IBB

OPPS sorry bout that! I wanted to include the quote above and make a comment. Anyways I was all set to pull the trigger on getting the Continentals at the https://biketiresdirect.com/ site, but I have one more question. The inside width on my rim is 20mm. From the above comment, it looks like the Grand Prix Size 20x1 1/8 (28x406), would fit correctly right?

Sorry for all the questions, promise this is my last one on this matter.

jur

I must say it never occurred to me that my Aeroheat rims might be too wide. The 35mm Comets are fine on it. My gut feel is it will be fine - manufacturers tend to err on the side of caution to avoid comebacks.

JackJ

Recent tests in Bicycle Quarterly magazine have actually shown that wider tires and moderate pressures are often faster than narrow, high pressure tires. (Vol. 5, No. 1 has the initial tests and tire reviews, with more in subsequent issues.) The jarring associated with high pressure tires is energy lost in moving the bicycle up and down. The greater compliance of a wider, lower pressure tire (if it has a thin tread and casing) provides suspension over minor surface irregularities (e.g., typical asphalt) that results in more efficiency, aka higher average speeds. Interestingly, there was little correlation between which tires "felt" fast to the testers, and which tires measured fast.

On a steel test drum, or a smooth velodrome track, high pressure is great. In the real world, not so much. The problem is that most tire manufacturers don't offer their best stuff on wider models; many wider tires are dogs due to very thick treads, flat resistant belts, and otherwise stiff casings.

I've switched from 1.125" Stelvios at about 100 psi to 1.25" IRC Metros at 80 psi on my Swift, thanks to James' endorsement. I can't say which is faster, but based on the BQ article, I'm hopeful I'm gaining a little speed, and I'm certain I'm gaining a lot of comfort. I like getting some cake with my cake.

Jack

jur

I have read somewhere that for average road conditions, 110psi is about the optimum. Any higher, and the lack of compliance begins to slow you down again.

This effect is probably quite small compared to wind resistance. And I also am leery about riders' reports about what "feels" faster. If there is one thing we can't trust, it's our feelings.

On my Swift, the Comets "feel" very comfortable at the back - but I think the frame is also flexing vertically a bit due to the absence of a main triangle, and this adds substantially to the comfort over small bumps. I often marvel at this comfort, it's almost as if there is suspension. The front "feels" more bumpy - explained by the short stubby forks which must have very little give in them.

So they are not like concrete doughnuts to me. But I have not tried out anything else, so that opinion is really not worth much. I am getting some Conti GPs and the Comets will go to my wife's Dahon Yeah/Helios.

IBB

Hello all,

I just got my order today and it looks like the inner tubes are too big in diameter. Looks like a factory error. In the pics, the inner tube is against the inside surface of the tire. There's no more room to spread the inner tube out to. There's no way that the inner tubes will work on this tire unless there's overlap of the tube. Anyone else had this problem?

I bought the tires and tubes from biketiresdirect.com. The tubes are Kenda 20 x 1 -1/8. On the website they're called Quality inner tubes.

Allan

IBB

Sorry, I'm not sure how to add pics with this forum yet.

https://www.flickr.com/photos/8168607@N02/1367472163/
https://www.flickr.com/photos/8168607@N02/1368369008/

BruceMetras

Hi Allen,


20 x 1 1/8 tubes will be for 451mm wheels/tires... looks like you need 20 x 1.25 or 1.50 (406mm wheels/tires)

jur

I installed my Conti GPs last weekend, I'll do a review a bit later, but for now I will comment that it feels as if the tread has regular bumps, knobblies almost ie when I roll over a smooth bit of road, I feel a regular "brrrrrr" which is unexpected. the pressure is about 100psi. I will do some more tests at different pressures tomorrow.

james_swift

Jur:

So how do the 1 1/8 Contis fit on your Aeroheat rims? Can you post some pics? I'd seriously consider these tires if I knew for sure that they'd fit on my rims.

jur

They fit just fine - my fears were ungrounded. I am using 1.35" Scwalbe tubes, also good. The tyre is still slightly wider than the rim, looks much like a road bike rim & tyre. The rim width I think is just ideal for the Contis. I'll get some pics and post them tonight.

Bacciagalupe

Higher pressure = faster / more efficient

Plus some people are less sensitive to road buzz than others, and can thus tolerate harsher tires.

awetmore

Narrow does not equal fast.

My vote is for the Avocet Fasgrip Freestyle. It's got a light and supple casing, is wide, and fast. It's also comfortable. I just switched my folding bike from 406mm wheels to 349mm wheels and wish the Avocet was available in that size too.

awetmore

In the testing in Bicycle Quarterly (which I was involved with) we found the differences above 85psi for most of our tires to be minimal. For wider tires (35mm) we didn't measure differences above 55psi for most tires.

We also found that you can't go by feel. Tires that "feel fast" often aren't, and visa-versa.

[quote]This effect is probably quite small compared to wind resistance.[/quote

This depends entirely on your speed. At lower speeds rolling resistance can be a larger component than wind resistance. You can see this by playing with analytic cycling and other computer models.

At my speeds (16-18mph sustained on the flats) rolling resistance is a meaningful component. At TdF speeds it is not. When I'm doing loaded touring (say 14mph sustained on the flats) rolling resistance is an even larger component.

alex

stevegor

You may be right there, I've also used Primo Comets at about 100psi, they're quick too and handling is good. The Contis, in my experience , at 110-115 psi are fast, but they can be twitchy, it's what you get used to.

IBB

Oh I see where I went wrong in my order. On this page, https://biketiresdirect.com/productdetail.asp?p=QUQTU I should have picked the 20x1.25/1.5 Presta (ISO 32/40-406) I picked the ones right above it. Chalk one up for learning the ins and outs.

Thanks all for the responses!

james_swift

Excellent! Looking forward to the pics.

jur

OK here are the pics:











I measured the rim & tyre widths:
Rim: 22mm
Tyre: 27.5mm

james_swift

Wow, they do look like a perfect fit. They have that characterisitic Conti high-profile, too. Nice!

Now you have me hooked...Contis and Michelins were my favorite tires back (way back) from my roadie days. These will look wicked on my fixie. Must get them.

One more favor, Jur: could you please measure the resulting diameter of your wheel? (What I do is pull the front wheel, stand it up parallel alongside a wall, then using a book as a straight-edge, measure from the floor to the bottom edge of the book).

So how do they ride? From memory, I always found them to be a bit more comfortable than other tires (I assumed from the flex induced by the trademark sidewall and higher-than-normal profile). I also found them extremely long-wearing and just-as (if not more) puncture resistant than kevlar tires.

Thanks!

awetmore

Conti tires often ride harsly due to their stiff sidewalls. The stiff sidewalls give them a higher rolling resistance (especially on wider/lower pressure tires) than most other brands. They are long wearing.

jur

The rollout was 1450mm. Diameter 47cm.

LittlePixel

I ❤ my conti Grand Prix 406's; The yummy amber sidewalls can sometimes be a bit prone to wear/peeling away from the beading but they're lovely grippy fast almost-slicks.

Mmm... Close up tyre pron!

james_swift

So they're .5 inch smaller in diameter than my IRC Metros. Gear calculator says I lose 1 gear inch, but no effect on speed at 100RPM overall. This will do just fine.

Must get these.

Thanks!

jur

Well I did some roll-down tests. I'm confused now.

I did 4 roll-downs for each condition to get the average result. I am just reporting the accumulated time for each case.

The test consisted of a standing start, then the clock started and brakes released simultaneously. Once I pass a reference point, the clock is stopped, only to be continued on the next one, so accumulating for 4 roll-downs.

I tested several bikes, and also included some variations in aero position.

The temperature was between 10-15degC, with little or no wind.

Results:

1. Swift with Conti GPs, normal position:
100psi - 2:56 (2min 56s)
80psi - 2:59
60psi - 3:00

Very little variation. All I can say is maybe harder tyres are faster. Don't read too much into the 4s difference on 100psi - I think my method could result in 1s variation.

During this batch of tests I was acutely aware of the wind rushing past me, so I kept looking for sings of wind, but there was none. Initially I wore a bit daggy/baggy clothes, so I thought I need to put on sleeker fitting bike stuff, but I don't really see any difference in the result. Just a maybe, again.

So I repeated those tests with me sitting as upright as I can be on the fairly aero-position Swift. (remember my bars are quite a bit lower than the saddle.) I kept the pressure at 80psi. Then again at as aero as I could get.

2. Swift non-aero, 80psi: 3:00
3. Swift aero, 80psi: 2:49. Here at last was a significant difference.
4. Swift, with differenr front wheel fitted (American Classic hub, Primo Comet tyre at 80psi): 3:00

Then I took my wife "Helios" with the Primo comets fitted, 100psi: 2:50! Big surprise. The position is anything but aero, but it was consistently faster on each run. Different clock used to measure though. There could be a second less in each run, making the difference less.

Lastly I took my Raleigh twenty: 3:00 The first thing the I felt, pedalling to the start point it felt like I was cycling through treacle. Very sluggish. But the roll-down was 3:00 again! The R20 has a cheapie Kenda Kwest on the fron, a Big Apple on the back, both at perhaps 50 - 60psi. It's been a while since I checked them.

So in this fun and non-rigorous test, I conclude:

* Tyre pressure makes very little difference overall. Other factors just dominate completely. So you might as well ride at 80. Forget about how slow it feels - it's not really slow. You can't trust your feelings.

* Aero position makes a big difference. But we knew that anyway. However, in my test there was very little difference on the Swift between "normal" (which I thought was quite aero) and as upright as I could get. The only big difference came in when I lay completely flat, tucked my legs together and arms against my body, and just barely able to see the road.

* Somehow the "Helios" is much faster. The only thing I can think of, is the rear wheel freehub and main bearings have less drag. But mostly the freehub, because I thought the Helios back wheel has more drag when just spinning it. But my American Classic hub's freehub body has some drag, I think from the rubber seal. It can't be the front wheel, mine has infinitesimal drag compared to the Helios one.

* Different tyre on the front had very little impact. I am sure it's not the hub - both those hubs are superbly drag-free.

* I am left wondering if the Raleigh 20's 8sp hub has a lot of drag. It sure felt hard pedalling that sucker.

james_swift

Nice work, Jur. It's my suspicion that differences in bike weight, as well as the distribution of the rider's weight between the 2 wheels (i.e. bikefit/position, also the bike's wheelbase) may also play a role.

I know it would be a lot of work to pull off, but I'd be very interested to see roll-down test results with each different tire (tyre) on the Swift alone.

stevegor

Wow Jur,

Now that's thorough,

I've found from experience during my racing days that some riders will swear that Campag Record is the ultimate and others say Shimano Durace is, the same goes with choice of tyres..."Contis are the best", "Vittorias are better" and so on, and so on. Even weekend warriors having coffees argue over tyres, brand of bikes etc etc......Most of us are not qualified to know the difference. In the end I think it's what you're happy with, I like the Contis on 406 rims and Stevlios on 451 rims, other don't. All I need to know is that when I'm leaning hard into a fast corner the tyre will keep grip, both my choices seem to do that.
I remember seeing a guy with hairy legs on an ancient Cannondale with ratty tyres often beating the pretty boys on their cf bikes in races, he was the Aust Vet champ in his age group numerous times, so my point is...It's not the bike or even the tyres, it's the engine, it's the legs that make the difference.