Topic: 750 K8 Tire size combos

[brewsky]

My definition of better is better quality rubber (ie traction, speed rating etc.) AND closeness to original design specs for sizing.
If I could find a 3.50-19 and 4.50-17 matching combo that didn't have a date that expired years ago, that's what I'd probably get.

My rims are stamped 1.85x19 and 2.50x17 and I assume that is the interior dimension at the inside of the flanges. I have no idea if the alloy rims from the F or A models are the same. I can't find the rim width listed in the shop manuals, although it might be hidden in there somewhere.

The outside width of the rims is much greater than the stamped dimension, but still no where near the width of the 100 and 130 tires that are on there now.

I also assume that the tire mfg charts are listing the inside width dimension, but I may be wrong on that?

[brewsky]

more pics

[brewsky]

one more.....

The bottom line is, the front tire is 1.1" wider than the rim,
and the rear tire is 1.6" wider than the rim
for 100/90 and 130/90

[Stev-o]

Brew - what rear tire is that? Don't recognize the tread pattern.

[brewsky]

It's a K627 Dunlop.....discontinued sometime in the past.
There's a few still available on ebay for cheap ($50 range), but the mfg date is 2003 and 2004 per the seller.

[TwoTired]

If I'm not mistaken, these bikes came w/Bridgestone tires, which are made in Japan.

..and sold to the world marketplace where brit  bikes (among others) were selling quite well.  Bridgestone was not a trend setter for size changes.  They met the market demand and then current pervasive labeling scheme.

The SOHC4 series was developed in their style to compete with the brit bikes.  And, I suspect more Bridgestone tires were used on the brit bikes than used on the Hondas.  Introduce a new product and incorporat something familiar to gain "converts".

I find it odd that they came w/inch sized tires.

It wouldn't be if you understood the timeline of metric conversion.

TT - you may be one of the few that do not think modern tires are better.

I didn't say that.  You assumed.  Which I suspected you were doing about "modern tires", as well.  Did you do research before or after I posed the question?

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. 

Mount those modern tires on wood rims and see how they compare in performance to tires and wheels of the period when the SOHC4 was made.
The SOHC4 design was serendipitous in its assembly of parts available at the time of manufacture.

Check out the concept of symbiosis.  Modern tires cannot perform to their potential, unless associated components perform at equal or better potential.

Besides, you don't ride on a tire, you ride on a motorcycle over varying roadway substrates.
Care to guess what the average traction component that the roadway half of the equation supplies in the entire world?  It is not just the tire that provides traction.  How does your "modern tire" provide increased traction on gravel roads?  Why do race cars use different composition tires depending on the track surface that are competing upon?

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.

I suspect the bikes frame geometry would have also been different, too.  Hind sight is 20-20.  But, have you noticed that putting wider tires on narrow rims is NOT an improvement?

Diamond studs are pretty and tough.  Diamond studs mounted on them, don't make turds pretty or tough.  (Although some flies may argue the point if I bothered to learn "Flyspeak".)   

Cheers,   

[Really?]

I just farted.  Really!

[brewsky]

Now that there has been time for the air to clear.........
I found this chart from Tower in a previous post:

[lucky]

My definition of better is better quality rubber (ie traction, speed rating etc.) AND closeness to original design specs for sizing.
If I could find a 3.50-19 and 4.50-17 matching combo that didn't have a date that expired years ago, that's what I'd probably get.

My rims are stamped 1.85x19 and 2.50x17 and I assume that is the interior dimension at the inside of the flanges. I have no idea if the alloy rims from the F or A models are the same. I can't find the rim width listed in the shop manuals, although it might be hidden in there somewhere.

The outside width of the rims is much greater than the stamped dimension, but still no where near the width of the 100 and 130 tires that are on there now.

I also assume that the tire mfg charts are listing the inside width dimension, but I may be wrong on that?

Lets just call it 1.85
Thats what I was talking about.
The most logical idea is that it should be the inside dimension but it is NOT!!-LUCKY

[lucky]

more pics

Lets just call it 2.50 and not quibble over .010 thousandths LOL..lol
Calipers were on a slight angle etc.,.

I mean really look at .010 on the calipers.

See what I mean???

[lucky]

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.

Not your fault.
What is not visible in the photo is the arrows stamped on the tire facing both directions to indicate it can be mounted in the front or the rear.
One arrow for facing forward, and one arrow for facing forward when placed on the rear of the bike. It indicates which direction for front mounting and which direction for rear mounting.

[lucky]

Now that there has been time for the air to clear.........
I found this chart from Tower in a previous post:

Yes...Very good, it shows 8 different tires that can work on a 1.85 rim.

There is a wide range of tires that can be accommodated.

[lucky]

The steel rims and the alloy rims are the same on the stock CB750A and the CB750K

[TwoTired]

The most logical idea is that it should be the inside dimension but it is NOT!!-LUCKY

I will ask you to prove that.
Or, state that it is only your opinion.

[TwoTired]

Now that there has been time for the air to clear.........
I found this chart from Tower in a previous post:

Yes...Very good, it shows 8 different tires that can work on a 1.85 rim.

No it does NOT!  It shows one that works correctly, 2 that are marginally acceptable, and 6 that fit and operate badly on a 1.85 rim width.

For a 1.85 rim, it shows that the stock sidewall pinch angle is 12.5 degrees.  ALL the metric tires have a pinch angle greater than that.  Yellow numbers read caution, non-ideal but kinda workable.  Red numbers are tires with a pinch angle that is unstable on that narrow rim.

For a 1.85 rim width, the closest replacement is a 90/90 metric and even that has a pinch angle alteration of ~10%.
A 110/90 alters the pinch angle by nearly 40%

Where did you learn to read engineering charts?

[lucky]

Now that there has been time for the air to clear.........
I found this chart from Tower in a previous post:

Yes...Very good, it shows 8 different tires that can work on a 1.85 rim.

No it does NOT!  It shows one that works correctly, 2 that are marginally acceptable, and 6 that fit and operate badly on a 1.85 rim width.

For a 1.85 rim, it shows that the stock sidewall pinch angle is 12.5 degrees.  ALL the metric tires have a pinch angle greater than that.  Yellow numbers read caution, non-ideal but kinda workable.  Red numbers are tires with a pinch angle that is unstable on that narrow rim.

For a 1.85 rim width, the closest replacement is a 90/90 metric and even that has a pinch angle alteration of ~10%.
A 110/90 alters the pinch angle by nearly 40%

Where did you learn to read engineering charts?

I said they fit ...I did not say they were optimal. Lets not get in a huff.
6+1+2=9 sizes?

[lucky]

The most logical idea is that it should be the inside dimension but it is NOT!!-LUCKY

I will ask you to prove that.
Or, state that it is only your opinion.

I did not say it was fact. I said it was my opinion that usually  a person would thinK that the inside of the rim where the tire fits is what is important.
But the OUTSIDE of the rim is 1.85

Anyway I put the Avon 100/90-19 on my 1.85 rim and it looks perfect.
Also my fender fits with this tire and no clearance issues.

[brewsky]

I haven't tried to do the math, but it looks like the 3.50-19 stock tire size fitted on the stock 1.85 rim would be out of the yellow zone, and it isn't even shown on Towers chart for some reason.

Also, to make things worse, it looks like the Avons run wider than the "standard" sizes,...ie the 100/90 is actually 109mm wide, making the angle even greater than that shown on the chart.

I'm even now thinking possibly a 3.25-19F, 120/90R Roadrider combo?......but that would actually be smaller stated size on the front than stock K-7&8....but, the 3.25-19 (3.86" wide)Roadrunner is actually wider than the "standard" 3.50 size shown in the chart.

[TwoTired]

I did not say it was fact. I said it was my opinion that usually  a person would thinK that the inside of the rim where the tire fits is what is important.
But the OUTSIDE of the rim is 1.85

No, it isn't.  On a steel rim, the outside edge is double or triple folded steel adding about 1/2 inch per side to the outside width measurement.
Have you ever actually measured a rim?

The outside measurement of my 1.85 inch steel rims is 2.917 inches.
The Comstar alloy 1.85 inch rim's outside diameter is 2.3 inches.

Tire manufacturers don't care about the wheel construction dimensions outside of the where the tire actually gets installed.  So, their rim width recommendations refer to where the tire bead seats.

[lucky]

I haven't tried to do the math, but it looks like the 3.50-19 stock tire size fitted on the stock 1.85 rim would be out of the yellow zone, and it isn't even shown on Towers chart for some reason.

Also, to make things worse, it looks like the Avons run wider than the "standard" sizes,...ie the 100/90 is actually 109mm wide, making the angle even greater than that shown on the chart.

I'm even now thinking possibly a 3.25-19F, 120/90R Roadrider combo?......but that would actually be smaller stated size on the front than stock K-7&8....but, the 3.25-19 (3.86" wide)Roadrunner is actually wider than the "standard" 3.50 size shown in the chart.

One of the things that happen with the tires when mounting them on different width rims is that the tire will have a different profile. The tire can be taller or fatter depending on the rim width. The 100/90-19 Avon looks right.
But it seems like you want a wider tire on that same rim.

There is another forum member right now complaining that he cannot put his fender on with a 110/90-19 tire because of clearance issues.

[lucky]

I did not say it was fact. I said it was my opinion that usually  a person would thinK that the inside of the rim where the tire fits is what is important.
But the OUTSIDE of the rim is 1.85

No, it isn't.  On a steel rim, the outside edge is double or triple folded steel adding about 1/2 inch per side to the outside width measurement.
Have you ever actually measured a rim?

The outside measurement of my 1.85 inch steel rims is 2.917 inches.
The Comstar alloy 1.85 inch rim's outside diameter is 2.3 inches.

Tire manufacturers don't care about the wheel construction dimensions outside of the where the tire actually gets installed.  So, their rim width recommendations refer to where the tire bead seats.

Brewsky actually shows a calipers ON the outside of a 1.85 rim in the photo.
That is what i was reffering to. The photo.

There is some kind of miscommunication because I agree with what you say.
It is stamped 1.85 on the outside of the rim and Brewsky shows the calipers ON THE outside of the rim. The calipers are showing 1.85

Anyway like I said I have a AVON 100/90-19 tier mounted on a 1.85 rim.
It looks right.

[TwoTired]

Brewsky actually shows a calipers ON the outside of a 1.85 rim in the photo.
That is what i was reffering to. The photo.

There is some kind of miscommunication because I agree with what you say.
It is stamped 1.85 on the outside of the rim and Brewsky shows the calipers ON THE outside of the rim. The calipers are showing 1.85

The caliper in the Brewsky's pic is reading way over 2 inches.  The dial is too fuzzy to make out.  Looks like it's about .8 past the 2 inch mark.

The 1.85 is the internal bead seat width.

Anyway like I said I have a AVON 100/90-19 tier mounted on a 1.85 rim.
It looks right.

Compared to what?
Do you do all engineering by looks?  To me, you've picked a style choice.  And, are disregarding any numbers that don't fit the style you've chosen.
I've done that, and paid for it with early wear pattern issues, and sluggish steering after the initial treads crown shape wears.  But, you CAN get used to it.  And, it really make you appreciate ANY new tire you put on to replace it.

[brewsky]

I did not say it was fact. I said it was my opinion that usually  a person would thinK that the inside of the rim where the tire fits is what is important.
But the OUTSIDE of the rim is 1.85

No, it isn't.  On a steel rim, the outside edge is double or triple folded steel adding about 1/2 inch per side to the outside width measurement.
Have you ever actually measured a rim?

The outside measurement of my 1.85 inch steel rims is 2.917 inches.
The Comstar alloy 1.85 inch rim's outside diameter is 2.3 inches.

Tire manufacturers don't care about the wheel construction dimensions outside of the where the tire actually gets installed.  So, their rim width recommendations refer to where the tire bead seats.

Brewsky actually shows a calipers ON the outside of a 1.85 rim in the photo..........There is some kind of miscommunication........ The calipers are showing 1.85

If you blow the picture up, you will see the caliper actually reads 2.78".

My 100/90 Dunlop 404 measures 98mm, but the Avon spec sheet says the 100/90 Roadrunner is 109mm........wonder what it actually measures?

I'm all for the big contact patch theory as long as it matches the original design parameters, but in the motorcycle case, I think the more the tread sticks out past the edge of the rim, the more you invite potential problems.

There's a whole "darksider" cult in the new goldwing community that advocates putting car tires on the rear, but I don't subscribe to that!

[lucky]

Brewsky actually shows a calipers ON the outside of a 1.85 rim in the photo.
That is what i was reffering to. The photo.

There is some kind of miscommunication because I agree with what you say.
It is stamped 1.85 on the outside of the rim and Brewsky shows the calipers ON THE outside of the rim. The calipers are showing 1.85

The caliper in the Brewsky's pic is reading way over 2 inches.  The dial is too fuzzy to make out.  Looks like it's about .8 past the 2 inch mark.

The 1.85 is the internal bead seat width.

Anyway like I said I have a AVON 100/90-19 tier mounted on a 1.85 rim.
It looks right.

Compared to what?
Do you do all engineering by looks?  To me, you've picked a style choice.  And, are disregarding any numbers that don't fit the style you've chosen.
I've done that, and paid for it with early wear pattern issues, and sluggish steering after the initial treads crown shape wears.  But, you CAN get used to it.  And, it really make you appreciate ANY new tire you put on to replace it.

No I do not do things just by how it looks.

I went to the AVON tire website and used it to pick my tires.
I also called the AVON rep to make sure it was the best choice.
For me safety is always the first concern.

[brewsky]

I bet if you call them again and tell them your rim is 1.85, they will sing a different song!
That's what they told me till I told them the rim size......