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 Motorcycle Safety
 Technical/Maintenance
 Steering Issue - '93-'03 Honda CB750's
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Jim B
Male Senior Member
491 Posts


Newark, Delaware
USA

Honda

CMX250 & CB750

Posted - 12/27/2008 :  10:28 PM                       Like
I have one annoying issue with my '95 Nighthawk.

At parking lot speeds, when I turn in either direction, the bike 'wants' to oversteer or forces the front wheel to turn more in the direction I want to go. This causes me to push very hard on the inside handlebar to keep the wheel from turning any more. Now, it only happens at very low speeds (<5MPH).

I've asked a few other NH owners, only one claims to have a similar problem, but did not follow up on the issue. I've wondered if it is because I am not used to the bike after only 500 miles of riding, whereas these other owners have had theirs for some time. Even my previous V-Strom did not have this issue.

The bike does not have this 'oversteer' tendency at normal road speeds.

I have checked the following on both the front and rear:
Tire condition
Tire pressure
Fork/shock condition

All are within specs.

I've been on a few other bikes and did not have this issue.

What I would like to know is:

Is this inherent to the CB750's design?
Is this caused by the design of the tires I have?
Can the fork oil/spring rate cause this?

I studied the front wheel's setup. Everything appears to be fine, and even when on the centerstand, the front wheel does not 'fall' to either side. When parked on the side stand, the front wheel will stay in any position I choose.

Also, while pushing the bike around the driveway, the front wheel does not seem to 'fight' my inputs. It all happens only when the bike is moving forward while making turns at slow speeds.

The tires on my bike are OEM design Dunlop K505's.

Thanks for any help.....

scottrnelson
Advanced Member
6937 Posts
[Mentor]


Meridian, ID
USA

Honda

XR650L, 790 Adv R

Posted - 12/28/2008 :  9:47 AM
A lot of motorcycles feel that way at low speeds. My ST2 Ducati has done that, depending on what front tire I have on it and how worn it is. When I have a worn front that is more triangulated (due to wear on the sides), it is more likely to fall into turns at low speeds.

The last Harley that I rode had a strong tendency to fall into turns at low speeds.

I would say just get used to it. You'll notice it less as you put more miles on the bike and do more low-speed practice on it.

You can help a bit by choosing a front tire with a flatter profile rather than a more pointy shape. Some tread patterns will also make a difference, but I can't help you select one for your bike, sorry.

You could also experiment with tire pressures and see if the behavior changes at 30 pounds, 35, and 40. I would expect lower pressure to tend to be better, but I could be wrong. Maybe you could try that out and report back. Keep notes on what you experience at the different pressures.
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James R. Davis
Male Administrator
17361 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 12/28/2008 :  10:13 AM Follow poster on Twitter  Join poster on Facebook as Friend  
All of what Scott said is true. Wider front tires steer more 'slowly'.

quote:
It all happens only when the bike is moving forward while making turns at slow speeds.

You need to visualize your front-end geometry to 'get this'. The greater the bike's trail, the greater will be the tendency for the bike to behave as you described.



When you turn the handlebars in either direction you are NOT turning the front tire using its contact patch (B) as the pivot point. Instead, you are attempting to slide that contact point laterally to one side or the other (from B1 to B2, for example) using the actual pivot point (C) which is directly in front of the contact patch and pointed to by your steering stem. When the bike is moving quickly it is quite easy to laterally slide the contact patch to do this. At very low speeds it is practically impossible.

Once you 'get this', you may well experience a Eureka moment as you then will understand one reason why a motorcycle will lean toward the INSIDE of a slow speed turn instead of to the outside as is the case while counter-steering. At slow speeds, if you turn to the left, for example, the contact patch tries to stay in place and point C (having no resistance) is pulled to the left ALONG WITH THE FRONT-END OF THE BIKE, where gravity is dominant over centrifugal force, and the bike leans/falls to the left (the inside of the turn).
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rioguy
Ex-Member

Posted - 12/28/2008 :  5:44 PM
quote:
James said:
Once you 'get this', you may well experience a Eureka moment as you then will understand one reason why a motorcycle will lean toward the INSIDE of a slow speed turn instead of to the outside as is the case while counter-steering. At slow speeds, if you turn to the left, for example, the contact patch tries to stay in place and point C (having no resistance) is pulled to the left ALONG WITH THE FRONT-END OF THE BIKE, where gravity is dominant over centrifugal force, and the bike leans/falls to the left (the inside of the turn).


James, you might want to move this to the physics thread.

About the time you were making this post, we were coincidentally in the parking lot trying to demonstrate your point and made a video.

I asked three riders to ride down the center line of a row of parking spaces and make U turns without telling them what I was looking for. The first U turns are a little too fast, and probably at counter-steering speeds. However, starting about 2:30 into the video they started slowing down to what we would consider steering speeds. Especially watch the rider making tight U turns. 6 minutes or so into the video is a real slow entry which definitely shows out track as do all the U turns.

All the riders turned opposite the U turn before steering into the U turn. It's only a matter of 2 or 3 inches, but it's clearly visible.

In my opinion, it helps to steer away from the turn very briefly (not a dip, but a matter of a couple inches) which will get the bike started to lean into the turn and then steer into the turn.

Here is the video:

http://www.youtube.com/watch?v=t6xo...channel_page
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(Deleted or Lost)

Posted - 12/28/2008 :  8:38 PM
Very interesting video.
I did notice, that all the riders, but especially the one with high and wide bars were, 'counter leaning' in the U-turns. WHich I found interesting in itself. Could you comment on the level of experience/training of the riders?
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rioguy
Ex-Member

Posted - 12/28/2008 :  9:04 PM
quote:
Originally posted by The Meromorph

Very interesting video.
I did notice, that all the riders, but especially the one with high and wide bars were, 'counter leaning' in the U-turns. WHich I found interesting in itself. Could you comment on the level of experience/training of the riders?



The first rider has been riding about 2 years. The one with the high and wide bars is Niebor who has been riding a long time. The one making the tight turns is obviously very skilled. We just happened to meet him at the gas station on the way out and he asked if he could join us.

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(Deleted or Lost)

Posted - 12/29/2008 :  10:51 AM
Jeez, I wish I could join you on these sessions...
I've never had the opportunity to watch other riders practising, without being too involved in my own training to pay much attention to them. Your videos are as close As I'm going to get, so thank you, but I'd love to be able to discuss and critique their and my own techniques live.
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Niebor
Ex-Member

Posted - 12/29/2008 :  10:53 AM
I'm guessing the "high and wide" referred to the Triumph. A 2300cc brute with amazing agility. I'm on the Dyna, black helmet, little-bitty running lights up front. I admit, I'm known to counter-lean a bit, seeking a cozy balance in a given turn. I'll let the bike lean, then follow, stay with it, or counter-lean it. Whatever feels right for the situation. Old habits? Perhaps, but they work for me.

The rider on the Triumph (Rocket III) was also inclined to leave his clutch fully released in the exercises, modulating speed strictly with his rear brake. The distinct smell of roasting brakes led me to encourage him to learn to work his clutch a bit. That monster has incredable torque at low engine speeds.
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Jim B
Male Senior Member
491 Posts


Newark, Delaware
USA

Honda

CMX250 & CB750

Posted - 12/29/2008 :  11:11 AM
Scott wrote:

quote:
I would say just get used to it. You'll notice it less as you put more miles on the bike and do more low-speed practice on it.

You can help a bit by choosing a front tire with a flatter profile rather than a more pointy shape. Some tread patterns will also make a difference, but I can't help you select one for your bike, sorry.


I will need to get new tires pretty soon, as mine are showing signs of dry rot. I did get used to the steering somewhat, but was wondering if anything else was causing it. Thanks for the advice.

James wrote:

quote:
Once you 'get this', you may well experience a Eureka moment as you then will understand one reason why a motorcycle will lean toward the INSIDE of a slow speed turn instead of to the outside as is the case while counter-steering. At slow speeds, if you turn to the left, for example, the contact patch tries to stay in place and point C (having no resistance) is pulled to the left ALONG WITH THE FRONT-END OF THE BIKE, where gravity is dominant over centrifugal force, and the bike leans/falls to the left (the inside of the turn).


It makes sense. The diagram helped me understand better. Guess I will have to get used to it. One of these days that 'Eureka Moment' will happen.... Thanks for the write up.


Rioguy wrote:

quote:
I asked three riders to ride down the center line of a row of parking spaces and make U turns without telling them what I was looking for. The first U turns are a little too fast, and probably at counter-steering speeds. However, starting about 2:30 into the video they started slowing down to what we would consider steering speeds. Especially watch the rider making tight U turns. 6 minutes or so into the video is a real slow entry which definitely shows out track as do all the U turns.


Interesting video....thanks. One question, though...the rider at 2:30-3:30 made a very sharp left turn WITHOUT turning his head, and seemed to briefly struggle getting out of the turn....did he do that on purpose? I am surprised he did not fall.
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(Deleted or Lost)

Posted - 12/29/2008 :  4:46 PM
quote:
Originally posted by Niebor

I'm guessing the "high and wide" referred to the Triumph. A 2300cc brute with amazing agility. I'm on the Dyna, black helmet, little-bitty running lights up front. I admit, I'm known to counter-lean a bit, seeking a cozy balance in a given turn. I'll let the bike lean, then follow, stay with it, or counter-lean it. Whatever feels right for the situation. Old habits? Perhaps, but they work for me.


We had a previous discussion of 'counter leaning' on another thread. As I recall, James doesn't favor the technique, and correctly insists that it is never necessary. I use it myself on tight U-turns, it having been suggested to me for use on a 'big' bike in my own first advanced training many years ago in England. Personally, I think it is most useful on larger bikes with rounder section tires. I also suspect that I and others favor it in certain circumstances for psychological (confidence) reasons. There may, or may not, be good physics to support that opinion I certainly don't argue with James's assertion that it is never necessary...
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