Road Fan

I just weighed myself, and discovered I have just turned clyde - 200#. Aside from general health (the obvious, plus I have knees that now ache after 20 minutes of warrior poses, I've just cut back my diet a bit and pulled it back down toe 190, in the past.

But today I was checking my tire pressures for a bike that has actual 700 x 25c tires on Mavic Open Pro rims, 32 spokes f/r. The Berto chart recommends pressures 101 psi front and 124 psi rear. I would not normally have thought this was a big problem, but I also just read the fine print sticker that Mavic pasted on the rim, and it says max pressure is 118 psi.

I guess I have too much information now, because I'm a little worried about stressing the rim. I realize these are lawyer stickers, but being an engineer I just wonder if it might be a real threshold. Previously I used pressures calculated based on 28 mm tires, which are what my tires are nominally.

Anybody been living on this edge? Am I near the edge of a cliff?

Has anybody seen Mavic rims fail due to stress of overpressure?

malcala622

I'm at 192 currently with my high school weight being at 185 (class of 06')

Cycling with the balance of burgers and hot dogs have kept me at this weight. If I slightly change my diet I'm sure I can drop to my HS weight.

Oh also there's a Clydesdale section in the home page

davester

I don't understand why anybody over about 170 lbs in this day and age rides with 25 mm tires. I'm not a clyde, but 28 mm is the narrowest I would go.

CV-6 

Yup...Clyde here. I would not put much stock in the Berto chart. I ride Conti GP4000 25s typically at 110R and 100F. Recently rode some Conti 23mm tubulars at 100R and 90F. But more realistically, I mount the bike and look at the bulge. It's an eyeball thing and if I think the bulge is too much, I add some air. The only time I had issues when I wasn't paying attention and ran over a large bolt in the road, pinch flatting both tires. I do a better job of looking down the road now.

sloar 

CV-6 

Personal preference for some. For me, a 28mm tire does not look right on the likes of a Moto Team Champion or a Masi GC. A good 25mm tubular is my choice for them. I do have 28mm on some of my rides.

jamesdak 

LOL. really??

Well for one, most of my bikes won't fit 28mm.....

I'll leave it at that.

ryansu

200lbs? pffft! light weight Sorry can't help you with those skinny tires I run 27" 36 spoke wheels with 1/4 to 3/8 widths (think 32 to 37mm) at 80 psi and they work very well. but then again this 50+ year old super clyde ain't racing nobody

Slightspeed

I'm finally down to 200 from 240. I run 25 Gatorskins at around 100 psi on most bikes, and have never had a wheel issue, except on a Mavic Open Sport rear that had cracks around two spoke nipples - but it took 10 years. I do run 28 Gators and Pasela PTs on two vintage bikes. Only one pinch flat in more than 20 years, and I think it had a slow leak first.

Before @240 lbs.


After: 195lbs at Eroica

gugie 

ThermionicScott 

Nice work, @Slightspeed!

@Road Fan, Mavic's maximum pressure rating is based on hoop stress, so it depends on the width of the tire. I don't know if the newest Open Pro's are marked this way, but mine allow a max pressure of 146 psi (!) if you are using 19mm (!) tires, so your 25's can safely be pumped a little over the 118 psi rating given for 28's.

ryansu

Looking good @Slightspeed !! any secrets to your 40lb drop?

Lascauxcaveman 

Yeah, I'm a Clyde. Just under 210 right now. But as you can see, I carry it well


Lascauxcaveman (with beer, naturally) sitting next to his skinny pal, Dave

I was riding around for about 15 miles on my purple Technium today, 23mm Panaracer Catalyst Sport tires at 90psi front and 100psi rear. (Tires carefully chosen for their yellow, bar tape-matching sidewalls and their $13 price tag ) The ride was more harsh than I'm used to on my cushy touring bikes I usually ride, but I didn't feel I was taxing the tire/rim combo in any way or courting a pinch flat. This was riding on typical crummy city streets and chipseal mountain roads, including my usual hell-bent descending.

SamSpade1941 

I prefer to not ride anything less than 700x32 and I really like 700x40 best. Having said that I could probably put 700x28 on my Allez but it had 700x25 tires on it when I purchased it and they look right on it so I went with the same when I completed the overhaul.

kunsunoke 

Currently at 215 lbs. and running 25 Sprinter Gatorskins at 155psi rear / 120psi front. It works.

Obviously, I won't be riding a Vitus anytime soon.

jjames1452 

I've cycled for the last 9 year's from 220-210. 25 mm tires, both set to 100 psi. I used to ride only 36 spoke wheels, but recently have switched to 32. ( I have broken spokes on rides a couple of rides, but they were an old wheel build) Now a shade below 200. It may be wrong, but I haven't had any problems.

Road Fan

LOL! Kudos on use of the beer to camouflage the double chin! I have to practice that move!

For this particular bike there isn't enough clearance for a true 28 mm width. I thought there would be, but ... not! But it's such a nice frame I can't really go to my other ones. Looks like my path is to ride more, keep the pressure up in the comfort range, don't sweat the rims, and practice my beer move!

The wheels are very well built, no rim dents in the three years I've had the bike, and the frame tubes are thin-walled ELOS Nivachrome steel. As long as I don't crash I'm confident the Mondonico build will hold up under my awesome power. I don't baby the bike, but I don't do "road bike parcour" on it, either. I always lift my body off the saddle when going over a road blip or bump.

I think I'll trust this steed to hold up as I try to lose some weight.

Road Fan

LOL!

I actually have a few in the works along those lines. One is a 1952 Rudge Aero Special (think Raleigh Super Lenton) with original or at least contemporary 27x1 ¼ rims, and another is a slightly modernized 1971-ish Peugeot UO-8 that will be shod with aluminum 27x1 ¼ aluminum rims. I'm on the verge of 65 and it's 1971 all over again! Keeping the Sturmey-Archer AW hub on the Rudge.

The Peug is destined to be an Ann Arbor city bike, which for me means vintage drop bars an inch above the saddle.

beicster 

I am currently around 250. I don't know for sure because I don't get on a scale anymore but I do keep track of how my pants fit. I haven't been below 200 since the mid 90's. In that time I have gone from 23's to the biggest tires I can fit on a given frame. I don't have anything less than 35 right now and those seem to work for me. I use the eyeball method on my tires combined with the riding sweet spot method to decide how much pressure. I define the sweet spot as somewhere between the bike squirming underneath me and every bump being a personal affront to my prostate. Too little pressure equals squirming and too much equals sidewalk cracks jolting me. Unscientific, but it works for me.

Road Fan

By "hoop stress" you mean the tension in the tire casing, which tends to separate the beads? Sounds like the rim is better able to support stress on the bead hook in the radial direction than stress in the direction perpendicular to that. So in terms of rim durability I might be better off with the 25 mm tires than 28's, even if 28's could fit the frame.

Related issue of course is tire carcass stress - I think the tires, old Continental Ultra 3000, have the strength needed. The friend I bought them from used them on his tandem for a while.

jamesdak 

LOL, don't buy into the nonsense. Nothing wrong with riding 25 mm tires.

Road Fan

Andy, I've found the Berto numbers avoid the extra harshness resulting from too-narrow tires pumped up too-high pressures, and the soft, sluggish feel of under-inflated tires that mean your innertubes are at risk of pinch-flatting. Those extremes always bounded by pressure preferences dating back to the 1970s. I can't say if they result in low rolling resistance as Jan Heine claims, but I have no complaints. It feels a lot like it did when I used my sense of a sweet-spot with my tubulars. Note: I understand pinch-flatting is real, but I haven't had any since starting to follow Berto, and becoming a lot more careful about how I install innertubes.

I wouldn't say the Berto method is scientific, I don't believe it was based on fundamental scientific principles that would establish that 15% drop is the best absolute criterion. Frank said in his writings of the time that 15% drop seemed to work for him, so he derived an equation to predict what pressures would result in 15% for various tire sizes, and plotted the results in the famous graph. Rather than being scientific, I see it as a consistent guideline that has no bad effects. He was trying to say in Bicycling, "hey guys, try this, I think it works pretty well!" Kudos to Heine and others for resurrecting it, but it's still just a practical guideline rather than a scientific theory.

palincss

One reason might be that that's the widest tire that will fit on that frame.

Road Fan

Thanks! Based on this thread my faith in my wheels remains intact!

Road Fan

That's the case with this frame - it's a Mondonico ELOS.