Why don't my 24 inch tyres fit my 24 inch wheels,

[one-eyed_jim]

Odd that they would sell slightly different wheel variants, surely that's not cost effective?

The problem is that there isn't a single 24" rim standard that takes both high-performance road tyres and fatter, more practical tyres. By supplying two different wheel variants they can reach a broader market with the same basic bike.

Would these tyres be any use?

No, they're yet another 24" standard - 540mm ETRTO. See here.

I'm still a little confused by this tbh, but I guess it explains why some tyres are hard to get on to a rim when others slip on easily.

That's another issue, and more a question of different rim and tyre manufacturers having different ideas of what constitutes proper fit.

I didn't know about all this ETRTO and that 24 inch doesn't mean 24 inch. It's a learning curve I was not expecting.

You don't have to stray far from the mainstream before issues like this start appearing. Even nominal 26" standards come in many flavours: 650c (571mm) for triathlon and small racing bikes; 26 x 1 3/8" (590mm) for old English roadsters; 650B (584mm) for old French touring bikes ...

The ETRTO number is always the one to check. It's just a shame it's not always listed!

 

[one-eyed_jim]

Spent some time googling and found this tyre which is listed as a 25 inch but has an ETRTO of 520. Adding to my confusion, but would this be the right or wrong size?

It's the right ETRTO, so in principle it will fit your rim. Width-wise it's unlikely to be a great match though. At low pressures, fat tyres tend to wallow and squirm on very narrow rims. At high pressures, they put a lot of strain on the rim walls. On the other hand, you could try a pair and see if you like them: it would be an inexpensive experiment.

The 25" designation comes from the overall diameter of the tyre - a bit like calling fat 700c tyres 29". 520mm + 57mm +57mm = 634mm = 24.96"

 

[ishaw]

Thanks for all the help. I was trying to find something I could run at slightly lower pressure for comfort on the commute as with the 1 inch tyres, you feel everything and they don't seem to have much room to be run lower.

I will measure up to see if the fat tyres will fit the frame, as you say it might not be an expensive experiment. I want to keep the weight down though.

I guess I have some 'spare' tyres now. Doh!

 

[one-eyed_jim]

I will measure up to see if the fat tyres will fit the frame

Yeah, I think that may be the sticking point in your case. I don't know which Airnimal you have, but there doesn't look to be a great deal of clearance between the chainstays.

Here's another possible option. This dapper fellow has a pair of slim nobblies that may be Specialized Spanky 24" 520-32 tyres. I couldn't find any for sale in a quick google though.

Have you considered a suspension seatpost?

 

[ishaw]

The seatpost is another sticking point as it's 30.2 so not that standard and shimming isn't really an option as the seat post is in two sections to help with the fold dimensions.

 

[danson67]

The ETRTO number is always the one to check. It's just a shame it's not always listed!

Nice to see that I'm not the only ETRTO obsessive around here

I'm still a little confused by this tbh, but I guess it explains why some tyres are hard to get on to a rim when others slip on easily.

According to Schwalbe's Technical Document, P21:

"Rims can have a diameter tolerance of ± 0.5 mm. In addition, each rim flange height can also have a tolerance of ± 0.5 mm. These figures add up to a total diameter tolerance of ± 1.5 mm, or 4.7 mm over the circumference. This corresponds to a maximum possible circumferential difference of 9.4 mm between the largest and the smallest rim."

Presumably the tyres themselves have similar manufacturing tolerances, so you could have a fit like a stick in a bucket or tight as you like...

All the best,

 

[ishaw]

Thanks for all the input. Looks like the panaracer it is shod with are the only available tyre. There is that rather fat tyre and I think it would fit the frame and forks but it would be massive on the rims so I think I can discount that. As this is a commuter first and foremost I guess it's fine for now, annoying that I have tyres and tubes that I can't use but perhaps this is an opportunity to build some wheels using 507 rims and either a spare set of xt or hope hubs that are currently kicking about doing nothing.

As I'm an amateur wheel builder at best, anyone got any rim suggestions? Spoke size will be next on the list.

As an aside, the bike rides really well and it may see more than just road use so a more burly wheelset might actually be useful and result in a few bikes leaving the fold If this can truly become a versatile beast.

 

[danson67]

Re:

Looks like the panaracer it is shod with are the only available tyre

Not quite...there's a similar tyre from CST (Cheng Shin/Primo) and the Schwalbe Durano comes in 23-520, too, so there is some life in the size still.
I can get both if you need them in the future.

All the best,

 

[ishaw]

Thanks. The durano is narrower than the panaracer, was looking to find a tyre allowing me to have more of a cushion Without risk of dining the rims on the mean streets of London. Further down the line some off road nobblies might come in handy too.

Tell me more about the cst tyres, I've not come across these during my many hours of googling.

 

[danson67]

It's a file tread lightish tyre in 25-520 which was used on recumbent handcycles about 10 years ago.
They've all moved over to 559 or 571 these days, but Cheng Shin (CST) still have one in that size.

It seems to be labelled CST Road King these days. Here are some at a Taiwanese supplier.
CST part number: C-739-1. 1000 Taiwan dollars each, about £21.
Or here for $500 TDollars on some sort of Taiwanese eBay.



We have about 6 slightly crispy ones in stock, grey tread with beige skinwall 235g and some proper sized Presta valve inners.

All the best,