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What causes a speed wobble (high speed weave)


makfai said:
That does sound tyre related. Might sound a daft question but is it fitted correctly? I have seen one where the fitter put it on the wrong way round! And more than one where he actually damaged the wheel! And several where the wheel wasn't balanced correctly after the new tyre was fitted and the regular . . . adjusters on the rear were not set correctly. Trust the "experts" - no way!
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Yes, front is fitted correctly and has been balanced multiple times by two different mechanics, just to make sure. I've ruled out balancing issues.
 
10mm drop on the forks? have you tried it back at the stock height? thats a big change in the rake and it usually results in less stability at high speed.
 
If I'm driving at less than 180kmh all the way, to avoid weaving, it will take quite a while :)
 
Triple Trouble said:
Mite be worth making sure the dot on the tyre is sat opposite the valve. Sounds silly but it makes a difference. Just saying.
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AFAIK Michelin doesn't have the yellow dot, and besides that, I'm guessing that the dynamic balancing machine should be able to cope and compensate for a wrongly placed tyre.


relz said:
Those were interesting videos, I've actually seen them in the past but have forgotten about them.
Assuming that a newer rounder front tyre can emphasize weave, as mentioned in the video, perhaps I'll try to run the recommended high pressure on the rear and a lower than recommended pressure on the front to kind of 'square it off' until it wears down a bit.

Or even better (but more of a pain) I could install a new rear, to match my new front, and keep my 4000km used rear tyre for my next change, at which point the front won't be so new anymore.
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OK, so today I had some more spare time for testing (I'm in the middle of a long stretch of duty in the military reserve force, due to that mess we had down south, so I'm making the best of my spare time between the guard duties and such :) )

At first I reduce the pressure to be 30/30 as per marthy's recommendation, and it did seem to stabilize things quite a bit. The weave was much less noticeable, at times I reached up to 190kmh without any weave and other times it still weaved at around 170kmh (triggered by uneven road surface, current lean angle etc.).

Next I filled up the rear tyre to 42psi, as per the spec, but left the front low at 30psi. This did not make the weaving any worse than before, so I concluded that removing air from the front tyre is what made the difference.

This lead me back to my theory (which was mentioned in the movie), that riding a flatter rear tyre (e.g. used tyre) with a rounder front tyre (e.g. newer tyre) is bad practice, and it may be what caused my weaving with the two different new tyres.



MT account said:
10mm drop on the forks? have you tried it back at the stock height? thats a big change in the rake and it usually results in less stability at high speed.
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The weaving started immediately after installing my new tyre, which was before I raised the forks to 10mm in the triple, prior to that my forks were only raised by about 3-4mm.

While experimenting (on my private airstrip), with the lowly inflated front tyre, I noticed that I can eliminate the weave by moving back on the seat. I tested this a few times, and sitting back on the seat (right on the ridge) at speeds up to 200kmh was steady, while sitting up front right next to the petrol tank would cause powerful weaving at 170kmh. hmm...
This led me to think that it might be related to the reduce trail that I caused, by lowering the triple so much after all. Perhaps when I sit back, I'm causing the front of the bike to raise a bit, and adding more trail... or perhaps simply removing weight from the front wheel has this effect.



So I bit the bullet yet again, and decided to install the rear Michelin PR4 too (praying that this will actually solve the problem), and went out for another fast paced ride.

The bike is back to being perfect :D
I can go as fast as I want, over bumpy roads and any angle and the bike is rock steady. Whenever the steering is knocked out of line, by a bump, or me letting go and then hitting one side of the handlebar for testing :rolleyes:, it immediately goes back to the straight line, as it should. Phew

I've kept my slightly used (4000km) rear PR3 tyre, for future use. Assuming the problem I encountered only exists when installing a rounder new tyre, together with an older not so round rear tyre, I sould be able to install the used PR3 tyre in a few months time after my rear PR4 tyre has worn out a bit more (hopefully at least another 10,000km from now). By that time the front tyre won't be so new and round, and it might play together will with the newer PR3 rear tyre.


Conclusions:
1. Do not install a new tyre, with an existing non-new rear tyre. Installing a new rear-tyre with an older front-tyre may still be fine (or may not). It's definitely safest to replace both tyres at the same time.
2. The Bridgestone T30 may or may not be compatible with the MT-09, my tests are inconclusive. I switched out my new T30 for a new PR4, before identifying the actual problem. Perhaps installing a new rear T30 would have solved my problems too (and saved me about 100GBP). Although this whole post (before I hijacked it) was started by stevecbr, who had issues with his set of Bridgestone Sport Touring tyres. So possibly the T30 would have weaved too, even if I did install a set.


I might try lowering the forks in the triple, back to the OEM spec, just for comparison to try add more trail and give it a even more stability (playing on the safe side now). I'll reconsider it to see if the slower turn-in really bothers me that much, or perhaps better to trade a bit of turn in time (or force) for a bit of stability. I've also encountered a bit of weaving when accelerating from fast corners, which I always accounted to the soft suspension. Perhaps this too can be reduce by adding a little more trail... it's worth testing as it's a very easy fix to change the forks height back and forth.



So this was a pretty expensive, tiring (, and at times scary) lesson, but I believe that lessons learned the hard way are those that you remember the best. I'm also always willing to pay for education, so the time and money wasn't all for waste.

I'm tempted to add a new post labelled "SOLVED: high speed weave after new front tyre installation", which just points to this thread, in order to help people with a similar problem in the future. Or we can just let them rely on memory, or search through tons and tons of posts, like the rest of us do so many times :p

Thanks for all your inputs and suggestions, you definitely helped put me on the right track.
 
makfai said:
Good point but I would have thought this would have resulted in wobble.

But the point is really valid. Have a look here

I thought this was really interesting:

As an example, a bike with a front tire having a circumference of 1890mm, a 23-degree rake and 27mm of offset will have 98.5mm of trail. Note that in the range of variables we are dealing with, using a tire with a smaller radius, increasing offset or decreasing rake can decrease trail. On most stock sportbikes, you cannot change two of the three variables (tire diameter and offset) without resorting to modifications, but the third variable, rake, we can change slightly by raising or lowering the fork tubes in the triple clamps.
An expert-level roadracer can notice a change in the order of 1mm in trail, and working equation 1 backward, we can calculate the change in rake required as just less than 0.2 degrees. Using an approximation based on the arc length from the rear axle to the steering head, we can further calculate that a fork-height change of just 4mm is enough to effect this angle change.

AND AS YOU MENTIONED THE PROBLEM ONLY APPEARING SINCE TYRE CHANGE

Tire diameter is one of the other variables affecting geometry, and we can calculate the change in trail resulting in a switch between two brands of tires. In our last tire test ("DOT Race Tire Test," Feb. '03), the tallest front tire was the Michelin Pilot Race 2, at 1910mm in circumference. The smallest tire was the Metzeler Rennsport/Pirelli Supercorsa, at 1878mm. We always measure tire circumference and change ride heights to make the overall chassis attitude (and rake) the same (see Ask the Geek, Feb. '02), and in this case, the fork tube height would need to be changed by 5mm just to level the chassis.
Even taking that into account, however, the change in trail due only to the change in tire size is 2mm. Add in the different tire's profile (that changes trail at various lean angles), and you can see why adjusting only to keep the bike's attitude the same when changing tire brands is sometimes not enough.


It would be an idea to return everything to OEM stock settings/fittings (including tyres if you have them or could borrow some!) then make changes one at a time to assess effect.
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This is all relevant but wheel base and weight distribution is all part of it and the more time you ride a bike you adapt to certain issue subconsciously.
As has already been said the supension is shit to be blunt and a personal set up would cure it in my opinion.
I have already in the space of 300 miles of owning this bike have dropped the forks through 10mm.
Pushed the bars forward 25 mm moved the controls in 25mm including grips so bars are not as wide wound all front and rear preload up full
It's still not right by no means i have acquired the zx10 shock all the US lads are fitting and enquired about uprated springs for the front if i'm still struggling.
 
nice 1 relz! you will get everyone coming to you now when they get weaving problems lol!


............i wonder how mines gonna handle with this lot on the back? :)
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i was gonna camp out on the shop front with a scabby dog and a tip cup............them sherbert helmets aint cheap are they?
 
MT account said:
nice 1 relz! you will get everyone coming to you now when they get weaving problems lol!
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Truth be told, if I would have swapped the pair of tyres like people here recommended me, rather than being a cheap bastard and swapping only the front, I would have saved a lot of headache :-|

But then it wouldn't have been as much fun solving the problem :p
 
Got a reply from Tyre guy at MCN, see below, but as already said Bridgestone BT023 or T30's are not suitable for the MT09

Hi Steve,

here's what our tyre expet had to say....

It has always been the case that not all tyres suit all bikes and the bikes that tyres manufacturers can have problems with tend to be big touring machinery and naked bikes.

The only tyres that Bridgestone has approved on the MT-09 are the S20 and BT-016 Pro, but these are both sports tyres and not what you’re looking for. I cannot say why Bridgestone has not approved the use of sports-touring tyres on this bike; it could be that they haven’t tested them yet or that they have tested them and found they didn’t measure up to the performance standards required for approval on this particular bike.

However, the following sports-touring tyres have been approved by their manufacturers for fitment on your bike, so you can be assured that high-speed stability will be fine. In alphabetical order:
· Continental RoadAttack 2 EVO
· Metzeler Roadtec Z8 M
· Michelin Pilot Road 4
· Pirelli Angel GT


All the best

Bryn Phillips
Sales & Technical

Cambrian Tyres Ltd
 
No Issues
I've been running the T30 front and back for over 2K KM and no issues what so ever, I've had the PR3's before and at this stage would rate them about the same.
Lots of "feel" I know what the bike is doing, the OEM Dunlop was like bakealite.
Great wet weather grip very confidence inspiring, just started drying up here so have had the pegs down only a couple of times and no issues, holds a line great.

Weaving never had any at any silly speed over very bumpy and uneven surfaces with lots of tram lines.
Pressures are stock but will look to lowering them as per Marty's recommendations as I did that with the OEM, but just waiting for the ZX10R shock and front springs to be changed first so I get a baseline.
 
View attachment 1804

Just my thoughts on this issue.

If the adjusting block has been deformed by 2mm, then the left hand end of this axle is 1mm further back than it should be compared with the right.
1mm of axle misalignment is a lot by the time it reaches the front tyre.

If the wheels are not checked after each adjustment, handling problems and unwanted tyre wear will occur.....
 
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Kinjane said:
View attachment 1804

Just my thoughts on this issue.

If the adjusting block has been deformed by 2mm, then the left hand end of this axle is 1mm further back than it should be compared with the right.
1mm of axle misalignment is a lot by the time it reaches the front tyre.

If the wheels are not checked after each adjustment, handling problems and unwanted tyre wear will occur.....
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That's y I bought the Gilles titanium adjusters. Far better quality and no deformation
 
I went for a cheaper, somewhat untidy, yet functional option. The axle is wedged in place with shims leaving wheel alignment totally dependent on the adjusting bolts.
The flats of both left and right adjuster boltheads have been synchronised to maintain wheel alignment by the insertion of a front shim.
Perhaps one day I'll tidy it all up rendering the shims almost invisible :)

P1010681_zpsc1684af9.jpg
 
Works for me

I also had speed wobbles that started about 170Kph but now it's fixed.

There is a design concern with the chain adjuster which is parallax error as the swing arm mark sits 10mm above the adjusting block. If your not square with the marks then you can end up with a substantial error. Before I made my first adjustment using the vernier, I found that I had a 1.5mm difference between the two adjustment blocks

I now use a vernier calliper to accurately measure the distance between the machined locknut web and the adjusting block. I then firmly tighten the axel nut and recheck the adjusting block measurements on both sides, check chain tension again, then torque the axle nut using a torque wrench set at 150Nm to do the job correctly.

This seems to have fixed my problem, best of luck with yours.
 

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