| Author | Message | ||
     Xl1200r |
If your clutch is always operating in a sliding friction mode, it's time for a new clutch. | ||
| Datsaxman |
Responding to other posts as promised: Mueller (10/22): What does an open diff car with two grossly mismatched tyres have to do with a MC tyre? Not much...I intend to measure the coefficient of friction of my own rear tyre on the local pavement, and I am confident it is well below 1. Like others, I am guessing. But this is my area of expertise and all, so I intend to test the piss out of my assumption. And I think the tabletop experiment is pretty sound. Amontons and Coulomb got famous and renowned from it, and 300 years later we still teach it. xl1200(10/22): Agree with some, disagree with other things you said. But nice thoughtful post. I am *still* planning on photos. Badweb bandwidth is pretty tight, so I will post a link here to a third party site. That is where the delay is right now. MrGrumpy (10/22): I expect that the tyre contact patch will have to be LARGER at even a moderate lean angle, for both tyre types, than it is vertically. Hang on for a little quick physics lesson here... At rest, the weight on the rear tyre is going to be called W(r), just some fraction of the total weight of the MC + rider(s), which will be just W. W = W(f) + W(r). Of course. Leaning implies cornering. Of course. Here we make a simplifying assumption, namely that things are at a steady state. Meaning constant speed whether going straight or turning. Also we will assume constant radius turns are being used. These are both so that the proportions of W(f) and W(r) are the same under all conditions. Now, when cornering, the force exerted by the tyres against the pavement is not *just* the tyres holding up the MC, but the tyre contact patches are also pushing the MC toward the center of the circle. If you were to be cornering with a lateral acceleration of, say 1.0 g, the force being exerted by the rear tyre would be (the square root of two) times W(r), which is about 1.41 W(r). Same for the front. Lateral acceleration of 1.0 g is A LOT, but I picked that value so I could do the vector calculation in my head here at the computer. Clearly, the extra force on the tyre is going to complicate things. The lateral force is trying very much to deform the carcass, as well as exert even more "downward" force in the tread. "Downward" is in quotes here because we now have a very un-car-like question to ponder: Are we interested in forces parallel and normal (perpendicular) to the road, or parallel and normal to the tilted tyre? In any event, I give you this: The contact patch will be larger in a 1.0 g turn that it is going straight. Larger by *some* amount, but less than 41% larger (sqrt of 2 - 1 = 41%). Measuring the contact patch at full chat through a corner is a little beyond what I think I can do without a nice grant for some glass and repaving and cameras, although I would love to do it just to see how the MC tyres and CTs behave. Kyrocket (10/23): Yes, the CT profiles vary greatly... Ducbsa (10/23): ha ha ha...Yes, this is a popular thing to say. "Well, if you never lean it over, I guess it might work...as long as you never went over 50 or so"...or something like that. Friend, I ride with a couple of pretty fast groups of locals...with the CT on...on the Ulysses with the full luggage. I usually ride at the tail end of the fast 3-5 riders and try not to run up on the guy in front of me. Nothing leisurely about *my* riding, and certainly no reduced exuberance due to the CT at all. I can't speak for anybody else, of course...but I know there are some Darksiders up your way that you could get in touch with for a little sporty riding perhaps. Of course, we *all* think we ride pretty well, right? So maybe I am just a dreamer. I did not get through tech soon enough to ride at El Mirage this weekend, but I expect the big Kawasaki will go a whole lot faster than any of us ride on the street. Not my first rodeo... I think you will have to try it yourself before you really know how well, or how poorly, it works. Or not try it, and keep guessing or repeating what you hear from somebody else who didn't try it? Sifo (10/23): Exactly the opposite of my experience. I am running 40+ psi in both the Ulysses rear and the Concours rear. The Concourse was *really* squirrelly at lower pressures, and liked to "wind up" in corners. Any change of throttle, or lean angle, or using the brakes, would un-wind or over-wind the sidewall. Very, very disconcerting for sure. After that purely speculative - and false - statement, you draw some pretty wild conclusions. Go for it. xl1200 (10/26): If you are using the clutch, it is certainly operating in a sliding mode. Right? | ||
| Sifo |
Sifo (10/23): Exactly the opposite of my experience. I am running 40+ psi in both the Ulysses rear and the Concours rear. The Concourse was *really* squirrelly at lower pressures, and liked to "wind up" in corners. Any change of throttle, or lean angle, or using the brakes, would un-wind or over-wind the sidewall. Very, very disconcerting for sure. After that purely speculative - and false - statement, you draw some pretty wild conclusions. Go for it. Apparently a bad assumption on my part. Thanks for setting the record straight. | ||
| Xl1200r |
xl1200 (10/26): If you are using the clutch, it is certainly operating in a sliding mode. Right? I mean, yeah... a clutch does slip in order to get rolling, but the point of a clutch is to NOT slip unless you take pressure off the springs to allow it to. | ||
| Datsaxman |
xl: The POINT of this discussion is tyres, and them NOT slipping. The function of the clutch is TO SLIP, in a controlled and predictable way. If the tyres slip, they are not doing what you want them to do. If the clutch slips when you do not want it to, it is broken. Completely irrelevant here. If the clutch does not slip when you want it to, it is broken. Again irrelevant here. Purpose of tyres: grip. Purpose of clutch: slip. My last word on that, so since you seem to need the last word, you can say what you say again and I will not reply. | ||
| Sifo |
If the tyres slip, they are not doing what you want them to do. This isn't necessarily true. Tires can be designed to grip right to the point of completely letting go, and tires can be designed to start slipping early, providing a lot of feedback that you are nearing the edge. While the pro racer will desire ultimate grip, the far less experienced rider on the street (despite what his ego tells him) usually needs far more feedback to keep him from sliding on his face. Granted, this is mostly beyond the scope of this discussion, and I would guess, far beyond the scope of what you can measure safely out of your garage easily. Back to our regularly scheduled discussion. | ||
| Datsaxman |
Sifo and bienhoabob, re: Bob's photo: Sifo, your "reduce pressure to make it turn better" expectation seems to be a corollary to the "small contact patch = less traction" thinking. In Bob's photo, you can see the tyre squirming under the lateral cornering load. Yes, it seems to be preserving the contact patch size! The reason for that, see earlier post from yesterday, the CAUSE of that, is the additional weight on the tyre from the cornering forces the tyre is exerting against the road. The MC would be dragging the chassis with the MT on it, so no different. Indeed, many folks with overweight cruisers and touring bikes report increased confidence with a CT under such conditions. CT contact "feel", and pressure, is a topic of vigorous discussion in Darksider forum discussions, and with very good reason. 1) There is a lot of misinformation out there about what works, what to do and not do , and the like. 2) There are no established standards for pressure, or even for which tyres to fit on which MCs. It is ALL experimental. This scares off a lot of folks, which is just fine. It puts the rest of us in the position of having to be OUR OWN SOURCE OF EXPERTISE. Nothing is more contrary to the current trends in our society than requiring self-reliance and a trail-and-self-improvement mentality. As a result, however, some standard true-isms have popped up. You can find those on the Darksider forum discussions if you are interested, but they have to do with which tyre on what MC, and how much pressure. Specific fitments that have worked for others in the past. Some good information in there, and a lot of the other kind too. Interesting to me was the fact that I could not find anyone who had tried a CT on a Kawasaki Concours. But riding in the BIG(gish) rally was going to either need a tyre change midway - or - a tyre that would stand up to the mileage of the whole week. That was what pushed me over the edge to the Darkside, folks. A desperate situation indeed. And then I could only find two CT that were likely to even fit in place of the 150/80R16 stock on the Concours. Merde. So I got one, put it on, and wondered about pressure. One particularly vocal Darksider advises a "one pressure fits all" approach, and that was where I started. Results in an earlier post. Somebody will certainly crash HARD taking that advice, judging from the way the Concours handled. Worst. Control. Ever. Really sensitive to changes during a corner. Changes in throttle setting, adjusting the line, position on the bike, using the brakes, EVERYTHING was a catastrophe at 30psi or so. As I experimented with pressure, again following the advice of others, 28 psi was even worse. 25 psi too. So I went to 35 psi and it was definitely better. At 4-psi, better still. At 44psi, it gave a harsh ride, so I went down to 42psi where I run it now. Anyway, the point: 1) The contact patch does not need to be "large". or "constant shape under all conditions" or "tread stuck to the road as if the tyre was vertical at all times". That kind of misinformation comes from repeating what somebody else said, or from just guessing about how it should work. As with all guesses, some folks guess better than others, and even really smart folks will make some really dumb guesses sometimes. 2.1) Some CT work better than others, and on some MC they work better than others too. It is a very uneven landscape out there, and I DO NOT RECOMMEND THAT YOU PUT A CT ON YOUR MC UNDER ANY CIRCUMSTANCES. 2.2) You may find that a lot of shops will not mount your CT. I have always fit my own, so no worries there. But MC shops will mostly not do it, and car tyre shops mostly will not do it either. some folks find that saying it is for a sidecar rig helps. 3.1) This thread is NOT a professional consultation. You DO NOT have any working knowledge of CTs on MC from this thread, or from any discussions you may have had elsewhere. NONE. You will have to figure it all out for yourself if you intend to embark on this CT madness. 3.2) Your friends (the few who even notice) will think you are nuts, and they are probably right. DO NOT DO IT. | ||
| Sifo |
Sifo, your "reduce pressure to make it turn better" expectation seems to be a corollary to the "small contact patch = less traction" thinking. Actually I was thinking that a softer tire would let the sidewall flex more and therefor make it easier to lean over when initiating a turn. I would also expect the squirm that you describe at low pressures. I'm more than happy to be corrected by those that have experience in these matters though. | ||
| Mr_grumpy |
Interesting stuff, many many thanks for all the info Saxman. | ||
| Diablobrian |
Interesting discussion guys and I'm terribly proud of us for keeping it civil and not becoming a battle of the Egos. Good job guys! | ||
| Datsaxman |
Sifo: Yes, of course, in racing where tyre life is measured in minutes rather than thousands of minutes, threshold slipping is important. Assume that every post comes with the disclaimer: "...for road use only, assuming that there are no spare wheels fitted with unobtanium tyres readily available, and that the rider is not circulating on a closed course..." etc. I actually did an experiment on this in April. I sometimes work as a MotoRef at pro and amateur bicycle races. This event was a criterium race, multiple loops on a short course. A full day of races, 10-12 different races for various ability and age and gender groups. So I was turning right. All. Day. Long. About a 1 mile rectangle, about 5:1 aspect ratio. Long and thin. Over the course of 225 laps, I progressively developed a "racing line" through the two adjacent turns at one end of the loop and took the turns pretty hard on many of the laps. Testing the characteristics of the rear CT on the Concours more than anything else. At the end of the day, the right hand side of the FRONT tyre was trashed. Rubbed raw, and all the rubber left on the road. We are talking about 20-25mph turns here, so you can figure I was pushing the Concours pretty hard to get that kind of wear. Conclusion 1: The CT sticks just fine under vigorous cornering. Conclusion 2: The Concours is not much of a race bike. I was tired from herding the pig around like that. But it was a good time! Conclusion 3: The rear CT is much more durable than a Bridgestone BT45 "rear only" tyre mounted on the front under such conditions. A pretty durable tyre, I think. | ||
| Mr_grumpy |
Jramsey, what's your point? There's no end of that sort of stuff on Killboy with people riding on proper motorcycle tyres too. You can see the tyre smoke & the thick black line where the rear wheel was locked, looks more like typical HD rear brake only rider error to me. What I find interesting for it's own sake is that black line of rubber looks quite wide in those pics, which would indicate a fair sized contact patch before the rider locked it up. | ||
| Jramsey |
My point was IMO a CT belong on a car,back in '76 I bought a '72 CB 750 that someone installed a 15" rim on the rear and mounted a Michelin CT, one of these intended for a VW Beetle IIRC,  It was the squirreliest handling motorcycle that I've ever ridden in my life. After owning it for about a month and almost crashing it many times for lacking cornering traction I found a used rear wheel and had a proper Dunlop fitted which turned it back to a reasonable handling safe ride. | ||
| Mr_grumpy |
I understand what your saying but don't forget that that was nearly 40 year old technology, both bikes & tyres have moved on a bit. | ||
| Sifo |
I'm still having a hard time getting past the need for this sort of experimentation, unless your needs are extremely unusual. Modern sport touring tires are capable of going past 25k miles, and are known to give great handling without "needing to adjust" to the quirks in switching to a car tire. Still an interesting thread on an intellectual level. | ||
| Datsaxman |
Sifo, After 4800 miles on the OEM rear on my Ulysses, what MC tyre will give 25,000 miles? Or even half that? ON MY BIKE? I was at 10,800 miles and three used up rears, from three different companies. OEM, then a Full Bore (first and last time...), then a Shinko. Same with the other Ulysses. Dunlop D616 (I think I am remembering the model...), Dunlop D404, etc. 4800 miles was by far the best for me. No hooligan stuff at all. Mr Grumpy, I have to call BS on your analysis entirely. B. S., amigo. Your statements about an ancient CB750 have nothing to do with here and now, or how my bikes with the CT work, at least with me on it. BTW, I had a Sportster a very long time ago with a 15" CT on it, and it was no more squirrelly than any other hardtail Sporty. If anything, the CT made it more secure in the corners. | ||
| Sifo |
I've done over 25K on a set of Pilot Road 2's. Very happy with them. Running them on all three bikes. | ||
| Mr_grumpy |
Saxman, I'm not following you, Perhaps I expressed myself badly (wouldn't be the first time) My point in reply to Jramsey's post about his Honda was that you can't compare bike & tyre technology from 35 years ago to todays offerings. Tyre compounds have improved enormously as has suspension technology. I don't think I made any statement about how your bikes work. I think the mis-communication problem arises with the fact that prior to the post about his Honda, Jramsey posted a series of pics of a guy on VRod with a CT losing it in the twisties with just the caption "Conclusion 1:The CT sticks just fine under vigorous cornering. " lifted from your preceding post. It was a little facetious of him but hey it's the internet. That post has now disappeared, changing the context of the following posts. Sorry for any confusion, but not of my doing. | ||
| Jramsey |
" a series of pics of a guy on VRod with a CT losing it in the twisties"  Back up for Grumpy. | ||
| Mr_grumpy |
Thanks Dude, I thought I'd lost the plot for a minute or two this morning.  | ||
| Blake |
I can't stand the way a bike handles when the tire pressure gets a little low. Tough to imagine how a freaking automobile tire would compare favorably. The extra weight alone would greatly compromise the suspension performance. Anecdotes aside, an automobile tire on a motorcycle just can't be a very good idea if handling and safety are major concerns. | ||
| Mr_grumpy |
That's exactly what prompted me to launch this thread Blake, I'd been having some tyre issues on the M2 which I'd resolved, but I'd been reading a bit on other fora, notably ADVrider. My initial thought was the same as I imagine most people have "Why would you do that?" However being of an enquiring mind my second thoughts were that evidently a good number of people are doing it, & apparently with good results, so there must be something in it. As Datsaxman has repeatedly said, it's not for everyone so don't do it, I'll not be doing it myself just yet for a number of reasons. 1. Here in France it would be illegal under the French construction & use regs. 2. I don't have a bike that I'd deem suitable such as a big cruiser or tourer. 3. I don't currently have the equipment for swapping tyres about. 4. I don't have the need to do so. None of this is to say that I never will go Darksiding, I may find myself one day with a Lead Wing going off to the ends of the earth for whatever reason, & at that point I'll be seriously considering the option. It's been an extremely interesting discussion if just on an intellectual plane for most folk, For that we mostly have to thank Saxman for his input & time as somebody who's actually taken the plunge & has freely shared his findings with us. I for one will be buying him a pint or two should the occasion arise that we meet up somewhere. | ||
| Buellhusker |
That's not a VRod | ||
| Mr_grumpy |
Whatever, the point being that it was rider error not tyre that caused him to lose it. Tough crowd today. | ||
| 86129squids |
Yeah- that's one of those fancy Yamaha/Star cruisers... I had a chance to talk with a guy a couple of months ago who had a newer 1800 GL, farkled out pretty well, with IIRC a "Volkswagen" tire on it... he was the kind of guy who as a kid, must've been a showboat in "Show and Tell"... he insisted that his particular tire on the rear worked very well. I remain steadfast in my doubts about car tires on bikes... | ||
| Datsaxman |
Grumpy, No problems. Every CB750 I ever rode seemed like it had the front end from a much smaller bike fit to it by mistake. Evil front end chatter, along with dreadful front tyre life. Made my H2 seem reasonable. Sure looked like you were blaming the evil handling on that Citroen (Renault?) tyre. My mistake. I have not had a CT blow at speed, but I have had the pleasure of riding a blown rear MC tyre down from a foolish speed. Not much to recommend about that experience at all. Lots of folks get hurt when that happens, at all speeds. SAFETY? I think a tyre that is much more flat-resistant than any MT...and is much more likely to stay on the wheel if it does flat, is a whole lot safer. But speculate away about the handling... agreed that the unsprung weight increase is a bummer. There are no other negatives that I have found. Better in the weather, better if it flats, etc. | ||
| Blake |
if I tried to ride my Uly as per usual (like a sport bike) but with a car tire on the rear, it would be a very dangerous and unpleasant situation. No? You seem to suggest this in advising that we not employ an Automobile tire on our motorcycles. >>> But speculate away about the handling... agreed that the unsprung weight increase is a bummer. There are no other negatives that I have found. Better in the weather, better if it flats, etc. You yourself spoke of the horrid handling. I'll wager some physics-informed speculation concerning handling is just as if not more accurate and objective than your anecdotal commentary on same. "There are no other negatives that I have found." You mean besides inferior handling and suspension performance? Well, okay. We agree. You contend that grip when leaned over is comparable? How do you know this? Better in rain? how do you know this? To know these sorts of things requires a valid test scheme. Maybe we can get the folks at Cycle World to do some testing. What do you wager their conclusion would be? Better resistance to puncture? How do you know this? A car tire presents a much wider contact patch, thus is subject to a much greater area of the road. Greater area of road encountered means greater likelyhood of encountering puncture. Car tires encounter puncture all the time. I've never feared a flat or a blowout. Not a primary concern for me as I only use premium quality tires. Handling and performance in emergency situations such as obstacle avoidance are major concerns for me in tire selection. In that, no car tire will compare to any properly sized and fit leading motorcycle sport bike or sport touring tire or touring tire. Car tires have little to no tread on the sidewall, upon which one would need to depend with the bike leaned over. How's the relative wear rate and puncture resistance in that regard? If what you contend were true, then why with all the incredibly fierce competition in the motorcycle tire market haven't any manufacturers introduced a super long range car type tire for motorcycles, especially in the big cruiser and touring bike market here in America? The answer is undoubtedly that they understand the inferiority in handling involved and fear the huge liability. That said, it sure would be nice to have a sport touring rear tire that would go 10K miles. I never get over 5K miles. (Message edited by Blake on November 19, 2012) | ||
| Mr_grumpy |
Or it could be that they can get suckers to replace their tyres every 5,000 instead of 10-20,000. $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ As for how he knows what he knows, as far as I understand it's personal experience. Empirical testing as it were. Also living in the most litigious country in the world I wouldn't encourage people to do it either. Basically it works for him, if you don't like the idea don't do it We all do stuff that's "not recommended", remember Incorrect operation of this(fill in the blank here) can cause injury or death!. | ||
| Syonyk |
How are you guys getting such short life on tires? I got over 12k miles on Pilot Road 2s, including some reasonably hard riding and, while unwise, two trackdays in the beginner group (note: I did spin the rear up and lowside on the second, so... not at all suggested). I fully expect to see north of 10k miles on my Road 3s. | ||
| Kyrocket |
Well, speaking from a cruiser standpoint, I've got a Vulcan 2000 and it could be one of the heaviest cruisers built. At 2053cc's it's also got some torque, I don't spin tires but I can get up to speed rather swiftly. It's not uncommon for us, (V2K owners)to replace a tire completely worn out at 8K miles. I use a Metzler ME880 and the consensus seems to be it's one of the longer lasting tires out there. Although Vee Rubber now makes a 200 with a wide whitewall so I may get one of those and try it out. |
