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Wide tyres on narrow rims

by rdmp2
Tue, Apr 18, 2017 08:58
7

Looking for advice here please.

My oldest bike (Spec Sirrus) has recently become the designated child carrying bike with a rear rack mounted seat. However it has not been a huge success due to the harsh ride over bumps. It currently has 28c tyres at ~70psi. I will lower the pressure, but unsure how low I can go (I am 66 kg,  rack+seat+child = ~ 15 kg right on the back wheel, plus upright position means most of my weight is also over the rear).

 

I would like to put wider tyres on (~35c), however according to Sheldon 28c is already about the limit for my rims (14 mm internal). I have plenty of clearance- but would it be safe to run 35c tyres on such narrow rims?

Thanks

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7 comments

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Carton | 7 years ago
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FWIW: many old MTBs have internal rim width / external tyre width ratios of over 3:1. I still run the stock 19mm rims on with the stock 2.2" (56mm) tyres (so Trek sees no issue with it) on my '15 MTB. ~5,000 up-and-down mostly road miles later: no issues bar broken spokes. I run even worse light bulbs on my commuter at 50PSI (with an > 100kg load) and no issues so far. But YMMV.

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dottigirl | 7 years ago
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What do the specs for the bike say is the maximum tyre width?

And is there any budget room for a cheap, wider pair of wheels? You may even be able to find some with tyres.

I noticed the lightbulb when cornering after putting 25c 4000s II on some Easton 50SLs. Think they were 14 ETRTO. I suppose it depends how hard you ride. 

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rdmp2 replied to dottigirl | 7 years ago
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Thanks all for advice

Certainly room for wider rims- can you still buy 8 speed wheels anywhere?

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TypeVertigo replied to rdmp2 | 7 years ago
3 likes

rdmp2 wrote:

Thanks all for advice

Certainly room for wider rims- can you still buy 8 speed wheels anywhere?

I'm fairly certain most, if not any, 9- or 10-speed wheel will fit an 8-speed cassette. All three cassettes use the same freehub length; they just make the cogs themselves thinner to smoosh more of them into the same space (hence the reason why the chains are incompatible with each other).

11-speed wheels should do the same with the 1.85 mm spacer usually thrown in for backward compatibility with 9- or 10-speed cassettes.

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rdmp2 replied to TypeVertigo | 7 years ago
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TypeVertigo wrote:

rdmp2 wrote:

Thanks all for advice

Certainly room for wider rims- can you still buy 8 speed wheels anywhere?

I'm fairly certain most, if not any, 9- or 10-speed wheel will fit an 8-speed cassette. All three cassettes use the same freehub length; they just make the cogs themselves thinner to smoosh more of them into the same space (hence the reason why the chains are incompatible with each other).

11-speed wheels should do the same with the 1.85 mm spacer usually thrown in for backward compatibility with 9- or 10-speed cassettes.

 

Thank you- you are correct. I had assumed the freehubs had widened as the number of sprockets increased. I will order the tyres and see how they feel. If I'm concerned I'll pick up some second hand wheels later.

Thanks all for help

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TypeVertigo | 7 years ago
0 likes

Good question.

In my experience folding bikes are a good example of this situation. Most 20" (406 mm) folding bike tires are anywhere from 1.1" to 1.75" wide (28-47 mm) but their wheelsets haven't really caught up with the fashion for wider rims.

14 mm internal width rims are still pretty common, and they're actually what I run on my Dahon. I'm around 85 kg, and I've had no problems with tires with widths of 1.5" (40 mm) and 1.75" (47 mm). Sure, the profile tends to more of a light bulb shape, but unless you're really leaning over hard in turns, I don't think it's a problem. I tend to run both widths at 60-65 psi.

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CXR94Di2 | 7 years ago
1 like

Assuming you're not bombing along with your kid on the back, they will be fine. I'm running 40mm tyres on less than desirable rim width and performance is great. I run about 50-55 psi and I weigh nearly 100kg

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