Author Topic: Tire FYI-how wide is wide?  (Read 25730 times)

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Offline canyon750

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Re: Tire FYI-how wide is wide?
« Reply #25 on: March 16, 2007, 07:51:17 PM »
Ok, I have a Dunlop D207 on the front at 120/60/17 and the rear is 160/60/17. Wait!  I cheated!  Never mind!   ;D ;D ;D
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Offline bwaller

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Re: Tire FYI-how wide is wide?
« Reply #26 on: March 16, 2007, 08:36:02 PM »
When we roadraced these babies everybody used K81's in 4:25/4:30x18 rears and 4:10x19 fronts. That 4:10 barely fit inside the fender bracket and they didn't upset handling any and I certainly never saw one come off the stock rim even under those conditions. As a matter of fact I've been harping for years about our tires getting skinnier. I mentioned recently replacing a GT501 and the new one was 3/8" narrower when mounted than the old one, 3/8 no less. A 120 tire is fine on a 2.15" rear rim.

TT is right of course, it is mostly perception and most people on these old bikes just putz around anyway.  Now to show you my perception is out of whack, the 550 I'm going to finish soon has a 110/80/18 on a 2.15 front and a 130/80/18 on a 2.5 rear. Next tires I'll look for 70 profiles if they can be had! 

Offline kslrr

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Re: Tire FYI-how wide is wide?
« Reply #27 on: March 16, 2007, 08:49:19 PM »
On my '72 CB350F, I have a Dunlap Sport Elite 120/80/18 on the rear which messures 4.75 in. across.  This is a wide tire made for what was considered standard width rims back in the '80's.  The bead and side walls are constructed in such a way that the tire retains it's proper shape and grips the rim tighter.  This little bike is stable at 100 mph!  Yes, the tires are 20 years old.  The front side walls are cracked, the rear looks like new but the rubber has probably lost it's grip.  Hope I can find something similar.



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Offline mrblasty

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Re: Tire FYI-how wide is wide?
« Reply #28 on: March 17, 2007, 12:31:15 AM »
You guys with all that tread left on your tires are making my jealous.
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Offline TwoTired

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Re: Tire FYI-how wide is wide?
« Reply #29 on: March 17, 2007, 12:42:41 AM »
Hey Blasty,
Isn't that front tire in your avatar mounted backwards?
My Metzlers all have the V pointing up in the front.  Thought that was for a water drainage effect.
Just wondering...
 ???

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Offline Tower

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Re: Tire FYI-how wide is wide?
« Reply #30 on: August 05, 2007, 10:08:29 PM »
In the 1969 -1979 Haynes Owners Workshop Manual
Recommended front tyre is 3.25 x 19" (2.15" rim?)
Recommended rear tyre is 4.00 x18" (2.50" rim?)

I believe tyre width is mostly based on rim width, hence the stock rims must have dictated this measurement.

To convert to metric/universal tyre measurements:
3.25 x 25.4 = 83 (metric) next size up is 90
4.00 x 25.4 = 102 (metric) next size up is 110

Front wheel height for 90 (3.5" wide) is:
 19" + 2 x aspect height (/90) = 25.4" tall
For a slightly taller tyre we could try 100/90 (3.9" wide - almost 3/4" too wide)
19" + 2 x aspect height (/90) = 26.1" tall

Rear wheel height for 110 (4.3" wide) would be:
 18" + 2 x aspect height (/80) = 24.9" or (/90) = 25.8" tall
Since this is not a good height fit we could also try a 120 tyre with a smaller aspect ratio

Rear wheel height for 120 (4.7" wide) would be:
 18" + 2 x aspect height (/80) = 25.6" tall (This is a much better fit height-wise, even though the tyre is almost 3/4" too wide)

So the "right" metric tyre sizes are,
Front: 90/90-19 (3.5"wide x 25.4" tall)
Rear: 120/80-18 (4.7" wide x 25.6" tall)
-and alternates-
Front: 100/90-19 (3.9" wide x 26.1" tall)
Rear: 110/90-18 (4.3" wide x 25.8" tall)

Or am I missing something? because what I see in this thread is discussion of tyres that are much wider.

My bike's PO put Michelin A48 100/90-19 front, and M48 130/80-18 on the rear (5.1" wide x 26.2" tall).  The front sidewall isn't bad, but the rear sidewall angle is prominently v-ed or pinched.  This Michelin combo wase made in 1981.  So, is it the mass appeal of wide tyres or is there another factor I'm missing?

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Re: Tire FYI-how wide is wide?
« Reply #31 on: September 30, 2007, 10:35:33 PM »
How about 77's and 78's with 17 inch? What is the correct size? I've been using 130-90.

Regards from Argentina.

BQ


Offline Tower

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Re: Tire FYI-how wide is wide?
« Reply #32 on: October 01, 2007, 06:52:41 AM »
K0 - K7 and F all had the same tyre recommendation from Honda, specifically:
Recommended front tyre is 3.25 x 19"
Recommended rear tyre is 4.00 x18"

K8 has wider specifications,
Recommended front tyre is 3.5 x 19
Recommended rear tyre is 4.5 x 17A

Front tyre:
3.5" wide is  89 (metric), next size up is 90
90/90-19 measures 3.5" width x 25.4" height

Rear tyre:
4.5" wide is 115 (metric), next size up is 120
120/90-17 measures 4.7" width x 25.5" height

Alternates (and arguably a better choice)
Front tyre: 100/80-19 (measures 3.9" width x 25.1" height)
Rear tyre: 130/80-17 (measures 5.1" width x 25.2" height)
-or-
Front tyre: 100/90-19 (measures 3.9" width x 26.1" height)
Rear tyre: 130/90-17 (measures 5.1" width x 26.2" height)

Pushing it, would be
Front: 110/80-19 (measures 4.3" width x 25.9" height) more than 3/4" wider than recommended
Rear: 140/80-17 (measures 5.5" width x 25.8" height) more than 1 1/2" wider than recommended
-or-
Front: 110/90-19 (measures 4.3" width x 26.8" height) about 1 1/2" taller than recommended
Rear: 140/90-17 (measures 5.5" width x 26.9" height) about 1 1/2" taller than recommended
« Last Edit: October 01, 2007, 06:59:52 AM by Tower »

Offline TwoTired

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Re: Tire FYI-how wide is wide?
« Reply #33 on: October 01, 2007, 09:22:34 AM »
Honda did not use metric tires on the original bikes.  And, I've never seen any engineering data from Honda of that era that is applicable to metric tires manufactured in the last decade or prior.
The only engineering sata I've found available for modern tire fitment is from the tire manufacturers.  The engineering data is not always easy to obtain for the MFGr, as the marketed public's eyes generally glaze over when presented a list of numbers.  And, such data often interferes with salesmen making higher profit margins on the larger sized tires.  Salesmen prey upon the vision driven buyers who think a bigger tire on their bike MUST be better. A clever salesmen will allow or guide the buyer toward that decision.

Anyway, most MFGrs do list the rim width recommendations for the tires they offer.  I've found that the strict application of inch/metric measurement numbers do NOT coincide with MFGs metric replacement recommendations.  But, so far, all replacement recommendations do adhere to the rim width guidelines for their tire offering.

On the CB550 the front and rear rim width is 1.85 inches.
I  *think* the rear rims of CB750 rear rims were 2.15, with the fronts 1.85, at least until 77.  My 77 and 78 F comstars have 1.85 front and 2.15 rear rim widths to coincide with the 3.25H front and 4.00H tire fitment.

Some here have reported that the rear 17 inch wheels of the K models were 2.50 inches in rim width.  I have none available to measure.  But, the shop manual does specify a wider front and rear tire than for years prior, to the F2/3 model. So, that is not too hard to accept.

After years of trying to adapt metric tires onto my 550s and suffering through poor handling, and rapid tire wear, I gave up, and now only put stock, or very nearly so, sizes on these old Hondas with the narrow rims.  For me, they handle far better, and provide predictable, even wear over an increased lifetime of use. YMMV  I rue the day when Metzler stops offering inch sized tires.  Hopefully, other brands will still offer the proper sizes.

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
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Offline scondon

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Re: Tire FYI-how wide is wide?
« Reply #34 on: October 01, 2007, 12:57:30 PM »
   TT & Tower, I'm with ya guys. After reading one too many "What's the fattest tire I can fit" threads I decided to go with tire manufacturers recommended sizes on my "new" '78 750F, just to see what it was like. Front Lester(2.15) rim got a 19/90/90, rear Comstar(2.15) got a 18/4.00, Avon Roadrunners.

    Profiles are obviously less "pinched" than the 100/90(F) 120/90(R) that I normally run. Cornering is improved, and after 4500 miles I have yet to see any flat spot developing on the rear. Of course, when I really hammer the bike I hear that voice saying "oh no, those tires are soooo skinny", but I have yet to have any experience that would make me believe that they grip the road any less than the fatter tires. Maybe when I hit the dragstrip???
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Offline azuredesign

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Re: Tire FYI-how wide is wide?
« Reply #35 on: October 01, 2007, 01:48:31 PM »
Hey Andy,
Whatdaya mean after the snow melts? Aren't we going for our October ride? Glad to see you made it back from Japan,
Ben

Offline Tower

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Re: Tire FYI-how wide is wide?
« Reply #36 on: October 01, 2007, 01:53:06 PM »
@TwoTired, perhaps one reason that metric tyres may be giving rise to straight stability issues is that the aspect of height to width on Imperial measure tyres is generally taller i.e 95% aspect ratio or more.  Also in the Imperial measure, tyre width varied with height and manufacturer - unlike the metric/universal tyres that have a standard width/height aspect. 

Because those old tryres were generally taller on the sidewall compared to equivalent width metric tyres, the height/overhang ratio (rise/run) would be correspondingly greater, and hence the angle of the overhang, as calculated by the arctangent of this ratio, would be smaller.  The smaller the angle, the more firmly the sidewall supports the tread, the less squirm on straight roads. 

Of course cornering stability is related to both sidewall rigidity as well as sidewall height, among other factors.  So, for any given angle less height is better.  Conversely, for any given sidewall height less overhang angle is better.
At some point there is a trade-off between the older taller tyres and the newer wider tyres, other factors such as bead-height notwithstanding.

e.g.1
 3.25-19 w/aspect of 95% on 1.85" rims overhang at 12.8o
The comparable 90/90-19 tyre has a 14.9o overhang angle (less stable), and
100/90-19 overhang at an angle of 16.4o (even less stable)
e.g.2
 4.00-18 on 2.15" rims w/aspect of 95% overhang the rims at an angle of 13.7o
corresponding 110/80-18 tyres overhang the rims at 17.5o (way less stable), and
120/80-18 overhang at 18.8o (very way less stable), and anyone with
130/80-18 is really asking for trouble with an overhang angle of 19.9o

BTW 2.15" seems narrow, given the outside rim bead measure about 3.15" on stock K3 rear rims.

EDIT: fixed some errors in my tangent calc
« Last Edit: October 01, 2007, 02:43:26 PM by Tower »

Offline scondon

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Re: Tire FYI-how wide is wide?
« Reply #37 on: October 01, 2007, 03:13:08 PM »
 My head just exploded(INSERT: exploding head icon)
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Offline TwoTired

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Re: Tire FYI-how wide is wide?
« Reply #38 on: October 01, 2007, 04:46:32 PM »
For those trying to re-assemble bits of cranium from the surrounding area, perhaps I can simplify?
Tower is speaking toward the sidewall angle from seating bead to tread edge.  (If I understand him correctly.)  Oversize tires on a narrow rims pinch the tire bead together and force a steeper sidewall angle.  An angled support is not as strong as one perpendicular to the opposing forces.  And worse, an angled support generally deflects at lateral angles to the opposing forces.  Therefore, leaned over in a turn with extra Gs applied,  the sidewalls won't keep the tread close to center of the wheel rim.  When this happens directional stability suffers, requiring operator correction.  The steeper the sidewall angle the more "squirmy" the tire becomes.  This is often improved with running higher tire pressures.  But, this causes more "crown" of the tire tread, and ultimately high center of the tread wear patterns.  Looking back at the above, I'm not sure this is of any help.  But, there it is anyway. :-\

Or, as has been recently stated "cornering is improved" with tires less pinched. ;D

Quote
BTW 2.15" seems narrow, given the outside rim bead measure about 3.15" on stock K3 rear rims.

I understand you're skeptical. I measured the outside rim width of my Cb550 wheels, known to be 1.85 I.D.  They measured 2.80 inches.  If I recall correctly, the wheel bead sidewalls are folded twice on each side leaving the edge with 3 thickness of steel.  This uses up about 1/2 inch per side.  I remember being surprised when I first learned this.

I can't say I noticed a handling problem with metric tires when they had near new tread while riding straight up.  But, the cornering unpredictability while handling road bumps was noticeable.  The bike didn't stay pointed where it was positioned and required more attention to corrections.  Higher tire pressure was the response to make it better.  Then abnormal tread wear gradually made the bike behave "oddly".

Cheers,

Lloyd... (SOHC4 #11 Original Mail List)
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Offline Tower

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Re: Tire FYI-how wide is wide?
« Reply #39 on: October 01, 2007, 04:59:00 PM »
The attached diagram might help.  Eerily, it resembles a large head :o
As expected TT, your interpretation is spot on.

Offline scondon

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Re: Tire FYI-how wide is wide?
« Reply #40 on: October 02, 2007, 09:09:24 AM »
 Aahhhhhhh, soothing pictures  :-*  I used the diagram to help piece my skull back together, but now my helmet fits a bit tight. Think I'll try again with a little less overhang angle this time. Thanks guys :) :)
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Re: Tire FYI-how wide is wide?
« Reply #41 on: October 02, 2007, 09:01:05 PM »
I wonder why so many take about tire size when there is no set standard for tires.
I use a 110/90 up front and a 130/90 in the back. Handles just fine even in downpours with 30mph crosswinds. I use bridgestone spitfires. Now if I went to another brand, the size is likely to vary a bit. Sidewall designs are different and tread patterns are different. So my 130 in a different brand is going to be different. The only thing a person can do is find a tire they like that works for them. Some day I will get a pic of my tires and post it. I do not feel the tires are pinched at all. I also do not have abnormal wear even though 90% of the roads in my area are straight as arrows, my centerline still rolls nicely to my sides. But then the bridgestone site listed 120 tires with 130 being acceptable.

Offline Tower

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Re: Tire FYI-how wide is wide?
« Reply #42 on: October 02, 2007, 09:41:08 PM »
I believe your 130/90-17 on a 2.5x17 rim is fine.  The pinch angle is still not too bad at 15.9o.  You rear tyre is within 20% of the recommended pinch angle of 13.2o for the recommended 4.50H17 tyres.  You've also matched the front tyre to the rear tyre. i.e 110/90-19 on a 2.15x19 rim has a pinch angle of 15.6o.  Meaning the front and rear handling characteristics are about even.

Given that the recommended tyres for the front are 25.8" tall and rear are 25.6" tall, height wise, the two tyres on your K8 are a bit far apart.  That is, your front is 26.8" tall and rear is 26.2" tall.  But, then I'm only guessing that heights should be about equal, I haven't read anything that directly apposes or supports that view.

All and all I'd say your choice of tyres is not at all outrageous.

Also, with the 110/90 on the front, selecting the 120/90 for the rear would probably not have been a great match.  The angle would have improved to 14.7o but the height difference would have been 1.3" shorter when compared to the front rear.

I think there is more physics and math to tyre selection than merely personal preference, so on that point I beg to differ.  Tyre size matters.

Offline Tower

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Re: Tire FYI-how wide is wide?
« Reply #43 on: October 02, 2007, 11:45:41 PM »
Here is a fitment chart that I've developed showing width, height, and pinch angle for various tyres that might be selected for CB750 DID rims.

Offline S-Dog

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Re: Tire FYI-how wide is wide?
« Reply #44 on: October 03, 2007, 01:31:40 AM »
Im BIIIG pinching on my rear tire....  Seems to handle and run nice.. 130/80 R18

It looks awesome.... the PPO(previous previous owner) put it on.
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Offline cben750f0

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Re: Tire FYI-how wide is wide?
« Reply #45 on: October 03, 2007, 02:30:26 AM »
am running on the 110F/130R combination, and the rear is more for the look than anything..... i admit it  ;D.





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Offline scondon

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Re: Tire FYI-how wide is wide?
« Reply #46 on: October 03, 2007, 07:29:38 AM »
Here is a fitment chart that I've developed showing width, height, and pinch angle for various tyres that might be selected for CB750 DID rims.


   A very handy reference chart you've made there,Tower. I've copied it to my files and hope it finds a permanent place in the FAQ. Thanks :)
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Offline malcolmgb

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Re: Tire FYI-how wide is wide?
« Reply #47 on: October 07, 2007, 09:48:33 AM »
Here is a fitment chart that I've developed showing width, height, and pinch angle for various tyres that might be selected for CB750 DID rims.


did you create this chart manually or use a spread sheet? I was wondering if it could be adapted for use on other bikes with different rim sizes.
Malcolm

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Offline Tower

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Re: Tire FYI-how wide is wide?
« Reply #48 on: October 07, 2007, 12:25:40 PM »
I've forgotten how to do trig on my slide rule, so its all spreadsheet stuff.   ;D

Let me know what rim size you want to compare and I'll post the equivalent fitment chart.

Offline malcolmgb

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Re: Tire FYI-how wide is wide?
« Reply #49 on: October 07, 2007, 02:31:36 PM »
I've forgotten how to do trig on my slide rule, so its all spreadsheet stuff.   ;D

Let me know what rim size you want to compare and I'll post the equivalent fitment chart.

It's for the 400f both 18" wheels, front rim 1.60 rear 1.85
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