Tyre pressure on wider rims

Quizmate

I've just switched to some H Son Archetype rims with an internal width of 23 mm from some much narrower FSA Vision wheels. Previously I ran my Fortezza Tri Comp 23 mm x 700 clinchers tyres at 120 psi on the old wheels, mostly to avoid flats but this was a somewhat bumpy / hard ride. These new wheels seem a bit more forgiving and I'm getting the impression that there's no need to run so high a psi. I'm 11 stone so pretty light so any ideas what would be a reasonable pressure to run them at (front and rear) to aid comfort, but not compromise re speed and avoiding flats? I can go the trial and error route of course, but any thoughts would be welcome.

Thanks

ai_1

what size are the tyres?

Quizmate

Ah yes good point. They're 23 mm

Quizmate

davidmt83 wrote:

Tire Width=20: Pressure(psi) = (0.33 * Rider Weight in lbs) + 63.33
Tire Width=23: Pressure(psi) = (0.33 * Rider Weight in lbs) + 53.33
Tire Width=25: Pressure(psi) = (0.33 * Rider Weight in lbs) + 43.33
Tire Width=28: Pressure(psi) = (0.33 * Rider Weight in lbs) + 33.33
Tire Width=32: Pressure(psi) = (0.17 * Rider Weight in lbs) + 41.67
Tire Width=37: Pressure(psi) = (0.17 * Rider Weight in lbs) + 26.67

The above applies to the rear tire as as that's where the majority of weight is. Run the front Run 5 - 10 PSI less.

Thanks for this very informative. At 154 lbs that puts the rear tyre at about 104 psi which sounds reasonable and feels firm enough. One question though, does the wider rim allow you to go any lower or is that inadvisable?

lostboysaint

Not convinced by those forumlae at all. On my 25mm tyres on my 23mm rims I run 95-100lbs/ft2 in the rear tyre with no issues whatsoever and the relevant formula there is telling me to put more than 10% more in!

Bar Shaker

I'm using 23mm wheels and tyres. I run 90 front 100 rear so about 7% under what the guide implies.

Are we sure that guide is for 23mm rims?

ai_1

lostboysaint wrote:

Not convinced by those forumlae at all. On my 25mm tyres on my 23mm rims I run 95-100lbs/ft2 in the rear tyre with no issues whatsoever and the relevant formula there is telling me to put more than 10% more in!

I don't think those formuale do a bad job giving a ball park figure for the back wheel but depending on the rim, the specific tyre and your own preferences there will be some variation between any chart/formula and what you actually find to be best. To be of real use it should also specifcy if those figures are intended to be front tyre, rear tyre or both. I always have my front pressure significantly lower. I'd say those formulae give results that err just slightly on the high side but not too far off what I use with my 25mm Conti 4 Seasons and 25mm Yksion Pro on the rear wheels of my two bikes (neither have wide rims which may drop the ideal pressure a few psi).

keezx

23 mm on wider rims: minimum is 6,5/6 bar for me (80 kg) on bumpy roads
Never more than 7/6,5.
Never mind that formula.

1 bar is 14 psi......

ai_1

davidmt83 wrote:

Ai_1 wrote:

To be of real use it should also specifcy if those figures are intended to be front tyre, rear tyre or both.

Ah but it did

Apologies, you are correct!

lostboysaint

Ai_1 wrote:

lostboysaint wrote:

Not convinced by those forumlae at all. On my 25mm tyres on my 23mm rims I run 95-100lbs/ft2 in the rear tyre with no issues whatsoever and the relevant formula there is telling me to put more than 10% more in!

I don't think those formuale do a bad job giving a ball park figure for the back wheel but depending on the rim, the specific tyre and your own preferences there will be some variation between any chart/formula and what you actually find to be best. To be of real use it should also specifcy if those figures are intended to be front tyre, rear tyre or both. I always have my front pressure significantly lower. I'd say those formulae give results that err just slightly on the high side but not too far off what I use with my 25mm Conti 4 Seasons and 25mm Yksion Pro on the rear wheels of my two bikes (neither have wide rims which may drop the ideal pressure a few psi).

We'll agree to disagree. I never ran pressures that high when I had 23mm on narrow Fulcrum rims, despite my weight, didn't come close to running those pressures when I ran 25mm on the Fulcrums and now run less pressure with 25mm on A23s. Never come close to snakebites, despite plenty of "CX" type riding in Portugal recently and roll fantastically. As I said, I reckon they are a very, very "safe" figure for the rear wheel and you could do at least 10% less - which has always got to be good for both comfort and cornering grip.

cougie

Of course it all depends on how accurate the average track pump is ? I've no idea how well these are calibrated or if they go off over years ?

ai_1

lostboysaint wrote:

Ai_1 wrote:

lostboysaint wrote:

Not convinced by those forumlae at all. On my 25mm tyres on my 23mm rims I run 95-100lbs/ft2 in the rear tyre with no issues whatsoever and the relevant formula there is telling me to put more than 10% more in!

I don't think those formuale do a bad job giving a ball park figure for the back wheel but depending on the rim, the specific tyre and your own preferences there will be some variation between any chart/formula and what you actually find to be best. To be of real use it should also specifcy if those figures are intended to be front tyre, rear tyre or both. I always have my front pressure significantly lower. I'd say those formulae give results that err just slightly on the high side but not too far off what I use with my 25mm Conti 4 Seasons and 25mm Yksion Pro on the rear wheels of my two bikes (neither have wide rims which may drop the ideal pressure a few psi).

We'll agree to disagree. I never ran pressures that high when I had 23mm on narrow Fulcrum rims, despite my weight, didn't come close to running those pressures when I ran 25mm on the Fulcrums and now run less pressure with 25mm on A23s. Never come close to snakebites, despite plenty of "CX" type riding in Portugal recently and roll fantastically. As I said, I reckon they are a very, very "safe" figure for the rear wheel and you could do at least 10% less - which has always got to be good for both comfort and cornering grip.

I don't think we need to agree to disagree. I'm not really disagreeing with you!

I was just saying it's not far off what I use myself. Not saying it's close to what everyone SHOULD use. Also while I tend to use pressures similar or just below these most of the time, I do actually drop 10psi or so for added comfort when I'm expecting bad road surfaces and like you I've seen no pinch punctures. I just prefer the feel of a little more solidity when climbing and sprinting out of the saddle so long as it doesn't mean comfort problems the rest of the time.

ai_1

cougie wrote:

Of course it all depends on how accurate the average track pump is ? I've no idea how well these are calibrated or if they go off over years ?

I've checked with a separate pressure gauge occassionally after inflating with my JoeBlow track pump and the separate gauge routinely gives readings that are about 7-10psi higher than the gauge on the pump. I think some variation would be expected anyway. The pump is reading the pressure in the pump/hose which must be slightly higher than the tyre pressure to open the valve and produce a flow into the tube. However, much of that difference could be down to gauge accuracy too.

desweller

I would not expect an el-cheapo gauge on an el-cheapo bicycle pump, that spends most of its time in a shed and never gets recalibrated, to be within 15% of the actual pressure.