18" rear wheel???

Derek Wilson said:
I run 26 psi in the front and 28 in the rear
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Thanks. I‘m running a 120/80/18 rear and a100/90/18 front- brain fade , thought it was 90/90 - as per Norman White’s recommendation. He suggested 30 psi front and 32 rear….it feels a bit ‘ squirrely ‘ . Did you try other pressures before settling on 26/28 ?
Derek Wilson said:
I run 26 psi in the front and 28 in the rea
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Lower tyre pressures cause the tyres to heat up quicker. In racing, it is common to reduce tyre pressures when it rains to get a bit more grip. In the dry lower tyre pressures probably cause the tyres to wear quicker. As they heat up they soften. I use Battlax tyres at 32 PSI, even when it rains. I was brought up racing on really bad tyres. Modern road tyres are much better than we ever had pre-1970.
 
TBW said:
Thanks. I‘m running a 120/80/18 rear and a100/90/18 front- brain fade , thought it was 90/90 - as per Norman White’s recommendation. He suggested 30 psi front and 32 rear….it feels a bit ‘ squirrely ‘ . Did you try other pressures before settling on 26/28 ?
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I tried higher pressures and always thought the bike felt twitchy, and not planted on the road. So I went little lower. If I were riding with a passenger, I would bump them up a bit.
 
All of my Commandos have been changed to an 18 inch rear eventually. A 120-90 works well and is a similar diameter to original.
One thing you have to do with modern tires is increase the tire pressure quite a bit. New tires have a more flexible construction. Unloaded I run about 36 front and 42 rear. Fully loaded I run them up another 4 lbs. That helps keep the handling light.
I started running Heidenau tires. A 120-90/18 rear and a 100-90/19 front will get me ~6500 miles.
They will let me make my normal fall trip without a change. For several years prior I had to mount a new rear tire at Barbers for the trip back home.
 
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comnoz said:
All of my Commandos have been changed to an 18 inch rear eventually. A 120-90 works well and is a similar diameter to original.
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In the thread How big of rear tire fits commando? (2010) I wrote a summary of member experiences (personally I am not there yet), and concluded 110/90-18 was the widest tyre which would fit the Commando.
Now you say you are running 120/90-18. Did you extend the swinging arm of your bike? Or is your tyre less wide than others have reported due to increased pressure?
With a stock swinging arm, the tyre/chaincase clearance must be rather small using a 120/90 tyre ?

Cheers,
Knut
 
mdt-son said:
In the thread How big of rear tire fits commando? (2010) I wrote a summary of member experiences (personally I am not there yet), and concluded 110/90-18 was the widest tyre which would fit the Commando.
Now you say you are running 120/90-18. Did you extend the swinging arm of your bike? Or is your tyre less wide than others have reported due to increased pressure?
With a stock swinging arm, the tyre/chaincase clearance must be rather small using a 120/90 tyre ?

Cheers,
Knut
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I think you are correct. My Mk2 has an aftermarket chainguard and it occasionally touches with a 120 Avon.
I looked at my mostly stock MK3 and it has a 110-18 on it. I haven't had to replace that tire for years since it seldom gets ridden.
My modified Commando doesn't have a chainguard -or a chain. It's belt drive and I could probably get a 130 on it if I wanted to.
 
I have a 120/90/17 bt45 on the 920. It clears the chain ok but the chain guard, which is an aluminium copy of a standard chain guard, needed a scoop out.
That tire just fits inside the swing arm with about 1/4" clearance each side.

Glen
 
Derek Wilson said:
I tried higher pressures and always thought the bike felt twitchy, and not planted on the road. So I went little lower. If I were riding with a passenger, I would bump them up a bit.
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Thanks. just how mine feels….dropped front to 30 today and felt better…but not there yet. I’ll follow your experience. Single seat so no pas
 
mdt-son said:
In the thread How big of rear tire fits commando? (2010) I wrote a summary of member experiences (personally I am not there yet), and concluded 110/90-18 was the widest tyre which would fit the Commando.
Now you say you are running 120/90-18. Did you extend the swinging arm of your bike? Or is your tyre less wide than others have reported due to increased pressure?
With a stock swinging arm, the tyre/chaincase clearance must be rather small using a 120/90 tyre ?

Cheers,
Knut
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Hi Knut, so I’ve a 120/80/18 on 750 stock swing arm. Reckon 7/16..3/8 clear each side…like Worntorn has.
 
TBW said:
Hi Knut, so I’ve a 120/80/18 on 750 stock swing arm. Reckon 7/16..3/8 clear each side…like Worntorn has.
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I guess you had to make a dent in the chain guard as well? Premise of my conlusion in the mentioned thread was "no change to the bike".
People who fit these wide tyres need to state the measures they took to enable this.

- Knut
 
I think I owe you all an apology. I have been talking rubbish again. When you fit an 18 inch wheel to the rear of your bike and a 19 inch on the front, the rear tyre is usually 4 inch cross-section and the front is 3,5 inch. So the height of the rear of the bike does not decrease and the trail remains the same. The trail depends on the rake of the steering head and the yoke offset. I have only ever had a bike mishandle once due to the rear tyre. Back in the 1960s, there was a tyre produced by Avon which was probably meant for sidecar use. It has a much squarer shape in its cross-section. It was the Avon SM. As you leanted the bike over in corners, that tyre could cause you to drop the bike.
Theoretically, different size tyres front and rear could cause a tyre alignment problem, but I have never found it to have any effect in practice. I have 18 inch wheles front and back on my Seeley . The front is a 3.50 and the rear is 4 inch. The bike still steers extremely quickly and never miss-handles.
 
I wonder about the SM I have one on my Interceptor and it does feel less then wonderful at times but it has a big contact patch for straight ahead and lasts a long time. Also have to ask about 110 and bigger rear tyres as they seem to wear out quickly in the middle making me wonder why such a big tyre if the contact patch is so small. No doubt you maintain good contact in the corners though.
 
While the size on tire will get you a close dimension, fact is that there is a difference between manufacturers and even models within manufacturers. So if you are talking about a certain size its also critical that you consider the manufacturer and model

I have for many years used a 120/90-18" tire as a standard size on my builds. This in a Bridgestone BT45 (now BT46). This tire is much narrower compared to an Avon. This since the Bridgestone has a shaved sidewall. That removes about 1/4" on each side yet leaves you with a footprint of a 120 tire. Few of us use that last 1/4" of thread and if you are actually on that part of the tire, its probably due to an 'O shit moment'.

The above tire will work with a stock chain guard in place and still room to adjust. Not a lot like a skinnier tire would but certainly no contact

I have ran a 130/80-17" (same Bridgestone BT 45/46) on some bikes and with that I do notch the inner part of the chain guard to get a bit more clearance

Matt
 
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mdt-son said:
I guess you had to make a dent in the chain guard as well? Premise of my conlusion in the mentioned thread was "no change to the bike".
People who fit these wide tyres need to state the measures they took to enable this.

- Knut
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Knut, fair comment. Ididn’t consider the chain guard as I don’t run with one.
 
cNw said:
While the size on tire will get you a close dimension, fact is that there is a difference between manufacturers and even models within manufacturers. So if you are talking about a certain size its also critical that you consider the manufacturer and model

I have for many years used a 120/90-18" tire as a standard size on my builds. This in a Bridgestone BT45 (now BT46). This tire is much narrower compared to an Avon. This since the Bridgestone has a shaved sidewall. That removes about 1/4" on each side yet leaves you with a footprint of a 120 tire. Few of use use that last 1/4" of thread and if you are actually on that part of the tire, its probably due to an 'O shit moment'.

The above tire will work with a stock chain guard in place and still room to adjust. Not a lot like a skinnier tire would but certainly no contact

I have ran a 130/80-17" (same Bridgestone BT 45/46) on some bikes and with that I do notch the inner part of the chain guard to get a bit more clearance

Matt
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Matt, interesting about BT46 width…poss explains in part why Norman White recommends BT45 / BT 46…
 
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