So I recently came back to the fold, bought a '19 R1250RS with a mere 12000kms (with all the goodies including factory panniers), and I'm again enjoying the heck out of it.
I do feel though that with the heaps of torque this bike forces onto the rear wheel, that it might make more sense having a 190 back there (it does tend to get a little squirmy when you yank the throttle open) and let's be honest, the 180 looks skinny on a "sport bike".
So the questions are ...
Will it fit without rubbing?
Will it negatively affect the handling?
You'd have to stick to a 55 profile, which makes it slightly higher and the speedo slightly slower, can this be corrected electronically somehow?
Insert forgotten questions here.
What do you guys think?
Thanks,
R
2019 R1250RS Black, 13k kms, Pilot Road 5 (front) 4 (Rear), All the bells & whistles, Factory Panniers
ex 2011 Honda VFR1200F DCT, Red, Road Smart 4, ABS, Factory Panniers, Powerbronze Screen
ex 2018 R1200RS Lupin Blue, 25k kms, Pirelli Angel GT Front & Rear, ESA, Gear Shift Assist Pro, Givi Panniers
A friend has run a 190 rear on his '16 RS without apparent problems. He ordered the tire online and doesn't know if he ordered wrong or was sent wrong, so he put it on anyway. You can postulate about the negative effects but unless you push to the limits you may never feel the difference.
It might be different in South Africa, but here in the UK you'd be advised to declare the non-standard tyre size to your insurance company, otherwise they might refuse to meet a claim if they could pin it in any way on the tyre.
(01-12-2025, 11:52 PM)rules Wrote: I very much doubt they would look any further than tread depth, unless of course you go way over or under size (something obvious).
In most instances I'm sure you're right. However, although the chances may be very small, you might end up crippling a child. If an insurance company is faced with paying a multi-million pound/dollar award they will find any excuse not to pay. Sure, you should be able to argue that the size of the tyre did not contribute to the accident, if indeed it didn't, but why take even the slightest risk of crippling debt for the rest of your life in order to save an entry on your insurance form and perhaps peanuts in extra premium?
01-22-2025, 02:14 PM (This post was last modified: 01-22-2025, 02:19 PM by mspratz.)
I would not change to a 190 tire. The 180 tire has plenty of grip, and a wider tire requires greater lean angle for a given corner at a given speed. On page 107 of Motorcycle Dynamics by Vittore Cossalter: "...the use of wider tires forces the rider to use greater lean angles [than with narrower tires]...".
There is a fairly simple formula to calculate the lean angle required for a given speed and turn radius. This formula calculates the lean angle for a line between the center of the tire's contact patch and the center of gravity of the motorcyle+rider. However, as the bike leans into the corner the contact patch moves over onto the side of the tire. The wider the tire, the further the contact patch moves to the side, and so the true lean angle (of the centerline of the bike) is greater.
Interestingly, another side effect is that the required lean angle is also greater with a lower center of gravity. Honda found this out the hard way back in the day. To lower the COG, they designed a 500cc 2-stroke GP race bike with the fuel tank under the engine and the expansion chambers over the top of the engine. It was a total failure because it just would not turn. Everyone learned that road race bikes need a high center of gravity.
Excellent points Michael. The wider tire offers a larger contact patch, which *could* result in greater grip for the same lean angle. If the contact patch with the standard tire width is sufficient, then going to a wider tire is unnecessary, unless it is for appearance.
Regards,
Grumpy Goat 2016 BMW R1200RS 2023 Triumph Tiger 900 Rally Pro
(01-22-2025, 02:14 PM)mspratz Wrote: I would not change to a 190 tire. The 180 tire has plenty of grip, and a wider tire requires greater lean angle for a given corner at a given speed. On page 107 of Motorcycle Dynamics by Vittore Cossalter: "...the use of wider tires forces the rider to use greater lean angles [than with narrower tires]...".
There is a fairly simple formula to calculate the lean angle required for a given speed and turn radius. This formula calculates the lean angle for a line between the center of the tire's contact patch and the center of gravity of the motorcyle+rider. However, as the bike leans into the corner the contact patch moves over onto the side of the tire. The wider the tire, the further the contact patch moves to the side, and so the true lean angle (of the centerline of the bike) is greater.
Interestingly, another side effect is that the required lean angle is also greater with a lower center of gravity. Honda found this out the hard way back in the day. To lower the COG, they designed a 500cc 2-stroke GP race bike with the fuel tank under the engine and the expansion chambers over the top of the engine. It was a total failure because it just would not turn. Everyone learned that road race bikes need a high center of gravity.
Now that is an answer and a half, and makes perfect sense. Thanks!
So what I need to do is wear this Michellin out quicker and fit a RoadSmart 4
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2019 R1250RS Black, 13k kms, Pilot Road 5 (front) 4 (Rear), All the bells & whistles, Factory Panniers
ex 2011 Honda VFR1200F DCT, Red, Road Smart 4, ABS, Factory Panniers, Powerbronze Screen
ex 2018 R1200RS Lupin Blue, 25k kms, Pirelli Angel GT Front & Rear, ESA, Gear Shift Assist Pro, Givi Panniers
This may have some random relevance to the discussion, even though the numbers are different.
My 92 900SS came from the factory with a 170/60 rear tire. I probably went through 3 tires, staying with the stock sizing. Approaching my second track day I spooned on some relatively sticky Metzeler Rennsports and stepped up to a 180/55. By then most bikes with a 5.5"- 6" rim were already fitted with that size anyway. Most of what I had researched up until that point suggested it could possibly increase the input effort required at tip in and fast left to right transitions (the Ducati, generally, already steered like a truck). Surprisingly I found the challenges I worried about didn't exist. In fact the bike was much easier steering in all aspects of that track day and then the street miles it took to wear them out. Turns out the crown profile of those tires made all of the difference, regardless of size.
I had the opposite experience with my '96 900SS. It came with a 170 Dunlop tire mounted on the 5.5" wheel. When that needed a change I went with a 180 Michelin since the wheel should take it. I noticed more effort on turn in right away. This is purely anecdotal since I was going from a worn tire to new and a different brand pair which could have skewed the results. From then on I used 170"s. That was also going on 20 years ago.
Duckbubbles, those Rennsports were a medium compound track tire with a noticable peaked crown with heavy drop off near the sidewalls. Quick steering with a large contact patch when cranked over. As my faded recollection goes, the input effort returned as I wore them down.
