Mixing tyres front/rear

[Ares]

Puncture on Sunday has led me to dump the GP4000s for GP4Seasons across all bikes.

I want to go 28mm, but even my 25mm are tight on the rear of the Dogma. Is it safe to run 28 front/25rear (both GP4season?)

Opinions?

Thanks!

[yellowjack]

Opinion but not experience?

Entirely safe, I'd have thought. So long as there's no frame rub or fouling on brake calipers. It's not as if we bicyclists reach speeds where stability would be adversely affected by tread pattern, rubber compound or carcass construction anyway.

I ran an original (almost plastic, it was so rigid) Michelin Tracer on the front of my 90s road bike, with a far more modern Hutchinson something-or-other on the rear for years.

It's quite the norm in mountain biking too. Completely different tyres, and tread patterns/sizes. Wide and agressive up front to bite in the turns, but narrower and with shallower tread on the back to reduce rolling resistance. I can't do it (I'm now way too OCD, I'd rather fall off than run mismatched tyres!!! ) but loads of MTBers, especially those who race, do it.

Plus, think of the pro peloton. You don't get to pick and choose which tyres you get when you need a wheel from the neutral service car, or even a swap with a team mate. If it was unsafe, they wouldn't do it. And they're kicking along pretty quickly, like!

[upsidedownmark]

Safe, sure, but why bother? 28 vs 25 on the front is not going to make any perceptible difference.

[Ares]

yellowjack said:

Opinion but not experience?

Entirely safe, I'd have thought. So long as there's no frame rub or fouling on brake calipers. It's not as if we bicyclists reach speeds where stability would be adversely affected by tread pattern, rubber compound or carcass construction anyway.

I ran an original (almost plastic, it was so rigid) Michelin Tracer on the front of my 90s road bike, with a far more modern Hutchinson something-or-other on the rear for years.

It's quite the norm in mountain biking too. Completely different tyres, and tread patterns/sizes. Wide and agressive up front to bite in the turns, but narrower and with shallower tread on the back to reduce rolling resistance. I can't do it (I'm now way too OCD, I'd rather fall off than run mismatched tyres!!! ) but loads of MTBers, especially those who race, do it.

Plus, think of the pro peloton. You don't get to pick and choose which tyres you get when you need a wheel from the neutral service car, or even a swap with a team mate. If it was unsafe, they wouldn't do it. And they're kicking along pretty quickly, like!

Opinions based on experience?

Thanks - echoes my thoughts, but always good the check.

[Ares]

upsidedownmark said:

Safe, sure, but why bother? 28 vs 25 on the front is not going to make any perceptible difference.

Perhaps, but the move from 23 to 25 did. In the wet and grotty winter, and extra 10% of contact patch is surely a good thing?

[upsidedownmark]

1) I'll bet you didn't just change the front to a 25 and keep everything the same(i.e. the rear on 23) . Most of the load goes through the rear, that is dominant.

2) You're not getting a 10% increase in contact patch. For the same download and tyre pressure, you get the same contact patch area. With a wider tyre you just get a shorter, wider contact patch. With a larger tyre you can drop the pressure to get a larger patch, provided you don't start getting pinch flats.. but that's unlikely limiting on the front tyre anyway, you can run lower pressures as it's not overly weighted compared to the rear.

2.5) Diminishing returns. You're not going to be better off on a 2 1/4 inch wide mountainbike slick (hypothetically assuming it would fit)

Edited by upsidedownmark on Tuesday 15th November 13:21

[Ares]

upsidedownmark said:

1) I'll bet you didn't just change the front to a 25 and keep everything the same(i.e. the rear on 23) . Most of the load goes through the rear, that is dominant.

2) You're not getting a 10% increase in contact patch. For the same download and tyre pressure, you get the same contact patch area. With a wider tyre you just get a shorter, wider contact patch. With a larger tyre you can drop the pressure to get a larger patch, provided you don't start getting pinch flats.. but that's unlikely limiting on the front tyre anyway, you can run lower pressures as it's not overly weighted compared to the rear.

2.5) Diminishing returns. You're not going to be better off on a 2 1/4 inch wide mountainbike slick (hypothetically assuming it would fit)

Edited by upsidedownmark on Tuesday 15th November 13:21

1) - yes I did. Swapped 23mm GP4000s for 25mm GP4000s (primarily as Wiggle didn't have 23mm in stock.

2) not sure, can't see why contact patch would be shorter on wider tyres?


Beyond that, I need to order 2 tyres. Do I order 2x 25 or 1x25 1x28. Same cost, same fit, if it's going to give just 1% more grip and no downside, it's worthy option?

[schmunk]

I'm currently running a semi-slick tyre on the front of my commuter (mountain bike) and a knobbly on the back. All fine.

[ALawson]

I run 25mm front, 23mm rear. Same make but slightly different designs (both tubeless).

Run at about 90psi for both (maybe 85psi on the front), I can get a 25mm in the rear by they came up very wide and if the tyre was clean there was 0,5mm clearance. Any muck etc and the S-Works SL4 Tarmac frame was get wear on the inside of the driveside rear triangle.

[yellowjack]

Ares said:

Opinions based on experience?

Thanks - echoes my thoughts, but always good the check.

Yeah. About that. When I wrote the first bit I'd forgotten the long-ago experience. Then, when I remembered the experience, I'd forgotten about writing the first sentence.

Ah well. It said on the news that Dementia is now the single biggest cause of death in the UK. Seems I'm well on the way then...

[upsidedownmark]

Ares said:

upsidedownmark said:

1) I'll bet you didn't just change the front to a 25 and keep everything the same(i.e. the rear on 23) . Most of the load goes through the rear, that is dominant.

2) You're not getting a 10% increase in contact patch. For the same download and tyre pressure, you get the same contact patch area. With a wider tyre you just get a shorter, wider contact patch. With a larger tyre you can drop the pressure to get a larger patch, provided you don't start getting pinch flats.. but that's unlikely limiting on the front tyre anyway, you can run lower pressures as it's not overly weighted compared to the rear.

2.5) Diminishing returns. You're not going to be better off on a 2 1/4 inch wide mountainbike slick (hypothetically assuming it would fit)

Edited by upsidedownmark on Tuesday 15th November 13:21

1) - yes I did. Swapped 23mm GP4000s for 25mm GP4000s (primarily as Wiggle didn't have 23mm in stock.

2) not sure, can't see why contact patch would be shorter on wider tyres?

Beyond that, I need to order 2 tyres. Do I order 2x 25 or 1x25 1x28. Same cost, same fit, if it's going to give just 1% more grip and no downside, it's worthy option?

1) You missed my point - sure swapping 25's for 23's will make a difference. Particularly on the rear. If you'd kept a 23 on the back and put a 25 on the front, bet you'd not have noticed. I'd even expect that you'd notice a 28 on the rear, but on the front.. nah

2)Because physics. What keeps you off the ground is air pressure. It doesn't care what size the tyre is, it squashes a bit (kinda like a spring) to achieve equilibrium. Same pressure, same squash (or same volume intruded into the tyre). The squash gives you a contact patch. If it's wide, less length is needed for that volume, so it'll be short, and if it's narrow it'll be long.

THAT is why a wider tyre rolls better: Whack a line between two points on a circle that are close, and two that are further apart; the longer contact patch of a narrower tyre deforms the carcass more, so more drag.

Whether you have more grip is more down to the tyres you run (probably pick up more grip running 4000's than going to a 28), the width of the rims (which will affect the shape of the tyre), pressure and so on.

If you want to do it, go for it, but there's no real justification. As for 1% you'll either have more grip than you need, or fall off anyway, 1% doesn't make a real world difference - you can't ride that close to the limits.

[Gren]

Why not. Plenty do it on the trails. Narrower less nobbly tyre at the back and fatter one out front.

I've also run 4 seasons on the back and gp4000s up front. Saves changing/buying a full set and it's usually the rear that punctures and so needs a bit more protection.

[thiscocks]

upsidedownmark said:

Ares said:

upsidedownmark said:

1) I'll bet you didn't just change the front to a 25 and keep everything the same(i.e. the rear on 23) . Most of the load goes through the rear, that is dominant.

2) You're not getting a 10% increase in contact patch. For the same download and tyre pressure, you get the same contact patch area. With a wider tyre you just get a shorter, wider contact patch. With a larger tyre you can drop the pressure to get a larger patch, provided you don't start getting pinch flats.. but that's unlikely limiting on the front tyre anyway, you can run lower pressures as it's not overly weighted compared to the rear.

2.5) Diminishing returns. You're not going to be better off on a 2 1/4 inch wide mountainbike slick (hypothetically assuming it would fit)

Edited by upsidedownmark on Tuesday 15th November 13:21

1) - yes I did. Swapped 23mm GP4000s for 25mm GP4000s (primarily as Wiggle didn't have 23mm in stock.

2) not sure, can't see why contact patch would be shorter on wider tyres?

Beyond that, I need to order 2 tyres. Do I order 2x 25 or 1x25 1x28. Same cost, same fit, if it's going to give just 1% more grip and no downside, it's worthy option?

1) You missed my point - sure swapping 25's for 23's will make a difference. Particularly on the rear. If you'd kept a 23 on the back and put a 25 on the front, bet you'd not have noticed. I'd even expect that you'd notice a 28 on the rear, but on the front.. nah

2)Because physics. What keeps you off the ground is air pressure. It doesn't care what size the tyre is, it squashes a bit (kinda like a spring) to achieve equilibrium. Same pressure, same squash (or same volume intruded into the tyre). The squash gives you a contact patch. If it's wide, less length is needed for that volume, so it'll be short, and if it's narrow it'll be long.

THAT is why a wider tyre rolls better: Whack a line between two points on a circle that are close, and two that are further apart; the longer contact patch of a narrower tyre deforms the carcass more, so more drag.

Whether you have more grip is more down to the tyres you run (probably pick up more grip running 4000's than going to a 28), the width of the rims (which will affect the shape of the tyre), pressure and so on.

If you want to do it, go for it, but there's no real justification. As for 1% you'll either have more grip than you need, or fall off anyway, 1% doesn't make a real world difference - you can't ride that close to the limits.

Well put. That's why I laugh when people say 'im putting wider tyres on my car for more grip'

[Ares]

upsidedownmark said:

Ares said:

upsidedownmark said:

1) I'll bet you didn't just change the front to a 25 and keep everything the same(i.e. the rear on 23) . Most of the load goes through the rear, that is dominant.

2) You're not getting a 10% increase in contact patch. For the same download and tyre pressure, you get the same contact patch area. With a wider tyre you just get a shorter, wider contact patch. With a larger tyre you can drop the pressure to get a larger patch, provided you don't start getting pinch flats.. but that's unlikely limiting on the front tyre anyway, you can run lower pressures as it's not overly weighted compared to the rear.

2.5) Diminishing returns. You're not going to be better off on a 2 1/4 inch wide mountainbike slick (hypothetically assuming it would fit)

Edited by upsidedownmark on Tuesday 15th November 13:21

1) - yes I did. Swapped 23mm GP4000s for 25mm GP4000s (primarily as Wiggle didn't have 23mm in stock.

2) not sure, can't see why contact patch would be shorter on wider tyres?

Beyond that, I need to order 2 tyres. Do I order 2x 25 or 1x25 1x28. Same cost, same fit, if it's going to give just 1% more grip and no downside, it's worthy option?

1) You missed my point - sure swapping 25's for 23's will make a difference. Particularly on the rear. If you'd kept a 23 on the back and put a 25 on the front, bet you'd not have noticed. I'd even expect that you'd notice a 28 on the rear, but on the front.. nah

2)Because physics. What keeps you off the ground is air pressure. It doesn't care what size the tyre is, it squashes a bit (kinda like a spring) to achieve equilibrium. Same pressure, same squash (or same volume intruded into the tyre). The squash gives you a contact patch. If it's wide, less length is needed for that volume, so it'll be short, and if it's narrow it'll be long.

THAT is why a wider tyre rolls better: Whack a line between two points on a circle that are close, and two that are further apart; the longer contact patch of a narrower tyre deforms the carcass more, so more drag.

Whether you have more grip is more down to the tyres you run (probably pick up more grip running 4000's than going to a 28), the width of the rims (which will affect the shape of the tyre), pressure and so on.

If you want to do it, go for it, but there's no real justification. As for 1% you'll either have more grip than you need, or fall off anyway, 1% doesn't make a real world difference - you can't ride that close to the limits.

Fair enough - I guess part of the rationale for going wider is the ability to run lower pressures. I dropped 10-psi going from 23s to 25s. I'd do 10 more (or rather less) running 28s.

As long as there is no reason not to, then thats a green light for me.

[Ares]

thiscocks said:

Well put. That's why I laugh when people say 'im putting wider tyres on my car for more grip'

Makes you laugh? Kind of makes you cruel. Especially in a thread where someone is merely asking for advice.

[Ares]

Gren said:

Why not. Plenty do it on the trails. Narrower less nobbly tyre at the back and fatter one out front.

I've also run 4 seasons on the back and gp4000s up front. Saves changing/buying a full set and it's usually the rear that punctures and so needs a bit more protection.

Thanks. Ironically, I've only had 2 punctures in over 10,000km of riding over the last 2 years. Both fronts, including Sunday's where is became irreparable on the roadside and left me limping home:

[thiscocks]

Ares said:

thiscocks said:

Well put. That's why I laugh when people say 'im putting wider tyres on my car for more grip'

Makes you laugh? Kind of makes you cruel. Especially in a thread where someone is merely asking for advice.

Not at you sir! I didnt think you were specifically talking about grip. Relating to your op I have put bigger /smaller tyres on my racer front and rear. There is no way you would tell any difference other than maybe comfort.

[upsidedownmark]

Ares said:

Fair enough - I guess part of the rationale for going wider is the ability to run lower pressures. I dropped 10-psi going from 23s to 25s. I'd do 10 more (or rather less) running 28s.

As long as there is no reason not to, then thats a green light for me.

I'd check the minimum pressure (which should be on the sidewall). conti recommend 110 for a 23, and 95 for both the 25 and the 28. I'd run less on the front, I use 85-90 in a (23), and 105 rear. I'd not be happy with 65 in a front, even in a 28, I don't think it would hold shape at that.

[WinstonWolf]

I used to do it a lot as a kid, the bike seemed fine to me.... (That one's got a knobbly front tyre! )

[Ares]

upsidedownmark said:

Ares said:

Fair enough - I guess part of the rationale for going wider is the ability to run lower pressures. I dropped 10-psi going from 23s to 25s. I'd do 10 more (or rather less) running 28s.

As long as there is no reason not to, then thats a green light for me.

I'd check the minimum pressure (which should be on the sidewall). conti recommend 110 for a 23, and 95 for both the 25 and the 28. I'd run less on the front, I use 85-90 in a (23), and 105 rear. I'd not be happy with 65 in a front, even in a 28, I don't think it would hold shape at that.

I run 100/105 on 25s, 110/115 on 23s. I'd drop to 90/95 on 28s if I go for it, but good point to check minimums.