jtuds

Hello

I bought 28mm Continental Gran Prix 4000s II tires to put on my wife's Fuji Granfondo Classico 1.3 to increase the comfort level and fitted them today.

The front fits fine.

However, when I install the rear wheel, the tire rubs on the peak/apex of the seat stays. This makes me angry, so I am going to rant as follows (the below is rhetorical so please feel no need to answer):

1. How the F does Fuji make a bike in their "endurance" line and not make sure the farm can handle a 28mm tire?
2. How can the same sized tire on the same sized wheel fit on the front but not he back of the same bike?

OK - this is one thing I'd like someone to help me understand - if the stock 25mm 700c Vittoria tires fit without rubbing then why wouldn't a 28mm 700c Continental tire also fit without rubbing? Do 700c tires not all have the same diameters?

And for the key question I want to ask - Would it be silly/ridiculous for me to for a 25mm Conti GP4000sII so the rear and leave the 28mm on the front?

I have a set of brand new 25s that I bought for myself buy don't need yet. She is not a serious rider. She rides pretty much only with me and for leisure, 80-90% on paved bike trails in parks at quite slow pace....so she wouldn't care if I do this...probably wouldn't even notice....but I am wondering what, if any, ill effects this could cause.

Thank you.

alcjphil

First of all I get that you love your wife and want to improve her riding experience. I back you 100%. However, you have failed in your attempt to make an improvement to her bike that she might never have been able to notice, somehow I fail to see the problem. The ill effects that could result will only happen if you stress over this. Let her enjoy her bike in the way that she enjoys her bike. No amount of tinkering with her bike will change the way she enjoys riding it

Johnny Mullet

I had a Fuji road bike with the same issue. I upgraded to a Huffy.

jtuds

Well the tires are already on the rims so I have todo something

I should have clarified by comment about what I think she will/won't notice.

I think she will notice the change from the 25mm (looked like 23s) Vittorias to the 28mm Contis. I don't think she'd notice the difference between a 28mm front/28mm rear Conti vs a 28mm front/25mm rear Conti.

rm -rf

Tire sizes are based on the bead seat on the rim, not the outside diameter of the tread. See Sheldon's page.

And the tread diameter depends on the actual size of the tire, and the width of the rim. Not all 25c tires are actually the same size, but there seems to be somewhat less variation these days.

And see this chart from HED:



Frame tire clearance

Yes, you'd think the front and back wheels would have similar clearances. Perhaps the fork is used on other frames.

The trend for room to fit 28c tires is fairly new. So a frame designed 5 or 7 years ago might not have had tires over 25c in mind.

smarkinson

1. How the F does Fuji make a bike in their "endurance" line and not make sure the farm can handle a 28mm tire?
It's perhaps the bike is older and 28mm tyres weren't the style of the time. Making a bike handle larger tyres means widening the chainstays, lengthening the chainstays (so you don't hit the bottom bracket) and perhaps even finding brake calipers that can handle 28mm tires.

2. How can the same sized tire on the same sized wheel fit on the front but not he back of the same bike?
Geometry. On the back wheel the seat stay is pretty much in line with the radius of the wheel so the brake mount is at the highest point of the wheel and the bottom of the brake caliper itself ends up sitting a further distance from the wheel. So the first thing you hit here is the brake mount.

On the front wheel, because of the bend in the fork shape, the bottom of the brake caliper is actually closer to the wheel than the arch of the forks. So the first thing you would hit here would be the brake caliper.

If you build a bike so that the distance between the brake calipers and the rims is the same for the front and rear wheels then the rear brake mount is the closest thing to either tyre.

You should have no problems running 28mm on the front and 25mm on the rear.

jtuds

Thank you, that is helpful.

So I suppose that a rim with a narrower internal width could also cause a 28mm tire to be a bit narrower and higher than on a wider rim, right?

I have a set of Bontrager wheels that may have a slightly wider internal width. If using those would widen/flatten out the tire a bit, maybe they'll fit...or I can just put the 25mm on the back and be done with it.

SkyDog75

The diagram rm-rf posted above shows the same tires mounted on rims of various widths. As you can see, rim width makes a *little* difference, but if your 28 mm tire rubs now, changing to a slightly different rim width probably won't make enough difference to matter. And you say you could change to a wider rim, but that would likely do the opposite of what you think and make the problem worse.

As for the question about why tire clearance is different from front to rear... I'd venture to guess that pretty few bikes have the exact same clearance front and rear. There's simply no reason to make sure they're exactly the same. And if they're not precisely the same, you'll run into some threshold where a tire of a given size fits front or rear but not both. In your case, that appears to be 28 mm.

Mobile 155

First don't take this as a defense for the manufacturer but do you know what a Gran Fondo is? The bike is named after a longer timed bicycle event that some describe as a race. not everyone I know. But in this case the bike is designed more along the lines of a Specialized Roubaix or a Trek Domane. You would be lucky to get a 25 on the Roubaix. So Endurance in this case is simply a name they give to a bit less aggressive road bike. The Fuji site lists the Granfondo Classico with these tires, Vittoria Zaffiro, 700 x 25, 26tpi

That being said the 2016 Bike radar specs say the disk Granfondo (not the Classico)comes with a 700c x28. So where does the tire rub? and maybe you need differnt tires? These are the 2016 spec TIRES, Vittoria Rubino Pro, 700 x 28, 150 tpi, folding or, Vittoria Open Corsa, 700 x 28, 320 tpi, folding.

AlexCyclistRoch

There is a LOT of variability in tires, Traditionally, 28mm would've beet the with, as well as the increase in radius above the 622mm diameter rim, but some tires (including long-life tires by Conti) add extra belts and tread, which makes them taller. I upgraded my road bike the other day to 24mm tires, and the rear almost touches the front derailleur cable now (although that might be unique to the replacement Campagnolo unit I have).

jtuds

Yeah, I know what a gran fondo is...which is specifically why I was confused about why a bike built for endurance/longer rides and more comfort than a performance bike would not have room for a tire that could increase comfort.

The 25mm Vittorias that were on the stock bike looked quite narrow for 25mm tires.

Like I said, I have 25mm Contis already so I could just switch these out for those and I expect that they would fit

gregf83 

If you measure the width of mounted GP4000s you'll see they are significantly wider than 28mm

Leebo

Umm, don't buy a race bike next time? Look at a cross bike or adventure bike. 35-40 mm tires and up will fit those.

ThermionicScott 

All is not lost. Depending on how much your wife weighs, you may be able to get away with less pressure in the 25mm tires, which would help with the comfort: https://www.bikequarterly.com/images/TireDrop.pdf

fietsbob

Fuji is the name of a Volcano-Mountain In Japan It has nothing to do with Bike making..

and the brand name keeps changing Ownership

Steve B.

As well with a women's size, the bike may have shorter chainstays and yet still use 700c wheels, thus tire size may be more of a limit on a smaller frame.

I'd never assume any road bike uses anything larger then 25mm unless it specifically says so. Dead give away is the tires the bike came with originally. If a 25, it probably not going to take a 28

jamesdak 

Yep, on my rims the Conti 28s are actually 31mm when inflated to only 80 psi. And pretty much the same experience. Plenty of room on the front but just barely clears on the rear. So comfy though!

jamesdak 

Or an older steel racer. I've managed to pull off 700 x 28s on my 1989 Greg LeMond, barely...

Moe Zhoost

Consider converting to 650B. But that would probably look a bit weird for this particular bike.

Paul Barnard

Trek Hardcase 28s will very likely fit.

Camilo

Here's probably what happened: The Vittorias run a little small, the Contis a little big. I've found Contis GP's to run a little larger than advertised - my 23's measure more than 24mm, almost 25mm when mounted and aired up. I don't know about Vittorias, but I use another Italian tire brand (Veloflex) which measure a tiny bit small - 23's measure a tad smaller than that. Same rim - because that can affect actual diameter too.

So there's a chance that you went from an actual, measured tire size of, say 23-24mm to an actual, measured tire size of 29+.

Stated tire diameters aren't always accurate - some measure small, some large. But you would think that a frame like that would accommodate a 28. That seems odd that it doesn't

jtuds

There's now a 25mm on the rear (she did it herself, which is cool). It's 28mm front/25mm rear at the moment....whatever, we'll leave it and see how it goes. We could just put a 25mm on the front too, I already have one...then I could throw the 28s on my aluminum Emonda for some extra comfort once my current tires wear out.

She's 5'1, 105lbs so I am thinking somewhere around 90psi in both to give some extra comfort and reduce the risk of pinch flats.

mlm

I had a Roubaix a few years ago and it came with 25's. the new ones , in fact, come with 26's. The assertion that you'd be lucky to get a 25 on a Roubaix is just not accurate.

BobbyG

FWIW, I own a 1983 Nishiki International which had 700x23s. I mostly commute, so I switched to 700x32s but can only inflate to 85psi for the same reason as you. The ride with the 32s at 85psi is more comfortable and cornering is better.

redlude97

I would run closer to 80psi in those sizes for someone 105lbs, and run the other set 25F/28R on your Emonda.