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"Float" or "Ground out" running wider tires on lower pressures?

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"Float" or "Ground out" running wider tires on lower pressures?

Old 02-15-24, 01:50 PM
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"Float" or "Ground out" running wider tires on lower pressures?

Anyone find that running lower pressures can lead to "ground outs," especially on the front rim? As my status correctly indicates, I am an actual newbie who is just learning how to do tire changes, cassette removals, mechanical shifter rewiring etc. I have always been a DIY guy and like older bikes that I can work on myself... I know the recent trend is pushing wider tire widths at lower pressures - and following in that, I recently made some changes to a bike I have - those changes led to some unexpected outcomes for me at least.

Background:
I started road cycling about 6 months ago (i mean I always rode bikes as a kid - but that was BMX with friends). I picked up a 2012 Tarmac Elite and was whipping around the local park paved roads on around 40 psi cause I just didnt know any better. Seemed fine tbh, but then about 3 weeks ago I hit a rather ugly bump doing around 22mph on a downhill curve and heard pretty unpleasant sound - at first I thought I might have cracked the carbon front fork. Luckily I did not.

I have since acquired a Kuota Ksano - also carbon frame. When I test rode the bike, the seller had the tires at 100psi - ride felt nice tbh. Since then I've swapped out the 23mm tires that were on the bike when I bought it and put on a 700X25mm GT5000 at in the rear and a 700X28mm Gatorskin on the front. These are on the Mavic 125 anniversaries which are 14/19mm inner/outer - so on the thin side. I used the axs.sram.com site to give me a recommended tire pressure - output from them was 70psi front and 88psi back which I inflated to using a parktool pump which is reasonably accurate.

Long short is that not only did the ride feel a bit "balloonish" meaning like I was riding on a beach ball in the front with some noticeable "float" versus what I've been used to so far. AND, I had the same albeit much less aggressive sounding "ground out"on my front tire hitting a shallow pothole at a fairly low speed on flat surface.

Finally to my questions:
1.) Anyone else get this sort of ballon float sensation moving to wider tires at lower pressure?
2.) Anyone else experience "ground outs" running at pressures closer to 70-80 psi on 25-28mm tires?
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Old 02-15-24, 02:12 PM
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You are describing exactly why I run higher pressures. I hate the feeling of "squish" and my days of considering rims expendable on a yearly basis are long gone. (I still run tubes and pinch flats also get old.)

I'm 150 pounds and run front 25s at around 92-95 psi. 28s at low 80s. Rears 5 psi higher.
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Old 02-15-24, 02:13 PM
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Unless you weigh 500 lbs it sounds like your pump gauge is wildly inaccurate. I would get a digital pressure gauge, handy for many uses and only $25 or so. I have run similar pressures and never had those issues.
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Old 02-15-24, 03:56 PM
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the narrow edge of concrete will 99% of the time cause that blunt hit feeling at respectful moving speeds while loaded. Lifting the load off of that wheel will decrease that feeling, but it still is not a pleasant feeling.

I'm sure many "veteran" road riders won't admit it, but they don't lessen the load when navigating rough pavement.
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Old 02-15-24, 04:35 PM
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Originally Posted by scottfsmith
Unless you weigh 500 lbs it sounds like your pump gauge is wildly inaccurate. I would get a digital pressure gauge, handy for many uses and only $25 or so. I have run similar pressures and never had those issues.
I have a digital Joe Blow as well as somebodies hand held digital gauge. They measure differently, being off by about 3 - 4 psi. Itís like the saying ďman with watch knows the exact time, man with 2 watches never knows exact timeĒ.
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Old 02-15-24, 04:56 PM
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The OPs issue could be 30 psi, not 3-4 psi. My pump which I recently replaced measured 20 psi too high on the gauge. I found this out only a couple years ago, and it meant that I had in fact been riding with the more recently fashionable low pressures for the last 20 or so years! 😆.
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Old 02-16-24, 04:08 AM
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Thatís a very narrow internal rim width for a 28mm tyre imho. I have 25s on a 19 and they sit about right. Just moved to 30s and they look a bit baloony but ride very nicely at just under 70psi. I avoid almost all of our many potholes so not had a groundout on those yet but they are almost impossible to eliminate completely. I run tubeless of course because itís awesome but still had a groundout once give me a flat because it deformed the tyre so violently it unseated the bead.

That pressure should be fine. Does it feel firm to the thumb?

Why different tyres front & back?

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Old 02-16-24, 08:18 AM
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Not to get too personal, but whatís your weight? I ride (what my pump says) is ~90psi on GP5000 25mm, on 19mm internal rims. They plump up to 27mm, and feel fine. Iím also about 195lbs, and running the tires lower than 80psi (indicated) starts to feel squishy and squirrelly to me. Even then, Iím ok with it, just not my favorite.

Unless youíre about my size or bigger, 70-88psi shouldnít feel too bad on 28mm. On my other bike, I run a 32mm at 80psi in front (Conti Ultra Sport 2 @28mm on an 18mm rim).
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Old 02-16-24, 08:30 AM
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If I had any of what you describe, I'd put more air pressure in the tires. I might consider different tires when the current tires finally wear out or frustrate me too often.
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Old 02-16-24, 10:33 AM
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Regarding the OPís questions 1 and 2, my answer is no to both.

21mm inner rim width, 28mm tires which measure 29mm when inflated, total weight of me plus bike plus gear is 195 lbs, tires inflated to 70/68psi r/f which is right in range according to the SRAM and Silca calculators.

I suspect it is the narrow internal rim width that is causing the OPís situation.
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Old 02-16-24, 01:50 PM
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I agree with @79pmooney .... everyone talks about pressures which sound ridiculously low to me. I do not find the ride more comfortable when the wheel moves independently of the tire contact patch while cornering, and while I have learned to ride light (lift off the saddle and bounce a little over big bumps ... which i avoid when possible any way) I still need enough air in the tires to protect the wheels if i do hit a big pothole or something.

Not saying my way is better for anyone else ....

Over time I have learned to dig a thumb into the tire tread and estimate the pressure .... not in precise units, but in "Is this too full or too empty?" I do little experiments ("This feels soft but let's try it") so that i can learn the limits ... definitely softer is more comfortable and apparently (if you believe those math/science folks) also faster, but the pressures some folks ride seem extremely low ....

I came from the age of "Ultra-narrow tires which feel like steel are fast tires" so it took a while before I was willing to experiment with wider, softer tires, but once I did, I was converted. However, I still have my standards ... the tire and wheel should never move independent of one another and the rim edges should never hit the inside of the tire (or crush the tubes, when not running tubeless.)

My advice is to forget the measuring devices. Pump your tires up hard, take a ride. Next day, feel if they have softened up much, and if not much or not too much, ride again. Keep letting the tires naturally seep air overnight until you feel While Riding that you don't like the ride quality. Then do a thumb test and next ride, pump the tires a little harder. if it feels good, you know you have found the lower limit if Your acceptable tire pressure range.

Because I did so much urban commuting, flats were not an infrequent thing, and I never had a mini-pump with a reliable pressure gauge, so I just learned to pinch-test. I don't think, for a non-competitive non-pro, that two or three pounds of pressure make a big difference .... I just go by "hard enough' or "need a shot of air."

You got this.
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Old 02-16-24, 02:10 PM
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I will concur with the various online calculators. They are built by people whose job is to know this stuff through & through. You may even try more than one to build a consensus. Keep in mind that most of them are geared towards running tubeless on appropriately wide modern rims. Just as a random wild a- guess, I'd add 5 psi to whatever it says for a skinny rim and another 5 just for tubes and call that "close enough."

So much is made out of "optimizing" to the nth that sometimes the bigger picture is lost...and on that note, stop hitting potholes!
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Old 02-16-24, 08:14 PM
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🙏Appreciate all the feedback - as a testament to how much of a newbie I am, bikeforums is rate limiting me to post/replies per day otherwise I would have responded to a bunch of your helpful answers/comments by now.
scottfsmith and Steve B. Im def going to grab a digital tire gauge with the understanding that, unless I pony up for some super calibration park tool thing, Im likely to be off by 5psi here and there. I like data, but ultimately I also see myself fitting in the trial by trying as described by Maelochs . +/-5 psi does not seem likely to be my issue. Its not like my tires are "squishy" to the touch. I checked with the ol unscientific squeeze between the fingers method post pump and post ride - not super accurate, but I think most of us can differentiate between around 3 level ranges, ie- 1Rock hard - likely 80+lbs, 2Med hard - 60-80 lbs, 3Soft, under 60 lbs. Both times my front tire was at that lower limit of rock hard. so in the 1-2 range. Anyways, can't hurt to check with a digital gauge - come to think of it, Ill prolly check intro a local bike shop and get a pressure check from them...
In response to aliasfox Im 145 - so weight likely not a factor in this case.
Reading through all the replies, it seems to me that -

A, I was prolly riding that Tarmac at waay too low a tire pressure (this was before I really gave tire pressure a lot of thought and just assumed that getting to "hard to pump" and reasonably stiff to squeeze" was ok. I remember commenting to my son awhile back that I found out that I'd been riding really low tire pressures for 23mm tires - like on the order of 40-50 psi). This is likely the culprit in that incident

B, The second incident with my newer bike and slightly more experienced me paying basic attention to tire pressure psi and inflated to 80ish I think the issue is most likely due to running 28mm tires on 19mm rims as suggested by choddo and Bikerpete .
To answer the question posed by choddo re why the different tires front and back.. to be perfectly honest, I was all pumped up on youtube videos about "wider is better" - users talking about having a feeling of more control in descents, and that wider at lower psi was actually more efficient than a high psi 23 esp on inconsistent pavement - yadda yadda. Coupled with the logic that your front tire is the action tire in terms of control and I thought, well heck, Ill just drop a 28mm on my front rim and see what happens. I was sort of expected more control and a better ride. That did NOT turn out to be the case AT all for me.
In fact, I was so eager to test out the "more control" theory that I was absolutely booking it into the first turn of the most aggressive descent on my normal 10K loop. Had a serious "uh-oh" moment when I realized my bike was not turning hard enough in response to my steering, or at least nearly as much as it did on 23mm tires. Infact, in the split second this was happening I remember wondering why the hell I couldn't get my bike to turn harder at all - that's when I finally hit both brakes and just narrowly avoided planting into the barrier.

Gonna hop out again one more time today on this set up before my final verdict - but suffice it to say that, no matter what, Ill dropping to a 25mm front and seeing how that feels. And if that ends up feeling like a halfway point from between a 23 and a 28, then Ill prob go back to the 23mm front - Im not a fan of giving up control for comfort for the kind of short distance hilly rides Im doing at the moment. I will say that when I moved to a 25MM rear from a 23, that actually felt like an improvement. So maybe 25mm for the rims Im running will be the sweet spot.

Conclusion is that there are just so many variables when it comes to ride control and comfort. Individual body geometry, rider weight, road condition including turns and elevation, bike geometry, frame material, etc etc etc.

Thanks again for all to responses - really glad to have found the forum!
Update: (posting rate limiting long enough for me to have an update &#128514 - Out for a second ride on this configuration equipped with some updated intel and outlook. Got a better sense of the tradeoffs this time around.
Out of the saddle climbs - (so less pressure on the front tire, right?) - the added comfort over some rough patches of pavement during one of the steeper climbs was appreciated - I can actually see where this smoothing out can clearly be an efficiency booster - those rough patches on high psi 23s had a way of slowing me down whereas on the 28s, i did not get the sense it was impacting me at all.

Low speed bumpy - I like the 28s less - Ill take the bone jarring rattle over the bouncy house effect

High Speed descent - 2nd time round was much better - I did feel the increase in stability and, being more on the "ready," I found steering to be reasonably controlled this time round - def not the razor precision of 23s, but workable with another experience repetition.

Mid to High Speed Steering - Here is where I hate the 28s - super floaty - kind like high speed steering on an old Lincoln Continental. This is where I felt the biggest trade off of comfort for control.

Back to all the Variables... My current bike is def an aggressive geometry - I swapped rides with one of my kids last week who has an Allez Sport, and that felt like sitting in a lazy recliner compared to my ride. This likely means that the configuration on the front of my bike has greater impact that it would on more endurance geometries. Starting to think that 25mm might be the sweet spot. Trial by trying to continue.

Out of country for a week - but eager to get back at it when I return - hopefully to some warmer weather!
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Old 02-16-24, 09:14 PM
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Scrib4lex - if I recall in one of your previous posts, the 28mm front tire you are running is a Continental Gatorskin (or was it a Hardshell?). I would mention this since this tire is more of a high mileage commuter tire with less than magical ride. Just because your “28” feels sluggish you really need to try some other nice rolling clinchers in 25mm or 28mm widths, and perhaps run these with latex inner tubes. With an “open tubular” like a Challenge Strada Pro 260, 28mm with a latex tube your new digital tire gauge will come in handy. I can’t remember what frame you said you have but setting optimal tire pressures is partly about your body weight but also the ideal pressure can be optimized by real world tuning just as you have been describing.

My aluminum bike has a harsh ride and hitting normal road bumps the shock through the frame can be fatiguing or detrimental to a smooth bike. In my case, my headset develops slop where the steer tube plug develops a tiny bit too much play. I think a punishing ride starts to be a certainty when I have like 85psi or higher in my wheelsets where I run 25mm tires (with either latex inner tubes or full tubeless) over bumpy roads. But with a quick 1/8 turn of my steer tube plug/headset cap bolt then re-torquing my stem bolts, I can then embark on a follow up ride over the same crappy roads but this time my tire pressures are more like 72 psi front and 75 psi rear. For my 195# self on my tubeless Panaracer or Hutchinson tires, this bumpy route is now more fun and tactile than punishing.
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Old 02-16-24, 09:54 PM
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There you go...experimentation pays off
It's a trade off and you have to decide what you want. But you can have it all...depending on the activity...if you know you are going to be riding on less than smooth roads, etc. you can use less psi to get comfort, control and shock absorbing with a bit less psi. If you are going to be on smooth roads up the psi a bit for a faster ride.
Yes I'm aware of the 'tests' that say wider and less is faster but those tests results are starting to be argued against.

It also depends on the rider's size and also riding style...I know some 'big' riders that are very 'light' on their bikes while I also know some riders that aren't 'big' but are 'tanks'...they ride heavily and use their bike like it is an excavator. I'm only 140lbs and a 'light' rider. I prefer 23 or 25mm tires and typically inflate them to 70psi on my road bike...I use Vittoria Corsa Pro tires and have been on Vittoria's since the 90's.
My gravel bike tires I usually run at 28 or 30psi

I use tubes...preferring them to tubeless...yes I know but it is a "me" thing...I prefer tubes and have no problems with plain Jane butyl tubes but currently use Tubolito's on my road bike and good old butyl on my gravelly bike.
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Old 02-17-24, 02:23 AM
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Interesting. Yeah the fact itís not a super grippy front tyre could be worth playing with when you try the 25. Just one thing - climbing out of the saddle puts more weight on the front tyre, not less.
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Old 02-17-24, 07:59 AM
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Since "marginal gains" are irrelevant to most of us, keep experimenting until you find that sweet spot. Feels fast, comfortable, no pinch flats.

Yup, I remember running 20mm tires at 110psi....but now have settled into 25mm Conti 5000's at 85-90psi. Seems like a good compromise. It just bothers me to look down and see a deformed tire.....just does.
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