Does anybody really use the Berto 15% drop tire pressure chart?

[drewellison]

The recent thread about lower tire pressures got me to try dropping my tire pressures from 90f/100r to 80f/90r. Nice, I like it. Until I got a pinch flat on my rear tire this morning when I don't think I ran over anything but I must have.

According to the chart, my front should be about 80 lbs. (so far, so good) but my rear should be 120! For me, I'm assuming 40/60 weight split and I'm 220 lbs. with my loaded bike, riding 700x25.

https://www.compasscycle.com/wp-content/uploads/2015/03/BQTireDrop.pdf

Anybody out there follow the chart or run a big difference between front and rear pressures?

Drew

[SlackMan]

I use it. And just coincidentally, I enlisted my dear wife to sit with her face near the ground and measure what appeared to be a 15% drop. It was surprisingly close to the chart. I weight 170+20 bike, and run 700x32s at 60psi rear and 55psi front.

[zoose]

Never measured or anything but glancing at this now I'd say it's pretty close to what I do on the front but way over on the rear. I'm 165 + 15 for bike with 23 tires and I usually run 80f/90r

[mvrider]

Something's funny. For example:

rider weight: 170 lbs with clothes, shoes, helmet
bike weight: 20 lbs with water, lights

--> total weight: 190 lbs

Using the 40/60 "road bike" rule, that's 76 lbs in front, 114 lbs in back.

So, for 25mm tires, the chart suggests ~66 psi in front, ~102 psi in back.

Somehow, that just doesn't smell right.

[jwalther]

I ride pretty close to what the chart recommends at 185 lbs bike plus rider. 80/90 on wide rims with 25s, 90/100 with 23s.

[thwart]

Following tradition, I think many (including myself) usually run a 10 psi difference between front and rear.

I don't know about anybody else, but I really don't like a squishy feeling front tire. Especially with big tires (28 or larger) I get some of that if I follow the Berto chart recommendations exactly... noticeable when climbing or sprinting out of the saddle.

Otherwise, I think the Berto chart is a very good tool.

[smontanaro]

Yes, I use it, though I don't consult it every time I inflate my tires. I weigh around 185. I looked things up once upon a time, then pretty much keep relative amounts in my head. On my Atala (700x25) I generally run 60f/80r. On my Trek commuter (700x35) it's more like 50f/75r. The Trek has a rack, and I tend to carry more stuff than when riding my other bikes. My other bikes are somewhere in between those two. Today I rode the Volare (700x28) and pumped the tires to 60/80. Probably could have gotten away with a few less psi. I don't have any bikes with narrow enough tires where I feel I need to go above 100psi. No pinch flats for me. Mixture of clinchers and tubulars.

The other day at the start of a group ride I heard someone talking to one of the other riders about inflating his tires to 180psi. Yowzers! Talk about a harsh ride.

[NHAero]

For me it's a bit low with the Vittoria Voyager Hypers 37mm tires I put on my Anderson not long ago. The chart puts me at below 40 psi front and about 45 psi rear (175 lbs bike + rider) and that felt too squirmy even before I get down that low. I run about 50 psi front and 55 rear and the ride is comfy and my times over typical routes don't seem slower than when I had narrower tires at 90-100 psi, even tho' Martha's Vineyard roads are pretty smoothly paved and the extra cush doesn't matter the way it would when I was riding NH and VT.

[FlashUNC]

Nope. I'm generally running the same pressure front and rear, between 90-100 psi depending.

[oldpotatoe]

Nope. I'm generally running the same pressure front and rear, between 90-100 psi depending.

Me neither. .1 offa ton plus about 20 pounds. About 90-95 psi, 25c tubies.

Bike tires, not exactly rocket surgery.

[R3awak3n]

/\ same here. Seems to be fine, dont get many pinch flats.

[Hindmost]

Nope. I'm generally running the same pressure front and rear, between 90-100 psi depending.

If one does any descending with significant braking the front/rear weight distribution get reversed in a major way. Same pressures front and rear makes sense.

[benb]

If you're doing significant descending the heat in the front rim will increase the pressure temporarily for you...

[zoose]

And on top of that, if you're doing any significant descending that means that you probably had to go up at some point. I just inflate the rear higher because you rarely hear of front pinch flats while rear ones are fairly common.

[drewellison]

The recent thread about lower tire pressures got me to try dropping my tire pressures from 90f/100r to 80f/90r. Nice, I like it. Until I got a pinch flat on my rear tire this morning when I don't think I ran over anything but I must have.

According to the chart, my front should be about 80 lbs. (so far, so good) but my rear should be 120! For me, I'm assuming 40/60 weight split and I'm 220 lbs. with my loaded bike, riding 700x25.

https://www.compasscycle.com/wp-content/uploads/2015/03/BQTireDrop.pdf

Anybody out there follow the chart or run a big difference between front and rear pressures?

Drew

Here's my update. With the help of my old freight postage scale (goes up to 150 lbs.) and my sweetie, on my favorite Serotta CSI, my weight distribution is about 76 lbs. front - 136 lbs. rear. According to the chart, I should be running 65 lbs front tire and 122 lbs rear tire. (25mm wide tires). No way.

I'm going to try 80-85lbs front and 105-110 lbs rear and see how I like that.

Drew

[etu]

Drew,
I think one of the limitations of Berto's recommendation is that it works for a static position on the bike. Tire inflation is optimized for the riding on the hood position. However when I get out of the saddle and put more weight on the front that's when I usually notice the tires getting a bit squirrely from under inflation. For my shorter, more aggressive rides, I keep the pressures even on the front and back - usually 90-95psi for 25c tires. Like all things related to ride quality, YMMV.

[smontanaro]

Of course, you can always do things empirically, assuming your sweetie is still available to help. Measure your tire height while off the bike, then, while on the bike, have your sweetie make the same measurements. Lather, rinse, repeat, adjusting pressure until you measure a 15% tire drop while on the bike. And Bob's your uncle...

[drewellison]

Of course, you can always do things empirically, assuming your sweetie is still available to help. Measure your tire height while off the bike, then, while on the bike, have your sweetie make the same measurements. Lather, rinse, repeat, adjusting pressure until you measure a 15% tire drop while on the bike. And Bob's your uncle...

My sweetie loves me, but I don't really want to find out if she loves me that much. :)

I think I'll just do the "let a few pounds out every ride until it's comfortable but when it starts feeling squishy, add some pressure" technique.

Thanks, all, for the great conversation!
Drew