Project CB350F cafe brat

jpmobius

where does this go?
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In general, I don't think a wider than desired rim is better than a narrower than desired rim, but it seems in my experience that tires of any particular size vary a fair bit depending on the manufacturer especially in cross section. In other words, a 90/90 x 18 tire from brand x can be distorted much differently than the same tire from brand y on the same wider (or narrower) than optimal rim. That's just an opinion based on my own experience and is totally non-scientific. Certainly a tire with a higher aspect ratio (the lower the second number is the higher the aspect ratio) will be more affected since the sidewall will be shorter. You can imagine how much different the installed cross section of a 110/80 tire will look on a 2.5 or 3.0 rim - how adversely this will impact the performance of the tire is hard to say and no doubt would depend on the manufacturer, but it is not something I would want to do. That said, I fit a tire that is appropriate to the rim, and if I am determined to fit a wider or narrower tire I change the rim width. I wouldn't worry at all about miss-matching rims aside from wanting them to look the same.

Keep in mind that your bike originally came with a 1.6 front and a 1.85 rear (from memory - which never was that great) and drove very nicely. Going up one size front and back, and fitting appropriate tires is a much more substantial change than may seem to be intuitively obvious as bikes as a rule are fairly sensitive to tire and wheel sizes. And remember, the wheel weight - which is all unsprung weight is at least as, if not more so, important as tire size and might even be a lot of the impact of fitting larger tires as bigger tires are substantially heavier. So when you go up just one size in rim width and fit appropriate tires, you are adding both wheel and tire weight both front and back and you can imagine that not being inconsequential. Plus, adding insult to injury, you will have to run inner tubes on the spoke wheels. All that extra weight is weight that your suspension has to deal with, and as likely you will be reducing the overall weight of the bike - none of it from the wheels, the unsprung weight ratio will become smaller which works against you even further. So you have a very strong incentive for making and keeping the wheel/tire package as light as possible. The smaller and lighter the bike, the more important the wheel weight is. In general, I go up one size in rim width if I am building new wheels, and fit the matching tires. Part of that is due to the tire size availability. A 90/90 x 18 tire is a mighty small tire these days!
 

stubsryan

New Member
jpmobius said:
In general, I don't think a wider than desired rim is better than a narrower than desired rim, but it seems in my experience that tires of any particular size vary a fair bit depending on the manufacturer especially in cross section. In other words, a 90/90 x 18 tire from brand x can be distorted much differently than the same tire from brand y on the same wider (or narrower) than optimal rim. That's just an opinion based on my own experience and is totally non-scientific. Certainly a tire with a higher aspect ratio (the lower the second number is the higher the aspect ratio) will be more affected since the sidewall will be shorter. You can imagine how much different the installed cross section of a 110/80 tire will look on a 2.5 or 3.0 rim - how adversely this will impact the performance of the tire is hard to say and no doubt would depend on the manufacturer, but it is not something I would want to do. That said, I fit a tire that is appropriate to the rim, and if I am determined to fit a wider or narrower tire I change the rim width. I wouldn't worry at all about miss-matching rims aside from wanting them to look the same.

Keep in mind that your bike originally came with a 1.6 front and a 1.85 rear (from memory - which never was that great) and drove very nicely. Going up one size front and back, and fitting appropriate tires is a much more substantial change than may seem to be intuitively obvious as bikes as a rule are fairly sensitive to tire and wheel sizes. And remember, the wheel weight - which is all unsprung weight is at least as, if not more so, important as tire size and might even be a lot of the impact of fitting larger tires as bigger tires are substantially heavier. So when you go up just one size in rim width and fit appropriate tires, you are adding both wheel and tire weight both front and back and you can imagine that not being inconsequential. Plus, adding insult to injury, you will have to run inner tubes on the spoke wheels. All that extra weight is weight that your suspension has to deal with, and as likely you will be reducing the overall weight of the bike - none of it from the wheels, the unsprung weight ratio will become smaller which works against you even further. So you have a very strong incentive for making and keeping the wheel/tire package as light as possible. The smaller and lighter the bike, the more important the wheel weight is. In general, I go up one size in rim width if I am building new wheels, and fit the matching tires. Part of that is due to the tire size availability. A 90/90 x 18 tire is a mighty small tire these days!
Excellent advice! I will change my order. Hopefully I can find 1.85 for the front and 2.15 for the rear. This bike is a combination of form and functionality with each being as important as the other. Short of that I will get 2.15 front and rear. It just seems really hard to get smaller than 2.15x18 rims on Alibaba. It’s all my budget will allow as I’m running a business with other commitments. Thanks mate


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farmer92

Member
Was going through Tony Foale’s book “Motorcycle handling and chassis design”
There’s a whole chapter on tires that makes for an interesting read.
There may be a PDF link floating around somewhere on the web, i recommend reading it.


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stubsryan

New Member
Thanks for the advice I have rims on the way. Also ordered a pamco electronic ignition with coils, leads and spark plug caps. Couldn’t help myself and ordered some rear shocks as well. I got some new carby rubbers which are way over priced. $80! Finally, I have a carb rebuild kit in the way and that’s what I’m working on at the moment. Just split it all down and have it soaking in mineral turpentine at the moment. It’s all filthy! probably going to buy an ultra sonic bath cleaner tomorrow to get them looking clean


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stubsryan

New Member
So I’m working on the tank at the moment while I can do some grinding during the day. Two areas that I have been putting off are the tank and rear hoop. So this tank isn’t original to the 350 so it’s being a bit difficult to make look right. I like the shape so I’m determined to make it work. Here’s the issue, I want the bottom line of the tank to run parallel with the seat section. Also it can’t foul the side covers. The straight up option is to lift the tank at the front and rear until it all clears the side covers and is level. Thing is, it sits super high up at the steering colum/triple clamp.


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stubsryan

New Member
There must be a way but I haven’t worked it out. One option is to go with the first picture. Grind the bottom of the tank line till I get the level I want and then tig weld it. If I go to that effort I will get rid of the curve at the back of the tank as per this photo


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Luugo86

'73 CB350, '78 XS650 Cafe Killer
Hey man, do you have any progress photos of where you cut the frame in the rear, and how u fit/welded up the frame slugs and the hoop? I'm about to do the same thing on a CB350, I don't see it being difficult but any advice/photos from someone who has already done it would be welcome.
 

LightsOut

Member
Luugo86 said:
Hey man, do you have any progress photos of where you cut the frame in the rear, and how u fit/welded up the frame slugs and the hoop? I'm about to do the same thing on a CB350, I don't see it being difficult but any advice/photos from someone who has already done it would be welcome.
Here's a pretty detailed video of it done really nicely. On a 550 I believe: https://www.youtube.com/watch?v=Mbx3jqKIUbo
 

stubsryan

New Member
Had a quick look at that video. Yeah that should help you. I’m fasting the seat a little differently so I can easily remove it if I ever want to. It will have flat bar bolted to the bottom of the seat. So this will sit down and in a locating grove in the rear where it won’t move and the front flat bar will sit on another aligning flat bar but it will also have adjustable latches to hold it down and tight into place. These latches will be hidden behind the side covers. I will post photos when I do it so people can look closely at my shitty tig welding skills ♂


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LightsOut

Member
Sounds cool, looking forward to seeing that solution. Most just go with bolting the seat on, but making it come off in a nice way is so much more elegant.


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stubsryan

New Member
Carbs are clean. Mixture screw was suck so I used an easy out which was a pain in the arse. Putting them back together now. New spokes are ordered. $150 from China. 304 stainless. Hopefully they fit. Will get to the seat next unless some valve bolts rock up from the UK.


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stubsryan

New Member
What a fucked process! I’m still at it. At least, the carbs will be clean, new everything and hopefully a worry free starting and running experience. I don’t know how you guys out there get a rebuild done with a missus and kids. This project has taken god knows how many hours and I’m probably only half way! Fark! Oh well, beats watching the lefty project here is Australia. Peace ✌


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