Replacement tires for OEM 4.00 x 10 Trailwings

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Samzilla

New Member
I've got a 1972 CT70H K1 and want to replace the original 4.00/10 tires with a street tire. I've read all of the threads and it seems that most of the recommended replacement sizes are closer matches to the 3.5 x 10 OEM tire found on some models.

By my calculations, the stock 4.00 x 10 tire equates to:

Diameter = 18"
Width = 4"
Height = 4"

The closest metric conversion to this would be either:

110/90/10 (a size which virtually doesn't exist) or
100/100/10 (again, not available)

Here are size combinations that were suggested from the various threads. I've limited them to only those that will fit the CT70 without rubbing and that do not require modifications whatsoever.

Size Diameter Width Height Front/Rear

120/70/10 16.6" 4.72" 3.3" Front
130/70/10 17.2" 5.1" 3.6" Rear


100/80/10 16.3" 3.93" 3.1" Front
120/70/10 16.6" 4.72" 3.3" Rear


110/80/10 16.9" 4.33" 3.4" Front & Rear


100/90/10 17.1" 3.93" 3.5" Front & Rear


120/90/10 18.5" 4.72" 4.2" Front & Rear

Based on the above, the 120/90/10 is the closest tire to the 4.00x10. It should fit without a problem and because the diameter is closer to OEM than any other tire, the speedometer should be relatively accurate.

Just my 2 cents. What are your thoughts?:yellow70:
 
OLD CT

OLD CT

Well-Known Member
Hi,DR ATV'S cheng shin ''why not'' street 3.50-10's arent a bad choice.with little if any noticable speedo calibration difference.when you pass those ''your speed is'' signs. there is also a nice tire by Continental called a Zippy3.it still retains 4.00-10 status and i run them now.a great dual purpose tire actually.you get the best of both worlds.they stick on the street and good on the trails.i like to go off road with mine from time to time.i have used both tire's with great results.
 
6

69ST

Well-Known Member
If you've been following the tire size discussion across multiple threads, then you've seen the term "nominal size" (what's shown on the sidewall). It can and does vary significantly from reality. Your metric size conversions and observations about what's available are reasonably accurate. Still, the only way to be sure of getting the size you want is to measure the circumference; there's no substitute and that's part of what makes your project difficult. Seemingly small differences in nominal tire size can have surprisingly large effects in reality, so your attention to detail is well worth the effort. OLD CT gave you some good advice, the Continental Zippy's have been popular with the small bike crowd, across the pond, for years.

Speedometer accuracy varies from one unit to the next. The only surprise is that these 40 year-old mechanical gauges work as well as most of them do. A tire size that gives one rider an accurate reading might be way off for someone else. The stock speedometer is calibrated for a tire with a 56.25" circumference, very close to the actual size of a typical Trailwing (They have ranged from just shy of 57", new, down to just over 54" worn). EU riders who run 3.50s almost always complain about overly optimistic indicated speed. 120/90 x 10 tires that I've actually measured have ranged from 59.5" to just over 61"; that's enough to affect speedo readings and overall gearing (revs per mile) by as much as 14%, even more compared to a 3.50 x 10 (or equivalent). Don't be surprised if you have to change one, or both, sprockets to restore gearing. That's also the limit of what will fit on a CT with stock rims; the tires will be crowned a little (pinched on the rim) and you'll lose chain adjustment range.

120 section width is the limit for stock width rims and standard sprockets, also the widest that will fit the front. Ideally, a 120-section tire would be mounted on a 3.50" wide rim. 130 section width is the limit for the rear, with a standard swingarm, and it's tight. 3.50" is the minimum wheel width, 4.0" ideal. You'll also have to run offset sprockets if you want the chain to clear the tire sidewall and the wheel centered.
 
S

Samzilla

New Member
racerx said:
If you've been following the tire size discussion across multiple threads, then you've seen the term "nominal size" (what's shown on the sidewall). It can and does vary significantly from reality. Your metric size conversions and observations about what's available are reasonably accurate. Still, the only way to be sure of getting the size you want is to measure the circumference; there's no substitute and that's part of what makes your project difficult. Seemingly small differences in nominal tire size can have surprisingly large effects in reality, so your attention to detail is well worth the effort. OLD CT gave you some good advice, the Continental Zippy's have been popular with the small bike crowd, across the pond, for years.

Speedometer accuracy varies from one unit to the next. The only surprise is that these 40 year-old mechanical gauges work as well as most of them do. A tire size that gives one rider an accurate reading might be way off for someone else. The stock speedometer is calibrated for a tire with a 56.25" circumference, very close to the actual size of a typical Trailwing (They have ranged from just shy of 57", new, down to just over 54" worn). EU riders who run 3.50s almost always complain about overly optimistic indicated speed. 120/90 x 10 tires that I've actually measured have ranged from 59.5" to just over 61"; that's enough to affect speedo readings and overall gearing (revs per mile) by as much as 14%, even more compared to a 3.50 x 10 (or equivalent). Don't be surprised if you have to change one, or both, sprockets to restore gearing. That's also the limit of what will fit on a CT with stock rims; the tires will be crowned a little (pinched on the rim) and you'll lose chain adjustment range.

120 section width is the limit for stock width rims and standard sprockets, also the widest that will fit the front. Ideally, a 120-section tire would be mounted on a 3.50" wide rim. 130 section width is the limit for the rear, with a standard swingarm, and it's tight. 3.50" is the minimum wheel width, 4.0" ideal. You'll also have to run offset sprockets if you want the chain to clear the tire sidewall and the wheel centered.
Click to expand...


Racerx,

You recommend the German street tires in 110/80/10 16.9" 4.33" 3.4" Front & Rear as the best overall street tire. I'm leaning towards this but you had also mentioned that the combination 120/70/10 16.6" 4.72" 3.3" Front and 130/70/10 17.2" 5.1" 3.6" Rear would give a wider look, superb handling and fit without any problems or modifications. Of these two options, which do you prefer?
 
6

69ST

Well-Known Member
Samzilla said:
Racerx,

You recommend the German street tires in 110/80/10 16.9" 4.33" 3.4" Front & Rear as the best overall street tire. I'm leaning towards this but you had also mentioned that the combination 120/70/10 16.6" 4.72" 3.3" Front and 130/70/10 17.2" 5.1" 3.6" Rear would give a wider look, superb handling and fit without any problems or modifications. Of these two options, which do you prefer?
Click to expand...

From a practicality standpoint, the 110-section width is the way to go...as in "bolt-on & go simplicity".

First off, it's as close as you'll get to matching the circumference (and with it, height) of the Trailwing. In nominal terms, a 4.00" section-width = 101.6mm. Assuming that 4.00 x 10 has a 90 aspect ratio, then the 110/80 x 10 should have 0.50" smaller circumference, a ~1% difference. The real-world measurements are different, but this is as close as you're going to get, going by nominal sizes that are actually available.

Second, fitting a 130-section width tire is a can of worms. It requires sourcing a wider, aftermarket, swingarm, at least a 3.50" wide rim and offset sprockets. Even then, it's "edge city". Take a look at the attached photo. The red arrows show the pinch points. This setup has the sprockets offset by 5mm; it leaves slightly less than 4mm chain clearance on either side. The head of the LH shock mount bolt had to be ground nearly flat; as-received, the chain didn't clear. This is with a G-Craft swingarm. This tire, wheel & sprocket setup won't fit a stock arm.

In terms of a pure road tire, the K61 is the best available in usable sizes, bar none. All else being equal, they're a quantum improvement in cornering & stability...on smooth, dry, pavement. They also carry an 84mph speed rating and wear quite well for a grippy performance tire.

Unlike fitment, handling is very subjective. Some riders claim that 120, or wider, tires ruin handling; personally, I disagree. But then, there are more skillfull and aggressive riders out there. I'm more of a grand-tourer than a road-racer, so take my opinions with a shovelful of salt:21: There are bigger improvements possible in handling/stability. However, they don't come close to the kind of bang for your buck possible by upgrading to good road tires and are waaay beyond the scope of what you asked.
 

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eca05rjc

New Member
Hi,
Sorry to jump on the back of this thread but i too currently have 4.00x10 tyre on my bike (not a honda im afraid) and they need replacing. My gearing is too high and altering the gearing etc is pretty much a no go as its an old russian scooter. Could anyone recommend sizing to lower by gearing a bit?
Was thinking 100/90-10?? that sound any good, any advise would be greatly appreciated.

Thanks
Richard
 
6

69ST

Well-Known Member
Tire circumference can have a significant affect on overall gearing, i.e. revs per mile. Since you're attempting to change effective gearing, now is the time to realize that there are some big differences between nominal (sidewall markings) sizes and actual sizes. Six different tires of the same nominal size can be six different actual sizes...varying from one manufacturer to another, even between different tires series (models) from the same manufacturer. Thus, there may be some trial & error in your future as you attempt to source the best real-world size.

If you're looking to go with a shorter tire (smaller circumference) your choices are: 3.50-10, 90/90 - 10, and 100/80 - 10

4.00x10 tire circumferences can range from a little more than 57" down to about 55". (Knobbies, such as Trailwings, tend to run larger than street tread tires) I've seen 3.50 x 10s as small as 52". My firsthand experience in actual tire sizes is limited, there is almost certainly a lot more variation, especially in-between the measured extremes I've encountered, so far. That still gives you roughly 8-10% to work with, possibly exceeding the minimum needed to correct your gearing issue.
 
D

drb930

New Member
racerx said:
From a practicality standpoint, the 110-section width is the way to go...as in "bolt-on & go simplicity".

First off, it's as close as you'll get to matching the circumference (and with it, height) of the Trailwing. In nominal terms, a 4.00" section-width = 101.6mm. Assuming that 4.00 x 10 has a 90 aspect ratio, then the 110/80 x 10 should have 0.50" smaller circumference, a ~1% difference. The real-world measurements are different, but this is as close as you're going to get, going by nominal sizes that are actually available.

Second, fitting a 130-section width tire is a can of worms. It requires sourcing a wider, aftermarket, swingarm, at least a 3.50" wide rim and offset sprockets. Even then, it's "edge city". Take a look at the attached photo. The red arrows show the pinch points. This setup has the sprockets offset by 5mm; it leaves slightly less than 4mm chain clearance on either side. The head of the LH shock mount bolt had to be ground nearly flat; as-received, the chain didn't clear. This is with a G-Craft swingarm. This tire, wheel & sprocket setup won't fit a stock arm.

In terms of a pure road tire, the K61 is the best available in usable sizes, bar none. All else being equal, they're a quantum improvement in cornering & stability...on smooth, dry, pavement. They also carry an 84mph speed rating and wear quite well for a grippy performance tire.

Unlike fitment, handling is very subjective. Some riders claim that 120, or wider, tires ruin handling; personally, I disagree. But then, there are more skillfull and aggressive riders out there. I'm more of a grand-tourer than a road-racer, so take my opinions with a shovelful of salt:21: There are bigger improvements possible in handling/stability. However, they don't come close to the kind of bang for your buck possible by upgrading to good road tires and are waaay beyond the scope of what you asked.
Click to expand...

What size rear rim width is that you are running, and where did you source it?
Also who makes the K61?

Thanks,
Dave
 
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