DougG

The 700x38s that came on my 2013 Specialized Crosstrail say "85-100psi" on the sidewall. That seems somewhat high to me, and even at the lower pressure the ride is a bit harsh. I had 700x32 tires on a road bike that rode well with 80-85psi in them, so it seems like I could go lower. (I'm a member of the "higher pressure is not always better" camp!)

This is a new tire size and new type of bike for me, so I'd appreciate hearing your experiences and recommendations.

teicher

Yeah, you can definitely go lower. I'd try running them at 65-80 and see how it goes. I have 700x35 michelin city tires and run those at 65-70 to smooth out the ride.

Wanderer

Buttttt, that Crosstrail sure does roll better at higher pressures.....................

okane

I run Kendas on my no suspension bike with a 50-85psi range at 85psi. Comfortable for me (214 lbs) but don't think I would like to go much higher.

DougG

I guess it would also depend on what kind of surfaces I was expecting on a particular day. For mostly pavement, the higher pressure would probably be best, and somewhat lower on rougher dirt such as a semi-improved rail-trail. I took a trip on the C&O Canalpath last year and noted that the bike I had then with 26x2" tires at about 65psi was more comfortable than what others on skinnier-tired bikes were experiencing.

Even on road bikes, higher is not always better. We have a lot of chip-seal roads around here and I've found that my aluminum bike with 700x32 tires at 85psi rolled just as easily and with less "buzz" than my carbon bike with high-pressure 700x25s. The high-pressure tires actually tend to "micro-bounce" over the unevenness of the surface, sapping more energy compared to a tire rolling smoothly.

fire

I'd go along with Doug on this one. Tyre pressure is a personal preference that to me will really depend on the surface you're riding, and personal comfort. I tend to ride my 700x32's at the maximum 85 if I'm riding on a paved trail, or the road. My MTB's both with 26"x 2" I generally ride offroad or on the unpaved trails, and I vary the pressure somewhere between 55 and 65, just to give me more surface area on the sand that we tend to have down here. If I ride them on tarmac, I put the pressure up to the max that I can to help them roll better.

I'd suggest its a bit of trial and error to get what feels right for you on the surfaces you ride. The frame pump will be your friend.

jsdavis

For what it's worth, I ride on 700x42 with about 45-50 PSI in the rear, around 40-45 in the front. My riding is 99% asphalt.

Above 50 PSI, my tires feel like rocks and I really can't tell any difference speed-wise. The sidewalls indicate a max pressure of 65PSI.

DougG

I guess it's also a question of risking pinch flats. And I'm wondering about the pressure spec on my tires. From the previous posts, we have a 700x32 with a max of 85 and a 700x42 with a max of 65, so why are my 700x38s rated 85-100? I thought that seemed high and I'll probably try dropping it to more like 75, especially in conditions where I'm not going to be hitting any chuckholes (I hate flats!).

Burton

If there's a minimum and maximum pressure indicated on the tire its related to the tire construction. Picking the 'right' tire is a combination of identifying the characteristics you want from a tire and picking a tire specifically engineered to deliver that.

Personally if you want to roll at a lower pressure I'd suggest you shop for other tires. 26x3" Kenda Flames used to be rated for MAX 40PSI. Nokian 240's used to have a single INFLATE TO 65PSI rating on them. Doing anything else just shortened life expectancy and compromised performance.

DougG

Well, maybe I can blame this whole post on my 66-year-old eyes. Today, in better light, I took another look at my tires and found that they recommend 75-100, not 85-100. This makes a lot more sense to me, so I'll definitely knock the pressure down to 75 or 80 psi when expecting to ride on rougher surfaces.

pierce

the goal here is so when your weight is on the bike, the tires 'sink' about 15% of their total sidewall height. the min/max numbers on the tire sidewalls are at best guidelines and heavily influenced by both marketing and legal liabilities., and frankly, 75 is really high for a 38c tire.

take a bathroom scale, and stack some books to be the same height, put the front wheel on the scale,back wheel on the books, adn get on the bike and balance, have someone read the weight on the front wheel. I suggest doing this in a doorway so you can balance with your elbows ... now swap the bike ends, and read the weight under the back wheel, and report those both back here...

if, for example, with 700x38, you have 100 lbs on the front wheel, and 120 lbs on the rear, you'd be surprised to find out, thats 45 psi front, 55 psi rear. I'd treat that as a minimum, but try and it and see (assuming those weights are in the ballpark, I intentionally picked a fairly heavy rider here)... I'm using this calculator, which sadly only goes up to 700x37. https://www.dorkypantsr.us/bike-tire-...alculator.html ... also see https://adventurecycling.org/resource...SIRX_Heine.pdf

DougG

Interesting material, but I'm thinking that pressures that low are getting into pinch-flat territory if you're not really careful. I'll do the weigh-in, though, and see what the result is. The easiest thing to do is probably to get the total weight by standing on the scale while holding the bike, and less likely to get me in trouble with the spouse.

pierce

the front/rear distribution ratio is important, too

dynaryder

According to that I should've been running 55psi in the tires on my old cross bikes. According to my experience riding the bike,that's too low.

We just had a dustup over in the General forum over this very issue:that calculator goes by width,without taking into consideration the design of the tire. I gave an example of two 700x28 tires that I had put on my road bike;one had a max of 85psi,the other had a range of 115-25. I've got the high pressures on the bike now,and it would not ride right at all running the pressures that calculator suggests.

There are tires designed for all different types of uses. Best advice is to go with what's on the sidewall and experiment from there to see what works for you. If you specifically want to run low or high pressures,than get tires designed to run what you want. A one-size-fits-all chart should be treated as a starting point,not the final answer.

I'm running 70psi(the max) in the Marathon Supremes on my Safari. They're 26x2",which is much wider than 38mm(roughly 1/2" wider). They ride awesome at that pressure. '75 too high for a 38mm' is a blanket statement;it may be too much for you on your bike with your tires on your roads,but for me on mine it might not.

pierce

I'm 220 lbs or so, riding a 30 lb hybrid, riding on bad pavement, occasionally hard pack dirt, and such, and I run about 80psi rear, 70 front on 700x32, and they are just fine, using high thread count Randonneur Hyper tires, which btw rock for a hybrid and/or trekking bike.

Burton

This is what Vittoria has to say about tire pressure:
They're generous enough to provide an online application to input parameters for their products to make it easier to select a starting point. It should apply to other tires with the same construction parameters.
https://www.vittoria.com/tech/recom-tyre-pressure/

pierce

whack, that didn't ask me what size tires, and half time time i entered what data it DID let me enter, it came up with 0,0.

Burton

There are two initial choices - ROAD and MTB. There are no tire size choices available in ROAD. Probably because they're all pretty close.
There are limited 26" and 29" sizes in MTB, and the results are very different from whats recommended for ROAD. And its a starting point to test drive with in any case.

pierce

yeah, and I'm in the middle with a 700c hybrid that uses what Vittoria calls 'trekking tires'.

Burton

On the same site there's a FAQ listing and under 'What is the ideal tire inflation pressure' you'll find a detailled chart that gives recommended starting tire pressures and instructions on how to find the ideal tire pressure for YOU based on the conditions and riding style YOU have to deal with. It won't be the same for everyone.

https://www.vittoria.com/tech/faq/

PatrickGSR94

Yeah that thing is ridiculous. I entered the TPI of the Vittoria tires that came stock on my road bike, tire type, my weight (209+ with bike) and conditions and it came up 0. Only way I could get a result is to use the next lower bike+rider weight.

fitzy1582

Hi all I got a vonder city hybrid ebike two weeks ago to get fit and healthy and go to different places. My weight is 103.4 kg and I would like to get my weight down this year but I'm not sure on the tyre pressure for my ebike. The tyre size is 700 X 38 C and on the tyre it say Min 3.4 50 PSI and Max 5.1 75 PSI . Any help would be greatly appreciated

pierce

I would probably run about 55 in the front, and 65 or 70 in the back. If either wheel feel too squishy when you're riding it add a little more air, and if either wheel feels too hard and harsh then I'd back off a few pounds.