Why is my new MTB slow? Please help me to make me faster again

Equipment
1

I’m one of the lucky ones who were able to buy a new bike in 2022.

I bought a new 2022 Scott Spark Comp and replaced my 2019 Scott Scale 950 hardtail.

I upgraded the Spark with quite light carbon rims 30mm internal (1514g) and a light Garbaruk cassette. The race weight is now around 12 kg. The previous Scale was 11.5 kg (aluminium frame and aluminium rims 25mm internal).

As I really like the handling of the new bike and enjoy the comfort of a full suspension bike, I made some observations from my races this year which I can’t complain and hope someone can help me.

I compared the Strava segments of the races last year with this year. Especially the climbing segments (where I can exclude drag influences like cda or drafting effects) showed significanlty slower times by higher power outputs. All these segments show comparable slower times.

I use the same Sigey AXO spider PM which I used on my Scale.

Some segment comparisons:

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The question is, what makes me slower? Why do I loose ~20W?

The parameters I’m currently looking at:

Tires on Scale: Maxxis Aspen 2.25 → Spark: Maxxis Recon Race 2.4

Bike weight Scale 11.5 kg → Spark: 12 kg

Tire pressure Scale ? (can’t remember) → Spark: 19/20psi

Unchanged parameters:

Rider weight 75 kg unchanged

Schwalbe Aerothan tubes in both years

1 bottle of mix on the bike on both bikes during the race

Surface conditions were very much the same in both years

I’m quite good at pacing the climbs in the race, so I don’t think that this is a huge influence

I fully locked my suspension on the Spark in all climbs.

As I’m having a new bike, I don’t assume that the bearings have an influence.

I trained much better this year and am convinced that I really put out the higher power which reflect my indoor training numbers. So I don’t think that the power difference is comming from a PM failure.

Regarding tire pressure I did a separate test yesterday on a gravel climb (surface comparable to race segments) ~5min @ 250 W evenly paced. I compared 24/25, 19/20 and 15/16psi. The results where within 3 s. So I couldn‘t see a significant influence of the tire pressure in terms of speed.

I don’t have other tires available at the moment. So I couldn’t test this yet. But it would surprise me if the Aspen 2.25 are that much faster than the Recon race 2.4 on a gravel climb!?

Any thought which make me faster again are welcome.

2

If the column headings on your screen shot are correct you’ve actually got faster.

If the column headings are the wrong way round then it’s very odd.
Same crank length and cadence?

3

You are right. I mixed up the headings and have correted it.

Yes, crank lenght (175mm NX eagle) was the same.
Cadence is „Trittfrequenz“. These are also very much the same.

4

On the trails i don’t notice much difference in rolling resistance, comparing my previous hardtail with schwalbe racing ray/ralph (2.25) with the Rekon race 2.4 on the spark (also upgraded to light wheels)

Most trail segments are equal or faster, but on the road, the difference is quite noticable! I think it’s for the same effort 2 km/h slower around 30 km/h.

I don’t have a PM to quantify this, but I do know my heart rate and rpe at different power outputs pretty well. So those tires roll pretty slow on roads, maybe too on gravel

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5

I would look into the tires first. Maxxis make many different versions of the same tire which could make a big difference

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I have these which were on the bike when I bought it.

On the Scale I had these: MAXXIS Aspen 29 x 2,25 DualCompound TR EXO

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It looks like there is a difference in Tpi where the Recon Race has 60 and the Aspen had 120. Good hint @ArHu74

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7

You’ve moved to a wider tire with more traction. This could mean more rolling resistance. Also, it could be your fit on the new bike, whereas you’re just not as efficient in this position.

Edit: I’ve been told, though not verified, that the tires that come on complete bikes are not the same quality of those same tires bought off the shelf.

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8

I thought about the position as well but it‘s not yet clear for me what that really means - maybe you can explain it to me. I adjusted the saddle exactly the same. The reach is slightly shorter which results in a slightly more upright position. But these differences are small. I would rather expect a difference in cda due to the more upright position, which is rather neglectable in these segments with ~10km/h.

9

If you’ve trained and raced on the hardtail a long time your body just might be accustomed to that position. I’m no expert on fit, so I have little to offer in that respect.

On another note, it would not surprise me that holding every other variable constant, that a hardtail is more efficient/faster up hill/flats and the smoother the better. That’s what they’re made to excel at. However, the full sus would likely be better in many other areas.

10

You’ve moved from a hardtail efficient rocket of a XC bike, to a progressive more capable “down country” bike. The new Spark is pushing the boundaries of what’s considered pure XC and it’s the first generation of a new design. A design that’s never been done before. You have to expect there will be trade offs when compared to a hardtail.

3 Likes
11

I also wrap my head around the hardtail/full sus thing. But if the position is comparable, the weight is the same and I can fully lock my suspension. Where are the losses?

Edit: when watching XCO races and they speak about bike choice you only hear the weight difference as the main driver which impacts climbing abilities.

12

I’m not sure two data points is really enough to say for sure your bike is slower. A race is pretty dynamic and unless you were riding alone the other riders and the trail conditions could have a significant impact. Also, these are really long segments, and while you may have felt that you were riding equally well, it’s quite easy to ride a mountain bike in an inefficient way. Perhaps you were digging a little deeper on the climbs, but not carrying as much speed as last year on the flats and twisty sections. If you could ride those segments a few more times perhaps you might have some more insight.

3 Likes
13

Have you still got the old bike, or the old tyres? Maybe you can make a test with the old tyres.

(Even the fact they were old tyres might make a difference - the centre knobs could have been lower due to use, and rolling resistance lower.)

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14

Thank you for your thought. These are only some example segments. I saw it in many more. It was a 3 lap race and all 3 were very comparable. I rode them alone and paced them quite evenly (I worked on this since I have a PM).

15

To be honest I miss my hardtail. I‘m a one-bike-person :slight_smile:
I would love to compare it again.

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16

Current conclusion: buy and try some better tires.
I have another race next week with quite a lot of climbing.
I have some Vittoria Mezcal 2.35 on the stock rims ( I followed your advise @MI-XC :slight_smile: ) but I‘m not able to put it on the carbon rims as they are too tight. So I think about better Recon Race or Aspens!?

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17

I’d go for the old Aspens in that case, 60 vs 120 TPI can make a big difference

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18

Dirt could just be rolling slower which happens often on a mtb.

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19

That‘s true. That‘s the reason why I compared only gravel sections with the same conditions in both years.

20

It’s probably the tires. In my experience, particularly at lower speeds, bike performance largely comes down to the tires.

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