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700x38C is Max, but...

Old 02-20-22, 05:52 AM
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SteveInConverse
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700x38C is Max, but...

...I have about 55-57 mm of space between the posts of the fork. Could I safely run a 40-45mm width tire?

2022 Trek FX1 Disc
Stock Bontraeger Connection rims. 20mm internal width.
Thank you for your replies!

Steve
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Old 02-20-22, 06:53 AM
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the rear chain stays is probably the real limiting factor. that's where I had tire rub when I went too big. with my older FX (Alpha 7.0) I use 40mm WTB Nanos w/ no trouble at all (they run true to size)
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Old 02-20-22, 11:32 AM
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How safe it is will be something you have to decide for yourself. You bike's maker probably has an idea of what they consider safe and suggested a max size tire. If you want to go any larger, why should any of us suggest what you might could use and then get the blame if it doesn't work for you.
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Old 02-20-22, 11:44 AM
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So we have to ask how big a piece of trail will your tires pick up and try to jam under the crown/between the blades. How much mud? When you know that we can reply with far better ability to predict your future WRT running really wide tires. Andy (hoping readers can see the satire here)
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Old 02-20-22, 11:49 AM
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I have a wider tire in front, which my fork allows. This gives a wee bit more pneumatic suspension and traction.
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Old 02-20-22, 08:38 PM
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SteveInConverse
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Originally Posted by rumrunn6 View Post
the rear chain stays is probably the real limiting factor. that's where I had tire rub when I went too big. with my older FX (Alpha 7.0) I use 40mm WTB Nanos w/ no trouble at all (they run true to size)
Ah, good to know! I'll check out the Nanos. I'm going to check the clearance at the chain stays too.
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Old 02-20-22, 08:41 PM
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Originally Posted by Andrew R Stewart View Post
So we have to ask how big a piece of trail will your tires pick up and try to jam under the crown/between the blades. How much mud? When you know that we can reply with far better ability to predict your future WRT running really wide tires. Andy (hoping readers can see the satire here)
I won't be doing more than very light trails, no mud (don't want to have to clean it lol). Just maybe also looking for a more aggressive tire to replace the stock Bontraeger tires.
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Old 02-20-22, 08:42 PM
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Originally Posted by Polaris OBark View Post
I have a wider tire in front, which my fork allows. This gives a wee bit more pneumatic suspension and traction.
I like this idea. How much wider did you go up front?
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Old 02-20-22, 08:58 PM
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Originally Posted by SteveInConverse View Post
I like this idea. How much wider did you go up front?
I have a different bike, but 42mm rear, 48mm front.
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Old 02-20-22, 09:17 PM
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chainstays ....forkblades ....yes

posts ....no

other parts not to be found on a bicycle ....doohickeys, thingamabobs and whatchamacallits
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Old 02-20-22, 10:02 PM
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Originally Posted by Polaris OBark View Post
I have a wider tire in front, which my fork allows. This gives a wee bit more pneumatic suspension and traction.
This is the old BMX tire trick. Run a wider tire in front for steering grip and a narrower in rear for quicker acceleration. If you have to have a tire loose grip at, the wrong moment, the rear is likely the better one to do it with. Andy
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Old 02-20-22, 10:05 PM
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I re-invented it for gravel biking. I think I will call it the mullet comb-over.


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Old 02-21-22, 12:06 AM
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Originally Posted by rumrunn6 View Post
the rear chain stays is probably the real limiting factor. that's where I had tire rub when I went too big. with my older FX (Alpha 7.0) I use 40mm WTB Nanos w/ no trouble at all (they run true to size)
Ok, had the wife measure the area as Im at work and she reported 52mm of space at the rear chainstay. I'm guessing I could comfortably run a 42-45mm tire back there?
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Old 02-21-22, 11:33 AM
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Originally Posted by SteveInConverse View Post
Ok, had the wife measure the area as Im at work and she reported 52mm of space at the rear chainstay. I'm guessing I could comfortably run a 42-45mm tire back there?
from what I've played with the rear wheel/tire isn't always centered between the stays. also not all tires measure as marked on the sidewall when fully inflated. I had some tires that were waay over & I could use them but they had to be underinflated (see link below). if I were you I would stick to 40s tops

on my bike (Trek FX Alpha 7.0) the Michelin Protek 700x40mm measure 43mm at 90 psi didn't fit. as I wrote in my 1st reply, the 40mm Nanos are true to size & fit

https://www.bikeforums.net/hybrid-bi...ek-700x35.html
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Old 02-21-22, 11:38 AM
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If you can get a credit card to fit between your tire and the frame, you will be living life to its fullest.

I try to cram in the widest tire I can get away with. Unless your wheels go badly out of true regularly, or you have a tendency to ride through sticky adhesive mud, or if you ride room for fenders, the official estimates for maximum tire width are usually quite conservative. Also, be aware that the number printed on the sidewall of the tire may be significantly different from what the tire expands to on your rims on your bike with your favorite tire pressure, tube/tubeless content, etc.
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Old 02-21-22, 11:48 AM
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Originally Posted by SteveInConverse View Post
I like this idea. How much wider did you go up front?
I run 38 in front and 35 in back on two older steel road bikes. (I could squeeze a 38 in back but I'd have to slide the wheel back (horizontal dropouts) and let air out to remove the wheel.) Rode this combo on the most challenging "gravel" I've ever ridden. Slopes to 17%, several thousand feet both up and down and 1 1/2 inch "pebbles". Worked really well.
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Old 02-21-22, 07:12 PM
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Originally Posted by rumrunn6 View Post
from what I've played with the rear wheel/tire isn't always centered between the stays. also not all tires measure as marked on the sidewall when fully inflated. I had some tires that were waay over & I could use them but they had to be underinflated (see link below). if I were you I would stick to 40s tops

on my bike (Trek FX Alpha 7.0) the Michelin Protek 700x40mm measure 43mm at 90 psi didn't fit. as I wrote in my 1st reply, the 40mm Nanos are true to size & fit

https://www.bikeforums.net/hybrid-bi...ek-700x35.html
Wow, I had no idea that they varied like that..my dumbself figured 42 was 42 was 42! I looked at the Nanos and that's probably what I'll go with as true to fit seems like the best choice, or like you said stay in the 40's...I figured really no more than 42-45 max. Thank you for your help!
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Old 02-21-22, 07:14 PM
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Originally Posted by 79pmooney View Post
I run 38 in front and 35 in back on two older steel road bikes. (I could squeeze a 38 in back but I'd have to slide the wheel back (horizontal dropouts) and let air out to remove the wheel.) Rode this combo on the most challenging "gravel" I've ever ridden. Slopes to 17%, several thousand feet both up and down and 1 1/2 inch "pebbles". Worked really well.
Nice! Far more ambitious than I will be at this point! I do like the idea of the two sizes.
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Old 02-21-22, 07:16 PM
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Originally Posted by Polaris OBark View Post
If you can get a credit card to fit between your tire and the frame, you will be living life to its fullest.

I try to cram in the widest tire I can get away with. Unless your wheels go badly out of true regularly, or you have a tendency to ride through sticky adhesive mud, or if you ride room for fenders, the official estimates for maximum tire width are usually quite conservative. Also, be aware that the number printed on the sidewall of the tire may be significantly different from what the tire expands to on your rims on your bike with your favorite tire pressure, tube/tubeless content, etc.
Ok, good to know. I'm really surprised that the tires vary as much as they apparently do considering the tolerances and sizes that we encounter on bikes in general. Thank you.
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Old 02-21-22, 07:44 PM
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[QUOTE=SteveInConverse;22417147]I looked at the Nanos and that's probably what I'll go with/QUOTE]if that's the tread you want. I wouldn't get them if most riding was on pavement. they're fine, but they are designed for hard packed unpaved surfaces, I think. on pavement they have a slight buzz. run them a little soft around campgrounds or stone dust trails. ok for me for summer vacations w/ the family when I want a versatile tire that can hit some dry dirt paths. or slower rides w/ Wifey on paved trails. most of my solo riding is either with the road bike (25mm tires) or mountain bike (2.25" tires). the hybrid w/ the Nanos seems to get less use
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Old 02-21-22, 09:23 PM
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Originally Posted by SteveInConverse View Post
Ok, had the wife measure the area as Im at work and she reported 52mm of space at the rear chainstay. I'm guessing I could comfortably run a 42-45mm tire back there?
Run it, yes, comfortably, no.
The basic recommendation is to run 6mm of spacing to either side of the tire so the tire should ideally be 12mm narrower than the frame, running closer is possible but this number is meant to deal with the fact people don't true their rims the moment it comes slightly out of true, offer space if a spoke breaks, deal with road debris. On the upside, you may never run into a problem, on the down side you might slightly tweak a wheel on a gravel road and never notice that the dirt on the tire ate its way through the frame where the tire was ever so slightly rubbing. I've seen this happen with two road bikes, one aluminum and one very high end, thin wall steel. I personally have a bike with a slight groove in the stay from hitting a pothole on a downhill hard enough to break two spokes, the tire survived but the multi-mile ride home wasn't gentle on the frame but 4130 cromoly isn't weak or thin. Your fx might not be a worry but you should be aware the recommended space is for a reason.
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Old 02-21-22, 09:59 PM
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Originally Posted by Russ Roth View Post
Run it, yes, comfortably, no.
The basic recommendation is to run 6mm of spacing to either side of the tire so the tire should ideally be 12mm narrower than the frame, running closer is possible but this number is meant to deal with the fact people don't true their rims the moment it comes slightly out of true, offer space if a spoke breaks, deal with road debris. On the upside, you may never run into a problem, on the down side you might slightly tweak a wheel on a gravel road and never notice that the dirt on the tire ate its way through the frame where the tire was ever so slightly rubbing. I've seen this happen with two road bikes, one aluminum and one very high end, thin wall steel. I personally have a bike with a slight groove in the stay from hitting a pothole on a downhill hard enough to break two spokes, the tire survived but the multi-mile ride home wasn't gentle on the frame but 4130 cromoly isn't weak or thin. Your fx might not be a worry but you should be aware the recommended space is for a reason.
Those are really good points to consider. Seems the largest I would want to go then would be 40 max. That's plenty, all things considered. I'll check the measurement again and stay with the 6mm to either side. Thank you!
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Old 02-21-22, 10:02 PM
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[QUOTE=rumrunn6;22417182]
Originally Posted by SteveInConverse View Post
I looked at the Nanos and that's probably what I'll go with/QUOTE]if that's the tread you want. I wouldn't get them if most riding was on pavement. they're fine, but they are designed for hard packed unpaved surfaces, I think. on pavement they have a slight buzz. run them a little soft around campgrounds or stone dust trails. ok for me for summer vacations w/ the family when I want a versatile tire that can hit some dry dirt paths. or slower rides w/ Wifey on paved trails. most of my solo riding is either with the road bike (25mm tires) or mountain bike (2.25" tires). the hybrid w/ the Nanos seems to get less use
I'm shooting for about 50/50 pavement. I found a few that seemed to be aimed at that ratio. I don't want to run something that might introduce another issue to deal with. Thank you!
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