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-   -   Downsizing tyre for low pressure straight rims? (https://www.bikeforums.net/classic-vintage/1125252-downsizing-tyre-low-pressure-straight-rims.html)

WillBradley1 10-17-17 06:36 AM

Downsizing tyre for low pressure straight rims?
 
Hey there,

I've had a problem with some old straight edge 26" 1 3/8 wheels on a 1960 DBS damecykel... Even riding on super low pressure and carefully centred, the bead of the tyre pops out regularly. It doesnt seem dangerous, I dont notice until I inspect it, but finally it ripped the bead of my rear (very cheap) tyre and its toast.

I know Im stupid riding on these ancient rims for my 25min commute everyday... But its my temporary bike while I restore my main road bike (and ideally until after winter)... Its not meant to be high performance bike... I fancy just keeping the original rims and I cant afford any major changes right now anyway so I was thinking whether just buying 26" 1 1/2 tyres could be a solution?

According to sheldon brown my 26 1 3/8 rims have a 590 mm, 26 1 1/2 tyres are 584 mm. I feel a 6mm tight fit could be perfect to keep them seated?

Anyone have any experience with interchanging tyre sizes? I used to have some road bike tyres that were there right size but near impossible to get on, Im almost feeling 6mm isnt much and I could get away with more? But really I have no idea!

Thanks

rhm 10-17-17 06:47 AM


Originally Posted by WillBradley1 (Post 19934580)
Hey there,

I've had a problem with some old straight edge 26" 1 3/8 wheels on a 1960 DBS damecykel... Even riding on super low pressure and carefully centred, the bead of the tyre pops out regularly. It doesnt seem dangerous, I dont notice until I inspect it, but finally it ripped the bead of my rear (very cheap) tyre and its toast.

I know Im stupid riding on these ancient rims for my 25min commute everyday... But its my temporary bike while I restore my main road bike (and ideally until after winter)... Its not meant to be high performance bike... I fancy just keeping the original rims and I cant afford any major changes right now anyway so I was thinking whether just buying 26" 1 1/2 tyres could be a solution?

According to sheldon brown my 26 1 3/8 rims have a 590 mm, 26 1 1/2 tyres are 584 mm. I feel a 6mm tight fit could be perfect to keep them seated?

Anyone have any experience with interchanging tyre sizes? I used to have some road bike tyres that were there right size but near impossible to get on, Im almost feeling 6mm isnt much and I could get away with more? But really I have no idea!

Thanks

No, you probably cannot get a 650b tire on a 650a rim. That 6 mm is too tight. If you do manage to get the tire on, you will never get it off. This has been tried many times and no, sorry, it is not the solution.

I wonder if you have the right tire now. Schwinn made an EA1 size rim and tire (597 mm) that for unclear reasons they labeled as if it were an EA3 or 650a rim and tire (590 mm). Perhaps you have a Schwinn size tire now? If so, then a proper 650a tire will solve your problem.

Alas it is also possible that the bead of your rim is damaged, in which case you will have no luck mounting tires safely.

Good luck!

WillBradley1 10-17-17 06:56 AM

Thanks for the reply. They are atleast marked the same dimensions for sure, but it was an incredibly sloppy fit. The tyres are just super cheap chinese ebay ones though so Im not suprised they ripped and I definatley wouldnt be suprised if they labelled it the wrong 26" sizing. I think there is about 6mm of movement before there inflated...

The quote "you will never get it off" seems rather appealing after having to put it back on maybe 10 times in the last month! Im hoping I can find a shop with a selection of vintage tyres and try some in there. I will post if I have any success.

WillBradley1 10-17-17 07:10 AM

Infact, Im sure the fit is correct sizing... When I first saw how lose the fit was I tired a pair of really crusty old original 26" 1 3/8 tyres off an old Raleigh I have and the fit was the same. Ive got a feeling its because the 1960 rims are just so old that was just how there meant to be. I mean, I was keeping them low pressure 65ish, but even thats probably high pressure for 1960.

Is the reason its not a solution just the fitting of them, or is there a dangourous factor to it? In the scenario you imagined where they were on but incredibly hard to get off, would that allow a safe high pressure of 90-100?

USAZorro 10-17-17 07:33 AM

Can you post a picture of the rim and any markings?

ThermionicScott 10-17-17 10:16 AM


Originally Posted by WillBradley1 (Post 19934646)
Infact, Im sure the fit is correct sizing... When I first saw how lose the fit was I tired a pair of really crusty old original 26" 1 3/8 tyres off an old Raleigh I have and the fit was the same. Ive got a feeling its because the 1960 rims are just so old that was just how there meant to be. I mean, I was keeping them low pressure 65ish, but even thats probably high pressure for 1960.

Is the reason its not a solution just the fitting of them, or is there a dangourous factor to it? In the scenario you imagined where they were on but incredibly hard to get off, would that allow a safe high pressure of 90-100?

Why would you want to pump them up to 90-100 psi anyway? If you want less rolling resistance, get better tires.

randyjawa 10-17-17 10:21 AM


They are atleast marked the same dimensions for sure, but it was an incredibly sloppy fit.
It has been my experience that you have to read the small print on the tires, when 26" units are involved. All 26" tires are not equal in size or diameter.

So, take a close look at the documentation on your old tires, assuming that you have kept them. Report all of the documented information here and then, perhaps, we can offer more specific help.

Lascauxcaveman 10-17-17 01:04 PM

There is often some variance in size between two different brands of the 'same size' tires. Same with rims. So one brand may fit a little tighter and solve your problem. The trick is finding which brand.

rhm 10-17-17 08:29 PM

I agree with Scott, you may be putting too much air in them. At my weight (under 170 lbs) I can run 35 mm tires much lower, maybe 40-46 psi in the rear, less in front). Tires that size don't need to go over 65 psi, and aren't made to.
There is a nifty table that shows you the ideal pressure for tires, based in diameter and load... If you're not familiar with it I'll find the link.

3alarmer 10-17-17 09:20 PM

.
...FWIW, Schwalbe used to make ad sell a 590 bead diameter tyre. Schwalbe tyres are notoriously tight to mount.

They are not particularly cheap, and you have to look online to order them. There are internet videos on how to mount a Schwalbe Marathon tyre the first time, that's how tight they are. The ones I've used roll relatively well and would make a good commute tyre.


EA3 or 650A
These tires have a bead-seat diameter of 23 1/4" (590mm) and are typically marked with 650A or EA3. The most common size is 26" x 1 3/8". These tires were used on department store 3-speed bikes, children's 10-speed bikes, and some Italian road bikes designed for smaller riders.
We suggest the affordable Kenda K40 Street 26 Inch Cruiser Tire (590) or the classy gumwall Michelin World Tour 26 Inch Tire 26 x 1 3/8 (35-590) to replace old EA3 tires.

https://www.biketiresdirect.com/olde...-sizes-article
Marathon HS 420 in 590

DELTA CRUISER HS 431 in 590

Insidious C. 10-18-17 12:01 AM

So, you've been commuting on "ancient rims?" Welcome, C&V brother! I once had a very cheap bike with steel 590 rims that was difficult to get the tire to fit evenly on. My daughters bike has alloy Nisi 590 rims. I've had better luck with those. The Marathon Plus tires currently mounted on these rims are stuck like glue.

WillBradley1 10-18-17 02:08 AM

2 Attachment(s)
Thanks for all the replies! Here are some photos of the old tire set up. Maybe I was trying to inflate them too much, Im not familiar with gauging pressures on feel and my pump doesnt have a dial. But its a poundshop pump so I just assumed it wasnt capable of too high pressures. And I probably shouldnt be commuting on this but I salvaged it and did a super cheap restoration of the poor bike, im now very fond of it and im currently living abroad and very poor so it has to do!

I am sure the rim is marked 26" 1 3/8. (its marked on the inside and I forgot to take a picture apologies). But I learnt the hard way about the different 26" sizes. I salvaged the bike with no front wheel, just a back wheel without a tire, so there were no old tires to compare it to. When I bought a new front rim hoop I happily just went off 26" and it was completely different, so I now am fully clued up on the plethora of 26" inch variations, the combination in the photos were meant to be correct.

It was urgent I sort this as a single hour walking commute is enough for this year, so yesterday after work I went to my local shop and pre-purchase borrowed a 584 low end schwalbe tire to just present to the 590 rim and scope out the fit. It look feasible so I went for it and with only alittle leverage at the end it was on like a dream! There was plenty of depth to the rim and its all very rounded and smooth so maybe its seated alittle deeply now but after all this **** I would call it a perfect fit!

Dont want to get too excited as its only made this mornings cycle in, but ill report back with some pictures after a week if its fully succesful.

Thanks for the replies :)


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