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Opto
| | Posted on Monday, December 15, 2003 - 01:57 am: | 
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The 3 roadbikes I owned before the XB12 all handled different with different tyres - once I found some tyres that were good, I stuck to them. I agree with Tripper, that tyres can make a huge difference, and I know that no amount of sag changes is going to stop my XB standing up going into a corner.
Until I change the tyres. |
Rocketman
| | Posted on Monday, December 15, 2003 - 05:06 am: |
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I don't know but reading this thread I'd say it's apparent no amount of different manufacturers tyre is going to make the occurrence go away, might improve the circumstance somewhat, but it's a feature related to the design and geometry there in of the XB's surely.
All that's going on cannot be tyre related - just enhanced or otherwise by them.
Rocket  |
Boulderbiker
| | Posted on Monday, December 15, 2003 - 07:28 am: |
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If you think about the force you put on the bars to make a bike stand up, then think about the force thats being put on the front tire under hard braking in the middle of a turn, THEN on top of that keep in mind that these tires are REALLY lightweight, it would make sense that since the other tires in the test eliminated this characteristic that the tires are probably distorting in some fashion that twists the forks and thereby raises the bike up out of the corner. I'd have to agree with the conclusions of the article. Makes sense. If it was the geometry there'd probably be a lot of 250cc 2 stroke race bikes out there with the same problem. Besides, all the magazine testers that took the time to fiddle with sag and fork height in the triples as we as other adjustments never did get that characteristic to disappear 1/10th as much as in the article where they just put a different tire on the bike. |
Austinrider
| | Posted on Monday, December 15, 2003 - 09:00 am: |
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Okay, maybe I will show my ignorance by asking this question but...
Why would you want to break hard witht he front tire when you are in a turn (read: leaned over, ass half off the seat, looking thru the turn etc).
Physics would dictate that the bike will stand up if you do it hard enough. At the track days I go to they make a very big point of telling you NOT to break (especially hard) while you are leaned over in a turn - its a good way to high side.
Just curious, thanks... |
Wyckedflesh
| | Posted on Monday, December 15, 2003 - 11:06 am: |
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Because sometimes you just have to change your line midcorner cause the situation changed. |
Boulderbiker
| | Posted on Monday, December 15, 2003 - 12:08 pm: |
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I.E. something lying across your lane that would not be advisable to run over or into. As far as the track, from the ones that I think know best in the instruction relm, you DONT want to brake hard in a corner, in fact not at all, is the take of some (Keith Code). |
Imonabuss
| | Posted on Monday, December 15, 2003 - 09:12 pm: |
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Oh Rocket, give it a rest. Yes it is the tires, but with the stock tires the effect is not dramatic and is easily ridden around. BTW, you should have watched Mike Cicotto beat the factory backed 748 in in the final Pro Thunder at Laguna Seca two years ago on an XB...he did it all with handling...the 748 definitely had motor on him. And the 748 is a 996, not a bad handling bike.
If you read Keith McCarty's comments on being beaten, all he could say was "Man, that Buell handles well." The factory Ducati World Superbike team guys were there, and they came over to the team from Hal's and congratulated them, telling them what a great motorcycle the XB was. Too bad folks with small minds and small riding talent can't be so gracious. But then, they wouldn't be wankers then would they? |
Rocketman
| | Posted on Monday, December 15, 2003 - 10:48 pm: |
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As clever as you may be NO fucking tyre in the world is single handedly gonna make a bike stand up in a corner.
I might be a wanker but tell me I'm a liar.
Rocket
edited by blake on December 21, 2003
edited by Rocket on December 24, 2003
edited by rocketman on December 23, 2003 |
Opto
| | Posted on Tuesday, December 16, 2003 - 03:15 am: |
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I'm getting a new front tyre next Sat as an experiment. Will report back in 1 week after doing approx 300 miles weather permitting. No more theory for me.
Before everyone jumps on my back, yes, I may need 2 tyres, but I'm gonna start with 1.
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Kevinfromwebb
| | Posted on Wednesday, December 17, 2003 - 12:21 am: |
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What kind of tire you getting Opto ???
Kevin |
Opto
| | Posted on Wednesday, December 17, 2003 - 01:38 am: |
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Bridgestone BT 012. |
Kevinfromwebb
| | Posted on Friday, December 19, 2003 - 10:39 pm: |
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Okay, so SportRider says 25 to 35mm sag??? Is that right??? What have yall had the best results with...
Kevin |
Unibear12r
| | Posted on Saturday, December 20, 2003 - 03:34 am: |
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Has anybody else used two different brand tires on an XB? I wouldnt do it. I had two different models of the same brand on a bike (Kawasaki) once and I think that helped put me into The Mother Of All 110mph high speed wobbles. Id change both at the same time. |
M1combat
| | Posted on Saturday, December 20, 2003 - 04:34 am: |
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I haven't tried braking hard in a corner. This happens with just a little brake and it's fairly subtle. I think the tire deformation theory could do it... |
Unibear12r
| | Posted on Saturday, December 20, 2003 - 05:27 am: |
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Opto got me to think on what forces are at work on a motorcycle in a curve. The major force that would tend to straighten up a bike would be its own inertia trying to keep it going straight. This is countered by forces generated in the lean and working through the tires to the road. Should the spot where the tire meets the road suddenly move these forces are no longer balanced and the lean angle has to change to regain balance... The center of mass of the bike and rider moves forward and down (rapidly/forcefuly) towards the front wheel during brakeing. This forces the front tire down and the rear up. This is why the front brake works better. This also causes the front tire to take a lot of stress... and distort. This could also be the reason why the XBR does not stand up as much as the XBS. On the S the rider is farther up and back and he represents much of the combined mass. Therfore the movement of the center of mass is that much more forceful...Distorting the tire even more. On older bikes like my Sportster1200S the forks, frame, swingarm etc would be flexing about now, and that flex would be takeing some of the stress off the tires. Handleing is less precise but less trying to stand up.... The XBs dont flex much at all....and have a lightweight tire.
It strikes me that a super strong frame needs a super strong tire
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Rocketman
| | Posted on Saturday, December 20, 2003 - 12:01 pm: |
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I've NEVER in all my years read a tyre performance test that mentions in the slightest a tyres tendency to make a motorcycle stand up - that theory is bollocks. Brake any motorcycle into a corner and there's always gonna be a tendency for the bike to 'stand-up' - how much depends on several factors - the geometry of said motorcycle and human input the two most influencing. Any bearing toward tyre performance characteristics playing a part in 'stand-up' I doubt very much probably impossible. The only exception where tyres are concerned in 'stand-up' being the shape of the profile which is obviously a different issue and a point of choice manufactured to suit certain user circumstances. It doesn't take an engineer to work that out.
Rocket |
Marcus_mcbain
| | Posted on Saturday, December 20, 2003 - 01:09 pm: |
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Mid corner "stand-up" is not uncommon in the racing/track day environment. Anyone who is riding agressively will trail brake late into a turn. I have raced twins and in-line fours from 250cc through GSXR-1000.
With all that said, there are several reasons for the "stand up" and some can be totally isolated to seperate causes. Here is what I have experienced in 16 years of road racing.
1) Geometry - A bike that has too much bias in either direction will cause a see-saw effect. What compounds this on the Buells especially is that there is no stock ride hieght adjustment for the shock while many riders drop springs, etc. into the forks. This usually leaves a soft low hanging rear with a high stiff front (Relative to the rear) under load.
2) Tire Profile - If you are using a profile that is different from stock this could be causing the issue. A 120/90 will have a much "Flatter" profile than a 120/60. Of course, each tire manufacturer also has their own "actual" size for tires with the same stamped profile.
3) Engine - On a big twin, high RPM's only enhance the "gyroscope" effect of the motor. Many riders instinctive use the engine as a brake not only because it is easy, but because we can feel the motor keeping the bike stable. This really is punctuated on the twins and that alone can make the bike stand up.
Personal Experience - My TLR-1000 I raced was bad about "standing up". What was really happening was the motor was dramatically falling in R's when the throttle was shut off. This consequently loaded up the front tire. The solution was to raise the idle to 2000-2500 RPM and this made the bike handle very neutral in turns while helping me actually maintain corner speed.
Good Luck,
Marcus |
Fbolt
| | Posted on Saturday, December 20, 2003 - 03:02 pm: |
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I have not noticed my 9r standing up in turns. I rarely brake in turns, but if I do, its just a tap or two on the rear. I've done this both on the road and the track. One thing that helped me improve handling was going to more aggressive suspension setups. That made a significant difference! |
Blake
| | Posted on Saturday, December 20, 2003 - 04:03 pm: |
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Way cool of you to stop by and share some of your big hairy suspension knowledge with us. For those who don't know Marcus, he is a seriously fast man on a motorcycle. He is fast becoming one of the premiere support/setup and training experts for motorcycle road racers in the TX/OK/AR/LA/CO area.
I hope to make it to OHR over the holidays. I'm off all next week. Just gotta transform the bike back into track mode and get a new muffler installed. Hope to see you there sometime soon. |
Bigsherm9r
| | Posted on Saturday, December 20, 2003 - 05:29 pm: |
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When I was in U.S. Army helicopter flight school, and a student would complain about it being hard to control the helicopter at a hover, the instructor would say something like "Who's in charge- you or the helicopter? Stop being such a little bitch and make it go where you want it to."
So what if it wants to stand up under braking? Make it go where you want. |
Marcus_mcbain
| | Posted on Saturday, December 20, 2003 - 06:42 pm: |
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Thanks Blake,
I got busy over the last few weeks and wasn't able to start visiting this board. I would like to work with you and Mark over the next few weeks and work on those Buells at OHR.
Marcus |
Needforspeed2
| | Posted on Saturday, December 20, 2003 - 06:58 pm: |
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Great to see you here, Marcus |
Unibear12r
| | Posted on Saturday, December 20, 2003 - 08:34 pm: |
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Thank you for not totally roasting me alive. I was really expecting it. I know that I was very very simplistic when I jumped into the conversation but I figured I would get somebody to post more in depth details about why standing up occurs besides just what different causes there could be to this. Even though I was going to get cut deep for my lack of expertise.
The bloods not too deep.....yet
Thank You |
Opto
| | Posted on Monday, December 22, 2003 - 03:48 pm: |
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Thanks everyone for their input. My concern with the standing up issue was only when using the front brake, not engine braking or rear wheel braking (just to clarify).
On one ride a got a good scare when I had to emergency brake just after entering the corner, I used a fair bit of front brake and the bike stood up straight real quick so I kept going straight ahead with full brakes and stopped before I ran out of road, luckily I wasn't going too fast and it was a very tight corner.
I changed the stock front tyre for a Bridgestone, coming back yesterday through some tight smooth winding roads I tested the new tyre for "standing up" and found only a slight "normal" tendency to do this. The steering feels more neutral when leaned over in the corner also.
These are just one rider's impressions, but I do feel a lot more comfortable with the bike and am a lot happier. Keep in mind this is my first Buell (XB12S) and that I'm still learning to ride it! Feels like a motocross bike in the really tight stuff, just point and squirt, then brake like hell for the next corner! |
Opto
| | Posted on Monday, December 22, 2003 - 03:58 pm: |
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PS thanks Marcus, your point #2 - is it possible that Buell have simply made a less than optimum choice for their "stock" tyres? |
Boulderbiker
| | Posted on Monday, December 22, 2003 - 04:43 pm: |
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Well, according to that test, by the German motojournalists, sure sounds like the tires were the culprit. With stock tires, behavior is very evident, with most other tires the symptom is either entirely gone or very nearly gone. No suspension setting changes in between. |
Sparky
| | Posted on Monday, December 22, 2003 - 07:37 pm: |
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I'm wondering if those people reporting handling problems such as standing up while braking with stock tires are scrupulously running the factory's recommended air pressures. |
Oconnor
| | Posted on Monday, December 22, 2003 - 08:06 pm: |
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For me, when I was running low airpressure (32 to 34), cuz I was dumb and lazy found that the tire washed out (understeer) on mid corner or entry braking. Now with it at 38-40 psi it stands up during braking.
Oh its the stock front tire. Soon to be replaced. Just not entirely sure with what.
My front is worn almost bald yet my rear has 70% tread on it. And now I don't do stoppies. I am not that skilled (or dumb or both [I think skilled]) Anyone else have premature front tire wear... |
Fullpower
| | Posted on Monday, December 22, 2003 - 08:16 pm: |
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bigsherm. great quote " who's in charge here, you or the motorcycle? Stop being a little bitch and make it go where you want it." nuff said |
Geofg
| | Posted on Monday, December 22, 2003 - 11:05 pm: |
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quote:Now with it at 38-40 psi it stands up during braking.
Factory recommended front tire pressure is 36psi. Rear is 38psi. Handling'll go to hell if you're over pressure, too.
-Geof |
Sparky
| | Posted on Tuesday, December 23, 2003 - 10:57 pm: |
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I'm about to replace my front Sportec 'cause I've run it down to the wear bars. Because it's worn & relatively flatter in the center now, I find it takes a lot more effort to steer with precision especially if, for instance, I'm trying to make the sharp left turn out of the parking lot at work when the signal just turns yellow and I'm wound out in second & haven't begun braking yet! This is when you notice if your bike has a tendency to stand up under braking -- or not. IMO, I feel the worn out Sportecs handle this situation better than the stockers did when new, they're that good. |
Opto
| | Posted on Thursday, January 01, 2004 - 05:14 am: |
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OK I've done 800 miles with the Bridgestone on the front...
The stock Dunlop D207 is what makes the bike stand up - end of story! |
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