ST1300 Aerodynamics

I bought a 2008 ST1300 several months ago from a friend. I loved the bike immediately except for one thing - it tended to yaw back and forth at highway speeds. Since it had 54,000 miles on it, I decided to rebuild the front end and see if that had any effect - RaceTech to get the springs right, lower viscosity oil to cure the overdamping plus new seals, bushings etc. Also replaced the head steering bearings with AllBalls.
Now the front end felt better, but still yawing around on the highway.
Felt like an aerodynamics problem - bike came fitted with a great big oversized windshield that creates a huge pressure differential in front of the rider - in other words, it tends to push you forward.

So, I decided to take off the (huge) Honda top box. Bingo - stable as a rock, even at 100+ mph. Evidently, the top box was acting like a wing over the back wheel!

I ordered a new windshield from Cee Baileys - the sport version. I may update this posting after I try it out.

hughanglin said:

So, I decided to take off the (huge) Honda top box. Bingo - stable as a rock, even at 100+ mph. Evidently, the top box was acting like a wing over the back wheel!

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My ST1100 acts like that too. If I pile stuff on the back for a long trip I get the same weaving you got, but its not generally noticable until 85+ MPH or so. That makes it more of a minor annoyance than a problem, and also actively encourages me to slow down and avoid getting a ticket, so its probably more of a 'feature' than anything else. When I get home and take the stuff off, the weaving goes away. Years ago a few other people on the old ST list said they had the same issue, but then others did not, so it remained a mystery as to what was different between the bikes that experienced it and the ones that did not.

For the ST1300, taking the top-box off OR putting a pillion on the back which fills the gap between rider and top-box both seem to help high-speed stability.

Try increasing your rear suspension preload, many folks find their stability issues are gone after this.

Same problem with the top box. Surprisingly the stock shield and top box is worse than the clearview medium which gives minimal turbulence. If someone is on the back it goes away or even if I have a bag on the rear set it lessens. I think the wind is closing around the rider and hitting just right on the top box to give this effect.

JasonFJ said:

Try increasing your rear suspension preload, many folks find their stability issues are gone after this.

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Ditto your findings. I also replaced the rear suspension hydraulic fluid per excellent directions of Larry "Igofar" and it made a more pleasant ride and a bit more stable. Be careful of what you want to achieve; I think the moderate width of the rear tire and the ST1300 crankshaft in line with the road all help to make the bike easy to corner. My Bandit 1200 with a wider tire and crankshaft perpendicular to the road made that bike more difficult to corner than the ST, even tho the Bandit weighed 100 lbs less.

Is this the same thing as a gemeral feeling of twitchyness that I get. I wound the bike up to 220km/h (130+) mph last week on the autobahn and the bike was feelng very lively so much so that i had to back off the throttle. The set up was a heavy solo rider with empty panniers and a lightly loaded honda top box. Tyre pressures were normal.

rich32257 said:

Is this the same thing as a gemeral feeling of twitchyness that I get. I wound the bike up to 220km/h (130+) mph last week on the autobahn and the bike was feelng very lively so much so that i had to back off the throttle. The set up was a heavy solo rider with empty panniers and a lightly loaded honda top box. Tyre pressures were normal.

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Then you should consider yourself fortunate as the top box max recommended speed is 130 km/h and anything above that is not going to be favourable.....

Instability at that speed can develop so fast that it is non-recoverable....

The UK Police officer killed on a ST1300 was doing 110mph, he didn't have a top box, but the other bits on a Police spec bike have as dramatic effect on stability as a top box, if anything the topbox is worse..... in this instance it was possibly only the riders weight that kept it within the boundary of vertical....

Just saying.....

My ST1300 also becomes uneasy at around 80 MPH, actual not indicated, with the Givi 46 liter box. I try to keep it under 80 with the box on and definitely keep it under 90 with the box. It is more stable without the box at faster speeds.
Ron

Firstpeke said:

Then you should consider yourself fortunate as the top box max recommended speed is 130 km/h and anything above that is not going to be favourable.....

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Wow! I guess I am lucky every day I come to work.

Where do you find this 130 km/h recomendation?

Firstpeke said:

The UK Police officer killed on a ST1300 was doing 110mph, he didn't have a top box, but the other bits on a Police spec bike have as dramatic effect on stability as a top box, if anything the topbox is worse.....

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Not wanting to hi-jack the thread but we had a police spec 1300 with the "weave" and we removed all the police equipment including rear pod, pole mounted light front strobes and it still weaved. The bike was returned to Honda and broken up, a Honda engineer who we worked with had a theory which was plausable and he mentioned rogue bikes where frame tolerences were not as exact as they should be hence some weaved, some didnt so Honda know what the issues were but instead of being honest and up-front have decided to keep it secret.

I had heard that too Brian..... certain bikes were inherently unstable even before the kit was fitted...

Honda had also made some torque increases on swing arm nuts and stuff but never cured it.....

As to the 130km/h, there is usually a label in the topbox, or a paragraph in the handbook about it.....

Certainly in my Honda topbox from my 650 Deauville had it....

The quickest fix for the onset of weave on a bike used to be putting your chin on the tank, but when there's a windscreen and a topbox I'm not sure the issue is the same....

My ST1100 was always rock solid, right up to (cough) autobahn speeds....... but never did that with a topbox on......

The 1300 has had various reports of instability, this perhaps due to the differences in design to make it handle quicker than the 1100....

I do know of an "unreported" incident when a Traffic Police Inspector in another English force thought he could prove the bikes were fine for high speed... did a test on a runway somewhere in England and promptly thew it down the road, so to speak....... survived, but was somewhat injured..... I believe the bikes were withdrawn not long after that....

West Midlands cut a vee in the right hand side frame and sold them off for scrap/parts.... only for some rather clever ally welders to get artistic and repair them.....

I always found the Police spec 1300 bikes a bit fidgety compared to the 1100 anyway.....

As an aside, there was some interesting airflow dynamics on the Guy Martin "Speed" programme the other week when he broke the cycle pursuit land speed record.....

The vortices around the back of the truck were fluctuating with a couple of bits that floated around away from the near and offside rear.....

I could not begin to imagine riding a pedal cycle at 112mph a few feet behind a truck, on sand.......

Firstpeke said:

As an aside, there was some interesting airflow dynamics on the Guy Martin "Speed" programme the other week when he broke the cycle pursuit land speed record.....

The vortices around the back of the truck were fluctuating with a couple of bits that floated around away from the near and offside rear.....

I could not begin to imagine riding a pedal cycle at 112mph a few feet behind a truck, on sand.......

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Saw it and I was amazed, it has been a been a fantastic series..

It's confusing for us Yanks.....the Honda accessory top box was never sold in the USA so we were never warned to stay under 80 mph / 130 kph with it installed. Any other accessory top box was not approved by Honda so they don't have to warn us about any placards or operating restrictions with one.

I think it does say in US market owner's manuals not to exceed 80 mph with the panniers loaded.

I will say that many times on a closed course and away from influences of traffic turbulence I have experienced the Pan Weave with my bike and at least with my bike the instability comes on slowly and increases in frequency and amplitude only with additional speed. The onset was typically 115 mph to 130 mph. No top box, OEM wind shield fully down. I believe wind speed/direction and bike load configuration is responsible for the onset with a bike predisposed to exhibit the weave. My results closely approximate those found by a UK motorcycle magazine that data logged an ST1300 then went to a track venue and documented the weave. Rider perhaps, maybe in 2008. The article can be found now and then on the internet before copyright issues remove the link. I had a copy of the magazine and kick myself for losing it.

If you feel the weave begin and stop at that speed of onset the weave is stable and does not increase unless you speed up and then it gets worse with additional speed. I could never accelerate out of the weave, it only gets worse with additional speed and always lessens and disappears by slowing below the speed of onset. The bike does not accelerate fast enough over 115 mph to get into the weave without feeling it begin and deal with it by slowing or stopping the rate of acceleration. At least with my example the weave does not suddenly appear without warning like a wobble from undamped fork movements may do so. (A tank slapper) A wobble is not a weave and these bikes weave. During some exploratory riding I determined with my particular ST1300 that you can ride hands off in the weave to see if unintended control inputs were the cause of the weave or unintended control inputs aggravate the frequency or amplitude and in my case they did not. The bike sustained the weave independently of any rider input and more or less speed affects frequency and amplitude just as if the rider was holding the bars. At 96,000 miles I replaced the original caged ball head bearings with tapered roller bearings and paid close attention to setting the preload to Honda specs. The OEM bearings under inspection had tiny dimples hammered into the races that were not noticeable with the fork and wheel installed but without the mass of these the bars would self-center in the dimples. After that job my bike was much less susceptible to the onset of weave at all or else moved the onset to a higher speed when it does occur. It's very rare now.

nice read about the weave i had a 1999 ST1100 and if you were on the high way around a tractor and trailor you could not ride the thing it felt like the rear tire was in oil you could take the side bags off of the thing and it was rock solid my solution i traded for a 1999 valkyrie i now have a 2007 St1300 with top box and the only time i feel the weave is around the trucks other then that it is fine love the bike and now honda has no replacement for it that will do what this bike does well for all situtations.

I only experience the weave in the air turbulence behind larger vehicles with or without a top box. Dualie pickups have sometimes caused it. I have a Givi top box which isn't as high as the Honda model. I don't experience the weave with the Givi unless there is turbulent air. I have experience this with high wind gusts from head on with and without a top box. I chalk all this up to the tupperware.

All motorcycle front wheels weave very slightly, barely perceptible. So wind turbulence would increase it especially with all the air we push due to the tupperware. Worn out bearings can cause greater issues with the weave. I can see where a frame issue could cause the weave to exaggerate.

Always wondered if the Honda Fairing Extender wingy things were an unofficial factory solution to the aerodynamic "weave" issue, rather than just a rider comfort accessory as advertised...

I agree with others that it is an aerodynamic issue that is greatly affected by the type of screen and top box. I have a Cee Bailey +2+2 vented screen and a CooCase top box, and have only felt the weave a handful of times, never in clean air or at high speed, but for me, it shows up when I'm in the crosswind slipstream of big trucks on the freeway.

Have been meaning to buy Honda aerodynamics package and see if it makes a difference, with the added bonus of (hopefully) keeping more heat away from the cockpit.

hughanglin said:

So, I decided to take off the (huge) Honda top box. Bingo - stable as a rock, even at 100+ mph.

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Solo with top-box plus improper settings of the rear suspension are probably the core of most cases...
Many riders in Germany state to have cured the issue by the installation of a properly matched & adjusted Wilbers rear shock...
There is also a faithful group who swears on a mystical set of hyper-precise, German made (of course...) swing-arm bearings as their ultimate salvation...

However, compared to the 'stoic' ST1100, the 1300 is designed a bit borderline... the 'consumers' screamed for a more agile motorcycle, so the D&D bowed to that demand... (when I was questioned by the Japanese envoy I insisted on heated rear-views as OEM equipment on the next Pan-European, which unfortunately echoed out unheard...)
The 1300 front end is shorter, angled steeper, thus in total a bit more on the nervous side...
Spreading with MFG-ing tolerances, most bikes can be found fully stable, whilst a few tend to slightly wiggle at speeds, some a bit more and if ignored/pushed further possibly up to the levels of tank-slapping...

However, we're talking about pure high speed issues, occurring above 100mph, which is why mostly German based and/or squad bikes where found 'effected' (and any US based rider ends up serving jail-time for 'attempting'... ;-) )
Them German riders knew about the issue and still insisted on taking the mount up to 240kph/150mph, solo with top-case installed, ignoring proper rear shock adjustments... simply over stubbornly claiming that they had paid for a high speed touring motorcycle, thus it has to perform at its top speed... basta...
Sorry, but already in riding school you're advised that its not a good plan to push a bike to its limits while having accessories like a top-case on it... and that huge Givi-thing for the ST1300 is as 'streamlined' as the Hall of Congress or the Buckingham Palace... the little ripples they'd glued to the sides just won't overcome basic physics, nor will that 'spoiler brake-light'...
So I wonder how all those 'Klingons' dealt with the era where Windjammer fairings got bolted to old beemers with ridiculously flexing frames/suspension...

Honda made recall works over here, replacing head bearings, inspecting/cleaning their seats in the frame, loosing and sequentially re-torquering engine mounts, adding stabilising plates to the frame, replacing swing-arm bearings, axle and locking nut, and replacing the crash bar covers with some that have vents added, to prevent congestions inside the fairing... they'd further added some foam seals toward the seat to deal with the heat issue and re-painted the rear sub-frame as some (Germans) claimed that there is rust (which is never was, only stains from the welding process...)...

120-140mph blasts on I-40 between Nashville and Knoxville regularly with topbox NO PILLION on PR3's....Always glass smooth.


Dump the Bridgestones for a real tire and SET the rear pre-load dont just crank it up and hope for the best.

Coucours Grad said:

Dump the Bridgestones for a real tire and SET the rear pre-load dont just crank it up and hope for the best.

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What tires are you running? Also, what do you mean by "SET the rear preload"? I would try increasing the preload 2 clicks at a time and see if that improved the ride. What do you recommend?

Scott