| Author | Message | ||
     Bob_thompson |
Datsaxman: "Most folks expect that the size of the contact patch is important. It is not." With due respect Steven but that seems like an awful positive statement given all the variables that are in play when riding a bike or driving any vehicle. You also said these things: "It sticks EXACTLY as well, so long as the surface is uniform." "Just takes a bit of extra effort to initiate a turn from center on the Ulysses." "That narrow contact patch DOES follow cracks, grooves, and seams in the road, though!" "The first trip up a driveway at an angle was not comfortable, but that has been the only trouble so far" "Disclaimer: Not recommending a CT for your MC in any way. You should only put approved Buell and H-D products on your Buell. I mean, you should have the Certified Technician at the Franchise Dealer install only OEM and Official Licensed parts" That goes for any make but sounds like sarcasm. Glad you posted that and I'll politely agree with all you said with your experience with CT tires but remind everybody to examine what your main purpose is when selecting a tire for "your" use. Good exchange Steven. Stay safe, ride safe all. Bob | ||
| Sifo |
While I agree with Datsaxman about contact patch and friction, there's a pretty important consideration to safety that he is overlooking. When you hit a stone in the road, the larger the contact patch you have, the lower the percentage of that contact patch will be on the stone. To put that another way, with a small enough contact patch, 100% of the contact patch can be on that stone. I think we all know where that will lead while carving through a corner. This could be a stone or anything else on the road surface that might reduce the coefficient of friction of a small area. A bigger contact patch may not offer more traction, but it may offer a better margin of safety when the road surface is less than perfect. On a separate note, I would think the corners of a CT would wear pretty quickly if you rode twisties much. I guess this is a thing more aimed at riding the superslab though. Personally, I know how a tire worn enough to change it's shape affects the handling of a bike. A car tire has to take this to another level. Perhaps some don't feel it's a big deal to them. I'll still go with tires designed to give precise handling on a MC. | ||
| Datsaxman |
Bob and Sifo, and All, Thanks so much for the lively and civil discussion. I have done this a few times now online, and this discussion has been the most pleasant. Not all have been... Bob, 25 years lecturing Physics, and researching, and doing the testing myself, at "The Big University", and I AM pretty confident of that statement. Very well tested for quite literally hundreds of years. Over 300 years. Try to find something in another branch of human endeavour that has been understood (in more or less its present form) for 300 years! Here we go... One standard student experiment involves dragging an object across the floor, or the lab table. Pull with a string, using a scale to measure the force needed to pull at a steady speed. A wooden block, say a section of 2x4, works well for this. Measure and drag. Many trials, as smoothness is learned. Add weight to the block, repeat. Result: Make a graph plotting pulling force against weight. The slope of that graph is the "coefficient of friction", CoF, referenced in my previous post. And it is seen to be constant. Conclusion: The CoF does not depend on the weight of the object, but is a property of the two surfaces that are in contact. Good science lesson! More experiment: Repeat the entire process, but with the block up on the 2" edge, instead of the 4" edge. EVERY student, without being told, will do the first part of the experiment on the 4" edge! There is a lesson there, too... Result: The two graphs are identical, within the range of skill of the (beginning scientists!) experimenters, and assuming the wood block is uniform. We sand the block surfaces and prepare the floor/lab bench by sweeping and washing. Drag across the identical section of table/floor of course. Conclusion: The CoF is found identical for the two graphs (the slopes of the two graphs are equal), which is to say: the force needed to move the same weight block is identical in both orientations. Further Conclusion: Friction does not depend on the surface area. Sifo: Point taken. I said "It sticks EXACTLY as well, so long as the surface is uniform." Not overlooking the hazards of a small surface area, but my post was turning into a book. Of course, you are correct. I find it pretty easy to miss isolated objects on the road with any MC, and I expect most folks do also. BUT your remark got me wondering about the contact patch area under different conditions... It should be true (I mean I am going to measure out in the garage this afternoon and see what I find!) that the contact patch is about the same size with both a MT and a CT, BUT with rather DIFFERENT SHAPES. The CT contact patch looks much smaller, but ONLY THE WIDTH can be seen from the rear, as in the photo above. I expect that the contact patch area is NEARLY IDENTICAL for the same MC under the same conditions. Here I go rambling... If the tyres were like balloons, with no structural rigidity when uninflated, the contact patch area (A) would be: A = W/P, where W = weight on that tyre, and P = air pressure above atmospheric pressure in the tyre ("gauge pressure"). Of course, the uninflated tyres ARE rather rigid, and the mounting provides additional adhesion in the tyre beads being stuck to the wheel. And certainly the CT is stiffer than the MT. So the area A is reduced by the fact that the stiffness (S) is helping to hold the MC up. But how much?? This would generate two equations, below. One for each tyre type. W and P should be the same (add a little weight to the MC to compensate for the weight difference in tyres, and adjust the preload to compensate for rear tyre height differences), to the difference in the areas can be measured directly, and from that the effects of stiffness can be deduced. I do not HAVE a scale that can do this measurement. BUT I do have two Ulysses, one with a MT and one with a CT. A = (W/P) - S A' = (W/P) - S' Remark: I expect that the difference in stiffness of the two tyres is the only thing that can cause the difference in contact patch sizes. More tomorrow after I have run some experiments. I conveniently have lots of spare MC and CT handy that are the same as what are mounted on the two Buells, and the two MCs! More for Sifo: 1) Agreed that I also expected the corners of the CT to wear out rather quickly. As stated earlier, EVERY ride for me starts and ends with a 15 mile twisty ride down/up the mountain. Ex novice road racer, so I have been known to lean it over a bit. Tyre photos tomorrow. You may be surprised. I know I have been! 2) It has been my experience that the CT changes shape a lot less than the rear MT as they wear! The CT cannot exactly "flatten out", since it starts that way. Boy, the MT sure does! Ever notice how different a fresh MT handles from the old one? That MT was trying to have a CT shape! Conclusion: However the two tyres handle, the CT changes less over the life of the tyre. And, since a CT seems to last much longer than the MT I have tried, the (smaller) change happens mush slower as well. saxman | ||
| Mr_grumpy |
This is getting really interesting, I'm looking forward to tomorrows installment. Cheers saxman. | ||
| Pikeben08 |
http://www.stevemunden.com/friction.html | ||
| Sifo |
Saxman, I will be interesting if you can get some data on contact patch areas when leaned over. Intuition tells me the MT will have a fair amount more area, but have nothing to back that up. Data tends to rule over intuition. I also agree that a single stone is normally easy to miss. I invite you to take a ride in WI where it seems to be a local game of 4 wheel vehicles to drive off the road at the apex of every curve. There's usually a line that will miss most of it, but you will hit some pieces. I would prefer to hit them with a larger contact patch. Conclusion: However the two tyres handle, the CT changes less over the life of the tyre. And, since a CT seems to last much longer than the MT I have tried, the (smaller) change happens mush slower as well. I agree with your conclusion to a point. Over the life of the tire the CT will no doubt remain more consistent. What I have a problem with is the fact that on day 1 of the CT being installed, the handling has been quite drastically changed from how it was designed. It's even quite bad compared to a very badly worn MT. Beyond that, I've had excellent experience with dual compound tires that are available today. They are quite resistant to going flat in the center, even living in the Chicago suburbs. It's because of these things that I think the benefits of a CT just aren't warranted in most situations. I am curious however, and forgive me if I missed this earlier in the thread. I assume you are using radial construction CTs. Have you experimented with bias ply tires? I would expect radials to be preferred, but I'm also guessing the use of CTs pre-dates radial construction, so I'm not sure what to think about all of this. Thanks for reasoned debate. It's educational! | ||
| Kenm123t |
What tire does the Can Am Spyder use? they look like Cts | ||
| Diablobrian |
hmmm wonder how the Donahue friction Circle or Keith Code's traction formulas apply to Car tires on bikes..... Would it be the same or would chassis differences and squirm change the threshold of traction especially when up on the edge of a car tire given that a sport bike only has a couple of square inches of contact patch under optimal conditions with tires engineered for sport riding. | ||
| Mr_grumpy |
Looks like there could be an episode of Mythbusters here. | ||
| Nobuell |
Amontons' First Law: The force of friction is directly proportional to the applied load. Amontons' Second Law: The force of friction is independent of the apparent area of contact. | ||
| Reepicheep |
Nobuell, that is true for the classic friction model in perfect conditions. In a street environment, there are other mechanics of grip operating other than friction. According to the "classic" friction model, a dragster with a 3 inch wide rear tire would be just as fast off the line as one with 3 foot wide tires. In practice, with really soft rubber, it is no contest, the wider tire (and contact patch) will crush the narrower one. That requires soft rubber, I don't know what the crossover point is between really hard rubber and really soft rubber, and where a car or motorcycle fits in that mix. | ||
| Al_lighton |
Bill, Exactly. As the contact patch shrinks, the force capable of being delivered becomes less about the "normal force * coefficient of friction" and more about the strength of the rubber itself. As the area shrinks, there comes a limit where the stress in the rubber (force/area) starts to dominate over the theoretical friction force. Ultimately, you can't deliver more force than the material strength will bear. You could keep repeating the experiment that Steve presented, halving the contact patch each time. The results would be the same as he wrote until there would be a big change. At that point, there would be a big dark stripe on the surface where there wasn't before. | ||
| Diablobrian |
Back in the late 70s early 80s I had this bicycle you see it looked Sooooooooooo cool with the long forks banana seat, pseudo ape hanger bars and square profile rear tire. Unfortunately after Santa left the thing I got to find out just how awful the thing was to ride....squirrelly doesn't even come close to covering it. Did I quit riding it? No, we weren't rich folks and it was a dear possession besides....It looked sooooo cool...  Until someone decided that they needed it worse than me and stole it. I was sad, but not as sad as I could have been. After all everything about riding it sucked except for how it looked. It was a trade-off early teen me was willing to make. seemed like a good idea...at the time. my earlier point especially at the relatively low loads a bike puts on a car tire. will it ever "warm up" and reach the temp it was designed to operate (and have maximum traction) at? Or is the low operating temp a major reason for the long tire life? As Aldous Huxley once wrote "I'll buy you lunch, but in return I have this bridge in New York for sale..."  Or something like that. Maybe it was more along the lines of TANSTAAFL (There Aint No Such Thing As A Free Lunch) These tires are designed around the compromises forced on the manufacturer by the laws of physics. Tire life and grip levels are inversely proportional if all other variables are negated. However we live in a complex world where things like operating temp area of contact patch at lean angle x, rubber compound as it relates to shedding water (silicates) tread patterns and how they work together and a million other variables affect your bike's handling and performance. Please remember that this is a single track vehicle and unlike a 3+ wheel vehicle a critical failure in either tire can lead to disaster in short order the only safety margin you have (especially at any sort of lean angle) is in the hands of your chosen tire's engineer. There is no limping the bike safely to a stop. I've had explosive decompression of a rear tire at freeway speeds and I never want to do that again despite the adrenalin rush I got from bringing my son and myself to a safe stop on a narrow shoulder in the middle of the night (thanks again to the late night Buell relay team that helped me out at Homecoming 05) I run sportier rubber than I NEED and take the trade-off in lower mileage in order to get the level of grip I want on the road even though I can no longer hang off the bike like I used to. Not saying that these tires are un-safe, just advocating caution. I really don't want to lose any more friends because they are trying to save a few bucks on gear or tires.... Bottom line riding a motorcycle is inherently risky. Do what you can to mitigate the risks. Don't make choices that seem like a good idea short term but can cause you pain in the long term...After all,  It seemed like a good idea at the time. | ||
| Mikef5000 |
I love darkside threads. Those with no experience go on and on about how stupid/dangerous it is. While those with real world experience come with surprisingly positive reviews the vast majority of the time. This has been, by far and away, the most civil and educational darkside thread I've ever read. Go Badweb! | ||
| Tom_b |
"What tire does the Can Am Spyder use? they look like Cts" They pretty much are. But the spyder is a whole different animal than a motorcycle. The tires do not lean any where close to a mc. | ||
| Tom_b |
Way cool discussion by the way.  Having rode many bikes over the years. some with CT. the CT thing isn't really a big deal to me. Like most bikes once you ge the hang of it is fine | ||
| Diablobrian |
I've herd the guys that stop at the border to remove their helmets tell me that they've never had a problem with head injuries but that does not make it a good idea in my book either. I may be...ok, I am...a tad over- cautious when it comes to motorcycle safety. Before being hit head-on in traffic by an inexperienced (300 whole miles!) driver my friends referred to me (good naturedly) as "The Gear Nazi" because I was always after them to wear their gear. Even for a trip down to the corner store. It's a pain, it's too hot, etc were their complaints. I was hit my morning commute with my wife on back at 45mph <2 miles from home, .5 miles from work. 45mph. Reason we are alive? We were both wearing full gear. I was held together by soft tissue and leather when my pelvis was shattered by the impact and my role as my wife's airbag. Died twice on the table and self resuscitated both times. So yeah, I'm a little cautious, but it has saved my wife's and my own lives, and kept our 3 kids from being orphans. My friends no longer require encouragement to wear their gear. Since the accident happened I have had a paralyzed left leg as a constant reminder of what could have been, not only for myself, but for them also. However up to that point none of us had never been in a bad accident. The odd low side etc. so that meant we had no worries right? Nothing could go wrong...until it did. The Oingo Boingo tune "Nothing Bad Ever Happens to Me" comes to mind about here..... http://www.youtube.com/watch?v=qpjHW4mr6qo As in Hey, it hasn't happened to ME so "why should I care?" to quote the song. It is very easy to make a bad choice based on anecdotal internet wisdom. I just want people to measure the full impact of that choice before making it. Even if 1000 riders got away with it for 100000 miles if you are the one that has the catastrophic failure it's kind of a small consolation don't you think? So just because the people here haven't heard of a downside it does not mean that one does not exist. Thats all I'm saying. While I endorse ATGATT I also oppose helmet laws for adults. kids need to be protected, but I don't think the government has any business telling an adult what they HAVE to wear. Same goes for your tires. I would never dream of telling you not to run them. I just encourage caution in the choice. (Message edited by Diablobrian on October 16, 2012) | ||
| Tom_b |
@ diablobrian.. i encourage caution to anyone that throws a leg over a motorcycle. Regardless of what they are riding, what kind of tires or whether sportbike or cruiser. I have refused to sell a mc or 2 in the past to inexperienced riders | ||
| Datsaxman |
Lots to review tonight...first some comments: Pikeben, thanks for posting the link to Munden. Mostly sound...although he (and this is a little dodgy) does not use all of the vocabulary words correctly. I only skimmed until I had seen enough to ascertain that he was still figuring it out for himself. Or just didn't have it totally sorted. Or something. He makes it more complicated than it needs to be, IMO. But worth a read if you don't have a nice college Physics book at home. I always recommend a textbook on the subject over a "popular" interpretation. It seems like some important things are usually lost in the "simplifying". Sifo...I forgot to remark yesterday...grew up in Middleton. So I know of those rocks firsthand. Agreed. We have the exact same phenomenon in the CA Sierras. The Eastern side, where the roads are (even) narrower. And I have only used radial CTs lately. Once upon a time there was this ironhead Sporty... Nobuell...yes, that was the same Amontons I was referring to. 1700 vintage. Brian: Mark Donohue? He was about 300 years too late to deserve credit for any of that friction circle stuff, he just got famous for using it in a race car before there were engineers and laptops everywhere. "Unfair Advantage" is a great read, IMO. Again with the Physics textbook for the whole story. Please provide a link to "Keith Code Friction Formulas". It is 3AM, so I am not going looking through the books for them. I am a big Keith Code fan, but Code *still* thinks that countersteering cannot be explained by physical laws. He just means that *he* cannot explain it. Newtonian mechanics all the way... Bill: The durometer tells a very interesting tale re: the hardness of a MT vs. a CT! The CT is typically SOFTER than the typical MT...I only tried the 10-12 MT I had on hand, so YMMV. 4 kinds of CT, 4 other truck tires, etc. Hi AL!! Yes...when the cohesion of the tyre material fails, the experiment changes very quickly. Brian, your analogy is severely flawed. Misleading at best, insulting at worst. Not to me, to the reader. I cannot be insulted, particularly by civil discussion. Running the CT is not at all comparable to riding without a helmet or protective gear. Running a different tyre is a substitution of one kind for another. Every MC gets a tyre. Riding without gear is discarding some equipment and doing without. See the difference? And actually, CTs on MCs do not have a history of catastrophic failure. Please cite even one example. I can certainly cite several examples, two with accident reports from LEOs, of MTs failing catastrophically. I expect everybody reading this can give an example. In fact, the load capacity of the CT is far greater than that of the MT. I have seen more than a few GWs - usually with large pilot and pillion - that exceeded the weight rating of their tyres. Oh, and I am too lazy to look for the post...but getting the CT up to temp. is not an issue. These are not race car tyres, they are all season or three-season general purpose skins, and seem to provide lots of traction at even freezing temps. And, just to repeat it one more time, I DO NOT recommend that you run any gear on your MC except OEM stuff installed by factory-certified techs at the local franchisee. DO NOT run a car tyre on your motorcycle. | ||
| Datsaxman |
How is the contact patch area related to the tyre pressure? Yesterday I committed to exploring some of this, and here are the results from today's limited testing: Used the 2006 XB12X, which has a Dunlop K591 rear tyre in 160/70R17. Has about 1200 miles since new, and the bike is essentially stock. I propped it up against the side of the garage so it was leaning at about 2 degrees from vertical, cleaned off the tread surface a little, and measured. 1. Set pressure (36, 26, 20, 16, 12, 6, then 0 PSI. Several trials at each pressure. Precision gauge.) 2. Sprayed WD40 on tread. Same tread patch for the whole experiment. 3. Jacked up rear tyre at the rear of the muffler using a floor jack. 4. Rotated tread so WD40 was at the bottom. 5. Put graph paper under tread. 6. Lowered tread onto graph paper. 7. Raised tread off graph paper immediately. 8. Outlined wet print areas with pencil before the WD40 had a chance to spread. 9. Counted the tiny boxes to get the contact patch area. Tiny, tiny boxes. Pretty annoying stuff. 10. Graphed the results on more graph paper! You may recall that I predicted this: A = W/P - S A = Area of contact patch W = Weight on the contact patch P = Gauge pressure in tyre S = Stiffness of tyre independent of inflation. Meaning the stiffness at 0PSI. Assuming the above relationship is correct, I made a graph of A (1/P). If you don't remember how to read that, I expect that the area will be inversely proportional to the pressure (more P gives less A), so this graph had better be linear. And so it is. YAY!! Extracting S from the graph is easy, and it seems that the Dunlop has stiffness equal to 23PSI of inflation. In other words, if a similar shape tyre made of Saran Wrap or something were totally limp when uninflated, it would take 23PSI to get just the air pressure to give the same results as the structure of the Dunlop does with the valve core removed. Stunning result, really. I expected it to be MUCH less. There is still a lot to do before I can even hope to address the big questions about contact patch under lateral acceleration. But we will get there. Tomorrow (if time permits): The same test procedure with the Kawasaki with the 175/78R16 CT, and again with the XB12XT with the extra phat 205/50R17 Bridgestone CT. Remark: The Bridgestone seemed to practically go on by itself once I had it lubed up and started waving tyre irons at it. I still do it the old old way with a plastic trash can and three long spoons and Ru-Glyde. The Bridgestone seated almost instantly and gave no problems at all. This is relevant since I hear horror stories of owners, MC shops, and car tyre shops having difficulty getting CGTs to seat on MC wheels. Sometimes destroying the CT by overinflating in a failed attempt to seat the bead. DANG!! Never overinflate them, folks! Lemmeesee...100PSI on a Buell rear tyre would be...about...17" wheel nominal size...carcass is actually about 12" bead to bead...25" circumference...so that's 30,000 pounds of force across that carcass!? "Hey, I think a little more pressure might be all it needs." BAD idea. VERY bad. Anyway, more to come tomorrow. And eventually some pictures. Not tonight. The question that is bugging me the most right now: How to measure the contact patch at speed in a corner? Probably not possible to do that solo. BUT I will measure leaned over in the garage and see how that behaves. And do some fancy Physics stuff to try and make it all make sense. saxman (Message edited by datsaxman on October 17, 2012) | ||
| Diablobrian |
Not trying to insult anyone here just making a point about anecdotal evidence not being proof of concept. with the helmet/no helmet example and the "evidence" given as "proof" of the safety of the act. It was the first semi-parallel kind of motorcycle related example I could come up with without doing a lot of research for what I'm enjoying as an informal discussion of the potential of trying something different. Donahue certainly did not invent the "friction circle" but he did do an admirable job of making the concept more user friendly to the teaming masses. I was too young to have been a real direct fan of Donahue (I was born in 69) but I do own a 72 Javelin that he and Penske had a fair bit of input into the design of   I'm not surprised to hear that the compound of the CT is of a lower durometer. It is precisely because of the lower operating temperature that it must be softer to generate grip. 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. Never said it wouldn't get there just asked a question that seemed pretty pertinent. Even though they do run cooler it does not mean they are designed to run stone cold if you want to get the most out of them. Then again, we are talking about very different applications, tire pressures, etc. Do you have access to a former colleague in the field of chemistry that could compare samples of the rubber between the two types of tire? it would be interesting to see how a heavy touring tire and a car tire compare. In Code's books the math is there but it comes back to the same old friction circle with only a maximum of 100 of the grip being used for anything so if 10% is used for braking then only 90% is available for cornering etc. Another simplification to keep the conversation low key and informal. Just considering if there was a kind of null zone you had to transition through while shifting from the flat treads to the side of the tire (and most CT users admit that there is a "tricky bit to get used to" when using the CTs) and if you are in that transition zone when an emergency happens, say a doe in the road, is there a delay while completing the transition before reaction can begin since focus and physical effort is required during this transition even if you become unaware of it due to repetition and muscle memory. Kind of like learning to ride a bike you start out needing every bit of focus your young mind possesses, but before the week is out you are riding down the street with you hands off of the handlebars. Not because the task became less complex but because you had trained your body and mind to manage the tasks subconsciously. I have had a catastrophic failure on a rear tire on my Buell. Scary as anything, near midnight in a group of other Buell riders, with my son on the back. initially thought he was wiggling around on the pillion when tire went. Brought it safely to a stop on the shoulder. Cannot imagine if this had been a heavier carcass tire delaminating and throwing chunks around, steel belts wrapping around swingarm and sprocket. Tires do sometimes escape the factory with a fatal flaw. the MC tire ^ had less than 200 miles on it when it happened. Modern tech makes it harder for them to get past QC, but there are always "friday afternoon" tires (or cars or whatever) that seem to slip past inspectors. You are obviously aware of mass times velocity and how that affects the way a motorcycle operates. Are the Car tires lighter or heavier than the motorcycle specific tire that came off of the bike? If heavier that extra inertia could feel friendly on a long freeway drone, but during emergency lane changes due to a bottle of some unknown substance falling off of the truck in front of you coupled with the delay mentioned earlier due to the tire shape and things could go VERY wrong. Again not claiming it has happened, just that there is potential there for issues. While I have no degree in physics I was a machinist and mechanic for years working jobs for such places as Solar Turbines and General Dynamics so I hope I have a pretty good grasp of the physical properties of matter, and am ALWAYS willing to learn about what I do not know. Thanks for keeping this light and entertaining! I'm now advocating the use of Sand paddles on the rear of sport bikes, you know 'cause it looks Soooo Cool! can't believe I have to do this, but DO NOT put a sand paddle on the back of your street bike.  | ||
| Natexlh1000 |
Sand paddles are so '80s. Hillclimb chains are in now. | ||
| Diablobrian |
ohhhhh I missed the memo. can you cc on the next one? | ||
| Reepicheep |
Never dreamed car tires would be softer than MC tires. Huh. So why do CTs last so much longer? Because their straight line contact patch is so huge? And if you railing a CT through the twisties does that mean it would wear out faster than a MT? I wouldn't do it because it would foul up handling. I can't even stand the Dunlop MT profile, much less a CT profile. But it's an interesting topic. | ||
| Sifo |
I think there are 2 simple reasons CT last longer (I assume you mean on a bike). First there is just far more tire to be worn down. A wider tire tends to last longer. Second, I'm pretty sure that CTs tend to have deeper tread to begin with. | ||
| Arcticktm |
I am no retired physics prof, just a still working engineer. However, at the risk of an academic smack down, my "big university" (IIRC, it was a while ago), taught me that the Coulomb model, which neglects contact area in friction force calculation, is actually a simplification to make it easier to calculate in the real world (where engineers like to live!). A very good approximation, for sure. It's practical limits are in cases where you had what amounts to adhesive friction (the surfaces are bonded even without an applied force). Like some insanely sticky rubber such as used in drag racing (and maybe even full race tires these days??). I remember some track-day Pirellis I had on a supermoto that would pick up a small bucket worth of gravel if you rolled the bike over it, and it was noticeably harder to push through the garage with those tires. Don't get me wrong, I love simply approximations. Without them I never would have made it through school! Also, I supposed this was assumed to be known, but your typical car tire certainly would not have the same traction as a sport touring tire if it was made out of much harder rubber (to get that high mileage). Never mind the contact patch. thanks to the old timers quoted previously. Glad I checked back on this thread. It did get me thinking over lunch. Now I have to look for a sand paddle tire for my Uly after work! | ||
| Sifo |
Slightly off topic here, but still pretty close to the general discussion... Why is it that off road knobbies have such a bad reputation on the street? I've never ridden knobbies on pavement, so I have no personal experience, but have heard plenty of bad stories. Thoughts. Saxman, I'm very impressed with your willingness to do some real world measurements. One comment though... A 2 degree lean angle? Not very representative of most peoples riding through turns. I can see where 20 degrees of lean might be tougher to work with in your garage. Still, I can't wait to see what data you come up with. | ||
| Azxb9r |
Why is it that off road knobbies have such a bad reputation on the street? With an aggressive knobby the knobs are spaced far apart so the tire has to "jump" from knob to knob as it rolls. I used to ride a Honda XL250 as a commuter many years ago. the stock tires were not bad at all, but when I replaced the rear with something more off road worthy I almost ended up sitting on the ground the first time I pushed it around a corner. It is especially bad in the rain. | ||
| Pikeben08 |
I would also think that this would go back to the tire strength part of the discussion as the knobs would probably flex and break contact with the road surface or overheat locally on the knobs and change the adhesion properties. | ||
| Diablobrian |
the relative height of the tread blocks on a knobby tire also lend themselves to tire squirm as they deflect from linear travel. I'm sure that the light weight carcass also bears some of the blame but the bottom line is that many knobbies feel very vague on the pavement and do not inspire confidence. |
