masi61

I have been enjoying going tubeless on both my 25mm width road bikes. I like the ride when tire pressures are lower both front and rear. I run about 70psi front & rear. Going over chipseal and riding along the white line bumps gives a nice ride at this pressure. I weigh 200 and I notice deflection of the front tire when I climb hills out of the saddle. I think it is OK but thought I should ask if is OK as is or should I inflate to a higher pressure to minimize the deflection of the sidewalls. Thanks for any suggestions about this.

Eric F 

I weigh 182, and run 25mm tires with 80 rear and 78 in the front, and haven't noticed deflection issues in any conditions. Some online pressure calculators recommend over 90psi for my weight and tires, but I've found that too harsh.

chaadster

That would not fly for me; I want-- verily need-- my handling to be precise all the time, whether I'm cruising, navigating a turn in a bunch, sprinting, or climbing. I don't like things getting spongy when I'm gettin' after it, because that's when I need the confidence most.

I'd move pressure up until the mush goes away...regardless of what any tire pressure calculator says. But that's me, and if the softness is okay for you, then it's ok.

tFUnK

At 200lbs with 25mm tires, I go 90-95psi with tubes. I understand you can go lower with tubeless but I still think 70psi is a bit low.

DaveSSS 

I would recommend consulting the zipp pressure calculator, that takes into account rider and bike weight, internal rim width, rim type, tubed or tubeless and tire casing.


https://axs.sram.com/guides/tire/pressure

Chandne

Can you go up to 28s? That will support your weight better. If you're comfy and not hitting the rim ever which is unlikely, it is fine though. When climbing, a lot of your weight is on that front wheels/tire and it is slow so not a big deal and quite normal. It used to happen to me all the time as well. I recently moved one bike to 28s, and another to 32s. I run 55-60. With 25s, I was running around 75-80. They felt a bit firm. With lower pressure and fatter tires, my downhill and cornering drip is far better with a much bigger contact patch. Your bike may not be able to fit bigger tires but I'm relaying my experience as I was on 25s for a long long time and moving to fatter tires was an incredibly positive experience and they deflect far less.

masi61

chadne - my new disc bike (that still is not finished being built) takes max of 28mm tires. My 2 rim brake bikes are limited to 25’s in the front. I do have a Hutchinson Secteur 28 on my titanium bike. It barely clears but yeah - It gives a really nice shock absorbing, nice cornering but plenty firm ride with about 70psi.

When I run tubes I almost always have more pressure in the rear and keep the front as soft as practical for increased comfort on bad pavement. But I’m having to re-think this formula and run 68-70 rear (for the 28) and 74-82 front to still be comfortable but also fast enough and to resist deflecting too much during standing climbing.

Chandne

But does the tire compression while climbing even matter? It does not to me...I'd rather keep the front a bit softer so my cornering grip is good. I also keep the front at 5-6 PSI softer. A harder-than-needed front tire will reduce your contact patch where it matters...fast corners downhill.

terrymorse 

It can matter a little when climbing out of the saddle, and the bike is rocked from side to side. The front end can feel a little "squirmy" or "squishy" if the pressure is too low.

I keep 85 psi in my 25mm front tire (me: 135 lbs).

Chandne

Yeah, it can. All my bikes have pretty wide (internal width) rims so I hardly feel it. When I climb standing, I also try to not put a lot of weight on the bars anymore (I used to) so maybe that is also why I feel it less. My primary bike has 25mm (internal) rims and I had it at 55 and 60 the last two rides with two diff tubeless tires. I did not feel any squirm but I bet with 25s, it gets more pronounced, especially if you have narrower rims. There are a lot of variables but I feel after 28 tires with wide rims, the squirm is less of a factor. The wider tires feel pretty solid even at 55-60.

Ryan_M

This seems to fit pretty well with my experience. I'm 190#, run 28mm P-zeros and run 75/70PSI. The OP at 200# and 25's, 70PSI seems a bit low.... but could be getting close to the limit depending on tire and rim combo. If they want to stay tubeless going wider could be the answer, or if less flex is desired (as it seems) go to tubes and up the pressure.

DaveSSS 

I do a lot of climbing out of the saddle on routes with 3-5,000 feet of climbing. I run my tires at pressures in the 50's as recommended by the zipp pressure calculator. It's not a problem.

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Chandne

I think this has to do with rim inner width and how it supports the tire. With narrow rims, the tire is more bulbous and can deflect and even "sway" more under that type of side-to-side pressure. I climbed ~3,600 ft in about 11-12 miles yesterday. The climbs were steep and twisty. I used 55 PSI on 30mm tires and 25mm rims. I was watching for any deflection or sway when I stood...nothing I could even feel though I was still careful with weight placement since there was a lot of sand on that section, due to the steepness of the roads. I'll soon switch to tires that measure 34.5 on those rims but I doubt it will change that much. On MTB tires, the old school narrow rims also produce a more bulbous shape and you can feel that sway or deflection when using newer wide tires...especially on downhill corners.

GhostRider62

Don't wrestle the bike so much. Lateral motion is wasted anyway. I'd only be concerned with squirm if it were abrupt deflection when cornering. Just my opinion

I'm about your size, I run 25mm tires 75-80F/80-85R

Typically on GP5000 tubeless 28mm front and 32mm rear that measure 30mm and 34mm respectively run at 50 psi front and 50 psi rear give or take. I was on really crappy chip seal yesterday and progressively let out air until it was tolerable. I measured 40 psi rear and 45 psi front when I got home. Seat of the pants scientificicy

obrentharris 

This doesn't tell us anything unless you tell us your weight and your tire width.
The OP is talking about a 200 pound rider on 25mm tires. Using the calculator that you reference the rider would have to weigh about 60 pounds to run those pressures with 25mm tires.
Brent

DaveSSS 

The zipp pressure calculator requires rider and wheel info, so a heavy rider on skinny tires would have a much higher recommended pressure. My point is to make use of pressure calculator software. I don't feel any need to go beyond the recommended value.

https://axs.sram.com/guides/tire/pressure

A 140 pound rider can use 62/66 psi with a 23mm internal width hookless rim and 25mm tires. With 21mm IW, the pressure goes up to 64/68.
A 200 pound rider on 25mm tires and only 19mm IW hooked rims requires 84/89.

Chandne

The calculator is quite useful, I must say. The only time I go higher is when a tire calls for a higher minimum PSI like the Specialized one I use now. It calls for 65 PSI and I prefer using 55-60 on most. I'll soon swap to the ENVE tires so that issue will go away. I'm also worried about mistakenly going past the 73 PSI wheel max if the pump is off. Still, I live dangerously and have started to use 58/60 in the Specialized. I'm sure they use a good margin of safety with that recommendation, and does ZIPP.

Kontact 

The point of lower front pressure is that, while riding on flats without braking, there is less weight on the front wheel.

The point of minimum pressures is to prevent pinch flats and to have a reasonably efficient rolling resistance.

If you are leaning over the bars while climbing or braking, your weight definitely shifts forward onto the front wheel and compresses the tire a lot more. This makes the tire have higher rolling resistance and makes it more susceptible to pinch flats.

Tubeless is much more pinch flat resistant than tubed, but the point is still that you have less protection against the deceleration that occurs when you hit the back edge of a pothole. Will the rim be damaged? And then do you care about the increased rolling resistance you get while climbing on an underinflated tire?