Recumbent - Rim size?

I know i could post this in a different section, but i feel like i get better advice from my fellow recumbent riders and this is semi recumbent related. Sometime in the next few months I will need to change out my tires. Currently I have a 26x1.5 armadillo tire on the back and a primo 20x1.35 on the front. This is working ok now and I would like to keep the tires sizes the same when i get new ones (and this time the same brand also...i got this used). The rims are sun rims AT 18. I'm sure since im running these tires now with no problems (even though im sure these werent the stock tires) that it would be safe to say i could buy the same sizes again. Just to make sure before i shell out some money...how do i tell the rim size? or do i simply have to take the tire off and measure the rim?

also is there a brand someone would suggest for the new tires? and maybe suggest a size if different from what im using. Mostly city riding...some paved/lite dirt bike paths. If it matters i ride about 200 miles a month....might be more soon if i decide to go car free.

kevlar or not?

Thanks so much in advance :) also i got my computer/lights/mirror situation all worked out and its working great (posted a thread a few weeks ago) And i need a picture already so i can add it to the main thread :)

I know i could post this in a different section, but i feel like i get better advice from my fellow recumbent riders and this is semi recumbent related. Sometime in the next few months I will need to change out my tires. Currently I have a 26x1.5 armadillo tire on the back and a primo 20x1.35 on the front. This is working ok now and I would like to keep the tires sizes the same when i get new ones (and this time the same brand also...i got this used). The rims are sun rims AT 18. I'm sure since im running these tires now with no problems (even though im sure these werent the stock tires) that it would be safe to say i could buy the same sizes again. Just to make sure before i shell out some money...how do i tell the rim size? or do i simply have to take the tire off and measure the rim?



The best answer I can give you for tire size is to visit http://sheldonbrown.com/tyres.html

Sheldon Brown's (r.i.p.) is the most informative place I've ever been on tire sizes. Safest bet before shelling out $$ is if the tires are not definitively marked is to measure. I've seen 4 different sizes of 20" tires - not counting the width.

As far as kevlar or not, width.... those are more personal preferences on how you ride. I have a 20" (23-406) front with a 26" (28-559) rear and I went as skinny as I could (and highest pressure- lowest rolling resistance) without getting new rims as my riding is all roadway commuting.

For a 20 X 1.35 you could also put on a Schwalbe Marathon Plus. You could put a Marathon Plus on the back, too. Vittoria Randoneur tires are supposed to hold up well against flats.

Primo Comets with and without Kevlar belts come in 20x1.35(406) 20x1.5(406) and 26x1.5(559) for a matching look. I've been satisfied with Comets.

The tires are clearly marked as 20x1.35 and 26x1.5 My question was, basically is there a way to fit the wrong tires size on a rim? or should i assume that since my bike is running these tire sizes now that i could safely order the exact same sizes again and it would be fine?

Or do i need to measure the RIM size and look at some kind of chart on sheldons website?

My knee-jerk reaction is to say just order the same size tires as you have now. I would think it's pretty hard to mis-match a tire and rim.

However, if you wish to satisfy your curiosity read...http://sheldonbrown.com/rim-sizing.html
...to learn about measuring rim sizes

and then read....http://sheldonbrown.com/tyre-sizing.html#traditional ....to learn about tire
sizes.

Then if you still are concerned, measure.

I didn't realize that there was a difference in 20" tires and tried to get by with a 20 X 1 1/2 tube in a 20 X 1.5 tire.
Well as you probably know, 20 X 1 1/2 is a 451mm and a 20 X 1.5 is a 406mm. It didn't work.

The tires are clearly marked as 20x1.35 and 26x1.5 My question was, basically is there a way to fit the wrong tires size on a rim? or should i assume that since my bike is running these tire sizes now that i could safely order the exact same sizes again and it would be fine?

Or do i need to measure the RIM size and look at some kind of chart on sheldons website?

You can't go wrong getting the exact same size tire as what you have now.

No, you cannot fit the wrong "diameter" tires on your rims. Either the tires will a terrible struggle to mount and never seat properly or they will blow off as soon as they're partially inflated.

However, there is a great deal of leeway in tire width that you can fit to your rims. Your rims will accept any 20" x x.xx" and 26" x x.xx" tire available. On the narrow end, you could install 20" x 1.10" (front) and 26 x 1.10" (rear), while on the wide end you could install 20" x 2.00" (front) and 26" x 2.35" (rear). Those tires will fit your rims- guaranteed.

However, they're not ideal- the narrow tires on the AT-18 rims will be prone to pinch flats, and the wide tires put additional stress on the rims and may not fit in your frame anyway. There are people in both camps: "narrow is faster" and "wider is more comfy". It's an endless debate, one that's best answered by experimentation. If all you want to do is ride, just buy the same size as what you've got.

Thanks for the help guys :)

also i was going to say according to shedlons chart any 559 mm 26x1.0-26x2.125 will fit on the rear rim....(though like u said might not be optimal or even fit the frame)

and for the front...well his website doesnt even list 20x1.35 on the chart which i find strange....under 406 mm he includes 20x1.5-20x2.125. Maybe thats a typo?

and im not racing or anything...so i was kinda wanting to take the middle area and go with 20x1.35 and 26x1.5 again....or maybe 1.5 on both front and back.

...Notice that a 26 x 1 3/4" tire is not the same size as a 26 x 1.75"????!!!!!!

...Notice that a 26 x 1 3/4" tire is not the same size as a 26 x 1.75"????!!!!!!

Yep- that's the strange thing about bike tire sizes. The same nominal "size" might not fit the same rim. That's why the ETRTO system makes more sense. It defines the diameter of the rim and the approximate width of the tire when mounted.

In fact, there's 7 or 8 different tire "sizes" that call themselves "twenty-six inch". 26 x 1.75" fits the very common mountain bike rim which is 559mm diameter at the bead seat. 25 x 1 3/4" is an obsolete Schwinn size with a 571mm BSD- oddly, this is the same BSD as "650C" tires commonly used on triathlon and some highracer recumbents.

and for the front...well his website doesnt even list 20x1.35 on the chart which i find strange....under 406 mm he includes 20x1.5-20x2.125. Maybe thats a typo?


I don't think Sheldon got a chance to update that chart before he passed. Fortunately, it's still the same "standard": a 20 x x.xx" tire will fit the 406mm bead seat diameter rim. 20 x 1.35", 20 x 1.25" (I have one of these), 20 x 1.125", and 20 x 1.10" will all fit that rim.

(The wild card is the Continental Grand Prix. Continental calls it a 20 x 1 1/8", but it also fits a 406mm BSD rim. Usually fractional sizes are used on the larger 451mm rims. Grrr...)