Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

New Tire Size?

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

New Tire Size?

Old 08-29-21, 02:44 PM
Riding my bike
Thread Starter
Join Date: Aug 2006
Location: Cape Cod
Posts: 168

Bikes: Giant TCR C2 / Giant Defy / Bianchi "beater"

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
New Tire Size?

Been I long time since I've posted here, but after several thousand more miles my trusty old Giant TCR C2 is once again in need of new tires. The old tires are Continental GS-4000 in 23mm (same size as all prior sets). Any reason to think there would be a problem with clearance if I move to 25mm? The brake calipers are Shimano 105's.

Baftap is offline  
Old 08-29-21, 03:15 PM
Andrew R Stewart 
Senior Member
Andrew R Stewart's Avatar
Join Date: Feb 2012
Location: Rochester, NY
Posts: 17,003

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3744 Post(s)
Liked 2,810 Times in 1,741 Posts
Sure there's every reason to check out whether there's clearance for wider (and thus taller) tires, especially if you are not buying from a LBS. Because the return of "found to be too big to fit" tires is a pain and costs some more $. The best way is to test fit before buying... The usual is to measure how much clearance there is with the old tires 9and what's their measured width), then get the next larger size and see what happens. Many consider about 4mm of open clearance between the tire and the sides of the blades.stays to be a minimum. Many don't consider the added height though. Here road stuff that gets picked up on the tire will increase the effective tire height.

My current weekend club bike has only a few mms of height clearance under the calipers and I feel/hear pebbles and such raking their way through that tight gap.

Really this question is one of those that is best answered by test fitting. Andy
Andrew R Stewart is offline  
Old 08-29-21, 04:54 PM
more daylight today!
Iride01's Avatar
Join Date: Jul 2017
Location: Mississippi
Posts: 12,230

Bikes: Tarmac Disc Comp Di2 - 2020

Mentioned: 43 Post(s)
Tagged: 0 Thread(s)
Quoted: 5008 Post(s)
Liked 3,515 Times in 2,440 Posts
Why should I have to look up what fits your bike? It's right there near you isn't it? Go look at how much clearance your 23 mm tires have to all parts of your bike. Find the narrowest clearance and that is how much bigger you can go.

What you have to decide on is how much clearance you want for safety. Mud sticking to the tire might slow you to a quick stop. Or a stick getting kicked up in that narrow clearance part might ruin your day.

23 to 25 mm is 2 mm more height on your tire and 2 mm more width. But you have to allow for differences between manufacturers. External tire dimensions aren't set in stone by any governing authority.
Iride01 is offline  
Likes For Iride01:
Old 08-29-21, 09:12 PM
Senior Member
Join Date: Jun 2002
Location: San Jose, CA
Posts: 3,041

Bikes: Too many bikes, too little time to ride

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 203 Post(s)
Liked 138 Times in 118 Posts
Best to measure but when I had a TCR from the mid 2000s, it can fit 28mm tires.
tFUnK is offline  
Old 08-29-21, 10:26 PM
Senior Member
70sSanO's Avatar
Join Date: Feb 2015
Location: Mission Viejo
Posts: 5,445

Bikes: 1986 Cannondale SR400 (Flat bar commuter), 1988 Cannondale Criterium XTR, 1992 Serotta T-Max, 1995 Trek 970

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1815 Post(s)
Liked 1,956 Times in 1,200 Posts
If you are referring to Continental GP4000, they have been replaced by GP5000. The only reason I mention that is that Continental has reduced the measured size of the GP5000 compared to the older GP4000 to reflect the size when mounted on modern wider rims.

Rim width does effect actual inflated tire dimensions so it isnít as cut and dry. Times have changed from the old 14mm internal width road rims.

If you go to rollingresistance.com you can get measured sizes.

70sSanO is offline  
Likes For 70sSanO:
Old 08-30-21, 01:51 AM
Senior Member
Join Date: Jul 2008
Location: Minas Ithil
Posts: 9,335
Mentioned: 66 Post(s)
Tagged: 0 Thread(s)
Quoted: 2431 Post(s)
Liked 630 Times in 389 Posts
They'll fit. I personally am one of the few 23mm holdouts. 2mm difference is almost nothing and I run the same air pressure anyway so I have no need to add any rotating weight.

However, some tires run small and in that case I would go up a size.
Lazyass is offline  
Old 08-30-21, 06:37 AM
Full Member
Join Date: Aug 2014
Posts: 257
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 72 Post(s)
Liked 44 Times in 33 Posts
The actual width and height of tires vary dependent on rim and manufacturer. You can get some idea from https://www.bicyclerollingresistance.com if your tire of interest is listed. However, there is no substitute for actually mounting the tire.
mitchmellow62 is offline  
Old 08-30-21, 02:50 PM
Senior Member
oldbobcat's Avatar
Join Date: Jul 2005
Location: Boulder County, CO
Posts: 3,878

Bikes: '79 Gios, '80 Masi, '06 Felt, early '60s Frejus

Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 334 Post(s)
Liked 273 Times in 205 Posts
I had one of those. The gap to the seat tube was pretty tight, as I remember. I always ran 23s because I didn't know better. But 25s should fit.
oldbobcat 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 or Share My Personal Information -

Copyright © 2023 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.