Topic: Handling problems in windy conditions - Help!

[CB750F2]

 G/Day all. I need some advice. Recently I took my bike - 78 CB750 F2 - out on the highway with the intention of giving it a good run. I was in a 15-20 knot wind with the wind coming across from approx. 10 o’clock. and my speed was 50-55 mph. The rear end felt very unstable – “skirmish” maybe a better word. I felt so uncomfortable that after about 15mins I turned around and came home. It was not as bad on the way home with the wind slightly behind me but the problem was still there.
            I put the bike up on the center stand and checked everything – swing arm, axle play, wheel alignment, suspension, tyre pressures-28psi, chain tension, comstar spokes, wheel wobble – but found nothing that would cause instability. Today, I increased the tire pressures to 35psi - front and 40psi - rear and went for another ride. The performance was better but not much.
The tyre specs are:
Brand    KINGS TIRE
Model    KT-932-01    4P.R.
Rear     110/90 18 Tubeless  Tread 3 PLY Nylon              Sidewalls 3PLY Nylon         Speed Rating    67H
Front    100/90 19 Tubeless  Tread 3 PLY Nylon              Sidewalls 3PLY Bylon         Speed Rating    57H

            The Honda manual specs are:
Rear     4 x 18 4PR
Front     4 x 19 4PR
            Have any of you experienced this problem? Maybe it is normal. I haven’t ridden for many years and even then on much lighter bikes but I cannot remember having felt so uncomfortable in windy conditions. What does 4PR mean? Does it mean 4 Ply Radial? Or does it mean something else?
            Any suggestions would be most welcome. It may not be a tire problem. Thanks Pat
           

[KB02]

My first though would be the tire presure, but you said you increased it? What is the recomended presure setting on the sidewall of th tire? I have been told that it is best to go by that setting rather than anything else (the tire manufacturers must know what they are talking about with their tires). 28 psi is pretty low. increasing to 40 didn't help too much? How old are the tires?

[ofreen]

4PR means 4 Ply Rating.

The question about the age of the tires is a good one, because that effects the compliance of the tires.  Also, how much wear is on them?  Are they wearing evenly?  Has the profile of the rear tire worn flat?  Any cupping of the front?

Greg
'75 CB750F

[Dennis]

What is the recomended presure setting on the sidewall of th tire? I have been told that it is best to go by that setting rather than anything else (the tire manufacturers must know what they are talking about with their tires).

 

Read carefully the text on the sidewall of the tire. It usually specifies maximum pressure for maximum allowable load (of the tire - not the bike, which I would hope is significantly lower). It does not give a recommended operating range for your bike.

It is a common misunderstanding that you should (or that it is best to) run your tires at the pressure stated on the sidewall. This is not true.

[TwoTired]

No answers, but some thoughts.  Feel free to dismiss out of hand if you want.

Have the frame members above the valve cover been cut?

Are you certain the rear axle bearings are fully intact?  I had a 550 where the wheel would spin fine and tight on the center stand.  But, half the rollers were crushed and missing.  They'd space themselves out evenly on the centerstand, behaving nicely.  But, out on the road under pressure they would intermittantly bunch up to one side and change the axle and wheel alignment.  Thought I'd crapped my pants a few times there, the butt was so unstable.  But, no, it was the whole seat moving around. 

Did you check the headstock bearings for tight fit and smooth pivoting with and without weight on the front wheel?

What about front to rear wheel alignment.  Can you ride a flat road hands off bar and still go straight?

How long have you had the oversize tires on the bike?  Stock rims?

The stock front is supposed to be 3.25 inch = 82.55 millimeter.  You've got a 100 millimeter = 3.9370079 inch, a .6870079 inch increase.  Did the manufacturer say that tire would fit onto your rim width?

The 110 rear is only about .3307087 inch larger than the stock 4.00 so it's probably okay on the rim.

Because of the narrow rim, oversize tires usually need more air pressure than bike manufacturer's recommendation, in order to get adequate sidewall support.  This also crowns or arches the tread shape more pronouncedly as well as firming up the whole tire.  Straight up on the bike and it centers on the crown of front and rear tire.  But, leaning into the wind, rolls you onto the sides of the thread arch.  If the front tire arch is larger than the rear, the bike may hunt for the sweet spot where equilibrium balance and tread track line coincide.

Just a theory...

Cheers,

[CB750F2]

G/Day. Sorry for not replying sooner but I have been at work all day and so this is my first chance to get back to all of you.
KB02 - I ncreased the rear pressure to 40psi and the front to 32psi. The tyres were supplied to me new by the local Honda dealer early this year.
Greg - The tyres are almost new and have travelled approx. 2000Km. They appear to be wearing evenly.
Dennis - The pressure molded on the side walls are 32psi front and 40psi rear at maximum load.
Two Tired - The frame is intact. Actually that was one of the first things I checked.
                  Bearings front and rear are fine.
                  There is a small amount of play in the headstock which I will fix tomorrow
                  I rechecked the rear wheel alignment this morning and found that the axle was not quite square - now fixed.
                  I take your point about the size of the tires. I checked the tire manufacturer's web site and the "suggested" rim
                  width for both tires is 2.5". My rim sizes are 1.75" front and 2.15" rear.
I think that all that I can do is to finish making the adjustments mentioned and wait for another windy day.
Thanks for your help. Pat from Aust.

[BobbyR]

Pat, you did not mention if you had any fairings, windshields, or sissy bar on the Bike. I find side winds have a greater effect on my 750 than I remembered on other bikes. It may be I am older, wiser, and more concerned than I was in my Teens, when I was immortal.  I read somewhere on this site a Sissy bar can change the aerodynamics somewhat. Bobby in NY

[CB750F2]

Bobby, there are no windshields, fairings, or sissy bars attached to the bike. However, I am 6'4" and something and the clothing that I was wearing was fairly loose so that may have been a factor. Then again it felt as if the rear end was moving around. I will re-check everything and make the adjustments mention earlier. Thanks, Pat from Aust.

[Hop on a Honda]

Bamboo Frame Syndrome.
My old CB had a similar exciting problem it was like riding a bike drunk!
Eventually I found that the Xtube on the center stand was broken right next to the frame.This gave the whole meaning of riding through the twisties of New South Wales South Coast a very different meaning almost like a dirt bike in every corner.
Weird sounds too.

Hang it like a side of beef and start welding cautiously as that area rusts.
Problem fixed.

Dave Australia.

[CB750F2]

Dave. Thanks for that. I will go and have another look shortly. This bike has been recently restored and I didn't notice any frame damage when I was preparing it for painting. My problem seems similar to the trouble that you had so I will certainly look closely. Thanks, Pat from Aust.

[Quail "Owner of the comfortable k8"]

one light jacket I wear at times billows out and makes anything over 60 life threating.

[CB750F2]

G/Day All. During the last couple of days I have checked over the frame to ensure that there is nothing broken, adjusted tire pressures to 35psi rear 30psi front, removed "play" from head stock bearings, and adjusted wheel alignment. Yesterday I went for a ride. The bike handled OK. There was some side wind effect but not as bad as it was during my previous ride. I guess I wiil just have to wait and see. I accept that windy conditions will adversely affect handling but not to the extent that it did last week. I will invest in some suitable clothing for riding - the jacket that I currently use may be acting like a "sail" as Quail has pointed out. Thanks everyone for all your help. Pat from Aust.

[Hop on a Honda]

Pat.
Where on earth besides Tasmania is it so windy?
Dave
Newcastle Australia.

[GeoffT]

Pat.
Where on earth besides Tasmania is it so windy?
Dave
Newcastle Australia.

Try anywhere near the North Atlantic. We got 35 gusting 50 just now and 45 gusting 65 for thies evening.
Just a slight breeze. 

[Bob Wessner]

I'll bet it's nice 'dry' wind though, right? 

[GeoffT]

Oh yeah very dry - inside the water/wind proofs!! 

[BobbyR]

Pat, after reading all you have written I would say in the wind speeds you are describing, you will get blown around. When we have winds over 30MPH they ban Bikes from bridges. You kind of get used to being banged around. When I see a large Dump Truck coming the other way, I duck down as close to the bars as I can.

[Buffo]

I to have a parka windbraker that is life threatening at 65mph+.

Just a thought...When I first put my rear wheel on I did not have the correct spacers and the castleated (?) nut "bottomed out" on the lip of the drive shaft. In my case it was just tight enough to hold the wheel in place while tring to move it by hand  but when you were moving the wheel would slide around a bit...The axle nut was...seemed tight as hell, and it was, but it was only tightened to the lip of the axle and just by chance it was slightly tight, but not tight enough on the swing arm.

[CB750F2]

Dave, I live in Ayr Nth Qld. I was travelling to Bowen through open country. the wind was 15 - 20 knots from the South East and "gusty". I lived in Newcastle for four years in the sixties and seventies and found the winters cold. I used to ride a motorcycle from Mayfield to Williamtown. It took me about 15mins to get dressed and I was almost frozen stiff when I got to work. At times it was "scary" riding across the crest of the bridge across the Hunter River and a big truck passed coming the opposite way. Pat,Aust.

[Hop on a Honda]

 ::)Hi Pat
I take it you were in the Willimtown version of the RAAF?
I know winters are too cold butt in my stupid 55th year I met a lovely lady in Nowra, NSW South coast & my body has never been the same Now that was a trip and a half  in any weather through Wollongong Kiama Berry Summer OK winter madness I nearly came to grief on the Kiama bends Day dreaming. It can get very cold there especially if the S/Westers are blowing their usuall 50 knots after Kiama.Really Chill factor.
It's amazing how much clothing and the Telegraph you can wear
Best I ever did was 3hours 40 minutes one day, Re fueled at Albion Park 320 Ks. Empty!
Imagine the trip to Canberra.
Cheers
Dave