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RT tires ?

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Kurt Bezoenik
(@kurt-bezoenik)
Posts: 2
Active Member
Topic starter
 

I usually wouldn't ask this question, it's right up there with " what type of oil to use" 

I found a 83 RT in a garage a few years ago, was parked for 12 years with many problems, it's back on the road after more work than I was counting on, turned out OK, learned a lot. I never went looking for a RT but now that I have one, it's going to stick around for awhile. They kind of grow on you. It has a Dunlop 491 on the rear and Elite S/T up front. Age unknow, at least 12 years sitting, threads not bad but they are hard as rock and like to kick out on corners. I think it's time for some new shoes. I run K 60's on my 91 GS, so that's out, don't have much experience with touring tires. I was a sport bike guy in Germany in the late 80's, ME99 was king back then. I've looked at the ME77, Avon roadrider Mk2, Continentals, etc. Some of this will come down to what I can get, many tire types are out of stock. I'm open to any input. The bike will be in the PNW so wet weather is on the list. 

 
Posted : 02/13/2022 17:50
Richard W
(@wobbly)
Posts: 2552
Member
 

• All tires made since the mid-1970's are marked with their manufacture date. The code is on one side ONLY. The code typically is done in a part of the tire mold that is changeable, so the area may be slightly recessed and typically oval. There will be a 4 number code that stands for the week and year the tire was made. Like this...

• The standard minimum tire is the Bridgestone Spitfire S11 which comes in appropriate sizes for both ends. They typically have a rear tire life of 10K-11K, with the front lasting through 2 rears.

• Air pressure is the key to good tire life and the numbers given in your 1983 owner's manual no longer apply !! This is because tire technology has vastly evolved. I was running 35F and 30R. If you run the older, lower pressures, then be prepared to get only about 20% of the projected tire life from any tire.

• On an RT you'll experience many type of road surfaces, a great many of which may have received the rain groove cutting treatment. This is where the concrete surface is cut with hundreds of tiny slots to get water off the road surface. The problem is if your front tire design is comprised of multiple parallel groves (like the older "Rib" design), then the road surface will begin to steer the bike. This can be anything from uncomfortable to dangerous. Pick a modern front tire with a block design and you can avoid this.

 

Hope this helps.

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 02/14/2022 07:14
Robert Whigham
(@1872)
Posts: 126
Estimable Member
 

I just did this with old tires-lots of tread, but too old. I went down once with a good looking tire which was maybe 6 years old and should not have turned loose in the corner. Change those things before riding!

Many of the inch sized tires are out of stock. I ended up with Conti-Gos because it was what I could find. Metric sizes which fit were more available. For many years, I ran Avon AM26 with success but no luck finding them last month. 

Good luck

 

Bob

 
Posted : 02/15/2022 12:21
Rick Schroeder
(@red-horse)
Posts: 57
Trusted Member
 

I'm also in the market for new tires.  I've been riding the Avon Roadmaster AM26 for many years and also have not been able to find them.  Trying to find the comparable metric size for the 4.00x18 and 3.25x19 sizes.  There isn't much room, on an RT, for a wider tire in the rear.  Has anyone found a quality tire marque to replace the Avons? I thought i saw an ad by Michelin for sizes that fit these "older" bikes.

thanks,

rick

81R100RT  

 
Posted : 02/24/2022 10:02
Richard W
(@wobbly)
Posts: 2552
Member
 

I think most people would agree that chasing the older tire sizes is a losing battle. The metric sized-tires offer better handling and more choices when it's time to replace tires.

Because of the drive shaft tube for the RH swing arm, tire sizes are limited unless you want to shim the rear wheel over to the left. At least the metric sizes offer the ability to go wider. You can't say that about traditional tire sizes.

I'm going to go check, but I believe the largest tire for the rear (without shimming) is 120/90-18. And it seems to me the tire for the front is 100/90-19.

• Bridgestone, Michelin, Heidenau, Dunlop and several others offer standard sized tires in limited numbers and models.

• Here's the thing about "standard size tires"... These are low demand tires. Factories may only make them for 1 week a year. Then they sell from stock until that time rolls around again 51 weeks later. So lets say that week falls on June 17th. If you are looking for that tire in May there may be zero to be had. The higher usage of metric tires means there's simply a lot more of them in the system.

• One thing you may see on metric tires is "dual compounding". This is a technology where harder rubber compounds are used in the center of the tire, while soft, grabbier compounds are used out on the edges. In this way you can get higher mileage and enjoy safety in the corners. I haven't seen this technology available at all on "standard size tires".

This post was modified 2 years ago by Richard W

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 02/25/2022 14:46
Joe Hall
(@joe-hall)
Posts: 70
Trusted Member
 

Using a calculator, a 120/90 mm tire is 4.25" wide. Back in the day, for over 200,000 miles, I mostly ran 4.25" rear tires on twin shock Airheads, but needed a spacer. I'd deflate the tire and add some kinda 'slick-em' to the rubber in order to slip the tire past the brake shoe. I also ran 4.25" on two RTs (1979 and 1982), and at least one of them had a rear disc brake. But I cannot recall the details as with rear drum, only that it was doable. I always preferred 4.25" because they got more mileage. Some say a wider tire effects handling, maybe so, but I was never a canyon carver, so never noticed a difference.

Looking at other metric rear tires for Airhead, 110/90 calculates to 3.9" wide, slightly narrower than the 'correct' 4" tire. I now have a mono-shock Airhead (95 R100RT), which calls for 120/90-18, so glad I do not have to fool with a spacer anymore.

Some metric tires come with dual compound, as described above, and I like those. But most metrics come with single compound, which handle well, but short service life. With the current RT, I've worn out the following: Kenda @3500 miles; Bridgestone SF @5500 miles; Avon RoadRunner AM21 @7000 miles; Metzler RoadTec @7300 miles. I am not a speed demon, in any sense, and used to get 20,000 to 25,000 out of rear tires back in the day. Most durable was Dunlop 491 Elite II, but they've been NLA for 10-15 years.

For front tires on the current RT's 18" wheels, I prefer 100/90 versus OEM 90/90, and replaced a Kenda at 3500 miles because it was junk. I got 20,300 miles out of the Kenda's replacement, an Avon RoadRider MK II. I next mounted a Bridgestone BT46, about 5000 miles ago, and looks like it will be gone in less than 5000 more miles. I have experience with the older BT-45 on other bikes; they were dual compound, and the center strip wore like iron. But the newer BT46 is single compound, and I predicted a mileage drop with its 'new and improved' single compound. The next tire will be another Avon RR MK II, which gave best mileage and good handling. Tire companies don't want our tires to last 25,000 to 30,000 miles anymore. They prefer to sell us 4-5 new ones in the same milage span.

Nearly 70 years old now, I ride all I can, and believe it helps keep me young. So tire mileage is important, but so is safety. Best advice, do not install Kenda, unless you really don't plan to ride the Airhead much.        

 
Posted : 03/29/2022 08:27
Richard W
(@wobbly)
Posts: 2552
Member
 

I do believe the "standard sizes" are measured in pure Width. So a tire marked 4.00-18 really is 4" wide.

My understanding of the "metric" tires is that their measurement comes from more of a circumferential measurement. IOW, a measurement following their curved surface, rather than simple Width. So the width of the casing on a 120/90-18 is really no wider than a 4.00-18. The "gotcha" is that the tire is only 90% as high as the corresponding "standard size" tire, so overall height is somewhat reduced. This can effect center stand use, ground clearance, and odometer accuracy.

?

This post was modified 2 years ago by Richard W

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 03/30/2022 16:07
(@Anonymous)
Posts: 0
New Member
 

Just a heads up that I've moved this topic to the "Parts is Parts" discussion area so more people will see it.

Also, I just went shopping for tires for the '95 RT, and here in April of '22, pickin's are mighty slim. Michelin retired the Pilot Activ last year, and the new Road Classic was the only thing I could find in stock. They're very proud of 'em at $350 for a pair, but when you need tires,  you need tires.

Every Avon I've ever used suffered cracking of the tread blocks, so even though I liked the Road Riders, I won't buy any more.

The old standby Metzler Lazer always tracked rain grooves for me, so it's also on the don't buy list.

 
Posted : 04/03/2022 07:34
Joe Hall
(@joe-hall)
Posts: 70
Trusted Member
 

@wobbly metric sized tires also are sized in pure width, by the first set of numbers, i.e. 110 or 120. The following /xx number gives profile percentage of the width, for example /90 means height is 90 percent of width. There are many charts on line, by most tire manufacturers that compare, contrast and explain metric v. inch sizing.

As for crossing the old inch sized tires to metric, as has been noted before, there are no exact matches, only 'close enough'. For example, a 100mm wide rear tire would be 3.9" wide, and a 110mm would 4.3". Probably either would work well on a twin shock Airhead, but the 110 is gonna be a tight squeeze when mounting, and would need a spacer.

The mono shock OEM rear tire size is 120mm, which calculates to 4.7" wide. I am sure there's some variance between brands, but that's how the specs line up.

Looking forward to some serious miles this summer, but also looking forward to warmer weather soon.   

 
Posted : 04/06/2022 22:50
David Elkow
(@4949)
Posts: 307
Reputable Member
 

78 R100/Hannigan - when I lived in KY, and when BMW of the Tri-State was my favorite dealer (Cincinnati), they sold me on Dunlop D404’s. Basic old technology tire, perfectly adequate for me, and very reasonably priced. I just acquired a new set for less than $160.  Had a little trouble finding supply, but succeeded. I use 100/90-19 on the front and 120/90-18 on the rear, with the spacer. Have used many sets over the years. They seem to last as well as anything else. I now live in Texas, so any tire just gets worn away quickly right down the middle. 

 
Posted : 04/07/2022 09:44
Joe Hall reacted

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