I've been very happily running fast wearing ultra-gripping Shinko 18" bias ply / cross ply tires for years on my friends' stock GS rims AND my 2.50-18 / 3.50-18 aftermarket D.I.D. & Sun wire spoke rims.
The last long ride on my Shinkos to visit my parents, I remember ripping it on backroads and being reminded of how much I loved the grip of these Shinko tires. Chuck Sr. pointed out that my tread depth was getting low for me taking off on a 10 day trip of mountain riding and camping all the way to Barber Vintage Motorcycle Festival in Alabama...
I figured what the heck, Shinko doesn't make a 130/80-18 (which fits a 3.50-18 rim on a GS-four the best), they only offer a taller 130/90-18 & sporty/wider 140/70-18,
So I figured I'd run some Pirelli Sport Demons this time around,even grippier than the beloved fast wearing Shinkos.
Pirelli = Out of stock until 2022...
I scrape the stator cover before I can get the 140/70 Shinko SR714 (on a 3.50 rim) to the edge of the tread. 130/80-18 is best on a 3.50 for the width of a GS750 & larger engine & it's cornering clearance, 130/90 is a bit tall and less sporty due to high sidewall but it'd work (Shinko 230 or 712).
Well... In searching for "130/80-18" tires, I found that the newest Continental Road Attack tires do come in these sizes!
So I dropped $290-ish on 130/80-18 & 100/90-18 RoadAttack3 radials...
First impressions. Rear is very sporty in profile, more of a V-shape vs smooth arcing radius tread profile. This gives far more contact patch leaned over vs upright.
The front seemed pretty narrow for a 100/90. Measures skinnier than same size Shinko, while the rear measures a very healthy & impressive width.
Rear is a refinement of a dual compound tire. It uses one rubber compound throughout so no transition between harder center tread rubber and softer sides, they cure the tire very carefully controlling the temperatures in middle vs sides, to allow portions to cure longer vs shorter, achieving a gradual durometer change for ultra soft sticky sides and longer wearing harder center.
First test rides, I noticed slightly less rear braking power before locking up while riding upright / not leaned over, a result of less upright traction on the rear vs my beloved Shinkos because of the sport cornering focused tread profile shape.
I tried to break loose the front on hard upright braking, only once on wet leafy pavement did I ever succeed.
Long 10 day road trip shows very little treadwear on the center of the rear, sides of tread look like a race bike tire or pencil eraser shavings...I was cookin' 'em pretty good pushing it in the mountain twisties.
It was a very wet road trip, we missed Tail of the Dragon completely due to torrential tropical storm rains while watching the radar on the Deal's Gap Motorcycle Resort WiFi... Rode most of Hellbender 28 before the torrents broke loose, however! Last 5 miles after the bridge/river & massive cliff faces turn on Rt 28, we got SOAKED...
I ripped most of the Cherohala Skyway pretty hard in the curves aside from the most wet/leafy/shaded areas. Ripped VA-16 Back of the Dragon 33 mile 3-mountain pass ultra tight twisty stretch real good, as well as US-421 the Snake, and portions of the Blue Ridge Parkway. US-58 the Mighty Python was wet and leafy both days but I got down a fair bit in some areas. That road is soooo nice & perfectly flowing but good & tight. Great link between WV-16/VA-16 Back of the Dragon, to Mt Rogers and then south out of Damascus VA into East TN to US421 "The Snake."
Tennessee 32, the tightest twisty road in the USA, was too tight to run hard for being wet leafy pavement. Many turns are so tight that the pavement stripe painting trucks couldn't make the radius and had to back up and paint an overlapping set of double center lines at the apex of many curves...lol
I've ridden it in the dry before, and most areas it's tough to hit 40-45mph in the short straights in between curves without race pace acceleration, and at that, hitting it real hard means 25-35mph top cornering speed blazing in the tight curves...until I looked at my speedo a few years back,I felt like I was doing 15mph ripping the tightest curves on TN-32, but speedo read 23-27mph when I did dare to take my eyes off the road for a split second to glance at my speedo...
These RoadAttack3 "Sport Touring" radials definitely check all the boxes for me to qualify as more sport than touring... The harder cured rear center tread rubber is the only thing "touring" about these tires.
I'm very pleased...
The Classic Attack radials get similar reviews although I don't believe they have the same harder cured center strip on the rear tread.
I dropped down to 18" front from 19" ages ago, & put on longer rear shocks, so my rake and trail have been steepened a bit for more aggressive cornering.
Going to these radials, the slight headshake that was caused by the quickened steering (only happens when I'd take hands off handlebars between 43-51mph on a 110/90-18 & 35-47mph on a 100/90-18), this was completely eliminated!
The radial carcass I noticed had very different tendencies vs bias ply or cross ply while I was mounting them. The rigidity is different, and they dont spring back as fast when deformed?
Cornering seemed to show me that they had a better compliance to the road surfaces, and perhaps a slightly smoother ride.
The only negative was at 85-95mph (on a closed course, of course!), while riding perpendicular to the prevailing winds I believe, & with fully stuffed Nelson-Rigg saddlebags, the drafts / air turbulence from semi trucks and large trucks occasionally induced a bit of annoying weave where the bike would undulate very slightly left and right rapidly for several seconds.
I was screwing with the back wheel alignment/chain tension mid trip and thought my gearbox (f'd shift forks) noise was possibly caused by chain misalignment, so I centered the rear wheel via chain adjusters by sighting the rear sprocket to the front. This may have put my tire slightly out of parallel, which could've caused this issue, but it also could be due to the carcass' radial construction vs GS750 un-braced frame rigidity, as well as the very skinny rear center tread contact patch with the bike upright, vs the front (34psi may've been too much for me@ 150lbs + luggage/gear, but I'd read to run a few psi more in radials so I was). Same wiggle tgat a GS550 gives on long 65mph sweepers leaned over hitting bumps or dips, which on a 550 is caused by the lack of two short pieces of tubing bracing the center spine of the frame behind the ignition coils. The 750 has braces there from the factory, but this was definitely some sort of frame flex springing back and forth issue caused by significant wind turbulence whipping the bike around, although my rear wheel alignment might have been cocked slightly sideways and also causing this, as I have had the bike up to very significantly high speeds (in test environments!) with bias supply tires and never had this issue, nor did I on the trip down but was not going as fast as it was mostly back roads.
Front to rear tires have to have a certain size relationship to handle properly. When you see retro bobbers/cruisers etc with similar / same size fat tires front and rear, this is a mismatch and not conducive to good sporty handling...the skinny upright contact patch of the nice & wide 130/80-18 may've been partly to blame? I should note that I didn't experience this on the first longer portions if the trip mostly on 2-lanes, only the interstate blast 600 miles directly home yesterday, and that was AFTER I was messing with chainline alignment vs rear wheel centering...
Could be a combination of all of the above including modern radial tires on a 1977 GS frame without the typical "OSS" performance bracing being added.
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