What size tyres and tubes?

I have new 19” alloy rims on my Slimline wheels, and I intend to use Avon 100/90-19 Road Rider mk11 tyres on them front and rear, exactly the same setup as on my T160 and 850 Commando

I have a 3.25-19 tube and a 3.50/4.00-19 tube to hand , can I use one or both with these tyres?

Flatspot said:

I have new 19” alloy rims on my Slimline wheels, and I intend to use Avon 100/90-19 Road Rider mk11 tyres on them front and rear, exactly the same setup as on my T160 and 850 Commando

I have a 3.25-19 tube and a 3.50/4.00-19 tube to hand , can I use one or both with these tyres?

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The 3.50/4.00 is no problem. The 3.25 will probably work but is a bit small.

marshg246 said:

The 3.50/4.00 is no problem. The 3.25 will probably work but is a bit small.

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Well, believe it or not, which is partly my reason for asking, my tyre company say to use the 3.25 as the 3.50/400 is a bit too big - this is despite the tyre removed being a 100/90-19

I wonder if any slimline featherbed owners read this are my choice of tyre size OK, or should it be a 90/90-19 front? Owner preference only?

Flatspot said:

Well, believe it or not, which is partly my reason for asking, my tyre company say to use the 3.25 as the 3.50/400 is a bit too big - this is despite the tyre removed being a 100/90-19

I wonder if any slimline featherbed owners read this are my choice of tyre size OK, or should it be a 90/90-19 front? Owner preference only?

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It's always hard to get correct info because there are no exact equivalents. I use 3.50/4.00 in 100/90 and 3.25 in 90/90 when I have them rather than metric tubes. Most places say that a 100/90 and 4.10 tube are equivalent so a 3.50/4.00 tube is actually a little small according to most!

Within reason, I cannot see a tube being "too big" if it is the right diameter.

I don't know anything about pre-Commandos. For a 69S I know that small tires are needed if you want the center stand to work properly and you want to stick with 19" tires.

I don't think any Featherbed Nortons used the same size tyres front and back as original. I prefer my Commando with the 90/90 front and 100/90 rear. I'm sure a Featherbed would handle 'nicer' with the narrower front tyre.
As for tubes, there is a fairly wide latitude in the sizing. Some makes of tube cover a very wide range of tyre widths. Both of those tubes would be ok in a 100/90 and 3.25 would be ideal for a 90/90.

Hold it there folks! Time for a rethink as I’m sorry I’ve made a mistake. When I had the wheels built I ordered 18” rear. So what I actually have is

Front wheel - WM2 x 19”

Rear wheel - WM3 x 18”

My Norton manual says

3.25 x 19 front tyres

4.00 x 18 rear tyres

So what are the new equivalents? 100/90-19 replaces the 3.25 I believe. What replaces the 4.00x18 ?

Flatspot said:

Hold it there folks! Time for a rethink as I’m sorry I’ve made a mistake. When I had the wheels built I ordered 18” rear. So what I actually have is

Front wheel - WM2 x 19”

Rear wheel - WM3 x 18”

My Norton manual says

3.25 x 19 front tyres

4.00 x 18 rear tyres

So what are the new equivalents? 100/90-19 replaces the 3.25 I believe. What replaces the 4.00x18 ?

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Both are suitable 4.00-18

Flatspot said:

Hold it there folks! Time for a rethink as I’m sorry I’ve made a mistake. When I had the wheels built I ordered 18” rear. So what I actually have is

Front wheel - WM2 x 19”

Rear wheel - WM3 x 18”

My Norton manual says

3.25 x 19 front tyres

4.00 x 18 rear tyres

So what are the new equivalents? 100/90-19 replaces the 3.25 I believe. What replaces the 4.00x18 ?

Click to expand...

The closest is 90/90 front and 100/90 rear. IMHO, the diameter -18 or -19 must match in tire and tube so use your 3.25-19 tube in front and buy a tube for the rear since you have an -18 wheel and the tube is -19.

I agree with Greg. 90/90 is 3.25 equivalent. 100/90 is 3.50 equivalent. IMHO 100/90 or 110/90 would be ok on the rear. You will have more choice of tyres using those sizes rather than 4.00x18.

Nortoniggy said:

I agree with Greg. 90/90 is 3.25 equivalent. 100/90 is 3.50 equivalent. IMHO 100/90 or 110/90 would be ok on the rear. You will have more choice of tyres using those sizes rather than 4.00x18.

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Rightly or wrongly, I’ll find out some time, but today I’ve had 100/90-19 front and 110/90-18 rear fitted. Both are Avon Road Rider mk2, same as on my T160 and Commando.


Another question though. The left side spacer on the front hub ‘floats’ inside the 4 peg lock ring, so how do you dynamically balance the wheel when the spacer won’t allow the machine to hold it?

Flatspot said:

Rightly or wrongly, I’ll find out some time, but today I’ve had 100/90-19 front and 110/90-18 rear fitted. Both are Avon Road Rider mk2, same as on my T160 and Commando.


Another question though. The left side spacer on the front hub ‘floats’ inside the 4 peg lock ring, so how do you dynamically balance the wheel when the spacer won’t allow the machine to hold it?

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Assuming balancing on the bike: Neither side spacer should float! Assuming pre-MK3, the shoulder of the axel pushes against the drive side spacer which pushes against the bearing, and the timing side spacer is pinched between that side bearing and fork leg. After the axel nut is tightened all spacers and bearings are locked into place. Then you tighten the pinch bolt to be sure the axel cannot turn. There will be/must be a gap between the drive side fork leg and spacer.

Off the bike it's the same except there are no fork legs so you need an additional spacer on the timing side to makeup the difference of the missing fork leg - nothing extra needed on the other side. The best spacer would be an ID that is a snug fit on the axel and an OD equal to the large end of the axel and a width approx. equal to the width of the axel area of the fork leg. Personally, I would not bother with off the bike balancing for normal road use.

Front hub. 1960 Dominator wheel. This is being balanced dynamically on a machine.

Flatspot said:

Front hub. 1960 Dominator wheel. This is being balanced dynamically on a machine.

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OK, as Sgt Schultz (Hogan's Heros) would say: "I know nothing!"

I didn't pay enough attention - I thought you were asking about a Commando - didn't notice the forum.

Hogans Heroes - now there’s a blast from the past. I was always a fan of F Troop, haven’t seen that for too many years (it probably hasn’t aged well)