Go Back  Bike Forums > Bike Forums > General Cycling Discussion
Reload this Page >

School me on tires please! Fat better than thin?

Notices
General Cycling Discussion Have a cycling related question or comment that doesn't fit in one of the other specialty forums? Drop on in and post in here! When possible, please select the forum above that most fits your post!

School me on tires please! Fat better than thin?

Old 03-21-21, 07:52 PM
  #1  
Wattsup
Senior Member
Thread Starter
 
Join Date: Jul 2018
Posts: 541
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 311 Post(s)
Liked 24 Times in 21 Posts
School me on tires please! Fat better than thin?

I own a set of 42mm (700) as well as 47mm for my gravel bike. I have a 30mi race coming up, and I expect all types terrain, asphalt, packed dirt and gravel. Assuming the tread profile is the same, will the 42 tires be faster than the 47, or vice versa?
Wattsup is offline  
Old 03-21-21, 08:17 PM
  #2  
cxwrench
Senior Member
 
cxwrench's Avatar
 
Join Date: Jul 2013
Location: Nor-Cal
Posts: 3,726

Bikes: lots

Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 1927 Post(s)
Liked 2,842 Times in 1,454 Posts
Wayyyyyy to many variables we don't know about. Short answer: There won't be a bit of difference between the 2.
cxwrench is online now  
Likes For cxwrench:
Old 03-21-21, 08:45 PM
  #3  
Russ Roth
Senior Member
 
Join Date: Dec 2019
Location: South Shore of Long Island
Posts: 2,128

Bikes: 2010 Carrera Volans, 2015 C-Dale Trail 2sl, 2017 Raleigh Rush Hour, 2017 Blue Proseccio, 1992 Giant Perigee, 80s Gitane Rallye Tandem

Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 807 Post(s)
Liked 645 Times in 487 Posts
Really depends a lot on the tire, a 47mm tire with smooth thread would be faster then a knobby 42mm. My preferred gravel tire going from dirt to packed gravel to pavement was a 38 with a smooth center tread, lighter tread to either side and small knobbies for cornering at the edges. I had no trouble maintaining 20mph over flattish terrain for 30 miles with that one and even used it for a couple of dry cross courses. The longer and scragglier the dirt and gravel the wider and more aggressive I'd want the tire.
Russ Roth is offline  
Old 03-22-21, 09:59 AM
  #4  
ClydeClydeson
Senior Member
 
Join Date: Mar 2019
Posts: 1,481
Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 516 Post(s)
Liked 794 Times in 458 Posts
@Russ Roth is on the right track, but tread is generally less of a factor than the overall construction of the tire - a lightweight and 'supple' casing on a tire means it will take less energy to keep moving than a similar tire with a thicker or heavier casing. There are aggressive off road tires with light and supple casings and narrow road slicks with a heavy and/or rigid casing. Flat preventative layers also generally count as a 'heavier and slower casing', but you get less flats, so it is a trade off.

Tires create drag in three ways: energy lost to casing deflection, aerodynamic resistance, and on soft surfaces it takes energy for the tire to push the dirt out of the way.

FOr casing deflection and carving a groove in the dirt, a wider tire is generally faster. For aerodynamics, a narrower tire is faster, especially if the wider tire is significantly wider than the rim such that it's cross section when mounted is an 'omega' shape - tires that are close in width to the rims are fastest. Aero losses are low at low speeds but become the primary source of drag as speed increases.

There are also 'suspension losses' - if the weight of the bike and rider is being jostled up and down over a rough road you are losing energy. A fatter tire at moderate pressure will absorb more road irregularities and mitigate suspension losses. The wider softer tire will also knock your body around less so that you are less fatigued at the end of the ride, even if the tires took marginally more effort to keep rolling.

So the correct answer is 'it depends'. If the rough sections are very rough then I would go with the wider tire, all other things being equal.
ClydeClydeson is offline  
Likes For ClydeClydeson:
Old 03-22-21, 10:03 AM
  #5  
Wattsup
Senior Member
Thread Starter
 
Join Date: Jul 2018
Posts: 541
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 311 Post(s)
Liked 24 Times in 21 Posts
Ok, so let's eliminate the variables. How much slower (if at all) would one tire be than the other....on asphalt?
Wattsup is offline  
Old 03-22-21, 10:05 AM
  #6  
burnthesheep
Newbie racer
 
Join Date: Feb 2018
Posts: 3,365

Bikes: Propel, red is faster

Mentioned: 34 Post(s)
Tagged: 0 Thread(s)
Quoted: 1564 Post(s)
Liked 1,528 Times in 949 Posts
The way BF rolls it with tires, if it isn't a Rene Hearse tire.......you might as well pack up the forum topic and go home as you won't get anywhere.
burnthesheep is offline  
Likes For burnthesheep:
Old 03-26-21, 07:36 AM
  #7  
Russ Roth
Senior Member
 
Join Date: Dec 2019
Location: South Shore of Long Island
Posts: 2,128

Bikes: 2010 Carrera Volans, 2015 C-Dale Trail 2sl, 2017 Raleigh Rush Hour, 2017 Blue Proseccio, 1992 Giant Perigee, 80s Gitane Rallye Tandem

Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 807 Post(s)
Liked 645 Times in 487 Posts
Originally Posted by Wattsup View Post
Ok, so let's eliminate the variables. How much slower (if at all) would one tire be than the other....on asphalt?
Really hard to say, https://www.bicyclerollingresistance...on-32-37-40-47
This suggests that pressures being the same the wider tire always has less rolling resistance to a point, resistance goes up for the 47 but still not as much as the 32 yet the weight difference between the 32 and the 47 is 3/4 of a pound, or 1.5lbs on a pair. So a 37 or 40 might be better as they're fairly wide for comfort, better rolling and not a weight extreme. I wouldn't mind 1.5lb extra rolling across Nebraska from west to east with a tail wind or riding all gravel and jeep trails in the Adirondacks. I wouldn't want it while riding through the hills of the fingerlakes which have decent roads and no flat areas longer then .5mi.
Russ Roth is offline  
Old 03-26-21, 08:06 AM
  #8  
Iride01 
Plz hurry Dec 22!
 
Iride01's Avatar
 
Join Date: Jul 2017
Location: Mississippi
Posts: 11,934

Bikes: Tarmac Disc Comp Di2 - 2020

Mentioned: 43 Post(s)
Tagged: 0 Thread(s)
Quoted: 4890 Post(s)
Liked 3,410 Times in 2,363 Posts
Best way to know is try different sizes and see. Try different inflation pressures too (but that another argument altogether).

As others have said it's a hard thing to quantify. Best will always be your own perception backed up by ride data from your cyclometer. Failing that, just your own perception.

Generally with anything there is too much and too little. You can go too far either way.

We don't know what kind of gravel you are on. Washed gravel and crushed limestone don't ride the same. Or if there are differences in what you consider packed hard, pack slightly or deep and loose compared to another.
Iride01 is offline  
Old 03-26-21, 10:01 AM
  #9  
alcjphil
Senior Member
 
alcjphil's Avatar
 
Join Date: Jun 2002
Location: Montreal, Quebec
Posts: 5,319
Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 1539 Post(s)
Liked 1,222 Times in 725 Posts
Originally Posted by Wattsup View Post
Ok, so let's eliminate the variables. How much slower (if at all) would one tire be than the other....on asphalt?
You have given the widths of both tires but nothing else. Are they both the same make and model? If not, the tread and casing construction of the tires will make a difference. A nice supple smooth tread tire will roll faster than a stiff casing tire with an aggressive tread no matter what the width
alcjphil is offline  
Old 03-26-21, 11:55 AM
  #10  
tyrion
Senior Member
 
tyrion's Avatar
 
Join Date: Oct 2015
Location: San Diego, California
Posts: 3,807

Bikes: Velo Orange Piolet

Mentioned: 27 Post(s)
Tagged: 0 Thread(s)
Quoted: 2051 Post(s)
Liked 1,635 Times in 793 Posts
Originally Posted by Wattsup View Post
Ok, so let's eliminate the variables. How much slower (if at all) would one tire be than the other....on asphalt?
The fatter tire would have lower rolling resistance but more weight and aero drag. To generalize: the fatter tire is faster at slow speeds and the skinnier tire is faster at high speeds.
tyrion is offline  
Old 03-29-21, 07:25 PM
  #11  
Toespeas
Senior Member
 
Join Date: Feb 2020
Posts: 302
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 164 Post(s)
Likes: 0
Liked 44 Times in 41 Posts
i think the general rule is if we are talking only gravel , is to compare weight vs puncture protection , then add in the rolling resistance vs rolling compliance , and in tghe end the larger tire on the same rim usually allows u run lower pressure and get the same RR , but there is still penalty of weight and aero drag , so u could go wider to get more stability and terrain crossing ability but be putting out way more power and energy to finish your effort ;0
Toespeas is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2022 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.