lbear

Does anyone find the your bike get less stable. (Need less rake more trail) When running smaller diameter tires on a cyclocross bike. My LBS guy mentioned his cyclocross bike was less stable with road wheels on then cyclocross set. I can see on paper how big changes in diameter would effect trail, but I don't know how much real world (23-32mm)changes would effect handling. Since I thinking of setting up a commuter/cyclocross bike I wanted to make sure I get a high speed stable set up on smaller tires.

Andy_K 

I've used 700x35 Maxxis Locust CX tires, 700x30 Michelin Mud2s, 700x25 Continental Gatorskins (which are virtually 23s) and 700x28 Panaracer RibMos on my Kona Jake. The difference in feel between the CX tires and the slicks is so huge that I don't think I'd notice any diameter-induced handling differences. I certainly haven't had any problems with the bike not feeling stable with the skinny tires.

I also am not convinced a 23mm tire would be significantly faster than a nice, smooth 32 like the Marathon Supreme.

lbear

So are the Marathon Supremes your favorite commuting tire. Since we are kinda neighbors you would understand my commuting conditions.

fuzz2050

my quick math says changing tires from 23s to 35s should change the trail by about 4mm.

lbear

Super! I just found a Bicycle trail Calculator.

https://yojimg.net/bike/web_tools/trailcalc.php

myclem

I put 23's on my CX bike and it spontaneously combusted! :-)

I race my CX bike on knobby 32's.
Off season, it becomes my commuter with slick 23's, even did double-centuries with this setup.
I don't notice any stability problems (but I don't take it over 40mph)

When I ride my CX bike with slicks on the road I find it's much more stable because I don't have to deal with mud or speedy dismounts or remounts or jumping barriers or cowdung piles or half naked bearded dudes in tutus yelling and throwing beer at me. (I wish the CX season wasn't over)

</tongue></cheek>

moralleper

I was commuting on 25 Conti gators and recently switched to 32 Pan Max city, they are now called T-servs. I do not think I will go back to the 25s. I feel so much more confident on the 32s and my time and speed did not change. I also do not feel so much slow down when I am in rough sections because the tire sucks up some of the bumps instead of the bike and me. As for the stablility I think that has more to do with the wheel base then the actual tires.

Andy_K 

I've got 700x50 Marathon Supremes on my rain bike (Marin Muirwoods 29er), and I love them. I'm thinking about getting a set of 32's or 35's for my cyclocross bikes. For commuting they're great -- lightweight, nice road feel, roll great, good grip on wet roads, puncture resistant. As long as you stay on pavement, the only drawback is the price.

meanwhile

You could get Extremes - Supremes with a fast rolling grip that's supposed to reasonably good on or off road. They come in 35 or 40mm.

Re stability: isn't more likely that you're feeling the effects of a contact patch that is 1. smaller to start with and 2. doesn't conform to the road as well, due to increased pressure? It's also possible that your wider tyres were grippier rubber, especially if you've gone from "real" cross tyres to generic 23mm tyres.

myclem

On the road, slicks are grippier.
Off the road, knobbies are grippier.

meanwhile

Grip is contact patch * grip per cm^2. If two tyres have an equal contact patch and are made out of the same rubber compound then, yes, the slick will be grippier on the road. But that isn't the case we are talking about! If the contact patch is smaller and the compound less grippy, then a narrow road tyre can have less grip even on the road. Tread reduces road grip, but it is a mistake to assume that every slick in the world will have more grip than every non-slick - especially when the non-slick will have double the contact patch!

myclem

Is there double the contact patch between 23mm and 32mm? (thread title sizes)
I dunno. I have to take my shoes off to count that high to do those scientifical numerations.

OP didn't specify exactly which tires, or how fast he thinks is "high speed". So...

Specifically, in my experience, I use 32mm WTB CrossWolf cyclocross tires for racing cross and switch to 23mm Vittoria Rubino Pros on the road.
In the wet PacNW (where the OP also lives), I definitely do not feel the CrossWolfs are grippier than my Rubinos on the road, and do not dare to lean the bike on 30mph turns on the knobbies like I do on the slicks.

Of course, I realize this is only anecdotal and an opinion and only a sample of 2 specific tires. Moreover, I ain't usin' no formulas to calculate contact patch size and gripperiosity. I'll concede to the gods of forum interwebs that you're right, but I'll still refrain from trying to overcook high speed turns on the road with knobbies.

meanwhile

The ratio of patch area is the inverse of PSI - ie halve the pressure, double the patch size.

Well, yes. Because you're comparing excellent slicks - Rubino Pros are great rubber - with pretty good (and severely treaded) cross tyres. I'm not saying that slicks will always be worse - anything but! - just that if there is a handling difference then the OP should consider that poor slicks might be the problem. Especially if he is comparing them to a high quality cross with a less aggressive tread. Which he might well be, because an awful lot of people go cheap when buying tyres...

Not all off road tyres have a problem with turning on the road. The ones that'll mess you up most are the ones with sharp "teeth" on the sides for digging into soft ground in turns. These teeth bend when you turn hard on hard surfaces. With tyres everything depends on the details.