Topic: Front-End Thinking Changed

[Retro Rocket]

I really don't understand what your thinking is here, cr750fan...that this bike performed well because it didn't have a fork brace?

He didn't say that. He said despite the lack of a brace, it felt extremely well-planted. As did two professional riders.

Exactly!

Sean: Just to clarify, I never said that using a fork brace was detrimental.  I only opined that it seemed unnecessary with this application, whereas I had previously thought it was almost a necessary component to making a CB front handle well.  And, I cannot say one way or another whether adding a fork brace would improve the handling on this bike, since I have not ridden this particular bike with one (nor has anyone). 

After further discussion (today) with the builder, he is a firm believer that weight reduction, weight distribution, frame geometry, tires, suspension set up and the proper balance of frame stiffness (with gusseting and bracing) combined with the correct amount of flex all combined to give this bike the great handling package it has. Ian does not think a fork brace would necessarily improve the handling characteristics of the bike.

I get that you disagree with this assessment. I would have joined you in that thinking, before riding this bike. It really got me to reassess.

With respect to the front brake, any benefit from a fork brace would not likely add sufficient stopping power. It simply needs a larger rotor. As built, Twinline was trying to get away with a smaller, lighter setup that would still provide enough stopping power. Ian is in the process of replacing the rotor.

Finally, I doubt any of us - even those members who race proficiently - are in or will EVER be in the same league as Eric or Ben Bostrom. Not only can they ride ridiculously fast, these guys have enough skill and experience that factory teams have relied on their feedback. Ben brought his chief to tech inspect and help test the bike.

Sorry boys, I'm with Sean here. Bostrom said he wanted more brakes, then a brace would have been the next move, Seriously, I could make those forks flex with the right brakes, If it were this easy to make a bike handle, why did all the motorcycle manufacturers start fitting braces, then upside down forks with no flex..?  Anyone that thinks that that bike couldn't be made to handle better really isn't thinking straight {I meant that in the nicest possible way guys }. Don, I garantee that rc51 of yours could be made to embarrass that little Honda if set up well.

[Retro Rocket]

And before anyone goes getting all butt hurt, I've always said that these old bikes, when set up properly, can handle quite well, I also know that the front ends on these same bikes flex and twist quite a bit, hence Sean's comments, I'm also really sure that someone with Bostram's talent could ride around these problems quite easily, Most guys at his level, {i've known a couple} are very good at riding any bike within 1% of its limits, I never read anywhere where he said it "didn't flex or twist, I think a damper and a brace would have made it just that little bit better, it only makes sense to come to that conclusion...

[bwaller]

Don, I raced TimV's stock CB350 and had an absolute blast. I think either Bostrom would feel the same way on anything under 100hp. 

Regardless, the bike is cool, Ian did a good job. It's not the silly season yet, let's not argue about this. 

[flatlander]

never mind the brace... would be nice to know what exactly he did on the frame.

[calj737]

... would be nice to know what exactly he did on the frame.

+1 Although, some of it was probably necessitated by the motor swap.

[calj737]

I'm curious Retro, is it your contention that a bike like the Bimota Supermono which is a track only bike doesn't use a front brace because the front forks are so beefy? They are conventional at 43mm and there is only a plastic fender tying them together. I equate that "package" to what the boys at Twinline produced from power:weight (48BHP@319#) footprint is why I use it as an example.

I'm not disagreeing with you, by the way, simply exploring ideas. It's hard for me to judge how a bike rides (Thorn) when I haven't ridden it, but others have. And when professional riders don't mention the lack of something, I take that as "its not needed". Perhaps, they didn't feel it would provide any further benefit to the already svelte handling. Maybe, after tracking the bike longer, they would have installed one, but for the street, quite possibly not. Who knows, its all conjecture on our parts.

I have ridden a Supermono on track back when I could fit on the damn thing, and I'll say, theres not a darn thing I would ever change about it. It took every thing I could throw at it and just yawned (Kenny Roberts Im not in case you're wondering).

[SOHC4 Cafe Racer Fan]

The frame has gussets at each of the triangle points, the welds have been reinforced where sloppy and there is a new cross member at the rear rear of the main frame with 45 degree braces - akin to an X brace. The swingarm is also braced.

[SOHC4 Cafe Racer Fan]

Debate aside, this ride surprised me in that a CB could handle so well with a stock front. I attribute this to the HUGE weight loss, chassis improvements and better weight balance of the Ninja twin motor. I think that this is also why supermonos may be so amazing.

I am not ruling out that a fork brace may have a positive effect. I'm just saying that the bike handled way beyond my expectations.

This bike was not better overall than my GSXR nor my RC51 (each of those bikes have good setups, and better brakes, tires, and awesome power plants), but it seemed to turn more effortlessly. Note: prototype race bikes are extremely lightweight.

[754]

I think certain "out of the box thinkers" can move beyond the textbook, once the goal in one area is reached. They then use their energy to improve other aspects of same package... To the betterment of the whole.
 Sure you can always spend more in any area.... But to what effect?
 The goal for for this is to win,  not be a textbook example..

[Retro Rocket]

I'm curious Retro, is it your contention that a bike like the Bimota Supermono which is a track only bike doesn't use a front brace because the front forks are so beefy? They are conventional at 43mm and there is only a plastic fender tying them together. I equate that "package" to what the boys at Twinline produced from power:weight (48BHP@319#) footprint is why I use it as an example.

I'm not disagreeing with you, by the way, simply exploring ideas. It's hard for me to judge how a bike rides (Thorn) when I haven't ridden it, but others have. And when professional riders don't mention the lack of something, I take that as "its not needed". Perhaps, they didn't feel it would provide any further benefit to the already svelte handling. Maybe, after tracking the bike longer, they would have installed one, but for the street, quite possibly not. Who knows, its all conjecture on our parts.

I have ridden a Supermono on track back when I could fit on the damn thing, and I'll say, theres not a darn thing I would ever change about it. It took every thing I could throw at it and just yawned (Kenny Roberts Im not in case you're wondering).

Interesting Cal, The Bimota supermono is a road registerable bike, well In Australia and Europe it is? , like every other bike from Bimota..?  Why would it have headlights if it were track only. What made you think it was track only..?  Any way, I looked for a couple of reviews on the Bimota and MCN say its brakes are good but not great compared to modern standards, it also only has 48HP and is flat out at around 90MPH  so its not like the 43mm forks are working that hard, I have 2 sets of Suzuki GSXR1100K multi adjustable 43mm forks that both have braces stock, but the gixxer is much faster and heavier, so the suspension forces are far greater, A much slower, far lighter bike would struggle to out do these forks   . In regards to "when professional riders don't mention things" comment, I have a good friend that has been a multiple Australian road race champion , he was even offered the Team Kawasaki world superbike ride Aaron Slight eventually took up in the 1980's, to make a long story short, I went for a ride with him one night , he borrowed his mates XS650 Yamaha, an average handler at best, both Greg and I had GSXR1100's, anyway, the guy that owned the 650 yammy said one thing before we left, "DON'T SCRAPE THE PEGS", they are brand new, within 2 minutes of being on the bike. Greg had not only scraped the pegs, he's scraped the entire left hand side of the lower left frame rail, he made that old Yammy do anything he wanted, and with me on the back... . My point is there is no way for you to know what Mr Bostrom was thinking and a good rider can ride anything well,  i'm absolutely sure that that bike could be made to handle  better, I'm not saying it doesn't handle well,but at speeds of around 100 MPH and being a light weight, its not doing a great deal to over stress the suspension or frame for that matter....

Good job finding a bike that almost has the exact same specs as an example...

[Roach Carver]

 I like it with or without. I wonder how much fab work was involved with the motor swap. Seems to be an overlooked component to the debate.

[calj737]

Oh, that bike is on my "List" to own. It and the Ducati Supermono! The originals were track oriented. They came out later with a "biposto" model for the street. Top speed of the tracker was 130MPH and from the factory it didn't have a brace, only a damper was offered as an option. I suspect that due to the girth of the forks that brace was deemed unnecessary, as well as the modern brakes, but who knows? I'm not a professional rider and can't thrash a motorcycle to its limits no matter my fantasies. I have and can ride pretty well, but have seldom found a properly adjusted stock suspension unable to meet my needs and riding venues.

But thanks for the reply! 

[turboguzzi]

gee, what a slogging boxing match... lets start with some FACTS? in the heydays of the 500 vintage class here in italy which was made of  90% CB500/4s, i've seen anything, from no bracing, to either frame or fork to fully braced everywhere, in the winners circle.
what does it mean? when you are at the sharp end, it's all down to rider preference, "feel" if you want, some like it super solid, some loose and slidy.
reminds of the anecdote of the time Kenny roberts did cagiva a favour and tested their 500 gp machine just to see why they were so slow.... they way he had set it up (super rigid suspension, steering damper full on), he made super fast times, but the bike was unrideable to anyone else!
even with pro riders, some are known to care little about setup, some are super finicky. draw your own conclusions!
 

 

[SOHC4 Cafe Racer Fan]

I've also heard the story where the young riders on the KR team made excuses to Roberts about the limitations of the bikes they were riding, so he suited up and blew them away on the same equipment.  King Kenny is on another planet.

I appreciate everyone's comments.  Like I said, the whole point of this thread was to post my realization that a stock front can actually provide a great ride; not that it cannot be improved even more.  Also, E-Boz and B-Boz were there all day to test the bike and provide feedback on what was good, bad or could be improved -- not just get footage for the tv show.  They are both very good at testing and development, which entails giving candid feedback.  So, if the bike "needed" a fork brace, they didn't let on, BUT that's not to say that a fork brace might not provide some improvement.  Does this bike compare to Ben's championship superstock Graves R6? Not likely.  So, I don't think they were judging it on that basis, but pointing out things that worked and things that needed improvement.  Again, this little bike is not a superbike or supersport killer -- but damn if it isn't one hell of a fun bike to ride! If only my 650 motor weighed 50-60 lbs less!  This 600 motor is far from the stock 500EX motor, with lots of internal performance upgrades.

One more amusing B-Boz story.  During one of his sessions on this bike, he did not like the line he was taking through a turn because it was going to affect his line on the next two turns.  SO, while leaned over and dragging knee, he used his knee to lift the bike up and move it over about 4 or so inches without missing a beat.      I don't know about the rest of you, but I've never head of such a thing.

Mock up



Pre-Test


Getting down

[SOHC4 Cafe Racer Fan]

never mind the brace... would be nice to know what exactly he did on the frame.

Here are some photos of the gussets, frame brace and swingarm brace.

[flatlander]

thanks, that's good to see. nothing further upfront, or at the steering head?

[SOHC4 Cafe Racer Fan]

Nope.

[Stev-o]

Great track action pics, Don. What track and who shot em?  Thx

[gschuld]

Cb750 cafe racer fan,

I'm curious, do you know whether the front axle was swapped put for a solid 20 mm rod instead of the factory front axle?  Rod (Voxonda) and others have mentioned that it makes a big difference stiffening up a CB front end, Rob says more so than a fork brace.  If so, that could help explain the good handling.

The front forks are also pulled up in the trees a bit.  It looks to have only about 3 1/2"  of travel between the sliders and lower tree static.  This reduces the unsupported span increasing the stiffness to some degree.

Regardless, thanks for sharing.  Nice looking bike.

George

[turboguzzi]

talking about ex500 powered racers, here's a proper one

[754]

XL 250 and 350 fork sliders are 4 bolt bottoms, and 35 mm.   They may be worth considering if limited to 35mm.
The bad part is mounting your calibers. Part of the 69-72 caliper mounts  are there, but higher up, may be a blessing if you want to run larger rotors........ Just an idea I thought worth mentioning.

[Retro Rocket]

gee, what a slogging boxing match... lets start with some FACTS? in the heydays of the 500 vintage class here in italy which was made of  90% CB500/4s, i've seen anything, from no bracing, to either frame or fork to fully braced everywhere, in the winners circle.
what does it mean? when you are at the sharp end, it's all down to rider preference, "feel" if you want, some like it super solid, some loose and slidy.
reminds of the anecdote of the time Kenny roberts did cagiva a favour and tested their 500 gp machine just to see why they were so slow.... they way he had set it up (super rigid suspension, steering damper full on), he made super fast times, but the bike was unrideable to anyone else!
even with pro riders, some are known to care little about setup, some are super finicky. draw your own conclusions!

Thats exactly what I covered above....   Good riders can adapt to almost anything....

[SOHC4 Cafe Racer Fan]

Cb750 cafe racer fan,

I'm curious, do you know whether the front axle was swapped put for a solid 20 mm rod instead of the factory front axle?  Rod (Voxonda) and others have mentioned that it makes a big difference stiffening up a CB front end, Rob says more so than a fork brace.  If so, that could help explain the good handling.

The front forks are also pulled up in the trees a bit.  It looks to have only about 3 1/2"  of travel between the sliders and lower tree static.  This reduces the unsupported span increasing the stiffness to some degree.

Regardless, thanks for sharing.  Nice looking bike.

George

George,

I, too, am curious on the solid bar axle upgrade/modification, but it was not used on this bike.

Yes, you are correct about the fork position and the resulting stiffness.  This is not the most cush of street rides -- it is set up for track/racing.

Thanks for your input!

Don

[SOHC4 Cafe Racer Fan]

Great track action pics, Don. What track and who shot em?  Thx

The track is Ridge Motorsports Park in Shelton, Washington.  Photo credit: unknown.

[SOHC4 Cafe Racer Fan]

talking about ex500 powered racers, here's a proper one

That's sexy!