How much tire clearance do I need? Is 40mm 700c enough?

16 replies · 4,209 views

TBtheWrecker
12 posts
#1May 12, 2020, 8:33 AM
I'm currently looking at 700x40c clearance on a bike I'm considering. The new specialized diverge has upto 47mm on 700c!

How much clearance do I actually need to ride gravel and light singletrack? Is 40mm enough?

Brand: Donnelly X Plor MSO, 700 x 40c
0
dangle
465 posts
#2May 12, 2020, 8:50 AMedited▲ Top
'Clearance' typically refers to the space between your tires and frame. It seems like you're asking about how big of a tire is right for you.

The answer to your question of how large a tire you need/want is pretty individual. Your weight has a bit to do with it too. Smaller tires may be okay for lighter individuals. The general answer is that most people are just fine on 38-42 mm tires. If your weight or the surfaces you desire to ride on fall much outside the bell curve of average rider size or conditions, then you may be looking for something outside of that range.

Anecdotally, it seems less people have regrets about going bigger than 40 mm than they do about going smaller than 40.

If you're new to gravel tires, pressure is key. I'm normally 80-85 psi in 25 mm tires and my 40 mm tires are perfect in the 28-33 psi range. They feel rough on anything but pavement near 40 psi.
4
TBtheWrecker
12 posts
#3May 12, 2020, 8:56 AM
Yes - the right tire size. However, I may consider a different bike as this one (Renegade C2) only has clearance for 40mm. I'm 195lbs and 6"3 and in decent shape.

I do want versatility to go on heavier gravel, forest roads, and single tracks. Will that 40mm be enough? Should I consider a bike that allows bigger tires?
0
SWGraveler
247 posts
#4May 12, 2020, 8:57 AM
There are a lot of variables that affect how much tire you need/want. How much you weigh will determine your minimum tire pressure. Take a look at the tire pressure chart on the Enve site and see what it recommends for you with different tire sizes..If you ride rough stuff and weigh on the heavier side and want a fair amount of cushion, you will want bigger tires. I went from 43mm to 50mm and the difference in comfort is substantial. I weigh 180ish and here in Az things are pretty hard but I also never see mud so extra clearance isn't a concern. If you are in a muddy local, that will add to wanting some space so you can have the tire size you want with mud room.
I will say that bikes are clearly moving towards having more clearance; I agree with one of the reviewers here who thinks 50mm will be the minimum within a year or two. My recommendation, unless you weigh 150 or less, would be to have room for 45mm or more as there are a lot of choices that do so why compromise.
2
dangle
465 posts
#5May 12, 2020, 9:20 AM▲ Top
TBtheWrecker wrote:Yes - the right tire size. However, I may consider a different bike as this one (Renegade C2) only has clearance for 40mm. I'm 195lbs and 6"3 and in decent shape.

I do want versatility to go on heavier gravel, forest roads, and single tracks. Will that 40mm be enough? Should I consider a bike that allows bigger tires?

We're really close in size. Outside of large chunks of rock/gravel dug up in freshly graded roads and roots/rocks on trails, I think 40ish is enough for a do-it-all, but maybe not best choice. The largest tires either of my frames take is 42 mm measured and that will still scrape a little paint in the right conditions. A ShockStop stem and those tires at low pressures will handle what I want to do until it's time for a mountain bike.

I would lean towards bigger than 40 in your case. Something like a WTB Riddler or Raddler in 44/45 might be a better choice since it's fairly efficient down the middle with nice edge knobs you would like on forest roads and single track. Lots of gravel tires have pretty wimpy edge knobs, so look for that if you truly want a tire to keep you upright on mountain bike type trails.

It's getting harder to find a bike that can't do a 700 x 40-45 (and subsequently 27.5 x 2.1 tire), so if you're bike shopping make sure you go that route. It's pretty easy to find 27.5 wheels on the used market for relatively little cost since they exploded in popularity right before mtb axle standards changed. If you feel like you are happy with your gravel tires but want more tire for dirt/trails, you would have an option of putting together a second wheelset.

Eventually you will go down the rabbit hole and have several wheelsets for your bikes. Fast 700 road tires. Fast 700 gravel tires. Chunky 700 gravel tires. 27.5 dirt tires.

Keep your expectations in check as well. I think bicycle marketing has done a great job of making us think we're going to pull off of a group ride, turn into a forest trail opening, cross a creek, ascend a gravel climb and rip down a forest road all on the same bike (and tires). There's always going to be compromises.
4
karl
15 posts
#6May 12, 2020, 10:38 AM
What they said.
0
baron
25 posts
#7May 12, 2020, 12:25 PM
Dangle had the best advice by saying it's "pretty individual." I started gravel riding on cyclocross orientated race tires in 700x33. I did everything from road group rides to larger gravel rides (my first Land Run was on these tires) with them. Tubeless, never more than 40 psi, they were extremely versatile. I went up to a 38 from there with a Panaracer SK and, tbh, I didn't notice a huge difference other than they were less prone to getting flats. I stuck with 38 in Panaracer and then a Teravail until I got a new bike. It came with 650x47. Those things were like riding in an 80's caddy. Floated over everything. Awful on anything wet, but wow, it was truly a comfortable ride. This year's Land Run necessitated something that would give me more clearance and handle the mud, so I went down to a 650x40. Every time I ride that bike, I keep thinking about swapping out the wheelset and going back to 700x33. Even on some light single track, the 700x33 was great.

SO, I say all this to emphasize that it really is a personal thing. Just like your saddle. You have to find what works for you. That said, looking at a bike that can accommodate something bigger than 700x40's isn't a terrible idea. You never know, you might be someone that really loves riding on 45's.
1
chas
1,305 posts
#8May 13, 2020, 7:55 AM
dangle wrote:
Keep your expectations in check as well. I think bicycle marketing has done a great job of making us think we're going to pull off of a group ride, turn into a forest trail opening, cross a creek, ascend a gravel climb and rip down a forest road all on the same bike (and tires). There's always going to be compromises.

I did that last fall. Slowed down at a regroup spot, the majority of people had too much testosterone to regroup like was planed. Lead a small group at ~25mph on gravel to catch up to the main pack for about 3 miles, which was a fun sprint. But then I notice the sunset was gorgeous and asked myself - why am I running this hard? Dropped of my followers back in the group, then pealed off, took some pictures of the sunset, had a nice quiet time hitting some twisty single track, enjoying how peaceful the evening was in contrast to the the fast pace of the race training ride. One of my favorite memories of last year.

(I was running a 50mm tire up front and 40mm in the rear for some high speed gravel a little bit of do everything versatility).
1
chas
1,305 posts
#9May 13, 2020, 7:59 AM
TJ, Sounds like you went ahead and bought the Diverge then. 47mm should do you fine. :-)
1
TBtheWrecker
12 posts
#10May 13, 2020, 10:26 AM
chas wrote:TJ, Sounds like you went ahead and bought the Diverge then. 47mm should do you fine. :-)

Yes! you guys made a great point, and I thought it's about the options more than anything. Now I can try anywhere from 33-47mm based on condition and preference. I'll be bothering you guys again with tire choices once my bike gets in next week, haha!
0
chas
1,305 posts
#11May 13, 2020, 11:26 AM
32mm conti GP5000
40mm conti Terra speed
45mm Maxis Rambler.
Or just anything Schwalbe makes. ;-)
0
Talabardio
34 posts
#12May 24, 2020, 11:44 AM
TBtheWrecker wrote:I'm currently looking at 700x40c clearance on a bike I'm considering. The new specialized diverge has upto 47mm on 700c!
How much clearance do I actually need to ride gravel and light singletrack? Is 40mm enough?

These are all an individual choice. Cross tires are enough for me. I’m living large at 35 and going wild at 38.
0
ccand51997
265 posts
#13May 24, 2020, 12:59 PM
TBtheWrecker wrote:I'm currently looking at 700x40c clearance on a bike I'm considering. The new specialized diverge has upto 47mm on 700c!

How much clearance do I actually need to ride gravel and light singletrack? Is 40mm enough?

Brand: Donnelly X Plor MSO, 700 x 40c

Where I live, the riding is a nice split of dirt and pavement, but there is always a patch of sand every so often and with 38s or 42s its either hike-a-bike or slipping and sliding. Now I run a Conti Raceking 2.2 on back with a 47mm Byway or Schwalbe Thunderburt on the front. I tested my mtb tires against my gravel tires and they were not a speed disadvantage (power meter testing) so really there was no downside other than an aero penalty at faster speeds on pavement.
Plus, I can run a 2.2 tire at 20 psi and it really smooths out the ride.
0
simplemind
71 posts
#14Jun 2, 2020, 10:20 AMedited
Bottom line...you need at least 4mm dry and 5mm wet clearance per side to be safe. And that’s assuming you have a true wheel/tire.
2
RadDogRoadWarrior
93 posts
#15Jun 3, 2020, 9:29 PMedited
I have tarmac to gravel/offroad, then tarmac to make it back home. A 42 handles about 95% of what I need offroad and is still fairly fast on pavement.
I will say this, if I were younger I could get away with smaller tires offroad. At 58 my skill set is not quite what it once was, and that is why I need a bit more tire.
Oh, and I am 220 lbs.

0
chas
1,305 posts
#16Jun 4, 2020, 3:43 PM
Bottom line...you need at least 4mm dry and 5mm wet clearance per side to be safe. And that’s assuming you have a true wheel/tire.

ISO standards are 6mm, so that is what the manufacture should be using when quoting tire sizes. I've gone down to zero vertical and 2mm horizontal, but under high torque that 2mm still may cause some rubbing.

1
NoCoGreg
512 posts
#17Jun 10, 2020, 11:45 AM
chas wrote:

ISO standards are 6mm, so that is what the manufacture should be using when quoting tire sizes. I've gone down to zero vertical and 2mm horizontal, but under high torque that 2mm still may cause some rubbing.

When discussing "clearance", as Chas noted, one needs to consider frame & wheel flex. A rider who uses taller gears and slower cadence will tend to flex the frame & wheel more than a rider with a high rpm spin.

My reading of this thread the question/issue isn't "clearance" but rather what is the ideal/appropriate tire size for the OP's intended use.

It's funny that the "new" 47mm tires are almost the same width as the standard 26x1.9" MTB tire from the 80's and early 90's.

I've seen lots of people getting around on singletrack with much narrower tires but as the MTB riders have discovered fatter tires hookup better and provide cushion.

One other thing to consider: gear ratios change with tire size. Wider tires increase the diameter which increases the overall gear ratio (i.e. gear inches). The change is not (IMO anyway) significant, but if one moves from a 47mm to 32mm tire for the road the tallest gear will be smaller.
0

Related threads

Chinese carbon gravel - Lightbicycle JourneyBikes · 4 replies · Sep 14, 2021
Roker Comp ReviewBikes · 128 replies · Sep 4, 2018
Quiver of One- Gravel/Road/Touring Bike?!Bikes · 18 replies · Feb 18, 2019
Bicycle Rolling Resistance tests gravelGravel Tires · 30 replies · Jul 10, 2020
Help me with some gravel tire knowlegeGravel Tires · 24 replies · Jul 11, 2018