What's the Deal With Motorcycle Tire Sizes?
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- čas přidán 12. 07. 2024
- With constant snow storms for the past week and a half, I've had trouble getting out for rides. Instead I've been shopping for tires... and deciphering the enigmatic nonsense that makes up their sizes.
I picked up the iconic dual sport combo - Dunlop D606 rear tire, and Pirelli MT21 front. Looking forward to putting them on.
**One thing to note that I didn't mention in the video - If you change the size of your rear tire, it's going to affect your speedometer and torque. For instance, since this D606 is a little bigger than the stock rear tire, each rotation of the axle is going to move me a little farther than it did before, which affects the speedo. Also, it's going to take a little more torque to get that bigger tire spinning. It's possible that I'll want to change the rear sprocket to something a little bigger to compensate for the change.
Below are Amazon links to the D606 and MT21 tires I'm talking about in the video. I am an Amazon affiliate, so I'll get a bit of a kickback if you use these links. They also happen to be a couple dollars cheaper here than most places I've looked:
Dunlop D606 (Rear):
amzn.to/3WHlH97
Pirelli MT21 (Front):
amzn.to/3vx80Ol
Here is a link to the reference table for determining weight and speed specs (Hosted at Rocky Mountain ATV's site):
www.rockymountainatvmc.com/do...
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Great Video. There is a little more that you didn't cover. 1 - The increased wheel diameter will change the qorque or gearing of the bike slightly. You could do some maths to calculate this. 2 - The stock speedo has been calibrated from the stock diameter tyre. This may change the speedo reading again depending on where the sensor is. Again, some maths required to see if this is significant, although I don't expect so. and finally you did cover that the width and gap to fitment is really important. Actually it may all fit and seem fine. But the larger diameter could foul on body work when you completely bottom the wheels out, say, full gear and hit a large dip that bottoms out your suspension. So maybe some rubbing under the front or rear fender. I haven't done any research to see if that's the case. You will see of hear the evidence of this later on. Overall, thanks for taking us on your (and ours) learning journey.
Lots of good info here...very helpful. Thank you
Glad it was helpful!
Great video, lots to think about.
Thanks for the feedback!
Thanks. Knowing is half the battle.
This was a good explanation! Thanks for doing the math for me on the same sized Shinko 804/805 set I’ve been enjoying. Would like to see the suspension geometry change for this example and you could talk about the theoretical effect as well as how it felt.
To stay legal when on the road, the new tire cannot have a lower Weight rating or Speed rating , at least that is the case where I live.
Good Vid
Good point. I don’t believe that’s the case here in Utah, but these tires are rated for both more weight and faster speed than stock 👍
Excellent, as usual. Thank you for that and other videos. Clear, well prepared, and conveyed in a friendly and humble manner. I finally got explained and understood what that second number means 👍
Glad it was helpful. For some reason it took a long time for that ratio thing to click with me.
I had to leave this comment right away . (I love your WTF comment at the beginning ) I just laughed .
Great video
Excellent video and tutorial Tyler. And good combination on tyres.
And cool shop there. Especially the desert sled.
Thanks Dick! Unfortunately, it’s not my garage behind me - just a green screen with a cool photo.
Thanks your explanation helped alot.
Glad it helped!
Great info, thanks! I'm about ready to replace the rear tire on my 300 Rally too.
Good luck with it!
Great video!!! Can't wait to get my 2022 CRF300L!
Thanks! Hope you get your 300L soon!
Many variables..for that reason I've just stuck with stock sizing F & R. 👍
Always a smart choice 👍
the 90/90-21 it will make the fork work at a more closed angle 👍
( and different feeling ride handling ) compared to stock ( 80/100-21 )
The different rear tyre (compared to stock) can change the "gear ratio" just like a different sprocket (teeth)
ciao ! (sorry for my english)
I’m anxious to try it out. Hopefully once I get these mounted the snow will stop coming down for a few minutes 😂
Very good...so the next video I hope to see is these tires on your bike! I have the 120/90 on the rear of my Rally and I also changed the rear sprocket to a 45 tooth (stock is 40)...it was absolutely necessary to re-gear the bike to accommodate the larger tire, otherwise the engine would annoyingly lug at the bottom end of 2nd gear...ride your bike right after you do this swap and you'll see what I mean. I couldn't stand it. 43 teeth will get you back to stock but I wanted even more low end torque...now that "area" between 1st and 2nd gear is perfect, IMO. For people that will ride the bike a lot on the roads in 6th gear at high speeds, go with the 43 tooth if you get the larger tire. Curious to hear your impressions and see what you do in this regard...
Thanks for the tip! I’ll definitely keep an eye on it when I do the swap. I didn’t even think about that, so I really appreciate the comment 👍
@@mtn2008 Most likely - depending on the change. I think going up 5 teeth in the back would probably require a new chain. Might be able to get away with 3 more teeth in the back with the stock chain, but I'm not sure.
HIi nice video ? just for info could you just confirm the size of the D606 rear you use !
Thanks - The size I'm using on the D606 is 120/90-18. There's a link in the description if you're looking for one.
I think you will feel like Graham Jarvis with your new tires ,over the stock IRCs. What is the vintage bike behind you on your left?
Unfortunately, what's behind me is a green screen 😂 I figured a picture of a cool garage would be more interesting to look at than my blank wall.
Well done on a very worthwhile video - what's the reason with the Dunlop rear/Pirelli front rather than dunlops front and rear?
People say the D606 in the front tends to wander, and the MT21 is more precise. I’ve never tried the D606 personally though, I just trusted the general consensus when purchasing this combo.
@@HighDesertHills Thanks for the explanation - good content you're doing here - keep it up!
I may be wrong, but I think a 90/90-21 is narrower than a 100/80-21. You said it is wider. Changing tyre sizes can also effect the accuracy of your speedo which I think runs off the gearbox. On my F650GS BMW my speedo over-read when I had road tyres on. When I put duel sport tyres on with a much deeper tread, it didn't.
The sizing on stock is 80/100, not 100/80. So 90/90 is a bit wider.
Also, thanks for the reminder about the tire size affecting the speedo. I really wish I would have mentioned that in the video.
I may be wrong but I believe the tires that have the standard inch widths are considered 100% aspect ratio if they are .0 or .5 but low profile if they are .1 or .6 and this detail makes things even murkier lol
Haha, good to know. Though I believe low profile tires are typically radials for street bikes, so I shouldn’t have to clutter my brain with yet one more odd piece of sizing data 😂
CRF takes speed from the rear tyre and I think from the gears so use GPS to know the difference if you change.
Studded Winter Tyres on my Rally now
90/80 21
and
110/80 18
I have some videos but not on a ride. Should buy some camera for that. Only filmed with a phone.
On my rat custom I use
DARK SIDE = car rear tyre.
Yeah, I really should have mentioned in the video that changing the tire size can affect the speedometer. Thanks for the reminder - I’ll add a note about that in the description.
And that’s awesome that you’re doing the car tire thing 🙂. I watched F9’s video about that a while ago. Didn’t even know it was possible before that.
@@HighDesertHills it is 3th Dark Side now on that rat chopper.
Dark side works just fine. There is even more friction and surface area. But maybe not so good idea with these Rally bikes :)
Front wheel on the rat chopper is 90/90 21" Michelin Sirac. And with the Dark Side works great even on the gravel roads. Waiting for the summer for that fun.
this is the only video you need to understand the stupid math of tyre sizes......would have been great if you talked about rim sizes too
Thanks! And good point about rim sizes.