s worth, I was offered a braced frame a few years ago. It had a bit of crpssbracing but the headstock was heavily plated.