Topic: Customized CB 750 - Chassis geometry

[anotherCB]

Hey everyone, I have a highly customized 750 and have been looking at the bike geometry, since my steering is kind of heavy. Bike started as a K8 and i pulled rake, trail, etc. from online sources and compared with mine. Turns out my trail is around 20mm more than stock. Bike runs great on the straight, but takes some work to push it around the corners. I am adding a pic and also a spreadsheet comparing a stock bike versus mine.

Can 20mm more trail have such an impact on handling? Otherwise the bike is amazing, I am just curious what the pros have to say. Thanks.

[Alan F.]

Yes 20mm more trail will slow handling and increase straight line stability.  Sport bikes have less trail than choppers. Pm me for a link to Tony Foale's book.

[robvangulik]

The longer wheelbase combined with the longer trail will indeed make it hard to change course, but looking at the pic of that very nice bike it shouldn't be too difficult to raise the rear an inch or so, that can make just the right difference...

[JLeather]

I assume you've checked that there is no drag in the steering bearings?  20 mm more trail will make a pretty slight change in handling.  You'll feel it, but I wouldn't expect you to have to "push" the bike to turn.

[anotherCB]

Alan F: DM coming

robvangulik: Thanks! Honestly I am not too worried about how it rides, more like curious of how the different parameters impact handling. Another factor that should make steering heavier is the fact that I am leaned over so far, because of the clip ons. And I don't think I can raise the rear much at all, it can't be seen in the pic, but the chain runs very close to the top of the swingarm. 

calj737: The triple actually is from cognito moto, with the integrated motogadget unit. I measured it at 30 mm offset. If I decide to keep this bike I might consider this change, we shall see.

JLeather: No drag, but the problem is that I can't get it adjusted properly that there is no play and no drag. I have give it a tiny bit of play, to eliminate drag. Need to do fork seals anyways, so I will see if I can get that any better.

[Alan F.]

Already sent the link, feel free to share but we can't post it out in the open, that wouldn't fly.

[anotherCB]

Thanks.

[CB750R]

Surprised to hear it’s heavier than stock, I have a much older and milder fork/wheel swap I did in 2005. With FZR600 wheels. Going to 17” front end and with less offset on the triple than the stock CB I find mine quite quick steering. I also found that clubmans or drag bars felt heavier than a taller superbike bar it kinda looks like you have clipons?

Cool looking bike! It’s amazing how far these modern custom builds have gone, when I did my fork swap there was ONE other guy who’d done a fork swap I could find that was using “modern” sportbike wheels.

[anotherCB]

I think one reason for heavy steering is that I am leaned over forward so far. Yes, I am using clip ons, because I have the Cognito Moto triple tree that doesn't have handle bar mounts.

[seanbarney41]

I think one reason for heavy steering is that I am leaned over forward so far. Yes, I am using clip ons, because I have the Cognito Moto triple tree that doesn't have handle bar mounts.

I see lots of guys having bad luck with clip on and other low handlebars because they are not using their body to ride properly.  Make sure you are not supporting your body weight by leaning on the handlebars.  Support your body weight with your legs and stomach, keep your elbows slightly bent.  You should be able to keep your arms loose enough that you can flap your elbows like wings.  Yes, it may require practice and exercise but riding is fun, right?

[HondaMan]

If you choose a taller rear tire with a more round profile, it will speed up the steering on that chassis.

[anotherCB]

I would love to flap my wings but it's not only the clip ons being low, the tank is like 8ft long and positions me very far back, so that I have to lean forward quite a bit. I am 6'2" and have to reach forward very far. I went from regular clip ons to drag type clip ons, they come up 2 inches or so, that helps. If I want to ride comfortable, luckily I have other choices (BMW R75/5 and 1200 GS). It's a fun bike and I can live with the downsides, just wanted to educate myself a bit about geometry and how different factors impact the handling.

Just switched from a 180/55-17 tire to a 160/60-17, because the 180 was rubbing a bit. Hadn't though about that, definitely not a round profile on either of the tires.

[HondaMan]

I would love to flap my wings but it's not only the clip ons being low, the tank is like 8ft long and positions me very far back, so that I have to lean forward quite a bit. I am 6'2" and have to reach forward very far. I went from regular clip ons to drag type clip ons, they come up 2 inches or so, that helps. If I want to ride comfortable, luckily I have other choices (BMW R75/5 and 1200 GS). It's a fun bike and I can live with the downsides, just wanted to educate myself a bit about geometry and how different factors impact the handling.

Just switched from a 180/55-17 tire to a 160/60-17, because the 180 was rubbing a bit. Hadn't though about that, definitely not a round profile on either of the tires.

Would flat handlebars fit? The old SuperHawk (250/305cc) used to come with flat handlebars, which became the "Western style" in 1967, which had 1.5" rise. I had both those, and clip-ons at different times on it, and found the Western bars afforded much better control as it left me free above the fuel tank, not having to be laid right on it. It improved my "english" over the turns, especially on really tight courses: we sometimes had to race on Go-Cart tracks, if you can imagine that!

[seanbarney41]

Well, I certainly understand as I have an 86 gsxr 750...very long tank, very low bars, very high pegs.  Just wanted to make sure, as really, your body is part of the chassis geometry.  Geometry problems are certainly the main drawback of the massive modernization that your bike has undergone.  It has always been the reason, that in my opinion, working with more period correct and subtle modifications yields a more rideable bike and better performance improvement.  But don't misunderstand.  Your bike is awesome.  It just may require continueing to tweak it so that it will do what you want.  I think most of the necessary info is already here in this thread, you just have to fill in the blanks.

[754]

Can  your triple tree be drilled to mount risers ?

[brewsky]

Not to hijack.....but is that a Delkevic with Cone engineering muffler......I really like the look!

[anotherCB]

Sorry gents for the long absence from the forum - but I made some progress! The geometry really was not the problem. The issue was that the PO did the fork conversion but did nothing swap the steering stem for a longer one! The GSX stem is about 20mm to short so what he was he ground off some of the frame at the bottom, removed the washer under the bottom steering bearing to make just enough room to assemble this way. When the front wheel was in the air (on a lift) all was good, however when put on the ground the bottom triple tree would run against the frame, very slightly but still enough to make the steering heavy. I replaced with a longer steering stem now and all is perfect! Handles really well now for the setup!
To answer some of your questions, drilling the triple foe handlebars would not work, since I have the Motogadget mini in there.
The header is Delcevic stainless steel, not sure what the cone is.
Just started a channel on TikTok, look for venticar66 if you want to see some videos.
(Typing this on my phone hopefully I’m making sense!)

[754]

Show a pic of top tree... there may be a way to mount risers...

[anotherCB]

Here you go.

[Alan F.]

Among others Woodcraft makes clip-ons that come with up to a 3" rise, some even have angle adjustments.
They're all over ebay too.



https://woodcraft-cfm.com/collections/clipons-hand-controls?page=3

[anotherCB]

Yes, I got similar ones a few weeks ago after I started this thread, definitely made a bit of a difference.

https://www.ebay.com/itm/Alloy-Handlebar-Adjustable-50mm-Clip-On-MultiClip-Fork-Clamps-Fit-For-Triumph/184527613443?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

[754]

You could mount risers, with a single bolt each, left one ahead of green light on left.
 Or run riser caps  with spacers under them , the bolts running right thru into tree. May have to notch left one to see green light.
Of course I don't know what underside of tree looks like.
 I can sketch something if you like..

[anotherCB]

754, after I had started the post, I have switched to clip ons with a 2 inch rise, similar to what Alan F. posted (just a cheaper version  ). I also have a "comfortable" seat now, with 1 inch foam, so actually the bike is pretty rideable. After I figured out the steering I have gone on several 50-70 mls rides, which is really not that bad.
For longer distance rides I'll jump on my Airhead!

[Alan F.]

Pictures?

[anotherCB]

Here you go!

[Alan F.]

Here you go!

I can't seem to open those, I've never heard of that file format. Sorry.

[StockRider]

Apple iOS, high efficiency image files..., not so efficient for sharing.

[anotherCB]

StockRider, please teach me, how did you do that?
I don't like the HEIC format, but haven't found an easy way to convert them.

[StockRider]

StockRider, please teach me, how did you do that?
I don't like the HEIC format, but haven't found an easy way to convert them.

anotherCB, I used an online conversion tool (https://convertio.co/heic-jpg/), there are quite a few out there. Some appear to shift the color/saturation a bit from the original image. There are many details here: https://www.cnet.com/news/tools-bridge-between-apple-heic-and-jpeg-photos/. Including how to change storage settings on your device..., that changes the amount of space taken up by photos as well though.

[anotherCB]

Thanks, I'll look into this!

[goodtryer]

If you're using the Photos app on a Mac, you can export the photos to jpeg for posting. (File > Export > Export Photos)

[Alan F.]

That's a pretty big difference in comfort from a small 30mm? change. Have you heard of https://cycle-ergo.com/ you can input your measurements and custom bike measurements too I think, and it'll show you a graphical representation of the change in riding position for small changes.

[anotherCB]

Alan F., yes I use that site occasionally, have selected risers for my GS based on it! And I agree those extra 30 mm and less of a down angle make a big difference.

Stockrider, you are a genius. I went to my iPhone camera settings to Camera-> Formats -> Camera Capture and changed the settings from High Efficiency to Most Compatible. Now all my pictures are saved as jpegs on my phone! Need a SOHC forum to learn about my apple product!!