llmercll

Hey everyone! I recently brought back an old mountain bike so my brother could ride with me. He's a bit smaller than me, at 350 pounds, but still very heavy.

When i inflate the tires, they don't even feel firm, but my meter is reading them at 120psi!!! The tire is literally soft and squishy, and when my brother rides it, it goes down considerably and makes a squealing rubber noise.

The tires are rated at 65psi max, and I was going to a little bit over that like I do on my 700x32's, but 120 is way too much and the tires feel way too soft. Will MTB tires feel softer at the same pressure as 700's?

Is it likely I'm getting a flase reading? Are MTB tires meant to be soft and squishy? I mean they are really soft, even at 120psi..I don't want them to be so low he gets a pinch flat and has bad rolling resistance, but i fear overinflation because of blowouts.

We're just doing some easy riding on pavement, no trials or anything.

thanks!

jethro56 

60 psi should be enough if they're 1.95" or larger. I'd question your guage.

kevrider

air is compressible and the mtn bike tire contains and larger volume of air, so it will feel softer than a narrower tire at the same pressure. putting 120# does seem a little extreme. a better bet would be narrower tires. brother needs some slicks.

KBentley57

120 PSI seems like it would be blowing tire shreds in a mtn bike tire! Remember, the larger the area the lower the pressure needs to be to hold the same amount of weight. +1 on the different guage; if you can squish them by hand they are not at 120 PSI.

Brutal.Roadrnr

MTB tires are supposed to be a bit squishy, they are meant to flex and grab the terrain as they traverse the terrain.

I do think you need new tires there though, maybe even tubes that doesn't sound right...

2manybikes

You are not opening the tire valve enough and just pumping up the hose to the pump. Spend more time getting the pump on better, or have some one help you. Then the pressure will read the correct pressure and the tires will get harder.

The pressure on all tires is marked on the side of the tire. No mtb tire is going to withstand 120 psi. The rims might not even take that.

Shimagnolo

In my experience, overinflating mtn tires is more likely to break the sidewall of the rim, than to hurt the tire. I was running a set of 2" tires rated for 70psi, when after cracking the *second* new Mavic rim, I came to realize the rims could not take it. For those who may be unaware, as the tire width increases, the force against the bead also increases at the *same* pressure.

llmercll

Thanks for the replies! The pump wasn't in far enough =p

I shoved it in really good and the psi read at less than 50! Pumped it up to about 60 and is doing great now =)

Only problem now is the rear wheel seems really uncentered. The side of the wheel rubs against the frame! Is that likely a wheel that needs to be dished?

2manybikes

Can you post a picture?

jethro56 

First check that the axle is all the way down into the drops.

llmercll

thanks guys I'll get a picture first thing tomorrow.

Also, I forgot to mention, the same wheel also feels kind of "loose" it wobbles a bit if I shake it back and forth.

thanks!

Arvadaman

Sounds like the axle is not seated all the way down in the drop outs. If it is, then it sounds like the spoke tension is too low and the wheel needs to be trued and properly tensioned.

contango 

Sounds to me like your meter is wrong. My MTB tyres are rated up to 70psi and at 60-70 they feel hard. If they feel soft and squishy my gauge will normally read the pressure somewhere around 30-40.

llmercll

It ended up being the axle not far enough in the dropout. A little adjustment fixed it really well! Then I trued it up a bit and it's spinning great =)

Here are some before pictures

https://img30.imageshack.us/img30/3387/dscn2950g.jpg
https://img819.imageshack.us/img819/5381/dscn2952n.jpg
https://img52.imageshack.us/img52/9813/dscn2953a.jpg

I had to do a little barrel adjustment on the derailleur afterwords, and for some reason the 2 large cogs closest to the wheel (gear 1 and 2 i believe) aren't working well. It's making a grinding noise. The other gears, 3-7, work fine. I realized the rear wheel still feels a little "loose" even though the locknuts are really tight, and that when the wheel spins the cogs and even the pedals, wiggle a little. Almost like it has a pulse =/

I made a video of it, you need to look really closely though

https://www.youtube.com/watch?v=TBOjU_tSqyU

thanks!

WonderMonkey

I have never given this thought. Glad you brought it up.

2manybikes

We learn from my mistakes.