Tire size help

Guys, what the largest 18 inch tire that I can fit in an '66 Atlas swingarm? The current tire on the bike is a 4.00 18 and there is about 1/4 inch space on each side to spare. Could I fit an Avon RoadRider 120/90 18? or is 110/90 18 the largest?

Hi Johnnymac, I currently have an 110/90 18 inch Avon Roadrider on the rear of my Dominatrix. As the size isn't actually 110 I've just measured it and it's 4.5 inches (115mm) at it's widest point. This is very tight against the chainguard as it is so I'll probably swap it for a 100/90 when it's worn out to give a tad more clearance. As I've got a 100/90 18inch Roadrider on the front at the moment (another tight fit so it'll go on the back and get swapped for a 90/90 18) I've measured that and it's 4.05 inches (103mm) at it's widest point. I've no idea what a 120/90 18 would measure. Hope that helps.

cab058 said:

Hi Johnnymac, I currently have an 110/90 18 inch Avon Roadrider on the rear of my Dominatrix , I've just measured it and it's 115mm at it's widest point. This is very tight against the chainguard as it is so I'll probably swap it for a 100/90 when it's worn out to give a tad more clearance. As I've got a 100/90 18inch Roadrider on the front at the moment (another tight fit so it'll go on the back and get swapped for a 90/90 18) I've measured that and it's 103mm at it's widest point. I've no idea what a 120/90 18 would measure. Hope that helps.

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Thanks cab058. I just learned that Avon still sells the RoadRider tire in the 4.00 - 18 size so I'm guessing that should be OK to swap out with my existing 4.00 - 18. I know that there are differences in sizes amongst the different manufacturers though.

Thanks cab058. I just learned that Avon still sells the RoadRider tire in the 4.00 - 18 size so I'm guessing that should be OK to swap out with my existing 4.00 - 18. I know that there are differences in sizes amongst the different manufacturers though.[/quote]

Yes, and they also sell the matching correct size for the front...I got a pair for my Atlas from Motorcycle Superstore and the price was right...

The Avon Roadrider 400x18 is quite a wide and heavy duty tire. At 4.6" in width, it is wider than I expected for a tire with a 4.00 width designation. It has a high load rating at 64, and is OK to fit on a wm3 rim.
It is also a rear tire, not a universal, so it has extra tread depth. I have just worn one out on my Vincent, 8,000 miles with a lot of two up riding. Prior to changing to an 18" rim, I used 100/90/19 Roadriders on this bike, 6,000 miles was it for those tires.
If you can squeeze it on the Atlas, I think you will be very pleased with it.
Do you have a WM3 rear rim on the bike? I believe the stock rim on back was only WM2 width, not wide enough for the 4.00, according to Avon.
Glen