johngwheeler

Sorry for yet another tire-clearance thread...but I haven't found the answer anywhere else.

I have a 2023 Merida Scultura (normal "race" model, not the Endurance version), which came with 17mm IW rims and 28mm Continental GrandSport Race tires. I want to replace these with tubeless GP5000 tires and need to decide between 28, 30mm and 32mm versions.

The Merida specs state support for 28mm tires, but as we know, manufacturers hedge their bets and don't tend to specify rim and tire combinations that will definitely fit (or not).Currently the 28mm GrandSport Race tires measure 29mm wide and 27mm tall. There is 5.5-6mm space at the narrowest point, between the rear tire and the chainstays.

Everything I have read about the 32mm GP5000 tubeless tires is that they measure narrower on narrow rims (17-19mm), but tend to grow a bit with usage, but are still less than true 32mm, e.g. BRR shows the max width as 31.4mm - https://www.bicyclerollingresistance...-tr-comparison

Even if the 32mm GP5000s measured 4mm wider than the current 28mm Grandsport Race, I would still have 3.5-4mm clearance at the chainstays. Clearance for height is a lot more generous on the Scultura - minimum of 10mm at the fork crown and to the seat tube, so I'm not concerned about height increase.

Just wanted a sanity check from someone who has actually fitted these tires before I buy a set!

Thanks!

Iride01 

Find the place on your tires that comes closest to rubbing anything on your bike. How much distance is that? Usually seat tubes, chain stays and the underside of the fork crown are problem points. If you have caliper rim brakes then check that too for how much clearance there is to it's mount point in the center.

If the difference in the tire size from what you want to get and currently have is less than the place you measured that has the least clearance to the tire, then you might be good. But different model tires measure slightly different from their stated nominal size. Also, you should leave a certain amount of space for times when your tires might pick up mud or other debris. I once went briefly through some gumbo mud we have here and quickly came to a stop on the other side because the mud jammed the tire. And I think that bike probably had a ¼ inch clearance as I wasn't running over size tires on it.

Tires change in height by about the same as they change in width. At least it's close enough. If you are needing to know to the last couple millimeters, then you probably aren't leaving nearly enough room for safety.

choddo

I have 30mm GP5000s on 19" internal rims and that doesn't seem ideal, a bit balloony, not sure I'd want to go to 17 on even wider tyres.

johngwheeler

The tire shape is certainly a consideration in terms of support when cornering, or for aerodynamics. That said, I think 17mm rims are compatible with up to 50mm tires, even though anything > 28mm is probably not optimal.

johngwheeler

Thanks for the reply. As mentioned in my post, I have about 5.5-6mm clearance at the closest point, which is between the rear tire and the chainstays. If the reports of the 32mm GP5000 width are correct (and that could be a risky assumption!), then tire width would increase about 3mm (1.5mm per side), and clearance would be about 4mm at the chainstays, which is I believe the ETRTO recommended minimum.

I'm really just trying to get some real-world experience from someone who has tried this. Theory is all well and good, but practice is better!

johngwheeler

Adding some information that I've just found relating to the Merida Scultura Team edition - which shares geometry with the (much!) cheaper Scultura 6000:

From: https://velo.outsideonline.com/road/...uled-for-2022/

"That tyre clearance now officially sits at 30 mm. Merida has indicated that this figure is playing it safe to ensure compatibility with all rim and tyre combinations. For example, it has been confirmed that Continental GP5000 tyres in a 32 mm width fit without issue. The bike comes fitted with 28 mm tyres. "

The article doesn't cite the reference for this confirmation, but it sounds positive. I have also seen another review of the custom Merida Reacto aero bike fitted with 32mm GP5000s (https://granfondo-cycling.com/merida...m-2021-review/ ), so it certainly seems to be something that Merida supports on some models of their road bikes.

I think I am confident enough to buy some 32mm GP5000s and give it a go. I will post an update to let you all know the results!

johngwheeler

I finally got round to fitting tubeless 32mm GP5000 S TR tires to the aluminum rims that came with my Merida Scultura 6000. [This is for the standard "race" version, not the endurance variant which takes up to 38mm (advertised) ]

The tires measure slightly less than 32mm (approx 31.5mm) when new on 17mm internal width rims , and I would expect them to stretch up to about 33mm wide over time. There is approximately 4.5-5mm clearance at the narrowest point (the chainstays), which seems to be ample for road riding, even allowing for a bit of stretch. Pressures were about 4.8bar / 70 PSI, which is near the maximum (73 PSI) for these tires, but I will probably run them a little lower depending on road conditions.

I'm very happy with the GP5000 S-TR tires - there is a very noticeable improvement over the stock 28mm Contintental Grandsport Race. They just feel a lot smoother and faster, and the fatter tires instill more confidence over bumpy surfaces. There is a bit of "lightbulb" effect on the narrow (17mm) rims, but it's not too obtrusive and doesn't seem to affect handling, although I do run the front tire pressure a little higher than some calculators suggest to avoid too much "squishiness" when out of the saddle.

I've upgraded tires on pretty much every bike I've ever had, and still feel that it is the "best bang for buck" upgrade you can make on a bike :-)

eduskator

28mm is your manufacturer's tire clearance to keep a safe gap between the tire and the frameset/fork. Now, will 30mm or 32mm fit? Yes, it probably will. It this recommended? No. Chances are that you won't have the 3-4-5mm recommended minimal clearance on each side of the tire.

I would not ride such setup given your manufacturer's tire clearance & how narrow your rims are.