RadRover : how slim (Tires) can we go ?

Timpo

Well-Known Member
Yes you do need to adjust your tire diameter in your display. Always necessary when fiddling with tire diameters. 29" is for big tires like a 4.5-4.8. 28" is what I am using right now with 4.0" tires on that orange bike. Arrived at via measuring.
I believe 28, 700C and 29 are all the same. People just call them differently.
Though, I could be completely wrong, I know they're all interchangeable from my experience.
 

m@Robertson

Well-Known Member
Region
USA
I believe 28, 700C and 29 are all the same. People just call them differently.
Though, I could be completely wrong, I know they're all interchangeable from my experience.
The correct answer is yes, no and maybe. A '29er' is a 700C road bike rim in mtb width. 700C is not accurate as a diameter. Its 622mm using the metric ETRTO standard found on the side of the tire. In the EU, 28" is commonly referred to as equivalent to 700C but the ETRTO diameter is 635.

Here take a look at a Schwalbe tire page. Expand out its tire size section down at the bottom. You'll see 700C and 28" tires side by side. Look at the ETRTO measurements.


I also think you might be missing what the '29' means on the display: '29' on a 29er is used as a term referring to the outside diameter of the tire on that 700C/622 rim (29"). '29' on an ebike display is the same thing (unless your display manual says differently). So typically on your various KT, Bafang etc. DIY/aftermarket displays the value is always the measured outside diameter of the tire. This makes sense because of course our subject in this thread is about different outside tire diameters on the same wheel diameter.

Life is a lot simpler if you dispense with imperial measurements and instead go with the metric system. The ETRTO on the side of every tire is a lot more useful and generally less influenced by marketing. The first number is the width of the tire casing, and the second is the bead seat diameter of the rim/tire. Easier said than done I still think in imperial sizes myself but I refer to the ETRTO when I want to know for sure if something fits a bike frame or fork.

As for the 'maybe'... 28" tires are often close enough to fit without issues on a 700C rim despite the 622 vs. 635 issue. Or so I've heard. Not something I mess with, personally.
 
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m@Robertson

Well-Known Member
Region
USA
Well not likely, because 2.4- 2.6 tires are designed for 25mm to 40mm max.
So obviously RadRover's 80mm is too wide for optimal performance.
Well here's where the instruction manual ends and experience picks up. People do this all the time so what are the real world consequences? Reality is you can fudge things quite a lot and you'll be fine. Can you put a too big tire on a too narrow rim? Up to a point. Will there be consequences? Yes, ranging from 'totally unnoticeable' to 'tire falls off and you crash'. You need to know what you are getting yourself into via experience. If you don't, that chart gives you some guardrails, although personally I prefer the much more complete DT Swiss Tire Pressure and Dimension guide (which is still conservative, but a good starting point).


What about the reverse? Too wide of a rim for a too-small tire? Consequences will range from 'totally unnoticeable to 'tire does not seat on the rim and you crash'. Here again you need to have the experience to know what you are up against. In this case the internet is your friend as you can see plenty of folks who have done this as it is a very common thing to do. As I noted above, I personally took the extra (and unusual) step of using an oversized 3.0" tube to ensure the tube helped the tire hook into the rim with authority. Most folks don't take that extra step and it still works for them.
On the bold, in your opinion, would the "desired results" include things like minimized rolling resistance and a great ride? Would love to know more about how rim vs. tire width play here.
The desired results were ultra smooth rolling resistance on hard rubber. I loved the ability to lift and just coast for what seemed like forever, unpowered. Is that part of a great ride? Yes. But there were undesired results too. That higher pressure tire with minimal (albeit sufficient) sidewall had a whole lot less cushion, and it changed how the bike handled imperfect road surfaces dramatically. Remember an ebike goes faster than a bicycle. So you come up on things faster and impacts are magnified by speed. The wheel's strength was just fine (a hand built wheel using double-wall Weinmann rim with DT Champion 2.0 spokes and brass nipples, so thats quite a bit stronger than any machine-built Chinese wheel).

As I've said it is not something I would do again, but it is something I know plenty of people do and never regret.
 
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m@Robertson

Well-Known Member
Region
USA
Well not likely, because 2.4- 2.6 tires are designed for 25mm to 40mm max.
So obviously RadRover's 80mm is too wide for optimal performance.
Something to note: That chart you linked is not gospel. If you look at the DT Swiss chart, they use increments of "2.35" to 2.6" as the closest to your 2.4-2.6 range. For a 2.35 tire, the possible rim combinations range from 20mm to 51mm, where the 'possible' combinations are that range, but the 'ideal' combinations are 25-33mm. For a 2.6" tire, max possible are 23-51mm, with ideal being the same 25-33. Also if you have hookless rims the separate chart gives slightly different guidelines.

I had a 2.4" tire that fit my front 20", 19mm inside-width rim on my Bullitt just fine. Thats outside the guidelines, and I only did it because I was sort of stuck and had to, but I was surprised to see it worked fine (I replaced that wheel with one that was 33mm with a 27mm inside width).
blacksheep_cross_section.jpg


So the two charts are different in their recommendations, and experience differs as well. The point being these are not hard and fast design rules. Some judgment is in play here.

Also note the Rad 80mm rims you mention... 80mm is the advertised external (marketing) width. Thats different from their inner width which is what you use for measuring tire/rim compatibility. Inner width on an 80mm hook-bead rim is typically in the ballpark of 73mm. Subtract 2mm for each rim wall and 2mm for each of the hooks as a good WAG.
DHL80简图 72.png


So when figuring up stuff like this, if you don't know the INNER width and you want to do calcs, pull the tire off and get out your calipers.
 
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AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.

Struggling with something these charts aren't showing. I have to wonder if there's an assumption regarding the design of the tires? Consider for a second a Schwalbe Marathon with it's stiff sidewalls, and then a balloon type like a Schwalbe Super Moto-X. They both have outstanding reputations for our purposes, but I believe the 2 tires are like night and day regarding designs. The Marathon is an outstanding tire, that is generally run with twice the air pressure that the Super Moto-X (and some similar tires like the Big Apple) typically run. If you've ridden the same bike equipped both ways, the extra pressure run in the Marathons makes them feel like you're on a roller skate riding down a brick road. Remove that tire and install one of the balloon types (like the Super Moto-x X or Big Apple), and things are very noticeably smoother. Expansion joints and dried out cracked pavement area seem to disappear!

This is what I'm talking about when I say "ride". Talking about the amount of vibration transferred to you wrists and your back side as you ride on a paved road.... minimizing that vibration.

We've seen the note regarding too big a tire on a rim (the Bell shape) causing a stiff ride - assuming it would be a softer ride if the tire and rim were properly matched. So what about when taken to the extreme, where we're installing a 2.25" tire on an 80mm rim?
 
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Timpo

Well-Known Member
Struggling with something these charts aren't showing. I have to wonder if there's an assumption regarding the design of the tires? Consider for a second a Schwalbe Marathon with it's stiff sidewalls, and then a balloon type like a Schwalbe Super Moto-X. They both have outstanding reputations for our purposes, but I believe the 2 tires are like night and day regarding designs. The Marathon is an outstanding tire, that is generally run with twice the air pressure that the Super Moto-X (and some similar tires like the Big Apple) typically run. If you've ridden the same bike equipped both ways, the extra pressure run in the Marathons makes them feel like you're on a roller skate riding down a brick road. Remove that tire and install one of the balloon types (like the Super Moto-x X or Big Apple), and things are very noticeably smoother. Expansion joints and dried out cracked pavement area seem to disappear!

This is what I'm talking about when I say "ride". Talking about the amount of vibration transferred to you wrists and your back side as you ride on a paved road.... minimizing that vibration.
In my experience, no two tires are the same. Continental for example, I found they're way narrower than what's indicated on the sidewall.

I know it's obvious but if you really want to know for sure, contact the manufacture.
Call Schwalbe and say, "I can put 26 x 2.25 size Marathon Plus HS468 on Rad Rover's 80mm rim?" and they will tell you yes or no.
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
In my experience, no two tires are the same. Continental for example, I found they're way narrower than what's indicated on the sidewall.

I know it's obvious but if you really want to know for sure, contact the manufacture.
Call Schwalbe and say, "I can put 26 x 2.25 size Marathon Plus HS468 on Rad Rover's 80mm rim?" and they will tell you yes or no.
I think it pretty safe to assume what they're going to say. Where they'll stumble is the why.....
 

Kyogiro

Member
For now, I had to put my spare Jumbo Jim 4" on the front wheel because my Kenda tire gave out yesterday. Second puncture in less than a month and this one couldn't get fully sealed with my tubeless liquid sealant. So I decided to change the tire since I have to use my bike pretty much everyday. The stock Kenda tires lasted me about 2000 miles (3000 km, this one was really all used up) for rear and 2500 miles (4000 km, probably could have gone longer if I would have worked on (temporary) fixing the puncture) for the front.

I'll probably test 3 inch tires next time but those Schwalbe Jumbo Jim are rated for a long(er) lifespan.
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
Noteworthy, to save others the time to look, is the fact the Jumbo Jim is a knobby tire
 

m@Robertson

Well-Known Member
Region
USA
Struggling with something these charts aren't showing. I have to wonder if there's an assumption regarding the design of the tires? Consider for a second a Schwalbe Marathon with it's stiff sidewalls, and then a balloon type like a Schwalbe Super Moto-X. They both have outstanding reputations for our purposes, but I believe the 2 tires are like night and day regarding designs. The Marathon is an outstanding tire, that is generally run with twice the air pressure that the Super Moto-X (and some similar tires like the Big Apple) typically run. If you've ridden the same bike equipped both ways, the extra pressure run in the Marathons makes them feel like you're on a roller skate riding down a brick road. Remove that tire and install one of the balloon types (like the Super Moto-x X or Big Apple), and things are very noticeably smoother. Expansion joints and dried out cracked pavement area seem to disappear!

This is what I'm talking about when I say "ride". Talking about the amount of vibration transferred to you wrists and your back side as you ride on a paved road.... minimizing that vibration.

We've seen the note regarding too big a tire on a rim (the Bell shape) causing a stiff ride - assuming it would be a softer ride if the tire and rim were properly matched. So what about when taken to the extreme, where we're installing a 2.25" tire on an 80mm rim?
Well, you probably know what I am going to say on that. the ride will SUCK. Purely for the reason that there is not enough sidewall to do any level of cushioning, and you still have to inflate the tire to its higher pressure limit - or risk the sidewall not being sufficient to absorb an impact, which means your rims will take the beating directly. Net result is your body takes a pounding. My Super Moto X's on 80mm rims were *horrible*. But they were also wonderful on my Stumpjumper conversion and its Alexrims, which were, IIRC, 30mm internal. BTW the performance difference is the same for car tires. Use skinny little rubber band 30 series tires versus 50-series sidewalls and exactly the same things happen.

My Schwalbe Marathons in 700x35 (which is really a 37) were like rolling rocks. But the same tire in 26x2.00 is great (I keep it at 60 psi which is underneath its 75 max). Different bikes, different rims... this is a big part of why I have a pile of tires in my garage. Everything is different and you just have to try stuff and see.

In my experience, no two tires are the same. Continental for example, I found they're way narrower than what's indicated on the sidewall.
^^^ This. For sure. On both counts. Contis have a reputation for being undersized and I count on this when I use them in a build. But be advised they do stretch into their size in a few weeks - but are still commonly undersized a bit even after they stretch out. On my Luna Fixed, I counted on this undersizing to get them to fit into that small frame triangle and they worked great. On my Mongoose Envoy, the 26x2.15 tires were actually right on spec for the first time ever, which was a surprise. And those bigger tires (Contact Plus City flatproofs) were like rolling on rocks. I got rid of them in favor of 2.8" Vee Speedsters and loved the pillow-soft ride enough to live without the security net of the belts on the Contis.