AM26 100/90 & TT100 4.10

T95 · May 12, 2011

I would like to know how the AM26 100/90-19 compare in size, both width and height, to the Dunlop TT100 4.10?

I am still trying to determine what will fit on my 71 Roadster with the stock WM2 or larger WM3 rims. Everything is apart so judging the correct fit is a problem. I measured the front fender/guard and it is narrow @ 4", and I am not sure how close the tyre will be to the fender or the fender stays.

FYI: My bike did have the 4.10's both front and rear on what I assume to be WM2 stock rims.

I know a wider Wm3 rim should flatten the tyer's profile while a narrow rim will increase the tyer's overall height. Without the forks and fenders assembled I have no way to reference this information.

I do know Avon recommends the Wm4 /2.15 rim for the 100/90 but other sources, including Central Wheel Works, routinely mount 100/90 on WM2 rims.

My apologies for rehashing this once again. I vow this will be my last request for information on this topic!!!!!

ILLF8ED · May 12, 2011

I have 100/90-19 Avon AM26 front and back on my '72 roadster. Should be the same fit for your '71. Pretty close to the fender stays on the front, but fits. The chrome plated fronts fenders are narrower than latter year stainless as you seem to be aware. Avon website shows AM26 100/90-19 diameter is 26.4". Look up Dunlop K81 TT100 for that data. Bottom line is these will fit your bike.

swooshdave · May 12, 2011

I have my old TT100s on the stock rims and the AM26s on WM3 alloy rims.

The perceived difference is huge!

If you can wait until tonite I should be able to measure both to give you a comparison.

rvich · May 12, 2011

I have the AM26s on W2 rims. Measured the width on the front one and came up with 4" even. Should be interesting to see what Dave comes up with on his tires.

Russ

T95 · May 12, 2011

illf8ed said:
I have 100/90-19 Avon AM26 front and back on my '72 roadster. Should be the same fit for your '71. Pretty close to the fender stays on the front, but fits. The chrome plated fronts fenders are narrower than latter year stainless as you seem to be aware. Avon website shows AM26 100/90-19 diameter is 26.4". Look up Dunlop K81 TT100 for that data. Bottom line is these will fit your bike.

Thanks for the info, are you running the Wm2 rims?

T95 · May 12, 2011

swooshdave said:
I have my old TT100s on the stock rims and the AM26s on WM3 alloy rims.

The perceived difference is huge!

If you can wait until tonite I should be able to measure both to give you a comparison.

Dave,
I can wait. It will be interesting to see what you come up with!
G

T95 · May 12, 2011

rvich said:
I have the AM26s on W2 rims. Measured the width on the front one and came up with 4" even. Should be interesting to see what Dave comes up with on his tires.

Russ

Russ, thanks for the post.
As you know my fender has an inside measurement of 4" as does the center bracket. The mystery will be how wide the tire is at that point?

Flo · May 12, 2011

The 100-90-19 Roadrider on a WM2 rim is 103mm (4-1/16" in english) at its widest point.

debby · May 12, 2011

Well, as it happens I have one of each on my bikes so I went out and had a look.

My 850 has a Borrani WM2-19 alloy rim on front with a 100/90-19 Avon AM26. I measured 100 mm tire width (imagine that!)

My 750 has the original Dunlop steel rims and I have 4.10-19 K81s fitted. The K81 (aka TT100) measured 104 mm.

I have a used stock front fender on my 850 that I bought off ebay and I think it has a slight misalignment. A K81 drags on the left side of the bridge. The AM26 just clears, due to the slightly narrower width.

Debby

debby · May 12, 2011

And some more info:

The WM2 Borrani on my 750 measured 62 mm wide using my Harbor Freight plastic calipers. The rear rim, which is not stamped with any sizing or branding that I can see (I think I got ripped off, it's supposed to be Borrani) measures 73 mm. The tire fitted is a 110/90-18 AM26.

The Dunlop steel rims measured 68 mm wide. According to my 1972 factory service manual, the stock rims are WM2-19. My front rim is stamped "Dunlop Made In England" and "MC275" on the front, and "MB41" on the rear.

So there you have it! Swoosh, your turn!

swooshdave · May 12, 2011

debby said:
So there you have it! Swoosh, your turn!

So much pressure!

The 4.10 Dunlop (made in Republic of Ireland!) on the stock steel rim was... 4.10 in (with a tape measure since I don't have a fancy caliper that big.

The 100/90 Avon on a WM3 Excel alloy was... 4.10 in (or so). Maybe a smudge less actually. Probably closer to 100mm.

With an eyeball I'd say they were more like 4in both.

How that for unscientific? :mrgreen:

rvich · May 12, 2011

I measured mine by using a carpenter square and a framing triangle as a caliper! I actually works pretty well. So what have we discovered? That a 4 inch tire is about 4 inches wide?

ILLF8ED · May 12, 2011

T95 said:
illf8ed said:

I have 100/90-19 Avon AM26 front and back on my '72 roadster. Should be the same fit for your '71. Pretty close to the fender stays on the front, but fits. The chrome plated fronts fenders are narrower than latter year stainless as you seem to be aware. Avon website shows AM26 100/90-19 diameter is 26.4". Look up Dunlop K81 TT100 for that data. Bottom line is these will fit your bike.

Click to expand...

Thanks for the info, are you running the Wm2 rims?

Yes original rims...WM2.

Fullauto · May 13, 2011

Hmm. Just measured my 100/90 x 19 Roadriders on WM4 (2.5 inch rims) at 4.26 inches. A Bridgestone 100/90 x 19 on a standard 2.15 rim is 3.63 inches (??)

mcvic750 · May 13, 2011

Gary,
This is exciting; until I joined this forum I’d never felt the urge to measure my tyres. As I tried to hold two flat surfaces against either side of the tyre with the use of elbows and Knees while holding the tape measure in my mouth my smart arsed mech engineering student Son walked into the garage. “What are you doing?” He asked a little bemused. “I’m measuring my tyres” I confidently replied. The look on his face became troubled and I could sense the word dementia travelling around his brain, then out came this pearl of wisdom from one so young “it’s written on the side of the tyre, its 100 ya numpty!” and he wandered off. Trying to keep a sense of decorum while tilting my head to keep my glasses on I focused in on the tape measure, imagine my surprise - 100!

Bike is a ’71 roadster, rims are original 19” Dunlop Wm2, and tyres are AM26 100/90-19. Front mudguard is replacement SS one and I don’t have front stay. Hope these pics help

Have you made a decision about the side stand?
Cheers
McVic

swooshdave · May 13, 2011

mcvic750 said:
“it’s written on the side of the tyre, its 100 ya numpty!” and he wandered off. Trying to keep a sense of decorum while tilting my head to keep my glasses on I focused in on the tape measure, imagine my surprise - 100!

Don't take that from him! Damn engineers think they know everything. So what is written on the spec is what is produced, eh? He has a lot to learn...

T95 · May 13, 2011

David, Dave, Russ, Flo, Debby, Fullauto, McVic & whoever I missed,

Thanks for taking the time to make this a science project and get out your tape measures, rulers, calipers, micrometers & electron microscopes to measure your tires. I think you left out a couple of important tools to do the job: surveyors wheel,interferometer, feeler gauges, sonar and the all important opisometer.

Anyway all that has convinced me to, ahhhhhhhh!

I let you know when they arrive!

Gary

T95 · May 13, 2011

mcvic750 said:
Gary,
This is exciting; until I joined this forum I’d never felt the urge to measure my tyres.

Bike is a ’71 roadster, rims are original 19” Dunlop Wm2, and tyres are AM26 100/90-19. Front mudguard is replacement SS one and I don’t have front stay. Hope these pics help

McVic,
What is really exciting is seeing the simple shots of your completed wheels. Pure eye candy for me and it really shows how nicely the tire tucks into the fender/guard. One more chore, how wide is that SS fender?

Have you made a decision about the side stand?
Cheers
McVic

batrider · May 13, 2011

Numbty is a new one for me. Scottish numbty = USA numbnuts ???

mcvic750 · May 13, 2011

T95 said:
mcvic750 said:

Gary,
One more chore, how wide is that SS fender?

Click to expand...

No problem more than happy to do measurement for you but wannabee mechanical eng. in house at present and couldn’t take the ridicule of being seen measuring my front fender today!! Also possibly to full of Gin at present to give accurate reading. I’m at work t’morrow but Sunday clear so will measure then
McVic

AM26 100/90 & TT100 4.10

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