Minimum Rim Width 2.8, 3.0, 3.25, 3.8?

PHeller · Oct 23, 2017

I've been running 275x2.6 tires for about a year now on my comparatively narrow 25mm internal rims. Aside from some tricky air pressure and not so fun squirming after larger drops, nothing really bad has happened with this combo.

I've got a new frame now, one with 96mm between chainstays, so I could comfortably fit a 85mm tire in the back. Thing is, I don't want a dedicated Plus wheelset. I want the ability to run 275x2.4 tires or 275x3.5 or (3.8) tires. So I wondered, is there some way of comparing numbers to determine what tire-to-rim-ratio I might currently be accustomed to, versus what is the max tire I could run on a 35mm internal rim?

If we convert 2.6" to mm, we get 66mm, divide that by 25mm (my current rim width) and we get a tire-to-rim-ratio (TTRR) of 2.64. The tire is roughly 2.64 times wider than the rim.

So, we can extrapolate that and say something like a 3.8 tire on a 35mm rim is TTRR of 2.74. Not that much worse.

While running a 3.8" tires on a 35mm rim wouldn't be ideal, the industry has long been running 2.3 tires (58mm) on 20mm internal rims, resulting in a TTRR of 2.9! We're already quite accustomed to big tires on little rims.

But, all of this is just numbers and theory, and so I'd like to get some feedback. For purposes of safety (not performance) what is minimum rim width you'd run on a 3", 3.2", or 3.8" tire?

I know we say that these tires perform better with wider rims, but from a safety standpoint, can we adjust tire width to fit a specific frame by running narrower or wider rims? Of course the other factor is that of tire selection. It may be easier to get a wider rim to use with common 3" tires (and get full 3" width) than to use narrow rims with relatively less common 3.25 or 3.8" tires (and pull the tire to a narrower 3.5").

Here's Bike Radar's take on the subject.

chelboed · Oct 23, 2017

If you have a set of 2.4" tires and 3.8" tires and only use 1x rim to run either...you're always going to be suboptimal.

A 3" tire with an i40 is as narrow as I'd wanna go and there's no way I'd run a 2.4" tire on that.

Impetus · Oct 23, 2017

It seems the industry is still sorting this out.

Maxxis says nothing narrower than i40 for a 3.0 (per the tag on the tires)
Stan's says i32 is good for 2.8, and i34 is fine for 3.0 (per the website)
Jones Bikes says i45-i50 is really nice for 2.4's (taken from somewhere on his site FAQ)

I personally think i40 is good for 3.0s. I have i43s and love them, but when I mounted a 2.4 to it, it went on fine, but was too square for my liking. I actually began my plus riding with 3.0s on i30s and wasn't super impressed. I'm a fan of wider is better, other's prefer narower.

I suspect that in the near future we'll start to hone in on an accepted ratio of tire/rim as the OP mentioned.

If I had to guess, I think that ratio will eventually fall between 1.8 and 2.1
For reference, that's between i36 and i43 for a 3.0.

I also have run 2.6's on i30 and thought it was really nice, but I like real plus tires.

mikesee · Oct 23, 2017

The answer is always going to be "It depends". And the dependencies are your height/weight/riding style, your preferences, your past, present, and future hang-ups, the types of trails you ride, the trail/soil/snow conditions, preferred tire pressures (actual vs. measured), casing construction, and, of course, angle of the dangle.

"The industry" hasn't sorted this out, and truthfully won't. Too many options, too many people, too many preferences.

bdundee · Oct 23, 2017

mikesee said:
The answer is always going to be "It depends". And the dependencies are your height/weight/riding style, your preferences, your past, present, and future hang-ups, the types of trails you ride, the trail/soil/snow conditions, preferred tire pressures (actual vs. measured), casing construction, and, of course, angle of the dangle.

"The industry" hasn't sorted this out, and truthfully won't. Too many options, too many people, too many preferences.

i.e. when in doubt by a set of each from Lace Mine 29 - Big Bicycle Wheels

mikesee · Oct 23, 2017

bdundee said:
i.e. when in doubt by a set of each from Lace Mine 29 - Big Bicycle Wheels

Doing so will also cure cancer.

PHeller · Oct 23, 2017

bdundee said:
i.e. when in doubt by a set of each from Lace Mine 29 - Big Bicycle Wheels

I wouldn't be asking this question if I had that kind of money. I'd be out riding my multiple wheelsets!

Steel Calf · Oct 24, 2017

PHeller said:
If we convert 2.6" to mm, we get 66mm, divide that by 25mm (my current rim width) and we get a tire-to-rim-ratio (TTRR) of 2.64. The tire is roughly 2.64 times wider than the rim.

So, we can extrapolate that and say something like a 3.8 tire on a 35mm rim is TTRR of 2.74. Not that much worse.

While running a 3.8" tires on a 35mm rim wouldn't be ideal, the industry has long been running 2.3 tires (58mm) on 20mm internal rims, resulting in a TTRR of 2.9! We're already quite accustomed to big tires on little rims.

Your math of a linear growth relationship between tire width and rim width only works out if assuming that wider tires scale in every way "bigger", e.g. more volume + thicker casting. However in reality plus tires do have a significantly higher air volume surrounded by a very thin casting to keep weight increase at an acceptable range. In order to compensate the stiffness disadvantage of thin sidewalls you need an overproportional wider rim to support the tire or it will buckle under heavy loads when cornering hard. 2.4 tires still work ok on 22.5-25mm rims, a 2.6 tire will need at least a 30mm rim and a 3.0 already needs a 45mm rim, so as you can see required rim width grows much more than the actual tire width.

Theoretically you could run a 3.8" on a 35mm rim with higher air pressures to stabilise the casting but it will nullify the grip advantage and lead to a far worse problem: The bigger air volume of the plus tire acts as an undamped airspring due to its thin casting and bounces off obstacles like a basketball. Imagine I double your fork travel but equally turn down rebound damping - how would that work out for you?

Either way I'd get a 35mm wheelset which should be good for 2.5 - 2.8 tires without adding too much weight. Everything above is a failed attempt to outsmart physics and won't stay in the (mass-)market much longer for obvious reasons.

phreeky · Oct 24, 2017

Opinions are like arseholes, but here is mine (opinion):
- 29mm IW rims are super common and good for 2.3-2.6, and I've found 2.8 OK on them too.
- 35mm would therefore step up a bit and prob be 2.5-3.0, however I'm not sure 2.3s would be too nice on them
- All of them have an element of uncertainty, and keep in mind that plenty of Maxxis 2.3s will measure at 2.2" and Schwalbe 2.3s at 2.4".

PHeller · Oct 25, 2017

Funny,

I was just reading that American Classic Smokin Gun 40mm internal rims are were designed with 2.5-3.0 tires in mind.

I could probably be really happy with the variety of high-volume, low weight 2.4-2.5 tires on the market, as long as they'd fit my narrow chainstays with 40mm rims. Err, this would be on my big travel Meta, which would rarely be equipped with such a wheel.

Currently I've got a Specialized Slaughter 2.6 on 25mm internal rims that's about as big as I can go. I've run a worn Breakout 2.5 on the same rim and it's a hair smaller. I'd probably need to stick with 2.4's if I was going to run them on 40mm rims, which means I'll need some heavily reinforced rear tires.

The 40mm rims would spend most of their lives on my new hardtail which I think would be good fun 3.25" Crux or 3.5" Hodag.

Just J · Oct 25, 2017

I don’t really have any mathematics to back this up, only real world testing done mainly on my Waltworks Ultimate Warrior.

I run 3.8” Hodags on 45mm rims and find them to work nicely. True width is a smidge over 3.6” on those rims. I could go wider of course but for the time I use this setup my Arc 45 wheels are more than up to it.

When I built my first 29+ wheels I used 35mm rims (Arc 35) and they were fine with Chupacabra but I now use 45mm LB rims and the profile is much squarer and the tyres just work better in all instances.

I run 2.4 and 2.5WT tyres on 28mm Reynolds rims on my Pivot and really like them but I’ve also used them on my 30mm LB’s and 35mm wide Arc 35 rims where they are obviously only very slightly wider.

2.6 Schwalbes work very nicely on 36mm Ibis 741’s and I have also used 2.25” Bontrager SE4 tyres on those rims with success although the SE4’s are much wider than advertised.

Hope this helps a little bit.

prj71 · Oct 26, 2017

I'm trying a 2.8 rekon on a 50mm width rim right now. So far I like it and see no downside yet.

Sent from my SM-G900V using Tapatalk

202cycle · Oct 26, 2017

mikesee said:
The answer is always going to be "It depends". And the dependencies are your height/weight/riding style, your preferences, your past, present, and future hang-ups, the types of trails you ride, the trail/soil/snow conditions, preferred tire pressures (actual vs. measured), casing construction, and, of course, angle of the dangle.

"The industry" hasn't sorted this out, and truthfully won't. Too many options, too many people, too many preferences.

This my friends is THE answer. Obviously there will be combinations that are physically impossible, but everything in between depends on all those factors. There's a sweet spot for everyone.

wjphillips · Oct 26, 2017

Well, there have always been some "rules of thumb" to follow on this.

It's always been said that your tire width should not exceed 2x your rim width. For example, 19mm rim = max tire width of 38mm, etc...

Conversely, the tire width should never be smaller than your rim width. On a road bike, for example, a 23mm road slick should never be mounted to, say, a 25mm rim. Just common sense...

But ya, in a lot of cases (as is true with almost all the tire questions) the answer is going to be it depends. (see above).

Guest · Oct 26, 2017

Depends, yup got me some, and Depending on the day's ride, it shall dictate size and weight......of course that Depends.

xblitzkriegx · Oct 27, 2017

rim to tire width ratios for plus tires

3.0 tire on i50: 1.52
3.0 tire on i45: 1.68
3.0 tire on i40: 1.90
2.8 tire on i50: 1.42
2.8 tire on i45: 1.57
2.8 tire on i40: 1.77
2.8 tire on i35: 2.02
2.6 tire on i45: 1.46
2.6 tire on i40: 1.65
2.6 tire on i35: 1.88
2.6 tire on i30: 2.20

For comparison, here are common rim widths for normal tires:

2.4 tire on i30: 2.03
2.4 tire on i28: 2.17
2.4 tire on i25: 2.44
2.3 tire on i30: 1.93
2.3 tire on i28: 2.17
2.3 tire on i25: 2.44

keep in mind that plus tires have more air volume compared to regular tires. doing a straight comparison to regular tire ratios, a 3" tire should be on an i40, a 2.8" on an i35, and a 2.6 on an i30. imo, those should be minimums, and maximums will be dictated by tire design. imo, id add 5mm to each rim width for each tire and call that ideal. ie, 3" = i45, 2.8 = i40, 2.6 = i35.

wilson1417 · Oct 27, 2017

Maybe a better thread for this feedback...

Been riding 27.5+ 45i Scrapers with various WTB 3.0 tires.
Getting ready to build a new Wheelset and am torn between two rims.

WTB 45i Scrapers
DT Swiss 40i XM551

Love some thoughts from anyone who's ridden both or ridden 40i rims with 3.0 tires.
thanks

Rusk · Dec 13, 2017

wilson1417 said:
Maybe a better thread for this feedback...

Been riding 27.5+ 45i Scrapers with various WTB 3.0 tires.
Getting ready to build a new Wheelset and am torn between two rims.

WTB 45i Scrapers
DT Swiss 40i XM551

Love some thoughts from anyone who's ridden both or ridden 40i rims with 3.0 tires.
thanks

I am looking at the same two rims. Which way did you end up going?

IAMTHRILL · Jan 8, 2018

Barnetts Manual for rim measuring

This should help clear things up :thumbsup:

Determine size of new tire by one or all of
following choices:
[ ] Look on sidewall of tire or molded in edge of
tread for nominal size description. Enter
here: __________
[ ] Look on sidewall of tire or molded in edge of
tread for ISO size description. Enter here:________

38. [ ] Measure width from bead-to-bead (edge-toedge)
of tire (flattened as best possible) and
record width here: __________
Flattened width between beads
Cross -section of flattened tire
19.22 Flatten the tire and measure bead-to-bead to determine
flattened width.
39. [ ] Divide answer in step 38 by 2.5 to determine
"section width" and record answer
here: __________
40. [ ] Multiply rim inside width from step 37 by 1.4
to determine narrowest acceptable "section
width" and record answer here: __________
41. [ ] Multiply rim inside width from step 37 by
2.0 (road bikes) or 3.0 (MTBs) to determine
widest acceptable "section width" and
record answer here: __________
42. Check one of following choices:
[ ] Step 39 is included in range of steps 40 and
41, so tire width is ideal for rim.
[ ] Step 39 is outside of range of steps 40 and
41, so tire width is potentially unacceptable
for rim.

PHeller · Jan 8, 2018

Apparently Jeff Jones was experimenting with higher volume 2.4 tires on 50mm rims back in 2013 and still likes that setup today.

I think if I ended up building a new wheelset out of some old hubs that I've got, I'd probably go 45 or 50 rim width to be able to comfortably run a 3.8 tire, and still have the ability to run a 2.6 as well.

After this weekend's bikepacking trip and getting beat up on my hardtail, lower pressures would be nice.

I think 2.6 is as small I like going anymore (nearly all "small" 275 tires have been cleared out of my garage.)

I figure if I need a long-distance fast rolling setup I'll switch to my 29x2.4 Ardents.

Minimum Rim Width 2.8, 3.0, 3.25, 3.8?

PHeller

chelboed

Impetus

mikesee

bdundee

mikesee

PHeller

Steel Calf

phreeky

PHeller

Just J

prj71

202cycle

wjphillips

Guest

xblitzkriegx

wilson1417

Rusk

IAMTHRILL

PHeller

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