[WindingRoadRider]

I am building a cafe racer with a combination fork brace/fender mount/caliper hanger. I need to know tire dimensions/clearances to complete this part of the project, but don't want to actually purchase the tires until the project is closer to completion, so the tires are fresh. (I've been "working" on this bike for nigh on 30 years, and it might be a couple more years before it's actually ready for tires.) Since no tire company other than Avon seems to publish actual measurements of their tires, I was hoping someone here could take a couple of measurements for me. The bike has an 18 x 2.15 Sun rim on the front. At this point, I am considering the 90/90 R 18 ContiClassicAttack and the Michelin 100/90-18 Pilot Activ. If anyone out there has either of these tires and can measure the actual overall diameter and width, I would greatly appreciate it. Thanks.

 

[TrialsRider]

Just how close are you trying to build it that the Avon numbers would not work? Or are they for a completely different profile tire.

When it has a profile number like 90

• 90 = aspect ratio (cross-section height is 90% of width)

If it has no profile number cross-section height is 100% of width

 

[TrialsRider]

That's a V rated tire, it's capable of 150 mph, they get bigger in outside diameter when you spin the up fast, might want to keep that in mind when you consider clearances, it trips up a lot of people.

 

[CaTacL1sm]

I ran into issues on the Dyno with the previous rear wheel setup I had on my Z1... at high speeds the tire diameter would increase and it would rub on the swingarm... wild stuff

 

[jcw]

Since no tire company other than Avon seems to publish actual measurements of their tires, I ...

Sure they do... u just don't know where to look

 

[jcw]

OK I actually cant find the link anymore for continental... so here is my copy.
specs start on page 276
on road radials on page 282
conti 18in classic attacks on page 283

 

[jcw]

You might consider writing to the company for tire info as well...
BTW, the two tires you are looking at are different. one is radial, the other bias.

 

[TrialsRider]

Centrifugal force is amazing stuff, watch the shape of the tire change here:

Imagine goodyear trying to give you outside dimensions for that tire.

 

[WindingRoadRider]

Thank you all for your replies. One of the reasons I am considering the ContiClassicAttack is because radials don't grow as much at speed as do bias-ply tires. The main reason, though, is that they are supposedly the best-handling of all tires narrow enough for older bikes, at least according to the March 2017 issue of the German magazine Motorrad Classic. Here are their test comparison results with point scores:
8th place, 156/250 -- Avon Road Rider
7th place, 167/250 -- Pirelli Sport Demon
6th place, 174/250 -- Metzler Sportek Klassik
4th place, 200/250 -- Bridgestone Battlax BT45
4th place, 200/250 -- Continental ContiGo!
3rd place, 201/250 -- Dunlop Arrowmax Streetsmart
2nd place, 204/250 -- Michelin Pilot Activ
1st place, 224/250 -- Conti RoadAttack 2 CR/ClassicAttack

(The 1st place RoadAttack happens to be in their "CR" DOT-approved race compoind, so it's a bit of a ringer.) The narrowest front RoadAttack, 100/90-18, requires a minimum rim width of 2.50", which is why I was looking at the 90/90-18 ClassicAttack. Thank you very much, JCW, for the PDF of the Conti catalog. As I assume you discovered, it is no longer on Continental's website and is much more comprehensive than the catalog currently posted. It is a tad confusing, however, in that they show the 90/90 as also requiring a 2.50 minimum rim width whereas their 110/90-18 is seemingly suitable for a 2.15" rim - go figure. Incidentally, they show the centrifigul growth as a mere 7mm on the 90/90, so that's good. I'm obviously going to have to read more in the Conti catalog before making any decisions.

I was definitely incorrect about Avon being the sole company that lists actual tire dimensions, since I discovered that Bridgestone also does so, and that Conti once did. That said, it's obvious that the manufacturers generally don't cater to custom builders, who need to know exact dimensions of all sorts of things. I haven't added anything to my build thread in years, but anyone who cares to take a look at it can google "T140 cafe project, cont. britbike".




.

 

[8ball]

Why would you build a bike with tire clearance so tight that you are committed to one specific brand of tire? If you plan for it to be functional, that tire may not be available when it comes time to replace them. Or, if this is not a functional build (not really something this crowd has much appreciation for) buy the tire you like the look of, and build the bike around it! It won’t matter because the tires never wear out in a Pipeburn build....

 

[TrialsRider]

You should be considering radials because they are far better then bias ply tires.

 

[WindingRoadRider]

Why would you build a bike with tire clearance so tight that you are committed to one specific brand of tire? If you plan for it to be functional, that tire may not be available when it comes time to replace them. Or, if this is not a functional build (not really something this crowd has much appreciation for) buy the tire you like the look of, and build the bike around it! It won’t matter because the tires never wear out in a Pipeburn build....

Actually, I am aiming for a .5-.75" clearance, just not a 1-1.5" gap. That way, I can build for the tire that is best (why would I do that if the bike isn't intended to be "functional"), and future owners can still - within generous limitts - change up as they wish. BTW, though their premium price might hold them back, I expect this new, narrow strain of radials to be the future of reto-bike rubber. You are right on, 8ball, about the tires never wearing out. Due to medical problems, I haven't been able to ride since 2004. I wouldn't expect the next owner to ride it on anything buy lovely Sundays, either. But I built my first cafe racer (low bars, pipe, seat and tank, extended swingarm) in 1968, and spent nearly 45 years in the motorcycle business, so I'm kinda in the habit of doing this. I will admit this bike has become a bit of an albatross by this time, but I am bound and determined to make it the best T140 cafe racer it can be. And it's well on its way.

 

[jcw]

The 90/90r18 conti classic attacks fit a 1.85 to 2.5 inch rim.
I'm not sure where or how you are reading the fitment chart...

30 year build???? And I thought I was a bad procrastinator

 

[WindingRoadRider]

The 90/90r18 conti classic attacks fit a 1.85 to 2.5 inch rim.
I'm not sure where or how you are reading the fitment chart...

View attachment 104714

30 year build???? And I thought I was a bad procrastinator

I was looking at page 283, which shows acceptable rims for the 90/90 R 18 Classic Attack to be 2.50 and 2.75. What page did you copy above? And yes, a 30 year build is ridiculous, but that's my life.

 

[jcw]

Oh yeah... forgot that the numbers listed there are a typo... if u notice they duplicate the 100 sized tire just below it. I ran into the same issue when I was researching myself.

I basically took the dimensions from the conti go tire (in the bias ply section) for the same sized tire... as a guide...

I have the tire mounted if you want me to measure.... I doubt there's gonna be much difference.
But since u asked originally, I will measure tonight when I get home...

 

[jcw]

I was looking at page 283, which shows acceptable rims for the 90/90 R 18 Classic Attack to be 2.50 and 2.75. What page did you copy above? And yes, a 30 year build is ridiculous, but that's my life.

From continentals current listing 2021 for classic attacks

 

[WindingRoadRider]

That would be terrific, JCW. Nothing beats an actual measurement. BTW, the ContGo is a bias ply, and so doesn't need as wide a rim as a radial. That said, there is a video on youtube of a guy who was mounting 100/80-18 RoadAttacks F & R on a Ducati single road racer (I googled conti roadattack). It had 2.15 rims F & R, which is apparently the widest rim size allowed in his Vintage racing class.

 

[WindingRoadRider]

I notice that all of the measurements in the PDF catalog you sent for the 90/90 ClassicAttack and the 100/90 RoadAttack are identical. That can't be right. My guess is the the 90/90 is, in fact, smaller in every dimension. Your ruler will rule!

 

[jcw]

I notice that all of the measurements in the PDF catalog you sent for the 90/90 ClassicAttack and the 100/90 RoadAttack are identical. That can't be right. My guess is the the 90/90 is, in fact, smaller in every dimension. Your ruler will rule!

That's what I said... the dimensions are a typo... as well as the recommended rim widths in the 2015 tech catalog I posted... basically they copied the exact dimensions of the 100 size tire in the next line.
so for dimensions i just went by the dimensions for the conti go bias tires at the 90/90 size. It's nearly the same as I recall.
I already knew the 90/90 tire would be fine for my 1.85" front wheel.
i got behind today but will get the actual measurements tomorrow but it's gonna be within mm's of the conti go tire

 

[WindingRoadRider]

I am sure you are right, JCW, but I am hoping the ClassicAttack is a bit wider than the ContiGo, even though their nominal sizes are the same. Thanks for checking.