Tyre Width v Rim Width.....

[Hacienda71]

I am currently running 35mm Land Cruisers on R380 Alexrims with a 15 mm internal diameter on my CAADX. They have been on for a couple of years and have been ridden on some reasonably gnarly ground and for quite a few miles with no issues. I was contemplating getting some lighter tyres as the Land Cruisers are not what you could describe as svelte.
Looking on a few online sites, some seem to indicate that a 35mm tyre is too big for that rim others don't. Is there a calculation that is generally accepted on rim tyre width combinations, or is it a bit of a suck it and see range?

 

[presta]

From Schwalbe technical info:

 

[Ajax Bay]

Sheldon would've said a max multiple of twice inner rim width is the limit for tire (sic) width which is a good rule of thumb.
So 'yes': 'generally accepted'.

 

[rogerzilla]

Rule of thumb for the perfect tyre is 2x internal rim width or 1.5x external width, so 30mm would be ideal. 35mm is ok but as wide as you would want to go. For low tyre pressures you can go much wider; MTBs could have 2.3" (58mm) tyres on rims not much above road bike width but, at 40psi, they won't blow off.

 

[fossyant]

I am currently running 35mm Land Cruisers on R380 Alexrims with a 15 mm internal diameter on my CAADX. They have been on for a couple of years and have been ridden on some reasonably gnarly ground and for quite a few miles with no issues. I was contemplating getting some lighter tyres as the Land Cruisers are not what you could describe as svelte.
Looking on a few online sites, some seem to indicate that a 35mm tyre is too big for that rim others don't. Is there a calculation that is generally accepted on rim tyre width combinations, or is it a bit of a suck it and see range?

I'm running 38mm's on my CX - standard old 2006 Aksium rims - External width 20mm and according to Mavic, max recommended 32mm and not to use the wheels on a CX bike

https://www.decathlon.co.uk/p/flex-bead-light-gravel-tyre-700x38-black/_/R-p-309510

 

[Ming the Merciless]

https://www.cyclinguk.org/cyclists-library/components/wheels-tyres/tyre-sizes

 

[Dogtrousers]

Sheldon has a chart. https://sheldonbrown.com/tire-sizing.html. Scroll down to "Width Considerations"

Your particular combination 15mm rim/35mm tyre is just outside the green range, but under the chart it says This chart may err a bit on the side of caution. Many cyclists use slightly wider tires with no problem. So you're OK

Here it is:

 

[Moodyman]

The charts posted upthread are good for understanding the safe range of tyre widths. But, they don’t tell you the optimum width for comfort or wheel protection.

As @rogerzilla posted, 1.5-1.75 x inner rim width is a the sweet spot. So, 15mm x 1.75 would equate to 26mm tyre.

 

[Ajax Bay]

Rule of thumb for the perfect tyre is 2x internal rim width

As @rogerzilla posted, 1.5-1.75 x inner rim width is a the sweet spot.

You are both making this up, which is fine, but not a 'general rule, widely accepted'.
And @Moodyman you are disagreeing with Roger: he say 2x; you say 1.5-1.75x (so not "as [he] posted".
"Perfect" "Sweet spot" Nope: it's a range, reflecting the different factors (eg comfort, rim/tube protection, contact area, surface) and their spectra.

 

[Hacienda71]

Cheers all.

The 35's I have on seem to have been fine and have been thoroughly tested, but given the various charts I will not go larger than that.
To be fair anything requiring bigger than a 35 mm I will be on the MTB anyway.
I also have a 2012 FS Stumpjumper which has very narrow rims which was the trend back then rather than today's wider rims. Will need to see if they fall into acceptable range on the various tables.

 

[Moodyman]

You are both making this up, which is fine, but not a 'general rule, widely accepted'.
And @Moodyman you are disagreeing with Roger: he say 2x; you say 1.5-1.75x (so not "as [he] posted".
"Perfect" "Sweet spot" Nope: it's a range, reflecting the different factors (eg comfort, rim/tube protection, contact area, surface) and their spectra.

I refer you to Sheldon:

 

[Ajax Bay]

The charts posted upthread are good for understanding the safe range of tyre widths. But, they don’t tell you the optimum width for comfort or wheel protection.
As @rogerzilla posted, 1.5-1.75 x inner rim width is a the sweet spot.

Where do you get 1.5-1.75 from Sheldon, whom I referenced in post #3 btw?
Whatever, Sheldon offers a decent range "A general guideline is that the tire width should be between 1.45/2.0 x the inner rim width.", not a "sweet spot".
@Dogtrousers accessed and shared the chart from Sheldon's page on this and I suggest it offers an excellent understanding of the safe range. One could deduce that the midpoint in that range will be 'sweet' but not sure the evidence is out there. Several of the factors are confounding: compromises have to be made (hence the merit of a range). Please share if you know of any.