What size wheels can I fit to a standard '75/'76 850 Commando e/s?

I have 18" rims back and front on my Mk111. I changed over years ago on the advice of Norman White.

Front is a 2.15" (WM3) with a 100/90 tyre and rear a 2.50" (which is often referred to as WM4) fitted with a 110/90.

It is said to be possible to squeeze a 120 tyre in but I find that the 110 on a wide rim has a less bulbous profile.

The nett effect of these changes is that the rear has roughly the same rolling radius as standard but the front is dropped a little. I have found no stability problems and I prefer the reduced tendency to run wide.

Do you mean in terms of accuracy ? I run an MPH clock in a KPH country so it's bound to read low !

Seriously, according to (rather old) Avon data, the revolutions per mile for a 110/90V18 Super Venom is 813 and for the old Roadrunner Universal in 4.10H19 it was 816 revs per mile.

I don't think that you'll notice any difference.

Cheers, Rich.

Previously wrote:

Richard - thanks for the advice. I'll get that sorted.

Norman White rebuilt my last Commando, a long time ago - wish I still had it!

Did you have any issues with the speedo drive?

Best Wishes

Jack

I fitted an 18" rear to my 1976 Mk3 several years ago and used a 110/90x18 Avon RoadRunner that had virtually the same diamater as the previous but worn 4.10x19 Avon GP- a new 4.10x19 TT100 wastwo tads (a half-inch)larger. The size change idea was publicised in Roadholder by Jem Nicholls. Now I have a 110/90x18 Avon Road Rider AM26, that is atad (quarter inch) smaller. It all means that the speedo drive gearing is relatively unaffected. I also have a calibrated 'bicycle type' mileometer picking up front wheel pulses and this shows the speedo to beten percent over-reading.

The fatter rear tyres are fashionable leanings towards superbikes and I see no improvement in handling. You would need to see if a 120 section fits in the swinging arm.

18" wheels are better for racing, which is why Norman White would recommend them. It's the need for more swift direction changes in tight corners. I am not sureit helps exiting the pub car park.

I use a 90/90x19 on the front, and there seems a recurrent view that fatter tyres on the front of a Command are bad news. I did hear that the factory planned a 3.60 section on the front and 4.10 on the rear, but it was easier for production to stock only the one tyre size, hence 4.10 ended up on the fronts as well. The new 90/90x19 AM26 RoadRideris smaller than the previous AM20 RoadRunner, which was itself a tad and an half (three eights of aninch) smaller than the 4.10 tyres.

Norm.

p.s. it should be noted that 'tads' are not SI Units of measurement.

I'm not sure about the pub car park thing Norm. Bend-wise I believe in "Slow in, fast out" but with pubs I'm afraid it's usually 'Fast in and slow out' Nevertheless, I'm quite happy with the steering.

My preferred type of road is tight twisties but I really haven't noticed a deterioration in straight line stability.

p.s. I'm sure 'tads' are SI. It does stand for 'Smidgen increment', doesn't it ?

Rich

I would stick to a 19" front, I tried an 18" and it made the bike unstable and unrideable over 80mph.

Gents - the 'Tad' IS a recognised measurement of length. Used originally in an Eastern European country for measuring small amphibians. The original word was 'Tadpoles' - subsequently abbreviated in the West to 'Tads'. ;o)

Sir,

I beg to differ !

Tad is a corruption of the word smidgen ! Smidgen is a derivation of a word used by a lesser known Uzbekistani sub-culture which did indeed describe a miniscule measurement.

The nomadic culture of this tribe in Uzbekistan did indeed cause them and their languageto travel west and in due courseend up as the good old british tad, however tadpole was never part of this metamorphosis !

God save the Queen !

Thank you for that. I thought a smidgen was a small pigeon - but you live and learn.

Not really helping Jack's wheel question but knowledge is priceless.

Sir,

Extensive research has proven that this ability with a knife displayed by the smidgeon ( another corruption from the english smidgeon ! ) can be traced back to its uzbekistani decendants who"s traditional weapon of choicewas the kumquat.

God save the Queen.

"Richard - what isolastics and head steady do you run?"

Sorry Jack, I missed this question.

It's a Mk111 so Mk111 isos and I'm very pleased with the Taylor headsteady. However, my frame is a recentish Andover item and is to imperial dimensions. Some Mk 111 frames seem to have been Italian metric items requiring a bit more work to secure a Taylor steady.

Rich