tire pressures

[Don Compton]

I have been riding 700x28 Grand Bois Cerfs for years. Yesterday, I finally lowered my pressures down to 60f and 70r. Why did I wait so long?

My Roadeo feels like a German car with great shocks.

[Fullylugged]

I rode a perm yesterday on my 95 Road which is converted to 650B. It has Grand Bois Oursons (35 mm +/-) and I had 50 lbs front and 60 rear. Really nice over the shake-and-bake chip seal, and according to the Berto pressure app, I could have run even lower pressure.

[John Hawrylak]

Don

28mm tires at 60psig F & 70psig R supports a TOTAL Weight (rider & bike) of 175 to 180 lb for a 15% Tire Drop (Berto's method) assuming a 45%F and 55%R weight distribution (typical Rando)..

John Hawrylak

Woodstown NJ

On Sunday, September 11, 2016 at 12:16:21 AM UTC-4, Don Compton wrote:

[Tim]

With the 700x38 Barlowe Pass on the Hilsen and the 650x42 Babyshoes on the new MAP and the lowest pressures I can get away with, I INTENTIONALLY ride on rumble strips because even after riding these supple Compass tires for a couple of years I still can't get over how damn comfortable they are.

[Eric Norris]

I split the difference and run about 65 front and rear in my Cerfs. My Singer rides like a Citroen with great shocks.

--Eric Norris
campyo...@me.com
www.campyonly.com
campyonlyguy.blogspot.com

On Sep 10, 2016, at 9:16 PM, Don Compton <dpc...@gmail.com> wrote:

I have been riding 700x28 Grand Bois Cerfs for years. Yesterday, I finally lowered my pressures down to 60f and 70r. Why did I wait so long?

My Roadeo feels like a German car with great shocks.

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[Don Compton]

Berto's old method does not take into consideration the benefits of wider rims.

[Patrick Moore]

175 rider + bike at sub 20 and another sub 25. Elk Pass tires, measuring ~27 and ~29 respectively; run at ~65-70. I don't sweat digits f/r, but I do use the pinch test to get front a wee bit softer. In fact, were it not for the gauge on the pump, which for all I know may be defective, I'd just go by feel -- indeed, I do, since the reported pressures are chosen because they feel right to my fingers.

When I used 23 mm tires on these bikes, I'd pump those to~80/85 or 80/90.

51 mm Furious Freds with at least half miles on sandy dirt: ~18/22 or 20/25. I'm pretty sure that the pump gauge reads too high, and I occasionally check with my low pressure gauge.

I remember long ago, circa 1972, learning to pump my Raleigh Sprite's cheap 27 X 1 1/4 tires to the 70 psi marked on the sidewall. What a difference! Higher pressures certainly do improve rolling, at least the feel (and no, not any goddam buzz; they were easier to pedal and went faster) compared to too soft -- I've verified this any number of times with cheap tires with heavy sidewalls. The roads in question ranged from super smooth to normally worn, nothing terrible or chipseal. 

Question: just went out to check tires with gauges and found that the high pressure one -- to 160 psi; steel and brass -- doesn't register anything despite an open valve core and road pressures as above. Does anyone have any idea about what might be wrong with it, and how to fix it?

Does anyone have a road presta gauge, reasonably accurate, to trade for something or sell for a few bucks?

Thanks.

[Edwin W]

On a side note, I took my sister in law to a few shops to test ride a bunch of bikes and found that a common complaint she had was they were too harsh. Well, the tires were all pumped up to rock hard!! Not to mention most stock tires on the hybrids we were looking at are not the supple ones we've been appreciating!

Supple and soft,

Edwin

[john.h...@verizon.net]

Ok, what is the actual width.  I interpolate on the slope and intercept of the published curves to get the curve for say a 29.5mm width.  tell me the actual width and I can get the 15% TDC pressure.

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[Patrick Moore]

I find that even good bike shops pump tires much too hard; there is a "too hard" even for cheap Kendas. When I pump tires for customers or friends, I try to leave a wee bit of cush -- the sweet spot is vanishingly small with cheap, thick-sidewalled tires.

Odd: I used otherwise very decent 559 X 32 Paselas for many years and miles, and found that they too had a small sweet spot between harsh and spongy. Kojaks are far better in this regard, and the Elk Passes better yet. Paselas rolled well if you hit the spot, though. (Paselas also flat much more easily, their sidewalls tear and wear and degradef easily, and skidding will peal off chunks of tread. My experience.)

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[John Hawrylak]

Patrick

Here are the tire pressures for the 15% tire drop method for the weights and widths you specified:

175 Lb  + 25 lb  =  195 lb total weight

       23          27

F

R

On Sunday, September 11, 2016 at 5:26:41 PM UTC-4, Patrick Moore wrote:

[John Hawrylak]

Opps , hit something & it got sent unfinished

Patrick

Here are the tire pressures for the 15% tire drop method for the weights and widths you specified:

175 Lb  + 20 lb  =  195 lb total weight  45%/55% distribution

       23          27      29

F     89         69       61      

R     112      86       75

175 Lb  + 25 lb  =  200 lb total weight  45%/55% distribution

       23          27      29

F     92         71       62     

R    114        88      77

Can't do 51mm widths

John Hawrylak

Woodstown

On Sunday, September 11, 2016 at 5:26:41 PM UTC-4, Patrick Moore wrote:

[Patrick Moore]

Thanks, John. I read Berto's article -- was it published in Bicycling? -- years ago, but I've never bothered to be as exact as the method entails. My thumbs and forefingers are pretty well educated by now, and I am thinking that even 65/70 for the Elk Passes is a wee bit high for my taste, unless I carry a heavy rear load. I think 60/65 or what my fingers feel when the pump reads those numbers might be smoother.

Segue: Nodding to Eric's mental Citroen, I briefly owned a 2 CV-derived Acadian van, which has such supple suspension that I could drive at 15-20 mph over the sharp bumps installed in parking lots without undue jarring. More gradual bumps, as on 25 mph-limit roads, could be taken at 35-40 with no undue jounce or bounce. And, the van would carry 4 58 c-c bikes with front wheels installed and saddles and bars in proper places.

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[Don Compton]

Fortunately or unfortunately, I have another new Grand Bois 28 Cerf,so it will be awhile until I need to purchase new tires. When I finally wear them out I am going to buy some Compass 700x32 extra lights. Some complain about the price of Grand Bois and Compass tires, but I get my money's worth because of their long wear compared to typical expensive race tires.

[John Hawrylak]

Patrick

15% TDC pressures for a 32mm El Pass for YOUR 200# Total Weight (175+25) is 52/64 psig F/R.  So YES 65/70 psig F/R would be HIGH

13 psig high in F

  6 psig high in R.

The rear is reasonable.  The front probably could lose 10 psig.

From the responses in another post on Tire Prressure, 2 or 3 members crashed due to collapse tires from UNDERINFLATION.  They were generally more than 25% under inflated, i.e., actual pressure was << 75% of 15% TDC pressure via Berto.

I feel if you religiously maintain pressures >= 75% of the 15% TDC pressure, you will be safe from collapsing tires, yet enjoy the benefits of lower pressure,i.e., a good compromise

John Hawrylak

Woodstown NJ

On Sunday, September 11, 2016 at 6:45:52 PM UTC-4, Patrick Moore wrote:

[Patrick Moore]

Thanks again for this. I'll try 55/65 or so, though because my only high pressure (ie, > 30 psi) gauge is the doubtful one on the pump, I'll have to get another one. The other day the pump gauge said 20-25 for the 51 mm F Freds, but the low pressure gauge showed ~ 15 in front; and indeed it felt soft to my thumb.

Does anyone have a road Presta valve gauge to sell cheap or to trade?

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[Lungimsam]

But werent Bertos calculations on stiff tires? Much stiffer than the sidewalls many use today? Compass, GB, etc.

Also on narrower rims than used today?

So does his table really apply anymore?

[Ron Mc]

on the last tire pressure thread, one of the posters plugged everybody's replies back into the Berto graphs and found out we were all but a couple riding within a narrow error window on those graphs - we have naturally gravitated there.  The people who were exceptionally low also reported wrecks.  The people who were exceptionally high?  Well, I guess they get short tire life, ride rough and bounce.  

[Lungimsam]

So if I am 175lbs., on 27.9 lbs. of Bleriot, with 5 lbs. of front baggage, on 650b x 38mm Compass Loup Loup tires, at 45psi front and back, where does that put me? 

[Brian Campbell]

Put enough air in your tires. Go for a ride. Let some out or put some in depending on what you think of the ride. Repeat process as/if necessary. There is no absolute. 

[john.h...@verizon.net]

Lungimsam

Front should be 47 psig,  Rear should be 54 psig.   This is for a 45%/55% distribution for Rider & Bike and the 5lb load only applied to the FRONT wheel weight.

Your 45psig/45psig results in the front at correct pressure and the rear underinflated by 9 psig (17% low).

John Hawrylak

Woodstown NJ 

 

 

On 09/13/16, Lungimsam<john1...@gmail.com> wrote:

 

So if I am 175lbs., on 27.9 lbs. of Bleriot, with 5 lbs. of front baggage, on 650b x 38mm Compass Loup Loup tires, at 45psi front and back, where does that put me? 

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[John Hawrylak]

Ron Mc wrote:  "The people who were exceptionally low also reported wrecks"

Yes, generally their tires were UNDERINFLATED by 25% to 50% of the 15% Tire Drop Calculated Pressure, from my review of the posts.

I would recommend maintain your tire pressure at between 75% to 100% of the 15% Tire Drop Calculated (Berto value) pressure.  This provides a 25% Safety Margin.

For example if the 15% Tire Drop Calculated pressure is 60 psig, then maintain between 45 psig to 60 psig in the tire.

I think this gives enough room to experiment with lower pressures and having a reasonable margin of safety.

John Hawrylak

Woodstown NJ

[Lungimsam]

I remember an rbw employee who said if he ain't bottoming out, he's good.

[GAJett]

Berto Tire Pressure App says 38 front, 52 rear.  So your 45 AVERAGE is spot on!  It just needs to be redistributed.
Cheers,
GAJett

[John Hawrylak]

The values I posted, 47/54 psig were INCORRECT for a 38mm tire.  I mistakenly used the pressures calculated for a 35mm tire.  I apologize.

The pressure for the 203lb rider & bike for 38mm are                               40psig F, 48psig R,

The pressures for the 203lb with 5lb extra on the Front for 38mm are      42psig F, 48psig R

Both assume a 45%/55% distribution.

John Hawrylak

Woodstown NJ

[Don Compton]

Just FYI. I increased my rear tire to 75psi, but I have left my front tire at 60psi.

[Lungimsam]

Ok, so now what if I am:
175lb rider on 27.9 lbs of Rambouillet bike with -~5lb front load on 700c x 28mm Compass Chinook pass tires?

I' m currently running them at 55psi, front and rear.

Thanks for the info, guys!

[john.h...@verizon.net]

 Lungimsam

28mm 203lb distributed 45%F 55%R and without and with 5lb front load and compared to a current 55psig F&R

No Front Load    68psig F / 84 psig R     Front underinflated by 13psig or 19%.  Rear underinflated by 19psig or 23%

5lb Front Load    72psig F / 84 psig R     Front underinflated by 17psig or 24%.  Rear underinflated by 19psig or 23%

Suggest not exceeding 25% Underinflated to preserve margin to tire collapse.

John Hawrylak

Woodstown NJ

[Lungimsam]

So then looks like 75psi front and rear would put me in the zone like the 45psi on the Bleriot would. Trouble is, last time I ran tires that high on a bike bike it made for some harsh riding.

I have been thinking of a 650b conversion.
The bb's of the Bleriot and Rambouillet are within .5cm of each other on these tires sets. Perhaps a 650b x 42 on the Rambouillet would get me close to that 24cm bb height. Same crank length as the Bleriot.

[Lungimsam]

The 24cm is measured bottom of bb shell to ground. 24 Bleriot 24.5 Rambouillet.

[Steve Palincsar]

Will your Rambouillet actually fit a 42mm tire? I have the vague
feeling I've seen that some will -- later ones -- but some of the
earlier ones will not.

[john.h...@verizon.net]

Lungimsam

I would use pressures between 100% and 75% of the calculated F/R pressures. There should be enough room to find a comfortabe pressure 

John Hawrylak

Woodstown NJ

 

 

On 09/15/16, Lungimsam<john1...@gmail.com> wrote:

 

So then looks like 75psi front and rear would put me in the zone like the 45psi on the Bleriot would. Trouble is, last time I ran tires that high on a bike bike it made for some harsh riding.

I have been thinking of a 650b conversion.
The bb's of the Bleriot and Rambouillet are within .5cm of each other on these tires sets. Perhaps a 650b x 42 on the Rambouillet would get me close to that 24cm bb height. Same crank length as the Bleriot.

[Lungimsam]

Thanks for the info and help.

This makes an interesting study to see at what percentage underinflation from the Berto recommended pressures correlates with tire collapse. Looks like 25% so far.

But I still wonder if Berto chart applies on supple tires with wide rims, as I think I read a BQ blog post ttat stated he used stouter tires on narrower rims for his study.

@Steve:
I like the 700c. I'll probably, at some point, experiment with 650b but don't know if that will work well. But I'm keeping it 700c for now. It rides great.

[john.h...@verizon.net]

1 Avoiding Tire Collapse

The members who crashed or fell seemed to have pressures 50% below the Berto Pressure.  I chose 25% (or keeping the pressure >= 75% of the Berto Pressure) since it provides margin.  I see it as a Lower Limit I do not wan to be below.

2 Supple Tires

Experiment with 10% or 15% below the Berto pressure (or 85% to 90% of it) and see if it improves. You are still above the 25% lower limit.

I feel a supple tire would drop 15% at a pressure of 85% to 90% of the Berto Pressure. The supple tires sound great, but they are not magic.

I think Compass is leery of endorsing any pressure except the Mfg Pressure since they are dealer.  If they say, "just the lower the pressure" and someone does, and then crashes due to a collapsed tire, Compass may have liability problems

Hope this helps

 

 

On 09/15/16, Lungimsam<john1...@gmail.com> wrote: