Scary moment on Compass Tires

[Clancy]

I just finished building up a Norco Slate XR steel frameset and have taken it out on a few shake down rides. I mounted a set of Compass Barrow Pass Tires, 38c, on a set of Reynolds ATR wheels and was out on the second ride with these tires. Prior I had a set of Panaracer GravelKings SK’s in 35c. These are on a 700c set-up, not 650B. The Compass tires were dramatically faster and noticeably more compliant.

All was good until I descended a steep hill hitting maybe 25 mph. This is on my regular loop that I’ve ridden countless times on different bikes. The descent has a very slight S curve, very slight. I gradually leaned into the curve when very suddenly the front tire tried to wash out from under me. I managed to somehow instinctively straighten up and avoid the fall but doing so had me cross over into the other lane. Fortunately there were no cars, I was able to continue on.

From there I paid more attention to specifically how the front end felt and how weighted it was. If I leaned into a a turn just a touch too much the front would want to collapse on me or fall in.

I had the tires inflated to 42 psi. After the scare I adjusted my saddle a touch more foreward to load the front tire more and dropped the pressure a bit but it seemed to make no difference.

I’ve built up dozens of bikes and know my measurements by heart. The only difference is the Compass tires. I have had two other sets of Compass tires In smaller sizes, 28c and 32c. The 38’s measure 39.5mm and are almost perfectly round in shape. There is such a tendency for the tire to roll over and fall in on itself when turning that I do not feel comfortable on the bike.

Thoughts???

[fbhidy]

What are the internal and external widths of the Reynolds ? Are they set up tubeless? How much do you and the outfitted bike weigh together?


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[charliedid]

Try more air

[joosttx]

Originally Posted by charliedid

Try more air

+1 exactly what I thought.

[R3awak3n]

Was this on gravel or pavement?

[David Kirk]

Originally Posted by fbhidy

What are the internal and external widths of the Reynolds ? Are they set up tubeless? How much do you and the outfitted bike weigh together?


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I echo this question - how wide is the rim?

A wide supple and soft tire on a narrow rim is not a good combo.

dave

[charliedid]

Originally Posted by David Kirk

I echo this question - how wide is the rim?

A wide supple and soft tire on a narrow rim is not a good combo.

dave

ATR's are 23 internal and 32 external. "The 38’s measure 39.5mm and are almost perfectly round in shape"

It's a great question but I'm guessing it's not the issue?

[R3awak3n]

was about to say, non issue on that rim, its pretty damn wide, I have one and its the widest rim I have.

If I remember this is not the first time I have heard of this happen, but usually on gravel

[thwart]

Looks like the ATR's have a 21 mm internal width according to Reynolds... at any rate narrow rim is not the cause here.

More air seems the culprit, or much less likely a defective tire.

I have the same tires, and they've been great, including fast descents with turns. I weigh 155 and run around 40/45 F/R.

[David Kirk]

I agree - that rim should be more than wide enough.

dave

[JAGI410]

Tires new or used?

I love my Barlow Pass tires. I run them on H Plus Son TB14s. Never below 50psi though, usually 52f/55r

[Clancy]

Originally Posted by JAGI410

Tires new or used?

I love my Barlow Pass tires. I run them on H Plus Son TB14s. Never below 50psi though, usually 52f/55r

here's answers to questions posted.

As mentioned, inner width 23mm
Tires new, second ride
Set-up tubeless
42 PSI front and rear
On pavement, semi-smooth chip seal
I weigh 155 kitted up.

And as mentioned, the front end feels as though it wants to flop over or fall in when I lean, even slightly.

I adjusted my saddle forward maybe 6-9 mm to put more weight on the front and lowered the pressure to mid 30's. No difference in the tendency for the front end wanting to wash out from under.

All of this was on pavement. I can't even imagine riding this sset-up on gravel.

[Pinned]

I've never understood all the praise for the Compass tires. The 28s I spent over $150 on for the set were one of my more regrettable bicycle related purchases - muted feel, slow, poor traction/grip, squared off seemingly instantly. I took them off the bike after a pretty squirrelly incident where it felt like I couldn't stop in traffic - a sensation I never experienced on any tire before or after.

Surely someone will disagree with me, as by all accounts online these are simply the best tires available. I just didn't have that experience at all.

[Hilltopperny]

I've felt this before on my ATR wheels in both 700 and 650b. I found that I had too little air in the tires. I am also 50lbs heavier, but I run them tubeless with no less than 50lbs of pressure.

Scary feeling when you drift into the opposite lane to avoid an impending crash. Glad you weren't hurt and didn't trash your bike!

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[Tall]

Did your sidewalls maybe collapse? This blog post (and the comments) has some info on the topic: https://janheine.wordpress.com/2018/...gher-pressure/

During hard braking, the entire weight of the rider is on the front wheel. Now the front tire carries three times as much weight as it usually does. If this isn’t factored into the tire pressure, then the tire can collapse during hard braking: Suddenly, the sidewall no longer holds up the tire. The tire loses the ability to transmit the forces from the road to the bike – braking and steering are seriously impaired. It’s like riding with a flat tire.

In recent years, the potential for trouble has increased as we now run supple tires at lower pressures. Back in 2010, when we published the chart, we inflated our 23 mm tires to 120 psi. Running the fronts at 80 psi was fine, since the stiff sidewalls of the tires most of us rode helped with holding up the bike.

These days, many of us are on supple 42 mm tires inflated to 35 psi. Dropping the front to 23 psi is fine when rolling along, but during hard braking, the sidewall will collapse.