The tyre clears in the seller’s photograph. Your wheel has a wider rim. Those two facts are enough to make the photograph a poor fit test. Measure the tyre on the wheel you will actually use.
The tyre’s nominal width, the rim’s internal width and the inflated tyre’s measured width describe different things. Schwalbe explains why actual dimensions vary with rim and tyre construction. A hypothetical tyre marked 38 mm that measures 40 mm consumes 2 mm more total lateral space—about 1 mm per side if centred. It is an example, not a prediction for a particular tyre.
Read the frame’s wording literally
The LCR018-D manufacturer specifies a measured maximum width of 38 mm. The dated Speedster SR record has drivetrain- and tread-dependent conditions. A maximum label is not a promise of spare clearance for mud or fenders, and a smooth tyre’s fit does not establish fit for knobs of the same marked width.
If that illustrative tyre measures 40 mm, it exceeds the LCR018-D’s stated 38 mm measured-width maximum. Having enough visible space in one photograph cannot turn it into an approved combination. For the drivetrain-dependent frame comparison, see 38 mm tyres on aero road bikes.
LightCarbon LCR018-D · Model detailsManufacturer’s example build on the LCR018-D frameset; pictured parts are not a confirmed sale package.LightCarbon; see sourcePhoto unavailable; open the source to view it.
Make a fit record you can repeat
First confirm the exact tyre/rim combination and permitted pressure with both manufacturers. A tyre that clears the frame can still be unsuitable for the rim. Measure the widest part, including any tread, at a permitted pressure; the clearance check comes after this compatibility check.
Record tyre model/size, wheel and internal width, pressure and measured width. Have the assembler check both lateral and radial clearance at the tightest points using the frame maker’s required margin. If the margin or compatibility is unresolved, choose a smaller approved combination rather than treating “doesn’t rub in the stand” as sufficient. Keep the record: it will be useful when the next tyre has the same number on its sidewall and a different shape.
