I'm not sure if this is an issue with my riding style/technique/lack thereof, the front suspension geometry, or just the roads I ride. Or maybe it's a combination of the above. I have a 1986 VFR700, stock wheels, with pirelli sport demons in the stock sizes. My commute is mostly mountain 2-lane roads, the rest is freeway. 40 miles each way. A lot of those 2-lane roads are medium-speed sweepers, but rough (lots of suspension action in the corners). I can clearly see my preferred lean angle in the wear of the tires. About half-way between the center and the edge of the tread, there's a stripe on each side that is clearly well-used, and well-heated when it's in used (rough surface, lots of little tears, like the back side of split leather). But in this region, on the front tire, the trailing edge of a tread block has twice the wear as the front of the block behind it. My dunlop GT501s did the same before the pirellis. I keep the tires at the proper pressure (32f, 42r), so my assumption at the moment is that this is due to the trail, and the angle of the tire against the pavement, and the way that the tire surface has to twist as it rotates through the contact patch. Right now, there is probably 4mm of tread depth at one end of the blocks, and 2mm at the other (which means a 2mm shift in adjacent blocks, about 5mm apart on either side of a groove). Also, in the last few weeks, it seems to be accelerating, and the front-end doesn't seem to have the bite that it had in the past, like it's more prone to run wide in a corner unless I just the line *just* right. Less forgiving, perhaps. For those of you with more mileage on bikes than me, is this just to-be-expected behavior for a tire as it wears? Or is the uneven wearing accelerating the demise of the tire? It's probably less than 1mm difference in tread-depth across a groove in the back tire. I'll take some pics when I get home, and attach them. The rear tire's surface looks the same, but isn't nearly so unevenly worn (which makes sense, as there's less twisting in the rear contact patch due to the length of the wheelbase).
Mileage on that tire is ?? The harder you ride, the faster you go, the more throttle coming out of corners, the rougher the road surface all cause wear, so the faster you ride, the more frequent the tire changes needed. The wear you describe might be something to see on tires after a few serious track laps. The generally accepted ratio is 2 fronts to one rear, i think. You could choose a harder-compound tire that would last longer if that's what you need. More tire money=faster riding potential with better control. Proper pressures?? I don't know, but your difference between front and rear is way more than most run.
Soft compound rubber has great grip but wears quickly. It sounds like the sort of wear seen from under-inflation on the front. The tread blocks twist and squirm when cornering and wear on the trailing edge more than the leading edge, so that is normal. And higher pressure would help minimize the wear. Sounds like they are close to worn out, but a picture is needed. Even if the gauge says it's "proper", you have to adjust the pressure based upon your riding style, the rubber compound, the wear, etc. The factory setting is a good starting point and then you adjust from there to make it ride the way you like it...
let's get that out of the way. Front tire: front tire wear - head on view by aaronwood77, on Flickr Close of up tire surface on left side of front tire by aaronwood77, on Flickr Close up of tire surface on right side of front tire. by aaronwood77, on Flickr Closeup of scalloping on right side of front tire by aaronwood77, on Flickr As you can see, there's still plenty of tread left, but the way it's wearing, it won't last too much longer.
Here's the rear tire: Untitled by aaronwood77, on Flickr Untitled by aaronwood77, on Flickr And in the closeup, you can see that the trailing edge of the tread blocks is more heavily worn than the front. Also, from these it should be clear that I ride a lot on curvy roads... Parking in the garage today, after riding home in the rain, I noticed that the front contact patch is about half the width of the rear. With the front being smaller in diameter, it's also going to be a shorter contact patch front to back. Given the weight distribution on the bike, that means that the front tire has almost twice the contact pressure as the rear. Which would further the notion that the rears last twice as long as the fronts. As for riding style, I'm not one to hammer it coming out of a corner. Nice and smooth roll-on out of the corner. Probably 3rd gear most of the time, around 4-6krpm. In general, I'm not one for point-and-shoot on Hwy 9, but prefer to swoop through the corners carrying a bunch of speed, rolling on as I come out, rolling off before the corner, and back on again as I turn in to keep the suspension setup nicely. Front springs are 1kg/mm, rear is still stock, with lots of preload. But it still wallows back there a fair bit. I want to get a rear shock/spring upgrade from Jamie. Maybe gold-valve the front-end at the same time (although not looking forward to taking the forks apart to do that). Forks were last rebuilt about 2-3 years ago, around when the tires were done, not sure of the fluid used by Lindemann when they did the forks. This is my very boring commute (locations are approximate): Boulder Creek, CA to Redwood Shores Pkwy - Google Maps On that route, I likely spend nearly as much time leaned over as upright. That particular commute is new, it used to be more freeway riding: Boulder Creek, CA to Park Blvd - Google Maps
I usually run 38 front and 42 rear on my dunlops and they seem fine but I don't get much of a chance to get into twisties as of late.
So, the general consensus is to not worry about it, or maybe run more air up front on the sport demons?
I'm trying to get a hold of Jamie about a new rear shock, it rides pretty soft back there. I upped the pre-load again and that helped, but I'm running a ton of pre-load vs. stock (but then, I'm running double the stock front springs, too). But adding pre-load really doesn't solve the problem, even with a progressive rate spring (and I think it's a constant rate spring), the rate isn't going to change much from the preload.
You haven't mentioned how many miles are on the bike, how many sets of tires you've used up, or whether this problem is 'new' or not. I share the concern about the large front/rear difference in pressure. I generally run a 5-6lb difference (36F/42R on my '86 VFR w/CBR wheels and all the fixin's). Don't know if that helps; but getting a few of those answers might help us help you.
26K miles on the bike, I've put 10K of them on it. The previous dunlops wore similarly (although with much worse handling as a result). I've been running 32/42 as that's what the manual said. But then tires have changed a lot since 1986... Edit: Oh, and I did the steering head bearings a couple years ago as well. (maybe 5K miles ago?).
I remember watching a video on youtube about suspension setup and hearing the guy talk about the kind of wear your experiencing being due to improper damping settings. Do a good search on something like motorcycle tire wear and suspension settings...
Riding home from work on thurs, I bumped the front up to 38psi. I've ridden about 120 miles like that now. Very different handling. Quicker response to my inputs, less upset by road irregularities. The bime is definitely more vompised when envountering large bumps mid-turn. Skyline is pretty rough for most of the distance between 84 and hwy 9. But it really points out how soft the rear is. Definitely time to get that dealt with.
Honestly, I would say that your tire wear is not so much from pressure but rather from damping. Those wear patterns are a sign of too much high speed damping - something both your shock and forks have a problem with. I think if you address that aspect you will see a big improvement in handling and your tire wear will actually decrease quite a bit.
Jamie, I'm glad that you chimed in here (since we're working on that rear shock). I've been thinking it's time to at least change the fluid in the front forks. From reading the Race Tech Suspension book, and knowing what I know about the forks, the issue is running heavy fluid in damper-rod forks, when I'd be better served with cartridge forks? Would lighter weight fluid and gold valve emulators (to get the compression damping under control) help? I've been worried that the low-speed rebound is too soft, but since it's a progessive rate, I'm pretty much stuck with soft low-speed and hard high-speed damping. When Lindemann rebuilt the forks, I *believe* that all that was done was new seals, bushings, and the upgrade to 1kg/mm springs, with a matching weight fluid to control the stronger front springs. I have two bottles of Amsoil #10 shock/fork fluid, but that might be too thin ( cross-references to RaceTech's US2 ), but RaceTech's website is recommending 15w fluid. What's your recommendation? At the moment, I don't think I want to get too crazy with the front-end. New fluid is about what I have time to do, gold valve emulators are going to be trickier to find time for (and still won't give me anything other than fixed orifice rebound damping).
Also, after a week at 38psi up front instead of 32psi, the handling has been much improved (although noticeably sharper). Does anyone know why the vin tag and FSM state 32/42 ? The weight distribution isn't *that* rear biased.
Honestly, so long as you have damping rods in there you are going to have problems. If you are considering an upgrade to emulators I would suggest waiting until that time before doing anything else. Damping rods will always have too little low speed and too much high speed damping - nothing you can do about that. Tire pressue has more to do with size and construction and not really weight bias. I'd say run whatever pressure that seems to work best for you!
I thought that the emulators wouldn't help with rebound damping, just give the ability to run linear or digressive compression damping. The Lee Parks/Race Tech suspension book was a good read for giving me background (but I don't have the experience to know what really works on _these_ bikes. I assume that a new rear shock is still a good idea, though.
