Tire fitment

[alehman]

Hey all,

I have a few questions. My bike is now roadworthy except for the dryrotted tires it came with, so I'm in the market for a new set. I don't really know anything about tire fitment.


Firstly, the wheels I have are the comstars off of the 79K limited edition. Are all different years of comstars the same dimensions? If not, does anyone know the dimensions of the comstars that went on the 79L?

Secondly, the syntax for the dimensions of the tires for these bikes is strange--- it's in the form of something like 4.50 H17 4PR, for example. How does this translate to the standard format WWW/AAXDD?

[shinyribs]

There are a few tires that you can find with the old 4.50 sizing. Most of the modern tread design are in the metric aspect ratio.like 110/90/19

I found a chart one time that converted this stuff.I'll see if I can find it

[shinyribs]

Here we are!  http://www.kgmotorcycletires.com/size_conversion_charts.htm

One thing is that different manufacturers tires can be sized slightly difference. For example my 120/90/18 Shinko 712 is waaay skinnier than my old Dunlop 404 of the same size. Sucks but it happens

[rrgunslinger]

There is a chart on this site some where.  I posted it several times. 

Harvey

On Aug 19, 2012 12:41 AM, "alehman [via Honda CB750'S]" <[hidden email]> wrote:

Hey all,

I have a few questions. My bike is now roadworthy except for the dryrotted tires it came with, so I'm in the market for a new set. I don't really know anything about tire fitment.


Firstly, the wheels I have are the comstars off of the 79K limited edition. Are all different years of comstars the same dimensions? If not, does anyone know the dimensions of the comstars that went on the 79L?

Secondly, the syntax for the dimensions of the tires for these bikes is strange--- it's in the form of something like 4.50 H17 4PR, for example. How does this translate to the standard format WWW/AAXDD?

1979 CB750 10th Anniversary Edition

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[alehman]

Great! thanks for the help guys. I'm going for some coker diamonds.

rear:
http://www.cokertire.com/450-18-coker-classic-cycle-diamond-tread-blackwall-tire.html

front:
http://www.cokertire.com/400-19-coker-classic-cycle-diamond-tread.html

It looks like I'll have to stick with spokes though, because they don't make 17-inch diamonds that'll fit my rear wheel (currently a comstar). That is, unless anyone has an 18-inch comstar rear that they'd sell to me/trade for spokers...

[shinyribs]

I have an 18" rear comstar. Dont know if it would fit your bike or not. Came off a 76 F .

[alehman]

is it drum or disc brake? Mine's drum. But even if yours were drum, I guess i still don't know if it would work on a 79K.

[shinyribs]

Actually, let me rephrase that. I used it on a 76 f . I have no idea what it originally came on. It is a disc brake wheel. Areu looking for an early comstar or the later model inverted style? They were the black ones. Mine is an early silver one

[alehman]

Ah yes, mine is inverted.  I might have to stick with the spokers. It's a bummer because I want to go for the brat look, and most brats have those blacked out comstar wheels. I had a strange coincidence, though. I was looking around the web for brat-racer inspiration and I stumbled across this guy's website:

http://www.taimoshancycleworks.com/bikes/1980-honda-cb750-brat-racer-the-brown-one/


which is the same bike in this thread on our site:

http://honda-cb750-s.456789.n3.nabble.com/Tuning-problem-on-1980-CB750F-brat-racer-td4023368.html#a4023767

I got in contact with him and he very kindly answered some questions for me about what tires he used and about modding CV carbs for pods.

[alehman]

Help, I also know nothing about tubes. Do I want to buy tubes with center metal stems or center rubber stems? Is that just a matter of preference or is one not compatible with my wheels?

[Thorby]

My 2 cents:  I would resist the temptation to install the fattest tire possible, bigger than the original specified tire.  Yes, your bike would look more badass and more like a modern v-twin cruiser but I discovered that handling is negatively affected by an oversized rear tire.  When I switched to the thinner, factory-specified, rear tire my CB750 became noticibly more nimble while maintaning the same traction.

[alehman]

Damn, I just ordered them a few hours before you posted... I would've gone down a size. How do you feel it affects handling?

[Thorby]

alehman wrote

Damn, I just ordered them a few hours before you posted... I would've gone down a size. How do you feel it affects handling?

The fatter tire I had before was less nimble.  By that I mean that it was more difficult to lean the bike into a curve and this was more noticeable during low-speed maneuvering.  I wonder how many first timers have been on a wreck just because they couldn't lean the bike on time to clear the curve?  Also, a bigger fatter tire will consume a bit more fuel. On the other hand, some people may like this resistance to leaning because it gives the bike stability when moving in a straight line.

Now regarding friction, I can both brake and accelerate just fine.  But then, my old '76 may not have enough power to cause skidding of the rear tire when accelerating (even though it's got plenty of balls, imho).

I compared the tirewall for a bigger tire and confirmed that the fatter ones are meant to carry more weight.  You can check this specification yourself and perhaps determine that you do need the bigger tire to be able to take the weight of  you, your passenger, and your payload.  I weight 140 lbs, my occassional passenger weighs about the same, and I don't have saddle bags or accesories so I didn't see the need for a bigger tire based based on weight tolerances.  

Finally, I commute daily on my bike due to economic reasons, and I'm trying to save wherever I can.  Bigger tires are more expensive, you pay for more rubber.

[pat english]

those tires look cool..just to clear things up,you dont need to run mags to be "brat style"..brat style is big firestone replica tires,clubmans,or clip ons,and a flat seat..and it must be murdered out.

[alehman]

Yeah, I've seen some great brats that run spokes. I just like the comstar look.

This is a fav of mine with comstars:



with spokes:



I've been reading up on how the tires affect handling. When it comes to the front wheel, a taller profile will increase your trail which will give you more stability at the price of responsive steering. On the rear wheel, profile doesn't matter so much as the cross section (maximum width of the tire from sidewall to sidewall). The wider the tire, the harder it is to really lean into turns because the road can't as easily "ride up" onto the side of the tire. The coker diamonds are 4 inches at their widest, which compared to the rear wheel on my 79L is about the same.

[pat english]

yeah i like that blue one too..

[shinyribs]

That blue bike is perfect,I think. But that rear tire doesn't have much profile.Doesn't look like you could lean very far on that tire before hitting the corner of the tread. If you have ever hit that corner you know how gross it feels to feel the bike rock on that edge. Thorby is spot on with everything he said IMO. I went back to stock sizes and felt the exact same things he described. The guy I get my tires from races SOHC's on road courses ( sooo love to do that!)and he told me what sizes to run that make the front and rear profile match. Before, i would have to push the bike down to corner,now it literally falls into a curve! It actually likes to lean so much better now that I find my self counter balancing to upright the bike out of a corner now. Seriously,the bike leans so well that I often find myself doing 60-65mph sweepers in the mountains while sitting upright on the bike trying to keep it from laying down so far. It's an odd feeling to be sitting vertical when you should be leaning,but it works-and feels so cool

[alehman]

The tires I got are the same as what the brown bike in the photo I posted has, although I got a 4.00x18 for the rear instead of the 4.50x18. I spoke with the builder of that bike and 4.50x18 is what he used. My wheel should be pleasantly smaller. He also made a point to say that they "ride pretty well," although at the time I wasn't sure why that was important--- now I see!

[seestheday]

Hey shiney, isn't that the exact opposite of how you're supposed to take a turn aggressively?  Shouldn't your body be leaning into the corner, or even hanging off the bike?  If you have your body vertical then aren't you risking a complete loss of traction by increasing the lean angle required to make the corner?

http://www.visordown.com/advanced-riding/advanced-motorcycle-riding-course-hanging-off/12990.html

That is unless you're just goofing around at low speeds, then by all means, I'm not going to ruin your fun .

[Thorby]

seestheday wrote

Hey shiney, isn't that the exact opposite of how you're supposed to take a turn aggressively?  Shouldn't your body be leaning into the corner, or even hanging off the bike?  If you have your body vertical then aren't you risking a complete loss of traction by increasing the lean angle required to make the corner?

http://www.visordown.com/advanced-riding/advanced-motorcycle-riding-course-hanging-off/12990.html

That is unless you're just goofing around at low speeds, then by all means, I'm not going to ruin your fun .

I agree.  It's a little odd.  I do straighten my body a little to see better though.