Bridgestone Battlax BT46 4.00 x 18 too wide for my Atlas

Just fitted a pair of Bridgestone Battlax BT46 tyres to my Atlas-framed special and it seems the 4.00 x 18 rear tyre is too wide to fit in the stock swingarm. Jams up solid unless I sit the axle right at the back end of the adjuster slots. Measured the tyre width with digital calipers at 4.560 inches, so it is slightly oversized for a 4.50 tyre, and massively oversized for a 4.00.
The front tyre too, is a 3.25 x 19 but measures at 3.60 wide, so again massively over the nominal width. Both rims are standard.

How can this be? Has anyone else found this with these tyres? Been fitting tyres to Nortons and other Brit bikes for 50 years and never came across this. Is it something new?

I figure I might, might get away with putting a half link in my brand new chain so the axle sits way back at the back of the adjuster slots, and then I might have about 1mm clearance each side of the tyre, which is less than ideal but cheaper than buying a different tyre in the hope it will be narrower. It is getting almost impossible to get old inch size tyres in Oz at the moment. Supply line issues blah blah.

So, although I know the BT46 to be a good tyre from running it on other bikes, can't advise its use on Nortons, so far.

I have also found that problem over the years. There doesn't seem to be any standard for sizes. A few years ago I measured three 4.00 x 18" tyres, a Roadrider 116mm wide, a Michelin Macadam 110mm wide, & a Bridgestone BT 45 124mm wide. These figures are from memory, but I think they are correct.
The best tyre web site is Avons which gives all the sizes.

Martyn.

Yes I had the same problem, I had a steel spike go through the side of my near new Metzler ME77 on my '66 Atlas and for some reason there was no Metzler ME77 available in NZ [a Metzler supply problem], I tried the Bridgestone 400x18 and had the same clearance problems, I ended up fitting a Michelin 400x18 which fitted fine.

I made the following chart earlier this year - may assist.
Note - the clearances are for my Commando. I had Bridgestone BT45s which had been discontinued
The list is not exhaustive, just what I was considering at the time.
Cheers

Thanks for the feedback guys. I knew that 4.00 was only a nominal size and to expect some variation, but not that much variation as the BT46 has. Sounds like it is common. And from Matchless's measurements, it looks like the BT46 is the worst offender. I reckon I could live with 110mm (4.3") but 117mm (4.6") is too much. The tyre is firmly in contact with the swingarm both sides for most of the available axle location range. I will have to contact the seller (online tyre warehouse) when they reopen after the holidays. Sigh. Took me three weeks to get this tyre delivered and I was hoping for a test ride on this bike next week, after having it sit in my shed unridden for more than 20 years. The best laid plans of mice and men...

I did measure a couple of other 4.00 tyres on my other bikes and found a nearly new Dunlop K70 at 4.1" and same for a 15-year-old Metzeler and a bit less for some really ancient tyre with no brand name. But I don't want to run a K70 on a cafe racer with a heavy Harley engine in it and can't get a Metzler at the moment due to shortages etc.

My other alternative is to go back to using the 19" conical hub Rocket 3 wheel that was in this bike before, with a 4.10 x 19 Dunlop TT100/K81 tyre on it. That tyre measures under 4.1" (104mm) but is a million years old so I don't know now if the modern version of the same size would still be as narrow, or would it be oversize like all these others?

Certainly has been a learning experience and thanks for all the info. Most informative.

If it’s out only a little bit take an angle grinder to it.

If it’s out only a little bit take an angle grinder to it

No the whole tyre was to big!

If your Atlas has 19 inch wheels, fitting fatter tyres will not improve it's handling. In about 1963, the two-strokes arrived. The first thing we noticed were their greater angles of lean in corners. They were a different concept motorcycle. It is very difficult to get extrema angles of lean with a featherbed Norton. So a fatter tyre does not do much. If you race a featherbed bike, climbing off the side of it, might make you think you are being quicker, when in fact you are probably not. I once watched Mike Hailwood race a Manx. He stayed all neatly tucked-in and lovely.
It is a mistake to compare old bikes with modern bikes and think you can apply the changes to the old ones. The old bikes were improved by racing and crashing - they are what they are.

nopdog said:

If it’s out only a little bit take an angle grinder to it.

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I thought about running the bike in gear up on the stand and applying a car body file to the edges of the tread on the tyre to slim it down a bit. Thought seriously about it. But it has to go through a roadworthy inspection to get registered so pretty sure the inspectors would take a dim view of file marks up the side of the tyre.

acotrel said:

If your Atlas has 19 inch wheels, fitting fatter tyres will not improve it's handling. In about 1963, the two-strokes arrived. The first thing we noticed were their greater angles of lean in corners. They were a different concept motorcycle. It is very difficult to get extrema angles of lean with a featherbed Norton. So a fatter tyre does not do much. If you race a featherbed bike, climbing off the side of it, might make you think you are being quicker, when in fact you are probably not. I once watched Mike Hailwood race a Manx. He stayed all neatly tucked-in and lovely.
It is a mistake to compare old bikes with modern bikes and think you can apply the changes to the old ones. The old bikes were improved by racing and crashing - they are what they are.

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That's my point, fitting fatter tyres is impossible with the stock Atlas swingarm. This 4.00 x 18 tyre is wider (4.560") than the old 4.10 x 19 I previously ran. So I have now decided to go back to the 19 with a new 4.10 TT100 and hope the new TT100 is no wider than the old one. PITA because I already put new bearings in the 18" wheel and polished it all up so now I have to do it all again on the 19. But that is Special building. Everything on this Harton project almost fits, but nothing quite fits. Seems like one step forward, two steps backwards all the way. I slapped it together in about 3 weeks 30 years ago. I must have not been as fussy in my yoof as I am now, doing the resurrection! But at least in those days, when you bought a 4.00 tyre it was actully 4.00 to 4.100 wide and fitted the bike as required. The world seems to have gone backwards in the interim.

As I have previously stated you were unlucky to choose a Bridgestone as the tyre is considerably oversize and probably bigger than a 450x18, also a 410x18 sized tyre is a totally different sizing to a 400x18 and is more similar to a 350x18. the Atlas was supplied new with a 400x18 tyre where as the 650SS was supplied with 350x19 rear but the 22586 swingarm is common to both models so they must have shared the same swingarm. I have both an Atlas and 650SS of the same year so when I encountered the oversize Bridgstone problem it was a big help, I suggest you find another brand of 400x18, I have a 400x18 Michelin Road Classic on mine and it fits fine, a 410x18 is a different "animal".

NorLuck said:

This is odd as I have the same exact tire and tried it on the Molnar Manx frame (fits even fully forward) and tried it on the Slimline frame (69) again fits fully forward. It's close like 1-1.5cm on each side but not touching.

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Yes that is odd. I would expect the Molnar Manx frame might have a swingarm made to take modern wider tyres but not the Slimline. I presume you mean 1-1.5mm not cm though? I don't even have that much, unless I put the wheel at the very back of the slots on the swingarm and even then I reckon it's closer to 0.5mm gap than 1mm. Not really do-able.

NorLuck said:

Just checked today after making that comment and it's about .5cm-.7cm on the slimline.

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5 to 7mm that is how much clearance I have with correctly sized 4.00 tyre that measures between 4.00 and 4.10 wide. So a 4.560 wide tyre definitely will not fit, as others above have found. Don't know what is going on with yours. My other two Atlas frames are the same, too narrow to fit a 4.560 wide tyre.

Controversial, and irrelevant: My recently determined personal solution for this kind of issue is run a front on the rear. Just turn it around. That said an old Norton with a Norton engine in it doesn't need a fat tire on the arse end.

The slimline is really slim. With my version of Norton I have .5" of room back there either side of the tire with the axle pulled all the way forward using a 4.00x18, but won't be running them back there any longer. Plan in the future is two fronts. Don't care about the difference in carcass design between fronts and rears (if there really is any). My Norton won't be hitting 150mph ever, so I doubt a front on the rear will be a problem.

Schwany said:

Controversial, and irrelevant: My recently determined personal solution for this kind of issue is run a front on the rear. Just turn it around. That said an old Norton with a Norton engine in it doesn't need a fat tire on the arse end.

The slimline is really slim. With my version of Norton I have .5" of room back there either side of the tire with the axle pulled all the way forward using a 4.00x18, but won't be running them back there any longer. Plan in the future is two fronts. Don't care about the difference in carcass design between fronts and rears (if there really is any). My Norton won't be hitting 150mph ever, so I doubt a front on the rear will be a problem.

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I am not sure what you are saying there. If you can fit a 4.00 x 18 on your bike, with half an inch clearance, why do you want to run a front tire in there, which is, what, 3.25? Why not just run the 4.00 like Norton designed it?
I have ended up using a conical hub 19" rear wheel I had on hand and fitted it with a 4.10 x 19 Dunlop TT100 and that fits with about 1/8" to 3/16" clearance each side.

This is what an Atlas framed bike looks like with a front tire on the back. That is a 3.60 x 18 I had on there just for the purposes of wheeling it around the shed. Just looks anemic to me.


The Atlas in the background has a 4.10 x 18 TT100 on there and even that looks a bit anemic to me. It is 4.100 wide as measured, but of course it is a low profile tire so does not fill up the space between the tire and the guard. And you lose a little cornering clearance as the bike sits that half inch or so lower.

Not a very good angle, but here is the 4.10 x 19 TT100 by comparison. It fills up the space better because it is the same outside diameter, more or less, as a 4.00 x 18.

HopperXL said:

I am not sure what you are saying there. If you can fit a 4.00 x 18 on your bike, with half an inch clearance, why do you want to run a front tire in there, which is, what, 3.25? Why not just run the 4.00 like Norton designed it?

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Modern tubeless tires have directional tread patterns. A motorcycle rear tire is basically the same as a front but turned around facing in the opposite direction.

I like skinny tires, and don't give a fart about what Norton did. I'm fairly certain they never put a HD motor in a featherbed frame either. lol

P11 from the factory is 19-inch front 18-inch rear. I have 18's on both ends.

I'd like to use a conical hub on the rear myself, but I wouldn't use one with a huge gear on it for the street.

Interesting project. Should handle well. How much does that weigh?

Why would you waste a featherbed frame by putting an iron head Sporty in it? LOL Have to admit if looks great!

It weighs slightly under a ton. That cast iron motor is heavy. Why? Gits and shiggles. And I had a spare motor for my Ironhead and a spare frame for my Atlas kicking around so what else was a guy to do? Built it back in the 1980s and rode it a few years. A hoot to ride. And doesn;t vibrate as much as an Atlas but is faster than the usual pre-unit Triumph 650 motor.