General Thoughts About Handling

cbxtacy · Post by **cbxtacy** » Fri Nov 21, 2008 9:39 am

A few things to consider when modifying a CBX with different tires/wheels/etc. It's possible to take a stock X and lean it until something drags. I've done it. So bracing the frame does what? Makes the frame heavier. Now if you were to do something to give the CBX more ground clearance, you could get more lean angle and then you might want to consider it. I said consider. With more lean angle the rubber available for those skinnyassed wheels might not like that. So you go to modern, wide, 17" rims for a cool look and modern rubber. Oop's you just lost ground clearance. You put a modern front end on it (upside down because that's what all the sport bikes have) and you just lost some more ground clearance because most all are shorter then the CBX's front end. What's the purpose-to make it handle better or look cool? So now you want to get some more ground clearance and better tire selection? Forks by Frank ( http://www.frankmain.qpg.com/ ) makes fork tubes. They also make them longer then stock. Sometimes. They will do that for older fork tubes (like the CBX) that are thick/heavy fork tubes. They will NOT do it for modern fork tubes that are thin wall because of liability reasons. The thin wall tubes are nice because they're light. I believe the '93 GSXR1100 had forks just about as long as the CBX. Real close. But then to keep the ground clearance you'd have to run a 19" wheel. Ground clearance = lean angle = more speed through turns. So here you are, trick front end, heavily braced frame, and less speed through the turns then stock because of less lean angle. If you're the kind of person that's never drug anything on a reasonable stock CBX going around turns you might not have any problem. If you're the kind of person that knows that one of the first thing to drag in right hand turns is the center stand return spring where it goes through the tab on the center stand and have been having fun until you're heard a horrible noise because the center stand is now dragging on the ground after the last right turn and it scared the s**t out of you, there could be a problem. So how can you get a good handling bike with decent (not less) ground clearance and modern wheels/brakes? I'm going to deal with prolinks and Dunlop tires because I like prolinks and Dunlop ( http://www.dunlopmotorcycle.com/tirecatalog.asp ) has all the dimensions of their tires on their web site.

The rear is easy. CBR600F2 (1991-1994). It has a 4.5X17" wheel. Use a 160/60-17. The roadsmart is a nice tire and the dia is 24.89 v/s 25.95 for the GT501 in a 130/80-18 so you only lose .53 " in ground clearance when verticle. When you consider the tire is 1.25" wider and the widest point is closer to the ground then the GT501 when verticle, you actually gain ground clearance in the rear when leaned over. If you use a wider rim and the proper tire to correspond with the rim, the tire will hit the linkage for the shock. You could extend the swingarm but we're trying to improve the cornering here. So a simple modification for the rear is CBR600F2 with 4.5" wide rear rim. I've done it and it was practically a bolt up. Be careful buying tires because the Dunlop Roadsmart is 6.25" wide and the Dunlop Qualifier in 160/60-17" is 6.69" wide at the widest point. For a sprocket there are plenty of aftermarket sprocket manufacturers that would be happy to sell you a sprocket for the F2 using a 530 chain.

Now for the front. This is what I've done. Get a CBR600F3 (1995-1998) front wheel. Not the F2 but the F3. Why the F3? It has full floating rotors. Noticably better then the fixed rotors on the F2. Get forks from you know who that are 1.5 inches longer then stock. You lose 1.1" ground clearance from tire dia and will make it up with the longer forks. And then you'll pick up a bit from using a wider tire (just like on the rear). Axle dia is different. Use the CBX axle, get some CBX front wheel bearings, and make a spacer to between the bearings in the wheel and between the wheel and forks. Not too difficult. The brake rotors are the same dia as the prolink CBX. And they line up with the rotors. I believe you can machine the CBX speedo drive to work but all the conversions I've done use electronic speedos.

Now, if you've done this, you have modern rubber with more ground clearance. That's what I did with a CBX I roadraced in the 90's for a few years and I never felt like the bike was suffering from frame flex in the turns.

Yes that's me and that's a bike that Chris in CO now has. And I never braced the frame. And those are modern sport bikes chasing me.

alimey4u2 · Post by **alimey4u2** » Fri Nov 21, 2008 10:10 am

Thank you for that George....

karl sparks · Post by **karl sparks** » Fri Nov 21, 2008 11:06 pm

Awesome picture

Terry · Post by **Terry** » Sat Nov 22, 2008 12:41 am

Nice lean George,

so what tires did you use on it? How about gearing? 530 or 630 chain? Comstars on the track?

cbxtacy · Post by **cbxtacy** » Sat Nov 22, 2008 1:39 am

CBR600 wheels, 530 chain and sprockets, stock rear shock, stock front calipers. If you look at Dr Tom's race bike, he raised the engine and moved it forward a couple inches. Ground clearance. If you drag stuff in the turns you don't need better suspension or stickier tires, you need more ground clearance. That's why I run Kenda Challengers on my stock 82. A pair costs less then $100 and I've gotten as much as 8000 miles out of them. And I can drag stuff. I do feel a little more comfortable with Dunlop GT501's but they cost 3 times as much and last half as long. I usually go through 2 sets of Kenda's a year.

jkotsi · Post by **jkotsi** » Thu Mar 19, 2009 9:51 pm

Hi, first post but might as well jump right in.

Longer range plan is to set up a CBX for the track.

This is what I was thinking:

41mm CBR F2 forks 30.5" in lenght, I don't have stock forks to compare lenght.

Custom triples allowing for 1" of drop.

Convert Prolink to twin shock with chrome moly swingarm 19.5" from pivot to centre of adjustment.

CBR Hurricane of CBR F2 rims depends on class limit.

How do you raise the engine and move it forward? Is this a relative description - cut the steering head off, tuck the forks and move it back?

I am having the head cut off a CB900 to steepen the steering, shorten the wheel base and raise the engine(ground clearance) as well as a shorter swingarm. Do you do this with the CBX? The trianglation at the head may make it a lot more work.

Jim

cbxtacy · Post by **cbxtacy** » Fri Mar 20, 2009 5:27 am

I'm cheap. Stock trees and no bracing anywhere except for the prolink linkage. I put clipons below the trees so I could drop the forks down in them. CBR600F3 front wheel has same dia rotors as stock. Plus they're floating. The CBR600F2 rotor is smaller in dia and not floating. Have to change the wheel bearing and spacer to a smaller dia. I cut off the inside arm of the prolink and braced the outer. That was so I could use a CBR600F3 rear wheel with a 170 tire. If I was going to do it again I would not cut the linkage because that's a weak link, instead I would use a CBR600F2 rear wheel. It's 4.5" wide and a 160 will fit. Putting a big, fat, wide tire on the back will not make the CBX any faster. You're limited by ground clearance. I'm really not a competitive person, I did it all to have fun and because I love my CBX's. If I was a competitive person I would have picked a bike that had a lot more potential. In the vintage classes the CBX ran in there are so many other bikes that make more power, are lighter, handle better, are cheaper and easier to find. Not that I want to discourage you, the CBX just sounds and looks sooooo bitchen'.

cbxtacy · Post by **cbxtacy** » Fri Mar 20, 2009 5:33 am

and the stock forks from the axle center to the top are 32.5".

bbqb4racin · Post by **bbqb4racin** » Fri Mar 20, 2009 7:08 am

cbxtacy wrote:
the CBX just sounds and looks sooooo bitchen'.

Gotta love that statement! Agreed!

cbxtacy · Post by **cbxtacy** » Fri Mar 20, 2009 5:14 pm

and here's Ray's bike dragging sidestand on Mulholland

and here's another pic, I like his pipe

jkotsi · Post by **jkotsi** » Sat Mar 21, 2009 10:28 am

Thanks cbxtacy,

I like your approach to the build keeping it simple. What bike did your seat/cowl come from?

The CBX isn't going to be the best in the field for track riding but it is the most watched/talked about.

The Pro Link that was on the bike needed a complete re-build with a new shock that is why I had changed to the twin shock. After seeing your build I may re work the Pro Link and install the F2 rims.

I'm getting a price to build cast iron 315mm fixed rotors for the rims that I race with, if the price is good I will have a set for the F2's. The SS version I had were more than enough brake on the CB900F, however they were over drilled and started to crack.

It looks like I need to put 2" back in the front, 1 will be in the triple clamps, the 2nd will have to wait until the front end is tucked.

Those Schule pipes on Ray's bike are outstanding!

jkotsi · Post by **jkotsi** » Sat Mar 21, 2009 10:44 am

I had dinner with a frame builder last night and had always wanted to have a backbone frame on a CB, but this is the direction I will be going over next winter.

Has anyone seen this Tony Foale frame with body work?

cbxtacy · Post by **cbxtacy** » Sat Mar 21, 2009 12:04 pm

Tail section is from a 93/94 CBR900RR. I just chopped off the tail on the CBX and made tabs to bolt up the 900RR subframe. All the CBX electronics fit in the 900 tail and I used the 900 battery. When the engine is unbolted you can see the frame flex but the engine is a stressed member of the frame and I always dragged stuff before flex ever became a problem (much less even felt).

and as you can see by this picture taken by Andy Chadwick at Road Atlanta if I felt like it I could drag my knee.

cbxtacy · Post by **cbxtacy** » Sat Mar 21, 2009 12:14 pm

That's a real interesting looking frame. I hate to be a spoilsport but two things come to mind
1-valve cover removal
2-the money spent fabricating a tank and other things to fit could buy a LOT of beer

but it looks like the engine sits much higher in the frame then stock. That in itself is good.

cbxtacy · Post by **cbxtacy** » Sat Mar 21, 2009 12:22 pm

and if you're going to use F2 forks, the 94 model year were much better then the earlier ones. If you machine a custom top fork clamp with a drop in it, you can get 1.5" out of it, I did that on a GPZ750 Turbo. Top clamp ran me $800 by the time it was finished, it required a big chunk of aluminum. And if you put clipons below the upper, you can get the rest of the lost ground clearance there. Or machine bosses for tubular handlebars on the clamp (that's what I did). It was a REALLY big chunk (I think about 4x6x12").