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Moving from 25mm to 30mm Tyres

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Moving from 25mm to 30mm Tyres

Old 10-15-21, 04:24 PM
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engpeter
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Moving from 25mm to 30mm Tyres

Hi, I mostly train on a SystemSix 2019 bike, running on a pair of GP4000 25mm tyres. For safety reasons I'm thinking of moving to a 30mm GP5000 pair. According to Cannondale Systemsix 2019 frame specs it seems like 30mm is the maximum that frame can allow.
I'm looking for people experience riding on wider tyres, the good/Bad about moving from 25 to 30mm.
Thanks heaps!

Last edited by engpeter; 10-18-21 at 04:43 PM.
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Old 10-15-21, 04:28 PM
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That is a huge jump, but should be fine if the frame will accept it. I went from a 25 to 32 on one bike I had and it took some getting used to, but I had no issues with it. I did enjoy the lower pressures making the riding a little smoother. I eventually moved back to a 28 and found that to be the sweet spot for that bike.
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Old 10-15-21, 04:34 PM
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Try 28 first?
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Old 10-15-21, 04:48 PM
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Thanks folks. It's really frame and rims I need to check if they accept 28 or 30? Anything else I need to check before going to wider tyres?
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Old 10-15-21, 04:53 PM
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Brake calipers, unless you have discs.
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Old 10-15-21, 06:06 PM
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Originally Posted by Mojo31 View Post
Brake calipers, unless you have discs.
yea I assumed disc, since it is 2019, but good point.
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Old 10-15-21, 08:06 PM
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Keep in mind that the GP4k is going to be a little oversized compared to the GP5k. In general, newer tires are a little smaller than previous generation tires because they're compensating for the additional width of modern rims. IOW, on the same rims, a 25mm GP4k is probably closer to the size of a 28mm GP5k, so a 30mm GP5k probably isn't going to be that much bigger than your current tires, maybe 1-1.5mm additional on each side (width and height/radius). I would probably get a 6mm allen wrench and use it as a feeler gauge around the tight spots of your current tires. 4mm worth of clearance, to all sides, is what's generally recommended, so if that 6mm spacer doesn't jam anywhere, you're probably good to go.

Oh, and FWIW, some tire manufacturers have started being a little more explicit with their sizing to alleviate guessing games like these. Some will tell you that they'll measure to size on a specific width rim ("28mm wide on a 19mm internal width rim" or something like that) while others have gone all out with WAM (Width as Mounted) and RAM (Radius as Mounted) charts for combinations of various tire sizes and rim widths. I don't think that Conti has jumped on to the WAM/RAM bandwagon, but I they might specify their reference rim width.
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Old 10-15-21, 09:27 PM
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Originally Posted by WhyFi View Post
Keep in mind that the GP4k is going to be a little oversized compared to the GP5k. In general, newer tires are a little smaller than previous generation tires because they're compensating for the additional width of modern rims. IOW, on the same rims, a 25mm GP4k is probably closer to the size of a 28mm GP5k, so a 30mm GP5k probably isn't going to be that much bigger than your current tires, maybe 1-1.5mm additional on each side (width and height/radius). I would probably get a 6mm allen wrench and use it as a feeler gauge around the tight spots of your current tires. 4mm worth of clearance, to all sides, is what's generally recommended, so if that 6mm spacer doesn't jam anywhere, you're probably good to go.

Oh, and FWIW, some tire manufacturers have started being a little more explicit with their sizing to alleviate guessing games like these. Some will tell you that they'll measure to size on a specific width rim ("28mm wide on a 19mm internal width rim" or something like that) while others have gone all out with WAM (Width as Mounted) and RAM (Radius as Mounted) charts for combinations of various tire sizes and rim widths. I don't think that Conti has jumped on to the WAM/RAM bandwagon, but I they might specify their reference rim width.
interesting...
do you have links to where you found this info?
Thx
Yuri
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Old 10-15-21, 09:47 PM
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If you have the stock wheels, looks like they are 17mm inside width. I estimate a Conti GP5000 28mm will be about 29 to 30 mm wide mounted. It will be taller too. A 30mm may be too close to the seat tube cut out. Fulcrum Racing 400 DB, Alloy clincher, 35mm deep
Fulcrum Racing 400 DB, Alloy clincher, 35mm deep
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Old 10-16-21, 12:47 AM
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Originally Posted by datlas View Post
Try 28 first?
This...for all the reasons noted above about sizing differences once mounted. I do run 30s on my SL7, but I ran 27s first, with enough space left that when it was time to replace, I bumped them up. As for comfort, it's a noticeable improvement, not squishy or bouncy, but definitely less harsh. As for perceived effort and actual measured speed, no change. I suspect that is a common experience with any higher end tire.
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Old 10-16-21, 06:06 AM
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Originally Posted by cyclezen View Post
interesting...
do you have links to where you found this info?
Thx
Yuri
Off the top of my head? No. It's a cumulation of wheel and tire shipping over the last few years. If you read reviews of the new tire releases, like the Schwalbe Pro One Addix TLE, you'll see references to their new sizing on 19mm int width rims. For WAM and RAM, I believe that it was 3T that pushed that forward, with tire manufacturers like Pirelli following their lead.
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Old 10-16-21, 07:06 AM
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Pirelli uses the WAM and RAM as well.
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Old 10-16-21, 07:54 AM
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Do the 28mm first. Or Best Buy one and check clearance from and rear. I donít have clearance issues with my Domane but run 25mm front and 28mm rear on the road. More aero input front or at least in my mind and softer in the rear. I had a Madone 5.0 with Aeroles 5 wheels before. Inside wide is 19mm. I tried GP5000 25mm tires and the did not fit. For the original 14mm inside width rims they would. Then pressure for your weight can be a factor if your close. So buy one tire and try fit.
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Old 10-16-21, 09:21 AM
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Originally Posted by biker128pedal View Post
Do the 28mm first. Or Best Buy one and check clearance from and rear. I don’t have clearance issues with my Domane but run 25mm front and 28mm rear on the road. More aero input front or at least in my mind and softer in the rear. I had a Madone 5.0 with Aeroles 5 wheels before. Inside wide is 19mm. I tried GP5000 25mm tires and the did not fit. For the original 14mm inside width rims they would. Then pressure for your weight can be a factor if your close. So buy one tire and try fit.
Interested/curious how your determined the GP 5000 25mm did not fit? From personal observation or some other reference?
I've had my HEDs since 2010, I believe their ETRTO is 18/19 - 622 ? and have initially used them with 23 and a lot with 25, many brands/models, including a bunch of GP4000s...
They worked perfectly, and with 3 sets of HEDs (Kermesse, Ardennes, Bastogne) they are my go-to wheels and alll have 25, except one Frt has a Vittoria 23...
Never had a problem, in fact, the tires has all improved 'feel', comfort and quite obvious better traction on fast curvy descents. "Speed' , maybe, but that's m0stly a 'motor' problem... LOL!
so what makes you say GP 5000-25 doesn't work ?
Thx
Yuri
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Old 10-16-21, 09:57 AM
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Originally Posted by Badger6 View Post
This...for all the reasons noted above about sizing differences once mounted. I do run 30s on my SL7, but I ran 27s first, with enough space left that when it was time to replace, I bumped them up. As for comfort, it's a noticeable improvement, not squishy or bouncy, but definitely less harsh. As for perceived effort and actual measured speed, no change. I suspect that is a common experience with any higher end tire.
When I switched up to 30mm from 25mm, there was zero difference in my average speed over a route I have ridden hundreds of times. The ride was far more plush and I felt a lot less fatigued when it was done. I had spent a lot of money trying to get more vertical compliance with changes in forks, seat posts and handlebars. All of those changes were tiny compared to the difference by switching up tire size and inflating to a proper lower pressure.
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Old 10-16-21, 09:58 AM
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Why is changing from 25 to 30mm a ‘safety issue’?

that is all.
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Old 10-16-21, 06:31 PM
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Originally Posted by cyclezen View Post
Interested/curious how your determined the GP 5000 25mm did not fit? From personal observation or some other reference?
I've had my HEDs since 2010, I believe their ETRTO is 18/19 - 622 ? and have initially used them with 23 and a lot with 25, many brands/models, including a bunch of GP4000s...
They worked perfectly, and with 3 sets of HEDs (Kermesse, Ardennes, Bastogne) they are my go-to wheels and alll have 25, except one Frt has a Vittoria 23...
Never had a problem, in fact, the tires has all improved 'feel', comfort and quite obvious better traction on fast curvy descents. "Speed' , maybe, but that's m0stly a 'motor' problem... LOL!
so what makes you say GP 5000-25 doesn't work ?
Thx
Yuri
Fit the frame. Frame Clearance. The 25mm rubbed the chainstays on the rear and up front there was about 1mm clearance to the fork. I filed it a little but rocks jammed in the gal and would cut a groove in the tire. Newer bikes have more room. But GP5000 tires must be sized for rims with less than 14mm inside width. Iíve put them on 14mm inside rims and the are wider that the rated width. This is for 23mm, 25mm and 28mm. The 25mm GP5000 on the 14mm inside width rim is 26mm. On a 19mm inside width rim it is 28mm. The 23mm GP4000 on a 19mm inside width rim was 27mm. The 25mm GP4000 on the 19mm was 28mm wide. Tire height was hard to measure getting a good reference point.

Now as for fit Iíve put 23mm on 25mm inside width rims. They fit but have a low profile. The 25mm GP5000 tires fit better and fall within the 105% guide for aero.

So my point is frame and fork clearance. Rim brake callipers can be an issue. If you have the clearance the charts are too conservative in my opinion. Heck see how narrow mountain bike rims are and the tire width.

The OPs bike is and aero bike with a small seat post clearance.

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Old 10-17-21, 06:57 AM
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Originally Posted by biker128pedal View Post
If you have the stock wheels, looks like they are 17mm inside width. I estimate a Conti GP5000 28mm will be about 29 to 30 mm wide mounted. It will be taller too. A 30mm may be too close to the seat tube cut out. Fulcrum Racing 400 DB, Alloy clincher, 35mm deep
Fulcrum Racing 400 DB, Alloy clincher, 35mm deep
For GP5ks, here's a comparison from BRR (https://www.bicyclerollingresistance...000-comparison ). I wish they did more of these 'family' comparisons. Mind you, not sure if they did what they said they did, and actually inflated all of these sizes to 100psi -- which doesn't make too much sense and might be making the WAM numbers a wee bit overinflated (pun intended).

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Old 10-17-21, 09:26 AM
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Originally Posted by biker128pedal View Post
Fit the frame. Frame Clearance. The 25mm rubbed the chainstays on the rear and up front there was about 1mm clearance to the fork. I filed it a little but rocks jammed in the gal and would cut a groove in the tire. Newer bikes have more room. But GP5000 tires must be sized for rims with less than 14mm inside width. Iíve put them on 14mm inside rims and the are wider that the rated width. This is for 23mm, 25mm and 28mm. The 25mm GP5000 on the 14mm inside width rim is 26mm. On a 19mm inside width rim it is 28mm. The 23mm GP4000 on a 19mm inside width rim was 27mm. The 25mm GP4000 on the 19mm was 28mm wide. Tire height was hard to measure getting a good reference point.

Now as for fit Iíve put 23mm on 25mm inside width rims. They fit but have a low profile. The 25mm GP5000 tires fit better and fall within the 105% guide for aero.

So my point is frame and fork clearance. Rim brake calipers can be an issue. If you have the clearance the charts are too conservative in my opinion. Heck see how narrow mountain bike rims are and the tire width.
The OPs bike is and aero bike with a small seat post clearance.
aaah, yes, understand... I read it as referring to RIM internal width issue...
I had same 'fit' issue with a Marin Argenta frame I had in early 00's - Alu and super tight chainstays - I bought specifically for Crit racing - so was running Ritchey Aero OCR Pro whls with an assortment of 23mm tires - only size which would fit !!! I tried 25, but only had about 2mm clearance on each side - one loose spoke and the wheel would get stuck !!! LOL!
eventually retired the Argenta in '07. Great riding frame, but sadly was hit hard by the "Fashion' stick of that era... super-tight, super low headtube, stoopid stiff - all fine for Crit racing, but not much of any other riding... LOL! I still felt 'younger' in those days... LOL!
btw, I still have the Ritchey whls ( 2 sets) which are still serving as my weekday rides (when not on the HEDS) - awesome wheels - one set prolly has 30K mi +, the other maybe 18K ish - replaced 2 rear spokes otherwise - bulletproof !
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Old 10-18-21, 04:18 PM
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I have 2019 systemsix. I did not like the 23mm tires that came with the bike. Kept getting flats. I installed 28mm gp5000. They fit fine. It's a little tight by the seat post.
If the 30mm tired you are getting are any taller than 28mm gp5000 I don't think they are going to fit. Width wise you should be fine.

maybe 30 front / 28 in the back ?




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Old 10-18-21, 04:24 PM
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If I had a 28mm on the bike I would take close up photos for you. I am using gp5000 25mm just because there where always on sale and available.
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Old 10-18-21, 04:38 PM
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I love this forum already! I have this exact same bike Thanks mate, nice to connect!
I have been riding on GP4000 25mm for 2 years, and recently changed to an old pair of Vittoria (25mm/ gum walls). Didn't think I would say this but riding on the older pair feels softer and nicer on the road, or so it feels.

How long have you had your SystemSix for? What was your riding experience changing from 25 to 28mm?
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Old 10-18-21, 05:47 PM
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Originally Posted by whyfi View Post
keep in mind that the gp4k is going to be a little oversized compared to the gp5k. In general, newer tires are a little smaller than previous generation tires because they're compensating for the additional width of modern rims. Iow, on the same rims, a 25mm gp4k is probably closer to the size of a 28mm gp5k, so a 30mm gp5k probably isn't going to be that much bigger than your current tires, maybe 1-1.5mm additional on each side (width and height/radius). I would probably get a 6mm allen wrench and use it as a feeler gauge around the tight spots of your current tires. 4mm worth of clearance, to all sides, is what's generally recommended, so if that 6mm spacer doesn't jam anywhere, you're probably good to go.

Oh, and fwiw, some tire manufacturers have started being a little more explicit with their sizing to alleviate guessing games like these. Some will tell you that they'll measure to size on a specific width rim ("28mm wide on a 19mm internal width rim" or something like that) while others have gone all out with wam (width as mounted) and ram (radius as mounted) charts for combinations of various tire sizes and rim widths. I don't think that conti has jumped on to the wam/ram bandwagon, but i they might specify their reference rim width.
wam ram thank you ma'am
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Old 10-18-21, 08:08 PM
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Originally Posted by engpeter View Post
I love this forum already! I have this exact same bike Thanks mate, nice to connect!
I have been riding on GP4000 25mm for 2 years, and recently changed to an old pair of Vittoria (25mm/ gum walls). Didn't think I would say this but riding on the older pair feels softer and nicer on the road, or so it feels.

How long have you had your SystemSix for? What was your riding experience changing from 25 to 28mm?
I got the systemsix march of last year.

I am probably the wrong guy to ask. I am crit 6 at best. ha-ha

things I noticed a difference:
-gravel bike vs road bike

-23mm tires that came on the bike vs 28mm gp5000. 23mm felt more harsh on the road and got a lot more flats. I think I only had those tires for about 2 months before I switched to 28mm gp5000. I hated the stock tires that came with the bike.

-gravel wheel/tires set vs road wheel/tires set ( on my gravel bike )

-change chainring from 36 to 30 to help with climbing. ( have bad knees from motorcycle accident. )

things if I was blindfolded I could NOT tell difference:
-carbon lightspeed wheels with dt swiss 240xp hubs vs alloy wheel set that came with the systemsix ( I bought the carbon wheel set so I could kick down the alloy wheels to my gravel bike so I was still happy that I got the carbon wheels ) I thought I was going to be able tell

-gp5000 25mm vs gp5000 28mm


If the 28mm ever become the same price as the 25mm again when I need new tires I will probably buy them instead of the 25mm even though I can't tell a difference. I think it's supposed to give a nicer ride and be tad faster for the surface I ride on.

I have been wanting to buy 32mm gp5000 to put on my alloy wheels I took from my systemsix to try try on my gravel bike but 32s or even more expensive the 28s.

Maybe you can just buy one 30mm tire and see if works on the back. If it doesn't just put it on the front and 28 on the back. if the 30 fits on the back you can buy the matching front tire.

oh my frame is 54mm. If that might make a difference.

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Old 10-19-21, 04:06 PM
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I was digging through my old photos and i found the 28mm when I first installed them last year.





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