rekmeyata

So lets say with you, the backpack, and the bike you weigh a total of 275 pounds. Your 27 x 1 1/4 tires are about 32mm wide, thus you're close to max psi you should be putting in those tires is 75 front and 90 rear no matter if the tire is rated 120 or even more unless the tire package gives you a different psi to use for the total weight. That pressure I recommended can be increased by 5 psi if you like a firmer ride or ride on rough streets, or you reduce it 5 psi if you want a more comfortable ride or your streets are smooth.

William I am

Thank you! That's very helpful to know.

And very frustrating that they list them like that. Hmmm. I don't want the bike to be any lower than it is, but a slightly larger wheel (like a 35 or 40) would be perfect.

I noticed a lot of the wheels listed their inner size as some weird decimal size - like 19.7 and 21.7. Any idea why?

JiveTurkey

Precision?

Drew Eckhardt 

With all else equal a wider tires has lower rolling resistance because its contact patch is shorter resulting in less tire deformation and corresponding losses due to elastic hysterisis and internal friction.

The issue here is that "all else" often isn't equal, with the rolling coefficient of friction varying by a factor of two between the slowest and fastest nominally slick road tires.

Thin, light, supple carcasses make for low rolling resistance but tires that don't last 2500 miles; and the market which wants such tires is generally happy with tires no wider than 25mm (Continental will ship next year's GP 4000s II in a 28mm width).

sunburst

Interesting. I never think about what I weigh when inflating tires. What PSI should I be running in a set of Marathon's, 27x1 1/4, with me @ 130lbs?
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OP, I've got old bikes too (including a U-18) and the 27" tire dilemma is real. That being said, I wouldn't hesitate to recommend the same Schwalbe Marathons in 27" for your Peugeot and your roads.

rekmeyata

You can do that easily yourself here: https://www.dorkypantsr.us/bike-tire-...alculator.html do the second calculator, add up your body weight clothed for riding including backpack with it stuffed, the bike weight with all accesories including full water bottles, then add them all up and enter it into the Rider + Bike area, next enter the F/R weight distribution, I like the 45/55 which is what I gave you before because it comes closer to the way I use to do it years ago, then put your size tire in (I know that a 1 1/4 tire is 32mm because I have a bike with that size and measured it with calipers to make sure the tire was that wide), the program automatically calculates it.

Like I said before the only time I wouldn't use that is if the box the tire came in has different psi levels for various weights listed on the box.

FastJake

I'd recommend a 700c wheelset assuming your brakes will reach (they probably will, but check to be sure.) Your UO-8 should easily be able to fit 700x35 tires and then you can run whatever pressure you want. And you'll appreciate the (probably) a lot lighter aluminum wheels.

Worrying about your tires blowing off is no fun. Running a narrower tire than optimal is less fun than it could be.

Pretty cool. I messed around with it a bit, and it comes very close to the actual pressures I've been running on various bikes. On my commuter, as I suspected, I've been running too high. I pump up the tires (25 front 28 rear) to 100psi Sunday night and they bleed down to about 70 or 80 by the end of the week. They feel better lower, and I'm probably just as fast. So from now on I'll run them lower!

sunburst

That U-08 should have the Mafac "Racer" brakes. They easily accommodate 700c wheels. I've done the wheel upgrade on two of my old Peugeots.

Darth Lefty 

I've been thinking about that Dorkypants calculator and I'm not sure its assumptions are right. Based on this article from Bicycles Quarterly (pdf), it's spitting out pressure that would allow a tire to compress 15% under the weight of the rider. This is supposed to be the best compromise between ride comfort and rolling resistance for a fast tire with a "supple thin casing" per the article. The Pasela is such a tire and the recommendations work great. But in reality a road bike tire will see a lot of worse conditions than the level, including wheelies and stoppies/endos, rocks and potholes and curbs. So the ideal might be higher to avoid pinch flats or denting the rim. Also, there are a lot of different tires... I read someone here saying they were riding on an ultra-thick Marathon without realizing it was flat. That tire's ideal might be lower, because some of it is being taken by the tire carcass. (The guy who wrote that tire pressure article would argue that you would be more comfortable and faster on the soft thin tires and you should avoid flats by craft.) Finally the article has a 35/65 split (not included in the calculator) for rear-rack city bikes which seems to imply pressure about twice as high in the rear as the front. For that you'd need stagger like a motorcycle with a fatter tire in the rear but I've never seen a common city bike set up that way.

Retro Grouch 

Converting to 700c may not require doing anything but readjusting the brakes or it may prove to be un-doable. My advice is to find somebody who will let you borrow their 700c wheelset and trial fit the wheels to your bike. Then you'll know exactly what you have to do to work the conversion.

achoo

Also check the width of the dropouts on your bike. The newer rear wheel will be for a bike with 130 mm dropouts.

rekmeyata

I have a bike with 27" wheels and I see no reason to convert it 700 because I think it should be kept original and there is still a decent howbeit small selection of high quality tires I can get from real heavy duty touring tires, to medium duty touring tires (which is what I have), to really nice training/racing tires, and of course dirt cheap crappy tires are available too. Conti makes the Gatorskin and the tougher Gator Hardshell tire in a 27, Panaracer makes the Pasela and the Pasela TG in a 27 (I have the TG's and their a fantastic tire), and Schwalbe makes the best touring tire in the world for 27's called the Marathon as well as a tough commuter tire called the HS 159. Personally I think the Pasela TG is all the tire one needs for commuting and up to medium weight touring, and that tire is about 1/2 the weight of the Schwalbe offerings and cheaper.

Anyway that's what I would do, you wouldn't have to change a thing on the bike and maybe save yourself from buying all new brakes plus keep the bike in original condition. Just an opinion.

sunburst

yeah, I've bought the Paselas for one Peugeot, and may do it again. Soooo much lighter than the Marathon. Come to think of it, I put Gator skins on my son's Peugeot (and he had 700c wheels so my choices were much wider). I do like the tread of the Marathons much better than either, especially when I venture off onto some hard pack. Definitely slowed the bike down though. I think for a commuter bike, and at your weight, the 27" tire selection is fine.

But a wheel upgrade is always attractive if you end up with an alloy rim, stainless spokes, etc. I've looked at those Niagara wheels and was baffled at the 130mm spacing for 27" wheels. Makes no sense to me. Long after wheels evolved to 700, dropout spacing was still 126mm. Your bike was 120mm from the factory, although it may have been spread at some point.

Your Mafac's will work for 700, and a bonus is that you can fit nice big cantilever pads.

sunburst

I got 36 front, 56 rear, at my weight plus bike. Hard to believe.

rekmeyata

It's based on an old and tested calculation of 15% tire deflection when loaded. Thus depending on your weight, the bikes weigh, etc and the tire size it is very possible if your running a large 32 or 35 tire and you don't weight much then the figure is right even though it doesn't seem so. Remember two things, if there is another set of guidelines printed on the tire package then go with that, I had a set of VITTS that came with recommended tire psi/weight chart and the funny thing is...it agreed with the Dorkypants Michelin calculator! But always check the tire package first to see if they have their own chart.

sunburst

I entered 160 lbs total and 32mm tires into the calculator. It makes sense to me that it would be tire dependent, so maybe I'll experiment with lower pressures. I don't remember Scwalbe including any helpful pressure info.

I pulled one seldom used bike off the hook last week, got out the pump and realized l had run it at about 35 PSI the last time I rode it. That was with some stout 32mm Continental Contacts. The Marathons are even beefier so I should have quite a working range (been running them at 70-80 PSI).

William I am

I "cold adjusted" the rear dropout spacing when I put on the 8-speed freewheel (it was fairly easy), so it's closer to 130mm. Won't be a problem anyway, since I'll just readjust it if necessary.

I'm set on getting 700's for the wider tire selection and because LBS actually stock them.
I've read in a lot of places that the mafac racer brakes will reach, and I'm sure they will.


What do people think about running different sized front and rear tires? I'm talking wider on the back. 35 on the front and 40 or 45 on the rear or so. And I'm running 27x1-1/4 tires now, not 1-1/8, so I essentially have 35mm tires now. I have dreams of doing a several-hundred mile bike trek, but that's not in the near future.

I am looking forward to some alloy wheels for the braking, but I like the momentum of the steelies. Oh well.

What's this about needing to run a lower pressure given a higher body/bike weight? That's counter-intuitive. More weight on the same pressure will give you more compression.

I'm inclined to get these, since I have them in the 27x1-1/4 size https://www.niagaracycle.com/categori...ipe-steel-bead

rydabent

Reading and pondering all these posts, I think that all rims should come stamped somewhere on them what the Max pressure allowed is.

FrenchFit 

On 27" inch rims I've run a 1&1/4 in the back and 1s or 1&1/8 up front. Steering stays quick and rear handles the weight of panniers nicely. Standing still the rear will sit a tad bit higher, but only you will notice it.

Faced with a similar decision as yours I went with Sun M13 polished rims (27) and laced then to the original hubs & spokes. It's been two years or so, those rims have stayed true and I've run with fairly high pressure; switching between Paselas, Bontragers, Gatorskins and Vittorias. I think the Bontis are rated at 120psi, but alas they've been discontinued.

I like the ride of 27" rims on vintage bikes, each to their own.

FastJake

It's a good idea and I've done it on some of my bikes. But I doubt you'll fit a 45mm tire in the back. Try it first and see.

Could you explain this please? A rim that's 8mm larger in diameter is not going to "ride" any different.

rekmeyata

I woudn't worry about getting brakes until you know for certain they won't fit. Borrow a set of 700's and see of the pad holders will drop down far enough to reach the rim correctly.

FrenchFit 

You've already announced that an 8mm greater rim diameter does make any difference, why are you asking for an explanation? You obviously have all the answers.

rekmeyata

A 27" rim is a tad more comfortable riding which is why there are tourists who embrace the 27, but the disadvantages is a 27" wheel handles a tad less as well as a 700c which isn't an important consideration to those touring, and the other disadvantage is the 27 will weigh more thus climbing hills and accelerating will be a tad less again not a consideration to tourists. When I say tad less in performance, I doubt there is more than a 1/2 of 1 percent to at the most 1% difference between the two, but racers are racers and a 1/2% to 1% is something. Of course there is the thought too that when it comes to comfort that no one can tell the difference, maybe not on an unloaded bike but I think a person could on a loaded bike and that's why some touring people prefer it.

Another disadvantage to a 27, depending on it's age, do not have a hooked rim edge to hold a tire bead as well, however that is only a concern if you need to run psi greater than 100. My Schwinn Le Tour Luxe came factory stock with Wiennman 27" rims and those do have a hooked rim edge to hold the bead better. Not sure if hook is the right word but you get the idea.

Also nowadays there are no high performance racing tires available for 27" tires, thus trying to race on a set would mean not only the slight extra weight of the larger rim and longer spokes but also a heavier tire being used, so you could easily end up with a wheelset/tire combination that is about a pound or maybe more heavier than a 700c.

Buying tubes for a 27 is no big deal, I use 700c tubes in mine and they fit fine.

Before you go crazy about wheel size, if the rim gets too small then you have to increase the chainring size to make up for the difference to maintain the gear ratios so at that point you offset the advantage of the smaller wheel. I don't know what that small size would be but I have feeling that a 650c is the smallest a person can go before the chainring ratio is considered. And I don't know if I explained that part well either, but I think it's close.

I hope I covered this well, if not someone chime in.

FastJake

I'm not as unreasonable as you make me out to be. If you have a legitimate explanation I'd be glad to hear it.

The wheel size isn't what's matters, but the overall tire diameter. A fat 2.4" MTB tire (26" wheel) is roughly as tall as a 700x23 tire.

rekmeyata

I'm not sure I understand you. The size of wheel combined with the a fat MTB tire, in your example is 26" which is as tall as a 700x23, but I wasn't talking about those two types of tires, and even if I were the size is the same from the ground to the top of both tires, thus whatever point you're trying to make is moot. The point of having chainring size change would be if you have two wheels, with tires, one would be say 27" and the other say 20" and to get the same speed from a similar performing cyclist riding each bike would require a different gear ring size on the smaller one so he can keep up with the larger wheel/tire cyclist, thus the weight of the larger chainring would off set the weight of the reduced size wheel/tire combo.

My point was the comfort issue more than anything else since I know so little about the other stuff, so I found this to help explain that more than I did: https://sheldonbrown.com/650b.html