Is a 21" front tire better than a 19" front tire?
Guest: Bill
Episode Summary:
What if the right tire could transform your off-road motorcycle experience? Join me, Bret Tkacs, as I explore this question alongside fellow rider Bill, who is debating between a BMW 1250 GSA with a 19-inch wheel and a Triumph Rally Explorer with a 21-inch wheel. Together, we dissect how these choices impact performance on rugged terrains like gravel and rocks. We delve into how tire size affects bike suspension and handling for riders of different physiques.
The journey doesn't stop at tires. We also explore the challenges and joys of choosing the right off-road motorcycle, with a special focus on large adventure bikes like the BMW GS and Triumph Tiger. As we discuss the need for modifications, such as stock suspension adjustments and custom handlebars, you'll gain a better understanding of how to enhance stability and comfort on rugged terrains.
Full Transcript:
This is Bret Tkacs, and welcome back to Around the Wheel. Today I'm chatting with Bill. Bill is just a regular rider, like the rest of you guys, and happened to send me an email that was loaded with lots of conversation but had a very specific question that I thought all of you would be interested in. Bill, do you mind just reading that email to the listeners here?
Not at all, Bret, love your video series. I'm 6'4", 270 pounds. I currently ride a 2019 Scrambler XE. I want something bigger to handle all my motorcycle camping gear and my weight easier. I have a good lead on a 2023 BMW 1250 GSA. My only concern is the 19-inch tire for off-road. I know you put a 21-inch tire setup on your GSA. How bad would a 19-inch tire be for minimal off-road sometimes gnarly (rocks, stones, heavy gravel) if we were doing a BDR / Smoky 500? I run Motaz tires on my Scrambler. I also have a good lead on a 2023 Triumph Rally Explorer which comes with a 21-inch wheel. I understand the issue in low gear with the T-plane and I want to know your thoughts on tire size on the bikes. Cheers, Bill.
Perfect. Thank you, Bill. That really, I mean, there's a lot of stuff going on here. When I'm listening to your email and I'm thinking of everything from your height and weight, you know you're 270, you're 6'4". That makes a difference because at that point we're also talking about making suspension adjustments to, you know, if we really want the bike to be ideal and if you're discussing 19" versus 21", we're definitely talking about, how do you get the most out of that machine. So, before I get into the whole wide versus narrow options modifying a bike, power delivery, suspension, the type of suspension that both those bikes use, I'm going to answer that first initial question. The question was, you know, 19" versus 21", and how much of a difference does that make? And that one's actually a fairly easy answer for me.
For most people, this is a really common question, Bill. By the way, I get asked this a lot by email and at camps and everything else. And when you mention minimal off-road, my initial response to that is a 19 is fine. It's great. If all you're doing is gravel roads, service roads and you're touring, a 19" is a fantastic tire.
But you didn't stop there. You didn't just say minimal off-road, you also mentioned some very difficult and challenging terrain. And that's when we start really going, okay, what are we buying the tires for? Or the wheel size for, is it for the 90% or 95% of the riding or is it for the 5%? And we get that with tire selection where people go, hey, do I really need this knobby? I've got a 95.5 and I only ride off-road 5%. Well, it doesn't matter about how long, it's what kind of off-road. If that off-road is basically 95% paved and 5% because it's got gravel on it, then that's fine. But when we start talking about the difficulty, that's where the change is. So you mentioned you had watched one of the videos I made about the 21". What did you get out of that video? What was your questions left from that? Because I'm gonna, I'm gonna expand on this some more.
Well, I was kind of worried about my height and this kind of goes back into one of the other podcasts, the triangle when I didn't, I didn't want to put risers on my bike and I was trying to find um. So I've been really practicing riding with that, that natural triangle, as I, as I lean over the handlebars, I have 21 inch tires on my scrambler and when I come up to an obstacle I actually go over it pretty well because I think the axle is lined up with the top of the obstacle and so when I hit I have that good ramp up and then also I kind of just skim over the top once I'm up and over it.
Well, and this is where, if we just look at the math of a 21 versus a 19, it's pretty hard to argue that a 19 is that much better Right now. I'm just going to throw it out there right now A 19 is significantly better off-road. But it's not just about the axle height. Because we're raising the axle height, we're changing the rotational speed of the wheel and generally we're going to a narrower tire wheel and generally we're going to a narrower tire like a stock GS is a 120, where we're talking a 90-90 or 90-100 on that 21. So there's more to it than just the diameter of the wheel. But if we look at just the diameter, you're not really talking about much of a difference. You're only gaining about an inch in axle height because it split the difference between a 1921. And even if you're looking at the profiles of the tires and the tread and everything else, you really only come out about 25 millimeters of actual increase. But also you're changing the angle of crossing. So if you think about and I'm going to try to create a visual for anybody else that's listening to this as well as you but if you were to have a, let's just keep it square and just put an eight by eight obstacle that you're going to drive over and you roll your tire up to that obstacle and park it there and you take that point of contact, that top edge of that contact, and you were to draw a line directly down to the point of contact on the ground, the center of the tire. Basically, you know, drop a line straight down from the axle, you know, or plumb line down from the axle and you measure that angle of climb. If you make that a larger diameter wheel, that point of contact moves back away from the axle. That decreases your rate of climb. Does it make sense? It's not a lot, but it's a little bit. Then, on top of that, now you've also raised that axle height, so now your point of impact and center also increases. So there's all these little factors that go into play. It's not just about the axle height, it's about the impact and rotational. I said there's a lot of different elements about this and what happens is they add up. So these little minor changes add up to a pretty significant difference off-road.
The other one that really has to be accounted for is the width of the tire, and this comes into play when we're talking about cutting through mud or cutting through sand or any kind of a even like soft grass, where we're kind of, you know, barreling down into it. And you know we often hear I want a bigger tire because I want to float, I want to get up on top of stuff, and I did a video on that as well in here. I want a bigger tire because I want to float, I want to get up on top of stuff, and I did a video on that as well. And essentially what I found is that any modification to air pressure or tire pressure that we get by airing down or anything like that really didn't have a big effect on that. But even when you go from one tire to another, that's relatively small.
But what happens is it's not that you have float right, because those tires actually have about the same contact area. The difference is the narrow tire is long and narrow in its contact. Where the wider tires are going to be shorter in their contact but wider, you end up with the same surface area. So if you think about a float factor that a lot of people like to talk about, the float factor is really insignificant. If there's any difference at all, it's insignificant.
But what does change is that your tire is constantly going left and right, where you have that rake and trail that tries to recenter the balance of the motorcycle.
And if you have a narrower tire, it's kind of like trail braking, you know, when you that first edge of the tire pushes everything out of the way and the rest of that contact patch gets a free ride when, if you have a wider tire, it has to displace a lot more of that material to the sides, which causes greater resistance, and that's often why the bikes feel less stable.
So if you're going through sand and mud, you might find a wider tire kind of floats left and right a little more, where a 21, because it's also narrower will feel more stable going through. So there is some other effects that will help that stability, but primarily, a lot of it has to do with the width of the tire. So that's something to keep in mind. So if you think about 2021, it's, it's, you know it's, it's those two categories now on. Now, to make this more complicated, why not run a 100 on that 21 right? So that will bring that width of that tire down and in fact, that will make it actually perform better off-road. And, of course, that width that we narrow down to depends on the actual rim width. Right, there's a range of proper size when it comes to tires, and so that's always something we want to keep in mind.
Okay.
So the questions that we didn't get into. So, as we're talking about, the 2021 is also looking at suspension. You mentioned two bikes very specifically. We talked about the GS versus the Tiger 1200 Rally Explorer bike with occasional off-road direction, which is good because both of these are touring bikes. These are not dirt bikes. They're big.
I love riding my GS but it is a big touring bike.