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I have a touring bike which I use for commuting, I carry about 30 kg of tools with me usually on this pannier type thing I made on the back. And usually a work belt on the front which is 7 kg

bike I'm wondering how much more I can safely carry on the bike without stressing it too much. The tyres seem to be under a lot of strain in particular. I'm 75 kg, unloaded with just me the bike tyres look fine, when loaded they're flattening out to an alarming amount.

I just ride on the road, but they're not good roads, I want to add about another 20 kg of tools and I'm wondering if I should put a fatter tyre on the back. I have 29 inch tyres on my mountain bike which look like they might fit. Or whether I'm worrying needlessly?

  • If you look for tyres (and posibly a rear wheel) recommended for tandems or even just heavy touring, you'll have no problem. I'm a few kg heavier than you, and sometimes carry a toddler in a seat as well as panniers and just run marathon plus. Whn my rear wheel broke (probably a kerb combined with not checking the spokes often enough; it had 10 000 -- 20 000 km on it) I replaced it with a 36-spoke touring wheel. – Chris H Aug 22 '16 at 15:00
  • Just a comment - don't do that thing with the plastic shopping bags on the handlebars.. Its workable at slow speeds but if you do a faster manoever, the bags whip around and will throw you. – Criggie Aug 22 '16 at 21:15
  • Bike manufacturers normally state weight limits for their bikes in the manual, which you can exceed at your own risk. – Batman Aug 22 '16 at 21:29
  • Those tires look to be 30-35 mm wide. Properly inflated, these should be able to handle a 100kg rider and 50 kg of additional load. "Properly inflated" would be roughly 500-700 kpa on reasonably smooth roads. – Daniel R Hicks Aug 23 '16 at 1:57
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The flattening is normal, since there is so much weight. Don't really try the MTB wheels. They will probably not fit and you will have to be rolling with different sizes of tyres that may not fit to the frame. Increase the air pressure (or go tubeless) and make sure you change tyres in short periods of time. Don't let them wear totally off.

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It's probably going to come down to testing, because fatter tyres generally have a lower maximum pressure. I suggest starting with a wider tyre, and it's likely that the 29" MTB tyres are also ISO 622 (700c), so they will fit the rims. If they fit in the frame then they're likely to work better as long as they're rated to a decent pressure.

The equation you care about here is weight/pressure = area, in this case weight on the wheel divided by pressure in the tyre = area of contact patch. The bigger the contact patch the more the tyre flexes as you pedal, so the more you have to work. But a wider tyre gives a wider contact patch, so you get less flexing for the same area. A wider tyre is also deeper, so when you hit a pothole there's more give before you pinch flat.

Particularly on bad roads, and with difficulty ordering cool new things from your "local" bike shop,the usual solution of high-quality, high-pressure tyres is not going to work too well. If you could, I would suggest such a tyre, but on potholes and gravel roads those give a rough ride (meaning you also want a high-quality hand-built wheel).

One other tweak is to suspend the load somewhat. If you put a partly inflated tube folded up under the tool bag in the pannier the tools will bounce on that, reducing the stress on the tyre and wheel when you hit bumps. It will also grind against the sides of the pannier, so I'd put the whole thing in a sack. If that works (I've never tried it, but it sounds plausible), it won't help with the load directly, just the punctures and broken wheels.

From memory of a long time ago, I used to carry 50kg or so on a fairly stock MTB when I weighed 70kg, on fairly rough roads. But I also used to go through a rear wheel every year or two.

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Consider a trailer - I've carried 50 kg of bike tools on a recycled kid's trailer successfully.

The trick was to cut a floor from some medium customwood. I notched the corners to fit exactly within the four up-posts, and to rest on the four horizontal rails. The longer term plan was to add some small lips to help prevent things falling off.

Another advantage, you can leave the tools on the trailer and merely unhitch it for storage, or to free the bike for a quick trip.

If you do go this way, get one hitch for every bike you might use as a tractor, and one spare that you can fasten to a stake. I've hammered my hitch/stake into the ground and used it as a pitching point, along with some stout buckets under the rear corners for a stable triangle.

Depending on your need, a small workbench could even be fastened on top. for sawing or whatever. Could even attach a small bench vise.

  • yeah, I made a trailer a month or so ago, it got hit the first day and it lasted almost a week before a car totally wiped it out, I'll get around to making another just for shopping trips and lugging kids around in the village, too dangerous in town though, drivers here just drive around in a daze. – Kilisi Aug 22 '16 at 21:44
  • So why is the driver or the driver's insurance not buying you a replacement trailer? Why did you not report it? – Criggie Aug 23 '16 at 0:30
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    I'm third World, no point, doubt they had insurance and they didn't stop. You're not supposed to stop even in a fatal accident here. You're supposed to drive straight to the police station and report it, but never heard of anyone actually doing that. – Kilisi Aug 23 '16 at 3:36

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