CityCyclingEdinburgh Forum » Questions/Support/Help

Do i need narrower tyres?

(13 posts)
  • Started 7 years ago by Neil
  • Latest reply from Neil
  • This topic is not resolved

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  1. Neil
    Member

    Geeky tyre width question...

    According to this tyre pressure calculator I should inflate my 25c tyres to 56psi at the front! That's being conservative with weights- I'm 65kg, bike is 10kg with pump etc... so I calculated it for 80kg (5kg of clothes, couple of water bottles)
    http://www.dorkypantsr.us/bike-tire-pressure-calculator.html

    It says that if calculated pressure is below the tyres safe minimum (which 56psi would be with current tyres) then choose a narrower tyre.

    Even with 5kg of panniers added to the weight it's still saying to run the front at 63psi.

    Should I actually be using 23c tyres? Would I be more/less comfortable on 23c tyres inflated according to this calculator, compared with 25c tyres "overinflated"?

    I appreciate that the validity of the formulas used in these calculators are probably contested, but curious to get peoples thoughts on this?

    This question stems from obsessive geekiness, not any concern over "performance" ;-)

    Posted 7 years ago #

  2. Nelly
    Member

    I refuse to declare a true weight !

    Suffice to say your site suggested a rear 117psi for a 25 tyre for me !!

    I currently run 28mm Gatorskins, usually carry a few kilos of clothes / work stuff in Carradice and inflate to 120 rear and 110 front.

    But thats more a puncture deflection strategy than anything else.

    Posted 7 years ago #

  3. Cyclops
    Member

    That site's the biggest load of nonsense I've seen in a while. I should seemingly be running my tyres at 194psi!

    Posted 7 years ago #

  4. Neil
    Member

    Haha

    I took saddle bag and pump off bike when I got home....fully clothed, helmeted and shod, me + everything extra carried on the bike came to 69kg so just under 79kg with the bike.

    I think the 15% drop thing has been around for while and is supposed to be the optimum balance of comfort and rolling resistance or something...

    Posted 7 years ago #

  5. gembo
    Member

    Long, long ago when this forum first started we had a 25/23 discussion. Along contrary lines that a 25 had less rolling resistance than a 23.

    I have 25 on my winter bike and switched a couple of weeks back to the 23 on my summer bike it felt incredibly different which was not great as I was immediately hurtling down ravelrig hill

    Posted 7 years ago #

  6. Neil
    Member

    Different in what way?

    Have any of the 25 vs 23 rolling resistance comparisons been done at a range of loads?

    Posted 7 years ago #

  7. gembo
    Member

    23 like a skittish young Colt skittering across the road

    Posted 7 years ago #

  8. Neil
    Member

    @cyclops you didn't use the top calculator did you? That's weight at each wheel e.g. 40% of the total weight

    Posted 7 years ago #

  9. Neil
    Member

    @gembo perhaps overinflated? I read somewhere that as you overinflate tyres they begin to "skitter" on rough surfaces.

    Part of the reason I'm even entertaining the idea of 23c tyres, if I'm over inflating my current ones. Currently my tyres are 85/95 (at the start of the week...). They feel better than at 95/105 or 100/110 I was previously running them at, but I do feel that there is still some skittering even at current pressure

    A couple of times I got punctures and when I got home checked the pressure I'd managed with the minipump and it was barely 70psi.....Both times I'd ended up managing particularly fast runs, so lower pressure didn't seem to hurt. Slightly wary if running them thay low generally in case risk of pinch flats? No idea if this risk is overstated though

    Posted 7 years ago #

  10. gembo
    Member

    I have never been one to over inflate compared with the rest of the peloton but probably go for around 100. Well below the max.

    This is not my commuting pressure but weekend rides.

    Commuting might be 90 on the schwalbe marathon plus. Once picked up a slow puncture and cycled home from commie pool to Balerno with back tyre scwalbe marathon and very little pressure in the inner at all.

    Posted 7 years ago #

  11. wingpig
    Member

    When I was stuck with 23 or 25mm I'd go up to 120psi to prevent snakebites (with a total rider/bike/overstuffedpannier weight of around 95kg) but can manage with 100psi on 28mm. If it drops as low as 80psi in a bumpy week it feels very squidgy.

    Posted 7 years ago #

  12. Snowy
    Member

    28mm Gatorskins, total weight of 125kg on the commute, 110psi front and back. Front gets skittish, but it's worth it for the p******e protection.

    Posted 7 years ago #

  13. Neil
    Member

    I played around with pressures last night, and rode into work this morning with the front at 70psi and rear at 85. It felt good, and although only one journey, didn't seem to be slower (I actually recorded my commute for the Strava global bike to work day thingy)

    The minimum pressure is stated as 73psi and I imagine that's conservative so I think I'll stick with 25c

    Another interesting link...
    http://www.bccclub.org/documents/Tireinflation.pdf

    Seems's one of the downsides of over inflating would be decreased cornering grip.

    Posted 7 years ago #

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