Bekologist

So,

I've read somewhere about the effects of tire size on trail of the fork.

if a fork is measured with trail for a 23mm tire, how much additional trail is gained from a 35mm tire on the same fork?

I seem to be experiencing a more stable and self correcting nature this morning since i had stuffed some 35c onto my travellers check, which has previously been sporting some more modestly sized tires.

anyway, i noticed a difference in handling on identical front rims and much larger tire.

BCRider

While the trail will change very slightly with a lift of the tire size it'll be so insignificant that it'll make little if any difference. But added to the change to the dimensions of the tire's contact patch the two things may just add up enough that you're noticiing the change in the bike's feel.

fuzz2050

my quick math shows that a change on tire size like that should give you about 5mm more trail. It's not much, but it might be significant, depending on just how sensitive you are. Likely, the change in ride from the new tires will overpower it though.

HillRider

My trail calculator says about 4 mm more trail with the larger tires assuming you fit them to both wheels so the effective headtube angle doesn't change. It would have about the same effect as changing from a 43 mm fork rake to a 40 mm fork rake.

zzyzx_xyzzy

There's a slight increase in geometric trail but you are probably also feeling a substantial increase in "pneumatic trail." Basically there is a self-correcting force that is generated by the tire's contact patch squirming as it rolls. A bigger, longer contact patch creates more pneumatic trail.

https://en.wikipedia.org/wiki/Pneumatic_trail

There isn't really a formula for pneumatic trail as it depends too much on the particular tire and loading.

formulaben

Can't wait to see the difference with my new 28mm Gatorskins on the road bike...

Andrew R Stewart 

I think the change in rotating weight will add afactor. Andy

Shimagnolo

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

formulaben

Nice!

sreten

Hi,

A wider tyre will have a bigger contact patch as it should
be ideally run a lower pressure, but there is no reason
to assume the patch becomes longer, more only wider.

rgds, sreten.

formulaben

Have you ever taken ink spots of the tire's contact patch before, as on this site?

FastJake

+1

When I switch from a heavy 35mm tire/wheel to a race weight 23mm tire/wheel on my commuter I can feel the difference on the front end. That might be more significant than the geometry change.

Bill Kapaun

Your gyroscope is more massive, thus less "twitchy"

Al1943

+1
Especially uphill.

fietsbob

Then there's 'Pneumatic trail', a factor of the size of the contact patch.

fuzz2050

I thought the effects of gyroscopic stabilization were minimal on bikes, as proven by that strange bike with two counter-rotating front wheels?

reddog3

Certainly there is a difference in HT angle, and as a result a change in trail when you switch to a larger tire. Others have provided the numbers, but I'm not certain those geometry changes alone would have a significent effect on handling if you made the changes with the same tire combo as original. My personal view is that the increased gyro effect from the increase in rotational weight (yes even at bicycle speeds) made what you perceived as an change in stabilty.

I can remember a day back when we were racing motorcycles we were always trying to figure a way to get them into, though, and out of corners better- we played a lot with what we had to work with at the time. We could change the HT angle, and as a result the trail. We didn't have the wherewithall to change trail alone.

Changing front end angles made handling difference noticible, but nothing I'd say was an improvement in stability- at least to the point that allowed us to get around corners faster. The biggest change in handling, and the one factor that allowed to achieve our goals was rotational weight (gyro).

Bicycles certainly are not the same animal (and they are not ridden the same) but I believe that rotational weight has a larger affect on handling than anything- thats assuming one isn't going to load the front end with a lot of luggage. That's a whole 'nother trip. Then there's the weight distribution thing (front to rear). There's a difference between motorcycles and pedal power, but I still feel the rotational weight of the front wheel has more to do with feel and stability than any other factor.

Airburst

Not if you change both tyres, which raises or lowers the front and rear ends by the same amount (assuming the front and rear tyres are identical both before and after)

gregjones

I replaced a front "deep vee" heavy (extra heavy) rim with a one that was over a pound lighter. I used the same tire and tube. The difference in the bike was incredible. It had been slow and sluggish but changed to quick and nimble so much that I stopped within a mile of the house to "check everything out".

Andrew R Stewart 

Independent of the rotating aspect of a wheel the increase of mass does get noticed in the swing effort. I will also add that I have seen a reduction of a bike's "speed wobble" (yes, this is a whole other topic but does overlap some with this thread) by changing out the ft wheel from a skinny light one to a touring wide and heavy one. Andy.

rdtindsm

The gyroscopic effect of wheels is not the primary reason that a bike is rideable. The counter rotating wheels show that the primary balancing technique is simply the steering corrections that keep the bike under you. Removing the gyroscope will make the bike very hard to ride no-handed.

oldbobcat

So the increase in trail will be greater if the head angle is slacker.