Would I notice a difference going from 27.5" to 29"?
 

I've seen lots of reviews and arguing about what's best, but this question is aimed for towards me.

I'm 5'11", 90kg/200lbs and a pretty novice/unfit/unadventurous cyclists who mostly deals with tracks rather than anything too technical.

I'm looking at (completely unnecessarily) upgrading my current bike (Carerra Vulcan) which is a 27.5" after having 26" bikes in the past, and it felt huge (the frame is bigger too), to a 1x drivetrain with remote lockout for the front suspension.

I've (temporarily) narrowed it down to 2 bikes:
Rockrider ST 900 - 27.5" tyres, 120mm travel, 32-11/46 microshift - £599
Rockrider XC 100 - 29" tyres, 100mm travel, 34-11/50 SRAM Eagle - £849

Would I be likely to notice enough difference going up to the XC 100 to justify the extra £250?

Both of those look like good bikes.
I tried 27.5 and bought a 29r
I ride on the street to get to dirt roads, and the 29r does this better.
If you are strictly riding dirt and single track, get the 27.5.
I ride mild single track with the 29r.
It's your chioice... can you go to a bike shop and test ride a 29r and a 27.5, even if they aren't the bike you want to buy?

I'm hoping I'll be able to test them out nearer the purchase time, but it doesn't seem possible to test them properly because the shop is in a city centre without any trails to run, and with covid there's no stock or touching stuff unnecessarily. So I may resort to buying without test if I miss a tax saving window.

From your brief description of your ride preferences, the XC 100 sounds like a better fit.

I recently bought a 29" with 3" wide tires. It's wheelbase is very long. Tight switchbacks are very difficult for me to ride without putting a foot down. Handling seems less finesse and more barrel over the top. I can bust over the top of terrain that would have pinch flatted my 26er. It's very comfortable, but definitely more awkward to ride in technical terrain. I'm still glad I brought it. It's going to work very well for bicycle packing, but I often wonder if it'd tackle technical terrain easier with 27.5 wheels.

The frame geometry changes the ride more than the wheel size.

I made the change form 27.5 to 29. At first I noticed a difference. Took getting used to but I would not go back.

I went from 26 to 29 last may.

The 29" is neither conclusively faster nor slower than the 26". And it's not an opinion. It's what my garmin over the same routes tells me.

Riding the 29er has a certain "I'm driving a dump truck" feeling though. It has a definite loss on agility, but it seems it's able to ride over anything. It's also heavier as everything is bigger.

In general, I feel like I'm slightly slower when climbing, and faster when descending.

What really made a difference for me is a dropper post. I love that thing. Places that were scary without it, are suddenly a piece of cake with it.

wheel sizes are not what makes one bike definitively different from one another. you have to take several other factors into consideration. if you're looking at two VERY similar bikes that mainly only differ in wheel size, the smaller wheels will be easier to toss around (think about bmx bikes and what you can do with smaller wheels) but the larger wheels will hold momentum better over terrain (think of a monster truck driving over a row of old cars). keep in mind that is a generalization and the real, specific differences would also take into account suspension, frame geometry, type of tires, drivetrain, choices, etc.

29”
- actually has more tyre on the ground because of diameter... so you should corner at high speed better, climb better and even brake more effectively
- higher Unsprung weight(bigger wheel and tyre) so acceleration is worse on two counts... this and the larger diameter
- will be less likely to get hooked up on things as the diameter sees the tyre roll over things that a smaller tyre might get hooked upon
- the modern 29ers now have their frame geometry sorted... early ones were trucks
- slower to move around in the air when jumping... that might be a good or bad thing depending where you are with your jumping skills
.

I was all in on a 29er for my first mountain bike, but my LBS talked me down and into a 27.5 with plus sized tires. The biggest reason is the 27.5 is a little easier to handle for a beginner. However, going with the plus sized tires I get about the same outside diameter. Therefore, I get about the same ground clearance. Also, since the bike was built for 27.5+ tires, it can also accommodate 29er's if I ever feel the need to make that jump.

My 2 cents.

https://cimg7.ibsrv.net/gimg/bikefor...5b582d8f33.jpg

My experience going from 26 to 29 is completely different than this. The loss of agility was marginal--I did have to take slightly wider lines in tight switchbacks but that became second nature very quickly and I ride even tighter stuff nowadays. As far as speed goes, the 29er was/is faster--I was PR'ing my local segments each ride--I also immediately placed higher in local XC races. Weight-wise , it's lighter as the 26 was a steel bike with heavy tubed WTB Velociraptors and beefy Araya rims and that 29er ( I have a new one) was a carbon frame with light Stans tubeless wheels and XC treaded tires. I got a dropper and that was a game changer for me too.

Well, I suppose it depends on what bike you're coming from, and what bike you're going to. There are lots of things that can affect agility, grip and speed apart from tire diameter.

I currently ride both an old 26" MTB (Turner 5-spot) and a new 29" MTB (Ibis Ripley). With few exceptions, I am substantially faster on my 29" MTB. I tend to feel faster on my old 26" MTB but in the end of the day, the numbers always favor the Ripley. And it is not really that close. On a quick 15 mile loop, I am almost 20 minutes faster on the 29" bike. But it is terrain specific. That is, on another trail - one that is only a 4 mile twisty loop, the bikes are the same (speed wise).

However, I love my 26" bike and won't get rid of it. Even though I am slower, I have tons of fun on the old bike and have no problem riding it anywhere.

The 26" bike is shockingly light as well- with carbon rims, 2.4" tires and a dropper post, the bike is roughly 26 lbs. My 29" bike is 2 lbs heavier - aluminum rims and big 2.6" tires don't help.