Just when I thought the Rolls-Royce (LSE: RR) share price had finally run out of gas, it started climbing again.

It rose another 7.36% over the last week, having been swept up in the excitement over the surprise drop in September’s inflation figure to 1.7%.

I’m still impressed to see Rolls-Royce shares power upwards. This is a stock that has grown 163.91% over 12 months and 695.03% over two years. How can it have any fuel left in the tank after that?

Transformative CEO Tufan Erginbilgiç has given the company new thrust, but even he couldn’t have imagined it would have this much staying power.

This FTSE 100 hero must slow at some point

It can’t go on forever, can it? The shares are now pretty pricey, trading at 41.38 times trailing earnings. The forward price-to-earnings ratio is 32.2 times for 2024 and 28.4 times for 2025. These are also pretty high.

Rolls-Royce has a price-to-sales (P/S) ratio of 2.9 times. This means investors are essentially paying 2.90p for each £1 of sales it makes.

The only way Rolls-Royce can justify that is to keep driving up earnings. It could happen. Revenues totalled £16.48bn in 2023 and are forecast to hit £17.11bn this year and £18.5bn in 2025. It will be punished for any undershoot, though.

It could beat expectations instead. At the start of the current financial year, the board predicted that full-year profits would total £1.7bn-£1.9bn. At the half-year stage on 1 August, it lifted that to between £2.1bn-£2.2bn.

It looks like brokers are losing faith. The 14 analysts offering one-year price forecasts for Rolls-Royce shares have a median prediction of just 581.6p per share. That’s a meagre increase of 2.99% from today’s price, if correct.

There’s a wide range, from 675p to 520p. Overall though, I’m disappointed. I expected more.

I still reckon we may see some growth

Nobody can forecast the future with any certainty, of course. Rolls-Royce has a massive opportunity with its mini-nuclear reactors, assuming it gets the green light from the UK government, and picks up orders from elsewhere.

Investors held their breath last month when the European Union aviation safety agency inspected its Trent XWB-97 engines after a long-haul Cathay Pacific was forced to return. Happily, it doesn’t look like the problem lay with Rolls.

Supply chain issues have returned across several sectors, including airlines, with British Airways-owner IAG complaining of delayed engines and parts from Rolls-Royce.

Airline ticket prices have softened, which could suggest a slowdown in travel demand. That will hit Rolls-Royce, which makes hefty revenues from the maintenance contract on its engines based on miles flown.

All good things come to an end, and the Rolls-Royce share price must flatten out soon. I hold the stock and I’m more upbeat than most brokers. So I felt vindicated to see broker Jefferies upgrade its target price from 640p to 650p on Friday. That’s up around 15% from Friday’s price of 562p per share.

I won’t be complaining if that happens. I’m in this for the long haul, and expect to be rewarded over a five to 10-year timeframe. As the share price slows, Rolls-Royce may have to drive up its dividend to keep loyal investors happy.