tennisplyr3

Hey guys,

I'm currently riding a 1994 Fuji Ace with Cheng Shin presta valve tires (700x28c) inflated to the recommended pressure of 100 psi. After about maybe 8 rides, the tire pressure drops down to about 80 psi -- especially the rear tire. After about 20 rides, the rear tire was down to about 40 psi, but it doesn't go any lower than this even if I ride 50+ times. Do I have some sort of slow leak or something? If I don't ride it, the pressure stays the same (I'm about 150 lbs.). Strangely enough, the front tire holds its pressure well.

Should I just replace the rear tube and hope for the best?

Also, I don't think these tires have ever been replaced. The tires are slicks, but they haven't worn down yet, for I can still see the tread patterns very prominently. However, I can see some cracking along the side and road-touching portions of the tire -- probably from age. I was looking for new tires as well and was wondering what I should go for. I use this bike for commuting to work along the streets of Philadelphia, which is pothole ridden and frequently an obstacle to navigate.

While I want a tire that is glass and puncture resistant (haven't gotten a flat yet in a year *crosses fingers*), I suppose anything should be a step up from my current tires. I would preferably like to keep the tires to slicks to keep the rolling friction to a minimum (but tires that work well in the rain would be a definite plus). I was looking at gatorskins and noticed that some people have issues with getting pinch flats with them. I also was looking at Marathon tires, but most of them don't fit my tire size. My budget would preferably be <$50 per tire. Does anyone have any suggestions?

Also, is there a disadvantage to always using tubes with long stems (as opposed to short ones)?

Thanks in advance...

neil0502

Didn't read your whole post, but ... top off before every ride.

Tubes leak.

Good tubes leak.

Brand new tubes leak.

It's the gas molecules sneaking out through the rubber ... or something like that.

tennisplyr3

Yeah, I realize that they leak, but for them to lose most of their pressure after a few rides seems a little strange to me. Also, are there any durable tires that are slicks w/ low rolling friction for <$50?

prathmann

As stated above, rubber that's thin enough to make a good bicycle tube is also slightly permeable to air molecules, so a slight pressure loss over time is to be expected. Another factor is that you lose a little bit of air every time you check the pressure. Since a bike tube is so small that can drop the pressure enough to be noticeable. That might be why you see more of a pressure drop when you go on more rides - you're probably checking more frequently then.

If you're not having problems with flats now then I wouldn't rush to get more puncture resistant tires. Note that these have additional belts which make them less flexible and will increase the rolling resistance, especially if the extra belts extend into the sidewall area. One of my bikes came with Armadillo tires that were very puncture resistant, but I was glad to replace them due to the higher rolling resistance making the bike feel sluggish.
Durable and low rolling resistance also don't generally go well together. For low rolling resistance you want thin rubber and a very flexible casing. For durability you want thick rubber and a casing that's resistant to any cuts or abrasion and that usually means it'll be less flexible.

No problem using the longer stem tubes, but they can be a little harder to pump up with a handpump without putting extra strain on the tube where the valve attaches.

jamisrider720

700x28c will loose that much air in a couple of rides. it happenes liek the other guy said top off before every ride the higher pressure the tire is and the smaller the more you gotta top off. as for pinch flats as long as you got air in the tire and your not hitting curbs/jumps no worries... kenda makes a good tire with the "iron cloak" its metal weaved into the tire and its puncture proof for around 30-50 bucks a tire =] kenda kontender has it as does the kalantie. and avoid white wall or brown wall tires its a bonded tire and wil go quicker then a black wall good luck!

zhefei

The higher pressure the tire is at, the more air want to escape, so the faster your tire "leaks". After it has leaked some, the rate slows way down, which is why to see it level off.

As others have stated, this is normal behavior. You may see a difference with other tubes, but I bet it won't be much.

tennisplyr3

Hmm, the smaller tube holding less air --> easier to lose a % of the total air makes sense I suppose. The thing is, I don't check my pressure frequently; I pump it up at day 0, and when I check it at the end of the week, it's lost about 60 psi (once). I ride ~1 mile each day, and I avoid potholes/bumps. I was just planning on taking a longer trip (~25 miles) and was concerned about the same thing happening.

I don't think my tires/tubes have ever been replaced, making them 15 years old. Are they about due for a replacement (cracking in outer rubber tire)?

I guess I want a slick tire replacement that's all around good with low rolling resistance. jamisrider720 suggested the kenda kontender and kalantie. Does anyone else have any other suggestions that will fit a 700x28c? Also, what are white wall/brown wall tires?

As for pumps, I was thinking about getting a new one. Is this one any good: https://www.amazon.com/Planet-Bike-10...pr_product_top ? Or are there any floor pumps that are well regarded on bikeforums?

urbanknight

Tubes lose pressure over time, period. No matter how many miles you ride, you should top them off regularly. Most of us on this forum will top them off before every ride or daily.

After 15 years, I think tires and tubes would be a good idea since the rubber has rotted and is ready to rip open at the most undesirable of moments. You might also notice a slower loss of pressure with new, supple tubes.

For good tires under $50, go to www.probikekit.com and have a blast. I've heard a lot of good things about Continental Gatorskins, although the set I just bought haven't been that impressive at one flat a month for the first 2 months so far.

For pumps, if yours is reading the pressure and is getting a good seal on the tube valve, keep using it. Other than that, I think Blackburns are awesome but really, if they put air in your tires, what more do you want?

jamisrider720

brown wall or also known as gum wall tires and white wall are where the sidewall of the tire is wither white or brown its found on older bikes but you can still purchase them is disered... the way there made though after time goes on where the brown side wall joins the black tread it will split same with white wall the shop i wrok at we always recomment using a black sidewall tire... you could get a junky slick tire and then just buy a pair of "mr. tuffy" tire liners ther sit between your tire and tube and are also "puncture risasnt"... sorry i know my spelling is rechid hope i could help

Panthers007

I filled a regular tube/tire with a CO2 cartridge, as an experiment, to 98psi. Came back in 18 hours. It was down to 68psi. Moral to the experiment: I still don't know why, but CO2 leaks out much faster than air.

As stated before: Top off your tires BEFORE each ride. It's simple and effective.

Berge20

I was about to post a similar question this morning, so looks like it happens.

As a new rider that's on the heavier side (~200 lbs), I just started noticing this happening during rides on my new bike. Didnt seem to occur the first couple months, but clearly now it's starting sooner than later. Causes a problem on rides that are longer than 5-7 miles cause lord knows it's harder pedaling along with half inflated tires.

Rustyoldbikes

The source of my tire leaks (tires that lose more than 5 pounds PSI per week) generally turn out to be the valve. Sometimes the leak is inside the valve, but most often it is where the valve is inserted into the rubber of the tube. I've had this problem with every brand of presta tube, except Continental. Never had that problem with a Schrader valve.

probe1957

Berge20, if you're losing air in 5-7 miles you need to check your tubes for leaks. That isn't normal.

DieselDan

Normal. Top off before every ride.

Al1943

+1

Before each and every ride. Rolling resistance is directly related to air pressure, unless the road surface is very rough.

bikeman715

pathers007, CO2 is lighter than air therefore the tube will leak faster. use of CO2 is good on the road but when you get home use the pump.

Shimagnolo

Are these the *original* tires?

prathmann

Actually CO2 (mol. wt. of 44) is significantly heavier than air (mainly N2 with mol. wt. of 28 and O2 with mol. wt. of 32, so the average is about 29).

What makes it diffuse through the tube faster are the chemical properties. CO2, with the oxygen atoms connected to the carbon with double bonds, can partially bond to the hydrocarbon molecules in the rubber tube. This holds the CO2 in proximity with the rubber and it can gradually diffuse through the thin tube wall and escape out the other side into the air. N2 molecules are essentially inert wrt the rubber tube and just bounce off the tube wall, so filling the tube with nitrogen would result in even less pressure loss than using air. O2 molecules, the other main constituent of air, are intermediate - they diffuse a little more than N2, but not nearly as fast as CO2.

PS to the OP: if you're buying new tubes don't get the real lightweight ones - they're thinner and will leak air more quickly.

Panthers007

Carbon Dioxide - CO2 - is quite a bit heavier than the air we breathe. If you like, I can post a simple at-home experiment which will prove this. I am a chemist, so it's likely I know of what I speak. Anywho...

I posted this as some people stated that CO2 leaks out of tubes/tires at a greater rate than regular air - in another thread. And I decided to do this experiment. This should prove that anyone saying this is so - is right on the spot. I didn't believe it at first so...

If you were to notice a rapid drop in pressure in a tire you blew up with a CO2 cartridge - it's not the tube. It's the nature of the beast. Now if I could only figure out why this is.

tennisplyr3

Thanks for all of the explanations, everyone. I have a few questions/responses after reading everyone's replies...

1) When you guys say "top off," do you mean inflating your tire to the recommended pressure frequently?

2) As for pumps, I'm currently using a mini-pump (difficult as hell to pump it up to 100 psi), and I check the pressure occasionally at the local bike shop. I was looking for a floor pump for myself and came across this one: https://www.amazon.com/Planet-Bike-10...pr_product_top . I was wondering if it was a good one to get.

3) I think my tires are brown walls (the sidewall is brown). I have noticed that a mountain bike that I had which had Shrader valves barely leaked. Too bad my rims are presta only, and I don't want to use the machine shop at work to drill some bigger holes.

4) Yes, these are the original tires. I think the original owner barely rode the bike and kept it in a garage on his estate, so it was in really good condition. Too bad I can't inflate my tires with an inert gas or something from the various gas tanks I have access to at work!

5) So I guess I'm just looking for good replacement tires for my 700x28c wheels. Scratch the thin tires/ scratch the high durability... I'm just looking for all-around good 700x28c tires for my 15 year old bike. I'm really surprised that I haven't gotten a flat on these tires while riding in Philly, and the rubber is starting to crack.

6) I am currently looking at https://www.probikekit.com/index.php for tires. Can anyone else recommend good places to look for tires?

Thanks in advance

Shimagnolo

Last year I was running a pair of Ritchey Crossbites on a mtn bike that I was using 99% on the street. The tires were from 1994, but had very little wear because they had spent most of their years hanging in the garage while I was running knobbies on the bike.

One Sunday morning I went out for my usual ride which included a 45mph descent on a fairly busy road.
I came home, hung the bike up in the garage, and about an hour later: BOOM!!!
I went out to the garage to see the fork cranked to one side, and a hole in the sidewall big enough for my thumb.

Do you think I will ever trust tires that old again?

Panthers007

Some really nice tires I've been riding on this year - in 28C (27C):

https://www.rivbike.com/products/list...product=10-043

And these are pretty bulletproof.

Harris usually has these.

tennisplyr3

Oh wow, Shimagnolo. I can see your point of view. I'm definitely looking to replace these tires. =)

And Panthers007: aren't those tires brown wall tires?

prathmann

Nothing wrong with 'brown wall' tires (generally referring to either gumwall or skinwall types). Nor are tires with black sidewalls immune from sometimes having delamination problems. I could take some pictures of one hanging in my garage right now if anyone needs evidence of that.

BTW, a very inexpensive tire that I've had good luck with is made by Cheng Shin (same as your current ones) and sold by Nashbar as their housebrand Prima. They frequently go on sale at about $10. Unfortunately they no longer sell the unbelted variety that I liked better, but the Kevlar-belted one is ok too.

Poppaspoke

Some enterprising bike shop owner should start offering nitrogen-filled road tires...complete with spiffy green caps for bragging rights.