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How much wider tire in the front?

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How much wider tire in the front?

Old 02-11-23, 03:11 AM
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urbanknight
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How much wider tire in the front?

Any of you ride with, say, 10mm wider front tire as compared to the rear? My bike is a little restricted in the rear but rather accommodating up front, and I'm wondering if there's a reason NOT to go 10mm wider (should actually come out to 8mm difference because of what rim the nominal sizes are apparently measured on). More interested in comfort than speed, and these will be designated for off road use as I have a second set of wheels with narrower tires with slicker tread for road and mixed surfaces.
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Old 02-11-23, 12:53 PM
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Go for it if that's what you want, it won't do any harm. I haven't run mismatched tires in a long time, but back when I had a cyclocross bike with limited tire clearance (38 in front, 35 in back) that's exactly what I did, and likewise with old rigid mountain bikes. When I did this it was to maximize grip for technical riding, but it would make at least some small difference for comfort as well.
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Old 02-11-23, 04:37 PM
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Way back in the day we used to do it on rigid mountain bikes all the time. There was typically a fairly small difference in size. It was mainly for traction, but comfort was a plus as well.
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Old 02-11-23, 08:02 PM
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Originally Posted by staehpj1
There was typically a fairly small difference in size.
So is a 10mm difference extreme? I could also go just 5mm wider up front instead, or might even be able to squeeze the middle size in the rear with (hypothetically) 5mm clearance on each side. But the front has room for the widest option, and the narrower option is guaranteed to fit the rear.

Extra traction is a bonus. I plan on riding dirt roads and fire trails, but will probably be lured into doing some single track as well.
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Old 02-11-23, 09:02 PM
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I don't think I've done it but I've been riding all sorts of tires long enough to know the nothing bad will happen unless they have different enough grip properties that you surprise yourself and push the poorer tire too hard on a turn or stop. But really that's no different than anything else. Ride what you got within its limits. And odds are you will find some cool thing this combo does better than what you've ridden before.

My two gravel worthy bikes both run 38s in front and 35s in back for exactly your reason. Only time I think about it is pumping up. I go a bigger front-rear difference. Not that I have to unless I'm running very low for gnarly conditions.
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Old 02-12-23, 06:13 AM
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Originally Posted by urbanknight
So is a 10mm difference extreme? I could also go just 5mm wider up front instead, or might even be able to squeeze the middle size in the rear with (hypothetically) 5mm clearance on each side. But the front has room for the widest option, and the narrower option is guaranteed to fit the rear.

Extra traction is a bonus. I plan on riding dirt roads and fire trails, but will probably be lured into doing some single track as well.
On mountain bikes we used to routinely go 10-15mm difference. Not sure what anyone does these days.
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Old 02-12-23, 11:11 AM
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My gravel bike is about 5 mm difference right now because Panaracer changed their tire sizes since I bought the front and I got it wrong when I bought a new rear tire. I have had tires front tires dig in on fresh gravel, so it doesn't seem like a bad idea to get a bigger front tire. I'm not sure if I could live with it long term though. My bikes all look like crap, that's somehow too much for me.
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Old 02-12-23, 04:49 PM
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My only concern would be that you might get comfortable smashing bigger gravel that a 45mm tire can handle, and forget that your rear is narrower and more likely to be subjected to rim strikes/pinch flats/etc.

Beyond that, I don't see any problem with 10mm difference. As others have mentioned, this used to be common on MTB.
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Old 02-12-23, 07:53 PM
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for my own sake, having 45mm in the back & 57mm in the front, would be disappointing. if I wanted 57mm, I would def. want them in the rear, where more of my weight was
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Old 02-12-23, 10:53 PM
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Originally Posted by rumrunn6
for my own sake, having 45mm in the back & 57mm in the front, would be disappointing. if I wanted 57mm, I would def. want them in the rear, where more of my weight was
Yeah it does seem backwards, and I would indeed prefer more cushion under my rump, but I'm pretty sure even a 42 rear would be pushing it on this bike. The anal retentive perfectionist in my is tempted to just try 40 or 42 front and rear (that should be plenty), but 50 on the front would probably feel a little cushier.
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Old 02-13-23, 05:20 AM
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Originally Posted by urbanknight
50 on the front would probably feel a little cushier.
which would be good when striking roots & rocks, especially if you play w/ the psi
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Old 02-13-23, 08:07 AM
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aw man, I had not thought of this recently when I increased the size of the tires on my CruX. I put 38s on it (it had 33s). Now I'm going to check if a 40 will fit on the front. Thanks for posting this.
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Old 02-14-23, 06:09 AM
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Originally Posted by msu2001la
My only concern would be that you might get comfortable smashing bigger gravel that a 45mm tire can handle, and forget that your rear is narrower and more likely to be subjected to rim strikes/pinch flats/etc.

Beyond that, I don't see any problem with 10mm difference. As others have mentioned, this used to be common on MTB.
That is why you run more pressure in the back.
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Old 02-16-23, 12:49 AM
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If you ride gravel/MTB trails the bigger front tire would help roll over things like a mullet setup on a MTB bike.

For a road bike seems like the smaller tire up front would help with the aero and the larger tire in the back for comfort.
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Old 02-16-23, 03:16 AM
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On the bike design for 35/38mm 700c tyres because of the more CX frame, I was considering doing that as the fork was of the generic type that accepts 45-700c.
With 650B wheels, the frame could take 40-584/42-584 and the fork could take 50-584/52-584 which may be good with the rear rolling quickly on tarmac/hardpack while the front provide grips on trails.

The thing I did not measure accurately was the change in perceived headset angle; with a 10mm rack angle due to tyres size, how much slack is added to the head angle? Rough angular calculation would suggest 0.5į added slack so 71 to 70.5į
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Old 02-16-23, 10:43 PM
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It's been mentioned, back in the 90s we might have a 2.3" up front and a 2.1-2" in the back. We did this due to clearance differences but also to get better traction up front.

You mention 10mm difference, well the difference between 25mm and 35mm is significant, but the difference between 35mm and 45mm is not too big. If your bike is like my bike, then you might go with 45mm up front with 38mm in the back. I've never thought to try this with gravel bikes because I feel like at gravel tire widths and pressures there would be little noticeable difference.
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Old 02-17-23, 02:39 AM
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I was looking at https://axs.sram.com/guides/tire/pressure

running 45c instead of 35c front allows a 15 psi drop which would be grip advantage off road and a comfort advantage of tarmac

That said, this is as limited application on a gravel bike with usually clearance for 42-622 to 45-622. However for cyclocross bike with frame designed for 33-35 and usually much larger clearance on the fork, it can be interesting as larger front may allow the rider to go on rougher terrains

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Old 02-17-23, 04:00 AM
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I have a 650b x 48mm tire on the front and a 650b x 42mm tire on the rear of my gravel/off-road wheel-set.

I did it for the same reasons you have, and it works out fine. I keep the large front tire comparatively lower in pressure, which helps with shock absorption and possibly more traction in sketchy parts.



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Old 02-17-23, 12:24 PM
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I'm doing the opposite, I'm running wider in the rear and skinnier in the front. Mainly to get more rear grip on the climbs. Ever since I switched to an extreme flare carbon gravel bar, it's dampened the trail vibrations quite noticeably.
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Old 02-19-23, 11:33 AM
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For anyone interested, I ended up discovering Mitas tires that come in 40 (42 etrto) and 38 (40 etrto) with great reviews. I figured with the 25mm (internal width) rims, the wider size might not fit as they would probably come out around 43-44, but the low price (discounted even more for buying a pair) would allow me to try the wider ones, and if that didnít fit Iíd just get a pair of the narrower ones and have a set of slightly offset sizes with a second pair on deck.

Well, the 42 etrto tires still measure only 40mm on my wide rims. Kind of disappointing, but itís a standard size people seem to like so Iím gonna ride them and see how I like them.
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Old 02-19-23, 11:34 AM
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You coul put the 42 (40) mm tire on the back, and get a wider one for the front, and keep the 38 mm as a spare.
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Old 02-19-23, 11:14 PM
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Originally Posted by Polaris OBark
You coul put the 42 (40) mm tire on the back, and get a wider one for the front, and keep the 38 mm as a spare.
I only bought the 40s so far, but yeah I guess I could still throw a 50 on the front if I decide to.
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Old 02-19-23, 11:31 PM
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The last couple of days have re-affirmed my decision to have a 48mm in the front. I would put something wider than the 42mm in the back if I could cram it in there.
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