Toe Overlap on Charge Mixer

[531colin]

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I'm more bothered about the mudguard release issue, because that happens at speed and I can't just move the blockage out of the way.

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With the silly safety device in topeak guards the whole mudguard comes adrift..............

Guys....I think this is a separate issue?

But it sounds nasty, maybe worth starting a new topic?

[MartinC]

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What I haven't learnt is why some think that TO is so dangerous.

Martin....see my post above......its because we don't have the reflexes to just move the pedal or wheel out of the way....therefore we are prevented from turning the wheel for a yard or two....therefore we are coming off......and at least in my case, I havn't learned to distinguish between just bumping the guard with my toe, and something nastier happening!
I don't think its unusual for folk to "freeze" when something happens that is unexpected, and might be hazardous?

Understand what you're saying but my experience is that this happens so slowly that reflexes aren't an issue (I picked my diamond card from B&Q a few weeks back!). I can also understand that familiarity is important too - it avoids the clipless pedal newbie moment where your conscious brain would tell you just to twist your foot but the unconscious part is loudly shouting at you to pull it out as quickly as possible.

[531colin]

Martin
We're not going to agree on this, but we have got to the point where we understand (and dare I say respect?) each others views.....I think thats pretty good going for a topic which has been characterised by some fairly heated exchanges.
May the wind be at your back!
Colin

[MartinC]

Colin, yes it's been interesting, even if no-ones's mind is change then there's a better understanding. One of the best features of this forum is the amount of knowledge it has on tap.

Have a good day - and a good weekend when it comes.

[Mick F]

I measured the radius of Barbarella's wheels (27x1.25) and found them as 355mm. With the mudguard, it goes out to 365mm. If I apply that measurement to my Mercian, I still wouldn't get TO.

This mystifies me. I have a bike with a short wheelbase, - so why, even with 27" wheels, would I still not get TO?

What causes it?

Short wheelbase?
Steep angles?
BB to front axle distance also short?
Wheels too big?

Perhaps all these things, so why don't I get it?

[Michael R]

I measured the radius of Barbarella's wheels (27x1.25) and found them as 355mm. With the mudguard, it goes out to 365mm. If I apply that measurement to my Mercian, I still wouldn't get TO.

This mystifies me. I have a bike with a short wheelbase, - so why, even with 27" wheels, would I still not get TO?

What causes it?

Short wheelbase?
Steep angles?
BB to front axle distance also short?
Wheels too big?

Perhaps all these things, so why don't I get it?

Decent bike, end of story. Better than a chopper

[531colin]

Mick
The first thing to look at is "front centres"....BB to front axle. (Forget wheelbase its influenced by chainstay length)
then you need tyre diameter, crank length, how far your toe comes in front of the pedal spindle, and mudguard clearance if you want 'guards.

When viewed from the saddle, the front wheel/guard moves in an arc....I suppose head angle/fork offset could slightly alter that, but I don't think its a big effect.

[Mick F]

Mick
The first thing to look at is "front centres"....BB to front axle. (Forget wheelbase its influenced by chainstay length)

Yes Colin.
Please look further back up this thread, and you'll see that's not the complete story.

I'm baffled.

[531colin]

Please look further back up this thread..........

Which bit, Mick? I really can't read it all again!

[snibgo]

Front centres, crank length and wheel size (including tyre and mudguard) are the major factors. Then come shoe size (or toeclips where used), pedal size (because it raises the foot), head angle and rake. Those last probably only matter in cases of "very nearly okay" or "not quite okay".

(But for a given top tube length and downtube angle, the head angle makes a big difference, because it changes the front centre: a 70 degree head will have about 37mm more toe-room than a 74 degree head.)

[mark a.]

I'm not quite sure about this, but I think the amount of trail will make a difference.

Essentially, the BB-to-front-wheel-axle distance will change as you turn the bars. The amount of movement will depend (somehow - I haven't figured out how) on head angle and rake i.e. trail.

So perhaps two bikes with identical BB-axle distances but with different trail will have different TO.

I can't figure out which way round it goes (more trail = more or less TO?), or whether it's a large effect.

[snibgo]

Yes, trail (or rake) does make a difference. The 3-D geometry is beyond my small brain.

I note that when I turn the steering from centre to worst-case TO, my clearance distance (from the mudguard to pedal axle) increases slightly (maybe 5mm). But another poster, somewhere upthread, finds that distance decreases.

[531colin]

.................................. But another poster, somewhere upthread, finds that distance decreases.

My tiny brain tripped over that at the time.
I'm afraid I need a bit of convincing that its actually possible, bearing in mind that when you sit on the bike and look down at the wheel, the bit that can touch your foot moves in an arc. That arc must be defined by the tyre contact patch with the road, which is straightforward, and head angle/offset/trail, which is complex, but I think can only have a small effect, ie. the arc the wheel moves in must be a "smiley face" arc. For the clearance to decrease needs a "sad face" arc, where can the pivot be? The wheel must sweep round like a windscreen wiper?

[patricktaylor]

... The wheel must sweep round like a windscreen wiper?

LOL

So if the foot could sweep round like a windscreen wiper there'd never be a problem.

[Mick F]

Please look further back up this thread..........

Which bit, Mick? I really can't read it all again!

Me neither!

It was Patrick and me comparing wheelbase and BB to front axle etc. He has a bit of TO, and me none, yet his dimensions are similar to mine. I seem to remember that his feet are smaller too.

Rake/trail/steering seems perhaps to have some effect. Straight measurement won't show it, but dynamic measurement might?