Michelin weave banished

A short while ago I fitted a pair of Michelin Pilot Activ tyres to the MK2a 920, 3.25 x 19 & 4.00 x 18. I did this to see if they would give longer milage than the Road Riders previously fitted. From the first ride onwards, the bike would weave badly at anything over 80 mph & the handling on fast bends & twisties was at times alarming, but once I realised it wasn't going spit me off I just tolerated it.
There is however a limit, & being convinced that the problem was coming from the rear end I have now fitted a 4.00 x 18 Road Rider whilst leaving the Michelin on the front. Went out for a spin yesterday & am pleased to say normal service has been resumed. The Michelin doesn't have a centre groove of any kind where as the Avon has a partial one. I wonder if this is the important difference?
Any thoughts?

Hello Matchless,

What sort of mileage were you getting from the Road Riders? I've just fitted a pair to my MKIII and am really pleased with them.

I found my Fastback with two 18 inch wheels and road riders weaved badly above 75. I bought a 19" front wheel from eBay and it came with a ten year old michelin macadam. the weave is almost gone but part of the issue is I've lost 22lb due to illness and I think this has a lot to do with the problem. A worn rear will amplify the problem though.

I'm swapping cast wheels to my commando from the stock spoke wheels. So far, I have the rear wheel installed and I'm waiting on the front wheel's caliper offset bracket to be made to mount the front wheel. The original spoke wheel's tire is a dunlop K81 (tt100) which has the center groove. The new cast wheel has a tire on it that I am going to replace eventually, but that tire has no center groove in it. ALL traces of high speed wobble are gone with the new back tire fitted. The new tire's profile is definately different also, so it gives a different feel when I lay the bike over into the turn. So far, the new tire's feel seems predictable so it's just a matter of getting accustomed to it, but I do believe that the center groove in a motorcycle tire tends to give a bike more of a wobble when the bike is verticle and going fast. Like so many things surrounding norton commandos, I'll never understand why those dunlop k81's had a mistique of being some magical tire, because in the 40 years I've owned a commando, I've always fitted them until recently and as soon as I fitted a tire without the center groove the bike feels much better over 80 mph.

o0Norton0o,
The centre groove idea is just a theory & maybe nothing to do with the weave, but as the Pilot Activ & Roadrider are of a similar shape, size & as far as I am aware construction, why does one tyre cause a weave & the other not? The Michelin is 109mm wide & the Avon is 116mm (fitted) but both are 4.00 x 18". It's funny you should mention TT100s because Norman White told me to fit them to banish the weave on my 750 MK1. Haven't tried that as yet.

Crusadersports,
As for mileage, the reason I changed to a 18" rear was for a proper rear tyre with 7.5mm tread depth as opposed to the universal 100/90/19" which has 5mm, out of which I was lucky to get 2,700 miles. The 18" RR gave me 3,700.

Gripper,
My 1968 MK1 tends towards a weave at speed which goes away when I move my weight to to rear. I have also fitted a hydraulic steering damper as an experiment. This seems to be working better than I had dared hope. As for you, maybe eat more pies!!

Well,... I have a theory too... I posted this image in another thread...



If you look at the image of the tire in the picture when it's verticle, you'll see that the design of a tire to have a narrow contact patch leads to quicker steering. In the case of the classic Dunlop K81's, they have been discribed as almost a triangular shaped profile so the narrowness of the contact patch is very narrow. Add to that narrow design, a groove down the middle of that narrow contact patch and you get a tire that attempts to align itself as the contact patch area varies as it travels along the undulating road surface. The wobble is felt because the groove forces the contact patch to be 2 competing contact patches that both attempt to track as minor variations in the road create a bias to make one align better than the other as it trails the front tire.

When you lay the bike over any amount with the dunlops this wobble is no longer felt. IMO, a center groove tire is a poor design for a TRAILING tire because forces on the trailing tire are always trying to make it align with the front tire which induces wobble in the continuous center groove tire design.

A rear tire without the center groove seeks to align itself also like any trailing tire, but it doesn't have a groove down the center to make it's area into two competing surface patches, so as the tire trails it seamlessly wanders across the contact patch without the feeling of wobble induced by "jumping the groove" when a slight angle change makes the other half of the contact patch more dominant...

That's my theory..

Interesting theory. What I might try next is a pair of the Metzler Klassic radials & also the Continental radials. Has anyone on this forum tried either of these?

I run Avon AV71's on both ends of my Commando. No center groove at all and no weave.
I get at least 6000 miles out of the rear. Jim

My 1972 had a nasty front end wobble at 35 mph. Took the worn Supervenom front tire off, replaced it with an older but good tread Roadrider. Totally fixed the front end wobble. The Supervenom had no rib in the centre, the Roadrider had a ribbed center. I think the ribbed center helped solve the problem. Course you could also make the case that the wear in the Supervenom caused the problem, regardless of the absence or presence of the rib.

Stephen Hill

comnoz said:

I run Avon AV71's on both ends of my Commando. No center groove at all and no weave.
I get at least 6000 miles out of the rear. Jim

Click to expand...

Jim, which ones do you run exactly? And on what rim widths?

Stephen Hill said:

My 1972 had a nasty front end wobble at 35 mph. Took the worn Supervenom front tire off, replaced it with an older but good tread Roadrider. Totally fixed the front end wobble. The Supervenom had no rib in the centre, the Roadrider had a ribbed center. I think the ribbed center helped solve the problem. Course you could also make the case that the wear in the Supervenom caused the problem, regardless of the absence or presence of the rib.

Stephen Hill

Click to expand...

I 'm not trying to be obnoxious,.... but I said the "groove effect" is something that is related to thej REAR tire. I also explained that the reason the groove creates a wobble on the REAR is because the REAR tire is subject to "TRAILING EFFECT" of the swingarm. I don't think a center groove hurts the front tire design because it's not subject to the trailing effect forces which the rear tire is subject to because the front tire not supported by a lateral swingarm in a trailing position like the REAR tire is...

I know that what I am saying is complicated, but if you read closely, it's kind of simple. It's a combination of the trailing effect forces on the rear wheel, and the way that the center groove in the rear tire makes the rear tire's contact patch act like 2 competing contact patches that cause a wobbly feel...

I don't think a groove in the center of a front wheel is a bad thing...

I just changed out my rear tire on my 850 interstate. I used a NOS Super Venom just to burn it up (it was old) 4404 was on the date stamp. put on, in the spring @50238 on odometer....replaced at @56340 today. I had a good 2 inch wide slick in the center of the tire but I didn't hit the cords yet. Not like the Hob... :mrgreen: He uses up the tires right to the cord and then some.
SV were known to be soft but I did 6102 miles.
cheers,
Thomas
CNN

comnoz said:

I run Avon AV71's on both ends of my Commando. No center groove at all and no weave.
I get at least 6000 miles out of the rear. Jim

Click to expand...

100-90-19 on the front 1.85 rim

120-90-18 on the rear -turned around since it's a front tire. 2.15 rim

weave, wobble, slop, groove............. yep, I have all of those!
TT100's, tired suspension, worn swingarm bushes, loose spokes, etc. probably all play a part.

It adds character! :lol:

CanukNortonNut said:

I just changed out my rear tire on my 850 interstate. I used a NOS Super Venom just to burn it up (it was old) 4404 was on the date stamp. put on, in the spring @50238 on odometer....replaced at @56340 today. I had a good 2 inch wide slick in the center of the tire but I didn't hit the cords yet. Not like the Hob... :mrgreen: He uses up the tires right to the cord and then some.
SV were known to be soft but I did 6102 miles.
cheers,
Thomas
CNN

Click to expand...

Want to buy some slightly used tires? They are only worn to the wear bars.....

comnoz said:

CanukNortonNut said:

I just changed out my rear tire on my 850 interstate. I used a NOS Super Venom just to burn it up (it was old) 4404 was on the date stamp. put on, in the spring @50238 on odometer....replaced at @56340 today. I had a good 2 inch wide slick in the center of the tire but I didn't hit the cords yet. Not like the Hob... :mrgreen: He uses up the tires right to the cord and then some.
SV were known to be soft but I did 6102 miles.
cheers,
Thomas
CNN

Click to expand...

Want to buy some slightly used tires? They are only worn to the wear bars.....

Click to expand...

Yea I got a few of them and they are cheap. pay for shipping and they are yours. :lol:
Cheers,
Thomas
CNN

comnoz wrote:
I run Avon AV71's on both ends of my Commando. No center groove at all and no weave.
I get at least 6000 miles out of the rear. Jim


Jim,

The AV71 120/90/18 is listed on Avons site as 5.1" (129mm) wide. How do you make it fit between the swingarm without rubbing on the chainguard? When I first acquired my 750 it was fitted with a Bridgestone BT45 120/90/18 which was 124mm wide & meant the chainguard could not be fitted.

Matchless,
I think comnoz is not running a chain final on his highly modified commando, but a belt. I think he can explain the fine details better.
Cheers,
Thomas

[quote="Matchless"
Jim,

The AV71 120/90/18 is listed on Avons site as 5.1" (129mm) wide. How do you make it fit between the swingarm without rubbing on the chainguard? When I first acquired my 750 it was fitted with a Bridgestone BT45 120/90/18 which was 124mm wide & meant the chainguard could not be fitted.[/quote]

I just checked the tire width. It measures 124mm at it's widest point.

I believe when I used to run a chainguard [before I went to a belt] I used a CNW chainguard and it just cleared with a little tweeking.

I have also removed the backside of a stock chainguard just where the tire rubbed many years ago.

The tire is also available in a 110-90-19 which is what I run on the back of my stock MK3. Jim

Thanks for clearing that up. That width would seem more realistic.
As a matter of interest are you using stock geometry with the upside down fork yokes?