Topic: Front-End Thinking Changed

[SOHC4 Cafe Racer Fan]

I used to think that the stock CB750 and CB550 forks were spindly and needed a fork brace and Race Tech internals to obtain a well-handling, higher-performance front end.

This last weekend, I rode my friend Ian's bike -- a 1977 CB550 frame gusseted with added cross-member bracing, a braced swingarm, but stock front forks (and no fork brace) -- and powered with a Kawasaki 500EX engine bored out to a 600cc (with cam) and head work producing 67 bhp at the WHEEL and 45 ft/lbs of torque across the board.  It is notable that the bike weighs ONLY 324 lbs. wet with a full tank of gas.  The bike is SUBSTANTIALLY narrower than a CB550 (due to a parallel twin engine) with a lower center of gravity (largely because the motor not only weighs less but is less top-heavy).  It feels neutral between your legs and effortless to flick from side to side.  Combine that with a powerplant that produces a good amount of power and torque and it is the epitome of a FUN MACHINE.  Ian and his shop Twinline built the bike in 2012 for Café Racer TV with the objective of building a race bike worthy of the Boz Brothers.

This IS the best handling CB I have ever ridden and one of the best handling bikes I have ever ridden.  Yes, I have ridden faster bikes, but this one carves sharper than my track-prepped 2003 GSX-R750 and way sharper than my 2005 RC51.  The turning is intuitive -- think left go left, think right go right. 

How then is this nearly 40 year old bike handle so damn nimble yet planted without any fork brace or Race Tech goodies??  Reduced weight, the right amount of chassis stiffness and flex, and the inherent frame geometry of the 550.  As Brent Waller will attest, the reduction of weight not only gives you speed but reduces the force needed to change direction and the stress placed on the suspension.
http://www.twinlinemotorcycles.com/?p=1428



Ian Halcott at a Backfire Night in Seattle this Summer


Ben Bostrom testing The Thorn


Moto Channel Video

[seanbarney41]

Do you know what Ian's reasoning for not using a fork brace was?...I believe that it handled excellent without a fork brace, but also believe it would be that much better with a fork brace. 

[bwaller]

I've never seen that bike, cool idea. Seeing it leaned against the pole it seems tiny.

We have a couple "breathed on" EX500's racing and they are formidable race bikes. (read...f'in fast) No wonder you enjoyed it Don.  Light weight & big power = mucho fun. Just ask turboguzzi about his 70hp big single in a modern TZ250 chassis. 

Like Sean says, if it's good now, a brace and modern fork internals would make it feel even more planted!

[Captain]

 This is light weight (171 kg) big power (180 RWHP) with altered rake, trail and all the bracing making it one of the best handling old school bikes there is.
 To do all this requires a very good of understanding of the dynamics involved................. But it can be done.

 Captain

[bear]

This is light weight (171 kg) big power (180 RWHP) with altered rake, trail and all the bracing making it one of the best handling old school bikes there is.
 To do all this requires a very good of understanding of the dynamics involved................. But it can be done.

 Captain

That you Brent?
Finaly decided to join us mate?

Cheers,
Brian

[Captain]

Yes it's me............ I've been reading & watching for a long time, but decided to take the plunge.

 Captain

[bear]

Hey all, Brent's the owner and builder of what is arguably the quickest DOHC Honda going around.
We use some of Bren'ts gear in our Hy-Vo motors.

Good to have you on board mate.



Cheers,
Brian

[calj737]

This is light weight (171 kg) big power (180 RWHP) with altered rake, trail and all the bracing making it one of the best handling old school bikes there is.
 To do all this requires a very good of understanding of the dynamics involved................. But it can be done.

 Captain

That bike looks like its screaming even though its standing still.... Scares me, and I'm fearless 

[Captain]

 Thank you for the kind words............

 I actually have a SOHC 750 that I turbo'd in 1973 and it was this bike that got me started on the Honda journey and that I'm still on today.
 Learnt a few things over the years about these bikes and engines and hopefully I can contribute to the forum here.

 Captain

[SOHC4 Cafe Racer Fan]

This is light weight (171 kg) big power (180 RWHP) with altered rake, trail and all the bracing making it one of the best handling old school bikes there is.
 To do all this requires a very good of understanding of the dynamics involved................. But it can be done.

 Captain

375 lbs with 180 RWHP is a formidable bike.  Nice ride, Captain (Brent).

[calj737]

375 lbs with 180 RWHP is a formidable bike.  Nice ride, Captain (Brent).

I'm thinking with that achievement, he may be due a promotion? Can I get a second to nominate him for General?

[SOHC4 Cafe Racer Fan]

Do you know what Ian's reasoning for not using a fork brace was?...I believe that it handled excellent without a fork brace, but also believe it would be that much better with a fork brace.

Sean,

I gave the bike a pretty spirited test ride and it did not need a fork brace, very much unlike my experience riding my other CBs.  Of course, I had never before ridden a CB weighing 320 lbs with a full tank of gas, with a gusseted and braced frame and braced swingarm.  The suspension was set up more for track than street with very sticky rubber, so it was not a comfort ride, but it was VERY well planted.  I would love to take it on a track.

I'll try to get some more feedback from Ian about the efficacy of a brace.

Note: this bike was ridden HARD by professionals Eric and Ben Bostrom at a track and neither complained about the suspension.  Their ONLY issue was the size of the front brake disc and the need for more front braking power.

[SOHC4 Cafe Racer Fan]

This is light weight (171 kg) big power (180 RWHP) with altered rake, trail and all the bracing making it one of the best handling old school bikes there is.
 To do all this requires a very good of understanding of the dynamics involved................. But it can be done.

 Captain

375 lbs with 180 RWHP is a formidable bike.  Nice ride, Captain (Brent).

Yeah, that's a bonafide race superbike even by modern standards -- with that hp to weight ratio.

[seanbarney41]

Do you know what Ian's reasoning for not using a fork brace was?...I believe that it handled excellent without a fork brace, but also believe it would be that much better with a fork brace.

Sean,

I gave the bike a pretty spirited test ride and it did not need a fork brace, very much unlike my experience riding my other CBs.  Of course, I had never before ridden a CB weighing 320 lbs with a full tank of gas, with a gusseted and braced frame and braced swingarm.  The suspension was set up more for track than street with very sticky rubber, so it was not a comfort ride, but it was VERY well planted.  I would love to take it on a track.

I'll try to get some more feedback from Ian about the efficacy of a brace.

Note: this bike was ridden HARD by professionals Eric and Ben Bostrom at a track and neither complained about the suspension.  Their ONLY issue was the size of the front brake disc and the need for more front braking power.

as I said before, I am sure it handled very well, but I am sure it would handle better with a fork brace.  Do you really think a fork brace is going to have any detrimental effect on an otherwise stock cb550 front end?  I bet the Bostrom bros would have had less issue with the front brake, because a fork brace helps braking too.  So, spend 90 more bucks, add maybe 1 pound of weight, get even better handling.  I really don't understand what your thinking is here, cr750fan...that this bike performed well because it didn't have a fork brace?

[bwaller]

Welcome to this area of motorcycle madness Brent. I've seen your bike previously and it is indeed a weapon. No wonder when I see what you're up against in that part of the world! I read with interest about some of your development work. Very determined to get to this point... congratulations and good luck.

[calj737]

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.

[seanbarney41]

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 right...so why not use a fork brace and make things even better?...that is my question

[calj737]

He also said, "He'd check with the builder and get his feedback and input." if a bike behaves extremely well without a brace, then unr what circumstance do you believe it requires one? If you ride the bike hard and have ZERO perceived need (even two pro riders) then what is it that makes you feel it's necessitated? Public roads don't really lend themselves to tire thrashing riding...

[seanbarney41]

this is just ridiculous...CalJ, I am not posting on anymore threads you become involved with

[754]

Welcome aboard Brent. What displacement is that beast.
Is the rear Dymag 4.0 or 4.5?  I have one of them..

[Stev-o]

375 lbs with 180 RWHP is a formidable bike.  Nice ride, Captain (Brent).

I'm thinking with that achievement, he may be due a promotion? Can I get a second to nominate him for General?

I'll second that!   180hp on a 375lb bike would scare me.

[Captain]

Welcome aboard Brent. What displacement is that beast.
Is the rear Dymag 4.0 or 4.5?  I have one of them..

 74 mm bore X 69 mm stroke............ 1187 cc   Rear Dymag is 17" x 5"  This all in accordance with NZ Pre 82 classic racing rules. (Period 5 in Australia)

 Captain

[754]

The 750 emblems are a very nice touch.!

[kmb69]

Yes it's me............ I've been reading & watching for a long time, but decided to take the plunge.

 Captain

Welcome aboard Brent. Look forward to your expertise applied to the SOHC's.
Been needing to call you but I've been busier than a cat covering it up.

Keith

[SOHC4 Cafe Racer Fan]

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.