Factory vs Silca vs SRAM Tire Pressure Calculators?

whv · September 18

What are y'all's thoughts on Factory vs Silca vs SRAM Tire Pressure Calculators? If Silca and SRAM pressures for road tires are under the factory recommended minimums do you trust Silca and SRAM ? Or never go below factory recommendations on tubed tires?

daniel_b · September 18

I've just used the Silca site today as chance would have it.

Originally went with 28mm width tyres in the calculator, as that is what they technically are, but then got my callipers out and measured, and they are 30mm wide on the rims, which lowered the pressures suggested by quite a bit.

It's not much different to what I normally ride, but was surprised how little difference it suggested between the rear and front, only 1.5psi, where as I tend to normally go around 5psi.

These are 28mm GP5000s with tpu tubes - what tyres are you using?

sungod · September 18

https://forum.bikeradar.com/discussion/13130798/factory-vs-silca-vs-sram-tire-pressure-calculators

i wouldn't go below (or above) tyre/rim manufacturers' range

low pressure increases risk of pinch flats and/or rim damage, or even the tyre detaching under load, but i'd think you'd need to be way under for that

whv · September 19

REAR: Specialized Armadillo Elite All Condition Anti-Flat 700x28C

Recommended

factory 85-95psi

Silca 75psi

SRAM 65psi

FRONT: Vittoria Rubino Pro Graphene 2.0 700x25C

Recommended

Factory 100-130psi

Silca 87.5 psi

SRAM 74 psi

Pretty dramatic different recommendations. I am accustomed to running lower that factory rec on my XC bike tubeless tires, but I am running tubes on my road tires and am not worried about pinch flats, but am worried about bead separations and wrecking. I don't ride at high speeds. I am more of a climber, but do like to whip around a bit. I am an old hand at riding XC, but new to the road and just don't know the capabilities of road tires and pressures, but would like to ride at the lowest possible pressure just for comfort's sake. Thoughts?

p.s. I am currently as I type watching Illi Gardner ride the Alpe d'Huez and she is AWESOME! Love her sense of humor!

mr.b-campag · September 19

I imagine your weight must come in to it. Does anyone run tyres at 100psi these days - maybe if you're 90kgs? I've run my tyres at much lower pressures (wasn't aware there were even recommended minimums tbh) mostly because I couldn't be bothered to keep pumping them up. Never had any problems but obv. YMMV.

pblakeney · September 19

https://forum.bikeradar.com/discussion/comment/21097446#Comment_21097446

Anecdotal evidence from an 80 kgs (usually) rider. My Vittorias state a minimum pressure of 100 psi. Calculators give me 85-90 psi. When I tried that I got pinch flats so I reverted to 100 psi. MMDV. 😉

daniel_b · September 19

I've never looked before to see what the recommended pressure is on these specific tyres.

Continental reckon 95-115!

Silca went with 70 \ 68, which I tried yesterday on a 90k ride, over a wide variety of terrain and quality of surfaces, and had reasonable speed, really good comfort, and no issues, grip or otherwise - admittedly it was dry.

sungod · September 19

https://forum.bikeradar.com/discussion/comment/21097452#Comment_21097452

i'm around 78kg, used to run (21mm/23mm front/rear) tubs at 7bar, cracked both rims on a really shallow but sharp-edged road defect, not really a pot hole

now i stick to 8bar, if roads are smooth i've used 10bar

@whv you need to mention total weight (you+bike), going too low is inefficient, and taken to extremes could make cornering fast/hard risky

if comfort is your concern, check what the fattest tyres compatible are for your frame/fork/wheels (and brakes if they're rim)

pblakeney · September 19

Oops! Yeah, should have said 25mm.

gethinceri · September 19

https://forum.bikeradar.com/discussion/comment/21097501#Comment_21097501

145psi?

REALLY??????????????????

sungod · September 19

https://forum.bikeradar.com/discussion/comment/21097543#Comment_21097543

yes, smooth roads with supple tubular tyres, it's good

plus, on a 6-7 hour ride at high temperature, tubs with latex tubes lose quite a bit of pressure, if one started out at 8bar, it certainly wouldn't be that at the end

but with clinchers, no way!

N0bodyOfTheGoat · September 19

If I can actually get out of the door on this last possible day of proper summer weather, I'm going to chance GP5000 with latex tubes...

25mm front @ 27mm @80psi

30mm rear @ 31mm @ 87psi

Bike ~9Kg, me ~96Kg, 1.5l fluids + kit + bits in pockets ~2Kg

Silca was suggesting ~76psi, I used higher when I was 80Kg two years back!😯🤣

Webboo2 · September 19

I put 90 psi in my 25 mm clinchers. I weigh about 75k, bike weighs about 6.8k, 2 500ml bottles and about 2 k of other stuff.

whv · September 19

Appreciate the info. Just wanted to know if I was missing out on the joys of lower road tire pressures.( Wider and lower pressures on my XC race back has been a life changer.) I accidentally went on a very short ride and realized my tires were low and when I got home they were 35 and 54 psi. Made think about my procrastination in getting my tire pressures figured out. Why I checked the Silca and SRAM charts. I grudgingly bought a road bike to train for XC and thought I would hate it... love it! But being a mountain bike guy it is taking some getting use to how rough it is on my hands and ass riding on bad roads with a shocks, so was hoping I could get away with lower road tire pressures. Maybe I will just stay at the low recommendation on this bike. Thanks!

mr.b-campag · September 20

ok the SRAM bike calculator is a bit nuts - I put my numbers in and it suggested 40psi! Currently riding at double that which feels about right - running GP4000s and tpu tubes.

ugo.santalucia · September 20

Just put some air in… unless you are going for the hour record on the track, it really makes no difference if you ride 10 PSI over or under on the road. Even in time trials, I have never been able to correlate tyre pressure with anything, within a sensible range.

molteni_man · September 22

https://forum.bikeradar.com/discussion/comment/21097767#Comment_21097767

With respect, I’ve got to disagree with that! A 10psi difference can be night and day. My Supersix runs super comfortable at 82/ 83 psi, but go too much over 85psi and the ride becomes harsh! There’s also the matter of grip in the cold and wet where a 10 psi difference and being too high a pressure can be lethal. Always best to do a check on tyre pressures every ride. Take seconds!

mrb123 · September 22

I'm with Paolo on this one. Can't honestly say I can detect much difference in a range of about 20-25 psi. Tend to pump my tyres up at about 3 week intervals. Obviously just a heavy handed brute.

Webboo2 · September 22

I check my mine about once a week, usually front has gone down a bit as it’s got one of those Chinese durex inner tubes.

N0bodyOfTheGoat · September 23

I check before each ride, but then latex tubes lose pressure quickly. Plus being so heavy these days at 96Kg, under-inflated tyres risks snake bites and carbon rim damage.

daniel_b · September 23

Latex tubes lose air as soon as you remove the pump 🤣

simon_e · September 23

I'll also side with ugo on this - changing pressure may have a significant effect on the feel but less so on the speed (except too high a pressure on really rough roads, which is awful).

Online calculators always seem too high for me. My starting point for 25mm tyres is bike+rider weight in KG = rear tyre pressure in PSI. Put 5 psi less in the front. Adjust each up or down in 5~10 psi steps and see how it feels.

For 28mm I'd knock 10 psi off those figures.

Start a bit higher if you are running supple high performance tyres, a bit lower for heavier tyres with greater puncture protection.

vincesummerskRoxcBTr · September 23

I use 80psi (28mm and 80kg) and check them before most rides, sometimes not. They have been down to below 60psi and I have never noticed whilst riding.

Factory vs Silca vs SRAM Tire Pressure Calculators?

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