Topic: 750 K8 Tire size combos

[brewsky]

The 17" rear really throws a kink into tire choices for OEM sizes (3.50-19F and 4.50-17R)

Currently running 100/90-19 qnd 130/90-17, the supposed "common metric equivalent", but they look too wide for the rims to me, and the rear is wearing flat as a pancake.

Anyone use the 90/90-19F, 120/90-17R combo? Lools like it would be slightly shorter, but still wider than the stock sizes. Those sizes appear to be available in the Avon Roadriders and would lower the bike approx 1/2" from way it is now.

[lucky]

The 17" rear really throws a kink into tire choices for OEM sizes (3.50-19F and 4.50-17R)

Currently running 100/90-19 qnd 130/90-17, the supposed "common metric equivalent", but they look too wide for the rims to me, and the rear is wearing flat as a pancake.

Anyone use the 90/90-19F, 120/90-17R combo? Lools like it would be slightly shorter, but still wider than the stock sizes. Those sizes appear to be available in the Avon Roadriders and would lower the bike approx 1/2" from way it is now.

Yes it takes some research and the choices get thin.
I worked on this problem for two weks.
I bought the AVON combo.
The 19 front and 17 rear.

The front Avon roadrider 26 can be mounted facing either direction.
The rear is made for the rear only.
The outside diameters are nearly the same.
The rear is 130/90-17

I looked at Pirellli,Michelin,Avon,Dunlop, and Bridgestone.

Avon is the only choice that made sense.
Reports from this forum said the Avons were good and sticky.
Go with the Roadrider 26"s

Photo of the AVONS below.

CLICK once on the photo for a larger image.

[lucky]

Oh, i forgot to mention.
Many of these motorcycle parts places only list tires that are popular and FAIL to tell you that there are many more choices.
Go to the AVON website to actually see what IS available.
http://www.avonmotorcycle.com/

On the navigation bar go down to the ROADRIDER option.

I bought mine at Rocky Mountain ATV/MC.
So they were available. They also had tubes.

[brewsky]

Lucky,
What rims are those?
Same width as stock K8 chrome version?

[Grabcon]

I am running similar Avons as mentioned by Lucky. I am running 100/90/19 front and 120/80/17 rear. They look good and do not seem to wide for the rims. I am running the alloy rims of a CB750A.

[Grabcon]

Brewsky. I found a picture of mine so you can get an idea of the look.

[lucky]

Lucky,
What rims are those?
Same width as stock K8 chrome version?

Those are CB750A (alloy) stock wheels and are the same size as the CB750K steel wheels for 1978.

I may have made a mistake and the rear IS a 120. Sorry Brewsky.
I will go check ...be right back.

NOPE mine IS a 130 on the rear.

[brewsky]

Thanks for the replies guys........now you've got me wanting alloy rims too!

Anyone running a 90/90 front?

[Really?]

Choices get thin with that 19" front if you want a matching set and want to go a bit out of the norm.

[lucky]

The Honda alloy wheels are about 6 lbs. lighter.

Metric weight -don't know.

[brewsky]

OK.....looked up Avon site and their recommendation for the 750 K7 is the 100/90 and 130/90 combo......BUT....their site also says the recommended rim width for a 100/90 is 2.50, with the minimum width of 2.15.
My front rim is 1.85 (DID) and sure looks like the stock one to me.

So I call Avon and they say NOT to run a 100/90 on a 1.85 rim, and that the stock front rim for the K7 must have been at least 2.15??

I don't think so.....am I wrong?

He said the reason I couldn't use the 90/90 and 120/90 combo is the load rating is less???

Using this logic, there is no acceptable tire for the front at all?

[Boulevard_beck]

I have some Avon Road Runner/Rider wheels ordered and on the way: 130/80-17 rear and 100/90-19 front. I know that someone else on the forum was running 130/90 and 100/90 currently on their 78 750k, so I would assume that you'd be ok with those. However, Dime City didn't have the 130/90 rear, so I went with the 130/80 rear. I guess I'll just hope that it works and see what happens.

[TwoTired]

Metzeler lasertec is available in 3.50 - 19 M/C 57H TL


You'd have to go with 130/90 rear from them, though.  Perhaps a bit big, but isn't the rear 17" rim a 2.50 width?
I do think a 120 rear is a "better" choice.


Cheers

[brewsky]

Thanks for the info TT...I'm getting google eyed from reading all the tire charts. The K7 and K8 are 17" rear rims, 2.50" wide.

The reason I was looking at the 90/90 and 120/90 combo was the diameters are equal and the widths are closer to stock, but the variences in manufacturers dimensions for the same size is frustrating.

IE, the Lazertec 3.50 and the 100/90 are both listed as 99mm wide, with recommended minimum rim of 1.85

The Roadrider 100/90 is 109mm wide, with minimum recommended rim of 2.15.

Since the Avon site recommends the 100/90 for the K7, but their own chart as well as their representative says not to use that size on a 1.85" rim,........and the K7 and K8 rims ARE 1.85....what gives??

It looks like everyone who is running a 100 or larger Roadrider on the front is at risk according to Avon, and that seems to be a large number according to all the tire posts I have read.

The Avon rep was at a loss to explain the inconsistency, except to say that IF the rim IS 1.85, then DON'T use that recommendation.

His reason not to use the 90/90 was the load rating was less. The 90/90 is rated at 52V (441 lbs), and the 100/90 at 57V (507 lbs)
(I'm assuming those ratings are per tire loads)

Is that a big enough difference to worry about? Is being at the edge of load rating worse than being at the edge of the pinch angle??

[bollingball]

Quote from lucky  The front Avon roadrider 26 can be mounted facing either direction.
I believe you but looking at the picture you posted it just looks back asswards to me. It looks like any water would be channeled to the center of the tire. Anyone else have this tire mounted this way? Am I missing something it will not be the first time.

Ken
edit here is the picture.

[bollingball]

So I call Avon and they say NOT to run a 100/90 on a 1.85 rim, and that the stock front rim for the K7 must have been at least 2.15??

I don't think so.....am I wrong?

Brew You are correct they don't know what they are talking about. Probably some kid that has never seen one of our bikes. Heck some older guys haven't either.

Ken

[Stev-o]

I just went through all this and ended up ordering Dunlop D404's:
130/90-17 R and 100/90-19 F [have not received/mounted them yet].

There are not a lot of options with the 130/90 and I wanted a better than average tire.

[brewsky]

Ken,

I'm not sure the guy I talked to was any older than my tires!

Steve,

I'm running Dunlops in those sizes now, they just look to me like there is an awful lot of rubber hanging out past the edges of the rims.
I've probably put about 30,000 miles on dunlops in that size combo on the K8 so far, so I'm sure they will "work".
I was just looking for something "better" and closer to stock, and the Avons were highly recommended on this board........and they are available in closer to stock sizes I mentioned (90/90F, 120/90R), but now I don't know.....

[Really?]

The 130/90's are a FAT tire for sure.  I am running that on a 3.5 inch rim. 

[lucky]

OK.....looked up Avon site and their recommendation for the 750 K7 is the 100/90 and 130/90 combo......BUT....their site also says the recommended rim width for a 100/90 is 2.50, with the minimum width of 2.15.
My front rim is 1.85 (DID) and sure looks like the stock one to me.

So I call Avon and they say NOT to run a 100/90 on a 1.85 rim, and that the stock front rim for the K7 must have been at least 2.15??

I don't think so.....am I wrong?

He said the reason I couldn't use the 90/90 and 120/90 combo is the load rating is less???

Using this logic, there is no acceptable tire for the front at all?

The stock rim IS 2.15

Make SURE you are measuring the rim the correct way.
I bet if you measure the outside it is 2.15. Try that.
=WM3

[TwoTired]

I bet if you measure the outside it is 2.15.

...and that is the wrong way to measure the bead seat width, unless you know beforehand exactly what the rim metal thickness is.

[Stev-o]

Steve,

I was just looking for something "better" and closer to stock, and the Avons were highly recommended on this board........and they are available in closer to stock sizes I mentioned (90/90F, 120/90R), but now I don't know.....

What do you mean by better?  Something that has not been discussed that I am aware of:

Our bikes were designed and manufactured with old tech inch size tires [and why inch? these are Japanese bikes!]

Modern rubber is far superior, no question there. But would differant metric size tires and wheels be recomended by the engineers in todays world?

[TwoTired]

Our bikes were designed and manufactured with old tech inch size tires [and why inch? these are Japanese bikes!]

Inch sized tires were what was being made, and most popular while the bike was being manufactured.  And, they were pursuing the popular marketplace.  Honda didn't make the tires.

Modern rubber is far superior, no question there.

I do question that.  Where/what is your support data?

But would differant metric size tires and wheels be recomended by the engineers in todays world?

Weird question phrasing.

Modern bikes are set up with the geometry to take advantage of modern tire availability.  But, you don't turn a 40 year old bike design into a modern one by putting modern tires on it.



I actually do question

[Stev-o]

Our bikes were designed and manufactured with old tech inch size tires [and why inch? these are Japanese bikes!]

Inch sized tires were what was being made, and most popular while the bike was being manufactured.  And, they were pursuing the popular marketplace.  Honda didn't make the tires.

Modern rubber is far superior, no question there.

I do question that.  Where/what is your support data?

But would differant metric size tires and wheels be recomended by the engineers in todays world?

Weird question phrasing.

Modern bikes are set up with the geometry to take advantage of modern tire availability.  But, you don't turn a 40 year old bike design into a modern one by putting modern tires on it.



I actually do question

If I'm not mistaken, these bikes came w/Bridgestone tires, which are made in Japan.
I find it odd that they came w/inch sized tires.

TT - you may be one of the few that do not think modern tires are better.
From the Motorcycle Safety Foundation:
Tires, which are particularly crucial components on a two-wheeled vehicle, have advanced significantly and have contributed much to vehicle performance, reliability, and safety. Modern tires are more durable, offer better traction for turning and stopping, and have contributed to significantly improving stability compared with their counterparts of the 1970s.

http://www.nhtsa.gov/people/injury/pedbimot/motorcycle/00-nht-212-motorcycle/motorcycle43-44.html

You are correct, cannot turn a 40 yr old bike into a modern one with tires alone.
Rephased question:  Would the Honda engineers designed the CB750 with wider rims and tires if today's tire technology was available then?
[Not looking for an answer, just something to think about]. I think so since all the modern bikes seem to have wider tires.

[lucky]

It only makes sense to increase the contact patch of the tires as you increase the HP. -LUCKY

BTW...The motorcycle does not know 33 years went by.  After it is rebuilt it just goes on more adventures. The roads still have asphalt on them..

I was just remembering that back when the CB750 was introduced, the Harley's still had big fat tires on them LOL..lol.