Moulton TSR rear tyre wear.

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Brucey
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Re: Moulton TSR rear tyre wear.

Postby Brucey » 13 Oct 2018, 10:59am

to assess the front weight distribution when braking down hill, try using a marker of some kind to gauge how much of the front suspension travel is being used. I would be very surprised if you don't hit about 80% weight on the front wheel.

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Mick F
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Re: Moulton TSR rear tyre wear.

Postby Mick F » 13 Oct 2018, 11:05am

Interesting thought though I don't know how you would quantify it.
The front suspension is just a helical spring of course ...... and therefore tightens up as it's compressed making the suspension non-linear.
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Brucey
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Re: Moulton TSR rear tyre wear.

Postby Brucey » 13 Oct 2018, 11:16am

on tele forks it is common practice to set a zip tie on one fork leg; this then acts as a telltale for maximum suspension travel. You may be able to rig up something similar on your moulton, or just arrange a pointer that is set (checked by dead weight loading of the front) to the 'sag' that corresponds to that load.

The former method will allow detection of transient loads, the latter may give you a better indication of average loads if you can keep an eye on it as you ride.

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Mick F
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Re: Moulton TSR rear tyre wear.

Postby Mick F » 13 Oct 2018, 11:25am

Zip tie idea has merit. Excellent idea.
Could fit one on the centre plunger where it goes up inside the head tube.
moulton-tsr-26.jpg


May get round to experimenting next week and it will show how much travel is involved. I should then be able to place the front end of the bike on the bathroom scales and see how much weight is involved to get the plunger to the same place.
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Mick F
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Re: Moulton TSR rear tyre wear.

Postby Mick F » 15 Oct 2018, 6:23pm

20miles yesterday with the new Conti Sport Contact on the rear.
Absolutely excellent! :D

The difference in ride with this tyre compared to the Schwalbe Durano was rather astounding. The Durano was harsh and hard, and also "wooden" in feel.
The Conti was smooth and lively, and at the same time compliant and quiet. I can't remember feeling the opposite effect when I went from Conti to Schwalbe, but the reverse was really noticeable.

As for the zip tie idea to see the front suspension travel, I intend to have a ride tomorrow and I'll fit a wrap right at the top with zero load on the front. The zip tie will need to be a big chunky one as the front suspension strut(?) thingy is narrow but the front hole into the head tube is wide with quite some clearance.

I'll have a fiddle tomorrow morning.
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Mick F
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Re: Moulton TSR rear tyre wear.

Postby Mick F » 16 Oct 2018, 8:16am

Put a white zip tie on, ready for a ride this morning. Photo isn't that clear as it's white, sorry.
Click for bigger/closer views.
IMG_0579.jpg

The "head" of the zip tie is hard up against the bottom of the head tube but not fastened too tight so it will be moved downwards when the suspension compresses.

I'll be doing only a short ride this morning as I don't have enough time available to do a long one. Dozen miles or so will be about it, but the ride will include some downhill braking, so we'll see how far the suspension dips downwards.

BTW, the suspension will not go upwards any further than it is when at rest as the dropout linkages have a designed "stop" to stop the suspension from falling apart when the bike is lifted! :lol:
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Mick F
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Re: Moulton TSR rear tyre wear.

Postby Mick F » 16 Oct 2018, 10:59am

Well .......... that was interesting, though I don't know why.

15miles, some bits flattish, some bits steep uphill, and some bits steep downhill. I reset the position of the zip tie a couple of times and experimented.

Flat Roads:
It seems that when riding slowly, the suspension only goes down a quarter of an inch. As soon as you brake, the suspension goes down further of course. Riding faster, the bumps appear harder of course, so it moves more like three eighths of an inch.
Braking HARD on the front brake only, it goes down the furthest maybe half an inch or more..
Front Brake Flat.jpg


Down Hill Steep:
This made the suspension go the furthest. In fact right down even though braking with both brakes and shifting my weight back.
IMG_0581.jpg
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Brucey
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Re: Moulton TSR rear tyre wear.

Postby Brucey » 16 Oct 2018, 11:30am

I would imagine that the lowest position corresponds with about three quarters of your body weight...?

BTW there is some 'anti-dive' in the front suspension when the links are below horizontal, which will interfere with the results a bit.

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Mick F
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Re: Moulton TSR rear tyre wear.

Postby Mick F » 16 Oct 2018, 3:10pm

Anti-dive?
How does that work?
Just by dint of the angles of the linkages I suppose, or the fact that the spring gets tighter as it compresses.

Next experiment is to see if I can lean on the front of the bike to depress it as far. Somehow I don't think I can for any length of time as well as read the bathroom scales. I could sit on the handlebars but staying vertical would be a trial! :lol:

I'll have a go and see how it reads at the max I can depress.
We know the static weights already ..........
Moulton plus me.
Front 34.8Kg
Rear 58.5Kg

Back later to this.
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Mick F
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Re: Moulton TSR rear tyre wear.

Postby Mick F » 16 Oct 2018, 3:35pm

Grief!
That was a strain! :shock:

I put the front end on the scales with the zip tie at the top of the strut.
I leant down hard whilst reading the weight and then releasing to see how far the tie had gone down.
I'm rather puny I fear, or I need to be a big chunky rugby player rather than a cyclist!

I leant with all my strength whilst still being able to hold the bike steady, but my feet were only just touching the floor.
8st was all that I could press which includes the front weight of the bike.
At 8st indicated on the scales = 51Kg, the zip tie went down to where it had been when braking hard front brake only on the flat. I couldn't get it any further.

51Kg pressing minus 5.9Kg of bare front weight of the bike, meant that I was actually pressing 45Kg
I weigh 12st in old money = 76.2Kg
This suggests that when braking hard, about half of my weight is pushed forwards.

Does that make sense?
Have I got the numbers right?
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Brucey
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Re: Moulton TSR rear tyre wear.

Postby Brucey » 16 Oct 2018, 6:03pm

45kg is 59% of your bodyweight. There is a small error because not all the dead weight of the bike is squashing the spring; the unsprung weight (front wheel and moving part of the fork ) isn't loading the spring.

the static weights you indicate suggest ~29kg bodyweight ( about 38%) over the front. So you are getting about 21% weight transfer to the front under braking, or there is about half as much again potential to use the front brake as the rear to slow you down.

This is less weight transfer than I expected but there is probably still enough that the rear wheel might be hopping and skipping over bumps whilst you are braking.

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Mick F
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Re: Moulton TSR rear tyre wear.

Postby Mick F » 17 Oct 2018, 9:45am

So that was a valid test then! :D

I was braking hard going down the steep hill into the back of the village on the way home, and the back wheel was definitely hopping and skipping - no doubt about it.

About a 20% hill I would think, and going into a 20mph limit with a crossroads at the bottom.
https://www.google.co.uk/maps/@50.52506 ... 312!8i6656
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Brucey
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Re: Moulton TSR rear tyre wear.

Postby Brucey » 17 Oct 2018, 10:00am

if the back wheel hops and skips when the brake is on, then this can wear the rear tyre double-quick. If previous rear tyres have shown very uneven wear, it might be that the brake is slightly more draggy in one spot (eg the rim join) and this causes more wear in one part of the tyre than another.

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