| Author | Message | ||
     Mr_grumpy |
My first bike was a brand new '77 TS250M Suzuki, with semi knobblies as they were then called. I tested those tyres to their limits & beyond many times & still have the scars. I just couldn't get it into my head why I couldn't get round those corners as fast as my road bike riding friends. | ||
| Reepicheep |
They grip really well, you can absolutely rail through the corners. For about 2000 miles, then you have worn them to nothing (they are generally REALLY soft rubber). The problem, as Azx described, is the knobs "walk". I used the term "catapiller" when I first noted it and tried to describe it. The knobs are an inch long, when you are cornering hard, they RELLY flex and stretch. As you transition from each flexed and extended knob to each un-flexed and un-extended knob, the tire shifts noticably. When you first do it, it feels like you lost the back end. But if you nerve it out and keep pushing, it will run wide but it will grip really really well. You just have to compensate with your line. | ||
| Diablobrian |
hmmmm can't seem to find a razor back  and paddle set in stock sizes, guess I'll have to convert to a spoked wheel so I can lace on a dirt rear rim. Heeeeeey Sport bikes with a big flotation razorback from a dune buggy on front and a sand paddle out back. Sounds like something the Icelanders would build a sport around racing across lakes doesn't it?  | ||
| Datsaxman |
Hi All Brian, I agree that temp. is important. No hard data, but the CT is probably cooler than a MT, but it sure sticks well for me... Nice AMX, by the way. Had a GS 455 of similar vintage for a lot of years... Yes, the CT treads average 8.5mm depth, and the MTs 6.0-7.0mm. For the ones in the garage. And the CT wears all the way across the tread instead of just the center. I have been expecting the CT to wear out on the edges. It has not. Current CT on the Concours has 19,966 miles. Should go to 30,000 before the wear bars. No real "transition" issues on the Concours CT at all. The Buell CT is so wide that it is a bit ponderous compared to the MT. But there is only a "delay" if you delay your input. You just have to be more deliberate. Neither one "winds up" or feels lose or rubbery. On the contrary, they feel even better connected than a MT. I will weigh them tomorrow, since I have spares int he garage for everything. Expecting the CT to be heavier, of course. Brian, I also expect that the CT would shred LESS than the MT. I have had MTs shred more than a couple of times, and that is the primary reason most folks try a CT in the first place. Safety, not economy. The CT on the MC is very understressed, whereas many MTs (on GoldWings and H-Ds) are actually overloaded, with two big folks and luggage. Arctic, I have been surprised to find that the CT has more traction than the MT. Much more secure feeling to the seat of my pants. Back to back Buell rides confirm this. ESPECIALLY turning hard. Say what you want, but I have 40,000 miles on two different CTs on two very different bikes. None of those miles were spent holding up traffic, either. Sifo, the 2 degrees was my lazy version of "vertical", not leaned over. Baseline readings. That way I could just lean it against the wall instead of some fancy rigging. Did the CT on the other Ulysses today. More in the next post. | ||
| Datsaxman |
One more comment...on mathematics and vectors and Keith Code. Code is a fine racer in his own right, and certainly his school is very successful. And I have read his books several times. But... He screws the math up in several important places. The precession/countersteering question, for one. The vector addition question also eludes him. His famous example has you think about the available traction as a $10 bill. Anything you spend on cornering cannot be spent on braking. He would say that if you spend $6.00 on cornering, you would only have $4.00 left for braking before you lose control. Great concept, but it is not true the way it is presented. Vectors (like force, for example) add quadratically. Question: If you actually spent 60% of the available traction on cornering, how much is left for braking, and how is this calculated? Even more next time... | ||
| Datsaxman |
DATA from the Ulysses with the CT: So I repeated yesterday's experiment, this time using the Ulysses shod with the CT. A beast of a thing, that CT is, at 6.46" across, 8.4mm initial tread depth, 205/50R17. I tried 42, 36, 30, 26, 20, 16, 10 PSI pressures and measured the size of the contact patch for each. Same procedure as before. In summary, the CT had about 10% larger contact patch at most of the same pressures (16, 20, 26 PSI). At 10PSI, the CT patch is 5% smaller, probably because the MT carcass is more flexible than the CT carcass at low pressure. Now I regret skipping the 0PSI trial today! I was tired of counting the graph paper boxes... At 36PSI, the CT patch was 6% smaller. Probably an artifact of the 2 degree lean, but that data point is from one trial today, not an average. Maybe another measurement would improve the result, but I am moving on. What does it all mean? 1) The CT carcass is stiffer than the MT carcass, so the MT contact patch changes a little more with pressure increases than the CT. 2) The CT AND the MT contact patch sizes are BOTH inversely proportional to the pressure. I made the graphs to see if that is true, which you will remember I already predicted. Actually, I just put today's data onto the same page in a second color. The two graph slopes are very similar, which might surprise you. 3) The contact patch sizes are very close between the MT and the CT. The pressure (not the carcass rigidity) is doing most of the holding up. Remark: The CT contact patch LOOKS big, but all you see is the width. Apparently the contact patch is SHORT front to rear when the MC is going straight. I may have to rig up a front wheel stand so I can test this with the Ulysses very vertical. Tomorrow I tilt the MCs over a bit and try to measure contact patches that way! THEN, I will make some mathematical arguments about contact patch behaviour when cornering. Not likely to be able to make good measurements at speed. Oh, and DO NOT try this at home... | ||
| 86129squids |
Data- THAT WAS MY BIKE!!! Mine had a "flamed" banana seat, and I could ride wheelies forever on that thing... until I broke the forks just below the triple trees...  | ||
| Mikef5000 |
So there's tons of information in here, but this stood out to me: I was simply questioning whether the weight of a motorcycle even a fully loaded tourer would be enough to bring it into it's proper operating temps when it was designed to be carrying literally tons of weight versus a 600lb load on a ULY or even 800 fully loaded two-up extra gas etc. Car tires will never carry literally tons of weight, most in this size are rated at a maximum of 1102 pounds. An average car weighs about 3200 pounds (approximately), which would put about 800 pounds on each tire; a touring bike easily passes that mark. A light weight car (which these tires must work on, as there's no minimum weight rating) can be closer to 2500 pounds, which is only 625 pounds per tire; a number that a Ulysses with rider is probably darn close to matching. | ||
| Diablobrian |
Mike, I got a little turned around on that one, someone had mentioned van tires on taxis and the data in my head got corrupted.......defective grey matter. Good catch! | ||
| Blake |
>>> Contact patch has NOTHING to do with traction 1. Tire traction is not mere friction. The tire compound actually interacts mechanically with the incongruencies in pavement. Think a bit like gears meshing, just more random and non uniform. 2. At some point as contact patch becomes too small, the shear strength of the tire compound becomes insufficient to hold itself together, thus loss of traction and the telltale black streaks. | ||
| Blake |
Just look to the massive contact patch of a top fuel dragster. Contact patch has a LOT to do with traction. Lower pressure for inversely proportionally change in size of contact patch. | ||
| Mr_grumpy |
Hmmm interestinger & interestinger. I thought that at first too, Blake, but on further reflection now reckon contact patch is much less relevant than you may intuitively think. After all snow tyres generally have a smaller footprint than summer ones. Off road tyres are generally narrower than road tyres. In fact Moto guzzi have gone to a narrower fitment on the latest gen of Stelvio for that very reason. These tyres are for operating in more extreme conditions I grant you. If you want another example look at the contact patch of a railway locomotive it's minuscule for the traction it has to provide. Note to self, get a spare rear wheel for next bike & do some testing. This is so intriguing. | ||
| Mikef5000 |
Snow and off-road; skinny tires are used specifically so they 'sink in' to a solid layer, rather than staying on the surface of a loose terrain. Irrelevant analogy when discussion traction on pavement. And railway locomotives do have severe issues with traction! http://science.howstuffworks.com/transport/engines -equipment/diesel-locomotive3.htm I think the Dragster example is perfect. Contact patch isn't everything (like mentioned, snow/dirt can change things), but on pavement, it does play a large role in traction. Traction:  (Message edited by Mikef5000 on October 20, 2012) | ||
| Sifo |
The reason a dragster tire has to be so big isn't directly a traction issue. It's a matter of the strength of the rubber. With a small contact patch, there's so much HP that the rubber will simply shred. Spread the load over a larger contact patch and now the rubber has enough strength to stand up to the traction. It's similar to selecting a steel beam large enough to hold the desired weight over a given span. If simply increasing the contact patch increased traction, dragster tires would be MUCH larger. Anyone ever hear of a train getting a flat? It can happen in the fall when leaves build up on the tracks. If they run them over while braking, the wheel can lose traction and lock causing a flat spot on the wheel. Sasman, still hoping you might find the time and sanity to test contact patches with the tire on a piece of gravel. | ||
| Mikef5000 |
If simply increasing the contact patch increased traction, dragster tires would be MUCH larger. My counter point is that the tire width is regulated. "NHRA rules allow a tire to have an 18- inch width and 118-inch circumference." Plus you get into the argument of 'too much traction' in a race setting:  Which opens an entirely new can or worms. | ||
| Fast1075 |
There are reasons why tire size is regulated. One is keeping control of the centrifugal forces at speed in relation to the mass of the tire. The other is managing the dynamics. Roll a tire around in the pits and observe the dynamics. Compare that to the ultra slo-mo of tires from the moment of launch through the first 60 feet. | ||
| Ft_bstrd |
Saw a guy on a Valkyre "darksiding" today. Couldn't turn worth a damn. | ||
| Tom_b |
"Saw a guy on a Valkyre "darksiding" today. Couldn't turn worth a damn" Wow imagine that. a valkyrie that couldn't turn worth a daman. probably an amutuer rider to boot  | ||
| Mueller |
This is an interesting thread... We had this exact same discussion in my vehicle design class in college. Blake may as well have been in the room, because those are the exact points. Contact area normally doesn't matter in friction. But friction isn't the only factor when it comes to tires. For instance, soft tires on fresh blacktop can have a "co-efficient of friction" greater than 1, telling you it is more than just friction. A simple test to prove that... put your little donut spare on an open differential car and leave the stock tire on the other side. Punch the accelerator and see what happens. I don't know how to quantify how much is the extra non-friction factor and how much is the strength of the rubber breaking down, but I know contact patch matters. | ||
| Mr_grumpy |
I agree that contact patch is a factor in some cases, but how much of one? We're not talking about drag racing 18" wide super sticky tyres on the back of a bike. I'm interested in the use of standard car tyres of more or less the same size on a bike. So far, according to the folk that have actually done it, it appears that there's not a whole lot of difference. So does the contact patch size matter that much in this case? I wonder if the fact that the MC tyre is a rounded profile prevents it having a larger contact patch while providing easier lean angle transition. The squarer profile car tyre however should give a greater contact patch at vertical or smaller angles due to the deformation of the tyre carcass, but a smaller patch at larger angles of lean. From what I've read elsewhere, many "Darksiders" reduce the inflation pressure to allow the square profile to deform, thus keeping the tyre in contact over a larger area. I'm no expert in these matters, but I'll not dismiss the idea just because it's not supposed to be like that. I've run automotive components on my bikes for many years with no ill effects, the economies of scale can provide great savings. As an example my M2 runs with oil filters for a Ford Escort, filtration is excellent, it holds twice as much oil as an HD filter & costs less than half. My FJ1200 ran with the fuel pump from a Suzuki Super Carry micro-van. Cost about 1/3 of the Yam item iirc. Sometimes necessity is the mother of invention, as the saying goes & sometimes it's interesting just for the sake of trying. | ||
| Bob_thompson |
This has been an interesting, and for the most part respectful thread and I have had a couple of inputs, most notably, choose a tire carefully for your specific intended use. One other thing that has not been discussed concerning this is; exactly why does no motorcycle manufacturer put car tires on from the factory, especially touring bikes, if they work so well. They could then brag about highly extended mileage from those tires which probably would be a selling point. I think we can assume the two biggest reasons why they do not. The biggest is liability and second to that is EPA requirements for safety. Again choose carefully and responsibly. Let the games again begin.............Bob | ||
| Xl1200r |
This IS an interesting thread! I have no qualms about admitting that I dropped out of physics class in high school, but I'm bright kid and can observe the following: As mentioned, a dragster has the skinny tires at the front for a reason. If the reason is the "strength of the rubber", that doesn't disprove that a larger contact is still desirable, in fact it proves that it is for more reasons than just friction. A Corvette uses wider tires than a Yugo. Lotus began fitting narrower front tires to the Elise in order to introduce some understeer to the chassis. Big brakes stop better than little ones. Our clutches are a multi-plate design. Once upon a time a 130-size tire was wide for the rear of a bike. Then it was a 150. Then a 170. Now, 180 is pretty much standard on a sportbike with 190s getting more and more popular. A race bike wouldn't get around a turn any better with a lower pressure in the tire (meaning a larger contact patch). Likewise, there would be no need to lower pressure on a dragster's tires, or your 4x4 when you go play in the dirt or on the rocks. Can go on and on... my point is not to call anyone a liar, physics a sham, or what have you, but instead to illustrate that there is more going on than a simplified tabletop experiment can cover - at least in my simple mind. I'd be interested to see some photos of CTs with some miles in a motorcycle application. I used to inspect cars for a living and I'm just curious if there's some wear happening that the casual observer wouldn't notice as potentially dangerous to the integrity of the tire. Again, not knocking anyone for anything. A CT on a bike is not for me, but I understand why people do it and don't think less of them for it. | ||
| Mr_grumpy |
I'd be interested to see some photos of CTs with some miles in a motorcycle application. I used to inspect cars for a living and I'm just curious if there's some wear happening that the casual observer wouldn't notice as potentially dangerous to the integrity of the tire. That's something that interests me too. For example on a car both sidewalls are subject to the same stresses at the same time (more or less) but on a bike the same tyre will get more load on one sidewall when the bike's leaned over. Will those more uneven stresses degrade the tyre carcass faster? Or will the fact that only one sidewall is being stressed at a time allow the tyre to run cooler & extend it's life? I can remember when all semis ran dual tyres, these days it's pretty rare, big singles are the norm, mileage is better, ride is better, longevity is better & handling too. The downside is that on the rare occasion when a tyre does blow it makes a helluva bang & the rim drops straight on the road. I'm not convinced that "Darksiding" is for me as I don't do mega-mileage trips & anyway there's too many twisties here. That's not to say I'd never do it though, I'm keeping an open mind. | ||
| Kyrocket |
Is there any one car tire with more rounded sidewalls than another? I'll have to revisit the Vulcan Forum and see what they're running and see if it's consistent or just what each individual prefers. | ||
| Kyrocket |
http://www.vulcanforums.com/forums/showthread.php? t=27694 Seems it's all over the board as to which one to use. | ||
| Ducbsa |
In the CW Forum thread on this topic, some poster said that no manufacturer has tested them, so wouldn't certify them. Your question "Why not?" claim the high mileage is probably related to being very cautious. We are pretty much sport oriented here and maybe the biggest CT proponents ride more leisurely. "Not that there is anything wrong with that." | ||
| Sifo |
For example on a car both sidewalls are subject to the same stresses at the same time (more or less) but on a bike the same tyre will get more load on one sidewall when the bike's leaned over. Will those more uneven stresses degrade the tyre carcass faster? This is an aspect that I really wonder about. I gather that they tend to run fairly low pressure in a CT to get it to turn better. It's impossible to predict what this may do if the sidewall is flexing excessively, especially when leaned over on the corner of the tire. Extended travel at high speed with underinflated tires can be very dangerous. At the same time, in most cases they are probably run way below their rated capacity. You are both abusing them in a way they weren't designed for and giving a greater margin of safety in one aspect. Pretty difficult to predict the outcome. I don't see myself EVER doing this, and would try to talk any friends into a more conventional solution, but I've seen people doing plenty of things that I find to be extremely dangerous. Running CTs probably wouldn't rank in the top 10. | ||
| Mikef5000 |
Interestingly, most treat this thread (and topic) as if it's new; asking about the stresses put on the CTs etc. Perhaps the easiest way to answer these more basic of questions is simply to google them, as other folks have been going dark side for decades. I would be interested to see a single incidence of a CT failure while on the back of a bike. Personally, I would run a CT without a second thought for a bike without performance in mind, and with limited lean angle:  But as I ride my current bikes hard, and thoroughly enjoy the excellent handling, they will continue to receive proper motorcycle tires. | ||
| Bienhoabob |
From the sparks on the above picture, I'd be more afraid of the floorboards or side stand catching a crack in the road and flipping the bike vs the CT. | ||
| Datsaxman |
What a lively thread...LOTS of pure speculation, and I am out of town with very limited time. When I am back in a few days I will address EVERY. ONE. OF. THEM. For now...I remind all that the laws of the universe - what we collectively like to call Physics - are true, whether you believe them or not. Difference between science and religion, right? Blake: #1. You have just given a definition of friction. The small, even microscopic, irregularities in the surface. #2. You should not substitute correlation with causation. And we are not talking about extreme "what if" cases here, folks. We are talking about actual MCs with actual passenger car tyres on them, and what are the hazards, perceived benefits and possible problems, etc. Top fuel dragsters, space shuttles, snowboards, GP motos, MC tyres with lifetimes of half an hour, etc. are simply not germane to this discussion. Clutches, and other surface area arguments? SLIDING friction. With tyres, we are talking about STATIC friction. Very different parameters. Much more on this later. Enjoying reading your comments, but many are rather poorly informed. Oh, and photos in 4-5 days when I am home. Interested to hear comments there as well. saxman |
